Chemistry of Renewables: An Introduction [1st ed. 2020] 9783662614297

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Arno Behr Thomas Seidensticker

Chemistry of Renewables An Introduction

Chemistry of Renewables

Arno Behr Thomas Seidensticker

Chemistry of Renewables An Introduction

Arno Behr Laboratory of Industrial Chemistry Department of Biochemical and Chemical Engineering TU Dortmund University Dortmund, North Rhine-Westphalia Germany

Thomas Seidensticker Laboratory of Industrial Chemistry Department of Biochemical and Chemical Engineering TU Dortmund University Dortmund, North Rhine-Westphalia Germany

ISBN 978-3-662-61429-7 ISBN 978-3-662-61430-3  (eBook) https://doi.org/10.1007/978-3-662-61430-3 Translation from the German language edition: Einführung in die Chemie nachwachsender Rohstoffe by Arno Behr and Thomas Seidensticker, © Springer-Verlag GmbH Deutschland, ein Teil von Springer Nature 2018. Published by Springer Spektrum. All Rights Reserved. © Springer-Verlag GmbH Germany, part of Springer Nature 2020 This work is subject to copyright. All rights are reserved by the Publisher, whether the whole or part of the material is concerned, specifically the rights of translation, reprinting, reuse of illustrations, recitation, broadcasting, reproduction on microfilms or in any other physical way, and transmission or information storage and retrieval, electronic adaptation, computer software, or by similar or dissimilar methodology now known or hereafter developed. The use of general descriptive names, registered names, trademarks, service marks, etc. in this publication does not imply, even in the absence of a specific statement, that such names are exempt from the relevant protective laws and regulations and therefore free for general use. The publisher, the authors and the editors are safe to assume that the advice and information in this book are believed to be true and accurate at the date of publication. Neither the publisher nor the authors or the editors give a warranty, expressed or implied, with respect to the material contained herein or for any errors or omissions that may have been made. The publisher remains neutral with regard to jurisdictional claims in published maps and institutional affiliations. This Springer imprint is published by the registered company Springer-Verlag GmbH, DE part of Springer Nature. The registered company address is: Heidelberger Platz 3, 14197 Berlin, Germany

V

Foreword What are we going to do now?

With an exponential increase in population, major concerns about global warming leading to climate change and with oil and gas becoming scarcer and more expensive to extract, we stand at a point in the world’s history where everything we do needs to change - and quickly. We need to turn to renewable resources and to make sure that we have enough land to grow food as well as to provide all the essential and luxury items that are currently produced from fossil fuel based starting materials. Most of our static energy needs will be provided by wind, solar, wave and tidal power. Cars will be powered by electricity from renewable resources but how will we continue to fly? How will we provide all the essential and luxury items that are so familiar to us and we love to have without using fossil fuelbased resources whilst at the same time increasing the amount of food we produce. The United Nations 17 Sustainable Devel­ opment Goals provide a road map to a future of peace, justice, equality and prosperity in a pollution-free world espousing a circular economy. They hint at the end point but how will we actually get there? Many grandiose schemes are proposed but who will actually bring them into practice? Much of the work will be done by chemists and chemical engineers working with a whole myriad of end users to provide solutions to all the problems. There has never been a better time to be starting out on a career in chemistry or chemical engineering. The challenges are huge, addressing them will require the most creative of minds and the rewards, intellectual, social and financial will be enormous. Are you up for this exciting journey? Where will it start and what is the final destination?

Nobody knows the answer to the second question but, if you have been hooked into wanting to set out on this journey and do not know where to start, this book, The Chemistry of Renewables, which gives a snapshot of where we are at present and a hint at directions we might take, is the book for you. There are some major differences between oil and naturally occurring feedstocks. Oil contains only carbon and hydrogen whilst feedstocks like natural oils, cellulose, lignin, etc also contain significant amounts of oxygen and sometimes other elements especially nitrogen, phosphorus and sulphur. Oil is mostly a mixture of various chain length hydrocarbons so is relatively simple. It has only C-H and C-C bonds and is mostly easy to handle as a liquid, which can be pumped from well-defined reservoirs. Natural resources are chemically much more complex and diverse often occurring naturally as solids, sometimes spread thinly over large areas making handling trickier but not impossible. Most of the many thousands of effect chemicals we use on everyday life contain oxygen or nitrogen as well as carbon and hydrogen so, to make them from oil, we must add these elements generally in oxidative-type chemistry whilst the chemistry of the future will require removal of oxygen or reductive chemistry. One possible way to solve the problem would be to gasify biomass to give carbon monoxide and hydrogen then carry out Fischer-Tropsch chemistry to make a mixture of hydrocarbons rather like the oil that we use already and feed it into a standard oil refinery. However, taking all the oxygen out of biomass and putting some of it back in again is not only inelegant, it is massively energy intensive and expensive so we really have to look for the direct production of effect chemicals from biomass. A whole new chemical industry

VI

Foreword

is begging to be invented and you could be in the forefront of that exciting development. One of the great things about this book is that it is easy to read with its quirky titles, interesting anecdotes and liberal sprinkling of lovely colour pictures. You can dip in and out of it to find nuggets of information, what is been done already and what still needs to be done or you could read it as a bedtime story. Just to make sure you have not fallen asleep whilst reading there are “Quickie’s” at the end of each chapter; questions which check what you have learnt and that you have retained it. Do not worry, though, the answers are collected at the end of the book, but you should really try to get them without looking them up - just use them to check you were right! The book starts like Under Milk Wood or the song Do Ray Me at the beginning with an excellent overview of the field and a critical appraisal of the advantages and disadvantages of the feedstocks that are available, before moving on to individual feedstocks starting with fats and oils because they are currently the most exploited. The discussion moves to gly­ cerol, a coproduct when making many derivatives from natural oils and sugar before things get much more complicated with cellulose, the world’s most abundant organic polymer, starch and other carbohydrates. It then moves on to the toughest nut of all, lignin. Masses of lignin is available from trees but it is hardly exploited because its structure is complex; it is difficult to dissolve or break down and really hard to get single products form it. It can be done, for example, in a complex process for making vanillin, a flavouring compound that can also be used as a starting material for pharmaceutical production. However, this work is in its infancy. There is so much more to do. It is difficult but the rewards will be extremely high. Things get a bit easier with the naturally occurring hydrocarbons, terpenes and their polymers, where significant

chemical advances have already been made. Then come amino acids and their condensation to form the elements of life, polypeptides and proteins followed by compounds which can be extracted from nature for use as dyes, flavours, vitamins, drugs or polymers, many of which are biodegradable. Every chapter is peppered with some history, finds some interesting character, comprehensively explores some really exciting chemistry, shows applications and potential uses and explains how all of this can be done. In the end, the authors take a comprehensive look at the possibility of integrating many processes in a biorefinery. Here, agriculture, chemistry and chemical engineering are brought together to make everything else in the book a reality. One or more bio-feeds are transformed into a range of different useful chemicals and products just as in an oil refinery using oil as the feedstock. Biorefineries are usually more complex than oil refineries but they must become commonplace exploiting different feedstocks according to local availability. They must be run in a clean environmentally friendly way so it is a bit sad that the picture of the plant producing bio-ethanol as a platform chemical or fuel from sugar in Brazil appears to show dense grey smoke emanating from the chimneys. The pilot plant for biomass to liquid products in Karlsruhe looks much more environmentally friendly! When you finish reading this book, you will be full of facts, ideas and enthusiasms - and you will be exhausted but I hope that you will be inspired to get involved, solve the major problems and really make a difference to our world by giving it a circular, sustainable and clean future. As a bonus, you will also have read a prize winning text book because the origi­ nal German version of The Chemistry of Renewables won the prize from the German Chemical Industry Association for the best German chemistry textbook of

VII Foreword

2020. Well done to the authors for winning the richly deserved prize and to you for reading the book! Quickies (You may have to read the book

to answer some of these!) 1. What are the two most abundant renewable natural resources from which effect chemicals might be made? 2. What are the two most difficult natu­ ral resources from which to make effect chemicals? 3. Why can’t we just grow plants in order to produce all the chemical feedstocks we need? 4. Where can you find renewable hydrocarbons in nature? 5. Name two resources where you can find aromatic rings in nature. 6. Cashew nut shell liquid is a nonfood oil which is available at 800,000 tonnes per year. Can you find it in this book?

7. What problems would there be in making all the chemicals we need through hydrocarbons made by Fischer-Tropsch Chemistry using carbon dioxide and hydrogen produced by electrolysis of water using renewable electricity during periods of overproduction of electricity? Scotland, UK, June 2020 David Cole-Hamilton



IX

Preface This book is the English version of a textbook on renewable raw materials that was published in German by Springer ­Spektrum at the beginning of 2018. Due to the great success in the German-speaking world, the two authors have decided to publish an extended and updated version in English. The content of the book is based on a lecture that the authors have been giving at the TU Dortmund University (Germany) for many years. The book offers the reader an introduction to the different groups of renewable raw materials, especially fats and oils, carbohydrates and terpenoids. Also, more specific topics such as lignin and natural pharmaceuticals, as well as colorants and fragrances, are addressed. Individual chapters are dedicated to current topics such as biopolymers or biorefineries. All sections focus on the chemical conversion of raw materials into valuable products. Also, technical aspects such as the methods of recovery or the industrial processing of the reactions are discussed. One of the authors, Prof. Behr, worked in the chemical industry for several years and acquired considerable experience in the process development of new processes with fats and oils, carbohydrates and terpenes. In addition, he has successfully carried out numerous research projects on these topics at the Technical University of Dortmund over the past 20 years. This unique knowledge from practice and research is passed on to the readers in this book. This textbook is intended for students of natural and engineering sciences as well as for practitioners. The book is unique in such a way that students can follow up well on their lectures or acquire the curriculum chapter by chapter in self-study. Practitioners can quickly learn about

important raw materials, products and processes, and can familiarize themselves more deeply with individual topics from the references. What is the structure of the book? 5 The book is divided into 20 chapters of similar size. Each of these chapters starts with a chapter timetable, which roughly announces the content and closes with a compact summary. Detailed illustrations, photos, flow diagrams and chemical equations illustrate the text. 5 At the end of each chapter, there are 10 test questions, so-called Quickies. In the appendix, the reader will find the answers to the 200 test questions. 5 There is a short literature overview for each chapter. It consists mainly of references to textbooks and reviews but also includes some important current original references. 5 In addition, the text contains numerous “boxes” that describe exciting aspects, such as historical backgrounds or current developments. The authors would like to thank Springer Verlag, especially Dr. Charlotte Hollingworth and Dr. Rainer Münz, for their support in the realization of this book project and Miss Andréia Bracht for her help drawing the figures and formulas. In recent decades, renewable raw materials have become increasingly important, and this trend continues. This book provides the basis for a better understanding of this future top topic. Have fun reading it! Arno Behr Thomas Seidensticker

Dortmund, Germany August 2020

X

Preface

Prof. Dr. Arno Behr (right) and Dr. Thomas Seidensticker (left)

XI

Contents 1 1.1 1.2 1.3 1.4

The Overview - Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1  Definitions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2  The Different Types of Renewable Raw Materials. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2  Comparison with Fossil Raw Materials. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4  Advantages and Disadvantages of Renewable Raw Materials . . . . . . . . . . . . . . . . . . 8 References. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

I

Fats and Oils

2 The Raw Materials of Oleochemistry - Oil Plants . . . . . . . . . . . . . . . . . . . . . . . . 17 2.1  Introduction to Oleochemistry. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 2.2  Overview of Important Vegetable Oils and Animal Fats. . . . . . . . . . . . . . . . . . . . . . . . 21 2.2.1  Coconut Oil. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21 2.2.2  Palm Oil and Palm Kernel Oil. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23 2.2.3  Rapeseed Oil. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 2.2.4  Sunflower Oil. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 2.2.5  Soybean Oil. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 2.2.6  Linseed Oil from Flax Plants. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 2.2.7  Castor Oil. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27 2.2.8  Olive Oil . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28 2.2.9  Safflower Oil . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29 2.2.10  Jatropha Oil. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29 2.2.11  Other Fats and Oils. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31 2.3  Some Numbers. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31 References. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34

The Basics of Oleochemistry - Basic Oleochemicals . . . . . . . . . . . . . . . . . . . . . 37 3 3.1 Production of Basic Oleochemicals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38 3.1.1  Fat Splitting. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38 3.1.2  Transesterification. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42 3.1.3  Saponification. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43 3.1.4  Direct Hydrogenation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43 3.2  Reactions at the Carboxy Group of Fatty Acids. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45 3.2.1  Hydrogenation to Fatty Alcohols. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45 3.2.2  Conversions of Fatty Alcohols. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50 3.2.3  Conversions to Fatty Amines. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56 3.2.4  Other Fatty Acid Derivatives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57 References. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59 4

There is More to Oleochemistry - Reactions at the Fatty Acid Alkyl Chain . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61

4.1  Synthesis of Substituted Fatty Acids. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62 4.2  Reactions at the C=C Double Bond of Unsaturated Oleochemicals . . . . . . . . . . . . . 63 4.2.1  Linkage of New C–O Bonds . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63 4.2.2  Linkage of New C–C Bonds. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66

XII

Contents

4.2.3  Linkage of New C-H Bonds. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83 4.2.4  Further Additions to the C=C Double Bonds of Oleochemicals . . . . . . . . . . . . . . . . . . . 84 References. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 86

The Coproduct of Oleochemistry - Glycerol. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89 5 5.1  Properties and Use of Glycerol . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 90 5.2  Glyceryl Esters. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 94 5.3  Glycerol Ether . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 98 5.3.1  Glycerol Oligomers. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 98 5.3.2  Glycerol Polymers. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 99 5.3.3  Glycerol Alkyl Ether. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 99 5.3.4  Glycerol Alkenyl Ether . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100 5.4  Glycerol Acetals and Ketals. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100 5.5  From Glycerol to Propanediols. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 101 5.6  From Glycerol to Epichlorohydrin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 103 5.7  Glycerol Oxidation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 104 5.8  Dehydration of Glycerol to Acrolein . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 104 5.9  From Glycerol to Synthesis Gas. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 105 References. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 108

II Carbohydrates 6 Sweet Chemistry - Mono- and Disaccharides . . . . . . . . . . . . . . . . . . . . . . . . . . . . 113 6.1  Introduction to Carbohydrates. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 114 6.2  Monosaccharides. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 117 6.2.1  Fermentative Conversions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 117 6.2.2  Chemical Conversions of Monosaccharides. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 120 6.3  Disaccharides. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 129 6.3.1  Sucrose Production. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 131 6.3.2  Sucrose Processing. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 134 6.4  Outlook on Further Oligo- and Polysaccharides. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 137 References. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 140

From Wood to Pulp - Cellulose . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 143 7 7.1  Occurrence and Production of Cellulose. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 144 7.2  Manufacture of Paper. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 150 7.3  Derivatization of Cellulose. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 152 7.3.1  Regenerated Cellulose. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 152 7.3.2  Cellulose Esters. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 154 7.3.3  Cellulose Ether. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 155 References. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 159 Products with a Little Twist - Starch . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 161 8 8.1  Structure and Occurrence. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 162 8.2  Starch Production . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 165 8.3  Use of Starch . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 166 8.4  Starch Products. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 168 8.4.1  Partially Hydrolyzed Starches . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 168 8.4.2  Starch Saccharification Products . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 169 8.4.3  Chemical Derivatization of Starch . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 170 References. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 176

XIII Contents



9 Carbohydrates from the Sea - Chitin, Chitosan and Algae. . . . . . . . . . . . . . 177 9.1  Structure and Occurrence of Chitin and Chitosan. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 178 9.2  Production of Chitin and Chitosan. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 180 9.3  Properties and Applications of Chitin and Chitosan. . . . . . . . . . . . . . . . . . . . . . . . . . . . 181 9.3.1  Properties and Applications of Chitin. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 182 9.3.2  Properties and Applications of Chitosan. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 183 9.4  Other Marine Polysaccharides. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 184 9.4.1  Alginic Acid and Alginates. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 184 9.4.2  Carrageenans. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 186 9.4.3  Agar-Agar. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 186 References. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 189 10 10.1 10.2 10.3 10.4

Cyclic Carbohydrates - Cyclodextrins. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 191  Chemical Structure of Cyclodextrins. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 192  Manufacture of Cyclodextrins. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 193  Applications of Cyclodextrins. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 194  Derivatives of Cyclodextrins. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 196 References. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 198

III Lignin 11 The “Wood-Stuff” - Lignin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 201 11.1  Occurrence of Lignin. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 202 11.2  Structure of Lignin. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 202 11.2.1  Monolignols . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 204 11.2.2  Binding Pattern of Lignin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 205 11.2.3  Composition of Lignin. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 206 11.3  Lignin Recovery. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 207 11.3.1  Classical Wood Pulping Processes. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 207 11.3.2  Alternative Wood Pulping Methods for Lignin Recovery. . . . . . . . . . . . . . . . . . . . . . . . . 207 11.4  Use of Lignin. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 209 11.4.1  Use of Lignin as a Dispersing Agent . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 209 11.4.2  Use of Lignin in Biomaterials. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 209 11.4.3  Use of Lignin for the Production of Chemicals. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 210 References. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 214

IV Terpenoids 12 12.1 12.2 12.3

The Balm of the Trees - Terpenes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 219  Structure and Production of Terpenes. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 220  Monoterpenes. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 223  Higher Terpene Oligomers. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 228 References. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 233

13 13.1 13.2 13.3

Elastomers from Nature! - Polyterpenes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 235  Introduction to Polyterpenes. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 236  Production of Natural Rubber. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 239  Properties, Processing and Use of Natural Rubber . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 241 References. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 247

XIV

Contents

V

Other Natural Substances

14 14.1 14.2 14.3

Building Blocks of Life - Amino Acids. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 251  Amino Acids. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 252  Peptides. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 259  Proteins . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 259 References. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 263

15 15.1 15.2 15.3 15.4 15.5

Showing Your Colors Sustainably! - Natural Dyes. . . . . . . . . . . . . . . . . . . . . . . 265  Looking Back in History. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 266  Tyrian Purple . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 267  Alizarin. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 268  Indigo, the “King of Dyes”. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 269  Other Natural Dyes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 273 References. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 275

16 16.1 16.2 16.3 16.4 16.5 16.6 16.7

Nature’s Pharmacy - Natural Pharmaceuticals. . . . . . . . . . . . . . . . . . . . . . . . . . . 277  Herbal Pharmaceuticals. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 278  Aspirin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 279  Caffeine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 281  Quinine. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 284  Morphine. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 285  Penicillins and Cephalosporins. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 286  Steroids . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 288 References. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 293

Vital Amines - Vitamins. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 295 17 17.1  Overview of the Vitamins . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 296 17.2  The Vitamins in Detail. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 297 17.2.1  Vitamin A (Retinol) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 297 17.2.2  Vitamin B1 (Thiamine). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 297 17.2.3  Vitamin B2 (Riboflavin). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 297 17.2.4  Vitamin B3 (Niacin). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 298 17.2.5  Vitamin B5 (Pantothenic Acid). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 298 17.2.6  Vitamin B6 (Pyridoxine) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 299 17.2.7  Vitamin B7 (Biotin, Vitamin H). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 299 17.2.8  Vitamin B9 (Folic Acid) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 299 17.2.9  Vitamin B12 (Cobalamin) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 300 17.2.10  Vitamin C (Ascorbic Acid). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 301 17.2.11  Vitamin D (Calciferols). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 303 17.2.12  Vitamin E (Tocopherols). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 303 17.2.13  Vitamin K (Phylloquinone and Others). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 304 References. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 306 18 18.1 18.2 18.3

Enchanting Chemistry - Natural Flavors and Fragrances . . . . . . . . . . . . . . . 309  Definition and History . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 310  Fragrances and Flavors in Chemical Industry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 315  Extraction of Essential Oils. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 318 References. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 321

XV Contents



19 Plastics from Nature - Biopolymers. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 323 19.1  Definition and Classifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 324 19.2  Biopolymer Representatives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 328 19.2.1  Polymers from Nature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 328 19.2.2  Biopolymers from Biogenic Monomers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 334 References. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 338

VI Biorefinery 20 20.1 20.2 20.3

Refined Raw Materials! – Biorefineries . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 343  Definition of Biorefineries. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 344  Classification of Biorefineries . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 345  Examples of Biorefineries. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 349 References. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 355 Supplementary Information. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 357 Answers to the Quickies. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 358 Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 373

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The Overview Introduction 1.1 Definitions – 2 1.2 The Different Types of Renewable Raw Materials – 2 1.3 Comparison with Fossil Raw Materials – 4 1.4 Advantages and Disadvantages of Renewable Raw Materials – 8 References – 13

© Springer-Verlag GmbH Germany, part of Springer Nature 2020 A. Behr and T. Seidensticker, Chemistry of Renewables, https://doi.org/10.1007/978-3-662-61430-3_1

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Chapter Timetable 5 Here, you can find out which materials belong to the renewable raw materials. 5 You will learn the most important renewable raw materials in terms of quantity (the primary ingredients), but also the structurally important secondary raw materials. 5 The renewable raw materials are compared with the fossil raw materials coal, petroleum and natural gas. We are discussing whether the renewable raw materials will reduce fossil fuel consumption or can completely replace it. 5 The advantages, but also the accompanying problems of the renewable raw materials, are explained.

1.1  Definitions

Actually, everyone knows what renewable raw materials are: These are substances that occur in nature and grow back every year. All plants, trees, plants, flowers, fruits, cereals, grasses and vegetables would be “renewable” according to this very general definition. In this book, however, mainly those substances are considered which can also serve as raw materials for the organic chemist, the pharmaceutical manufacturer or the energy producer. The food sector, e.g. the calorie content, the taste or the health advantages or disadvantages of different olive oils, is not covered in this book. But we must be aware that many of the natural substances considered are suitable both as food and as chemical raw materials and that, of course, the use for the nutrition of the continually growing human race has the higher priority. In addition to the term renewables, there is also the term biomass, which is usually used in a very similar way. In order to exclude its use as a foodstuff, there is also the term industrial biomass. In this book, we want to use the term renewable raw materials throughout and determine the following definition:



Renewable raw materials are any organic materials that grow and are available again and again. They are used in agriculture or forestry and are mainly used for in the non-food sector. They can be used both materially and energetically.

Old trees that must be preserved are expressly excluded from this definition. The definition includes any organic residues from agriculture and forestry, e.g. sawdust from wood processing or straw from the grain harvest. Also, vegetable raw materials of marine origin, e.g. seaweed, are also considered, although they are not produced in traditional agriculture and forestry but have to be collected or cultivated specially. The definition of renewable raw materials includes all living organisms and thus not only vegetable but also animal sources. In slaughterhouses, for example, large quantities of beef tallow are produced which are less suitable for our nutrition but can be used well for further processing into soaps. The source of all renewable raw materials is ultimately the sun, because the growth of plants, and thus the production of food for animals and humans, is only made possible by the energy of sunlight. The decisive chemical reaction is the photosynthesis of carbohydrates from carbon dioxide and water with release of oxygen (Eq. 1.1.). h·v

nCO2 + nH2 O → (CH2 O)n + nO2

(1.1)

1.2  The Different Types

of Renewable Raw Materials

Biology distinguishes between primary and secondary plant substances. The primary ingredients are substances that are essential for the structure and reproduction of plants. They ensure that the plant is stable but also elastic and, for example, that a tree is not blown down even by extreme winds. Many plants also build up energy reserves for their propagation, e.g.

3 1.2  The Different Types of Renewable Raw Materials

. Table 1.1  Primary substances of plants and animals and their sources (examples) Renewable resource

Ingredients

Plant or animal origin

Fats and oils

Triglycerides

Soy, rape, sunflower, coconut palm, linens

Sugar

Glucose, fructose, sucrose

Sugar beet, sugar cane

Wood

Cellulose, hemicelluloses, lignin

Oak, beech, poplar, birch

Natural fibers

Cellulose, hemicelluloses

Flax, hemp, jute, sisal, cotton

Starch

Amylose, amylopectin

Potato, corn, pea, wheat

Exoskeletons

Chitin

Crabs, lobsters, shrimps, fungi, insects

Algae

Heteropolysaccharides, e.g. Agar-Agar

Red algae, brown algae

Proteins

Amino acids

Soy

. Table 1.2  Secondary substances of plants and their sources (examples) Renewable resource

Ingredient

Plant origin

Terpenoids

Monoterpenes, diterpenes, polyterpenes

Pine tree, rubber tree

Natural dyes

Alizarin, Tyrian purple, indigo

safflower, madder, woad

Natural pharmaceuticals

Pyrethroids, alkaloids, steroids

St. John’s wort, fennel, belladonna, thyme, camomile

Vitamins

Vitamin E, Vitamin C

Soy, Rape, Citrus fruits

Nutraceuticals

Flavonoides, polyphenols, carotinoids

Soy, rape, sage, tomato, paprika

Natural fragrances

Essential oils, damascon, jonon

Rose, jasmine, violet, iris

Waxes

Monoesters

Jojoba

Cork

Suberin

Cork oak

the sugar beet hoards sugar reserves in its roots or the potato plant hoards starch reserves in its tubers. . Table 1.1 provides an overview of these primary substances. The first column in this table contains the different groups of renewable raw materials, Column 2 some typical representatives of these groups and Column 3 some crops containing these ingredients. You probably would not know all the terms in . Table 1.1; however, you will learn all the terms in detail in the following chapters. As . Table 1.1 shows, many ingredients are found in a wide variety of plants, e.g. cellulose in wood, hemp and sisal. In these cases, it is, therefore, possible to decide which plant is to be used to obtain this renewable raw material. On the other hand, plants always consist of several ingredients: Soybeans contain not only fats and oils, but also proteins, for example. This results

in the major task of separating these substances from each other and isolating them in sufficient quality. The primary ingredients are found in particularly large quantities in nature. In addition to the primary ingredients, there are also the secondary ingredients, which occur in the plant in much smaller amounts, often only in traces. They were gradually trained in the course of a plant’s development in order to pursue specific strategies, e.g. fending off predators or attracting pollinating insects. These include certain fragrances and dyes as well as substances that we now use as pharmaceuticals. . Table 1.2 gives an overview and presents some typical examples. . Table 1.2 shows that very complex molecules, e.g. steroids, vitamins or alkaloids, can be obtained from some plants. Some of these substances, e.g. the red dye of the purple snail, have been known for many centuries. But even today,

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Chapter 1 · The Overview - Introduction

Other polysaccharides (chitin, hemicelluloses, starch)

Cellulose

26% 39%

30% 5%

Fats, oils, terpenes, proteins, etc.

Lignin

. Fig. 1.1  Main ingredients of renewable substances (in weight-%)

plants with new active substances are still being sought in tropical forests that can either be used directly or serve as models for new synthetic pharmaceuticals. It is estimated that approximately 170 billion tons of renewable raw materials are produced annually worldwide of which only a small fraction (approx. 6 billion tons, i.e. approx. 3.5%) is used by mankind. However, these and other figures in this book should be handled with caution, as they are estimates only. In some literature sources, quantities of renewable raw materials of between 140 and 180 billion tons per year can also be found. Nevertheless, such figures are useful to get a feeling for the order of magnitude. What are the most important renewable raw materials in terms of quantity? Here, too, there are only estimates shown in . Fig. 1.1. The most important renewable raw material in terms of volume is cellulose, which accounts for over a third (39%) of the pie chart. Lignin accounts for almost another third (30%). These figures can be explained simply by the fact that a large part of the earth’s landmass is covered by forests and that the main components of forest wood are cellulose and lignin. Cellulose belongs chemically to the polysaccharides. Other polysaccharides, such as chitin, starch and hemicelluloses, are also crucial in terms of quantity and represent a further quarter (26%). Chitin (. Table 1.1) is a structural substance found in the crabs and cancers of our oceans and is the second most important polysaccharide after cellulose with an annual

occurrence of about 100 million tons per year. All other natural substances (fats and oils, terpenes, proteins et al.) together make up only about 5% in terms of quantity, but due to their special structures and properties, they have to be classified very highly in terms of value. 1.3  Comparison with Fossil Raw

Materials

Wood, a renewable resource, has been a companion of mankind for thousands of years, whether as a material for building houses and ships, as a fuel for generating heat or in the form of charcoal as a fuel for reducing ores for metal extraction. Other renewable raw materials have also long been used by humans, e.g. flax, wool and cotton for the production of clothing or certain plants for the production of natural remedies. In the middle of the nineteenth century, the fossil raw material coal became increasingly popular. Coal was used for heating, and later, steam engines, steamships and steam locomotives were powered by coal: Industrialization began. People also learned - by coking the coal - to produce coke, coal tar and coke oven gases which are used to produce steel, to isolate aromatic hydrocarbons and to generate light. By coal gasification, the synthesis gas - a mixture of carbon ­monoxide and hydrogen - and by coal hydrogenation, coal fuel was finally produced. Until the 1950s, coal was converted to acetylene (ethyne) via the inter-

5 1.3  Comparison with Fossil Raw Materials

Billion t. 900 800 700

Hard coal 770 fossil sources

600

annual renewable

500 400 300

Brown coal 283

200 100

Crude oil 169

Renewable raw materials 170

0 . Fig. 1.2  Reserves of carbonaceous raw materials (World 2012). Source German Federal Institute for Geosciences and Raw Materials (Bundesanstalt für Geowissenschaften und Rohstoffe, BGR)

mediate stage of carbide, which in turn is an excellent reactive building block for the synthesis of numerous chemical intermediates such as ethanol, acetaldehyde or acrylic acid. In the 1940s started the era of two further fossil raw materials, crude oil and natural gas. In many regions of the world, first in North ­America and then especially in the Middle East, large deposits have been discovered, the mining of which began immediately. Large quantities of oil have been used to meet the enormous energy demands of modern society, whether in form of heavy fuel oils for industry and shipping, as kerosene for air traffic, as light heating oils for private households, as gasoline and diesel for automobiles or for generating electrical energy for industry and households. However, it soon became clear that the reserves of fossil raw materials are limited in quantity despite all the successes in the exploration of crude oil and natural gas. . Figure 1.2 shows clearly that we still have relatively large reserves of hard coal and lignite (with currently approx. 169 billion tons), but that our recoverable oil reserves are slowly coming to an end. If we continue to use oil in the same way as yet, we would still have enough oil reserves - statistically speaking - for 41 years, that is, until 2058, but in this year we will certainly not come to a sudden end, because humanity is already looking for new solutions to the open energy issues, so that there are high hopes that crude oil for the syn-

thesis of important chemicals will continue to be preserved for even longer. Similar considerations apply to natural gas: The current estimated world reserves of approx. 181 × 1012 m3 will last - also statistically speaking - for another 63 years. . Figure 1.2 shows that renewable raw materials represent an important alternative in the medium and long term: At 170 billion tons per year, they are of a similar order of magnitude to the current oil reserves, but through photosynthesis, they grow back each year from the raw materials carbon dioxide and water in the earth’s carbon cycle. For this, only the sun must shine (cf. Eq. 1.1.), and hopefully, it will continue to do so for a few million years. The reserves are one side of the coin, the annual consumption of raw materials is the other. . Table 1.3 shows the consumption of various renewable raw materials in the German chemical industry in 2016 compared to the current consumption of fossil raw materials for the production of petrochemicals. It is interesting to compare . Table 1.3 with . Fig. 1.1, i.e. the global occurrence of the various renewable raw materials: Although the earth has mainly cellulose and lignin available because of the large forest stands, the German chemical industry uses vegetable and animal fats and oils (total: 1.17 million tons per year), followed by cellulose and starch by far. The lignin listed in . Fig. 1.1 as a globally important component does not appear at all in . Table 1.3!

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. Table 1.3  Consumption of renewable raw materials in the chemical industry (Germany 2016) Renewable resource Oils and fats

Consumption (t) 1,170,000

Starch

296,000

Cellulose (pulp)

380,000

Sugar

156,000

Proteins

119,000

Others (natural fibers, waxes, resins, etc.)

572,000

Sum: renewable resources

2,690,000

Cf. Petrochemicals

17,700,000

Share renewable resources

ca. 13%

The reasons for this will be explained in more detail in the following chapters: Fats and oils have very defined structures closely related to petrochemical basic chemicals, while starch, cellulose and lignin are composed of macromolecules with completely different structures. In wood, lignin and cellulose are additionally linked (lignocellulose), which makes their pure production and their subsequent chemistry even more difficult. So, the chemical industry took the simpler (and cheaper) path and first developed an extensive chemistry of fats and oils, the so-called oleochemistry. Only in recent decades, increased efforts have been made to exploit lignocellulose. At the end of . Table 1.3, another important comparison can be drawn, namely the ratio of petrochemicals to the chemistry of renewable raw materials in Germany. 17.7 million metric tons of petrochemicals were produced in Germany in 2016 compared to 2.7 million metric tons of products on a renewable basis. This means that the proportion of renewable raw materials is around 13%, which is slightly lower worldwide. This relatively high percentage is partly due to the fact that more than 100 years ago already pioneers such as Fritz Henkel set up an extensive oleochemistry business in Germany. The declared political goal of both the EU and the USA at the beginning of the 2000s was to increase the share of renewable raw materials in chemical production to 20–25% by 2020, but since the introduction of completely new chemical processes requires careful process development of several years, this goal was clearly too optimistic.

The question quickly arises: Could renewable raw materials one day completely replace fossil raw materials? Radio Yerevan replies: “In principle, yes!” However, this would still be far too expensive at present, because despite the increase in oil and natural gas prices in recent decades, the use of renewable raw materials is still comparatively uneconomical in many cases. In a very simplified scheme, . Fig. 1.3 attempts to compare the paths of the fossil raw materials coal, natural gas and crude oil (above) with the paths based on the renewable raw materials fats, carbohydrates and lignin (below) to the intermediate and end products of the chemical industry (right). Follow the individual reaction arrows together with us: 5 Currently, distillation cuts of crude oil in the steamcracker are used to produce the important olefins ethene, propene and butenes, and in the reformer the important aromatics benzene, toluene and xylenes (BTX). In addition, both crude oil, natural gas and coal can be converted into the synthesis gas of carbon monoxide and hydrogen. From these relatively small molecules (C1 to C8), the majority of chemical intermediates (alcohols, aldehydes, carboxylic acids, amines …) is produced, which in turn are starting compounds for significant classes of chemi­ cal end products, e.g. polymers, surfactants, pharmaceuticals or agrochemical chemicals. As already mentioned at the beginning, coal can also be converted via the intermediate stage of acetylene into intermediates. 5 Fats, carbohydrates and lignin can also be gasified to synthesis gas. Since synthesis gas can be converted into olefins and aromatics via the intermediate stage of methanol (not shown in . Fig. 1.3), the same basic chemicals and thus the same intermediate and end products are available from the renewable raw materials as on the basis of fossil raw materials. 5 However, it is particularly advantageous if the chemist succeeds in using the renewable raw materials as directly as possible - i.e. without “breaking down” the starting materials into the synthesis gas - and producing end products such as biosurfactants or biopolymers from fats and/or carbohydrates, for example. In this case, the synthesis performance of nature is fully exploited and the renewable raw materials are converted into valuable products with energy benefits.

7 1.3  Comparison with Fossil Raw Materials

Coal

Natural gas

Crude oil

Acetylene

Olefins

Chemical Intermediates and Products

Synthesis gas Aromatics

Carbohydrates

Fats

Lignin

. Fig. 1.3  Comparison of the paths from the raw materials to the intermediates and end products

Millennia

Before our times

In our days

Renewable raw Coal materials, Crude oil Use of CO2, Natural gas H2 technologies

Hydropower

Renewable raw materials -5

-4

Stone Age

Wind power

-3

-2 Bronze Age

-1

+1

+2

+3

+4

Iron Age Intermediate fossil period

Solar period1

Solar period2

. Fig. 1.4  Substance and energy sources of mankind over the millennia

In the long term, renewable raw materials can replace fossil raw materials for the synthesis of organic materials without us having to significantly change the technologies already known. The readers of this book should realize that they live in a very extraordinary “interim”. As

. Fig. 1.4 shows, since the beginning of its existence mankind has only been able to use energies and materials of solar origin (“first solar period”). We are currently in a very small “fossil interim period” from a historical point of view, in which the carbon deposited in the ground in

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Chapter 1 · The Overview - Introduction

. Fig. 1.5  Current fields of application of crude oil and renewable raw materials

93% Energy

a) Crude oil

7% Chemical industry

95% Food

b) Renewable raw materials 5% Chemical industry, energy, fuels et al.

millions of years as coal, natural gas or crude oil is removed from the soil and is mainly used for energy purposes. In these combustion processes, carbon is ultimately converted into carbon dioxide, which poses the problem of increasing CO2 concentrations in our atmosphere. In a few decades, the oil and gas reserves will slowly run out, in a few centuries also the coal reserves. By then at the latest, the “second solar period” of mankind will begin with the almost exclusive use of renewable raw materials and probably with increased use of carbon dioxide and hydrogen electrolytically produced from water. But there is still a long way to go. The primary task at present is to reduce the enormous consumption of crude oil for energy purposes (. Fig. 1.5a), i.e. to build more economical cars or power plants or to better insulate our houses: 93% of crude oil is currently used in energy applications and only 7% in chemicals. A similar balancing act currently exists for renewable raw materials (. Fig. 1.5b): The quantities of renewable raw materials currently used by humans (approx. 6 billion tons of the approx. 170 billion tons newly formed annually) are primarily used as food (95%) and only 5% are used industrially, e.g. in chemical synthesis. Another complicating factor is that in the last ten years, renewable raw materials such as biodiesel or bioethanol have also been increasingly used for energy purposes. Here, markets must be decoupled so that industrial and energy applications do not lead to a shortage of basic foodstuffs and thus

to an increase in food prices. In the long term, the use of renewable raw materials for energy purposes makes little sense, but here hydrogen technology using solar energy is the much better way (. Fig. 1.4). 1.4  Advantages and Disadvantages

of Renewable Raw Materials

Let us start with the benefits: 5 Since renewable raw materials are constantly being created, unlike fossil raw materials (see 7 Sect. 1.3), they are available to us almost infinitely. This means that we can first of all conserve fossil raw materials and also replace them in the long term. Renewable raw materials thus fit well into the concept of “sustainability” and can be assigned to “green chemistry”. 5 The renewable raw materials are almost CO2-neutral, because the carbon released during their decomposition can be converted back into a natural substance through photosynthesis. This means that no additional greenhouse effect occurs when they are used. However, this calculation is somewhat simplified: The maintenance, fertilization, harvesting and processing of renewable raw materials always require energy, which is currently still predominantly generated by burning fossil raw materials. 5 Products based on renewable raw materials often have ecological advantages. For example,

9 1.4  Advantages and Disadvantages of Renewable Raw Materials

lubricating oils based on natural oils and fats are ecologically degradable and can therefore also be used safely in nature, e.g. for the lubrication of chainsaws in forestry operations. However, one must also consider this statement with caution: Products made from renew­ able raw materials are not automatically easily degradable, as even small molecular changes can cause a change in the degradation behavior. A “bioproduct” must therefore also be carefully tested for degradability or toxicity. 5 In the last decade, one problem has played an important role in Germany’s agricultural policy: the use of fallow arable land. Due to overproduction in Europe, not all agricultural land is used, and thus, the possibility arises to use these industrially for materially used plants, so-called industrial plants, or for energetically used plants, so-called energy plants. These measures can help to strengthen the agricultural economy and maintain or create new jobs in rural areas. 5 Another major advantage of renewable raw materials has already been briefly mentioned during the discussion of . Fig. 1.3: Renewable raw materials have relative complex structures that the chemist can use directly for specific purposes, without the complex synthesis steps required in the petrochemical industry. A well-known example of this is the synthesis of soaps, the alkali salts of long-chained carboxylic acids: While they are derived from alkenes or alkanes only in numerous steps, they can be produced in oleochemical industry in a single step by saponifying the fats and oils with caustic soda or potassium hydroxide solution. The synthesis power of nature is fully utilized for the desired end product and costly synthesis steps are omitted. A major disadvantage of renewable raw materials is often their procurement and logistics. While it is relatively easy to extract crude oil or

natural gas at the drilling site and transport it in pipelines, cellulose-containing tree trunks or starchy potatoes first have to be laboriously collected on a large area of forest or arable land and then transported to a central processing site. The same applies if you want to get any residual material, such as sawdust from numerous sawmills or straw from many individual fields. The procurement of renewable raw materials is therefore usually connected with complex (expensive) transport measures. An important question in chemical industry is always the economic efficiency of a chemical process. The most beautiful chemistry is not carried out industrially if the customer is not willing to pay the price of the product. . Table 1.3 has shown us that products based on renewable raw materials in the order of 2.7 million tons per year are already manufactured and sold in Germany. The economic efficiency of these products must therefore be guaranteed. But does this generally apply to all renewable raw materials? Let us look at . Table 1.4, which lists the purchase prices for some important basic chemicals based on fossil or renewable raw materials. These prices are often subject to significant fluctuations. The values in this table are not based on current daily prices, but we are only interested in the order of magnitude and the rough value comparison of the products with each other. . Table 1.4 shows us that the large basic chemicals based on crude oil, the olefins ethene and propene as well as the aromatics benzene and toluene, both in terms of production volumes and prices, are of a similar order of magnitude as the large products from the range of renewable raw materials, e.g. cellulose or sucrose. However, some renewable raw materials, e.g. the sugars d-xylose and l-sorbose, are currently only produced in small quantities and also have significantly higher prices. In the case of renewable raw materials, it therefore depends very much on the purposes for which they are to be used. An expansive starting compound can only be used if the product justifies this price.

1

10

1

Chapter 1 · The Overview - Introduction

BOX: The SWOT analysis The SWOT analysis is a generally applicable method to systematically examine and evaluate a difficult situation, e.g. a new idea. The acronym SWOT is derived from the initial letters of the following four terms: 5 Strength: What are the advantages and strengths of the new idea? 5 Weaknesses: What are the disadvantages of the new idea? 5 Opportunities: What opportunities will arise if I realize the new idea? 5 Threats: What risks, i.e. dangers, arise when implementing the new idea? In order to obtain a conclusive analysis, all relevant aspects must be considered when answering these four questions, i.e. all economic, social and environmental aspects. Today, SWOT analysis is the first step in strategic planning for many corporate decisions. The SWOT analysis considering the use of renewable raw materials for energy and material purposes provides the following overall picture:

z Strength:

5 The limited, fossil raw materials coal, oil and natural gas are conserved. 5 This reduces greenhouse gas emissions. 5 Ideally, this will result in almost closed and thus sustainable cycles, e.g. of carbon dioxide. 5 The income of workers in forestry and agriculture will be expanded: Jobs will be created and regional benefit increased. 5 Products will be available locally and people are no longer dependent on foreign raw materials: The security of supply is increased.

5 The spectrum of useful plants is extended and crop rotation can be varied more widely: The cultural landscape is enriched.

z Weaknesses:

5 The available agricultural land must be divided between crops and food production. 5 For some uses of products (e.g. rape cultivation for the production of biodiesel), this competitive situation leads to acceptance problems among consumers. 5 In some markets, renewable raw materials are not (yet) competitive. This leads to undesirable long-term political regulations (introduction of biodiesel) and/or subsidies (use of biogas). 5 In order to convert renewable raw materials into innovative and competitive products, extensive and thus time-consuming and expensive research and development is required.

z Opportunities:

5 As a result of increased research and development, innovative products based on renewable raw materials are being developed that significantly improve competitiveness compared to fossil raw materials. 5 The supply of raw materials can thus be placed on a sustainable basis: Respective countries are no longer dependent on expensive imports. 5 Rising prices for fossil raw materials can lead to products based on renewable raw materials becoming economically attractive. However, it must be considered that rising prices for fossil raw materials can also lead to higher agricultural costs.

5 Breeding improvements in crops and technological improvements in their production can significantly strengthen the competitive position of sustainable raw materials. 5 In general, a trend toward greater sustainability and more natural approaches is recognized in industrialized countries. If, in addition, mandatory certification of sustainable products is introduced in these countries, this can significantly increase the social acceptance of products based on renewable raw materials.

z Threats:

5 The above-mentioned competition between commercial crop production on the one hand and food production on the other may lead to a situation in which the cultivation of commercial crops is not accepted by society in the long term. 5 With the world population continuing to grow and the increased demand for food, this effect may become even greater. 5 For many products based on renewable raw materials, it is highly questionable whether they can be produced economically in the long term compared to products based on fossil raw materials. The opportunities offered by renewable raw materials seem to exceed their threats by far. However, only future will show how the opportunities of renewable raw materials will develop. Since different countries have different agricultural preconditions, different solutions will be found globally.

1

11 1.4  Advantages and Disadvantages of Renewable Raw Materials

. Table 1.4  Price comparison of basic chemicals on a petrochemical and renewable basis (World 2005, without guarantee) Resource

Basic chemical

Crude oil

Ethene

Renewable resources

Amount (106 t a−1)

Price (€ t−1)

100

1000

Propene

64

1000

Methanol

25

150

Benzene

23

900

Toluene

7

250

Cellulose

320

500

Sucrose

169

200

Starch

55

250

Bioethanol

32

650

d-Glucose

30

300

Isomaltulose

0.07

2000

d-Xylose

0.03

4500

l-Sorbose

0.06

7500

A general problem of renewable raw materials is related to their molecular structure and element composition. Petrochemical basic chemicals usually consist only of carbon and hydrogen. In the large groups of renewable raw materials, only the basic substances of terpenes belong to the hydrocarbons; all other renewable raw materials additionally contain oxygen, nitrogen or further elements. . Table 1.5 gives the first comparison between fossil and renewable raw materials with regard to their molar element composition. Oxygen is often present in large ­ quantities in renewable raw materials. This oxygen is

present in the form of carboxylic acid, aldehyde, ketone and/or alcohol groups and makes the molecules relatively hydrophilic, i.e. water soluble. For example, comparing the formu­ las of the industrially important C6 hydrocarbons n-hexene[C6H12], cyclohexane[C6H12] and benzene[C6H6] with the C6 carbohydrate glucose[C6H12O6] reveals that the carbohydrate must have completely different properties: The hydrocarbons are almost insoluble in water, whereas glucose is very soluble in water due to its hydroxyl groups. If you want to use glucose for a similar chemistry as with hydrocarbons, you have to dehydrate or hydrogenate the carbohydrate in

. Table 1.5  Comparison of fossil and renewable raw materials with respect to their elemental composition (the molar C/H/O/N ratio is given in relation to carbon)

Fossil resource

Renewable resource

Resource

Molecular formula

C

H

O

N

Coal

C

1

0

0

0

Crude oil

–CH2–

1

2

0

0

Dry natural gas

CH4

1

4

0

0

Oleochemicals, e.g. glyceroltrioleate

C57H104O6

1

1.8

0.1

0

Carbohydrates, e.g. glucose

C6H12O6

1

2

1

0

Terpenes, e.g. myrcene

C10H16

1

1.6

0

0

Amino acids, e.g. alanine

C 3H 7O 2N

1

2.3

0.7

0.3

12

1

Chapter 1 · The Overview - Introduction

. Table 1.6  Elementary composition of the raw materials (in % by weight) Resource

C

H

O

Crude oil

85–90

10–14

0–1.5

Fats and oils

76

13

6

Lignocellulose

50

6

43

beet) or they are first chemically and/or biotechnologically converted into a more manageable synthetic building block (conversion), e.g. starch, which is often first hydrolyzed biotechnologically into smaller carbohydrate fragments (see 7 Chap. 8). Summary (Take-Home Messages)

order to remove the “excess” oxygen. In the eyes of a petrochemist, the carbohydrates are therefore overfunctionalized and first have to be defunctionalized for some applications. The particular characteristics of renewable raw materials in terms of their elemental composition become even more obvious when one looks at the weight ratios rather than at the molar ratios as shown in . Table 1.5. . Table 1.6 shows the approximate compositions of carbon, hydrogen and oxygen in percent by weight for crude oil, fats and oils and for lignocellulose. While fats and oils are still relatively similar to crude oil, lignocellulose, with only 50% C but 43% O, is a completely different raw material for which new processing and recovery methods have to be developed. The details of processing depend strongly on the renewable raw material and are discussed in the special chapters of this book. In general, however, the basic scheme described in . Fig. 1.6 applies to natural raw materials (cf. 7 Chap. 20): After transport, the raw materials are usually first crushed mechanically in mills and/or isolated in sufficient purity by disintegration processes or extractions. Either they can then be used directly as synthesis components (e.g. sucrose from sugar

. Fig. 1.6 Pretreatment and conversion of renewable feedstocks

5 Renewable raw materials are organic materials from nature, which can be used as substances or energetically in the non-food sector. 5 Important primary ingredients are triglycerides in fats and oils and the carbohydrates, which can be subdivided in sugar, cellulose, hemicelluloses, chitin and starch. 5 Important secondary ingredients are terpenoids and natural coloring agents, fragrances, pharmaceuticals and vitamins. 5 The renewable raw materials are formed worldwide annually by photosynthesis in a quantity of approx. 170 billion tons. The fossil raw materials coal, natural gas and crude oil are still available to us for many years, but its reserves are finite. 5 The share of renewable raw materials in the production of chemicals amounts currently in Germany approx. 13%. Fats and oils are most commonly used, followed by cellulose, starch, proteins and sugars. 5 Renewable raw materials have completely different structures and compositions than petrochemicals.

Processing Renewable raw materials

- Crushing - Disintegration - Extraction

Conversion - chemical - biotechnological

Synthesis Building Block

13

1.4  Advantages and Disadvantages of Renewable Raw Materials

Nevertheless, it is theoretically possible to replace the current petrochemical industry in the long term with the chemistry of renewable raw materials. 5 However, some renewable raw materials, especially carbohydrates, are “overfunctionalized” and methods for defunctionalization must be developed. 5 Great advantages of renewable raw materials are their “infinite availability”, their CO2 neutrality and their good degradability. In addition, they can help with the use of uncultivated farmland. They are particularly advantageous when they can be used directly for chemical purposes without complex multistage syntheses due to their usually complex structures. 5 A disadvantage is the complex cultivation and/or collection of renewable raw materials. As a result, their prices are often still too high compared to petrochemicals. But there are also a number of renewable raw materials that are already available in sufficient quantities and at a reasonable price which can be used in a wide range of applications. 5 In the chemical use of renewable raw materials, a physical treatment must usually first be carried out before a chemical or biotechnological conversion can be applied.

? Ten Quickies

1. Formulate the general equation of photosynthesis! 2. Name some important sugars! If necessary, see . Table 1.1 or . Table 1.4. 3. Compare the molecular formula of the terpene myrcene (. Table 1.5) with that of the petrochemical decatriene! 4. Are there also renewable resources in the oceans? 5. Does cellulose only occur in tree wood? 6. Do soybeans contain exclusively oils and fats? 7. What can be derived from the jojoba plant?

8. Name the two most important renewable raw materials in terms of quantity! 9. Which group of renewable raw materials is used in Germany at the most often processed into chemicals? Who was one of the pioneers of these developments? 10. Differentiate between industrial and energy crops! Do you know any examples?

References Monographs and Review Articles Choudhury I, Hashmi S (eds) (2020) Encyclopedia of renewable and sustainable materials. Elsevier, Amsterdam Popa V, Volf I (eds) (2018) Biomass as renewable raw material to obtain bioproducts of high-tech value. Elsevier, Amsterdam Diepenbrook W (2014) Nachwachsende Rohstoffe. Ulmer, Stuttgart Vogel GH (2014) Chemie erneuerbarer kohlenstoffbasierter Rohstoffe zur Produktion von Chemikalien und Kraftstoffen. Chem Ing Tech 86:2135–2149 Türk O (2014) Stoffliche Nutzung nachwachsender Rohstoffe. Springer Vieweg, Wiesbaden Behrens M, Datye AK (eds) (2013) Catalysis for the conversion of biomass and its derivatives. Open Access, Berlin Imhof P, van der Waal JC (eds) (2013) Catalytic process development for renewable materials. Wiley-VCH, Weinheim Tojo S, Hirasawa T (2013) Research approaches to sustainable biomass systems. Academic Press Himmel ME (ed) (2012) Biomass conversion - methods and protocols. Springer Nature Ulber R, Sell D, Hirth T (2011) Renewable raw materials. Wiley-VCH, Weinheim Hood EE, Nelson P, Power R (2011) Plant biomass conversion. Wiley-VCH, Weinheim Lancaster M (2010) Green chemistry. Renewable resources (Chap. 6). RSC Paperbacks, Royal Society of Chemistry, London Behr A, Johnen L (2009) Alternative feedstocks for synthesis. In: Anastas PT (ed) Handbook of green chemistry. Wiley-VCH-Verlag, Weinheim Langeveld H, Meeusen M, Sanders J (2010) The biobased economy: biofuels, materials and chemicals in the post-oil era. Earthscan, London Hill K, Höfer R (2009) Biomass for green chemistry. In: Höfer R (Hrsg) Sustainable solutions for modern economies. Royal Society of Chemistry, London Behr A (2008) Angewandte homogene Katalyse. Homogene Katalyse mit nachwachsenden Rohstoffen (Kap. 44). Wiley-VCH Verlag, Weinheim Clark J, Deswarte F (Hrsg) (2008) Introduction to chemicals from biomass. Wiley, New York

1

14

1

Chapter 1 · The Overview - Introduction

Corma A, Iborra S, Velty A (2007) Chemical routes for the transformation of biomass into chemicals. Chem Rev 107:2411–2502 Graziani M, Fornasiero P (2007) Renewable resources and renewable energy - a global challenge. CRC Press, Taylor & Francis Group, Boca Raton Centi G, Van Santen RA (eds) (2007) Catalysis for renewables: from feedstock to energy production. ­Wiley-VCH, Weinheim Schäfer B (2007) Naturstoffe der chemischen Industrie. Spektrum Akademischer Verlag, Heidelberg Steglich W, Fugmann B, Lang-Fugmann S (2000) Römpp Encyclopedia - Natural Products. Georg Thieme ­Verlag, Stuttgart Original Publications and Web Links Fachagentur Nachwachsende Rohstoffe - FNR (Hrsg) (2018) Anbau und Verwendung nachwachsender Rohstoffe in Deutschland. 7 https://fnr.de/fileadmin/ fnr/pdf/mediathek/22004416.pdf Verband der Chemischen Industrie - VCI (2015) Chances and limitations for the use of renewable raw materials in the chemical industry. 7 https://www.vci.de/langfassungen-pdf/chances-and-limitations-for-the-use-of-renewable-raw-materials-in-the-chemical-industry.pdf, May 2015

Fukuoka A, Murzin DY, Roman-Leshkov Y (2014) Special issue on biomass catalysis. J Mol Catal A Chem 388– 389:1–188 Besson M, Gallezot P, Pinel C (2014) Conversion of biomass into chemicals over metal catalysts. Chem Rev 114:1827–1870 Keim W, Röper M et al (2010) Positionspapier: Rohstoffbasis im Wandel. GDCh, Dechema, DGMK, VCI, Frankfurt Behr A, Johnen L, Vorholt A (2009) Katalytische Verfahren mit nachwachsenden Rohstoffen. Nachr Chem 57:757–761 Fonds der Chemischen Industrie - FCI (2009) Folienserie „Nachwachsende Rohstoffe“. Can be downloaded at: 7 https://www.vci.de/fonds DECHEMA (2008) Positionspapier Einsatz nachwachsender Rohstoffe in der chemischen Industrie. Frankfurt Diercks R et al (2008) Raw material changes in the chemical industry. Chem Eng Technol 31:631–637 Busch R et al (2006) Nutzung nachwachsender Rohstoffe in der industriellen Stoffproduktion. ChemIng Tech 78:219–228 Van Bekkum H, Gallezot P (Hrsg) (2004) Catalytic conversion of renewables. Special issue: Top Catal 27(1–4) U.S. Department of Energy (2004) Top value added chemicals from biomass. 7 https://www.nrel.gov

15

Fats and Oils Chapter 2

The Raw Materials of Oleochemistry Oil Plants – 17

Chapter 3

The Basics of Oleochemistry - Basic Oleochemicals – 37

Chapter 4

There is More to Oleochemistry - Reactions at the Fatty Acid Alkyl Chain – 61

Chapter 5

The Coproduct of Oleochemistry Glycerol – 89

I

17

The Raw Materials of  Oleochemistry - Oil Plants 2.1 Introduction to Oleochemistry – 18 2.2 Overview of Important Vegetable Oils and Animal Fats – 21 2.2.1 Coconut Oil – 21 2.2.2 Palm Oil and Palm Kernel Oil – 23 2.2.3 Rapeseed Oil – 25 2.2.4 Sunflower Oil – 25 2.2.5 Soybean Oil – 26 2.2.6 Linseed Oil from Flax Plants – 26 2.2.7 Castor Oil – 27 2.2.8 Olive Oil – 28 2.2.9 Safflower Oil – 29 2.2.10 Jatropha Oil – 29 2.2.11 Other Fats and Oils – 31

2.3 Some Numbers – 31 References – 34

© Springer-Verlag GmbH Germany, part of Springer Nature 2020 A. Behr and T. Seidensticker, Chemistry of Renewables, https://doi.org/10.1007/978-3-662-61430-3_2

2

18

Chapter 2 · The Raw Materials of Oleochemistry - Oil Plants

ever kept liquid olive oil in the refrigerator will certainly have observed a slight cloudiness after some time. In the following sections, we will simply refer to “fats”, but we will always refer to “fats and oils”. Fats are chemically predominantly triglycerides, i.e. triesters of glycerol (1,2,3-propanetriol) with long-chain carboxylic acids, the so-called fatty acids. The three fatty acids in triglyceride can have the same but also different structures. A typical example of a fat molecule is shown at . Fig. 2.1. By splitting with three moles of water, the triester can be converted into the triol ­glycerol and the three fatty acids, in this example into the fatty acids stearic acid, oleic acid and palmitic acid. This process is also called fat ­splitting or hydrolysis. In . Fig. 2.1, the fat chain is represented by dashes; this simplifies considerably the writing of the long chemical structures. The figure also shows that this reaction is reversible, i.e. triglycerides can also be synthesized chemically from glycerol and fatty acids. In the laboratory, an acid is usually used as a catalyst. In . Fig. 2.1, we see three different fatty acids (from top to bottom): the saturated octadecanoic acid with the trivial name stearic acid, the unsaturated cis-9-octadecenoic acid, the oleic acid, and the saturated hexadecanoic acid with

Chapter Timetable

2

5 The nomenclature of oleochemistry is explained and the most important fatty acids are discussed. 5 You will learn which fats and oils are of technical importance and why. 5 The twelve most important vegetable fats and oils are presented, each with a description of the plant, the oil, its extraction, its composition and its most important applications. 5 The animal fats and oils are briefly introduced to you. 5 At the end, you will get an insight into the production figures of fats and oils.

2.1  Introduction to Oleochemistry

Fats and oils have the same chemical structure; they differ only in their melting points. Oils have a melting point below room temperature, are therefore (viscous) liquid, fats have a melting point above room temperature and are therefore solid. In oleochemistry, however, the term “solid” usually refers to an aggregate state similar to margarine. Fats can thus be thermally converted into oils and vice versa. Anyone who has

. Fig. 2.1  Fat splitting of a triglyceride with water in glycerol and fatty acids

O H2C O C O

+ 3 H2O

HC O C O

- 3 H2O

H2C O C

Triglyceride

HOOC

H2C OH

Stearic acid HC OH

+

HOOC

Oleic acid

H2C OH

Glycerol

HOOC

Palmitic acid

19

2.1 · Introduction to Oleochemistry

the trivial name palmitic acid. It is obvious that these are only even-numbered carboxylic acids. In fact, odd-numbered carboxylic acids such as pentadecanoic acid are rarely found in nature.

All carboxylic acids have an IUPAC designation; however, this is rarely used in oleochemistry. Trivial names were often introduced many decades ago.

BOX: The Lazy Oleochemist The oleochemist often makes it a little easier and describes the fatty acids with an abbreviation. In this abbreviation stands first the symbol of carbon, followed by the number of carbon atoms. Then comes after a colon the number of C=C double bonds. Stearic acid is therefore C18:0 acid, palmitic acid C16:0 acid and oleic acid C18:1 acid

(. Fig. 2.1). If the oleochemist still wants to indicate at which position the double bond is located, he writes this in brackets after a large Greek delta Δ. If he wants to indicate a cis double bond, this is done with the abbreviation “c.”, a trans-double bond correspondingly with “t.”. The complete abbreviation for

Which long-chain carboxylic acids are found in natural fats? Here, somewhat different data are given in the literature, but usually the even-numbered saturated or unsaturated aliphatic carboxylic acids in the C number range between C8 and C22 are included; in exceptional cases, also carboxylic acids up to C30 are considered. In very rare cases, fatty acids with chains that contain an aliphatic cycle or are branched are also found. The most important saturated fatty acids are listed below in . Table 2.1 and the most important unsaturated fatty acids in . Table 2.2. This information is not intended for memorization, but for reference. In addition to these fatty acids, which have exclusively an aliphatic hydrocarbon rest, there

oleic acid is therefore: C18:1 (Δ9/c.). If there are several double bonds in the fat chain, these are listed one after the other in parentheses. The eicosapentaenoic acid in fish oil, for example, consists of 20 C-atoms and has five cis double bonds in positions 5, 8, 11, 14 and 17; the abbreviation is C20:5 (Δ5, 8, 11, 14, 17/all c.).

are also some fatty acids, which carry a further functional group, e.g. a hydroxy, keto or epoxy group, in addition to the carboxyl group. The best-known representatives of these fatty acids are listed in . Fig. 2.2. In the following, 7  Sect. 2.2 the plants and animals are introduced, in which fats with the most different fatty acid patterns occur. 7   Chapter 3 explains the technical processing of fats into fatty esters, fatty alcohols and fatty amines. In 7  Chap. 4, you will find an overview of the further follow-up ­chemistry of fats, especially unsaturated oleochemicals. In 7  Chap. 5, we then turn to glycerol, the inevitable by-product of oleochemistry ( .  Fig. 2.1).

. Table 2.1  Important saturated fatty acids Abbreviation

IUPAC name

Trivial name

Occurrence

C8:0

Octanoic acid

Caprylic acid

Butter, coconut oil

C10:0

Decanoic acid

Capric acid

Butter, coconut oil

C12:0

Dodecanoic acid

Lauric acid

Animal fats, coconut oil

C14:0

Tetradecanoic acid

Myristic acid

Animal fats, coconut oil

C16:0

Hexadecanoic acid

Palmitic acid

Animal fats, palm oil

C18:0

Octadecanoic acid

Stearic acid

Animal fats, palm oil

C20:0

Eicosanoic acid

Arachidic acid

Peanut, beet and cocoa oil

C22:0

Docosanoic acid

Behenic acid

Canola oil, peanut oil

2

20

Chapter 2 · The Raw Materials of Oleochemistry - Oil Plants

. Table 2.2  Important unsaturated fatty acids

2

Abbreviation

IUPAC name

Trivial name

Occurrence

C16:1(Δ9/c.)

cis-hexadecenoic acid

Palmitoleic acid

Seed oils

C18:1(Δ6/c.)

cis-6-octadecenoic acid

Petroselinic acid

Parsley seeds

C18:1(Δ9/c.)

cis-9-octadecenoic acid

Oleic acid

Palm oil, animal fats

C18:1(Δ9/t.)

trans-9-octadecenoic acid

Elaidic acid

Ruminant fats

C18:2(Δ9,12/c.c.)

Octadecadienic acid

Linoleic acid

Sunflower oil

C18:3(Δ9,12,15/all c.)

9,12,15-octadecatrienoic acid

Linolenic acid

Hemp/linen oils

C18:3(Δ8,10,12/t.t.c.)

8,10,12-octadecatrienoic acid

Calendulic acid

Marigold

C20:1(Δ5/c.)

cis-5-eicosenoic acid

Eicosenoic acid

White marshbill

C20:4(Δ5,8,11,14/all c.)

all-cis-5,8,11,14-eicosatetraenoic acid

Arachidonic acid

Liver, fish oils

C22:1(Δ13/c.)

cis-13-docosenoic acid

Erucic acid

Old canola

C22:1(Δ13/t.)

trans-13-docosenoic acid

Brassidic acid

Isomerization of erucic acid

12

COOH

OH 12-Hydroxystearic acid O

9

COOH

12,13-Epoxy-9-octadecenoic acid (Vernolic acid) 4

COOH

O 4-Oxo-9,11,13-octadecatrienoic acid (Licanic acid) OH

9

12

COOH

12-Hydroxy-9-octadecenoic acid (Ricinoleic acid) OH

11

14

14-Hydroxy-11-eicosenoic acid (Lesquerolic acid) . Fig. 2.2  Natural fatty acids with several functional groups

COOH

2

21

2.2 · Overview of Important Vegetable Oils and Animal Fats

2.2  Overview of Important

comparison with animal fats, grease is also listed at the end of . Table 2.3. It should be noted that the information in . Table 2.3 on the fatty acid composition of the various fats are mean values. There are not only the one coconut palm, but very different breeds with different fatty acid contents. For fats where the fat composition varies greatly (e.g. peanut oil and linseed oil), sub and upper values were given in the table. In addition, the quantities harvested and the composition of the fats are also strongly dependent on the course of growth and thus on the weather.

Vegetable Oils and Animal Fats

In advance, . Table 2.3 gives you an overview of the most important fats in food and chemical industry. A very first glance at this table reveals that there are two very different classes of fats: One class contains in particular the short-chain C12 and C14 fatty acids, namely coconut oil and palm kernel oil. These short-chain fatty acids are simply called laurics in industry, a term that ­naturally comes from the C12:0 acid, lauric acid. As we will see in 7 Chap. 3, the laurics are of great importance for the production of special surfactants. Coconut oil and palm kernel oil are therefore used exclusively for the production of these surfactants. The second major class of fats contains predominantly C18 and C16 fatty acids. . Table 2.3 also shows two examples that fats can be modified and further developed by ­breeding or by using genetic engineering. The original rapeseed oil (“old”) contains a lot of erucic acid (C22:1) and is therefore unsuitable for human consumption. The “new” rapeseed oil was developed by breeding, which contains a lot of oleic acid (C18:1) and linoleic acid (C18:2) instead of erucic acid. The development was ­similar for sunflowers: the old variety contains a lot of linoleic acid; the new sunflower quality is also called high oleic because it contains up to 91% oleic acid. In order to be able to draw a

2.2.1  Coconut Oil

Palms are important plants that supply fats, starch and protein. With approximately 2000 different species, the “Palmae” form one of the largest botanical families in the tropical region. An important representative is the coconut palm (Cocos nucifera), whose distribution is limited to the equatorial zone. The coconut palm can grow up to 30 m high and bears 10–15 coconuts that ripen throughout the year (. Fig. 2.3). A coconut weighs 1–2.5 kg. Each coconut contains the flesh (the copra) inside, which contains about 60% fat. In young, unripe fruits, there is still some coconut water, in a cavity of the fruit flesh (. Fig. 2.4). The copra

. Table 2.3  Overview of industrially important oil plants and their fatty acid composition (typical mean values in % by weight) Fat/oil

12:0

14:0

16:0

18:0

18:1

18:2

18:3

20:1

Coconut oil

48

17

9

Palm kernel oil

50

15

Palm oil

0

Rapeseed oil (old)

0

22:1

2

7

1

0

0

0

7

2

15

1

0

0

0

2

42

5

41

10

0

0

0

1

2

1

15

15

7

5

50

Rapeseed oil (new)

0

1

4

1

60

20

9

2

2

Sunflower (old)

0

0

6

4

28

61

0

0

0

Sunflower (new)

0

0

4

2

91

3

0

0

0

Soybean oil

0

0

8

4

28

53

6

1

0

Peanut oil

0

1

10

4

36–72

13–45

1

1

0

Linseed oil

0

0

6

3

15–25

10–30

50–60

0

0

Grease

0

1

31

13

46

6

0

0

0

22

Chapter 2 · The Raw Materials of Oleochemistry - Oil Plants

2

Epidermis Husk Shell Copra Coco water

. Fig. 2.3  Coconut palm (© tobrother/Fotolia)

. Fig. 2.4  Cross-section through a coconut

is surrounded by a wooden stone shell, which in turn is surrounded by the husk, a layer of coconut fibers several centimeters thick, the bast layer. The outermost layer of the coconut is a leathery epidermis. Newer varieties of the coconut palm aim to develop coconut palms with

shorter stems. They are thus better able to withstand tropical storms, have increased resistance to disease and are easier to harvest, e.g. with harvesting machines. Meanwhile, there are dwarf mutants of the Cocos nucifera, which grow only about 2 m high.

BOX: The Trained Monkeys The classic harvesting of coconuts is done in several ways: You can drop the ripe nuts on the ground and collect them there. However, this leads

to harvest losses. In Africa and Asia, the harvest is still carried out by pickers who climb up the 30 m high stems to reach the fruit stands. In Malaysia,

The epidermis and bast layer is removed from the coconuts and the stone shell is mechanically broken to preserve the copra. The typical further processing of oil fruits is presented below using the example of copra. This processing is carried out in the following steps (. Fig. 2.5): 5 The copra is first crushed roughly and then finely by crushers and roller mills. 5 The crushed plant material is finally heated in a heat pan to temperatures of e.g. 70 °C: This lowers the viscosity of the oil, which becomes more fluid. In addition, cell membranes are destroyed and proteins coagulated: Both lead to a better extractability of the oil. 5 The next stage of processing is the pressing of the oil in a continuously operated press. For this purpose, screw presses are used in which a press

there are specially trained monkeys for the harvest, the macaques, which climb up the palms and throw down the fruits.

shaft in the form of a screw is located, similar to a meat mincer. In order to increase the pressure in the course of the pressing process, the diameter of the worm gear tapers in the conveying direction. The pressing pressure produces temperatures of up to approx. 100 °C. The screw presses have a sieve on the outside through which the oil runs out. This turbid oil is filtered in a filter press and then flows into a storage tank. Both the crushing and pressing processes can be repeated to increase the oil yield. The remaining plant residues usually still contain a residual oil content of 8% or more after this process. These residues can be used as very high-quality animal feed, but often the oil content is further reduced by subsequent extraction:

2

23

2.2 · Overview of Important Vegetable Oils and Animal Fats

Screw press Extraction

Crusher

Silo Crude oil Filter press Grinding mill

Oil

Oil tank

Heating

. Fig. 2.5  Mechanical processes for oil extraction from oil fruits

5 This extraction can be carried out, for example, with n-hexane or with gasoline, whereby the extraction material is fed in countercurrent to the solvent. The solvent is then separated off again by distillation. 5 Modern processes use supercritical carbon dioxide (scCO2) as extraction agent. However, these processes require high pressures and are therefore more expensive. The advantage is that the carbon dioxide evaporates completely when the solution is released and thus no residual solvents are contained in the oil. The “crude oils” isolated in this way still have to be processed in a further refinery: 5 During degumming, hydrolysis precipitates proteins and phospholipids, making the oil much more stable in storage. 5 Enzymatically or microbially the triglycerides can split off free fatty acids which give the oil unfavorable properties. These fatty acids are neutralized in deacidification by adding alkali solutions, e.g. diluted NaOH. 5 Oils may contain natural colorants, e.g. ­carotenoids or chlorophyll. Most of these ­substances are already removed in the first

two steps. If necessary, bleaching with bleaching earth or adsorption on activated carbon can follow. 5 The last step is damping the oil. Volatile products of the oil are removed according to the well-known principle of vacuum steam distillation. Since unpleasant odors are also removed during this damping process, this is referred to as deodorization of the oil. If one examines the chemical composition of the coconut oil thus obtained, the fatty acid distribution already presented in . Table 2.3 (line 1) results: The triglycerides of coconut oil contain in large proportions the “lauric”, i.e. the lauric acid and the myristic acid, and in only small proportions the palmitic, stearic and oleic acids. Coconut oil is therefore an excellent raw material for detergent alcohols (cf. 7 Chap. 3). 2.2.2  Palm Oil and Palm Kernel Oil

Another important type of palm is the oil palm (Elaeis guineensis). It originates from the rainforests of Guinea and has therefore been given its botanical name. Already in 1466, the Portuguese

24

Chapter 2 · The Raw Materials of Oleochemistry - Oil Plants

2 Husk Pulp (flesh) Shell Kernel

. Fig. 2.6  Fruit of an oil palm (© Thomas Leonhardy/ Fotolia)

got to know the oil palm during their exploration trips through West Africa, but it was not until the middle of the nineteenth century that the Dutch brought the first specimens to Indonesia, where today - as in neighboring Malaysia - large plantations of the oil palm exist. While the coconut palms are very slender and the aging leaves shed completely, the Elaeis is relatively compact. The oil palms have a height of 6 to a maximum of 15 m; their stem remains intact for many years. The oil palm supplies oil fruits with an annual production of up to 6 tons per hectare for 50 years. Thousands of small fruits (. Fig. 2.6) grow closely pressed together in the 20 kg heavy fruit stands of the oil palm. These fruits contain a soft flesh rich in fat

. Fig. 2.7  Cross-section of a palm fruit

and three rock-hard seeds. If the nutshell of these seeds is broken, the “palm kernel”, which also contains fat, is reached (. Fig. 2.7). Both components of the oil fruit are processed separately and produce oils with different compositions: palm kernel oil, like coconut oil, contains many laurics. The palm oil obtained from the flesh consists mainly of the triglycerides of palmitic acid (which takes its name from the oil palm) and oleic acid. The pulp must be processed immediately after harvesting; otherwise, the damaged fruit will undergo enzymatic decomposition, which greatly increases the acid number of the oil (BOX: Quality Criteria for the Oleochemist). The hard-shelled cores, on the other hand, can be stored well.

BOX: Quality Criteria for Oleochemists In order to be able to assess the quality of the raw materials quickly, the oleochemist has introduced several fast measures that can be determined relatively quickly by titration: 5 The iodine value (IV) is a measure of the number of C=C double bonds and thus of the content of unsaturated fatty acids. It is determined either by titration with elemental bromine or by determining the uptake of hydrogen.

5 The acid value or number (AV or AN) is a measure of the content of “free” (i.e. not glycerol-bonded) fatty acids that have split off from the triglycerides upon aging. The AV is the mass of KOH (in mg) used to neutralize one gram of oil. Oils with a high acid number are of lower quality and therefore also lower in price. 5 The saponification value or number (SV or SN) indicates the mass of KOH (in mg)

required to bind the free acids contained in a gram of oil and to saponify the esters. 5 The hydroxyl value (HV) is a measure of the OH groups present in the oil. To determine the hydroxyl value, the oil is first esterified with acetic anhydride. The hydroxyl number then indicates the mass of KOH (in mg) required to neutralize the amount of acetic acid released during esterification.

25

2.2 · Overview of Important Vegetable Oils and Animal Fats

2.2.3  Rapeseed Oil

Rapeseed oil is obtained from the seeds of rape (Brassica napus oleifera). Rapeseed has long been one of the most important oil plants in the temperate zone. Rapeseed grains were already found in excavations of Germanic settlements. In the late MiddleAges, rape oil was used in Germany for lighting purposes. With the introduction of petroleum at the end of the nineteenth century, however, it lost this use. Rape belongs botanically to the cruciferous family. The plants grow up to 1.5 m high; the bright yellow flowers (. Fig. 2.8) later form the seed pods. The almost spherical seeds contained therein have a diameter of up to 3 mm. If the seeds are shiny black, the rape can be harvested and processed. Former (“old”) rapeseed oils mainly contain erucic acid (C22:1), oleic acid (C18:1) and linoleic acid (C18:2) (. Table 2.3). However, erucic acid is worthless for human nutrition because it cannot be digested in the human body. Larger amounts of erucic acid can even lead to coronary artery disease. In 1974 succeeded the breeding of rape varieties low in erucic acid, the so-called 0 variants. In 1978, a further improvement was achieved, namely the introduction of the “00 variants”. With these 00 rape variants, it was also possible to prevent the formation of glucosinolates (mustard oils bound to glucose, bitter

. Fig. 2.8  Rapeseed field (© artaxx/Fotolia)

substances), which can lead to thyroid dysfunction. The “new” rapeseed mainly contains oleic and linoleic acid and, in smaller quantities, linolenic acid. The old rape is of some importance as an industrial and energy plant; the new rape can be used safely for high-quality food. 2.2.4  Sunflower Oil

The original home of the sunflower is North America. In 1510, the Spaniards brought the sunflower to Europe, but it was not until the nineteenth century that its importance as an oil plant was recognized, when Peter the Great had it planted on a larger scale in southern Russia. The sunflower (Helianthus annuus) belongs to the daisy family and is an annual plant that can grow up to 5 m high. For commercial cultivation, however, 1–1.5 m high varieties are preferred, which can be harvested mechanically. The plant forms a disk-shaped inflorescence (see title picture of the book), which can contain several thousand small fruits. These sunflower seeds have an oil content of up to 57%, the rest are mainly proteins, carbohydrates and minerals. The (old) sunflower oil contains mainly linoleic acid (44–70%) and oleic acid (14–43%, . Table 2.3) and is an excellent raw material for the production of edible oil and margarine due to the high proportion of essential linoleic acid (BOX: MUFA or PUFA?). In the industry, it is processed to soaps and varnishes and partly serves as a substitute for linseed oil. The press cake remaining after extraction contains up to 50% protein and is often used as animal feed. Important new sunflower varieties have been introduced, particularly in Russia. The “new” sunflower is also called “high oleic” because it contains up to 91% oleic acid but only a little linoleic acid (3%) (. Table 2.3). This raw material leads to an oleic acid with a high degree of purity and is therefore ideally suited for chemical use, e.g. for the production of lacquers, paints and technical esters as well as for ­cosmetic products.

2

26

Chapter 2 · The Raw Materials of Oleochemistry - Oil Plants

BOX: MUFA or PUFA?

2

MUFA and PUFA are not sea monsters, but only common abbreviations used by oleochemists and nutritionists: 5 MUFA are monounsaturated fatty acids, e.g. the frequently occurring oleic acid. 5 PUFA are polyunsaturated fatty acids. These include

linoleic acid (C18:2), linolenic acid (C18:3), eicosapentaenoic acid C20:5 (Δ5, 8, 11, 14, 17/all c., EPA) and docosahexaenoic acid C22:6 (Δ4, 7, 10, 13, 16, 19/all c., DHA). EPA is a precursor of prostaglandins

and thus has important pharmacological properties. The polyunsaturated fatty acids belong to the essential fatty acids, which must be supplied to the human body with food, since it cannot produce them itself (. Fig. 2.9).

O OH Docosahexaenoic acid (DHA) O OH Eicosapentaenoic acid (EPA) . Fig. 2.9  Chemical structures of EPA and DHA

2.2.5  Soybean Oil

The soy plant (glycine max) belongs to the legume family and was planted in China as early as 1000 BC. It was not until the nineteenth century that it reached Europe and America. The soy plant produces soybeans, which contain both the oil (20%) and larger amounts of protein (40%). On the outside, the plant resembles the bush bean: It is heavily hairy and grows in the form of shrubs up to 80 cm high (. Fig. 2.10). The soy oil is obtained by extraction and contains approx. 50% linoleic acid, 30% oleic acid and between 3 and 11% linolenic acid, which is also responsible for the slight rancidity of the soy oil (. Table 2.3). In Germany, it is used for margarine production, in the USA also for the production of edible oils. Soy oil contains up to 3% lecithins, which are used as emulsifiers in the food sector as well as for technical purposes. The press cake produced during soy oil extraction, soy meal, contains almost all proteins and carbo-

hydrates and is used in the form of soy flour, soy milk and soy quark (tofu) as food for humans, but is also used as concentrated feed for animals. After dissolving in alkali, the soy protein can also be spun into threads which, after flavoring, produce artificial “soy meat”. The high content of linoleic acid is crucial for the technical use of soy oil: Lacquers, varnishes, lubricants, resins, plasticizers and paints are produced with soy oil. In recent years, soy oilbased polyols have increasingly been discussed as starting materials for biopolymers (polyester, polyurethanes, 7 Chap. 19). 2.2.6  Linseed Oil from Flax Plants

Flax belongs botanically to the large family of Linaceae, but only the linum usitatissimum (translated: the extremely useful linen) has gained importance as a cultivated plant. The fruit of the flax forms a spherical or oval capsule

27

2.2 · Overview of Important Vegetable Oils and Animal Fats

. Fig. 2.10  Soy plant (© chungking/Fotolia)

containing the linseeds (. Fig. 2.11). Flax can be divided into oil flax, oil fiber flax and fiber flax, with the linseed oil content decreasing and the fiber content increasing in this order. The fabric of the flax fiber is called linen. Linen was already known to the Sumerians and Egyptians 5000 years ago, and also in Europe, linen was already cultivated in the younger Stone Age. Fiber flax needs relatively much water for its growth; the oil flax prefers drier, warmer regions with temperatures around 20 °C. Linseed has an oil content between 30 and 50%. As . Table 2.3 shows, linseed oil obtained by grinding, pressing and/ or extraction contains high proportions of linolenic acid (50–60% C18:3) in addition to oleic acid (C18:1) and linoleic acid (C18:2). However, the key figures for linseed oil are sometimes subject to very strong fluctuations, especially the iodine value (BOX: Quality Criteria for Oleochemists). The high proportion of triple unsaturated fatty acid leads to the fact that linseed oil gradually polymerizes in the air by reactions with

. Fig. 2.11  Flax plants (© Janine Fretz Weber/Fotolia)

atmospheric oxygen and finally becomes solid: Several fatty acid molecules combine to form a large, branched molecule. An oil with this behavior is also called “drying oil“. These drying oils are excellently suited for the production of ecologically compatible lacquers, paints, printing inks and varnishes. Further applications can be found in the paper, leather and oilcloth industries and in the production of linoleum floor coverings (7 Sect. 4.2.2.5). The name “linoleum” already refers to the name of the main raw material, linseed oil (lat. oleum lini). 2.2.7  Castor Oil

Castor oil (Ricinus communis) belongs to the Euphorbiaceae family and comes from the tropics of Asia and Africa. Today, India, China, Brazil and Thailand are the main growing areas;

2

28

Chapter 2 · The Raw Materials of Oleochemistry - Oil Plants

2.2.8  Olive Oil

2

. Fig. 2.12  Seedpot of the castor plant (© LianeM/ Fotolia)

in Europe, for example, the plant is cultivated in Romania and Spain. The plants grow up to 2 m high, have large leaves up to 40 cm long and form inflorescences with up to 20 fruits (. Fig. 2.12). The spiny, red-green fruits contain seeds with an oil content of approx. 50%. The special feature of castor oil is the high content (87%) of triglycerides of ricinoleic acid, which we already got to know in . Fig. 2.2: Like oleic acid, it is a cis-C18:1 acid, but with an additional OH group in the C12 position. In addition, castor oil contains small amounts of oleic acid (7%) and linoleic acid (3%) as well as a few saturated acids. However, the castor oil plant also contains some toxic substances, such as the protein ricin and the alkaloid ricinine, which remain in the press cake after pressing. However, by physical or chemical methods, e.g. by short heating to 140 °C and/or by treatment with bases, the toxins can be eliminated and thus the press cake can also be used as animal feed. Castor oil has been cultivated and used for a long time, including 6000 years ago in ancient Egypt. In the pharmaceutical industry, it is used as a laxative and in cosmetics for the production of bath oils, lipsticks and shampoos. In technology, the good lubricating properties and high viscosity of castor oil are used for the production of lubricating oils. Due to its unusual functionality for fatty substances, ricinolic acid is also increasingly used as an oleochemical reactive component in the production of paints, lacquers, inks, foams and polymers (7 Sect. 19.2.2).

The olive tree (Olea europaea) has also been native in our culture for a long time: It has been known to the Sumerians and Egyptians for about 5000 years and was planted in Homer’s time in Greece. The ancient medium-high shrub forms a tree that can grow up to 20 m high and whose trunk can grow up to 4 m thick. Due to its intensive root system, the olive tree is very undemanding and requires only little water. The stone fruits, the olives (. Fig. 2.13) can grow up to 2.5 cm thick and are green, reddish, purple or black, depending on the variety. Olive oil is obtained by pressing ripe, whole or pitted fruits. At a first pressing under moderate pressure and temperatures up to 25 °C, the almost colorless oleum virgineum forms; at higher pressing pressure and higher temperatures, yellow to brown oils are formed. The main components of olive oil are triglycerides with oleic acid (84%), palmitic acid (9%), linolenic acid (4%) and arachidic acid (1%). It is an excellent edible oil, but is also used for skin care, for the production of soaps and for technical purposes, e.g. for machine oils. Because of its high-oleic acid content, it is an important raw material in oleochemistry, and we will encounter oleic acid and its derivatives even more frequently in 7 Chaps. 3 and 4.

. Fig. 2.13  Fruit and leaves of the olive tree (© Maceo/ Fotolia)

29

2.2 · Overview of Important Vegetable Oils and Animal Fats

2.2.9  Safflower Oil

2.2.10  Jatropha Oil

The safflower (Carthamus tinctorius) belongs - like the sunflower - to the family of daisies. It is a thistle plant which was originally cultivated as a color plant. The red dye from the petals was used in the Middle Ages to dye textiles (. Fig. 2.14). The seeds of the safflower contain up to 37% oil and are also very rich in protein (20–55%). The viscous oil is golden to reddish yellow and roughly comparable to linseed oil: It contains 70–80% linoleic acid and up to 20% oleic acid, is therefore highly unsaturated and can therefore be used as drying oil in the paint industry like linseed oil. It does not darken and is therefore also suitable for light colors and lacquers. However, its shelf life is very limited: It can only be stored for up to 12 months if cooled. Because of its n ­ut-like taste, safflower oil is also valued as an edible oil and is also used as a ­dietary food.

The jatropha (Jatropha curcas) belongs to the spurge family (Euphorbiaceae) and is native in ­tropical and subtropical areas. The special feature of this plant is that, due to its frugality and robustness, it also grows in dry savannahs, where food plants cannot survive. It is therefore ideal for growing oil plants in desert-like and erosion-endangered areas. The jatropha shrub can grow up to 8 m high and forms plum-sized fruits that contain several seeds. These seeds consist of up to 60% oil (. Fig. 2.15). Although the press cake contains up to 60% crude protein, it is unsuitable as food for humans or animals because it contains toxic substances, the ­phorbol esters, which cannot yet be removed. Jatropha oil contains about 75% unsaturated fatty acids, especially oleic acid (42%) and l­inoleic acid (35%), and only small amounts of saturated fatty acids such as palmitic acid (14%) or stearic acid (6%). However, the composition of the ­jatropha oils varies considerably. In recent years, jatropha oil has attracted special attention because it can also be used as diesel fuel (“biodiesel”) due to its high cetane numbers (approx. 60). Parts of South America, Africa and Asia have therefore seen a sharp increase in the cultivation of jatropha. However, this plant will not be able to solve the energy problems of the industrialized countries.

. Fig. 2.14  Flowering of safflower (© Dr. R. KaiserAlexnat, Institut für Färbepflanzen, Michelstadt)

. Fig. 2.15  Jatropha seeds (© Prashant ZI/Fotolia)

2

30

Chapter 2 · The Raw Materials of Oleochemistry - Oil Plants

BOX: An Oil that Is not an Oil at All

2

The jojoba plant (Simmondsia chinensis) with its gray-green, leathery leaves also loves the sun: It comes from the Sonora desert between California and Mexico and is now also native in dry locations in Argentina, South Africa and South Australia. The jojoba plant can be planted - like jatropha - on land that is no longer suitable for food production. By the way, the name is of Indian origin and should actually be pronounced “Ho–Ho-Ba”. The yellowish oil obtained from the seeds of the evergreen jojoba bush is by our definition not an oil at all, but a wax! Oils are defined as triesters of glycerol (. Fig. 2.1), but waxes

. Fig. 2.16  Seeds of the jojoba bush (© Roman Dean/Fotolia)

are monoesters of fatty acids with primary alcohols. However, since jojoba oil is a wax with a very low melting point (7 °C), it is still often included in the list of oils. Jojoba oil consists of esters of the unsaturated fatty acids eicosenoic acid (C20:1) and docosenoic acid (C22:1) with unsaturated C11 and C12 alcohols. It is thus very similar to sperm oil, which was formerly obtained from the sperm whale. However, since whaling has been severely restricted, sperm oil is hardly available today. The seeds of the jojoba plant are very similar to the olives (. Fig. 2.16).

Jojoba oil is mainly used in cosmetics such as skin creams and lipsticks, but also as a wax coating for citrus fruits or sweets. Jojoba is also used for pharmaceutical purposes, e.g. to cure skin diseases and burns. Since it almost maintains its viscosity at high temperatures, it is also used as a lubricant for high-speed engines. Some also consume jojoba oil as cooking oil: Since there are no enzymes in the human body that can break down the monoester, this trick allows you to enjoy very fatty foods without getting thicker. However, we do not recommend this “reduction diet”, as the oil that has not been degraded remains in the intestine and can then cause diarrhea.

31

2.2 · Overview of Important Vegetable Oils and Animal Fats

2.2.11  Other Fats and Oils

Since a textbook has only a very limited scope, we hereby end the description of the most important oil plants. Poppy, peanut, cottonseed and walnut oils, sandalwood and pumpkin seed oils and many others are therefore not explained here. Hemp oil will be presented in 7 Chap. 7. Altogether, there are about 1400 species of oil plants, of which about 20 are commercially cultivated. At the end of this chapter, however, we will take a look at some important fats of animal origin: 5 Grease is a collective term for spreadable animal fats. Typical representatives are grease

from pigs, geese and butter. Important fatty acids of grease are oleic, palmitic and stearic acid (. Table 2.3). 5 Tallow is a solid, granular fat mass that is usually less suitable for human consumption. For this reason, tallow is also relatively inexpensive. The most important representatives of tallow are beef tallow and mutton tallow. They also contain odd C number fatty acids, e.g. margaric acid (C17:0), trans-fatty acids such as elaidic acid (. Table 2.2) and branched fatty acids. Triglycerides of oleic, palmitic and stearic acid also dominate in beef tallow - as in grease.

BOX: The Healthy Eskimo Fish oils are obtained from herring fish or from fish processing waste. Characteristic for fish oils is the very high content of polyunsaturated fatty acids, PUFA, with four to six C=C

double bonds, e.g. arachidonic acid (. Table 2.2). These have a special nutritional significance for humans: They have a beneficial effect on the prevention and treatment of arteriosclerosis

2.3  Some Numbers

The worldwide production of fats and oils has increased enormously in recent decades, especially for the production of food fats. The development in the last four decades shows . Fig. 2.17: The total consumption of fats and oils has increased from 41 million tons in 1970 to about 200 million tons in the market year 2014/15 and has thus increased fivefold during this time! Simi­ lar growth rates are also expected in the future. . Figure 2.18 shows once again in more detail how the world production increases for the individual oils have developed over the last decade. For a long time, soybean oil was the most important oil worldwide; in the meantime, it has been overtaken by palm oil due to constantly new oil palm plantations in the Asian region. The order of the most important oils today is therefore: Palm oil > Soybean oil > Rapeseed oil > Sunflower oil >  Tallow > Palm kernel oil > Coconut oil. A brief look at the average oil prices in Europe for the four most important oils in June 2017 (source: 7 www.oilworld.biz):

and cardiovascular diseases. This effect has been found in the Eskimo people, which, despite their very high caloric and high-fat diet, including fish, are hardly prone to heart disease.

5 Palm oil 0.69–0.72 $ kg−1 5 Soybean oil 0.67–0.82 $ kg−1 5 Sunflower oil 0.72–0.78 $ kg−1 5 Rapeseed oil 0.83 $ kg−1. Finally, some statistical data from the “Fachagentur Nachwachsende Rohstoffe” on the special situation of fats and oils in Germany is presented: 5 In 2013, 1.2 million tons of fats and oils were used (Table 1.3). 5 These 1.2 million tons are divided into almost 20% animal fats and 80% vegetable oils, in particular rapeseed oil, linseed oil, sunflower oil, palm oil, soybean oil, coconut oil and castor oil. 5 The domestic industrial plants were cultivated on 153,000 ha of arable land. These include rape (140,000 ha), sunflower (9000 ha) and linseed oil (3500 ha). Please note that the field of energy crops is not included in these figures: Rape is still being planted on a further 616,000 ha in Germany to produce biodiesel (7 Chap. 20).

2

Chapter 2 · The Raw Materials of Oleochemistry - Oil Plants

32

200 180 160

Mio. Tonnes

140 120 100 80 60 40 20 0

1970

1980

1990

2000

2010

2015

Year

70

60

50 Production in Mio. t

2

. Fig. 2.17 Global consumption of fats and oils. From 1970 to 2014/15, source 7 www.oilworld.biz

40 1991/92 2014/15

30

20

10

0

Palm oil

Palm kernel oil & Soybean oil coconut oil

Rapeseed oil Sunflower oil Others & animal fats

Laurics . Fig. 2.18  World production of various fats and oils. Source 7 www.oilworld.biz

33

2.3 · Some Numbers

Summary (Take-Home Messages) 5 A distinction is made between vegetable fats with predominantly short fatty acid chains (C12–C14) and fats with predominantly longer chains (C16–C22). 5 The laurics include coconut oil and palm kernel oil. They play an important role as raw materials for the production of oleochemical surfactants. 5 The extraction of oils from seeds and nuts was explained using the example of coconuts: these are crushed, heated and pressed out in screw presses. The cloudy oil is then filtered. The remaining press cake can still be extracted with hydrocarbons or supercritical CO2. 5 The old rapeseed oil contains erucic acid (C22:1) and is therefore unsuitable for human consumption. The new rapeseed oil with high content of oleic acid (C18:1) and linoleic acid (C18:2) was created by new breeding. 5 The oil of the old sunflower contains a lot of linoleic acid, similar to soy oil. The newly bred high-oleic sunflowers, on the other hand, contain almost exclusively oleic acid. Oleic acid is also the main fatty acid of olive oil. 5 Linseed is used to produce linseed oil, which contains a high proportion of linolenic acid (50–60% C18:3). This polyunsaturated fatty acid (PUFA) can polymerize in air to a solid layer. Linseed oil is therefore also called drying oil. Safflower oil also contains a higher proportion of PUFA and is therefore used similarly to linseed oil in the paint and varnish industry. 5 The main fatty acid of castor oil is ricinoleic acid, a C18:1 acid with an additional hydroxy function in the C12 position. The oil has good lubricating properties, but because of its alcohol group it can also be chemically converted in many ways. 5 Jatropha oil can become more important in developing countries because it is also growing in arid areas. Due to its

high cetane number, it can be used as “biodiesel”. 5 Jojoba oil is not a fat but a wax, i.e. a monoester of a fatty acid with a long-chain alcohol. Jojoba oil is used in cosmetics, pharmaceuticals and as a lubricant. 5 Important animal fats and oils are grease, tallow and fish oils. Grease and tallow contain high levels of oleic and palmitic acid; fish oils contain the four to sixfold unsaturated fatty acids that are important for nutrition. 5 In the market year 2014/15, the worldwide production of fats and oils amounted to approx. 202 million tons. The world’s most important oils in terms of quantity are palm oil, soybean oil, rapeseed oil and sunflower oil. 5 In Germany, about 1.2 million tons of fats and oils are currently used each year in chemical industry.

? Ten Quickies

1. Are there odd-numbered fatty acids in natural fats? Do you know an example? 2. Write down the abbreviations for cis-6-octadecenoic acid (petroselic acid), trans-9-octadecenoic acid (elaidic acid) and trans-13-docosenoic acid (brassidic acid)! 3. Name (at least) one fatty acid with a hydroxy group! 4. What are “laurics”? In which oils do these fatty acids occur? 5. Distinguish between MUFA and PUFA. Give examples! 6. You are offered the untreated press cake of the castor oil plant as dog food. How do you react? 7. Which oil plants are particularly undemanding? 8. Give examples of “drying oils”! Where did they get her name? 9. Which fats and oils contain a relatively high proportion of oleic acid? 10. Why is the extraction of oil plants with supercritical carbon dioxide particularly advantageous?

2

34

Chapter 2 · The Raw Materials of Oleochemistry - Oil Plants

References Monographs and Review Articles

2

Beyerlee D, Falcon WP, Naylor RL (2017) The tropic oil crop revolution. Oxford University Press Bilyeu K, Ratnaparkhe MB, Kole C (2017) Genetics, genomics, and breeding of soybean. CRC Press Soh AC, Mayes S, Roberts JA (2017) Oil palm breeding: genetics and genomics. CRC Press Holt B (ed) (2016) Vegetable oil: properties, uses and benefits. Nova Publications McKeon TA, Hayes DS, Hildebrand DF, Weselake RJ (2016) Industrial oil crops. AOCS Press, Elsevier Johnson LA, White PJ, Galloway R (2015) Soybeans chemistry, production, processing and utilization. AOCS Press, Elsevier Martínez-Force E, Dunford NT, Salas JJ (ed) (2015) Sunflower: chemistry, production, processing, and utilization. AOCS Press, Elsevier Bockisch M (ed) (2015) Fats and oils handbook. AOCS Press, Elsevier Erickson (ed) D (2015) Practical handbook of soybean processing and utilization. Academic Press, AOCS Press Corley RHV, Tinker PBH (2015) The oil palm, 5th ed. Wiley-Blackwell Mallikarjuna N, Varshney RK (2014) Genetics, genomics and breeding of peanuts. CRC Press (2014) Krist S, Buchbauer G, Klausberger C (2013) Lexikon der pflanzlichen Fette und Öle, vol 2. Springer. Ausgabe Matthäus B, Fiebig H-J (eds) (2013) Speiseöle und Fette. Erling-Verlag, Clenze Firestone D (ed) (2013) Physical and chemical characteristics of oils, fats, and waxes. AOCS Press Lai O-M, Tan C-P, Akoh CC (eds) (2012) Palm oil: production, processing, characterization, and uses. AOCS Press Gupta SK (ed) (2012) Technological innovations in major world oil crops, vol 1: breeding, vol 2: perspectives. Springer Nature Hernandez EM, Hosokawa M (eds) (2011) Omega-3 oils: application and functional foods. AOCS Press Gunstone F (ed) (2011) Vegetable oils in food technology. Wiley-Blackwell Michael JD, Eskin NA, Hickling D (2011) Canola, chemistry, production, processing and utilization, Acedemic Press, AOCS Press Biermann U, Bornscheuer U, Meier MAR, Metzger JO, Schäfer HJ (2011) Fette und Öle als nachwachsende Rohstoffe in der Chemie. Angew Chem 123:3938–3956 Hu J, Seiler G, Kole C (2010) Genetics, genomics and breeding of sunflower. CRC Press O’Brien RD (2009) Fats and oils: formulating and processing for applications, 3rd ed. CRC Press Rossell B (ed) (2009) Fish oils. Wiley-Blackwell Gunstone F (2009) The chemistry of oils and fats: sources, composition, properties and uses. Wiley-Blackwell Vollmann J, Rajcan I (eds) (2009) Oil crops. Springer, Heidelberg

Matthäus B, Münch EW (eds) (2009) Warenkunde Ölpflanzen/Pflanzenöle. AgriMedia. Erling-Verlag, Clenze Nowak B, Schulz B (2008) Taschenlexikon tropischer Nutzpflanzen und ihrer Früchte. Quelle & Meyer Verlag, Wiebelsheim Boskou D (2006) Olive oil, chemistry and technology, 2nd ed. AOCS Press Roth L, Kormann K (eds) (2005) Atlas of oil plants and vegetable oils. Erling-Verlag, Clenze Shahidi F (ed) (2005) Bailey’s industrial oil and fat products, vol 1–6, 6th ed. Wiley (7th ed. in preparation) Löw H (2003) Pflanzenöle. Leopold Stocker Verlag, Graz Christie WW (2003) Lipid analysis. The Oily Press, Bridgewater Bickel-Sandkötter S (2001) Nutzpflanzen und ihre Inhaltsstoffe. Quelle & Meyer-Verlag, Wiebelsheim Thomas (2000) Fats and fatty oils. In: Ullmann’s encyclopedia of industrial chemistry. Online edn. Wiley-VCH, Weinheim International Coconut Community. 7 https://coconutcommunity.org/ United States Department of Agriculture (2019) Oil crops yearbook. 7 https://www.ers.usda.gov/data-products/ oil-crops-yearbook/ Original Publications Vichi S, Tres A, Quintanilla-Casas B, Bustamante J, Guardiola F, Marti E, Hermoso JF, Ninot A, Romero A (2019) Catalan virgin olive oil protected designations of origin: physicochemical and major sensory attributes. Eur J Lipid Sci Technol 121(3):1800130 Beszterda M, Nogala-Kalucka M (2019) Current research developments on the processing and improvement of the nutritional quality of rapeseed (Brassica napus L.). Eur J Lipid Sci Technol 121(5):1800045 Bernardini E, Visioli F (2017) High quality, good health: the case for olive oil. Eur J Lipid Sci Technol 119(1): 1500505 Gunstone FD (2011) Supplies of vegetable oils for ­non-food purposes. Eur J Lipid Sci Technol 113:3–7 Mutlu H, Meier MAR (2010) Castor oil as renewable resource for the chemical industry. Eur J Lipid Sci Technol 112:10–30 Mielke T (2008) Global outlook for oilseeds & products for the next 10 years. Technical report. Oilworld Achten WMJ, Verchot L, Franken YJ, Mathijs E, Singh VP, Aerts R, Muys B (2008) Jatropha biodiesel production and use. Biomass Bioenergy 32:1063–1084 Meier MAR (2008) Pflanzenöle für die chemische Industrie. Nachr Chem 56:738–742 Rupilius W, Ahmad S (2007) Palm oil and palm kernel oil as raw materials for basic oleochemicals and biodiesel. Eur J Lipid Sci Technol 109:433–439 Carter W, Finley J, Fry D, Jackson L Willis (2007) Palm oil markets and future supply. Eur J Lipid Sci Technol 109:307–314 Daimler-Chrysler (2004) Hightech report 2/2004: Öl vom Ödland - Das Indische Jatropha-Projekt

35 References

Hahn A Ströhle (2004) ω-3-Fettsäuren. Chem Unserer Zeit 38:310–318 Gunstone FD (ed) (2004) Rapeseed and canola oil. CRC Press, Blackwell Publications Guinda MC, Dobarganes MV, Ruiz-Mendez M Mancha (2003) Chemical and physical properties of a sunflower oil with high levels of oleic and palmitic acids. Eur J Lipid Sci Technol 105:130–137

Luchetti F (2002) Importance and future of olive oil in the world market. Eur J Lipid Sci Technol 104:559–563 Piazza GJ, Foglia TA (2001) Rapeseed oil for oleochemical usage. Eur J Lipid Sci Technol 103:450–454 Deutsche Gesellschaft für Fettwissenschaft e.V. (DGF), 7 www.dgfett.de/

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37

The Basics of Oleochemistry Basic Oleochemicals 3.1 Production of Basic Oleochemicals – 38 3.1.1 Fat Splitting – 38 3.1.2 Transesterification – 42 3.1.3 Saponification – 43 3.1.4 Direct Hydrogenation – 43

3.2 Reactions at the Carboxy Group of Fatty Acids – 45 3.2.1 Hydrogenation to Fatty Alcohols – 45 3.2.2 Conversions of Fatty Alcohols – 50 3.2.3 Conversions to Fatty Amines – 56 3.2.4 Other Fatty Acid Derivatives – 57

References – 59

© Springer-Verlag GmbH Germany, part of Springer Nature 2020 A. Behr and T. Seidensticker, Chemistry of Renewables, https://doi.org/10.1007/978-3-662-61430-3_3

3

38

Chapter 3 · The Basics of Oleochemistry - Basic Oleochemicals

Chapter Timetable

3

5 You will learn several methods for splitting triglycerides into the basic chemicals fatty acids (or fatty acid esters, respectively) and glycerol. 5 We will discuss the chemistry of the carboxy group of fatty acids, which leads us to fatty alcohols and fatty amines, among others.

This chapter describes the basic reactions of the chemistry of fats and oils, the so-called ole­ ochemistry. They have been known for over a century and have long been used in industry. On the other hand, a great deal of research has been carried out in this field in recent years, and new types of reactions have been developed. We will get to know these in 7 Chap. 4. 3.1  Production of Basic

Oleochemicals

In the petrochemical industry, petroleum hydrocarbons are used to produce a large variety of chemical intermediates and end products. This process involves splitting the mixture of aliphatic and aromatic compounds contained in crude oil into smaller units in the steam cracker and the reformer before producing specific secondary chemicals. These smaller units are, for instance, ethene, propene, butadiene, benzene, toluene and xylenes. These are called “petrochemical basic chemicals”. In oleochemistry, too, only little chemistry is carried out directly with fats and oils, but triglycerides are often broken down into glycerol and fatty acids or their derivatives. There are several variants: 5 As already described in . Fig. 2.1, triglycerides can be broken down into free fatty acids and glycerol by hydrolysis, i.e. by reaction with water. This process is called fat splitting. 5 Triglycerides can also be split into fatty acid (methyl) esters and glycerol by transesterification, e.g. with methanol. 5 The third way is saponification of fats with bases, e.g. sodium hydroxide, resulting in glycerol and in the sodium salts of fatty acids, i.e. soaps, respectively. Soaps are usually

no longer chemically converted, but used directly by the consumer as cleaning and washing agents. 5 The fourth method, which has not (yet) been technically implemented, is the direct­ hydrogenation of fats and oils into glycerol and fatty alcohols. Fatty alcohols can also be formed indirectly by hydrogenation of either fatty acids or fatty esters, respectively. Fatty acids, fatty esters and fatty alcohols as well as the coproduct glycerol can be regarded as basic oleochemicals in analogy to basic petrochemicals. As we will see in this and the following chapters, these basic chemicals can be converted into numerous important derivatives. . Figure 3.1 gives us an overview of the routes leading to the oleochemical basic products. 3.1.1  Fat Splitting

When one mole of triglyceride is split with three moles of water, three moles of fatty acids and one mole of glycerol are formed. Looking at the quantities, depending on the type of fatty acids, approx. 950 kg of fatty acids and 100 kg of glycerol are formed from one ton of fat. According to the equilibrium equation in . Fig. 2.1, it is obvious that good space–time yields are obtained especially if 5 water is in large surplus, 5 one product is constantly removed from the equilibrium, 5 the reaction rate is accelerated by the process conditions or by a catalyst. There are several industrial processes for fat splitting that consider these three effects: 5 The Twitchell process was developed as early as 1890: At ambient pressure, fats were heated in the presence of an aqueous sulfuric acid solution with the addition of organic sulfonic acids as catalysts. Mixing was carried out with superheated steam. However, this batch process, which was carried out in tanks coated with lead due to the sulfuric acid, has the major disadvantage of a very long reaction time of up to 24 h. Nevertheless, it is still occasionally carried out in small companies. 5 The Twitchell process makes good use of the possibilities of influencing the equilibrium:

39

3.1 · Production of Basic Oleochemicals

. Fig. 3.1  Production of basic oleochemicals from fats and oils

The substrate water is present in large excess; the formed product glycerol is water-soluble and migrates from the fatty phase into the water phase during its formation, thus moving away from the equilibrium in the organic phase. The catalysts, mostly sulfonated naphthenic acids, are readily soluble in the fat phase and can therefore become active right from the start. As soon as the splitting starts, di- and monoglycerides are formed, which increase the water solubility in the fat phase and thus contribute to a better turnover. The increased temperature of, e.g., 100 °C also causes more water to dissolve in the fat phase and simultaneously increases the reaction rate. 5 To make the process more economical, a continuous Twitchell process was developed, consisting of a cascade of three reactors, in which the aqueous sulfuric acid solution that absorbs the glycerol was conducted in countercurrent flow. The reaction time could be reduced to 4–5 h. A further disadvantage was that the neutralization and treatment of the water phase remained very costly and that undesirable soaps were produced during the neutralization.

5 These disadvantages can be avoided by working at high temperatures and under pressure to accelerate the reaction during fat splitting without using a catalyst. Therefore, discontinuous pressure processes were developed which operate at temperatures of 200–240 °C and pressures of 25–30 bar. After a reaction time of 4 h, a hydrolysis conversion of 90–96% can be achieved, which is sufficient for most purposes. If a higher turnover is desired, the reactor is depressurized, the water/glycerol phase is replaced by fresh water and the operation is repeated: Turnovers of up to 98% can be achieved. 5 The most economical and therefore exclusively used process in large plants today is the continuous pressure process developed in the years 1938–1942, which is described in more detail in . Fig. 3.2. The continuous pressure process is operated at pressures of 30–40 bar and temperatures around 240–260 °C, similar to the discontinuous pressure process. The splitting water is fed in with a pressure pump just below the head of the

3

40

Chapter 3 · The Basics of Oleochemistry - Basic Oleochemicals

3

. Fig. 3.2  Reactor of continuously operated pressure fat splitting

reaction column, and the fat is also fed in with a pressure pump just above the sump of the reactor. Due to the different densities, the lighter fat slowly moves upward, and the heavier water flows toward the fat from top to bottom. In the middle area of the reaction column, the so-called

cracking zone, superheated steam is injected, which ensures not only the necessary heating but also high turbulence in the reactor. As a result, the fat and water phases are intensively mixed, which leads to a large interface and thus to a faster reaction. This mixing can be further

41

3.1 · Production of Basic Oleochemicals

intensified by additional installations in the column. After an average residence time of 1–2.5 h in the reactor, a conversion rate of approx. 99% is achieved and the fatty acids can be removed at the top of the column. The glycerol water mixture, which contains approx. 15% glycerol, is drawn off at the bottom of the column via an automatically operating level controller. Modern processes of this type can be operated for one year without interruption. After that the plant is shut down, and any impurities resulting from polymerization or carbonization are removed. However, the use of continuous pressure splitting also has its limits: Fats with too high iodine values tend to polymerize under harsh reaction conditions; castor oil (7 Sect. 2.2.7) is dehydrated to polyunsaturated fatty acids. Batch processes with milder conditions are still common for such fats. Recent developments try to incorporate solid catalysts into the reaction columns, which are already active under mild conditions and accelerate the splitting process even more. Both immobilized enzymes (lipases) and heterogeneous catalysts such as ion exchange resins or zeolites are investigated. However, these systems have not yet been established in industry. The fatty acids thus produced must be further purified after the splitting process, because they still contain partial glycerides, ­ non-hydrolysable plant components and colorants: The fatty acids from fat splitting are usually yellow to brown in color, while the pure fatty acids are almost colorless. Fatty acids can be purified in various ways,

Coatings Rubber

6%

An overview of the fatty acid markets is provided by . Fig. 3.3. It shows that we encounter fatty acids in many areas of daily life, e.g. in lubricants, paints or personal care products.

Cosmetics

Paper

Lubricants

e.g. by crystallization or adsorption, but very often refining by continuous distillation is preferred in industry. However, fatty acids have relatively high boiling temperatures: Capric acid (C10:0) boils at 270 °C, stearic acid (C18:0) even at 370 °C, for example. Distillation must therefore be carried out in a vacuum, e.g. at 2–5 mbar. Technically, there are many variants of vacuum distillation of fatty acids. Today, distillation columns that contain structural packings and thus minimize the pressure loss of the column are preferred. Modern plants can continuously purify up to 100,000 tons of fatty acids per year. In 2017, the capacity for fatty acids from vegetable oils worldwide was approx. 13 million tons, of which approx. 50% in the oil-producing countries of Southeast Asia (Malaysia, Indonesia, China, Thailand, Philippines) alone. These figures do not include the amount of fatty acids used in soap production (7 Sect. 3.1.3). Fatty acids are widely used: 5 They are used directly, e.g. as auxiliaries in the plastics or rubber industry. 5 They are converted at the carboxy group, e.g. ethoxylated, esterified or amidated (7 Sect. 3.2). 5 They are chemically modified in the fat chain, e.g. by chlorination, epoxidation or dimerization (7 Chap. 4).

6%

6%

5 %

Soaps, detergents 30%

6% 9% 18% 14%

Others Intermediates Plastics

. Fig. 3.3  Fatty acid markets (in % by weight)

3

42

Chapter 3 · The Basics of Oleochemistry - Basic Oleochemicals

3.1.2  Transesterification

3

The second important variant of cleaving fats and oils is transesterification (. Fig. 3.1). Theoretically, it can be carried out with different alcohols, but technically transesterification is almost exclusively performed with methanol. The general reaction equation is shown in . Fig. 3.4. Today, transesterification - like fat splitting - is carried out on an industrial scale continuously under pressure: Common conditions of the so-called high-pressure transesterification are 90 bar and 240 °C. The fatty substrates can be used without major pretreatment: Fats with higher acid values, i.e. with a relatively high content of free fatty acids, can easily be processed, as these are directly esterified under the reaction conditions. Transesterification is usually catalyzed by alkaline catalysts, e.g. with alkali hydroxides, alkali carbonates or alkali alcoholates. In this reaction, too, one substrate, this time methanol, is added in excess to shift the reaction equilibrium to the right. A typical flow diagram of a high-pressure transesterification is shown in . Fig. 3.5.

In this reaction, fats, methanol and catalyst are usually soluble in each other, so that the reactor is operated in direct current mode. The reaction proceeds from trigly­ cerides, to diglycerides and ­monoglycerides to glycerol and fatty acid methyl esters (FAME). In a gas/liquid separator, the gas phase, which consists mainly of unreacted methanol, and the liquid phase consisting of FAME and glycerol are separated from each other. Methanol is purified in a column and fed back into the reactor. The ­ non-polar FAME phase is separated from the polar ­g lycerol phase in the liquid–liquid separator and also subjected to distillation. Besides high-pressure transesterification, also low-pressure transesterification exists, which is carried out at 60–90 °C and 2–4 bar. It requires deacidified oils as starting material, but has advantages in terms of investment and energy costs. The advantage of both processes compared to hydrolysis is that glycerol is produced in a relatively high concentration (90%) and is therefore easier to process.

O H2C

O

COOCH3

C O

HC

O

C

H 2C

OH

HC

OH

H2C

OH

[cat.] +

3 CH3OH

COOCH3

+

O H2C

O

C

COOCH3

. Fig. 3.4  Transesterification of fats with methanol to fatty acid methyl esters (FAME) and glycerol

. Fig. 3.5  Continuously operated high-pressure transesterification of fats to fatty acid methyl esters (FAME)

Fatty acid methyl esters have numerous applications: 5 Direct use, e.g. as “biodiesel” in combustion engines (7 Chap. 20), 5 By conversions of the ester group, interesting products, e.g. fatty alcohols or fatty acid alkanolamides are produced (7 Sect. 3.2), 5 Many important derivatives, e.g. sulfofatty acid esters, epoxides or aldehydes (7 Chap. 4), are formed by functionalizing the carbon chain of the fatty esters. 3.1.3  Saponification Soaps (from lat. sapo) are usually referred

to as the water-soluble sodium or potassium salts of fatty acids. Solid sodium soaps are also called hard or curd soaps, the greasy-liquid potassium soaps are also called soft soaps. The salts of fatty acids with other metals, such as calcium or zinc, are called “metal soaps”. Soaps are produced by reacting fats and oils with the corresponding bases, e.g. with caustic soda solution (. Fig. 3.6). Soap recipes were already recorded on clay tablets of the Sumerians around 2500 B.C., which were adopted by the Egyptians. The Romans used soap from the second century onward according to our calendar. However, their greater distribution only began in the nineteenth century, when bases were available in technical quantities. Soaps belong to the surfactants: Dissolved in water above the critical micelle concen­ tration (CMC), they form micelles in which dirt particles can dissolve. In this way, soaps can be used for body cleaning or washing textiles. In earlier times, soaps were produced by the discontinuous “soap boiling” process. This first produces a viscous “soap glue”, which then solidifies into a “glue soap” which, however, still contains a large amount of water and glycerol. Only

. Fig. 3.6 Saponification of a fat with caustic soda to curd soap

3

43

3.1 · Production of Basic Oleochemicals

after salting out with common salt the “soap core” is finally formed, which is processed into soap after further washing. Today, modern industrial processes are predominantly continuous. Low-cost tallow (80%) is usually used as raw material, but coconut oil and palm kernel oil are also used. In addition, also special soaps are made from other raw materials, such as the “Savon de Marseille”, which is made from olive oil. Soaps can also be produced by neutralizing free fatty acids. . Figure 3.7 schematically shows the continuous production of fine soaps from fats or fatty acids and alkali: Saponification produces a soap brew from which the water is removed in a dryer. The soap chips formed are mixed with perfume and color additives. The mixture is then transferred in an extruder into a soap strand, which is cut into handy units in the soap bar cutter. After passing through a cooling tunnel, an imprint is finally punched onto the soap bar. 3.1.4  Direct Hydrogenation

Besides the splitting of fats by hydrolysis, transesterification or saponification, one can also try to achieve fat splitting by hydrogenation. . Figure 3.8 shows that the fatty acids of ­triglycerides are hydrogenated to fatty alcohols. In the 1980s, the German Henkel company carried out extensive work on this reaction. Unfortunately, it turned out that even with the best catalysts one problem cannot be solved: If good yields of fatty alcohols are to be achieved, drastic reaction conditions must be applied under which the coproduct glycerol is dehydrated by hydrogenation. 1,2-Propanediol is formed by cleavage if one water molecule, and isopropanol by cleavage of a second one, respectively. Since these products are (so far) not as valuable as glycerol and, additionally, would have to

O H2C

O

COONa

C

H 2C

OH

HC

OH

H2C

OH

O HC

O

C

+

3 NaOH

COONa

+

O H2C

O

C

COONa

44

Chapter 3 · The Basics of Oleochemistry - Basic Oleochemicals

3

. Fig. 3.7  Soap production from fats or fatty acids and alkali

O H2 C O C O HC O C

HOCH2

H2C OH + 6 H2

[cat.]

+

HC OH

HOCH2

O H2 C O C

HOCH2

H2C OH

+ H2 - H2O

H2C OH HC OH CH3

CH3 +

HC OH et al. CH3

. Fig. 3.8  Direct fat hydrogenation to fatty alcohols

be separated at great expense, this process is not (yet) economical. As we will see in 7 Sect. 3.2.1, fatty alcohols are therefore preferably produced in such a way that initially fat splitting or trans-

esterification is carried (in which the glycerol is retained) followed by the hydrogenation of the intermediate fatty acids or fatty esters to the ­corresponding fatty alcohols.

45

3.1 · Production of Basic Oleochemicals

BOX: The Oleochemical Industry: Yesterday - Today - Tomorrow Until the 1990s, large companies from Europe, the USA and Japan (e.g. Henkel, Procter and Gamble, Unilever, Akzo Nobel or Kao) dominated industrial oleochemistry. This has changed significantly in recent decades. There are several reasons for this development: 5 The production of basic oleochemicals must nowadays be carried out in continuously operated large-scale plants in order to be economical. However, a complete fatty acid plant with a capacity of 100,000 t a−1 (splitting including fatty acid fractionation and glycerol processing) requires an investment of 80–100 million US dollars.

However, a company only makes this investment if it can open up new markets with its products - if possible locally. 5 Due to strong competition from Asian companies and the associated overcapacities, the profitability of basic oleochemicals has decreased significantly. 5 Since many important oil plants (7 Chap. 2) are cultivated in Asia (Malaysia, Thailand, Indonesia, etc.), also oleochemical raw materials are cheaply available there. Due to the high cost of capital and relatively low profit, many traditional oleochemical

companies have left the market and left it to Asian companies. Henkel, for example, first spun off its oleochemicals activities under the name Cognis; parts of Cognis were subsequently acquired by BASF. Instead, Henkel specializes more in sales goods (adhesives, detergents, cosmetics) that are less capital-intensive and generate higher profits. In the long term, it cannot be ruled out that the majority of oleochemical production plants in Europe and the USA will be taken over by Asian companies. European oleochemical companies wishing to assert themselves in the market are well advised to concentrate on specialty products and open up new innovative markets.

3.2  Reactions at the Carboxy Group

3.2.1  Hydrogenation to Fatty

At the carboxy group of fatty acids or the ester group of fatty acid esters, respectively, the same organic chemistry can be carried out as with short-chain carboxylic acids. These include, for example, amination to fatty acid amides or fatty nitriles and conversion to fatty acid chlorides or fatty acid anhydrides. Of particular importance, however, is the reduction of fatty acids and esters to fatty alcohols already mentioned in the last section. These, in turn, have a very extensive follow-up chemistry, in particular to detergents, and are therefore described in detail in the following 7 Sect. 3.2.1.

Depending on their chain length, fatty alcohols have quite different properties: 5 Short-chain C8–C12 alcohols are clear, high-boiling and oily liquids with a characteristic inherent odor. From C10, fatty alcohols are hardly miscible with water. 5 Starting from myristyl alcohol with a chain length of C14, fatty alcohols have a “wax-like” consistency. 5 From C16 on, fatty alcohols aresolid wax alcohols, which are sold as flakes or pellets.

of Fatty Acids

Alcohols

3

Chapter 3 · The Basics of Oleochemistry - Basic Oleochemicals

46

3

. Table 3.1 gives an overview of the melting and boiling points of fatty alcohols. It can be seen from the values of the C18 alcohols that if double bonds are present - the melting points decrease. Fatty alcohols are produced by hydrogenating the fatty acids or fatty acid esters with hydrogen under high pressure, respectively. This is illustrated in . Fig. 3.9 using the example of fatty acid methyl esters. The transesterification of fats with

methanol (. Fig. 3.4) is shown again in this figure (as step 1). If the three methyl esters released from the triglyceride are reacted with six moles of hydrogen (step 2), three moles of fatty alcohols are produced and in addition three moles of methanol, which can be reused in step 1. Summing up steps 1 and 2 gives the equation from . Fig. 3.8, i.e. the equation of direct hydrogenation: from triglycerides and hydrogen to fatty alcohols and glycerol!

. Table 3.1  Physical properties of fatty alcohols C number

Name

Melting point (°C)

Boiling point (°C)

C8

Capryl alcohol

−16

194

C10

Capric alcohol

7

229

C12

Lauryl alcohol

24

260

C14

Myristyl alcohol

38

172 (2.7 kPa)

C16

Cetyl alcohol

49

194 (2.7 kPa)

C18:0

Stearyl alcohol

59

214 (2.7 kPa)

C18:1

Oleyl alcohol

−8

208 (2.0 kPa)

C18:2

Linoleyl alcohol

−5

153 (0.4 kPa)

O H2C 1)

HC H2C

O O O

O

C O

C

OCH3

H2C

OH

HC

OH

H2C

OH

O +

C

3 CH3OH

C

O

O

C

C

OCH3

+

OCH3

O C

OCH3

CH2

OH

CH2

OH

CH2

OH

O 2)

C

OCH3

+

6 H2

O C

OCH3

. Fig. 3.9  Fat transesterification with subsequent hydrogenation of the fatty esters to fatty alcohols

+

3 CH3OH

47 3.2 · Reactions at the Carboxy Group of Fatty Acids

BOX: Fatty Alcohols - A Retroperspective and a Look at the Competitors Historically, the conversion of fatty esters to fatty alcohols on a technical scale was first carried out (since 1903) using the Bouveault–Blanc process by reduction with liquid metallic sodium. In 1931, Deutsche Hydrierwerke AG (Dehydag) built the first catalytic ester hydrogenation plant in Rodleben/Germany. This ester hydrogenation is still in strong competition with two synthetic

processes for the production of long-chain alcohols, which are also known as “fatty alcohols”, although they are based on petrochemicals. These two syntheses (. Fig. 3.10) are 5 The Alfol process developed by Karl Ziegler and 5 The hydroformylation of 1-alkenes to long-chain aldehydes (“fatty aldehydes”) discovered by Otto Roelen with

subsequent hydrogenation of the aldehydes to alcohols. In 2015, the worldwide production capacity of fatty alcohols based on vegetable oils was estimated at approx. 4.5–106 t a−1. The proportion of synthetic fatty alcohols is steadily losing importance as more and more plants are being built for the hydrogenation of natural fat esters.

. Fig. 3.10  Production of “synthetic fatty alcohols” from naphtha by the Alfol process or hydroformylation/ hydrogenation

Hydrogenation of fat esters is carried out in the presence of heterogeneous catalysts. It can proceed in two ways: 5 The solid catalyst is crushed into very small particles. These particles are suspended in the liquid fat ester, and then gaseous hydrogen is passed through. Since hydrogenation takes place in the lower part (“sump”) of the reactor, it is called sump phase hydrogenation. Since the subsequent separation of the finely suspended catalyst from the product is quite complex, this process is not used very often. 5 The solid catalyst is filled into a tubular reactor as larger pieces. The catalyst is thus fixed in the reactor, while the fluid product flows out of the reactor. Catalyst separation is therefore generally unproblematic. This process is called fixed bed hydrogenation. A typical flow diagram of the fixed bed hydrogenation is shown in . Fig. 3.11: The fat ester is pumped into the reactor R by the high-pressure piston pump P1 and mixed with

compressed hydrogen (compressor P2, 200– 300 bar). The heat exchanger H1 and the heater H2 carry out heating to reaction temperature (200–250 °C). After the reaction, the product stream gives part of its energy to the input flow (“feed”) and is further cooled in the cooler H3. The reaction is carried out with a large excess of hydrogen in order to achieve almost 100% conversion of the fatty ester. To separate the excess gaseous hydrogen from the liquid product stream, a separator S and a cyclone C are connected in series. The excess hydrogen is recycled, while the liquid stream is expanded in a flash with valve V and separated into gaseous methanol and liquid crude fatty alcohols. The composition of the heterogeneous catalysts in reactor R can vary. Catalysts made from copper oxide and chromium oxide are often used. Palladium/rhenium and rhodium/tin cata­ lysts have also been patented for this reaction. These catalysts hydrogenate both the carboxyl group to the alcohol group and the C=C double bonds in the chain. If zinc is added during the

3

48

Chapter 3 · The Basics of Oleochemistry - Basic Oleochemicals

3

. Fig. 3.11  Flow diagram of fixed bed hydrogenation of fatty acid methyl esters to fatty alcohols

production of the copper chromite catalysts or a chromium oxide catalyst coated on alumina with cadmium oxide as the “poisoning component” is used, the C=C double bonds are retained. Hence, not the waxy stearyl alcohol is yielded from methyl oleate, but the liquid oleyl alcohol, also known under its trade name “Ocenol®” (. Fig. 3.12). Because of the toxicity of chromium, this metal is now being replaced by other metals, e.g. manganese. Usually, the crude fatty alcohols from pressure hydrogenation are still purified by distillation to increase quality. Since they are

thermally sensitive, they are gently distilled in packed columns under vacuum (boiling points, . Table 3.1). Fatty alcohols have become very important, especially because they can be converted into numerous detergent substances. An overview of the fatty alcohol markets can be found in . Fig. 3.13. Due to the reactive hydroxyl group, fatty alcohols have a very extensive downstream chemistry. An overview of these reactions can be found in . Fig. 3.14. However, in this textbook, only the most important of these follow-up reactions can be briefly presented in the following.

+ 3 H2/-MeOH O 7

[CuO/Cr2O3]

OH 16

Stearyl alcohol

7

O

+ 2 H2/-MeOH [Al2O3/Cr2O3/CdO]

OH 7

Oleyl alcohol

. Fig. 3.12  Pressure hydrogenation of methyl oleate to either stearyl or oleyl alcohol

7

49 3.2 · Reactions at the Carboxy Group of Fatty Acids

Fatty amines

Lubricants Others

6%

Surfactants

4%

15% 55% 20%

Personal care . Fig. 3.13  Markets for fatty alcohols (in % by weight)

. Fig. 3.14  Important follow-up reactions of fatty alcohols

3

50

Chapter 3 · The Basics of Oleochemistry - Basic Oleochemicals

3.2.2  Conversions of Fatty Alcohols

Ethoxylation of Fatty Alcohols to Fatty Alcohol Ethoxylates (FAE)

3

In ethoxylation, fatty alcohols are reacted with ethylene oxide (EO, oxirane). This results in fatty alcohol ethoxylates (FAE), also known as fatty alcohol polyglycol ethers or alkyl polyglycol ethers. These are always mixtures with a different number of glycol units. The stoichiometry of the reaction makes it possible to set an “average degree of ethoxylation”. A general reaction equation is shown in . Fig. 3.15. As . Fig. 3.15 also explains, the distribution of ethylene oxide units can be controlled by the catalyst applied. In both examples, an average degree of ethoxylation of 7 was maintained. With the classic catalyst sodium methanolate, however, the EO distribution is quite broad (broad range ethoxylates, BRE) and a considerable part of the fatty alcohol (6%) has no ethylene oxide at all. However, with calcined hydrotalcite as catalyst, the narrow range ethoxylates (NRE) are formed with a high proportion of ethers with the desired seven EO units at the fatty alkyl chain. This distribution is important for the application of FAE: The molecule in . Fig. 3.15 consists on the left-hand side of a long hydrophobic alkyl chain

(from the fatty alcohol) and on the right hand side of an ether chain with numerous ether oxygen atoms and a terminal hydroxyl group (from the ethylene oxide molecules). The right part of the molecule consists of a hydrophilic and therefore very water-soluble group. This combination hydrophobic/hydrophilic is a feature for surfactants which are able to dissolve dirt particles (e.g. a grease spot on the shirt) with their hydrophobic end and at the same time transfer the dirt into the aqueous washing liquor with their hydrophilic end. The more uniform the distribution of EO on the fatty alcohol, the more uniform the properties of the surfactant. FAE are excellent low-foaming non-ionic surfactants with high washing and dispersing ability and good biodegradability. However, working with ethylene oxide is quite dangerous due to its high reactivity and high flammability. The conversion in . Fig. 3.15 must therefore be carried out under strong precautions. The flow diagram in . Fig. 3.16 shows how to proceed best: Using the inert gas nitrogen, ethylene oxide EO is pressed from its storage tank into an intermediate chamber and further mixed with nitrogen. This very diluted mixture is fed into the stirred reactor, into which the fatty alcohol (FA) is also slowly and continuously pumped. The highly exothermic reaction can thus be carried out very gently and safely.

. Fig. 3.15  Ethoxylation of fatty alcohols to fatty alcohol ethoxylates (FAE)

51 3.2 · Reactions at the Carboxy Group of Fatty Acids

. Fig. 3.16  Process flow diagram of fatty alcohol ethoxylate (FAE) synthesis

BOX: The Correct Nomenclature for SO3 Reactions 5 In general, reactions with sulfur trioxide (SO3) or chlorosulfonic acid (ClSO3H) are called sulfations. 5 If an aromatic or an alkene is sulfated, sulfonic

acids RSO3H (with a sulfur-carbon bond) are formed which is called sulfonation. 5 When an alcohol is sulfated, half esters of sulfuric acid are formed (sulfates with an

Sulfation of Fatty Alcohols to Fatty Alcohol Sulfates (FAS)

As the overview in . Fig. 3.14 shows, another important conversion of fatty alcohols is the reaction with chlorosulfonic acid or sulfur trioxide to fatty alcohol sulfates (FAS). Due to their good water solubility and their low sensitivity to water hardness (i.e. content of Ca and Mg ions in water), they are also very good surfactants. Their washing capacity is particularly high if the C12 or C14 chains obtained

­ xygen-carbon bond). This is o called sulfatation. Worldwide, approx. 500 sulfation plants are in operation with capacities between 1000 and 100,000 t a−1 sulfation products.

from the Laurics (7 Sect. 2.1) of coconut or palm kernel oil are used as fatty alkyl radicals. Due to their linearity, they are also easily biodegradable. Typical fields of application of the FAS are: 5 Powder or liquid laundry detergents for household laundry, 5 Shampoos (see the box “A typical shampoo”), 5 Wetting agents in the textile industry, 5 Stabilizers during bleaching, 5 Dispersants and emulsifiers in cosmetics.

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52

Chapter 3 · The Basics of Oleochemistry - Basic Oleochemicals

BOX: A Typical Hair Shampoo

3

If a consumer selects a hair shampoo from the huge assortment in a supermarket, he is usually influenced by commercials and the smell. Very few people are asking which ingredients the shampoo contains. But we want to know more: 5 The main purpose of a shampoo is the good cleaning of the hair and the head skin. One or more surfactants are needed for this: The main surfactant (primary surfactant) is usually an anionic surfactant, e.g. the fatty alcohol sulfates (FAS) or the very skin-friendly fatty alcohol ether sulfates (FAES), both presented in 7 Sect. 3.2.2. The primary surfactant is present in the shampoo at approx. 10–15% (see . Fig. 3.17).

5 In addition, there is usually a cosurfactant (secondary surfactant), which is present in the formulation to approx. 5%. Typical cosurfactants are the non-ionic alkyl polyglucosides (APG), which are also very skin-friendly. We will learn more about them in 7 Sect. 6.2.2.4 5 Many consumers are convinced that strong foam formation is of great importance for hair washing. Foam stabilizers (1–3%) are therefore frequently added, e.g. lauric acid monoethanolamide. 5 Electrolytes, usually sodium or ammonium chloride or -sulfate (1–3%), are used to adjust the desired viscosity. 5 Up to 0.2% ethylenediaminetetraacetic acid (EDTA) or nitrilotriacetic acid (NTA)

. Fig. 3.17  Composition of a typical shampoo

5

5

5 5

5

are added as complexing agents for metal ions. The highly water-diluted shampoos must be protected from attack by microorganisms. Small amounts of preservatives (0.1%) are added. Important preservatives in shampoos are the parabens, the salts of the methyl or propyl esters of p-hydroxybenzoic acid. Phosphate or lactate buffers are used to stabilize the pH value. Of course, perfumes (0.2%) and dyes are also essential. In special shampoos, additional care substances are used. In anti-dandruff shampoos, for example, small amounts of zinc pyrithione or piroctone olamine are added. The rest of the shampoo, usually two-thirds, is water.

53 3.2 · Reactions at the Carboxy Group of Fatty Acids

The synthesis of FAS from fatty alcohols is carried out according to two variants: 5 By reaction with chlorosulfonic acid (ClSO3H) produced from hydrogen chloride and sulfur trioxide, 5 By direct reaction with sulfur trioxide obtained by oxidation of SO2. The processes with chlorosulfonic acid are used in particular for the production of smaller product quantities, i.e. for special products. The reaction equations and the process flow diagram are shown in . Fig. 3.18: Chlorosulfonic acid and the fatty alcohol are first mixed in a nozzle; further reaction to the sulfuric acid half-ester takes place in a thermostatic reactor. HCl is separated from the product in the deaerator by applying the mixture to a rotating plate. The gaseous HCl leaves the deaerator at the head and is converted

into 30% hydrochloric acid with water in an absorber. The liquid product leaves the deaerator at the bottom and is mixed with caustic soda in an intensive mixer. The neutralization to FAS is finally continued in a stirred tank until complete conversion is achieved. For continuous sulfation on a large scale, only processes with sulfur trioxide are used nowadays, in which both the more expensive starting material chlorosulfonic acid and the complex separation of HCl are avoided. However, it is not easy to convert the liquid fatty alcohols and the gaseous SO3 so slowly and gently that no undesirable (brown and black colored) by-products are produced. . Figure 3.19 shows the reaction equations and details of the sulfation reactor, nowadays often a falling film reactor with several reaction tubes, a tube bundle reactor. Similar to ethoxylation (. Fig. 3.16), an inert gas is

. Fig. 3.18  FAS synthesis using the chlorosulfonic acid process

3

54

Chapter 3 · The Basics of Oleochemistry - Basic Oleochemicals

3

. Fig. 3.19  Sulfation in the tube bundle reactor (left: distributor head; middle: tube bundle reactor; right: temperature profile in the reactor tube with and without equalizing air)

used again to dilute the SO3, in this case air. In addition, the externally cooled reaction tubes (in . Fig. 3.19 only three tubes are exemplary shown) are fed with the two starting materials in such a way that an inert gas layer, the so-called equalizing air, is located between FA and SO3 at the beginning of the tube (cut-out “distributor head”). Only in the further course of the reaction tube do the starting materials slowly mix with each other and react to form the FAS. Since the resulting reaction heat is distributed over the entire reactor tube (length L), no overheating (“hotspot”) takes place in the reactor and the desired products are formed almost exclusively. Finally, a few details about the tube bundle falling film reactor: It can contain up to 180 individual tubes with a diameter of 2.5 cm and a length of up to 8 m each. The tubes are reactor and heat exchanger at the same time and

thus enable an almost isothermal operation. This results in sulfonation degrees of up to 98%. Approx. 30 kg of products can be produced per hour per reactor tube. Scale-up, i.e. the increase in reactor capacity, can be achieved quite simply by feeding a larger number of pipes with reactants.

Sulfation of Fatty Alcohol Ethoxylates to Fatty Alcohol Ether Sulfates (FAES) In the reaction overview (. Fig. 3.14), it has already been pointed out that fatty alcohol ethoxylates (FAE) can also be sulfated to fatty alcohol ether sulfates (FAES), as they also contain a terminal hydroxyl group, just like fatty alcohols. FAES are also excellent surfactants, which are mainly used in shampoos (see BOX: A Typical Hair Shampoo). Compared to FAS, they are more water-soluble due to the additional glycol units.

3

55 3.2 · Reactions at the Carboxy Group of Fatty Acids

O

CH2 CH2 O H + SO3 n

O

CH2 CH2 O

SO3H n

+ NaOH

O

- H2O

CH2 CH2 O

SO3Na n

FAES

FAE

. Fig. 3.20  Sulfation of fatty alcohol ethoxylates to fatty alcohol ether sulfates (FAES)

. Figure 3.20 shows the two-stage reaction using

the example of neutralization with caustic soda. For special applications, neutralization with potash lye, aqueous ammonia solution or triethanolamine is also possible.

Fischer Reaction of Fatty Alcohols with Glucose to Alkyl Polyglucosides (APG) This reaction, which also leads to interesting non-ionic surfactants, is described in more detail in 7 Sect. 6.2.2, which deals with sugar chemistry.

Condensation of Fatty Alcohols Using the Guerbet Reaction The fatty alcohols we have come to know so far are all linear, because they are made from linear fatty acids or their esters, respectively. For some applications, however, one would also like to have branched long chain alcohols, because these have very special physical properties, e.g. lower melting points or viscosities. In some properties, the branched alcohols are similar to the unsaturated alcohols, but are much more stable to oxidation because of the lack of C=C double bonds. One possibility of obtaining branched fatty alcohols is the condensation of two (identical or unequal) fatty alcohols, known as the Guerbet reaction, found by the French scientist Marcel Guerbet as early as 1899. It always leads to primary alcohols branched at C atom number 2. . Figure 3.21 shows the general equation for the Guerbet reaction of two identical fatty alcohols. In this way, the following Guerbet alcohols can be produced from the corresponding ­short-chain fatty alcohols: 5 From 2 × n-octanol (capryl alcohol) the 2-hexyl-1-decanol (C16),

R

[KOH] - H2O

OH

R

+

OH

H R

OH R

. Fig. 3.21  General equation of the Guerbet reaction

5 From 2 × n-decanol (caprin alcohol) the 2-octyl-1-dodecanol (C20), 5 From 2 × n-dodecanol (lauryl alcohol) the 2-decyl-1-tetradecanol (C24), etc. A mixture of two different fatty alcohols results in four different Guerbet alcohols, e.g. from an octanol/decanol mixture in addition to the homo-condensates listed above, the C18 mixed condensates 2-octyl-1-decanol and 2­-hexyl-1dodecanol are formed. The reaction is carried out at 250–300 °C in the presence of basic catalysts such as KOH or potassium alcoholates. Salts of the metals iron, nickel, copper or lead are also added. The mecha­ nism is similar to aldol condensation, but has not yet been fully clarified due to the parallel dehydrogenations, dehydrations and hydrogenations. The Guerbet alcohols listed above in the C number range C16–C24 are used as plasticizers for nitrocellulose, as solvents for printing inks and as components of lubricants and textile auxiliaries. The main application of Guerbet alcohols are cosmetic or pharmaceutical oils. However, global production is relatively low (2000–3,000 t a−1). As . Fig. 3.22 shows, Guerbet alcohols also have an extensive downstream chemistry. Of industrial importance are, for example, Guerbet acids and Guerbet esters.

56

Chapter 3 · The Basics of Oleochemistry - Basic Oleochemicals

. Fig. 3.22 Some follow-up reactions of Guerbet alcohols

R

O

R

SO3

OSO3Na

NaOH

R'

R

Ox.

OH

- H2O

R' Guerbet alcohols

Guerbet sulfates

3

+ n EO

R

O

nH

R

R' Guerbet alcohol ethoxylates

SO3

R

3.2.3  Conversions to Fatty Amines

+ NH3

O R'

Guerbet ester

NaOH - H2O

O

n SO3Na R' Guerbet alcohol ether sulfates O

COO NH4

O

- H2O

C

NH2

- H2O + H2

CH2 NH2

CH

NH

+ H2

C

N

Fatty nitrile

Imine

Prim. Amine

+ R CH2 NH2 CH2 HN

CH

+ H2 - NH3

CH2

NH2

HN CH2

Sec. Amine + R

CH2 CH

NH

R''

Production of fatty amines from fatty acids (or their esters) occurs in two stages (. Fig. 3.23): 5 In the first stage, fatty nitriles are produced by reaction with ammonia via the intermediate stage of fatty amides. This releases a total of two moles of water, which means that dehydrating catalysts are required. In industry, the reaction with ammonia is carried out in

As already mentioned at the beginning, n ­ itrogencontaining fats are also of industrial importance. Fatty amines in particular are coveted intermediates, as they are used for the production of ammonium compounds with long alkyl chains, which are used as cationic surfactants.

COOH

+ R´´OH

- H2O

O

O

OH

R' Guerbet acids

CH N

CH2

NH2

. Fig. 3.23  Production of fatty amines from fatty acids (via fatty nitriles)

+ H2 - NH3

N

CH2 Tert. Amine

3

3

57 3.2 · Reactions at the Carboxy Group of Fatty Acids

a single stage at 280–360 °C at ambient pressure; e.g. silica gel, aluminum oxide, bauxite or iron oxide are used as catalysts. Processes that directly convert triglycerides into fatty nitriles are particularly interesting: First, the fat is converted with ammonia in the presence of tin catalysts into a mixture of fatty nitriles, fatty amides and glycerol, the glycerol is then separated, and the reaction is continued until complete conversion is achieved. 5 In the second stage, the hydrogenation of the fatty nitriles to the fatty amines takes place. As . Fig. 3.23 shows, primary, secondary and tertiary amines can be produced via imines as intermediates. The selectivity of the process can be controlled by both the addition of ammonia and the nature of the catalyst, for instance, nickel and cobalt catalysts promote the formation of primary amines.

of a carboxyethylbetain from dodecyldime­ thylamine and acrylic acid. C12H25 NMe2 +

CH2

CH COOH C12H25 NMe2 CH2

CH2 COO

(3.2)

Fatty amine oxides should also be mentioned as derivatives of fatty amines: They are mostly obtained by oxidation of fatty alkyldimethylamines with hydrogen peroxide (Eq. 3.3) and behave like weak cationic surfactants. In amine oxides, the nitrogen and oxygen atoms are linked by a covalent bond, with a higher electron density at the oxygen atom. Accordingly, the fatty amine oxides have a high dipole moment and preferably dissolve in polar solvents. Me N

Me + H2O2

N

O + H2O (3.3)

Fatty amines can also be produced from fatty Me Me alcohols (7 Sect. 3.2.1), either by reaction with ammonia or primary or secondary amines. Equation 3.1 shows as an example the reaction of a fatty alcohol with dimethylamine to a dimeth- 3.2.4  Other Fatty Acid Derivatives ylalkylamine. The reaction is carried out in the presence of hydrogen with a copper catalyst. This section summarizes some other important fatty acid derivatives. CuO/Cr2O3 NMe2 + H2O OH + HNMe2 Fatty acid chlorides are obtained by react+ H2 ing fatty acids with thionyl chloride, phospho(3.1) rus trichloride or phosgene (. Fig. 3.24). Fatty Fatty amines are used in many areas: acid chlorides are highly reactive intermediates 5 Primary fatty amines RNH2 and their salts are and can be converted into fatty aldehydes, e.g. by used, for example, as flotation agents, corro“Rosenmund reduction.” sion inhibitors, lubricants, bactericides or fuel There are also several syntheses for fatty additives. acid anhydrides, which are summarized in 5 Secondary fatty amines R2NH are usually . Fig. 3.25. These run either via the mixed fatty further processed to their corresponding acid-acetic anhydride or via the fatty acid chloquaternary dialkyldimethylammonium salts ride as intermediates: R2Me2N+X−, e.g. by methylation with methyl 5 The mixed anhydride is produced either by chloride. Distearyldimethylammonium reaction with acetic anhydride (AA) or with chloride is an important plasticizer, and didecyldimethylammonium chloride is an important bactericide. + SOCl2 - SO2, -HCl 5 Tertiary fatty amines R3N are used as O emulsifiers, fungicides, foam regulators or + PCl3 C Cl COOH cosmetic ingredients. They are also used for - HOPCl2 the production of amphoteric surfactants, + COCl2 the so-called betaines. These contain both - CO2, -HCl a cationic and an anionic group and are particularly skin-friendly detergents. Equa. Fig. 3.24  Synthesis of fatty acid chlorides from fatty tion 3.2 shows as an example the production acids

58

Chapter 3 · The Basics of Oleochemistry - Basic Oleochemicals

. Fig. 3.25  Syntheses of fatty acid anhydrides from fatty acids

+ AA - HOAc O C

COOH

3

+ H2C

C

We have already learned about the most important fatty acid esters, methyl esters and their production in the chapter on fat transesterification (7 Sect. 3.1.2). However, some other fatty acid esters have also gained industrial importance: 5 The isopropyl esters of fatty acids can be produced simply by reaction with propene or isopropanol, the phenyl esters by reaction with phenol and the fatty alkyl esters by reaction with fatty alcohols. The fatty acid alkyl esters are waxes, which we already got to know when discussing jojoba oil (box in 7 Sect. 2.2.10). They are important lubricants, softeners and cosmetic ingredients. 5 Fatty acids can also be esterified with various polyols. In addition to the glycerol already known from fats, glycol, sorbitol, sucrose or neopentylglycol are used, for example. 5 Another variant is the esterification of fatty acids with ethylene oxide to poly(oxy­ ethylene) esters, the fatty acid ethoxylates (Eq. 3.4). They are (like the related fatty alcohol ethoxylates FAE, 7 Sect. 3.2.2.1) ­non-ionic surfactants which are used in households and industry due to their relatively low manufacturing costs and low foaming power, e.g. for textile cleaning, as detergents or for surface cleaning of metals. The fatty acid ethoxylates can be produced in the same ethoxy­ lation plants as FAE. However, despite their

+ RCOOH - HOAc

CH3

C

O

+ RCOOH - HCl

O

ketene and then reacted with another mole of fatty acid. 5 The fatty acid chloride is produced as described in . Fig. 3.24 and then reacted with either fatty acid or its salt (soap) to the fatty acid anhydride.

C

O

+ SOCl2

- SO2,- HCl

O O

C O

Cl C

+ RCOONa - NaCl

O

excellent biodegradability, they are (so far) less important than FAE, as the ester bond is quite reactive and therefore tends to undesirable secondary reactions. COOH + n C2H4O O C

O

O

nH

(3.4)

Summary (Take-Home Messages) 5 The most important basic chemicals in oleochemistry are fatty acids, fatty acid esters, fatty alcohols and the coproduct glycerol. 5 Fat splitting is the conversion of triglycerides with water to fatty acids and glycerol. Due to a high excess of water and continuous separation of glycerol, the equilibrium reaction can be shifted to the fatty acid side. 5 Industrially, fat splitting is mainly carried out as continuously operated pressure–fat splitting with pressures up to 40 bar and temperatures up to 260 °C. The reactors are columns in which the fat and the water phase are reacted in countercurrent mode. 5 Fatty acids are usually purified by continuous distillation. They are used as soaps or as additives for rubbers, paper, lubricants, paints or personal care products.

59 3.2 · Reactions at the Carboxy Group of Fatty Acids

5 Fatty acid esters are produced by esterification of the fatty acids with alcohols or preferably by transesterification of the triglycerides with methanol to fatty acid methyl esters and glycerol. 5 Saponification of fats with caustic soda or potash lye to soaps and the coproduct glycerol has been a known technology for centuries. Today, this reaction is also predominantly carried out continuously. 5 In the direct hydrogenation of triglycerides with hydrogen to fatty alcohols, glycerol, 1,2-propanediol and isopropanol are the by-products. It has not yet been carried out on an industrial scale. 5 The most important way to obtain fatty alcohols is the hydrogenation of fatty acids or fatty acid methyl esters, respectively. Depending on the chain length, liquid-to-solid products are formed, which are further processed into surfactants, fatty amines or lubricants, for example. Natural fatty alcohols based on renewable raw materials are competing with synthetic fatty alcohols produced by the Alfol process or by hydroformylation. 5 Important secondary reactions of fatty alcohols are ethoxylation to fatty alcohol ethoxylates (FAE), sulfation to fatty alcohol sulfates (FAS), sulfation of FAE to fatty alcohol ether sulfates (FAES), Fischer reaction with glucose to alkyl polyglucosides (APG) and condensation to Guerbet alcohols. 5 Fatty amines can be produced in two stages from fatty acids or fatty alcohols. As the corresponding ammonium salts, they are used as cationic surfactants, emulsifiers, plasticizers or flotation aids. 5 Other important derivatives are fatty acid chlorides and fatty acid anhydrides.

? Ten Quickies

1. Name three basic chemicals of oleochemistry! 2. Compare the glycerol qualities produced during fat hydrolysis and transesterification of fats!

3. In an oleochemical factory, stearic acid on the one hand and stearyl alcohol on the other hand are to be purified by distillation. How to proceed? 4. Why did soap production in Europe increase sharply in the second half of the nineteenth century? 5. Why are 1,2-propanediol and isopropanol by-products of direct hydrogenation of fats? Why not 1,3-propanediol? 6. How can fat esters be industrially hydrogenated to fatty alcohols? Describe the arrangement of the catalyst in the reactor! 7. How can fatty alcohols also be produced by hydroformylation? What chain lengths can be achieved? Give examples! 8. How can oleyl alcohol be produced from methyl oleate? 9. Describe the four-step path from the fat molecule to the fatty alcohol ether sulfates! 10. Describe the two syntheses of the important laundry softener distearyldimethylammonium chloride, starting with either stearic acid or stearyl alcohol!

References Monographs and Review Articles Hayes D, Solaiman D, Ashby R (2019) Biobased surfactants, 2nd ed. Academic Press Rabiu A, Elias S, Oyekola O (2018) Oleochemicals from palm oil for the Petroleum Industry. IntechOpen (2018) Bornscheuer U (2018) Lipid modification by enzymes and engineered microbes. Academic Press Ahmad MU (2017) Fatty acids - chemistry, synthesis and applications, 1st ed. Academic Press Gupta M (2017) Practical guide to vegetable oil processing, 2nd ed. Academic Press Spitz L (2016) Soap manufacturing technology, 2nd ed. Academic Press (2016) Farr WE, Proctor A (2016) Green vegetable oil processing, 1st rev. ed. AOCS Elsevier List GR, King JW (eds) (2015) Hydrogenation of fats and oils: theory and practice, 2nd ed. AOCS-Press Hernandez EM, Kamal-Eldin A (2013) Processing and nutrition of fats and oils. Wiley-Blackwell Ahmad M, Khan MA, Zafar M, Sultana S (2012) Practical handbook on biodiesel production and properties. CRC Press

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3

Chapter 3 · The Basics of Oleochemistry - Basic Oleochemicals

Kjellin M, Johansson I (eds) (2011) Surfactants from renewable resources. Wiley-VCH, Weinheim Gunstone FD, Harwood JL, Dijkstra AJ (2007) The lipid handbook, 3rd ed. CRC Press, Boca Raton Anneken DJ, Both S, Christoph R, Fieg G, Steinberner U, Westfechtel A (2006) Fatty acids. In: Ullmann’s encyclopedia of industrial chemistry. Wiley-VCH, Weinheim, online edition Noweck K, Grafahrend W (2006) Fatty alcohols. In: Ullmann’s encyclopedia of industrial chemistry. ­Wiley-VCH, Weinheim, online edition Shahidi F (ed) (2005) Bailey’s industrial oil and fat products, 6th ed. Wiley, Vol. 1: Chemistry, properties and health effects, vol. 3: specialty oils and oil products, vol. 4: Products and applications, vol. 5: processing technologies, vol. 6: industrial and nonedible products from oils and fats Visek K (2003) Amines, Fatty. In: Kirk-Othmer encyclopedia of chemical technology. Wiley Mostofsky DI, Yehuda S, Salem N Jr (eds) (2001) Fatty acids - physiological and behavioral functions. Humana Press (2001) Gunstone FD, Hamilton RJ (2001) Oleochemical manufacture and applications. Sheffield Academic Press, Sheffield Gunstone FD (1998) Lipid synthesis and manufacture. Blackwell Dieckelmann G, Heinz HJ (1989) The basics of industrial oleochemistry. Peter Pomp GmbH, Essen Johnson RW, Fritz E (eds) (1989) Fatty acids in industry. Marcel Dekker Inc., New York

Original papers Yildirim A, Mudaber S, Öztürk S (2019) Improved sustainable ionic liquid catalyzed production of symmetrical and non-symmetrical biological wax monoesters. Eur J Lipid Sci Technol 121(2):1800303 Ho DP, Ngo HH, Guo W (2014) A mini review on renewable sources for biofuel. Biores Technol 169:742–749 Ronda JC, Lligadas G, Galià M, Cádiz V (2011) Vegetable oils as platform chemicals for polymer synthesis. Eur J Lipid Sci Technol 113:46–58 Rupilius W, Ahmad S (2005) The changing world of oleochemicals. Palm Oil Devel. 44:15–28 Hoydonckx HE, De Vos DE, Chavan SA, Jacobs PA (2004) Esterification and transesterification of renewable chemicals. Topics in Catal. 27:83–96 Bondioli P (2004) The preparation of fatty acid esters by means of catalytic reactions. Topics in Catal 27:77–82 Hills G (2003) Industrial use of lipases to produce fatty acid esters. Eur J Lipid Sci Technol 105:601–607 Steinigeweg S, Gmehling J (2003) Esterification of a fatty acid by reactive distillation. Ind Eng Chem Res 42:3612–3619 Gunstone FD, Hamilton RJ (2002) Oleochemical manu­ facture and applications. Eur J Lipid Sci Technol 104:448–449 Gunstone FD (2001) Chemical reactions of fatty acids with special reference to the carboxyl group. Eur J Lipid Sci Technol 103:307–314 Jordan V, Gutsche B (2001) Development of an environmentally benign process for the production of fatty acid methyl esters. Chemosphere 43:99–105

61

There is More to Oleochemistry - Reactions at the Fatty Acid Alkyl Chain 4.1 Synthesis of Substituted Fatty Acids – 62 4.2 Reactions at the C=C Double Bond of Unsaturated Oleochemicals – 63 4.2.1 Linkage of New C–O Bonds – 63 4.2.2 Linkage of New C–C Bonds – 66 4.2.3 Linkage of New C-H Bonds – 83 4.2.4 Further Additions to the C=C Double Bonds of Oleochemicals – 84

References – 86

© Springer-Verlag GmbH Germany, part of Springer Nature 2020 A. Behr and T. Seidensticker, Chemistry of Renewables, https://doi.org/10.1007/978-3-662-61430-3_4

4

62

Chapter 4 · There is More to Oleochemistry - Reactions at the Fatty Acid Alkyl Chain

4.1  Synthesis of Substituted Fatty

Chapter Timetable

4

5 We briefly discuss the chemistry of the saturated fatty acid alkyl chain. 5 Much more versatile is the chemistry of the C=C double bond of unsaturated fatty acid compounds. Here you will get to know the possibilities of using C–O and C–C linkages to derive new functionalized or branched molecules. 5 The selective hydrogenation of C=C double bonds is also discussed.

In addition to reactions at the carboxyl group, a fatty acid can also undergo reactions at the alkyl chain (or alkylene chain). The chemical attack can take place at different positions: 5 At any non-activated methylene group, e.g. at the CH2 groups of the carbon atoms C3 to C17 of stearic acid, 5 At the terminal methyl group (C18), 5 On the methylene group (C2) which is next to the carboxyl group, 5 At the carbon atom of a C=C double bond (e.g. C9 and C10 of oleic acid), 5 At the methylene group allyl to the C=C double bond (C8 and C11 of oleic acid).

Acids

Common substitution reactions on the aliphatic chain, for instance chlorination, take place with almost statistical distribution of the chlorine atoms on the fatty acid alkyl chain. Only the methylene groups directly adjacent to the carboxyl group are somewhat shielded from the electrophilic attack of the chlorine radicals by the I-effect of the COOH substituent. The result is a mixture of chlorinated fatty acids that can be converted into hydroxyl- or amino-substituted fatty acids (. Fig. 4.1). However, this reaction sequence is only industrially useful if it is possible to carry out chlorination more regioselectively. One approach is the Hell–Volhard–Zelinsky reaction, in which chlorination is carried out in chlorosulfonic acid as a solvent and a strong radical scavenger prevents statistical chlorination: The α-chloro fatty acid is formed selectively. Some further substitution reactions at the fatty alkyl chain are listed in . Table 4.1. In particular, the regioselective sulfonation of the α-methylene group might gain greater industrial significance. Sulfonation of fatty acid methyl esters with sulfur trioxide and air produces the

+ 2 NH3 - NH4Cl COOH

+ Cl2

COOH NH2

COOH

- HCl

Cl

+ H2O - HCl

COOH OH

. Fig. 4.1  Substitution reactions at the saturated fatty acid alkyl chain

. Table 4.1  Substitution reactions at the saturated fatty alkyl chain Reaction

Reagents

Products

Sulfochlorination

SO2, chlorine

Sulfochlorides

Sulfoxidation

SO2, oxygen

Sulfonic acids

Chlorophosphonylation

PCl3, oxygen

Phosphonic acid dichlorides

Fluorination

HF, electrochemical

Perfluoro fatty acids

Sulfonation

SO3, air

α-Sulfofatty acids and their esters

CH2 COOMe + SO3/Air

4

63

4.1 · Synthesis of Substituted Fatty Acids

CH SO3H

COOMe

NaOH

CH

- H2O

SO3Na

COOMe

. Fig. 4.2  Synthesis of α-ester sulfonates (AES)

α-sulfofatty acid esters, which can be converted with sodium hydroxide into their corresponding sodium salts, the so-called alpha ester sulfonates (AES) or methyl ester sulfonates (MES), having very good surfactant properties and a high biodegradability (. Fig. 4.2). Sulfation can take place in similar falling film reactors as described in 7 Sect. 3.2.1. However, due to the (relatively high) sulfation temperature of 90 °C and the (relatively long) reaction time of 30 min, the products are dark colored and must first be bleached with hydrogen peroxide prior to application. By the company Chemithon, AES have long been discussed as a possible surfactant alternative for petrochemical linear alkylbenzene sulfonates (LABS), which are produced worldwide at 3.5 million metric tons per year. The first AES plant with a capacity of 80,000 metric tons per year was built in Texas, USA, in 2003. Since the product is produced in the form of anhydrous flakes or powders, it can also be easily transported over long distances. 4.2  Reactions at the C=C Double

Bond of Unsaturated Oleochemicals

If unsaturated fatty acids (or their esters) are used as starting materials, the C = C double bond provides a reactive group that can be used for very specific reactions, which can often be controlled with the aid of homogeneous catalysts. Some of these reactions have been used in industry for a long time, others - in particular reactions with transition metal catalysts - have only recently been developed and require further development. In the following, the reactions are subdivided according to which bonds are newly formed. New C–O–, C–C–, C–H– and some other linkages are presented. 4.2.1  Linkage of New C–O Bonds

As early as 1909, the Russian chemist Nikolai Prileschajev discovered the conversion of

unsaturated compounds with a peracid to epoxides (oxiranes). This epoxidation was sub­ sequently further developed and also applied to unsaturated oleo chemicals, in particular on the basis of soybean oil. Perbenzoic acid was origi­ nally used as peracid; today, performic acid or peracetic acid is used almost exclusively in industry. Peracids are produced relatively e­asily from the corresponding carboxylic acid and hydrogen peroxide. Two basic approaches can be distinguished here: On the one hand, peracid is produced separately and then reacted with the unsaturated oleochemical. On the other hand, the peracid can also be produced in situ during epoxidation. A typical example of an epoxidation, the reaction of triolein (glyceryl trioleate) with performic acid, is shown in . Fig. 4.3. Recently, numerous catalysts have been developed which either accelerate in situ peracid formation or epoxidation itself. Typical examples are acidic ion exchangers, zeolites, hydrotalcites and transition metal salts or oxides. The use of enzymes is also a newer path to epoxidized oleochemicals. Lipases, e.g. Novozym 435, catalyze the conversion of fatty acids with hydrogen peroxide to peroxy fatty acids, which then lead to epoxidized fatty acids by intermolecular oxygen transfer. Epoxidized oleochemicals are widely used, especially in plastics. They are excellent plasticizers and are used as flame retardants, antioxidants and light stabilizers in plastics. Epoxidized soybean oil (ESBO) is widely used in ­ polyvinyl-chloride and related polymers. If hydrogen chloride is split off in a chlorine-­ containing plastic by the influence of heat or light, it is scavenged by a reaction with the ­epoxide groups present in ESBO. The epoxy group can also undergo numerous subsequent reactions. Protic substrates lead to ring opening: Diols are formed with water, ether alcohols with alcohols, amino alcohols with secondary amines, hydroxyacetates with acetic acid (. Fig. 4.4). Epoxidized triolein (see . Fig. 4.3) thus forms a hexol that can be processed with diisocyanates to polyurethane foams. F ­urther

Chapter 4 · There is More to Oleochemistry - Reactions at the Fatty Acid Alkyl Chain

64

. Fig. 4.3 Complete epoxidation of triolein with performic acid

O O O O O

4

O + 3 HCOOOH - 3 HCOOH O

O

O

O

O

O

O

O

O

R

OH

OH

C

C

H

R'

H

R + H2O

Diols

OR''

OH

C

C

H

H

[H+]

R'

R + Et2NH

+ R''OH

NEt2

OH

C

C

H

H

OAc

OH

C

C

H

H

R'

[ZnCl2]

O R

+ NaN3

C

C

H

H

[Sn]

R'

+ CO2

+ HOAc

H N R

O

C

C

H

H

R

R' O R

O C

C

H

H

R'

R'

. Fig. 4.4  Some subsequent reactions of the fatty epoxides

subsequent reactions of the epoxide group take place while retaining the three-membered ring structure, e.g. the conversion with sodium azide to the aziridines, which possess pharma-

cological activity. By tin catalysis, the epoxy ­three-membered ring can be extended with carbon dioxide to form the five-membered ring of a cyclic carbonate.

65

4.2 · Reactions at the C = C Double Bond of Unsaturated Oleochemicals

Another oxidation reaction is the direct

bishydroxylation of the C=C double bond to

vicinal diols. In the past, this reaction was only possible stoichiometrically with the aid of the highly toxic osmium tetroxide. In the meantime, catalytic variants with the oxidizing agent hydrogen peroxide have been developed. Typical catalysts are tungstic acid (H4WO4) or methyl­ trioxorhenium (CH3ReO3). The vicinal diols can then be cleaved, e.g. with oxygen under cobalt catalysis, to form a mono- and a dicarboxylic acid. . Figure 4.5 shows the entire

HO

reaction chain using oleic acid as an example: ­9,10-dihydroxystearic acid is formed by epoxidation to 9,10-epoxystearic acid and subsequent hydrolysis or also by direct bishydroxylation, which is cleaved into pelargonic acid (=nonanoic acid) and azelaic acid (=nonanedioic acid). Azelaic acid is a highly sought-after dicarboxylic acid used in the production of polyester films and fibers, plasticizers and synthetic lubricants. . Figure 4.5 also shows a direct C=C cleavage of oleic acid to the two products - pelargonic acid and azelaic acid. Up to now, this direct

O

OH

OH

Diol cleavage 9,10-Dihydroxystearic acid

Hydrolysis

O

O

OH 9,10-Epoxystearic acid

Epoxidation O

Dihydroxylation OH

Oleic acid

C=C-Cleavage

OH

+

O Pelargonic acid . Fig. 4.5  Oxidation steps using oleic acid as an example

HO

OH O

O Azelaic acid

4

Chapter 4 · There is More to Oleochemistry - Reactions at the Fatty Acid Alkyl Chain

66

Pelargonic acid

-

+ Ozonizer

D1

O2

D2

E

D3

4

Oleic acid

R

O3 Oxidizer

Ozonides

H2O

Azelaic acid Residue

O2 . Fig. 4.6  Process flow diagram of oleic acid ozonolysis

cleavage has been carried out by ozonolysis of oleic acid. . Figure 4.6 shows a simplified process flow diagram of an Emery plant in Cincinnati/ USA: Oxygen (O2) is converted into ozone (O3) in an ozonizer by silent electrical discharge and fed into the reactor R together with oleic acid. The intermediate ozonides are split in the oxidizer with oxygen into the two carboxylic acids, which are then separated from each other in the distillation columns D1 and D2. To increase the purity of azelaic acid, the crude azelaic acid is extracted from column D2 in the extractor E with water which is then separated in evaporators and dryers (D3). In order to obtain a highly pure azelaic acid (polymer grade), it can be further purified, e.g. by crystallization (mp. 108 °C). As the flow diagram shows, the process is quite complex and the handling of toxic ozone and decomposing ozonides is not harmless. A cata­ lytic variant with a more manageable oxidizing agent such as oxygen or hydrogen peroxide would therefore be very advantageous. For this reason, intensive research is currently being conducted into the catalytic variant of this direct cleavage. An industrial process for the homogeneously catalyzed oxidative cleavage of fats using hydrogen peroxide as an alternative to ozonolysis has been developed by Matrica, a joint venture of Novamont and Versalis, and is performed with a capacity of 35,000 t/a. The production site is located in Porto Torres/Sardinia, and the raw material is oil from a type of this-

tle cultivated in Sardinia. In a first reactor, the corresponding methyl esters are converted with hydrogen peroxide to diol (see . Fig. 4.5) using tungstic acid. The process is carried out continuously so that the mixture already contains a high proportion of diol. In the second step, the diol is split using cobalt acetate and oxygen (see . Fig. 4.5). This process step is also carried out continuously so that the mixture is enriched with cleaved products. Both catalysts are recovered only after the second reaction step. A phase separation takes place, and the aqueous phase is first passed over a cation exchanger, whereby the cobalt ions are retained and the tungstic acid is returned to the first reaction step. The cobalt ions are then desorbed and returned to the second reaction step. 4.2.2  Linkage of New C–C Bonds

Over the past decade, numerous reactions have been developed for C–C bond formation with unsaturated oleochemicals which have led to completely new fat derivatives. In particular, the use of homogeneous transition metal cata­ lysts has opened up interesting possibilities. . Figure 4.7 provides an initial rough ­overview: A monounsaturated oleochemical RX (with X=COOH, COOR, CH2OH, et al.) can, for example, be hydroformylated, hydroxycarbon­ ylated, alkoxycarbonylated or hydroaminome­ thylated at the C=C double bond. In all cases,

4

67

4.2 · Reactions at the C = C Double Bond of Unsaturated Oleochemicals

. Fig. 4.7 Examples for C–C bond formation of unsaturated fatty compounds (the molecules are schematically drawn as lines)

X Dimerization

X

+

+

Self metathesis

X X

Cross metathesis X

+ C=C

X

Hydroaminomethylation

NR2 X

+ CO/H2 + HNR2 Hydroxycarbonylation

COOH X

+ CO/H2O

Alkoxycarbonylation

COOR X

CO/ROH CHO Hydroformylation + CO/H2

X Hydrogenation + H2 OH X

functionalization results in bifunctional com­ pounds, e.g. when oleic acid is used, hydroxylor aminocarboxylic acids or dicarboxylic acids are obtained. Such bifunctional compounds are of interest for a number of subsequent reactions, e.g. for the synthesis of polymers.

Unsaturated fatty acids can also be dimerized to dimer fatty acids or lead to completely new unsaturated carbon chains by self-metathesis or cross-metathesis with alkenes. The ­ ­ individual reaction types are described in more detail below.

Chapter 4 · There is More to Oleochemistry - Reactions at the Fatty Acid Alkyl Chain

68

Hydroformylation and Related Reactions

4

Hydroformylation with petrochemical substrates has long been carried out on an industrial scale: Olefins are converted with synthesis gas, a 1:1 mixture of carbon monoxide and hydrogen, to aldehydes, which can then react with further hydrogen to form primary alcohols. This reaction is already carried out worldwide in industrial plants with capacities of approx. 12 million tons per year. Homogeneous cobalt or rhodium catalysts are used to control the reaction. Hydroformylation of oleochemicals has been known for a long time. Back in the 1960s, E. Ucciani and E. N. Frankel started using hydroformylation catalysts. Frankel converted fatty acid methyl esters into the corresponding aldehydes or alcohols using cobalt catalysts. More recent investigations use rhodium catalyst complexes, which are much more active under milder reaction con-

ditions. The reaction is described in more detail in . Fig. 4.8 for methyl oleate (MO). The addition of the formyl group takes place at both the C9 and C10 position. Depending on the catalyst used, an isomerization of the C=C double bond can also take place in advance, and adducts with formyl groups are formed at all possible C atoms. Such isomerizing hydroformylation is particularly interesting if it selectively leads to the formylation of the terminal C18 carbon atom. The corresponding ω-formyl- (or after further hydrogenation the ω-hydroxyl-) functionalized oleochemicals are formed, which are important for the synthesis of unbranched (i.e. linear) polymers. An undesirable side reaction is the hydrogenation of MO with hydrogen from the synthesis gas to methyl stearate (MS). Triglycerides, e.g. soybean oil, can also be hydroformylated several times and - after hydrogenation - polyols are formed that are very suitable for the production of polyurethanes.

O HO

OMe + H2 O OMe

O

O Stearic acid methylester

Isomer. + CO/H2

+ H2 9

COOMe

Methyl oleate + CO/H2 9

COOMe

CHO + H2 9

COOMe OH

. Fig. 4.8  (Isomerizing) hydroformylation of methyl oleate

OMe

4.2 · Reactions at the C = C Double Bond of Unsaturated Oleochemicals

The hydroformylation of oleochemicals has now found its way into industrial applications with two processes: 5 In the Dow-Chemical process, soybean oil is used as a raw material. As already explained in . Table 2.1, soybean oil contains 53% linoleic acid and 6% linolenic acid, i.e. a high proportion of fatty acids with several C=C double bonds. Dow produces polyols from soybean oil in three stages, which are sold under the trade name RENUVA®. Initially, the soybean oil is transesterified to the corresponding methyl esters, followed by hydroformylation of the multiple double bonds present in the esters, and finally, the oligoaldehyde esters formed in this way are hydrogenated to oligohydroxyl esters, the RENUVA polyols. These polyols have multiple applications: Diisocyanates are used to convert them into viscoelastic polyurethanes (PU), having a high resistance. In the Ford Mustang, these PUs are used, for example, in car seats. RENUVA polyols are also used in the manufacture of flexible elastomers, foams, adhesives, coatings and sealants. 5 Castor oil is used as the raw material in the BASF process. Castor oil (7 Sect. 2.2.7) contains a high proportion of ricinoleic acid, i.e. a C18:1 acid with an additional hydroxyl group at the C12 position. BASF uses the castor oil, i.e. the triglyceride, directly in the hydroformylation and obtains a new trigly­ ceride containing up to three hydroxyl groups and three aldehyde functions. Hydrogenation thus produces a polyol again. In a third step, this polyol is etherified with ethylene oxide or propylene oxide to form the final product, the polyether polyols, which are marketed under the name Lupranol Balance 35®. These polyether polyols are used to produce rigid foams for mattresses. Both processes have the issue that a broad product spectrum is obtained by functionalization. In addition, the resulting foams have relatively low molecular weights. Closely related to hydroformylation is hydroaminomethylation (HAM), a reaction with synthesis gas and amines that leads to oleo compounds carrying an additional methylene amino

69

group –CH2–NR2 (. Fig. 4.7). These amino compounds could be of interest for the synthesis of new polyamides based on renewable raw materials. HAM is a tandem reaction, i.e. a series of successive reactions: First, hydroformylation takes place with the synthesis gas to form the corresponding aldehyde, which then condenses with the amine present to form an imine or an enamine, which is then hydrogenated with excess hydrogen to form the amine. A catalyst, usually a rhodium complex, is required for both the hydroformylation step and the hydrogenation. Under mild reaction conditions (140 °C, 10 bar synthesis gas) almost quantitative yields are achieved. Various amines can be used, e.g. ­hexylor benzylamine as well as morpholine. Ammonia is also investigated as an amine component in more recent work.

Hydrocarboxylation and Alkoxycarbonylation Another catalytic reaction with carbon monoxide is hydrocarboxylation, in which oleochemicals are converted with CO/water ­ mixtures. Dicarboxylic acids are formed from fatty acids, e.g. a branched C19 dicarboxylic acid from oleic acid (. Fig. 4.7). This reaction, originally discovered by Walter Reppe (BASF) with nickel catalysts, is now preferably carried out with cobalt or palladium catalysts. There is also a metal ­complex-free variant, the so-called Koch reaction, which is carried out with strong mineral acids as catalysts. Instead of water, the reaction can also be carried out with alcohols directly leading to the ­ corresponding esters. This is referred to as alkoxy­ carbonylation (also known as hydrocarbalkoxy­ lation or hydroesterification). Typical cobalt catalysts are cobalt carbonyl pyridine systems; a typical palladium catalyst is, e.g., palladium dichloride/ triphenylphosphine. More recently, the isomerizing alkoxycarbonylation in particular has been studied more closely: David J. C ­ ole-Hamilton succeeded in producing the linear dimethyl 1,19-nonadecanedi­ oate from methyl oleate by ­methoxycarbonylation interesting with 95% selectivity (. Fig. 4.9), an ­ monomer for the production of polyesters. A palladium complex with the special ligand ­bis(di-tertiary-butyl-phosphinomethyl)benzene was used as catalyst.

4

70

Chapter 4 · There is More to Oleochemistry - Reactions at the Fatty Acid Alkyl Chain

COOMe

+ CO, MeOH

MeOOC

COOMe

[Pd] . Fig. 4.9  Isomerizing methoxycarbonylation of methyl oleate

4 Dimerization A further C–C bond formation is dimerization to dimer fatty acids. These can already be produced by heating PUFA to 300–400 °C. More frequently, however, catalytic processes are used with special clays as heterogeneous catalysts, e.g. with montmorillonite. These reactions do not produce a uniform product, but always a complex mixture of dimer fatty acids. Some structural examples of acyclic, monocyclic and bicyclic dimer fatty acids are given in . Fig. 4.10. The examples show dimers of C18 fatty acids, i.e. C36 dicarboxylic acids. The synthesis of dimer fatty acids is hence a relatively simple method for obtaining ­high-boiling dicarboxylic acids on the basis of renewable raw materials. These dicarboxylic acids are used to produce corrosion inhibitors, coatings or synthetic lubricants. The conversion of dimer fatty acids with diamines to polyamides is particularly important. If dimer fatty acids are converted with ethylenediamine, for instance, a polyamide with a melting range between 90 and

110 °C is obtained. These polyamides are used as adhesives for shoes, packaging and bookbinding. They are sold as solids, liquefy upon brief heating during application and are then applied thinly to the adhesive surfaces. An immediate adhesive effect occurs, which after cooling leads to a very strong binding of the two parts. Because of this procedure, these adhesives are also known as “hot melts”. Important by-products of dimer fatty acid synthesis are monomer fatty acids and trimer fatty acids. The monomer fatty acids contain a large amount of branched fatty acids, especially methyl-branched acids. The dimer fatty acids can also be reduced to the corresponding diols. These dimer diols may again be important for polyesters or polyurethanes.

Metathesis A particularly exciting reaction is metathesis. It is a C–C bond forming and a C–C bond breaking reaction at the same time. In order to understand the functional principle of this reaction,

COOH COOH

COOH COOH

COOH COOH

. Fig. 4.10  Structural examples of dimer fatty acids

. Fig. 4.11 Important ruthenium metathesis catalysts (Cy=cyclohexyl)

N

PCy3

Cl

CH

Ru

Cl

CH

Ru

Ph

PCy3

N

N Ru

N

Grubbs II

Grubbs I

Cl

Cl Cl

PCy3

N

Ph

4

71

4.2 · Reactions at the C = C Double Bond of Unsaturated Oleochemicals

CH

Cl

Cl

N Ru

CH

Cl O

Hoveyda-Grubbs

we first have a look at a petrochemical reaction, the metathesis of two molecules of propene (Eq. 4.1), as an example: Both propene molecules are cleaved with the aid of a catalyst, breaking the two C=C double bonds. The cleavage products immediately combine again to form two new alkenes, 2-butene and ethene. However, the cleavage products are not freely present in the solution, but remain bound to the catalyst metal during the reaction.

(4.1)

Metathesis is an equilibrium reaction, hence only half of the propylene is converted into products. In self-metathesis, two identical alkenes react, whereas if two different unsaturated compounds react, it is called cross-metathesis. ­Cross-metathesis can also be found in Eq. 4.1, namely the back reaction of one mole of 2-butene and one mole of ethene yielding two moles of propene. In cross-metathesis, the C=C double bonds also break again; in Eq. 4.1, this is represented by a dashed auxiliary line. The catalysts for metathesis are heterogeneous or homogeneous transition metal catalysts. Typical heterogeneous catalysts are oxides of tungsten, molybdenum or rhenium; typical ­homogeneous

O

NO2

Grela

catalysts are salts or complexes of tungsten, molybdenum or ruthenium. They have been used in the petrochemical industry since the 1960s. In oleochemistry, metathesis has been known for a long time, but it is only in recent years that the development of new catalysts has made industrial implementation possible. Important newer homogeneous ruthenium catalysts are listed in . Fig. 4.11. These are carbene complexes with a ruthenium–carbon double bond, which are particularly suitable for starting the metathesis mechanism, going via metallacyclobutanes. The listed metathesis catalysts are named after their discoverers Grubbs, Hoveyda and Grela. With these ­catalysts, turnover numbers (TON) of 200,000 mol substrate per mol catalyst are achieved. The application of metathesis to oleochemicals was already carried out in 1972 by C. Boelhouwer and subsequently developed further by J. C. Mol and S. Warwel. The simplest example of oleochemical metathesis is the self-metathesis of two molecules of methyl oleate (. Fig. 4.12). The products formed are 9-octadecene and dimethyl octadec-9-enedioate. Like oxidations and functionalizations of the oleochemicals already discussed, metathesis also leads to the desired bifunctional compounds. The diester formed can be converted to (relatively hydrophobic) polyesters by reaction with diols or to polyamides with diamines, respectively. The coproduct of MO metathesis, 9-octa-

72

Chapter 4 · There is More to Oleochemistry - Reactions at the Fatty Acid Alkyl Chain

COOMe

[cat.]

COOMe

4

COOMe

+

COOMe

. Fig. 4.12  Self-metathesis of methyl oleate

O COOMe COOMe

O COOMe

Dieckmann-

+ H2O

condensation

- CH3OH - CO2

civetone . Fig. 4.13  Civetone synthesis on the basis of methyl oleate self-metathesis

decene, is an excellent starting material for the synthesis of lubricants and surfactants. Dimethyl octadec-9-enedioate is itself also suitable for the synthesis of fine chemicals: Dieckmann condensation followed by hydrolysis produces, for example, 9-cycloheptadecen-1-one, the musk fragrance civetone, which is used in numerous perfumes (. Fig. 4.13). Instead of methyl oleate, methyl erucate can also be used in self-metathesis. In addition to 9-octadecene, the C18 diester is then replaced by the corresponding C26 diester. Such long-chain α,ω-diesters are difficult to access by classical organic reactions. In addition to fatty acids and their esters, triglycerides can also be used directly in metathesis. . Figure 4.14 shows an example of the intermolecular self-metathesis of two triolein molecules, e.g. present in olive oil. By splitting off octadecene, a “dimeric triglyceride” with a total of 96 carbon atoms and five double bonds is formed. This highly viscous oil has excellent drying properties and is used in the production of resins, lacquers and printing inks.

Cross-metathesis is even more versatile than self-metathesis because the molecule reacting with the unsaturated oleochemical can be widely varied. However, this also poses a danger: In addition to the self-metathesis products of the two starting compounds, the use of asymmetric metathesis partners can lead to the formation of several unsaturated cross-products, which in turn can continue to react and thus form a complex mixture of products that cannot be used industrially. Therefore, in the investigation of oleochemical cross-metatheses, it is obvious to use very reactive symmetrical alkenes. Here, metathesis with the industrially well available ethene is a good choice. Metatheses with ethene are also referred to as ethenolyses. Since the metathesis of ethylene with itself produces only ethene, no undesirable ­self-metathesis products of ethene are produced. Since crossmetathesis takes place much more rapidly than self-metathesis of the oleochemical in the presence of a large excess of ethene, this reaction can be carried out very selectively.

. Fig. 4.14 Selfmetathesis of triolein

4

73

4.2 · Reactions at the C = C Double Bond of Unsaturated Oleochemicals

O O 2

O

O

[cat.]

O

O O O O O O O

O O O

+

O O

O

. Fig. 4.15 shows the ethenolysis of methyl oleate with the formation of the two C10 products 1-decene and methyl 9-decenoate. Thus, two terminal unsaturated compounds are formed which are very reactive and can therefore be used for many subsequent reactions: 5 Methyl 9-decenoate can be converted to dimethyl undecanoate by alkoxycarbonylation, to methyl 10-aminodecanoate by amination or to methyl 9,10-epoxydecanoate by epoxidation. These compounds are in turn excellent monomers for polyesters, polyamides or epoxy resins. Because of these properties, methyl 9-decenoate is also regarded as a potential new “key oleochemical substance”. 5 Methyl 9-decenoate can also be dimerized to a long-chain α,ω diester. 5 The coproduct of this metathesis, 1-decene, can be used for the production of lubricants or surfactants or copolymerized with ethene and is therefore also a valuable product.

Ethenolysis of oleochemicals is advantageously carried out at high ethene surpluses, e.g. in an autoclave at 50 bar ethene pressure. According to Le Chatelier’s principle, high conversion rates of the oleochemical can thus be achieved. This requires only low concentrations (0.01 mol%)

of the Grubbs I catalyst. The inverse reaction of ethenolysis, the metathesis of two terminal alkenes with separation of ethene, is also a popular reaction: Because the resulting gaseous ethene can be separated in a slight vacuum during the reaction, the equilibrium is completely shifted to the product side and thus a 100% conversion is achieved. The cross-metathesis of MO with alkenes can also be carried out with other symmetrical alkenes instead of ethene. With 2-butene, methyl 9-undecenoate is obtained, with 3-hexene methyl 9-dodecenoate. With cyclohexene, the chain is extended by six carbon atoms, however, also various coproducts and derivatives are formed (. Fig. 4.16). Ethenolysis can also be performed directly with unsaturated triglycerides. . Figure 4.17 shows the ethenolysis of a triolein as an example. In addition to the co-product 1-decene, a triglyceride of ω-decenoic acid is formed, which can be hydrogenated to tricaprin. With this metathesis variant, it is thus possible to produce a ­short-chain from a long-chain triglyceride. The metathetic ethenolysis of jojoba oil is also of interest (box in 7 Sect. 2.2.10). Jojoba oil consists of monoesters of unsaturated carboxylic acids having a C=C double bond at position 9

74

Chapter 4 · There is More to Oleochemistry - Reactions at the Fatty Acid Alkyl Chain

COOMe H2C

CH2

[cat.]

4 1-Decene + COOMe

Methyl 9-decenoate

HOOC

COOMe

Polyesters

Undecanedioic acid

H2N

COOMe

Nylon-10

10-Aminodecanoic acid

COOMe

O

Epoxy Resins

9,10-Epoxydecanoic acid . Fig. 4.15  Ethenolysis of methyl oleate

COOMe

[cat.]

COOMe

. Fig. 4.16  Cross-metathesis of methyl oleate with cyclohexene

4.2 · Reactions at the C = C Double Bond of Unsaturated Oleochemicals

75

O O O O O O

+/- 3 H2C

CH2

O O O + 3

O O O

+ 3 H2

O O O O O O . Fig. 4.17  Ethenolysis of triolein

with corresponding unsaturated fatty alcohols and thus contains two C=C double bonds per ester molecule, which can react with ethene. By double ethenolysis with high ethene pressure, two molecules 1-decene split off and a α,ω-unsaturated ester remains, which in turn can undergo numerous subsequent reactions (. Fig. 4.18). As already briefly mentioned, asymmetric alkenes can also be used in cross-metathesis with oleochemicals, which, however, is usually associated with a large product range. . Figure 4.19

shows the principle using the example of methyl oleate and some unsaturated reaction partners which have already been successfully used in this cross-metathesis: methyl acrylate, acrylonitrile and allyl chloride. This combination of oleo­ chemical and petrochemical starting materials produces valuable bifunctional compounds. Metathesis of oleochemicals has now also found industrial application. The American company Elevance Renewable Sciences, based in Woodridge (Illinois/USA), has done pioneering

4

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Chapter 4 · There is More to Oleochemistry - Reactions at the Fatty Acid Alkyl Chain

4

. Fig. 4.18  Ethenolysis of jojoba oil

COOMe + X

HC

CH2

[cat.] C8

X C8

COOMe

+ +

COOMe

X

Alkenes

X

Methylacrylate Acrylonitrile Allylchloride

COOMe CN CH2Cl

. Fig. 4.19  Cross-metathesis of methyl oleate with asymmetric alkenes

work in this field. The company was founded in 2007 by a joint venture between Cargill, which traditionally deals with renewable raw materials, and Materia, which holds the worldwide rights to ruthenium-based Grubbs metathesis catalysts. Elevance commissioned a biochemical refinery in Gresik, Indonesia, in 2013. This plant on the island of Java has a capacity of 180,000 tons per year and uses palm oil as its preferred raw material, but can also process other oils such as jatropha or algae oils. A mixture of unsaturated diesters, unsaturated monoesters (e.g. methyl 9-decenoate) and olefins is formed by cross-metathesis of methyl oleate with 1-butene (butenolysis) and a parallel self-metathesis of the oleochemical. In the biorefinery in Gresik, the palm oil is directly metathesized with 1-butene, the olefins produced are separated by

distillation, and the remaining triglycerides are then transesterified with methanol. In further separation steps, the product mixture is then separated into individual components and partially hydrogenated. Among others, dimethyl ­α,ω-octadecanedioate is formed, an interesting monomer for biopolymers (7 Chap. 19). Functionalized poly-olefins, which are used as lubricants, and biofuels (7 Chap. 20) are also available in the Gresik biorefinery. At the beginning of 2016, Elevance announced that it now also has a second generation of technology: It can now also use S­ chrock-type molybdenum or tungsten catalysts suitable for ethenolysis of fats and oils. A first demonstration plant with this technology was successfully operated in Budapest (Hungary). Ethenolysis can significantly expand the existing metathesis product portfolio.

4.2 · Reactions at the C = C Double Bond of Unsaturated Oleochemicals

77

BOX: Can Cashew Nuts Attract Tsetse Flies? Tsetse flies are widespread in many parts of Africa. They are much feared because they are the carriers of the so-called sleeping sickness, which is usually fatal without therapy. What can be done about this and what is the role of cashew nuts? The cashew tree was first discovered by the Portuguese in northeastern Brazil and can now be found in many tropical countries. The trees, up to 12 m high, bear kidney-shaped fruits in whose shells the cashew kernels (or cashew nuts) are found (. Fig. 4.20). The production of cashew kernels worldwide in 2016 was 4.9 million t a−1. These nuts are mainly roasted and

salted and offered as food, but they can also be used to press an oil consisting mainly of oleic and linoleic acid. The shells remain as a waste material. But these cashew shells are of particular interest. Out of them, an oil can be extracted, the cashew nut shell liquid (CNSL), which is available worldwide at approx. 0.5 Mio t a−1. It is toxic and therefore not suitable as food. It contains cardanol, a mixture of phenols which have long-chain, unsaturated alkyl groups bound in meta-position (. Fig. 4.21). The researchers L. Gooßen and D. Cole-Hamilton have

. Fig. 4.20  Mature cashew fruits

. Fig. 4.21  The path from cardanol to 3-ethylphenol

jointly succeeded in producing 3-ethylphenol from these alkenylphenols. They use the method of homogeneously catalyzed metathesis, which we learned in 7 Sect. 4.2.2 for unsaturated fats. Using a mixture of an isomerizing Pd catalyst and a metathetically active Ru catalyst, they perform an “isomerizing metathesis” leading to 3-vinyl-phenol. If hydrogen is then pressed into the same reactor, 3-ethylphenol is produced (. Fig. 4.21). This compound is a very effective attractant (=pheromone) for tsetse flies. With 3-ethylphenol, the flies can be lured into traps containing insecticides.

4

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Chapter 4 · There is More to Oleochemistry - Reactions at the Fatty Acid Alkyl Chain

Chemistry of Polyunsaturated Fatty Acids

4

In this section “C–C linkages”, some reactions shall be presented, which are especially common for polyunsaturated fatty acids, the PUFA, i.e. linoleic acid and linolenic acid, which occur frequently in nature. These reactions usually take place in such a way that the two isolated double bonds in the fatty alkyl chain first isomerize to a conjugated diene and only then do these “conjuenic acids” undergo a subsequent reaction. This isomerization is also carried out industrially as a single step by heating the PUFA at high temperatures in the presence of alkali for a longer period of time. The conjuenic acids produced in this way are usually isomeric mixtures. If, for example, linoleic acid, which has two cis-double bonds in positions 9 and 12, is used as substrate, a single conjugation leads to two conjuenic acids with double bonds in positions 9 and 11 or 10 and 12, respectively. However, since the double bonds can still be in cis or trans, a broad mixture of isomers results. Conjuenic acids often undergo C–C bond forming reactions, which are also known from petrochemical 1,3-dienes. One example is the Diels–Alder reaction with maleic anhydride presented in . Fig. 4.22. It can be carried out in boiling xylene in the presence of catalytic iodine amounts with high yields. The conjugation step can be performed separately or simultaneously. Conjugated linoleic acid or its derivatives can also undergo catalytic co-oligomerization. An important example is rhodium catalyzed

cooligomerization with ethene, which leads to unsaturated mono-, di- and triadducts of ethene (. Fig. 4.23). Hydrogenation of these adducts, e.g. in the presence of a heterogeneous palladium catalyst, produces saturated fatty acid esters with an alkyl branching in the middle of the fatty acid alkyl chain. These are potentially suitable as lubricants due to their high thermal stability, ­relatively low viscosity and their low pour point. Finally, the chemistry of triple unsaturated linolenic acid is briefly discussed. If it is conjugated in alkali medium, conjutrienic acids are formed which can undergo, either thermally or catalytically, intramolecular Diels–Alder reaction. Substituted cyclohexadiene rings are formed by cyclization (. Fig. 4.24). These can be disproportionated into a mixture of c­ ycloalkanes and aromatics in the presence of heterogeneous hydrogenation catalysts, e.g. by palladium on activated carbon. The cyclic unsaturated fatty acids can be used for the synthesis of alkyd resins. Their esters with branched diols are synthetic lubricants for highly stressed aircraft turbines. Plastic plasticizers are produced on the basis of cyclohexane derivatives. It was already mentioned in 7 Sect. 2.2.6 on linseed oil that linolenic acid tends to polymerize in air and finally forms a solid layer. Linseed oil is therefore also referred to as “drying oil”. The primary process of this polymerization is the formation of hydroperoxides, which decompose into radicals, which in turn lead to (disordered) C–C linkages of linolenic acid. This process can be accelerated by the addition of cobalt salts,

. Fig. 4.22 Diels–Alder reaction of a conjugated methyl linoleate with maleic anhydride

COOMe

Isomerization COOMe

+

O

O

O

COOMe O

O

O

4

79

4.2 · Reactions at the C = C Double Bond of Unsaturated Oleochemicals

COOMe 4/5

8/7

[Rh] + n C2H4 1:1-Adduct

COOMe 5/6

8/7

3:1-Adduct

2:1-Adduct

COOMe 5/6

8/7

COOMe 5/6

8/7

5/6

8/7

[Pd] H2

COOMe 5/6

8/7

COOMe 5/6

8/7

COOMe

. Fig. 4.23  Cooligomerization of conjugated methyl linoleate with ethene to branched fatty acid esters

so-called siccatives. In this way, varnishes are formed that can be used for painting purposes. Another application of this polymerization is the production of linoleum. The first step is the gassing of heated linseed oil with air. The resulting rubber-like mass, linoxyn, is processed with natural resins, e.g. colophony, to the so-called linoleum cement, which is then further mixed with cork or wood flour as well as color pigments or chalk. This mixture is calendared onto jute fabric. The resulting sheets are matured in 15 m high, 60 °C thermostatized rooms, the so-called ripening chambers, for two to four weeks to form linoleum (. Fig. 4.25). Linoleum is already a well-known product: Initial examples, the wax or oil cloths, were already described in 1627. In 1860, Walton received a patent on linoleum. It was used

for floor coverings until the 1960s, when it was replaced by PVC floor coverings and carpets. It was not until the 1980s that there was a partial renaissance of this product, because some consumers wanted a floor covering based on renewable raw materials. Linoleum is also antistatic and suitable for rooms with underfloor heating.

New Oleochemical Polymers The polymerizations described so far follow radical mechanisms and are difficult to control. In recent years, M. A. R. Meier and S. Mecking in particular have developed numerous approaches to find new ways to specifically structured polymers, in particular with the aid of cata­ lytic processes (7 Sect. 19.2.2). Unfortunately, the internal double bonds of the unsaturated oleochemicals are not active enough to enter

80

Chapter 4 · There is More to Oleochemistry - Reactions at the Fatty Acid Alkyl Chain

15

13

12

Isomerization

11

9

9

COOH

COOH

Linolenic acid Cyclization

4

COOH [Pd] Disproportionation

H

COOH

COOH

. Fig. 4.24  Intramolecular cyclization of linolenic acid with subsequent disproportionation of the cyclohexadiene derivatives

Linseed oil

Siccatives Natural resins

Calender

Ripening chamber

Linoleum Air

T=80°C T=60°C Linoleum cement

Pigments,Chalk

Jute fabric

Grounded cork

Mixer . Fig. 4.25  Simplified flow diagram of linoleum production

a catalytic polyinsertion like the petrochemical alkenes ethene or propene. One trick is to first produce a terminally unsaturated, more active molecule from oleochemicals, which is

then polymerized. We already came across this procedure in the ethenolysis of MO to methyl 9-decenoate having a terminal double bond. The situation is very similar with ricinoleic acid

4

81

4.2 · Reactions at the C = C Double Bond of Unsaturated Oleochemicals

OH COOH Ricinoleic acid Pyrolysis (T > 350 °C)

1-Heptanal

COOH 10-Undecenoic acid

1) + HCN 2) + 2 H2

H 2N

COOH

1) + HBr 2) + NH3

COOH

H2 N

+ 1,3Propanediol

Nylon 12

(CH2)8

C

O

(CH2)3

O

O

C

Nylon 11 (Rilsan)

Metathesis

(CH2)8

[Ru] - CH2 CH2

O

Polyesters

Alkoxycarbonylation

Red.

OH

10-Undecenol

[Co] + CO

O O Polyesters

Red.

n

CHO 10-Undecenal Aldol Condensation CHO

Metathesis [Ru] - CH2 CH2 Polymers

. Fig. 4.26  10-Undecenoic acid and its subsequent chemistry to polymers

obtained from castor oil (7 Sect. 2.2.7), which can be selectively cleaved into heptanal and 10-undecenoic acid by pyrolysis, i.e. heating to

temperatures >350 °C. The esters of 10-undecenoic acid can be catalytically copolymerized with alkenes such as ethene. . Figure 4.26 shows a

Chapter 4 · There is More to Oleochemistry - Reactions at the Fatty Acid Alkyl Chain

82

4

converted into a polyester by cobalt-catalyzed alkoxycarbonylation. 5 If the acid is only reduced to the level of 10-undecenal and then aldol condensation is carried out, the result is again a molecule with two terminal double bonds, which can be polymerized again by ADMET.

number of additional possibilities for obtaining a wide variety of polymers from the basic chemical 10-undecenoic acid: 5 Hydrocyanation and subsequent hydrogenation of the nitrile potentially leads to ω-aminododecanoic acid, which could thus be converted to nylon-12. However, linear selective hydrocyanation of unactivated alkenes is still a huge challenge in catalysis. 5 Hydrobromination and reaction of the alkyl bromide with ammonia yields the ­ω-aminoundecanoic acid, which leads to nylon-11 (commercial product: “Rilanit” or “Rilsan”) (7 Chap. 19). 5 By reacting two molecules of ­10-undecenoic acid with a diol, e.g. 1,3-propanediol, a doubly unsaturated ester with two terminal double bonds is formed. This ester undergoes self-metathesis and splits off ethene to form a longchain polyester. This variant of metathesis is a reversal of ethenolysis. Since the starting product is an acyclic α,ω-diene, it is also referred to as acyclic diene metathesis (ADMET). 5 By reduction of methyl 10-undecenoate, it is possible to obtain 10-undecenol, which is

A major disadvantage of ricinoleic acid is that it occurs exclusively in castor oil, of which only relatively small amounts are available. If one ­ compares the 10-undecenoic acid accessible from castor oil with the 9-decenoic acid produced by ethenolysis of methyl oleate, it becomes obvious that there is a much broader raw material basis for the latter. One way of synthesizing a polymer in a few steps from methyl oleate is isomerizing methoxy­ carbonylation as already described, i.e. the ­palladium-catalyzed reaction with carbon monoxide and methanol (. Fig. 4.27). Dimethyl nonadecanedioate is formed, which can be reduced to 1,19-nonadecanediol. With titanium catalysts both react with each other to form the corresponding polyester-19,19.

COOMe Methyl oleate [Pd] + CO + MeOH

Isomerizing Alkoxycarbonylation

MeOOC

COOMe C19-Diester Reduction

- 2 MeOH [Ti] OH

HO C19-Diol

(CH2)19

O

(CH2)17 O

O O

Polyesters . Fig. 4.27  Polyester based on methyl oleate

n

4.2.3  Linkage of New C-H Bonds

New C–H bonds are formed in the catalytic hydrogenation of unsaturated oleochemicals with hydrogen. The first heterogeneous hydrogenation catalysts were discovered in 1897 by Paul Sabatier and Jean Baptiste Senderens and then applied to unsaturated fats in 1901 by Wilhelm Normann. The use of heterogeneous nickel catalysts is today an industrial standard to improve the color and odor stability of oleochemicals or to convert (liquid) oils into (solid) margarine. The latter reaction is also the reason why hydrogenation in oleochemistry is often referred to as “hardening”. Selective hydrogenations (“selective harden­ ings”) are difficult to carry out, e.g. to selectively hydrogenate only one double bond of linoleic acid (to C18:1 acid) and not the one as well (to stearic acid) (. Fig. 4.28). However, this is feasible with the aid of homogeneous transition metal compounds as hydrogenation catalysts. Since the 1960s, complexes of precious and non-precious metals with a wide variety of ligands have been used to gain control during hydrogenation. With precious metal compounds, e.g. platinum and palladium, however, the quantitative separation and recycling of the homogeneous catalyst is often a major problem.

4

83

4.2 · Reactions at the C = C Double Bond of Unsaturated Oleochemicals

Homogeneous mixed organometallic catalysts found by Ziegler, Sloan and Lapporte (ZSL catalysts) and further developed by Bernhard Fell have a good chance of industrial application. They are based on the metals nickel or cobalt and are activated by aluminum alkyls. Another possibility for the selective hydrogenation of oleochemicals is the use of special palladium nanocatalysts. They can be produced relatively easily in situ from palladium dichloride by reduction with hydrogen in the presence of a relatively polar solvent such as propylene carbonate. Palladium colloids of only a few nanometers in size are formed, which are long-term stabilized by the coordinating solvent. Due to the large surface area of the nanoparticles, they are very active, so that some selective hydrogenations of oleochemicals are completed after only a few minutes. At the same time, they lead very selectively to the desired mono-unsaturated oleochemicals. A further advantage of these catalysts is their easy recyclability: The nanocatalyst remains completely dissolved in the propylene carbonate phase, which can be ­easily separated after the reaction has taken place. For faster separation, only a few percent of water is added to the propylene carbonate phase (. Fig. 4.29).

. Fig. 4.28 Selective hydrogenation of linoleic acid to C18:1 acid

O OH Linoleic acid

+ H2

[cat.] O OH

C18:1-Acid, e. g. Oleic acid

+ H2

[cat.] O OH

Stearic acid

84

Chapter 4 · There is More to Oleochemistry - Reactions at the Fatty Acid Alkyl Chain

M Separator

Reactor

C18:1-Acids Linoleic Acid

4

Pd

Hydrogen Pd- nanocatalyst H2O/Propylene carbonate

. Fig. 4.29  Recycle concept for palladium nanohydrogenation catalysts

4.2.4  Further Additions

to the C=C Double Bonds of Oleochemicals

This section briefly mentions some (more exotic) additions to unsaturated fats that lead to unusual products and could therefore become important: 5 Hydrosilylation of unsaturated fats with silanes is one way of forming C-Si bonds and thus producing special silicones with fatty alkyl chains. Such products are being discussed for hydrophobizing building surfaces or as specialty lubricants. One example is the hydrosilylation of methyl linoleate with dimethylchlorosilane shown in Eq. 4.2. The Speier catalyst, hexachloroplatinic acid, is used as catalyst. 5 Hydrozirconation of alkenes is important because - independent of the position of the double bond in the alkene - the corresponding primary zirconium organic compounds

are exclusively formed. Before addition to zirconium, an internal double bond is always isomerized to a terminal double bond. Unfortunately, unsaturated fatty acids cannot be used directly in this reaction: The carboxy group must first be protected by a reaction with amino alcohols as oxazoline group. This reaction is also stoichiometric in relation to zirconium and would first have to be converted into a catalytic reaction. Catalytic hydrozirconation could be used to specifically produce oleochemicals with terminal double bonds, the advantages of which we have already learned about. 5 The situation with hydroalumination is quite analogous: Alkenes with internal double bonds also react exclusively to primary aluminum alkylene. This reaction can be carried out catalytically with titanium catalysts. A transfer to oleochemicals is still pending.

(4.2)

4.2 · Reactions at the C = C Double Bond of Unsaturated Oleochemicals

5 The same applies to hydrocyanation, i.e. the reaction of unsaturated oleochemicals with hydrocyanic acid. This reaction is well established in petrochemical industry: The nickel–phosphite-catalyzed bishydrocyanation of 1,3-butadiene is carried out industrially to produce adipodinitrile, an important intermediate for the synthesis of adipic acid and hexamethylene diamine. A large-scale use in oleochemistry does not yet exist. Summary (Take-Home Messages) 5 Substitution reactions on the saturated fatty acid alkyl chain are industrially only used to a limited extent, as they usually lead to complex mixtures. An exception is the selective sulfonation at the methylene group adjacent to the carboxyl group: α-Estersulfonates are produced, which have very good surfactant properties and can be used as substitutes for petrochemical linear alkylbenzene sulfonates. 5 Unsaturated oleochemicals can be transferred into the corresponding epoxides with the aid of performic or peracetic acid. If the epoxy rings are opened with water, diols are formed which are used for polyurethane production. 5 Bishydroxylation with hydrogen peroxide also leads directly to the vicinal diols. 5 Ozonolysis of the C = C bond of a fatty acid produces a mono- and a diacid. Pelargonic and azelaic acids, for instance, are formed from oleic acid. 5 Unsaturated oleochemicals can also be functionalized by catalytic C–C linkages on the alkyl chain. Bifunctional compounds are formed which are suitable for the synthesis of polymers (polyester, polyamides, etc.). 5 Aldehyde esters are formed by hydroformylation, amino esters by hydroaminomethylation. Hydrocarboxylation and alkoxycarbonylation lead to branched dicarboxylic acids or their esters, respectively.

85

5 Dimer fatty acids are formed by catalytic dimerization of two fatty acids. By reacting the dimer fatty acids with diamines, polyamides are formed, which are used as adhesives (hot melts). 5 Metathesis of unsaturated oleochemicals has so far only been carried out on an industrial scale in special cases, but has great potential. Self-metathesis of methyl oleate results in a diester; intermolecular metathesis of two unsaturated triglycerides results in “dimeric triglycerides” with high viscosity and good drying properties. 5 By cross-metathesis of methyl oleate with ethene (the so-called ethenolysis), methyl 9-decenoate is formed. Because of its terminal C=C double bond, it is a valuable starting chemical for bifunctional compounds. 5 Ethenolysis of triglycerides can be used to produce fats with short-chain fatty acids. Ethenolysis of wax esters, e.g. jojoba oil, produces α,ω-unsaturated monoesters. 5 Cross-metatheses with asymmetric alkenes usually lead to mixtures. Valuable bifunctional products can be synthesized by controlling them with the metathesis catalyst, usually a ruthenium carbene complex. 5 Polyunsaturated fatty acids, e.g. linoleic acid, can undergo Diels–Alder reactions or catalytic cooligomerizations after isomerization to the corresponding conjuenic acids. Cyclic or branched products are formed which can be used, for example, as lubricants. 5 Triple unsaturated linolenic acid can also undergo Diels–Alder reactions, e.g. intramolecularly with itself to form ring molecules. The production of linoleum is industrially important: Under the influence of atmospheric oxygen, linolenic acid containing linseed oil polymerizes to form a rubber-like mass, which is then processed with fillers and jute sheets to form floor coverings.

4

86

4

Chapter 4 · There is More to Oleochemistry - Reactions at the Fatty Acid Alkyl Chain

5 The production of oleochemical polymers is currently an important research goal. Approaches to this are, for example, follow-up reactions of the 10-undecenoic acid accessible from ricinoleic acid or the isomerizing alkoxycarbonylation of methyl oleate with subsequent condensation to polyesters. 5 Selective hardening of polyunsaturated oleochemicals can be carried out with palladium nanocatalysts, which can be easily produced and recycled. 5 Numerous further additions to the C=C double bond are possible, e.g. ­platinum-catalyzed hydrosilylation, which can be used to produce special hydrophobic silicones.

? Ten Quickies

1. How many steps are required to synthesize an α-ester sulfonate (AES) from a (saturated) triglyceride? Can you compare the synthesis of the competitor product, linear alkylbenzene sulfonates (LABS)? 2. Name (up to seven) methods for synthesizing oleochemical di- or polyols suitable for the production of polyurethanes! 3. Compare the ozonolyses of oleic acid and erucic acid with each other! 4. In the hydroformylation of unsaturated oleochemicals, internal or terminal formyl groups can be obtained. How, in principle, can this be controlled? 5. How can alkyl-branched fatty acids be obtained? We got to know three methods in 7 Chaps. 3 and this chapter. 6. Carry out (on paper) the ethenolysis of petroselinic acid C18:1 (Δ6/c.)! Which two products are formed? 7. Which four products can be produced by cross-metathesis of methyl oleate with allyl chloride? 8. Briefly describe the current ruthenium metathesis catalysts!

9. How can polyunsaturated fatty acids (PUFA) be converted into conjuenic acids? 10. Name some typical catalysts for the hydrogenation of C=C double bonds of oleochemicals!

References Monographs and Review Articles Vorholt AJ, Behr A (2017) Oleochemistry. In: Cornils B, Herrmann WA, Beller M, Paciello R (eds) Applied homogeneous catalysis with organometallic compounds (Chap. 34). Wiley-VCH, Weinheim Behr A, Vorholt AJ (2017) Homogeneous Catalysis with Renewables. Springer International Publications Parambath A (ed) (2017) Cashew nut shell liquid. Springer International Publications Enferadi Kerenkan A, Béland F, Do T-O (2016) Chemically catalyzed oxidative cleavage of unsaturated fatty acids and their derivatives into valuable products for industrial applications: a review and perspective. Catal Sci Technol 6:971–987 Seidensticker T, Vorholt AJ, Behr A (2016) The mission of addition and fission - catalytic functionalization of oleochemicals. Eur J Lipid Sci Technol 118:3–25 Behr A, Vorholt AJ, Ostrowski KA, Seidensticker T (2014) Towards resource efficient chemistry: tandem reactions with renewables. Green Chem 16:982–1006 Honary L, Richter E (2011) Biobased Lubricants and Greases, Wiley-VCH, Weinheim Behr A, Westfechtel A, Perez Gomes J (2008) Catalytic processes for the technical use of natural fats and oils. Chem Eng Technol 31:700–714 Behr A (2008) Angewandte homogene Katalyse. Wiley, Weinheim, Kap. 44: Homogene Katalyse mit nachwachsenden Rohstoffen Corma A, Iborra S, Velty A (2007) Chemical routes for the transformation of biomass into chemicals. Chem Rev 107:2411–2502 Meier MAR, Metzger JO, Schubert US (2007) Plant oil renewable resources as green alternatives in polymer science. Chem Soc Rev 36:1788–1802 Centi G, van Santen RA (eds) (2007) Catalysis for renewables: from feedstock to energy production. ­Wiley-VCH, Weinheim van Bekkum H, Gallezot P (eds) Catalytic conversion of renewables. Special issue of “Topics in Catalysis” 27(1–4) Biermann U, Friedt W, Lang S, Lühs W, Machmüller G, Metzger JO, Rüsch gen. Klaas M, Schäfer HJ, Schneider MP (2000) Neue Synthesen mit Ölen und Fetten als nachwachsende Rohstoffe für die chemische Industrie. Angew Chem 112:2292–2310

87 References Original Publications Vanbésien T, Le Nôtre J, Monflier E, Hapiot F (2018) Hydroaminomethylation of oleochemicals: a comprehensive overview. Eur J Lipid Sci Technol 120(1):1700190 Vorholt AJ, Immohr S, Ostrowski KA, Fuchs S, Behr A (2017) Catalyst recycling in the hydroaminomethylation of methyl oleate: a route to novel polyamide monomers. Eur J Lipid Sci Technol 119:1600211 Furst M, Korkmaz V, Gaide T, Seidensticker T, Behr A, Vorholt AJ (2017) Tandem reductive hydroformylation of castor oil derived substrates and catalyst recycling by selective product crystallization. ChemCatChem 9:4319–4323 Danov SM, Kazantsev OA, Esipovich AL, Belousov AS, Rogozhin AE, Kanakov EA (2017) Recent advances in the field of selective epoxidation of vegetable oils and their derivatives: a review and perspective. Catal Sci Technol 7:3659–3675 Gaide T, Bianga J, Schlipköter K, Behr A, Vorholt AJ (2017) Linear selective isomerization/hydroformylation of unsaturated fatty acid methyl esters: a bimetallic approach. ACS Catal 7:4163–4171 Gaide T, Dreimann JM, Behr A, Vorholt AJ (2016) Overcoming phase-transfer limitations in the conversion of lipophilic oleo compounds in aqueous media - a thermomorphic approach. Angew Chem Int 55:2977– 2981 Haßelberg J, Behr A (2016) Saturated branched fatty compounds: proven industrial processes and new alternatives. Eur J Lipid Sci Technol 118:36–46 Haßelberg J, Behr A, Weiser C, Bially JB, Sinev I (2016) Process development for the synthesis of saturated branched fatty derivatives: combination of homogeneous and heterogeneous catalysis in miniplant scale. Chem Eng Sci 143:256–269 Vanbésien T, Monflier E, Hapiot F (2016) Hydroformylation of vegetable oils. Eur J Lipid Sci Technol 118:26–35 Goldbach V, Falivene L, Caporaso L, Cavallo L, Mecking S (2016) Single-step access to long-chain α, ­ω-dicarboxylic acids by isomerizing hydroxycarbonylation of unsaturated fatty acids. ACS Catal 6:8229– 8238 Butilkov D, Lemcoff NG (2014) Jojoba oil olefin metathe­ sis: a valuable source for bio-renewable materials. Green Chem 16:4728–4733 Behr A, Witte H, Kämper A, Haßelberg J, Nickel M (2014) Entwicklung und Untersuchung eines Verfahrens zur Herstellung verzweigter Fettstoffe im ­Miniplant-Maßstab. Chem Ing Tech 86:458–466 Behr A, Tenhumberg N, Wintzer A (2014) Selective oxidation and functionalisation of renewables. ­DGMK-Tagungsbericht 3:11–15

Hübner K (2014) Linoleum. Chem unserer Zeit 48:396–401 Philippaerts A, Jacobs PA, Sels BF (2013) Hat die Hydrie­ rung von Pflanzenölen noch eine Zukunft? Angew Chem 125:5328–5334 Kadyrov R, Azap C, Weidlich S, Wolf D (2012) Robust and selective metathesis catalysts for oleochemical applications. Top Catal 55:538–542 Biermann U, Bornscheuer U, Meier MAR, Metzger JO, Schäfer HJ (2011) Oils and fats as renewable raw materials in chemistry. Angew Chem Int Ed 50:3854– 3871 Trzaskowski J, Quinzler D, Bährle C, Mecking S (2011) Aliphatic long-chain C20 polyesters from olefin metathesis. Macromol Rapid Commun 32:1352–1356 Behr A, Krema S (2011) Metathesis applied to unsaturated lipid compounds. Lipid Technol 23:156–157 Saurabh T, Patnaik M, Bhagt SL, Renge V (2011) Epoxidation of vegetable oils - a review. Int J Adv Eng Technol 2:491–501 Köckritz A, Blumenstein M, Martin A (2010) Catalytic cleavage of methyl oleate or oleic acid. Eur J Lipid Sci Technol 112:58–63 Dierker M (2004) Oleochemical carbonates - an overview. Lipid Technol 16:130–134 Dierker M, Schäfer HJ (2010) Surfactants from oleic, erucic and petroselinic acid: synthesis and properties. Eur J Lipid Sci Technol 112:122–136 Behr A, Johnen L, Vorholt A (2009) Katalytische Verfahren mit nachwachsenden Rohstoffen. Nachr Chem 57:757–761 Meier MAR (2009) Metathesis with oleochemicals: new approaches for the utilization of plant oils as renewable resources in polymer science. Macromol Chem Phys 210:1073–1079 Köckritz A, Martin A (2008) Oxidation of unsaturated fatty acid derivatives and vegetable oils - a current review. Eur J Lipid Sci Technol 110:812–824 Beller M (2008) A personal view on homogeneous catalysis and its perspectives for the use of renewables. Eur J Lipid Sci Technol 110:789–796 Rybak A, Fokou PA, Meier MAR (2008) Metathesis as a versatile tool in Oleochemistry. Eur J Lipid Sci Technol 110:797–804 Mol JC (2004) Catalytic metathesis of unsaturated fatty acid esters and oils. Top Catal 27:97–104 Behr A (2004) Oleochemistry. In: Cornils B, Herrmann WA (Hrsg) Aqueous-phase organometallic catalysis, 2nd ed (Chap. 6.13). Wiley-VCH, Weinheim, pp 593–605 Heidbreder A, Höfer R, Grützmacher R, Westfechtel A, Blewett CW (1999) Oleochemical products as building blocks for polymers. Fett/Lipid 101:418–424 Behr A (1990) Anwendungsmöglichkeiten der homogenen Übergangsmetallkatalyse in der Fettchemie. Fat Sci Technol 92:375–388

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The Coproduct of  Oleochemistry - Glycerol 5.1 Properties and Use of Glycerol – 90 5.2 Glyceryl Esters – 94 5.3 Glycerol Ether – 98 5.3.1 Glycerol Oligomers – 98 5.3.2 Glycerol Polymers – 99 5.3.3 Glycerol Alkyl Ether – 99 5.3.4 Glycerol Alkenyl Ether – 100

5.4 Glycerol Acetals and Ketals – 100 5.5 From Glycerol to Propanediols – 101 5.6 From Glycerol to Epichlorohydrin – 103 5.7 Glycerol Oxidation – 104 5.8 Dehydration of Glycerol to Acrolein – 104 5.9 From Glycerol to Synthesis Gas – 105 References – 108

© Springer-Verlag GmbH Germany, part of Springer Nature 2020 A. Behr and T. Seidensticker, Chemistry of Renewables, https://doi.org/10.1007/978-3-662-61430-3_5

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Chapter 5 · The Coproduct of Oleochemistry - Glycerol

Chapter Timetable 5 You will learn about the properties of glycerol and where it can be used. 5 The main part of this chapter deals with the follow-up chemistry of glycerol, which has been intensively investigated in recent years.

5

Already at the beginning of the book section “fats and oils”, we learned that fats and oils are triglycerides, i.e. triesters of glycerol. By cleaving these triesters (7 Sect. 3.1) - no matter which method is used glycerol is automatically released as a coproduct. In terms of quantity, the proportion of glycerol in fats is certainly significant: In coconut oil (which is made up of relatively short-chain fatty acids), the proportion by weight of glycerol is 17%, in soya oil and tallow (with long-chain fatty acids) approx. 10%.

BOX: A Brief Look at the History of Glycerol The Swedish chemist and pharmacist Karl Wilhelm Scheele produced a “lead plaster” in 1779 by mixing olive oil with lead oxide. As you already know from 7 Sect. 3.1.3, he saponified the triglyceride (at least partially) and released glycerol. He put a finger into his paste and realized

it tasted sweet. Since then, this new compound has been called “Scheele’s Sweet”. Only three decades later, in 1813, the Frenchman Michel–Eugène Chevreul was able to prove that fats are glycerol esters of fatty acids and gave glycerol its final trivial name in 1823, derived

5.1  Properties and Use of Glycerol . Table 5.1 lists some characteristic properties of glycerol. Particularly, important properties are the strongly hygroscopic behavior, the large liquid range, the non-toxicity and the viscosity that can be adjusted by dilution with water. The aqueous and partially salt-containing glycerol obtained in the various manufacturing processes (7 Sect. 3.1) has to be laboriously concentrated and purified. In principle, various

from the Greek word for sweet (glykys). P.S.: Despite the great success of Scheele, we strongly advise you not to analyze unknown product mixtures by tasting them. Otherwise, it could have been your last analysis!

options are available for this purpose, which are summarized in . Fig. 5.1. The “glycerol water” from fat cleavage and transesterification is highly diluted: Because of the high excess water during fat cleavage (. Fig. 3.2), this process produces a 15–20% aqueous glycerol solution; in the transesterification process (. Fig. 3.5), glycerol concentration is higher. Also, the glycerol liquor resulting from saponification is diluted and additionally contaminated by a strong salt load.

. Table 5.1  Properties of glycerol Property

Substance values

Appearance/behavior

Colorless, clear, hygroscopic liquid, non-corrosive, antiseptic

Melting point

Low: 18 °C (but mostly still liquid below)

Boiling point

High: 290 °C (under decomposition) 182 °C (at 3 hPa)

Toxicity

Non-toxic (permitted in food)

Density

1.26 g ml−1

Viscosity

Undiluted: high viscosity (1760 mPa s at 20 °C); as 50–60% aqueous solution: low viscosity

Miscibility

Miscible with water and ethanol, slightly soluble in ether, insoluble in hydrocarbons

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5.1 · Properties and Use of Glycerol

. Fig. 5.1  Possibilities of glycerol purification

Glycerolwater

Evaporation

Pre-cleaning

Rectification

Ion exchanger

Refining

Evaporation

Pure Glycerol

5 Hence, the solutions must be concentrated in all cases. This usually takes place in multiple stages in evaporators connected in series, which are operated at different pressures. In these multistage evaporators, the water can be removed with relatively little energy input: For each kilogram of water to be removed, 0.3 kg of a four-bar steam is required. 5 Many glycerol plants also have a precleaning unit. Impurities such as protein degradation products are bound to coagulants such as aluminum or iron salts, which are then filtered off. In some cases, fatty acids present as impurities can also be coagulated and removed by acid addition. Finally, the excess acid must be neutralized.

5 Classically, the next cleaning step is distillation. This step can be carried out in a vacuum both in multibed distillation columns and in a thin-film evaporator. 5 Depending on the quality of the distillate, refining may be necessary. This can be done, for instance, by “bleaching”, i.e. by adsorption of remaining color bodies on activated carbon. 5 An alternative to distillation is ion exchange. However, it can only be used for glycerol waters low in salt content from fat cleavage or transesterification. If the glycerol liquor from the saponification process having high salt content was used, the ion exchange capacities would not last long. Ion exchange always requires two stages: In the cation exchange,

5

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Chapter 5 · The Coproduct of Oleochemistry - Glycerol

for instance, alkali cations are exchanged for protons; in the anion exchange, undesirable anions such as chloride are exchanged for hydroxyl ions. In this ion exchange unit, not only inorganic salts are removed, but also fats, soaps and pigments are retained by adsorption. Ion exchange can only be carried out with 30–40% aqueous solutions of glycerol and not with concentrated ones. Therefore, an additional evaporation is required after ion exchange. Of course, the ion exchange units have to be regenerated after some time by treatment with bases and acids. By evaluating the different variants of glycerol preparation, one can simply summarize: 5 Distillation enables a larger feed spectrum and is also suitable for high ion concentrations; however, it requires a high energy input. 5 Ion exchange consumes less energy and is therefore somewhat more economical. Since glycerol is not obtained at the top of the distillation column, its quality must be monitored very closely. The ion concentration in the feed is limited. During the regeneration of the ion exchange units, wastewater is produced which must be disposed of properly. 5 Depending on the quality of the distillate, refining may be necessary. This can be done, for instance, by “bleaching”, i.e. by adsorption of remaining color components on activated carbon.

Cl

Propene

+ Cl2 - HCl

OH

OH

Cl

Cl

At the beginning of the twentieth century, the glycerol demand was covered exclusively from fat processing, in particular from the saponifica­ tion of fats. When in the 1940s soaps were partly replaced by synthetic detergents in the USA and at the same time, the demand for glycerol increased, competing processes for the production of synthetic glycerol from propene were developed. . Figure 5.2 gives an overview of these synthetic routes:

+ 1/2 Ca(OH) 2 - 1/2 CaCl2

or

I

After passing through the different purification stages, glycerol is sold in various degrees of purity: 5 The highest quality consists of 99.8% glycerol and approx. 0.2% water. It is also known as “high-purity pharmaceutical quality” and can be used in food, pharmaceuticals and cosmetics. The density at room temperature is 1.26 g ml−1. 5 For many purposes, the (cheaper) 86% glycerol is more suitable. The rest is again predominantly water. Due to its lower viscosity, it can be processed much easier. 5 In addition, several other qualities do exist on the market containing more or less heavy impurities and which can be yellow or brown in color. 5 A special case is “kosher glycerol”, which is obtained exclusively from vegetable fats, i.e. not from animal fats.

O Cl

Cl

Epichlorohydrin

Dichlorohydrins

- NaCl

+ NaOH + H2O

+ HOCl

Cl

OH

+ NaOH

Allyl chloride

+ H2O2

- NaCl II

OH Allyl alcohol

[WO3]

. Fig. 5.2  Synthetic routes from propene to glycerol

+ H2O

O

OH

Glycerol OH

Glycidol

OH

5.1 · Properties and Use of Glycerol

5 Via Route I, propene is the first chlorinated to allyl chloride. This is converted with hypochlorous acid to the two dichlorohydrins, which react with calcium hydroxide to epichlorohydrin. Subsequently, the latter is converted into glycerol with caustic soda. 5 Route II also goes via allyl chloride, which reacts with caustic soda to form allyl alcohol. However, there are also some chlorine-free alternatives to obtain allyl alcohol from propene. Allyl alcohol subsequently is catalytically converted with hydrogen peroxide into glycidol, which is finally hydrolyzed to glycerol. Both routes have four stages and are therefore very complex. If chlorine is used, it finally ends up as worthless salts. Nevertheless, for a long time, synthetic glycerol was a strong competitor to natural glycerol, as the raw material propene obtained from crude oil was available at relatively low cost. Due to the increased supply of natural glycerol due to biodiesel production, synthetic glycerol processes have lost much of their importance. Glycerol has found a wealth of direct applications for many decades. The most important are listed below: 5 Glycerol is often used in medical and phar­ maceutical formulations because of its ­non-toxicity, e.g. in cough syrups or expectorants. Very often, its hygroscopic property also plays an important role: Glycerol helps to keep a drug moist and to control water activity. 5 The use of glycerol in body care products is very similar: Glycerol is used as a solvent, plasticizer, lubricant and humectant in skin creams, toothpastes, mouthwashes, shaving foam, hair care products and glycerol soaps. With the help of glycerol, it is possible to re-soften dry skin. 5 Glycerol is also used in the tobacco industry because of its moisturizing properties: The crumbling of pipe tobacco or cigarettes is prevented by soaking them with glycerol. 5 There are also many applications in the food industry: Glycerol is used as a solvent and sweetener with the European designation (E)422 in food and beverages. It is classified by the US Food and Drug Administration (FDA) as “generally recognized as safe (GRAS)”. In sweets and cakes, it acts as a softener and humectant. Glycerol can prevent

93

cakes from drying out during prolonged storage. Glycerol has about 60% of the sweetening power of sucrose and about the same number of calories per gram. Compared to sucrose, glycerol does not increase the blood sugar level and does not enable bacterial growth. 5 Other direct applications of glycerol include adhesives, plasticizers in regenerated cellulose and special paper grades. 5 Finally, there are a number of technical applications in which glycerol is chemically converted. These include, for instance, the use as polyol in polyurethane foams or alkyd resins. We will learn more about this follow-up chemistry of glycerol in the coming sections of this chapter. . Figure  5.3 attempts to summarize these applications once again. The percentages are estimates. What is striking is the large market share of pharmaceuticals and personal care products, both of which require very high glycerol purity. At the end of this section, we have a look at some market data. The worldwide fat production, currently approx. 200 million tons per year, has already been discussed in 7 Sect. 2.3. About 10% of this amount (about 20 million tons per year) is glycerol! However, we have also heard that the majority of fats and oils are used in the food sector (approx. 75%) and thus do not serve glycerol production. Approx. 22% of fats and oils (approx. 44 million tons per year) are processed industrially either to chemicals or fuels, whereby larger quantities of glycerol are produced. In recent decades, the European glycerol market has had a volume of 250,000–400,000 tons per year. This has changed significantly in the last decades: With the introduction of biodiesel, i.e. fatty acid methyl esters especially based on rapeseed, as a fuel, additional quantities of glycerol were brought onto the market. In 2006, global biodiesel production amounted to approx. 6 million tons per year and by 2014 had risen to just under 30 million tons per year. This means that several hundred thousand tons of glycerol have been added to the European market that were not needed by traditional customers. Accordingly, glycerol prices changed: While in the years 2000–2003 prices of 1000–1300 Euro per ton could still be achieved, between 2004 and

5

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Chapter 5 · The Coproduct of Oleochemistry - Glycerol

. Fig. 5.3 Traditional applications of glycerol (estimated values in % by weight)

Food Polyols

Personal care 9%

12%

23%

16%

24% 16%

5

Tobacco

Pharmaceuticals Others

2006, the price for one ton of ultrapure glycerol fell to 500–700 Euro and in 2011 was 750 Euro per ton. The price for technical glycerol qualities is significantly lower, by a factor of about five. However, if the price of a basic chemical drops significantly, it can also be used for applications for which it was previously too expensive because cheaper petrochemical competitor products existed. Glycerol, for example, is now being discussed for applications for which ethylene glycol or 1,2-propanediol was previously used. However, when large quantities of a basic chemical are available, the question must also be asked whether completely new glycerol deriva­ tives have a chance of conquering the market. Such new products have been the subject of intensive research in recent years and some of them have already been successfully transferred to production scale. These new glycerol derivatives will be presented in more detail in the coming sections. We will first look at “classical” alcohol derivatives, i.e. esters, ethers, acetals and ketals of glycerol. Further sections deal with the conversion of glycerol into diols and epoxides.

Finally, we present methods to oxidize and dehydrate glycerol to valuable products. At the end of the chapter, glycerol is regarded as a pure carbon source and converted into synthesis gas, which in turn can be converted into numerous industrial chemicals according to already known methods. 5.2  Glyceryl Esters

Glyceryl trinitrate, an ester of glycerol with the inorganic nitric acid, has long been known (Eq. 5.1). This triester is also incorrectly called “nitroglycerol”; however, it is not a nitro compound (with a C–NO2 bond), but a nitrate (with a C–O–NO2 bond). It is produced by reacting glycerol with a mixture of nitric acid and sulfuric acid, also called “nitrating acid”. OH + 3 HNO3 OH

OH

[H2SO4] - 3 H2O

ONO2 O2NO

ONO2

(5.1)

5

95

5.2 · Glyceryl Esters

BOX: The History of “Nitroglycerol” Glyceryl trinitrate was discovered as early as 1846 by the Italian chemist Ascanio Sobrero. As a liquid, this compound is unstable and can easily explode when heated or hit. In 1866, Alfred Nobel discovered that a mixture of glyceryl trinitrate and diatomaceous earth produced a deformable paste that was easy and relatively safe to handle. It could easily be placed in drill holes to perform rock blasting. Nobel called this paste “dynamite” and thus

OH HO

OH

+ x HOAC

earned a huge fortune. Today, the interest on these assets is distributed annually as “Nobel Prizes” to exceptionally creative researchers. Nobel was fortunate enough to invent dynamite at exactly the right time: In the second half of the nineteenth century, numerous railway lines were built in Europe, for which many tunnels had to be blown up. The construction of canals also depended on the new explosives: From 1879, the first Panama Canal with a total

- x H2O

of 30,000 tons of dynamite was blown free. Today, glyceryl trinitrate no longer plays a major role as an explosive. Together with nitrocellulose, it is still a component of propellants and rocket fuels. It is also used - in very small amounts - as a drug in asthma, heart failure and arteriosclerosis: Glyceryl trinitrate decomposes rapidly in the body and forms nitric oxide, which expands the coronary arteries and improves blood flow to the heart.

OH HO

OAc

Monoacetin

OAc

Diacetin

OAc

Triacetin

OH AcO

(5.2)

OAc AcO

The esters of glycerol with organic acids are much more important. The three acetins, mono-, di- and triacetine, for example, are produced with acetic acid (Eq. 5.2). In order to produce triacetin as pure as ­possible, glycerol is first reacted with acetic acid

and then with acetic anhydride. An almost complete conversion of glycerol is achieved. The flow diagram of the triacetin synthesis is shown in . Fig. 5.4. In reactor I, glycerol is esterified with acetic acid where conversion into monoacetins occurs. Water is formed and is removed under

Recycle - HOAc Vacuum system

Acetic anhydride

Triacetin

Acetic acid

Evaporator

Glycerol

Waste Reactor I . Fig. 5.4  Flow diagram of triacetin production

Reactor II

96

Chapter 5 · The Coproduct of Oleochemistry - Glycerol

+1

COOH - H2O

OH HO

+1 OH

HO

- MeOH

2 Glycerol

+

H2C

O

C O

HC

O

C O

H2C

O

C

O O

C

Monoglyceride

O

5

OH

COOMe

3 Monoglycerides

. Fig. 5.5  Three methods for the preparation of glycerolmonofatty acid esters (monoglycerides)

vacuum using an azeotropic distillation. In reactor II, the monoacetins are further esterified using acetic anhydride. In this reaction step, acetic acid is formed which is recycled to reactor I. The triacetin formed is purified in an evaporator separating higher boiling waste products. Triacetin is a stable product with low toxicity which is used as a cellulose plasticizer, as a solvent for perfumes and as a textile auxiliary. We already know triesters of glycerol with long-chain carboxylic acids as fats and oils. In addition to triesters, monoesters of glycerol (monoglycerides, monoacylglycerols, MAG) are of particular importance because they contain both a hydrophilic and a hydrophobic moiety and can therefore be used as emulsifiers. Monoesters can be synthesized from glycerol by esterification with one mole of fatty acid, by transesterification with one mole of fatty acid methyl ester or

by transesterification of two moles glycerol with one mole of triglyceride (obtaining three moles of monoester) (. Fig. 5.5). The latter variant is also called “glycerolysis”. However, the selective synthesis of monogly­ cerides is not trivial, because tri- and diglycerides are always produced as by-products. Controlling the reaction to monoglycerides by the reaction conditions is usually attempted, however, especially homogeneous, heterogeneous or enzyme catalysts have already reached selectivities of 80–90%. Monoglycerides of different chain lengths are available, which have a purity of more than 90% due to short-path evaporation. They are used as emulsifiers in the food industry and cosmetics as well as for technical purposes. However, technical applications are limited, since the ester bond can be hydrolyzed and therefore is not very stable.

BOX: The Slim Japanese Special diglycerides (diacylglycerols, DAG) have also found greater interest in recent years. The Japanese company Kao produces diglycerides that are stable even at higher temperatures. Since 1999, large-scale enzymatic

production has been carried out from soy and rapeseed oils. The product is marketed under the name Econa oil and can be used for cooking, baking and deep-frying. In 2000, Japanese researchers published that the diglycerides

of Econa oil significantly reduce fat accumulation in the human body. Econa has thus become Japan’s best-selling vegetable oil and can now also be purchased in grocery stores in Europe and America. Bon appétit!

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5.3 · Glycerol Ether

BOX: Anything Is Good, if It Is Made of Chocolate Triesters with a defined composition of certain fatty acids also play a major role in chocolate production. Chocolate essentially consists of dry cocoa mass, cocoa butter and sugar (sucrose). Cocoa butter is the fat of the cocoa

bean. The cocoa butter melts slowly in the mouth and leaves a cooling impression. This particularly pleasant melting behavior is only observed with special triglyceride structures: Cocoa butter consists of 50% oleopalmitostearin and 25%

Special mixed triglycerides also enable interesting applications. For example, it is possible to specifically produce monofatty acid esters of diacetine. Diacetostearin, diacetoolein and diacetolaurine are in turn emulsifiers for food applications. The total market for food emulsifiers was estimated at 800,000 tons in 2015. A very special ester of glycerol is glycerol ­carbonate (. Fig. 5.6): 5 It has been produced indirectly from ­glycerol, e.g. by reaction with ethylene carbonate, which in turn is accessible from ethylene oxide and carbon dioxide. In this reaction, ethylene glycol is formed as coproduct. Instead of ethylene carbonate, dimethyl ­carbonate can also be used, thus obtaining two moles of methanol as a coproduct. 5 A particularly clever alternative is the direct synthesis of glycerol carbonate from glycerol and carbon dioxide. So far, tin catalysts have been able to synthesize glycerol carbonate with a yield of a few percent; however, a technical process is not yet in sight.

oleodistearin; the rest are palmitodiolein and stearodiolein. By selective esterifications of glycerol, it is possible to mimic the characteristic triglyceride structure of cocoa butter and thus to produce low-cost cocoa butter substitutes.

Glycerol carbonate is a colorless ­protic-polar liquid and soluble in both water and organic ­solvents. In water, it is stable at pH values below pH 5. These properties result in various fields of application: 5 Glycerol carbonate (and its esters) can be used as a solvent: They can be used in the manufacture of paints and varnishes, adhesives, cosmetics and pharmaceuticals. Glycerol carbonate dissolves nitrocellulose, cellulose acetates, nylons and polyacrylonitrile. 5 Its use as an extracting agent or lubricant is also being discussed. 5 As a monomer, it is used for the production of branched polymers. The French company Condat has developed the synthesis of glycerol polycarbonates and glycerol carbonate polyesters. 5 Glycerol carbonate can also be converted into glycidol (. Fig. 5.2) releasing CO2. Glycidol can be converted into numerous downstream products.

. Fig. 5.6  Syntheses of glycerol carbonate

+ O

O O

- Glycol O

OH HO

O

OH

HO + CO2 - H2O

O

Glycerol carbonate

98

Chapter 5 · The Coproduct of Oleochemistry - Glycerol

5.3  Glycerol Ether

5

In the following, we will get to know different ethers of glycerol: 5 If glycerol reacts with itself by splitting off water, glycerol oligomers are formed in which the individual glycerol molecules are linked to each other by an ether bridge. 5 If this linkage is repeated many times, glycerol polymers are ultimately formed. The nomenclature of oligo- and polymers is not uniform and some authors refer to both together simply as polyglycerols. 5 Glycerol can also be reacted with alkenes, aliphatic monoalcohols or alkyl halides to form glycerol alkyl ether. 5 A special case is the catalytic telomerization of glycerol with butadiene, which leads to glycerol alkenyl ether with an octadienyl chain. 5.3.1  Glycerol Oligomers

The simplest case of glycerol oligomerization is the dimerization of two glycerol molecules to diglycerols. Since glycerol is a trifunctional

molecule, several linear and cyclic derivatives occur during dimerization. . Figure 5.7 shows the different isomers of diglycerol. The cyclic dimers are diols, the linear tetroles. In general, glycerol oligomers belong to the class of polyols. Glycerol oligomers are widely used in cosmetics, as food additives or in lubricants. Traditionally, these oligomers are produced by homogeneous base catalysis. However, a very broad spectrum of oligomers is obtained, till pentamers or hexamers. The short-chain oligomers, i.e. dimers and trimers, are particularly popular for the above-mentioned applications. Therefore, special heterogeneous catalysts such as zeolites, ion exchangers and mesoporous molecular sieves are used to reduce the number of glycerolunits. Although it is possible to achieve higher selectivities toward diglycerols, conversions are significantly lower. The majority of glycerol oligomers are further processed to polyglycerol esters (PGE), which behave like non-ionic surfactants. Synthesis can take place by esterification of the oligoglycerols with fatty acids or by transesterification with fats. This results in complex mixtures, and the product properties very much depend on the degree of oligomerization of the glycerol and on the

. Fig. 5.7 Possible isomers of diglycerol

HO

HO

OH

OH

OH

HO O

O

β,β '-Diglycerol

α,α '-Diglycerol

HO

OH

HO

OH

O

HO OH O

α,β -Diglycerol

O HO

O

OH

O

OH

8-membered cyclic Diglycerol

OH

HO

O O

Isomeric 6-membered cyclic Diglycerols

OH

99

5.3 · Glycerol Ether

5.3.3  Glycerol Alkyl Ether

number of esterified hydroxyl groups. PGE are used in cosmetics such as hair gels, baby creams and skin cleansers, as emulsifiers and for viscosity control. Especially, important products are diglyceroldiisostearate, diglycerolmonolaurate and diglycerolmonooleate.

The synthesis of glycerol alkyl ether can be performed according to three methods: 5 by acid-catalyzed reaction of glycerol with alkenes, especially with isobutene 5 by Williamson synthesis of sodium glycerolate with an alkyl halide 5 by condensation of glycerol with aliphatic alcohols underwater elimination.

5.3.2  Glycerol Polymers

In recent years, highly branched polyglycerols (hyperbranched polyglycerols) have been intensively investigated. An example for this product class is depicted in . Fig. 5.8. However, these special polyglycerols are not yet produced directly from glycerol, but, for instance, by a build-up reaction starting from trimethylolpropane with glycidol. These products are used as catalyst carriers or to improve the solubility of pharmaceuticals.

A very elegant method is the conversion with isobutene, which leads to glycerol tertiary butyl ether (GTBE). The monoether m-GTBE are produced along with the di- and triether, from which the latter two are summarized under the term “higher ether” (h-GTBE) (. Fig. 5.9). m-GTBE are soluble in polar solvents, h-GTBE only in non-polar solvents such as hydrocarbons.

HO

OH HO

O

OH O

O

O

HO HO HO

OH

O

O O

O

OH

O OH

O

OH

O

HO HO

O

OH

OH O

O O O HO

OH O

HO OH . Fig. 5.8  Highly branched polyglycerol (example)

OH

5

100

Chapter 5 · The Coproduct of Oleochemistry - Glycerol

OH

HO

OH

OH

n

+

+

n

HO

OH

[Pd] [H+]

O

OH

OH

+

5

OH

O

OH

OH O

OH

m-GTBE

OH OH O

O

OH

O

OH

O

+

O

O

+

O O

O

OH O

h-GTBE

. Fig. 5.9  Synthesis of glycerol tertiary butyl ether (GTBE)

O O O

h-GTBE can be used as an oxygen-containing diesel fuel additive, which significantly reduces particle emissions. Due to the branched alkyl chains, h-GTBE can also be used in gasolines as an “octane booster” to replace the less advantageous methyl tertiary butyl ether (MTBE). Synthesis takes place in the presence of acidic homogeneous catalysts such as ­p-toluenesulfonic acid or sulfuric acid. The process has now been optimized on a miniplant scale so that only the desired h-GTBE leaves the plant, while the m-GTBE is extractively separated and returned to the reactor for further reaction with isobutene. 5.3.4  Glycerol Alkenyl Ether

An atom economic method for the synthesis of unsaturated glycerol ether is the palladium-­ catalyzed telomerization of glycerol with the petrochemical 1,3-butadiene to glycerol octadienyl ether (. Fig. 5.10). In this reaction, two butadiene molecules combine to form a C8 chain and add to the hydroxyl groups of the glycerol.

. Fig. 5.10  Telomerization of glycerol with butadiene to glycerol octadienyl ether

The monotelomer is particularly interesting for application in detergents. By hydrogenation of the monotelomer, glycerol monooctylether is formed, which can be used as emulsifier or surfactant. Telomerization is a homogeneously catalyzed reaction that takes place under very mild reaction conditions. In a continuously operated miniplant, almost complete recycling of the homogeneous palladium catalyst and control of the selectivity to the monotelomer was achieved. 5.4  Glycerol Acetals and Ketals

Aldehydes form acetals with di- or polyols (gly­ cerol, for instance), whereas ketones form ketals, respectively. The corresponding products have a wide range of applications: 5 Acetals and ketals of glycerol have long been used in the synthesis of active ingredients.

5

101

5.4 · Glycerol Acetals and Ketals

Acetals of phenylacetaldehyde or of vanillin with glycerol, for example, lead to fragrances with a hyacinth or vanilla note. 5 Some acetals are also used industrially as solvents or detergents. 5 More recently, the use of glycerol acetals in the fuel sector has been investigated. The acetal of glycerol with tridecanal results in a product with an unusually high cetane number of 71 and is therefore excellently suited as diesel fuel. The structures of the acetals are shown in

. Fig. 5.11 using the example of the glycerol for-

mal from glycerol and formaldehyde. Both the five and the six-membered ring are formed; the

ratio is approx. 60/40. Both molecules still have a free hydroxyl group, which is available for further reactions. . Figure 5.11 shows etherification using diethoxymethane as an example. The colorless glycerol formal is stable at pH values above 2.8. It is an industrial product and is used as a viscous, high-boiling solvent and disinfectant (Bp. 195 °C) for medical or cosmetic applications. In some cases, the ratio between five to six-membered rings can be controlled by the reaction conditions. Equation 5.3 shows as an example the ketalization of glycerol with acetone. In the solvent dichloromethane at a reaction temperature of 40 °C, the five-membered ring is formed almost exclusively.

O OH HO

+

OH

O

OH CH2O

+ OH

OH

[H+] - H2O OH

O

O

+ O

O

OH

- EtOH

O

+

- H2O

O

(5.3)

OH

An acid has to be used as catalyst. Both homogeneous acids such as p-toluenesulfonic acid and acidic heterogeneous catalysts such as zeolites or acidic ion exchange resins are used. In a more recent variant of glycerol acetal synthesis, aldehyde synthesis and subsequent acetalization of the intermediate aldehyde are carried out as a one-pot process. For example, rhodium catalyzed hydroformylation of1-dodecene yields tridecanal which can be acetalized in situ with glycerol using p-toluenesulfonic acid as catalyst. The five-membered ring acetal, a dioxolane, is produced in a kinetically controlled manner and is thermodynamically converted into the six-ring acetal, a dioxane, at prolonged reaction times (. Fig. 5.12).

O O

5.5  From Glycerol to Propanediols

O

O

O +

O

O

O

O

. Fig. 5.11  Synthesis of glycerol formal and subsequent reaction with diethoxymethane

The diols 1,2-propanediol (propylene glycol) and 1,3-propanediol are produced worldwide in a quantity of approx. 1.2 million tons per year. Let us first have a look at the most important petrochemical synthesis routes (. Fig. 5.13) and their applications:

102

Chapter 5 · The Coproduct of Oleochemistry - Glycerol

+ CO/H2 [H+]

O 6

5

CHO

[Rh]

1-Dodecene

+ Glycerol O

Isom. 6

O

O

OH

HO . Fig. 5.12  One-pot process for the synthesis of long-chain glycerol acetals

OH OH

HO

+ H2 -H2O O

+ H2O

[cat.]

+ CO/H2

OH HO 1,2-Propanediol

O

O

Glycerol

OH

OH

+ H2

HO

+ H2O

O

1,3-Propanediol

. Fig. 5.13  Alternative synthetic routes to propanediols

5 1,2-Propanediol is produced petrochemically by hydrolysis of propylene oxide. It is used as an antifreeze, hydraulic fluid, lubricant, brake fluid, solvent for paints and coatings, and in the cosmetics and food industries. It also serves as substrate for emulsifiers and plasticizers. 5 Petrochemically, 1,3-propanediol is produced in two ways: In the Shell process, ethene is oxidized to ethylene oxide, which is then hydroformylated with synthesis gas to 3-hydroxypropanal. In the Degussa–DuPont process, propene is oxidized to acrolein, which is then hydrated to ­3-hydroxypropanal. In both processes, the 3-hydroxypropanal is hydrogenated to 1,3-propanediol in the final step. Due to its linear structure, ­1,3-propanediol is ideally suited for the production of polyesters, polycarbonates and polyurethanes. The reaction

with terephthalic acid produces polyester fibers known on the market under the trade names Sorona (DuPont) and Corterra (Shell). In order to obtain 1,2-propanediol from gly­ cerol, a primary hydroxyl group of glycerol must be removed. This can be achieved by dehydration–hydrogenation, which can be either metal-catalyzed or biocatalyzed. For the hydrogenation, both homogeneous and heterogeneous catalysts can be used. If heterogeneous copper, cobalt or manganese catalysts are used, high hydrogen pressures of up to 250 bar and temperatures of up to 300 °C are usually required. Under these drastic conditions, however, the selectivity to 1,2-propanediol is only low. However, recent research results, e.g. from Davy Process Technology, show that good selectivities to ­ 1,2-propanediol can be achieved with

heterogeneous copper catalysts at low hydrogen pressure up to 20 bar. Ashland Inc. and Cargill have taken an alternative path: They have built a plant for the biocatalytic dehydration–hydrogenation of glycerol to “bio-propylene glycol”. Intensive efforts are also being made to achieve 1,3-propanediol by metal-catalyzed dehydration–hydrogenation of glycerol. However, there is still no technical solution: the heterogeneous catalysts often have a high activity, but only a low selectivity. Conversely, homogeneous catalysts are often more selective but not sufficiently active. The best way seems to be the biochemical variant: Using bacteria of the genera Clostridium, Enterobacter or Citrobac­ ter, enzymes can produce 1,3-propanediol via the intermediate stage of 3-hydroxypropanal. DuPont has built a plant for the enzymatic synthesis of 1,3-propanediol in the USA. This plant currently uses cheaper glucose as a raw material but can also be operated with glycerol.

meantime, the market situation has changed so much that it even makes sense to take the opposite route, i.e. to produce epichlorohydrin from glycerol. Epichlorohydrin is a valuable intermediate product of polymer chemistry because it can be converted with bisphenol A to linear epoxy resins. After curing the epoxy resins with amines, duromers are formed which are used as casting resins in the electrical industry as well as in tool and vehicle construction (. Fig. 5.14). The production of epichlorohydrin from glycerol proceeds in two stages (Eq. 5.4): 5 In the first stage, glycerol is converted to 1,3-dichloropropanol with two moles of hydrogen chloride at 110–120 °C. The reaction is carried out in a two-stage process. Caprylic acid is used as the catalyst. Due to the low temperature, no corrosion occurs in the enameled reactor. 5 In the second stage, the dichloropropanol is dechlorinated with sodium hydroxide solution. An aqueous phase with a high sodium chloride content is formed as a coproduct, which can be used in sodium chloride ­electrolysis for chlorine production.

5.6  From Glycerol

to Epichlorohydrin

OH

In . Fig. 5.2 (Route I), we have already seen that glycerol can be produced synthetically from epichlorohydrin. However, this method has lost much of its importance in recent years. In the

OH

OH

[cat.] + 2 HCl - 2 H2 O

OH + NaOH Cl

Cl

- NaCl - H2O

O Cl

(5.4)

CH3

O + n-1 HO

n

C

OH

CH3

Cl Epichlorohydrin

O

5

103

5.5 · From Glycerol to Propanediols

Bisphenol A

CH3

CH3 O

C CH3

O

O OH

n-2

Epoxy resin . Fig. 5.14  Use of epichlorohydrin in the production of epoxy resins

C CH3

O

O

104

Chapter 5 · The Coproduct of Oleochemistry - Glycerol

The advantages of this new epichlorohydrin process (compared to the propene route in . Fig. 5.2) are obvious: 5 Instead of producing HCl from chlorine, HCl is consumed. 5 Chlorine consumption is significantly reduced. 5 Significantly less salt-contaminated waste is produced.

5

Under the tradename Epicerol®, Solvay sells glycerol-based EPH using their propriatary Process. In 2010, Dow Chemicals commissioned an epichlorohydrin production facility based on glycerol with a capacity of 150,000 t a−1 in Shanghai. 5.7  Glycerol Oxidation

Oxidation of glycerol can take place at both the secondary hydroxyl group (Route I in . Fig. 5.15) or at one of the primary hydroxyl groups (Route II). If the secondary hydroxyl group is oxidized, dihydroxyacetone (DHA) is formed, which was previously produced exclusively by fermentation. Acetobacter suboxidans or various yeasts can be used as bacterial strains. A disadvantage is that DHA inhibits bacterial growth and the production stops at a DHA concentration of 60 kg m−3. The processing of the very diluted fermentation broths is quite complex, so that the manufacturing costs are relatively high. Alternatively, an electrochemical glycerol oxidation has been developed, which also provides unde-

sirable by-products, e.g. hydroxypyruvic acid (. Fig. 5.14). Catalytic variants, including catalysts of the platinum group and gold catalysts, are also currently being intensively investigated. For example, R. M. Waymouth reported in 2010 that glycerol can be converted into DHA in the presence of a cationic palladium complex with atmospheric oxygen with a yield of 73%. Dihydroxyacetone is a worthwhile target molecule because it is used in cosmetics as a self-tanning agent. The world market for this very special use is estimated at approx. 2000 t a−1 tons per year. The oxidation of one of the primary hydroxyl groups of glycerol produces glycerol aldehyde in the first step. Further oxidation produces glyceric acid (dihydroxypropionic acid) and tartronic acid (hydroxymalonic acid). If oxidation is continued, C2 and C1 products are formed under C-C cleavage. Glyceric acid is used in the manu­ facture of textile softeners or emulsifiers, while tartronic acid is used in the medical sector. 5.8  Dehydration of Glycerol

to Acrolein

Acrolein is produced petrochemically by catalytic oxidation of propene. Acrolein is a toxic and potentially explosive substance. It is used directly as a herbicide or to produce the amino acid methionine (7 Chap. 14). However, the largest part of acrolein is further oxidized to acrylic acid. Acrylic acid is a major product (world production approx.

OH HO OH O

OH

OH Glycerol

II

Glyceraldehyde

O HO

OH OH

Glyceric acid . Fig. 5.15  Oxidation products of glycerol

OH

1,3-Dihydroxyacetone

OH HOOC

I

HOOC

O COOH

Tartronic acid

HO

COOH

Hydroxypyruvic acid

5

105

5.8 · Dehydration of Glycerol to Acrolein

. Fig. 5.16 Synthesis pathways to acrolein and acrylic acid

OH O

+ O2 - H2O

Acrolein

- 2 H2O

OH

OH

+ 1/2 O2

+ 3/2 O2 - H2O

3.4 × 106 t a−1) because it is required for the production of polyacrylic acid and polyacrylates. As . Fig. 5.16 shows, acrylic acid can also be formed by propene oxidation in one step, but with a lower yield. Acrolein can also be obtained by dehydration of glycerol. This reaction can be carried out in the gas or in the liquid phase in the presence of heterogeneous catalysts. Typical catalysts are e.g. nafion-composites, tungsten-doped zirconium oxides (ZrO2–WO3) or silica-supported hetero­ polyacids. The direct oxidative dehydration of glycerol to acrylic acid is also attempted. During the discussion of propandioles in 7 Sect. 5.5, we already mentioned that glycerol can be converted into 3-hydroxypropanal by fermentation. Another alternative for acrolein synthesis is to thermally dehydrate this 3-hydroxypropanal to acrolein (Eq. 5.5). OH - H2O

- H2O

[enz.] OH

OH

OH

O

' O

(5.5)

5.9  From Glycerol to Synthesis Gas

In the follow-up reactions of glycerol presented so far, efforts have always been made to preserve the C3 carbon skeleton of the starting material as good as possible and to vary only the functional groups on this skeleton. Another possibility, however, is to simply regard glycerol as a natural carbon source and to obtain a C1 building block, carbon monoxide, as well as hydrogen by bond cleavage. Such a mixture of carbon monoxide and hydrogen is called synthesis gas (syngas).

COOH Acrylic acid

+ 1/2 O2 - 2 H 2O

Synthesis gas is a worthwhile target for the utilization of surplus glycerol, because synthesis gas can be used in many ways: 5 Synthesis gas is converted into methanol on an industrial scale. Methanol has an extensive downstream chemistry and can, for instance, be converted into gasoline, alkenes or aromatics. Methanol is also needed for the production of biodiesel. A fatty acid methyl ester produced with “bio-methanol” would then be based exclusively on renewable raw materials. 5 Alkenes are converted to aldehydes or alcohols with synthesis gas in hydroformylation. 5 The carbon monoxide in the synthesis gas can also be catalytically converted with water into carbon dioxide (Water–gas shift reaction, WGSR) and then separated. Pure hydrogen remains, which can be used, for instance, in ammonia production or in fuel cells. 5 Synthesis gas can also be catalytically converted in the Fischer–Tropsch reaction into liquid hydrocarbons, which can be used as fuels. In . Fig. 5.17, the most important applications of synthesis gas are briefly summarized once again. The conversion of glycerol into synthesis gas is called reforming. In this reaction, one equi­ valent of glycerol is split into a hydrogen–carbon monoxide mixture with a molar ratio of 1.33:1 (Eq. 5.6).

C3 H8 O3 → 3CO + 4H2

(5.6)

If more (or even exclusively) hydrogen is desired, an additional conversion with water (water–gas shift reaction, Eq. 5.7) has to be carried out.

106

Chapter 5 · The Coproduct of Oleochemistry - Glycerol

. Fig. 5.17 Formation and use of synthesis gas based on fat

Fat

+ Methanol

Transesterification Biodiesel

5

Glycerol

Synthesis gas

Methanol Fischer Tropsch Reaction

Alkenes , aromatics

3CO + 3H2 O → 3CO2 + 3H2

Alkanes , fuels

(5.7)

Both Eqs. 5.6 and 5.7, result in the sum Eq. 5.8. Overall, according to this equation, glycerol is converted into hydrogen and carbon dioxide.

C3 H8 O3 + 3H2 O → 3CO2 + 7H2

(5.8)

There are currently three process variants for the technical reforming of glycerol into synthesis gas: 5 Reforming in the vapor phase (Steam reform­ ing) 5 Reforming in the liquid phase (Aqueous phase reforming, APR) 5 Reforming in the supercritical phase (Super­ critical water gasification, SCWG). In steam reforming, glycerol is converted with steam into synthesis gas in the gas phase at normal pressure and temperatures between 400 and 1000 °C. Typical heterogeneous catalysts are platinum/carbon or rhodium/ceriumoxide. Platinum catalysts produce particularly high carbon monoxide yields. The disadvantage of this process is its relatively high reaction temperatures. In the APR process, glycerol is kept in the liquid phase. This requires an increased pres-

Water gas shift reaction (WGSR)

+ H2 O / - CO2 Hydroformylation

Aldehydes , alcohols

Hydrogen

sure (20–40 bar). The temperature is significantly lower compared to steam reforming and is between 125 and 250 °C, depending on the cata­ lyst. Typical heterogeneous catalysts are based on the metals platinum or palladium; nickel–tin alloys are also used. The catalyst support is also of great importance: The formation of hydrogen is preferred by neutral or basic supports, e.g. aluminum oxides. In the SCWG process, glycerol is decomposed into synthesis gas in supercritical water. If very dilute solutions (