Sonochemistry: Applications and Developments 9783110999938, 9783110999907

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Timothy J. Mason, Mircea Vinatoru Sonochemistry

Also of Interest Sonochemistry. Volume : Fundamentals and Evolution Timothy J. Mason and Mircea Vinatoru,  ISBN ----, e-ISBN ---- Also available as a set – Set-ISBN: ---- Flow Chemistry. Volume : Fundamentals nd Edition Ferenc Darvas, György Dormán, Volker Hessel and Steven V. Ley (Eds.),  ISBN ----, e-ISBN ---- Flow Chemistry. Volume : Applications nd Edition Ferenc Darvas, György Dormán, Volker Hessel and Steven V. Ley (Eds.),  ISBN ----, e-ISBN ---- Green Chemisty. Water and its Treatment Green Chemical Processing, Volume  Mark Anthony Benvenuto and Heinz Plaumann (Eds.),  ISBN ----, e-ISBN ---- Green Chemistry. Principles and Designing of Green Synthesis Syed Kazim Moosvi, Waseem Gulzar Naqash and Mohd. Hanief Najar,  ISBN ----, e-ISBN ---- Process Technology. An Introduction nd Edition André B. de Haan and Johan T. Padding,  ISBN ----, e-ISBN ----

Timothy J. Mason, Mircea Vinatoru

Sonochemistry

Volume 2: Applications and Developments

Authors Prof. Dr. em. Timothy J. Mason Faculty of Health and Life Sciences Coventry University Priory Street Coventry CV1 5FB United Kingdom [email protected] Dr. Mircea Vinatoru Faculty of Chemical Engineering and Biotechnology University POLITEHNICA of Bucharest Spl. Independentei nr. 313 060042 Bucharest Romania [email protected]

ISBN 978-3-11-099990-7 e-ISBN (PDF) 978-3-11-099993-8 e-ISBN (EPUB) 978-3-11-098972-4 Library of Congress Control Number: 2022941982 Bibliographic information published by the Deutsche Nationalbibliothek The Deutsche Nationalbibliothek lists this publication in the Deutsche Nationalbibliografie; detailed bibliographic data are available on the internet at http://dnb.dnb.de. © 2023 Walter de Gruyter GmbH, Berlin/Boston Cover image: NiPlot/iStock/Getty Images Plus Typesetting: Integra Software Services Pvt. Ltd. Printing and binding: CPI books GmbH, Leck www.degruyter.com

Preface for Volume 2 This two-volume book “Sonochemistry” is not written in the style that might be expected of such a comprehensive history of the subject. This is because the authors, Tim Mason and Mircea Vinatoru, were active participants in its development from the 1990s to the present day and the text reflects their experiences. In the early days it was used mainly in the field of chemistry but within a few years the subject had begun to extend into other disciplines including environmental protection, the extraction of natural materials, food technology and medicine. In his opening address at the 17th meeting of the European Society of Sonochemistry in Jena in August 2022 Tim Mason used a term to describe his entry into the subject as a case of “Serendipity” which is defined as the occurrence and development of events “by chance” and “in a happy way”. It certainly applied when he gained his first permanent teaching post at Coventry Polytechnic because it corresponded exactly in time to the appointment of another chemist, Phil Lorimer, in the same department. It was these two who were to go on and establish the Sonochemistry Centre in Coventry. There are many other examples of serendipity recounted in the book, one of which was the arrival of an unsolicited letter from Mircea Vinatoru to Tim Mason in July 1990 which asked for some guidance on sonochemistry. This led to the two scientists meeting in Bucharest and resulted in a long-lasting friendship. Many years later and after continued research collaboration it led to the writing of this book. An important source of information for the authors was the paperwork that Tim Mason had collected from the very start of his time in Coventry. He had remained in the same building for the whole of his 40 years there and amassed a wealth of material, the earliest parts of which were not stored electronically amongst which were some significant but faded faxes that have now become very difficult to read. Coventry University closed the Sonochemistry Centre in 2018 and some years later the whole building within which it had been housed was demolished. The collected historical material was saved and transferred in several filing cabinets to Tim’s garage at home. Volume 2 “Applications and Developments” contains 6 chapters which detail the developments of sonochemistry in fields which continue to attract considerable research and development interest from academia, medicine, and industry. The authors have made contributions to all of these fields and they have approached the content in a way which they hope will prove to be understandable to readers whose expertise is not primarily in the individual topic. Each of the applications and developments described here help to illustrate the diverse nature of sonochemistry but also the unifying theme of the effects of acoustic energy on a wide range of technologies.

https://doi.org/10.1515/9783110999938-202

Contents Preface for Volume 2

V

Chapter 5 Sonochemical synthesis 1 5.1 Historical introduction 1 5.1.1 Mechanistic aspects 2 5.1.2 Synthetic aspects 5 5.2 Sonochemical synthesis in Coventry 13 5.2.1 The Ullmann reaction 13 5.2.2 Halogenation of aromatics using CuBr2 supported on alumina 14 5.2.3 O-Alkylation of hindered phenols 15 5.2.4 O-Alkylation of 5-hydroxychromones 18 5.2.5 Ultrasonic effects on metal powders and sonochemical catalysis 22 5.3 Sonochemical synthesis in Romania 35 5.3.1 Charge transfer complexes 35 5.3.2 Self-assembly membranes 49 5.3.3 Attempts to cause automerization of C13-labelled naphthalene 51 5.3.4 Ultrasound-assisted esterification using enzymes 51 5.3.5 Sonochemical preparation of catalysts 54 5.4 Concluding remarks 56 References 56 Chapter 6 Surface coating, metallurgy and materials technology 6.1 Introduction 63 6.2 Electroplating with ultrasound 63 6.2.1 Introduction 63 6.2.2 Electroplating in Coventry 67 6.3 Electroless plating with ultrasound 73 6.3.1 Electroless nickel 74 6.3.2 Electroless copper 75 6.4 Printed circuit board technology 77 6.4.1 Surface preparation 78 6.4.2 Electroless plating on PCBs 82 6.4.3 Improved solder joints in PCBs 84 6.5 Production of nanoparticles using pulsed sonoelectrochemistry 86

63

VIII

6.5.1 6.5.2 6.6 6.6.1 6.6.2 6.6.3 6.7 6.7.1 6.7.2 6.7.3 6.7.4 6.7.5 6.8 6.8.1 6.8.2 6.8.3 6.8.4 6.9 6.9.1 6.9.2 6.9.3 6.10

Contents

Introduction 86 Metal nanoparticle synthesis in Coventry – the SELECTNANO project 88 Metallurgy 90 Introduction to light metal casting 92 Preliminary work at Coventry 93 1996 Coventry group visit Moscow 96 The joint venture company Industrial Applications for Ultrasonics (IUS) 97 Ultrasonic treatment of molten and solidifying aluminium 98 Ultrasonic impact treatment of metal surfaces 100 Electric arc welding with ultrasonics 100 Ultrasonically assisted metal on metal coating 101 Ultrasonics for Al–Pb antifriction composites 101 Polymer science 102 Polymer degradation 102 Radical polymerization 104 Emulsion polymerization 105 Electroinitiated polymerization 106 Small projects with industry 107 Ultrasonically assisted spray coating 107 Encapsulation 109 Crystallization – the synthesis of zeolites 110 Concluding remarks 111 References 112

Chapter 7 Therapeutic ultrasound 117 7.1 General introduction 117 7.2 Low-frequency ultrasound 20–100 kHz 118 7.2.1 Cutting and drilling in dentistry and surgery 118 7.2.2 Emulsification for removal of tissue 119 7.2.3 Ultrasonic thrombolysis for the removal of blood clots 119 7.2.4 Synthesis of microcapsules for drug delivery 120 7.3 High-frequency ultrasound 1–5 MHz 121 7.3.1 Non-therapeutic applications of high-frequency ultrasound 121 7.3.2 Therapeutic applications of high-frequency ultrasound 123 7.4 The Sonochemistry Centre and therapeutic ultrasound 127 7.4.1 Conferences involving sonochemistry and therapeutic medicine 128 7.4.2 Dentistry 132 7.4.3 Transdermal drug delivery and enhanced cell permeability 134

IX

Contents

7.4.4 7.4.5 7.4.6 7.5

The links between HIFU in Chongqing and the Sonochemistry Centre in Coventry 138 Microcapsules for targeted drug delivery 146 Research collaboration with Wu Wei 153 Concluding remarks 155 References 155

Chapter 8 Power ultrasound in food technology 161 8.1 Historical introduction 161 8.1.1 Mechanical effects of ultrasound 161 8.1.2 Chemical and biological effects of ultrasound 173 8.2 Food technology at Coventry: links with industry 178 8.2.1 Leatherhead Food Research Association (LFRA) 179 8.2.2 Campden and Chorleywood Food Research Association (CCFRA) 182 8.2.3 Mars Foods 186 8.2.4 Unilever 189 8.2.5 Kraft Foods 190 8.3 Ultrasound and food technology at Coventry: academic links 8.3.1 1996 food conference and the book Ultrasound in food processing 193 8.3.2 Review articles from the Coventry group 194 8.3.3 International collaboration via research exchanges with other university groups 198 8.4 Food research in Romania 202 8.4.1 Sonicated champagne research project 202 8.4.2 Extraction of natural sweeteners from Stevia 203 8.5 Concluding remarks 204 References 205 Chapter 9 Textile and leather processing 213 9.1 Introduction 213 9.2 Production processes in the textile industry 9.2.1 Fibre production 213 9.2.2 Yarn production 216 9.2.3 Fabric production 219 9.3 Fabric treatment 221 9.3.1 Washing 223 9.3.2 Scouring 226 9.3.3 Carbonizing 227

213

193

X

9.3.4 9.3.5 9.3.6 9.3.7 9.3.8 9.4 9.4.1 9.4.2 9.5 9.5.1 9.5.2 9.5.3 9.5.4 9.5.5 9.6 9.6.1 9.6.2 9.6.3 9.7 9.7.1 9.7.2 9.7.3 9.8 9.8.1 9.8.2 9.9 9.10

Contents

Sizing 227 Desizing 228 Mercerization 228 Bleaching 229 The use of enzymes 229 Final treatment of fabrics 230 Dyeing 230 Biocidal treatment 232 Sonochemical production of antimicrobial fabrics 233 The SONO project for antimicrobial fabrics 234 Mechanism for the production of metal oxide nanoparticles in the SONO process 235 Impregnation of metal oxide nanoparticles into the fabric in the SONO process 236 The pilot plant installations 237 Biocidal efficiency of the treated fabrics 238 Developments in the impregnation of fabrics with biocidal nanoparticles after the SONO project 239 Modification of the Viatech system 239 Developments in Coventry 240 Developments in Bucharest 241 Production processes in the leather industry 242 Historical 243 Production processes in the leather industry 244 Leather processing in Coventry 244 Further developments in leather processing 246 Developments in tanning 247 Developments in dyeing 248 Leather processing in Bucharest 249 Concluding remarks 250 References 251

Chapter 10 Ultrasonically assisted biodiesel synthesis 257 10.1 An introduction to biofuels 257 10.1.1 First-generation biofuels 257 10.1.2 Second-generation biofuels 257 10.1.3 Third-generation biofuels 258 10.2 A general introduction to diesel fuel 258 10.3 The history of biodiesel 260 10.3.1 The first synthetic biodiesel fuel 261

Contents

10.3.2 10.4 10.4.1 10.4.2 10.5 10.5.1 10.5.2 10.5.3 10.5.4 10.5.5 10.6 10.7

Index

The first reference to the chemical transesterification of a glyceride 262 Ultrasonically assisted biodiesel synthesis (UABS) 263 The chemistry involved in UABS 264 Ultrasonically induced oil and methanol emulsification 267 The work of Mircea Vinatoru (MV) on Ultrasonically Assisted Biodiesel Synthesis (UABS) 268 MV and UABS – Japan 268 MV and UABS – Romania (Part 1) 278 MV and UABS – Canada 279 MV and UABS – Texas 280 MV and UABS – Romania (Part 2) 289 Some comments on the scale-up of UABS for use as an agricultural fuel 298 Some comments on UABS production 301 References 302 307

XI

Chapter 5 Sonochemical synthesis 5.1 Historical introduction There were two main interests in the use of ultrasound in chemistry from the beginning of research in this field: one involved the use of low-power ultrasound for analysis and the other with chemical changes that could be affected by high-power ultrasound. This was identified by Weissler in his seminal paper “Ultrasonics in chemistry” which was published in 1948 [1]. In the introduction, he stated that: There are two main fields in which ultrasonics contributes valuable information to chemistry. One of these is the investigation of molecular properties of fluids by measurement of the velocity of weak ultrasonic waves; the other is the study of chemical reactions which are caused or accelerated by intense ultrasonic irradiation.

Ultrasound used for chemical analysis is not one of the topics of this book but is a research field that has attracted a lot of interest. This was presented in the first sonochemistry symposium in 1986 [2] but since it involves low power, usually highfrequency measurement of velocity, attenuation and scattering of ultrasound it fits more squarely with non-destructive evaluation of materials and acoustics. Nevertheless, at much higher ultrasound powers, there must be a connection between the way in which sound waves interact with a medium and the creation of acoustic cavitation. This was what first brought the attention of chemists to a new branch of chemistry – sonochemistry – a term that was first used by Weyl [3] and Weissler [4] in the 1950s (see Volume 1, Chapter 1). In 1986, Tim Mason published a short review on the uses of ultrasound in chemical synthesis [5]. In this paper, he championed the use of the term “sonochemistry”: “A new word has recently appeared in the chemical literature to cover this rapidly expanding field, the use of ultrasound in chemistry which is now generally referred to as sonochemistry.” He also made the prediction that: Sonochemistry may be as important a topic within chemistry as photochemistry, thermochemistry or high-pressure chemistry. It might even be argued that it could become more important because of its greater general applicability.

Together with Jim Lindley, a colleague from Coventry University, over 100 references on the synthetic aspects of sonochemistry were gathered together and reviewed in the following year, 1987 [6]. It is our opinion that 1986 should be considered to be the year which saw the renaissance (rebirth) of sonochemistry. During that year, the first-ever international symposium on a subject identified as sonochemistry was organized at Warwick University, United Kingdom, as part of the Autumn Meeting of the Royal Society of https://doi.org/10.1515/9783110999938-001

2

Chapter 5 Sonochemical synthesis

Chemistry [7]. This meeting signified the beginning of serious interest in the uses of ultrasound in chemistry, which now spreads across almost all possible areas of chemical sciences and beyond.

5.1.1 Mechanistic aspects Many researchers who became involved in sonochemistry began asking questions about how sound energy could cause changes in chemical reactions. It had been recognized from the very beginning that there could not be a direct interaction between ultrasound and the bonds holding together atoms in molecules but, despite this, ultrasound could influence chemical reactions. In 1927, Richard and Loomis had considered the direct effect of acoustic vibrations observing that the frequencies of ultrasonic waves are much lower than the vibrations of molecular bonds [8]. The words that they used in their paper were: A third possible effect should be mentioned, although it cannot be treated in detail in this communication, namely, the effect of the vibration frequency of the sound wave itself on an unstable molecule, apart from its local kinetic effect upon molecules collectively. Although the frequencies used in the work described below (289,000 per second unless otherwise stated) were of a magnitude far below that of molecular vibration, certain effects, to be discussed later, seems to substantiate such an hypothesis.

Scientists began asking deeper questions about the reasons for the interaction between sound and chemistry. This included delving into the energies evolved during cavitation bubble collapse particularly in terms of sonoluminescence [9]. The most accepted explanation emerged from the idea that acoustic bubbles generated by the passage of ultrasound through a solution of chemicals would be subject to collapse through normal cavitation processes. Such cavitation bubble collapse can produce high local temperatures and pressures around each bubble, and this was identified by Fitzgerald et al., in their paper in which “hot spot” chemistry was introduced to scientists for the first time [10]. The authors raised the question about why do any chemical reactions occur when a system is irradiated with high-intensity ultrasound? They explored the influence of different gases upon the cavitation threshold of liquids and the outcomes below and above that threshold. The conclusion was that: Since the threshold of cavitation is strongly affected by so many factors, we would like to emphasize that studies of chemical effects of ultrasonics must always include a measurement of the threshold of cavitation for the particular experiments being undertaken.

It is our opinion that cavitation threshold is indeed an important factor in sonochemistry. There are, however, two problems associated with this measurement. Firstly, the values are normally obtained for very pure solvents (and chemistry seldom uses materials of such purity), and secondly, chemical reactions almost always

5.1 Historical introduction

3

involve mixtures and these also change the cavitation threshold of a liquid. It is an area of research which traditionally belongs to the physicist or physical chemist but maybe some new research should be opened to investigate “A list of liquids (common laboratory solvents) and their cavitation threshold as a function of ultrasonic frequency and power”. When sonochemistry became the subject for conferences, there were some questions about whether sonochemical effects were mainly mechanical rather than chemical. This was a reasonable point given that cavitation collapse could produce effects similar to high shear mixing: – extremely good mixing, – emulsification, – powder deaggregation and dispersal, – particle size reduction, – surface cleaning, – mass transfer to surfaces. Some scientists were not happy that sonochemistry might be considered simply to be the result of some form of super mixing. In the 1990s, there were attempts made to predict the effect of power ultrasound on reactions themselves and to try and formulate rules governing such predictions. It was Jean-Louis Luche who made the most concerted effort to introduce some order in this part of chemistry [11]. He suggested that sonication promotes reactions proceeding through radical pathways [12, 13] and began to examine the chemical effects of ultrasound and defined any accompanying mechanical effects as “False sonochemistry”. He went on to suggest that “True sonochemistry” could occur either in homogeneous or heterogeneous systems through processes in which the reactive intermediate was a radical or a radical ion since the production of such species could be stimulated by cavitation. He developed three rules covering sonochemical reactions which were written in the following terms in a book published in 1996 entitled Chemistry Under Extreme or Non-Classical Conditions [14]. – Rule 1 applies to homogeneous processes and states that those reactions which are sensitive to the sonochemical effect are those which proceed via radical or radical-ion intermediates. This statement means that sonication is able to affect reactions proceeding through radicals and that ionic reactions are not likely to be modified by such irradiation. – Rule 2 applies to heterogeneous systems where a more complex situation occurs, and here reactions proceeding via ionic intermediates can be stimulated by the mechanical effects of cavitational agitation. This has been termed “false sonochemistry” although many would argue that the term “false” may not be correct, because if the ultrasonic irradiation assists a reaction, it should still be considered to be aided by sonication and thus “sonochemical”. In fact, the right test for “false sonochemistry” is that similar results should, in principle, be obtained using an efficient mixing system in place of sonication. Such a comparison is not always possible.

4

–

Chapter 5 Sonochemical synthesis

Rule 3 applies to heterogeneous reactions with mixed mechanisms, that is, radical and ionic. These will have their radical components enhanced by sonication, although the general mechanical effect from Rule 2 may still apply. There are two situations that can occur in heterogeneous systems involving both of these mechanistic paths: (a) When the two mechanisms lead to the same product(s), which we will term a “convergent” process, in this case the result is an overall rate increase (b) if the radical and ionic mechanisms lead to different products, then sonochemical switching can take place by enhancing the radical pathway only. In such “divergent” processes, the nature of the reaction products is actually changed by sonication.

The study of kinetics in sonochemistry led to some insights into the possible mechanisms of such reactions. In 1967, Chen and Kalback reported that the hydrolysis rate of methyl acetate using hydrochloric acid increased with increasing sonic amplitude but varying the frequency had only a negligible effect [15]. In the following year, Fogler and Barnes attributed the increase in reaction rate caused by ultrasound in this reaction to the high temperatures reached within the cavitation bubbles [16]. They also noted that the yield did not increase indefinitely with increasing power applied to the transducer, but instead reached an optimum. The optimum power changed with temperature because the collapse time increases with increasing temperature. This was the direct result of the change in solvent vapour pressure with the temperature of the reaction. Solvolysis was the subject of the first research work on sonochemistry in Coventry (see Volume 1, Chapter 1). We chose the homogeneous hydrolysis of 2-chloro-2methylpropane (t-butyl chloride) in aqueous alcoholic media (Scheme 5.1) because it is one of the classic examples of a unimolecular nucleophilic displacement reaction (termed SN1). The reactions were monitored by conductance changes due to the liberated HCl. CH3 H3C

C Cl CH3

aqueous ethanol

CH3 H3C

C OH + HCl CH3

Scheme 5.1: The hydrolysis of 2-chloro-2-methylpropane in aqueous alcoholic media.

The reactions were performed at 25 °C and ultrasound was introduced by dipping the reaction vessel into an ultrasonic cleaning bath (45 kHz). An increase in the alcohol content of the solvent led to slower reactions but the rate ratio (kultrasonic/ksilent) increased up to a maximum of 2 fold [17]. Later results suggested that there was a region of maximum structure in the binary solvent mixture [18]. Similar results were found for the solvolysis in aqueous isopropanol and tert-butyl alcohol. Detailed studies of the aqueous ethanol system led to the following main conclusions:

5.1 Historical introduction

– –

–

5

The effect of ultrasound increased with increased ethanol content and decreased temperature giving rate enhancements up to 20-fold at 10 °C in 60% w/w. At ethanol concentrations of 50% and 60%, the actual rates of reaction under ultrasonic irradiation increased as the temperature was reduced from 20 to 10 °C (by factors of 1.4 and 2.1, respectively). A maximum effect of ultrasound appeared to occur at a solvent composition of around 50% w/w at 25 °C.

There are two factors which contribute to these conclusions. Firstly, there is the effect of increasing cavitational collapse energy via a lowering in vapour pressure as the temperature is reduced (see earlier). This does not adequately explain the effect of the change in solvent. The primary process is unlikely to occur inside the cavitation bubbles and a radical pathway should be discarded. The most likely explanation is that the disruption induced by cavitation bubble collapse in the aqueous ethanolic media is able to break the weak intermolecular forces in the solvents. This will alter the solvation of the reactive species present. Significantly, the maximum effect is found in 50% w/w ethanol/water composition – a composition very close to that which contains the maximum hydrogen bonded structure. Some years later, in 1997, this explanation was supported by Tuulmets [19]. After a thorough analysis of the experimental data he concluded that the idea that the application of ultrasound had led to a perturbation of the bonding within the reacting system was justified and that the effect on the kinetics was a direct result of this perturbation. The work of Tuulmets group was mainly based on the concept of the perturbation of the solvation of reacting particles by the application of ultrasound. This, in principle, was similar to the one that we had used. However, he added a note of caution that the detailed mechanism of the action of ultrasound remains to some extent uncertain. The development of rules for sonochemistry continues to this day and recently the authors of this book launched a discussion paper [20]: “Can sonochemistry take place in the absence of cavitation? – A complementary view of how ultrasound can interact with materials”. It was intended to invite researchers to consider (or reconsider) the way in which ultrasound could intervene in chemical reactions. Further discussion of sonochemical mechanisms can be found later in this chapter and elsewhere in this book.

5.1.2 Synthetic aspects In the early years of sonochemistry, there were many publications in the field of synthesis which were not labelled as sonochemistry since that terminology did not exist. In this section, we will try and draw together what might be considered significant publications during that period.

6

Chapter 5 Sonochemical synthesis

The pioneering work of Richard and Loomis published in 1927 seems to be the first recorded instance of the effect of ultrasound on chemical reactions [8]. The examples chosen were not strictly from synthesis but included the influence of ultrasound on the hydrolysis of dimethyl sulphate in the presence of sodium hydroxide and the iodine “clock”, a classical oscillating reaction first reported in 1886 by Landolt [21]. These are examples of ultrasound influencing the rate of chemical reactions, but it is difficult to find synthetic uses from this early period. The acceleration of solvolysis reactions remains an important and wide-ranging application of sonochemistry, oscillating reactions such as the iodine clock have not been examined in detail except by Margulis and Maximenko [22]. From the very beginning of sonochemistry, hydrogen peroxide production was observed as a product of the sonication of water. This was reported in 1929 by Schmitt et al. [23]. Weissler and Henglein separately observed the formation of hydrogen peroxide when water containing oxygen was irradiated with ultrasound [24, 25]. The formation of H2O2 is a consequence of the homolytic split of water molecules into radical species and subsequent reactions (Scheme 5.2).

H2 O

H . + O2

. 2HO2 . 2HO

))))

.

HO + H

.

HO2 . H2O2 H2O2 + O2

Scheme 5.2: Decomposition of water under sonication.

The oxygenated radicals HO• and HO2• are powerful oxidizing agents and provide the means by which organic pollutants in water can be destroyed by sonication, a topic which is explored in Volume 1, Chapter 4 of this book dealing with environmental protection. The formation of hydrogen peroxide in the presence of KI is the basis of a dosimeter now widely used in sonochemistry whose sensitivity can be enhanced when carbon tetrachloride (CCl4) is added to the solution. Sonication of water containing CCl4 produces molecular chlorine, which reacts quickly with iodide ions in solution to liberate molecular iodine. In 1950, Weissler investigated this reaction “Chemical Effect of Ultrasonic Waves: Oxidation of Potassium Iodide Solution by Carbon Tetrachloride” and it now carries his name [26]. Weissler was one of the pioneers of sonochemistry and produced a review “Sonochemistry: The Production of Chemical Changes with Sound Waves” in 1953 [4]. In this paper, he attempted to summarize the existing knowledge on the chemical, physical and biological effects of ultrasound. He also referred to some of the work of Moriguchi who is perhaps better known for his early contributions to electrochemistry in the 1930s. However, in 1933, Moriguchi had

5.1 Historical introduction

7

begun to publish a series of papers (in Japanese) on the effects of ultrasound on chemical phenomena. In the first of these dealing with heterogeneous reactions, he observed that the reaction of zinc with hydrochloric acid is accelerated as was the reaction of calcium carbonate with sulphuric acid [27]. The enhanced dissolution of metals and solids would later become an important consideration in the mechanical effects of ultrasound used in synthesis. Probably the first application of ultrasound in a catalytic reaction involving gases came in 1950 with the publication of a patent entitled “Ammonia synthesis” (Scheme 5.3) [28]. The overall method is similar to the well-known Haber process dating from the early twentieth century. The patent claims: “A process for the synthesis of ammonia from its constituent elements which comprises subjecting a gaseous mixture of nitrogen and hydrogen carrying a finely divided catalyst in suspension therein to ultrasonic vibrations of a frequency greater than twenty thousand cycles per second.” This conversion took place at lower pressures and temperatures than any established process at that time. H2 + N2 + Fe2 O3 + Al2 O3 + K2 O + ultrasound ! 2NH3 Scheme 5.3: Ammonia production under sonication.

What makes this application of ultrasound particularly interesting is the way in which it was applied to a gaseous mixture of nitrogen and hydrogen together with a finely divided catalyst because sonochemistry is almost exclusively employed in a liquid medium However, there is no evidence of this procedure has been used in industry. At that time, the effect of ultrasound on nitrogen fixation in aqueous conditions was an active area of research. One of the first to publish in this field was the Finnish scientist Artturi Ilmari Virtanen who was the 1945 Chemistry Nobel Laureate. He had received his award for his work on the biological fixation of nitrogen and the preservation of fodder in agriculture, and their importance to human nutrition. Together with Nils Ellfolk, he investigated the oxidative fixation of nitrogen in water exposed to the atmosphere at a frequency of 300 kc/s and a radiating intensity of 10 W/cm2 [29]. They attributed the cavitation energy to electrical discharges on bubble collapse. The products included NO2¯ and NO3¯ ions but when hydrogen and carbon monoxide were bubbled through the solution nitrogen fixation was inhibited. In a subsequent study, volatile organic substances belonging to homologous series of aliphatic fatty acids, aldehydes, alcohols, aromatic hydrocarbons, and amines were also found to inhibit fixation [30]. On the basis of the results, the most likely reason suggested for this is the influence of the volatile substances on surface activity and the resultant energetic changes in the cavitation. Diffusion of substances into the cavitation bubbles was not thought to be a sufficient explanation. Sonochemical nitrogen fixation was further explored in one of the earliest books involving sonochemistry written by Isaak El’piner entitled Ultrasound: Physical,

8

Chapter 5 Sonochemical synthesis

Chemical, and Biological Effects [31]. The original text was published in 1963 in the Russian language and a year after translated into English. He makes an interesting comment in the book concerning the fixation of nitrogen in an ultrasonic field and the formation of biologically important substances. When water containing nitrogen and hydrogen was irradiated with ultrasound (in a sealed glass tube), ammonia was formed up to 12.5 μg/mL in around 6 h. Introducing carbon monoxide in the gaseous mixture did not inhibit the ammonia formation in sonicated water. El’piner also describes in his book some of his research in which ultrasonic irradiation of water saturated with nitrogen and hydrogen containing organic fatty acids (in the absence of oxygen). The nitrogen is fixed by the organic aliphatic acids, resulting in the formation of several amino acids (citation 56 in chapter IV of his book). The significance of such results is that one can consider the conditions which existed in the very early stages of the birth of our planet Earth. Then the natural conditions that existed included vibrations, UV light, electrical discharges as well and radioactive decay of some elements. It seems likely that such a combination of conditions in the presence of very simple chemicals could provide enough energy to trigger the synthesis of amino acids. These are the building blocks for the construction of living organisms, thus perhaps primeval conditions, especially in water, might be similar to the extremes developed during acoustic cavitation and lead on to the development of early forms of life on our planet. Conditions might be particularly beneficial for such reactions in the “black smokers” or deep-sea hydrothermal vents found on the seabed at great depths where high pressures, heat and bubbles of gas mix. 5.1.2.1 Organic reactions with ultrasound It is not an easy task to find references to the very first organic reaction activated by ultrasound. However, there is a section in El’piner’s book, chapter V, pages 79–115 [31], in which he describes how the early stage of research was mostly related to irradiation of aqueous solutions of organic compounds with ultrasound at different frequencies. This type of research was aimed mostly at studies of the decomposition of organic compounds. It is clear that these transformations occur as a consequence of water dissociation (Scheme 5.2). An example published in 1955 is the case of benzene sonication in the presence of water and atmospheric air [32]. In this paper, Robert, Prudhomme and Grabar reported that they had detected in the products phenol, resorcinol, diazotized p-nitroaniline as well as compounds having aldehydes in the structure. This is a clear indication that hydroxyl radicals are generated by ultrasound which then react with benzene. The results showed the formation of similar products to those resulting from X-ray irradiation [33] despite the fact that the latter is an ionizing radiation, whereas ultrasound is not. The presence of nitrogen-containing compounds in the products resulting from the sonication of benzene in air provides further evidence of oxidative nitrogen fixation previously observed by Virtanen (see earlier) [29]. He also noticed that argon and

5.1 Historical introduction

9

oxygen gases enhanced nitrogen oxidation [34], while some volatile compounds inhibited the process [35]. In 1965, Prakash and Pandey investigated the behaviour of saturated aqueous solutions of iodoethane, iodobenzene and 1,2-dichlorobenzene under ultrasonic irradiation [36]. They used an ultrasonic bath (1 MHz) and found that aromatic compounds containing halogens generated the halogen in the form of acids, whereas aliphatic compounds liberated both acids and free halogens. This was an early paper in the field, and it suggested that generally only aqueous systems support sonochemical reactions, which do not take place in pure organic liquids. They attributed this to the unique properties of water which are responsible for the abnormal high release of energy from aqueous cavitation bubbles. 5.1.2.2 Organometallic reactions with ultrasound Some of the early uses of ultrasound in chemical synthesis have been somewhat overlooked since they did not explicitly mention ultrasound. Such was the case in one of a series of papers entitled “Electron donor and acceptor complexes with aromatic systems”. In 1957 Part 4 appeared entitled “An improved method of preparing metal addition complexes with aromatic systems” this included a diagram of an apparatus involving an ultrasound probe for sodium activation [37]. Three types of preparation were compared for the reaction of sodium with benzoquinoline: 1. Direct reaction of sodium wire with benzoquinoline dissolved in diethylether 2. Direct reaction of sodium with the benzoquinoline in boiling dimethoxyethane or dioxan 3. Ultrasonic activation of a sodium cube immersed in a solution of the benzoquinoline in diethylether or dimethoxyethane.

A

F G B

N2

E D

C

Figure 5.1: Schematic apparatus for the ultrasonically activated reaction of sodium with benzoquinoline, where A is the 25 kHz magnetostrictive transducer, B is a stainless steel probe, C is a stainless steel screw-on basket, D is the side arm for nitrogen as protective gas, E is the condenser, F is a rubber gasket and G is a polyethylene disc, protecting the rubber gasket.

10

Chapter 5 Sonochemical synthesis

The ultrasonic method proved to be the most effective and the apparatus looked remarkably similar to what might be used today (Figure 5.1). A nitrogen atmosphere was used, and a Mullard magnetostrictive 25 kHz transducer (A) was attached to a stainless steel probe (B) which was adjusted to give maximum output to a sodium metal cube contained in a stainless steel basket (C) attached to the base of the probe. In 1980, serious interest began in organometallic sonochemistry. In that year, a paper from Luche and Damiano described the effects of ultrasound on a modified Barbier reaction (Scheme 5.4). He reported the direct, in situ formation of alkyl and aryl lithium (3) by the reaction of an organic halide (2) with lithium wire (or lithium with 2% sodium sand) in ether immersed in an ultrasonic bath. The organolithium reacted with the carbonyl compound present (1) to lead, after work up to product (4). The technique avoided the use of activating reagents (e.g. I2) and afforded a significant amelioration of the reaction both by increasing reactivity and removing the induction period which is often involved in this type of reaction [38]. These syntheses are largely free from side reactions such as reduction and enolization which are common using conventional methodology. O

R3 + R3

R1

X + Metal

R2

R3

OH C

Metal R1

R2

Scheme 5.4: The Barbier reaction.

The work of this group on ultrasound in organometallic synthesis continued with a series of some 20 papers involving different metals such as lithium, potassium, copper, magnesium, zinc, nickel and mercury. A further advantage when using ultrasound is that such reactions can be performed in damp, technical-grade tetrahydrofuran (THF), a potential boon for large-scale industrial operations. Almost all of these papers were summarized along with attempts to rationalize their mechanisms in a book chapter from Luche and Cintas in 2007 [39]. Synthetic applications of the effects of ultrasound (using an ultrasonic cleaning bath) on the coupling reactions of organic halides using lithium metal in THF were published as a series from 1981 by Boudjouk and Han [40]. Several organic halides such as chlorobenzene, bromobenzene, iodobenzene, p-bromotoluene, p-iodotoluene, m-bromotoluene, benzyl chloride, benzoyl chloride and 1-chloropropane in THF solution were sonicated in the presence of lithium wire with results as shown in Table 5.1. The group also investigated the coupling of chlorosilanes under similar conditions [41]. In 1982, Repič described a modification of the Simmons–Smith cyclopropanation reaction using diiodomethane and sonochemically activated zinc which avoided the sudden exotherm normally associated with this type of reaction [42]. Up to this time, most methods for this reaction relied upon activation of zinc by using zinc-silver or zinc-copper couples and/or the use of iodine or lithium. In the sonochemical procedure

5.1 Historical introduction

11

no special activation of the zinc was required, indeed equally good – and reproducible – yields were obtained using zinc in the form of dust, foil, mossy or metallic rod. The ultrasonic source employed was a small laboratory cleaning bath. Table 5.1: Ultrasound-induced coupling of organic halides with lithium. RX

Product

Time (h)

CHCl CHBr CHI p-CHCHBr p-CHCHI m-CHCHBr CHCHCl CHCOCl CHCHCHCl

CH–CH CH–CH CH–CH (p-CHCH) (p-CHCH) (m-CHCH) CHCHCHCH CHCO–COCH CH(CH)CH

        

Yield (%)       a  

a

Yield by NMR. All others are isolated yields (>95% pure).

The method using solid zinc metal and ultrasound was successfully scaled up to achieve the cyclopropanation of methyl oleate in 0.5 kg quantities (Figure 5.2) [43]. The reactor consists of a 22-L four-necked flask immersed in a 50-gallon ultrasonic bath (3,000 W, 80 kHz). Two zinc cones were suspended in the reaction mixture and could be withdrawn if the reaction became too violent. The metal was not reactive stirrer suspension wires nitrogen inlet condenser

addition funnel

stirrer heating coil

thermocouple

Ultrasonic bath

zinc cones Figure 5.2: Large-scale cyclopropanation reactor.

12

Chapter 5 Sonochemical synthesis

until the ultrasound was turned on, and several advantages over more traditional procedures were claimed: – Foaming of the solution is reduced. – The exotherm of the reaction is more evenly distributed over the reaction period as only a small area of fresh zinc surface is continuously being exposed to the reaction. – The zinc can be raised out of the reaction mixture at any time that the exotherm and the reflux become too vigorous. – Any excess zinc can be easily recovered as the remaining part of the solid metal block. One of the most common laboratory applications of ultrasound is the initiation of a reluctant Grignard reaction (Scheme 5.5). The quantitative effects of ultrasound on the induction times for the formation of a Grignard reagent in various grades of ether are given in Table 5.2 [44]. CH3 CH2 CHBrCH3 + Mg ! CH3 CH2 CHðMgBrÞCH3 Scheme 5.5: Grignard reaction. Table 5.2: The preparation of butan-2-yl magnesium bromide in ether in an ultrasonic bath. Type of diethyl ether used

Method

Induction time

.% water .% ethanol .% water .% ethanol % saturated .% ethanol

Stirred Sonicated Stirred Sonicated Stirred Sonicated

– min Ph3 C − Br > Ph3 C − Cl  Ph3 C − OH > Ph3 C − H Sonochemical: Ph3 C − I > Ph3 C − Br > Ph3 C − Cl  Ph3 C − H > Ph3 C − OH Scheme 5.17: Order of reactivity of triphenylmethyl compounds.

This suggested that sonochemistry plays an important role in how such compounds react with nitrobenzene. The triphenylmethyl derivatives cannot enter cavitation bubbles (see earlier) and so cannot undergo the type of thermal reactions expected in these “hot spots” [10]. Nevertheless, some of products from sonication and thermal activation are common to both reactions (see Tables 5.18 and 5.19). In the traditional and hence well-known chemistry of nitrobenzene reduction, the final compound is aniline, but it is also possible to stop the reduction process at previous stages where azo-benzene or azoxy-benzene are formed as intermediates leading to the formation of aniline (Scheme 5.18):

Ph

NH2

Ph

N N

Ph

Ph

N N

Ph

O Scheme 5.18: Compounds generated during the reduction of nitrobenzene.

The presence of such compounds in the reaction products would provide some important support to the proposed redox reaction between triphenylmethyl derivatives

39

5.3 Sonochemical synthesis in Romania

and NB. Indeed, these compounds were detected in the products from thermal activation (Schemes 5.19 and 5.20) but only in trace amounts. The thermal and the ultrasonic reactions of TPCM with NB were conducted using the apparatus setup shown in Figure 5.6.

1 5 1

3

5 2

4

Argon

Argon Legend: 1. Condenser 2. Dean-Stark collector 3. Gas trap 4. Heating plate 5. Pressure valve

4

(a)

Legend: 1. Condenser 2. Ultrasonic bath 3. Ultrasonic transducer 4. Gas trap (with water) 5. Pressure valve

2 3

(b)

Figure 5.6: Equipment used for thermal (a) and ultrasonic (b) reactions.

The thermal reaction was conducted at the boiling point of NB (210 °C) for 8 h, under argon as protective gas, returning NB into the reaction flask. The ultrasonic reaction was conducted at 40 °C, for 30 h, using a Langford Sonomatic cleaning bath T175, working at 40 kHz and 180 W electrical power. 5.3.1.2.1 Products of reaction between triphenylchloromethane and nitrobenzene For TPCM, the possible reaction products from thermal and sonochemical activation are shown in Scheme 5.19 and their molar distribution in Table 5.18. There is a clear difference between the products from thermal and ultrasonic activation. While thermal activation yields detectable quantities of reduction compounds of NB, the sonochemical reaction produces only a trace of only one such compound (7). The main two differences are highlighted in bold in the table: 1. In the thermal process, hydrochloric acid is evolved, while in the ultrasonic process molecular chlorine is formed.

40

2.

Chapter 5 Sonochemical synthesis

A common product for both is triphenylcarbinol (8) but it is >37 times more abundant in the sonochemical reaction. O CPh3 Ph

HCl Ph3C

H

Ph

N N

Ph

Ph

N N

Ph

Ph2C O

O

Ph 1

2

3

4

4'

5

Cl Ph3C OH

Ph2C NPh Ph2C N

Ph3C

OH

Ph

NO 2

(o, m, p) 6

7

8

Cl2 11

9 OH

Cl 12

10

13

14

Scheme 5.19: Reaction products of triphenylchloromethane with nitrobenzene under thermal and sonochemical activation. Table 5.18: Molar distribution of the main products from the reaction of TPCM with NB. Compound number in Scheme .   (HCl)   ’        (Cl)   

Molar amount in the reaction mixture Thermal activation

Ultrasonic activation

. . . . . . . . . . Traces – Traces – –

– – . – – . – Traces . – Traces . Traces Traces .

An important conclusion from these results is that this reaction provides another example of sonochemical switching, that is a reaction whose pathway can be changed by applying sonication.

5.3 Sonochemical synthesis in Romania

41

5.3.1.2.2 Reaction products of triphenylbromomethane with nitrobenzene For TPBM, the possible reaction products from thermal and sonochemical activation are shown in Scheme 5.20 and their molar distribution in Table 5.19:

Ph

O

Ph3C H Ph2C O Ph2C N Ph Ph3C

Ph Ph

3

Ph

HBr

1"

5

OH

8

NO2 10

25

Br

Br

26 NO2

O2N

Br

Ph

Ph 16

9

Ph2C N

Ph2C N

24

Ph3C OH Ph

6 Br

OH

19

20

27

Scheme 5.20: Reaction products of triphenylbromomethane with nitrobenzene thermal and sonochemical activation.

Table 5.19: Molar distribution of the main compounds from the reaction of TPBM with NB. Compound number in Scheme . ”       HBr ()   

Molar amount in the reaction mixture Thermal activation

Ultrasonic activation

. . . . – . – . . . –

– . . – . – . – – – .

42

Chapter 5 Sonochemical synthesis

5.3.1.2.3 Comparison of results Comparing the reaction of the chloro and bromo compounds under thermal activation, the most noticeable result is that the xanthene-type compounds 1 and 1” have different structures (as confirmed by NMR), but their formation mechanism is similar [81]. In the sonochemical process, the amount of chlorine generated corresponds exactly to the quantity of triphenylcarbinol produced suggesting that both compounds result from a common reaction pathway (the sonochemical decomposition of a charge transfer complex). Therefore both reactions could be considered as examples of sonochemical switching. Unfortunately, in the case of TPBM it was not possible to detect the evolution of bromine, but it was found as bromine compounds in the solid residue of the sonochemical reaction. There are two possible explanations for this difference in behaviour between TPBM and TBCM. Firstly, the bromine atoms are likely to react faster with any possible substrate and so there is no time to dimerize to escape from the system. Secondly, the boiling point of chlorine is –34.04 °C while bromine is 58.8 °C, and this will make chlorine more likely to escape from the sonochemical system as gas. This also explains why the halogenated products are different from the two triphenylmethyl halogen derivatives. 5.3.1.3 The chemical reactions of triphenyliodomethane with nitrobenzene (NB) The reaction of triphenyliodomethane with NB was somewhat different from the reactions of TPCM and TPBM. As soon as the reagents were mixed, the reaction started, the solution became dark in colour which was a sign of the liberation of iodine. The thermal reaction was very energetic, iodine crystals became visible on the inner walls of the condenser as the iodine sublimed from the reaction mixture (this also occurred in the sonochemical reaction). This suggested common pathways for both reactions. Unfortunately, it was not possible to isolate and identify the organic products from these reactions and so mechanistic conclusions could not be made. 5.3.1.4 The reactions of triphenylmethane and triphenylmethyl carbinol with NB We embarked upon this stage of our investigations of the effect of ultrasound on charge transfer reactions together with Jean-Louis Luche who had taken an interest in our work. It led to a joint publication “Sonochemical and thermal redox reactions of triphenylmethane and triphenylmethyl carbinol in nitrobenzene” [82]. The reactions were performed in the apparatus shown in Figure 5.6, and the same conditions were employed as those for TPBM and TPCM. The reaction progress could not be monitored chemically, but at the end of the respective reaction times, the mixtures were cooled to crystallize the excess starting materials which were filtered off. The excess NB was reduced to half by steam distillation and a second crop of starting materials was crystallized and removed, followed by a second steam distillation to remove all unreacted NB.

5.3 Sonochemical synthesis in Romania

43

The products from the reaction of triphenylmethane (TMH) with NB are shown in Scheme 5.21 and Table 5.20, and those of triphenylmethyl carbinol (TMOH) with NB in Scheme 5.22 and Table 5.21 [82]. Here again a xanthene-type compound (1””) is produced but in this case only under sonochemical conditions. OH O Ph2C

O Ph2C

N

Ph Ph3C

OH Ph

CH3 Ph

Ph Ph

5

6

8

29

CPh3 9

30

Ph

CPh3

1""

Scheme 5.21: Thermal and sonochemical products of TMH with NB. Table 5.20: Product yields for thermal and sonochemical activation for TMH with NB. Compound number in Scheme .

Yields (%) in the reaction mixture Thermal activation

Ultrasonic activation

. . . Traces . . .

98%) when compared to a conventional transesterification method [78]. This laboratory exercise suggested considerable savings in time and energy when applied to existing methods. The conventional transesterification requires a large reactor (over 5,000 L volume), an initial heating of the oil to 70–80 °C, the addition of ethanol/catalyst solution and mechanical stirring. The reaction time for the transesterification reaction alone was 2 h to produce 98% conversion of fish oil into FAEE. The use of ultrasonic energy did not affect the quality of the final product, giving a slightly higher conversion of fish oil. The other parameters of FAEE were good: the polyunsaturated fatty acids (PUFA) content was high and contained the valuable target omega-3 fatty acids eicosapentaenoic (EPA) and docosahaenoic acid (DHA). This study showed that ultrasound had the potential to be used for the efficient sonochemical production of EPA and DHA. It seems that this paper [78] was and still is the only one in which the use of ultrasound is employed for fish oil transesterification with ethanol.

10.5.4 MV and UABS – Texas While I was in Canada, I was contacted via email by a lawyer (Ronald Holland Wills) from Texas asking me if it was possible to have a meeting to talk about biodiesel. He wrote in his email that the reason for contacting me was that he was very interested in the patent already published in the USA [76] and he wanted to create a new industrial facility for biodiesel production in Texas. Ron arrived in PEI Canada one afternoon in August 2005, and we met for the first time in the parking lot of FTC in his rented car until late in the night. We stopped when a security person come to see what we were doing there. We talked about biodiesel and Ron also asked me if I was willing to quit my FTC job to move to Texas. I asked for a few days to think it over and I also asked him to write to me with an official employment proposal when he returned to Texas. The next day, he and I went sightseeing around PEI and visiting friends. The scenery in this province and the friends whom I made there are perhaps the fondest memories of my time spent in Canada. During this meeting I said that I would like more details about the type of business he was proposing and asked him to start the US visa procedures for me. Somehow the prospect of a new opportunity in the USA was enough to persuade me that my time in Canada should come to an end and it contributed to my decision to resign from FTC which I did in October 2005.

10.5 Biodiesel research of Mircea Vinatoru

281

Just after I returned from Canada to Bucharest, my group proposed a project on biodiesel. In 2006, it was selected and funded by the Romanian Government under the Romanian title “Transesterificarea trigliceridelor în cataliză heterogenă asistată de energii neconveţionale: ultrasunete şi microunde –TRANSCATUM” (English translation: “Heterogenous transesterification of triglycerides assisted by nonconventional energies: ultrasound and microwaves” – TRANSCATUM), a 3-year project involving five Romanian partners. It was while working on this in 2007 that Ron Holland Wills and an investor from Louisiana come to see me in Romania where we discussed further aspects of the business proposal that we had first talked about in Canada. I organized for them a sightseeing trip around Romania and at the end of their visit I convinced both of them that in order to set up a biodiesel business at an industrial level, it was necessary first to have a laboratory able to acquire the necessary parameters for ultrasonic biodiesel synthesis. Based on the results of this we could then go on to design a factory able to produce fuel at pilot and/or industrial level. The existing patent listed five inventors: three were Japanese and the other two were myself and Carmen Stavarache [76]. It was obvious to Ron Wills and his investor that it would be a good idea to have the Romanian inventors as initial members of the new Texas business. So it was that Carmen and I entered in a long and complicated procedure to obtain a working visa for the USA. We pushed them to apply for the Outstanding Abilities O-1 working visa rather than a regular visa because we were both pioneers in the UABS technology. After that the visa procedure was started, and Carmen and I obtained O-1 visas to work in the United States. A new company “ReEnergy LLC” was established in McKinney, Texas. The business was set up as: “A project to have as primary objectives the development of a next generation commercial biodiesel reactor employing ultrasonics to improve operational performance, efficiency and scalability.” The first laboratory was located in Dallas, not far from Love Field airport. It was empty and it had some benches but nothing else (Figure 10.16a). It was a struggle to get official approval from the Food and Drug Administration to change it into a research laboratory and to purchase the necessary equipment and chemicals. Eventually, however, we equipped it with analytical instruments, the normal glassware and chemicals so that we could start the real research work (Figure 10.16b). One year after that first laboratory had been commissioned, we moved to a brandnew facility also in Texas, located in Frisco City, again in an empty room, this time without any working benches. The move to Frisco was a decision taken by the company since it had commercial advantages because we were to be located in a hub of businesses dedicated to research and development in that city. During this second stage in Texas, we developed at least five technologies for the production of biodiesel which included ultrasound. These involved the uses of: 1. calcium oxide (suspended in methanol) as catalyst 2. a dual-feed ultrasonic reactor

282

Chapter 10 Ultrasonically assisted biodiesel synthesis

(a)

(b)

Figure 10.16: Dallas first laboratory: (a) empty and (b) after starting to get equipment.

3.

a dual-frequency reactor

4. a refrigerant fluid as solvent 5. a reactor based on colliding ultrasonic sprays There was another technology which we wanted to pursue. It concerned the use of magnetic nanoparticles with superbase properties as catalysts in the process because these would be easy to remove from the products with a magnetic field. Unfortunately, it was not possible to start significant work in this field but in 2021 we renewed our interest in magnetic nanoparticles in a project related to drug delivery (see 7.4.5.2) [79]. 10.5.4.1 The use of calcium oxide (suspended in methanol) as catalyst The use of calcium oxide as base is very simple but it normally requires an extended time to complete the transesterification process. We were able to speed this up by activating the catalyst by pre-sonicating it in methanol before adding it as a reagent to the vegetable oil. This improved the subsequent non-ultrasonic transesterification to FAME (heating 3 h, at the boiling point of methanol); see Figure 10.17. Clearly ultrasonic activation (using an ultrasonic cleaning bath, 40 kHz, 250 W power) for 30 min of CaO (0.5%) produces a good activation of CaO to provide around 98% conversion into FAME. A minimum concentration of 96.5% FAME in the product at the end of the process is required to satisfy the EU standard for a transesterification process [69]. In the same research work, we were able to show that CaO activated via sonication in methanol retained its catalytic activity for as long as 1 month. However, in spite of using this inexpensive catalyst, in a fairly low concentration, we did not consider this to be a viable technology due to the residual calcium compounds present in the final product, FAME. After removing glycerol and methanol by washing the calcium content was found to be around 557 ppm. This might have been present as

10.5 Biodiesel research of Mircea Vinatoru

FAME %

100 90

283

97.29

80

91.69

91.44

90.19

Activation 60 min

Activation 30 min

Activation 60 min

70 60 50 40 30 20 10 0 Activation 30 min

CaO 0.5%

CaO 0.1%

Figure 10.17: FAME concentration at different catalyst concentrations/ultrasonic activation, after 3 h reflux.

the calcium soap of fatty acids (it was visible as a crust on the top of biodiesel – similar to thin ice on water). To overcome this, the final FAME product was washed with 5% sulphuric acid and filtering over a cotton filter which removed almost all residual calcium from biodiesel ( UC >MS” where:

302

Chapter 10 Ultrasonically assisted biodiesel synthesis

HC MW UC MS

means the hydrodynamic cavitation process, means the microwave process, means the ultrasonic cavitation process and means the mechanical stirring process.

When the method involves the use of ultrasound it is our experience, based on the many years that we have been involved in this field, that the five main criteria listed above can be met. We consider that the most convenient method of producing biodiesel is a dualfeed ultrasonic reactor followed by static mixing columns (Figure 10.18b). It has a small footprint, and once working parameters are established, it needs very few supervising personnel. It is also very easy to increase the production by multiplying up to the required number of similar ultrasonic units.

References [1] [2] [3] [4] [5] [6] [7] [8] [9]

[10] [11] [12] [13]

[14]

R. Diesel, Arbeitsverfahren und Ausführungsart für Verbrennungsmaschinen, https://www. dhm.de/lemo/bestand/objekt/patentschrift-von-rudolf-diesel-1893.html, Germany, 1892. R. Diesel, Method of Igniting and Regulating Combustion for Internal-Combustion Engines, US Patent App. 673,160, 1898. Diesel Oil, Encyclopædia Britannica, inc., Chicago, 2017. K.S. Varde, Bulk modulus of vegetable oil-diesel fuel blends, Fuel, 63 (1984) 713–715. ASTMD975, Standard Specification for Diesel Fuel Oils, Standards & Publications, West Conshohocken, PA 2010. ASTMD97, Standard Test Method for Pour Point of Petroleum Products, Standards & Publications, West Conshohocken, PA 2005. ASTMD2500, Standard Test Method for Cloud Point of Petroleum Products, Standards & Publications, West Conshohocken, PA 2005. ASTMD93, Standard Test Method for Flash Point By Pensky-Martens Closed Cup Tester, Standards & Publications, West Conshohocken, PA 2002. ASTMD7094, Modified Continuously Closed Cup Flash Point Standard Accepted as a Safe Alternative Method in Various Fuel Specs, Standards & Publications, West Conshohocken, PA 2004. ASTMD86, Standard Test Method for Distillation of Petroleum Products and Liquid Fuels at Atmospheric Pressure, Standards & Publications, West Conshohocken, PA 2015. ASTMD613, Standard Test Method for Cetane Number of Diesel Fuel Oil, Standards & Publications, West Conshohocken, PA 2015. ASTMD4737, Standard Test Method for Calculated Cetane Index by Four Variable Equation, Standards & Publications, West Conshohocken, PA 2010. ASTMD2622, Standard Test Method for Sulfur in Petroleum Products by Wavelength Dispersive X-ray Fluorescence Spectrometry, Standards & Publications, West Conshohocken, PA. ASTMD4294, Standard Test Method for Sulfur in Petroleum and Petroleum Products by Energy Dispersive X-ray Fluorescence Spectrometry, Standards & Publications, West Conshohocken, PA 1998.

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Index airborne ultrasound 196 Algae Biofuels Challenge.the Carbon Trust 2009 258 atomizers 107 – gas driven 107 – ultrasonic 108 biodiesel 262 – blended with fossil fuel 262 – Canada, Food Technology Centre (FTC), Prince Edward Island 2005/6 279 – ethyl esters of palm oil 1937 262 – exhaust gas pollution tests 275 – Ford Motor Company Conservation of Energy Awards 278 – history 260 – Japan, Osaka Prefecture University 2002/3 263 – pilot plant using sonochemistry 277 – USA, ReEnergy LLC, Texas 281 biodiesel and the concept of a self-sustaining farm 300 biodiesel synthesis – comparative results of reactors 293 – hybrid ultrasound and microwave reactor 295 – hydrodynamic cavitation reactor 292 – important parameters 301 – microwave reactor 293 – MMM clamp-on reactor 289 – push–pull reactor 274, 277 – stand-alone biodiesel facility 300 – synergetic effect for ultrasound combined with microwave 297 – ultrasonic probe flow reactor 291 biofuels 257 – first generation 257 – second generation 258 – third generation 258 Campden and Chorleywood Food Research Association (CCFRA) 178 cavitation threshold 2 Conferences – 1st International Summit of Non-Invasive Ultrasound Treatment, Chongqing, 2009 145

https://doi.org/10.1515/9783110999938-007

– 7th Annual Congress of the International College of Gynaecological Imaging, London, 2005 146 – Asia-Oceanic Society of Sonochemistry (AOSS4), Nanjing, 2019 153 – ESS2, Gargano 1991 91 – ESS3, Figuero da Foz, 1993 130 – ESS5, Cambridge, 1996 130 – first international workshop on the application of HIFU in medicine, Chongqing, 2001 144 – Free Radicals in Chemistry and Medicine, London, 1992 128 – ICA14, Beijing, 1992 140 – International R&D Institutions Mission to Chongqing, 2009 145 – International Workshop on Modern Acoustics, Nanjing, 1994 140 – Power ultrasound for process efficiency improvement” Sheffield 1994 95 – The 1st Yangtze International Summit of Minimally-invasive and Non-invasive Medicine, Chongqing, 2013 145 – UI87 London 1987 15 – Ultrasonics International (UI89) Madrid 105 – Ultrasound in food technology, Leeds, 2008 193 crystallization of zeolites 111 – increased nucleation and crystallization rates 111 – Laporte Inorganics 111 – void space 111 dentistry – advanced health care 132 – Cavitron descaler and radical formation 133 – ultrasonic setting of glass ionomer cements 133 – Ultrasonics International (UI89) 1989 Madrid 132 Diesel engine – first biofuel peanut oil 258 – fossil fuel specifications 259 – Rudolph Diesel 258 diffusion layer 64

308

Index

electrochemistry 63 – processes at electrode surface 64 electrochemistry with ultrasound – beneficial effects 65 – history – electrochemical applications of ultrasonic waves Yeager 1953 65 – electrodeposition Young 1936 65 – first use of term sonoelectrochemistry Mason Lorimer and Walton 1990 65 – metal passivity and the liberation of gases Schmid and Ehret 1937 65 – Moriguchi concentration changes near electrode 1934 65 electroless copper plating of PCBs – plating ‘vias’ the conducting link between PCB strips 83 electroless plating with ultrasound – Alcan Aluminium Ltd. 75 – copper coating of ceramics 77 – copper 76, 83 – crystallization processes 75 – Electronics Manufacturing Research Centre (IeMRC) 78–79 – nickel 74 – plating on plastic surfaces 76 – preliminary surface etching of plastic surface 76 – printed circuit board manufacture 78 electroplating 64 – surface preparation 66 electroplating with ultrasound chromium (VI) – air-borne emitter for mist supression 68 – chromic acid mist 67 – controlling emissions of chromic acid mist 67 – larger scale experiments 71 – lip extraction of mist 71 – mist suppressant (PFOS) 69 – reduction of emissions at laboratory scale 68 electroplating with ultrasound nickel-based composite coatings – containing particles of boron nitride or tungsten disulphide 73 – improvement in dispersion and deagglomeration of particles 73 – Knowledge Transfer Partnership (KTP) with Daido Industrial Bearings Europe 72

electroplating with ultrasound – improved microhardness, brightness and deposition rate 66 encapsulation of TiO2 – coverage by polymethylmethacralate 110 – tioxide, stockton-on-tees 110 – uniform coating of every particle 110 European research programmes – FP6-NMP – Nanotechnologies and Nanosciences, 88 European research projects – A pilot line of antibacterial and antifungal medical textiles based on a sonochemical process for NPs fabrication – SONO 234 – Biodegradable and antimicrobial re-tanning and finishing agents for the ecological and safe production of natural leather (BIOSAFE) 249 – multifunctional nanometallic particles using a new process – sonoelectrochemistry (SELECTNANO) 89 – SONO 249 – ULTRA-MINT 249 fabric and acoustic transmission – acoustic parameters involved 220 – problem with transducers facing opposite sides of a fabric 220 – problems of dampening of acoustic waves 219 FAEE – as extraction solvent 298 – fatty acid ethyl esters 279 FAME – comparison of conventional versus ultrasonic methods 268 – derived from different vegetable oils 270 – fatty acid methyl esters 266 – solvent properties 278 – ultrasonic emulsification 267 fibres and yarns 216 – impregnation with chemicals laboratory apparatus 218 – impregnation with chemicals 217 – wood fibres treated with ultrasound 216 – yarn treatment stagnant and convective shells 217

Index

food processing – changes to enzyme action 176, 181 – cleaning vegetable surfaces 185 – crystallization 162 – cutting 164 – defoaming 167 – degassing 166 – depolymerization of starch 178 – drying 167 – drying of vegetables 199 – emulsification 169 – enhanced freezing 181 – enhanced microbial activity 175 – enhanced seed germination 175 – extraction of stevia sweetener 203 – fermentation 198 – filtration 171 – heat transfer 163, 184 – hydrogenation 171 – Kraft Foods 190 – fermentation of yeast 192 – gel time of rice 191 – manothermosonication 174 – Mars Confectionery 186 – caramel production and the Maillard reaction 188 – extraction of cocoa butter 188 – mixing of powders with water 187 – meat 172 – brining 172 – marinating and brining 201 – tenderization 180 – thawing 172 – physicochemical and functional properties of whey and soy protein 199 – review articles involving Coventry sonochemistry group 195 – thermosonication 173, 183 – Ultrasonically Assisted Extraction (UAE) 170 – Unilever – Colworth House 189 – sonocrystallization of vegetable oils 189 – wine and champagne 202 HIFU – Chongqing HAIFU visit Oxford Churchill hospital 1999 142 – Chongqing Haifu Medical Technology Co. Ltd 138

309

– installation and set-up of HIFU at Oxford Churchill 2002 144 – linking Technoform Sonics with Chongqing HAIFU 1992 142 – Oxford Churchill HIFU Unit in 2017 151 – Technoform Sonics and focused ultrasound 139 – Technoform Sonics and the cold drawing of metal pipes 138 – Technoform Sonics and water treatment 139 – the control of bleeding haemostasis 127 – the Second Hospital of Chongqing Medical University 142 – treatment of uterine fibroids 146 – ultrasound therapeutics Ltd (UTL) 143 HIFU high intensity focused ultrasound 126, 138 hospital-acquired (nosocomial) infections 233 Journals – Circuit World 80 leather processing – British School of Leather Technology (BSLT) at Nene College, Northampton 244 – effects of ultrasound on dyeing 248 – effects of ultrasound 243 – PhD project The influence of power ultrasound on leather processing completed 1988 245 – steps involved 242 – tanning – removal of residual chromium 249 – ultrasound and tanning 244, 247 – using submersible transducer 245 Leatherhead Food Research Association (LFRA) 178 medical ultrasound – cell permeation sonoporation 125 – conference programme 1-day session therapeutic ultrasound ESS5 1996 130 – conference programme Free Radicals in Chemistry and Medicine 1992 128 – diagnostic 117, 121 – enhanced cell permeability to deliver plasmid DNA 135 – physiotherapy 123 – sonodynamic therapy (SDT) 123

310

Index

– sonoporation 5-fluorouracil (5ʹ-FU) into Hep-2 cells 137 – transdermal drug delivery 134 – transdermal drug delivery sonophoresis 125 – transrectal focused ultrasound 131 – triggered dopamine release to combat Parkinson’s disease 154 – ultrasonic standing wave (USW) separation 123 – ultrasound triggered release of ovarian cancer biomarkers 153 – wound and bone healing 123 megasonic surface cleaning 84 metallurgy – Alcan Aluminium in Banbury 91 – aluminium dendrites 94 – casting of light metals 92 – direct chill (DC) casting 92 – gravity casting 92 – Coventry group visit Moscow 96 – Energy Technology Support Unit (ETSU) – energy-efficient use of power ultrasound in industry) 95 – fragmentation of crystallites in melt 92 – grain refinement 93 – Industrial Applications for Ultrasonics (IUS) 91 – Institute of All Union Institute of Light Alloys (VILS) 91 – IUS Al-Pb antifriction composite 101 – IUS arc welding process 100 – IUS metal coating using solder pot method 101 – IUS schematic ultrasound during melt treatment 98 – IUS shot peening 100 – joint venture company “Industrial Applications for Ultrasonics (IUS)” 1993 97 – Kaye (Presteigne) metal foundry 93 – Kaye Presteigne metal foundry 91 – Light Metals Founders Association (LMFA) 93 – N. S. Kurnakov Institute of General and Inorganic Chemistry 96 – ultrasonic degassing 92 polymers – degradation 102 – Fisons Pharmaceuticals, Loughborough 103

– iron dextran complexes 103 – monodispersed system 102 – raw dextran acid hydrolysis 104 – shearing 102 – electroinitiated polymerization 106 – conducting film formed on the anode 107 – European Human Capital and Mobility Network ERB CHRX CT940475 106 – polypyrrole 106 – emulsion polymerization 105 – CASE award “The effect of ultrasound on the emulsion polymerization of styrene” 106 – latex and polymer coatings Doverstrand 105 – shortening of induction period 106 – radical polymerization 104 – N-vinyl carbazole 105 – photoconductive polymers 105 – reduction in viscosity 102 Printed Circuit Board (PCB) manufacturing 78 – desmear/surface modification process 79 – Traditional “wet” manufacturing techniques 78 pulsed sonoelectrochemistry – Barbier reaction 87 – laboratory apparatus 87 – parameters 87 – zinc nanoparticles 86 Research grants – Knowledge Transfer Enterprise Grant (KTEG), ultrasonic surface modification 78 – NATO Linkage Grant (HTECH. LG 941291) “Development of ultrasonic treatment of aluminium alloys during solidification” 96 scaling up sonochemistry – numbering up 298 SELECTNANO – copper nanoparticles using titanium electrodes 89 – Pometon 89 solders improved with nanoparticles 84 – gold coated silica nanoparticles 84 – metallization of polymer microspheres with copper 85

Index

SONO project – antibacterial activity values for CuO and ZnO 238 – impregnating antibacterial nanoparticles 234 – impregnation process 236 – pilot installation at DAVO Viatech transducers 237 – pilot installation at DAVO, Bucharest, Romania 237 – pilot installation at Klopman, Frosinone, Italy 237 – pilot installation at Klopman, Telsonic transducers 237 – start 2009 234 – underlying chemistry 235 sonochemical reactions – automerization of C13-labelled naphthalene 51 – hydrolysis of 2-chloro-2-methylpropane 4 – oscillating reactions 6 – sonication of pure nitrobenzene 47 – sonochemical switching 34 sonochemistry and surface treatment 63, 80 – effect of changes in ultrasonic frequency 81 synthesis – Diels–Alder 29 – Friedel–Crafts reaction 31 – O-alkylation of 5-hydroxychromones 18 synthesis catalysis – aromatic halogenation using copper halide on alumina 14 – copper nanoparticles on silica supports 54 – enzyme reactions 51 – hydrogenation 27 – particle size reduction 22 – effect of bubbled gas 24 – effect of frequency 22 – effect of solvent temperature 25 synthesis charge transfer complexes 36 – triphenylchloromethane with nitrobenzene 39 – triphenyliodomethane with nitrobenzene 42 – triphenylmethane and triphenylmethyl carbinol with nitrobenzene 42–43 – triphenylmethyl halogen derivatives with nitrobenzene 37 synthesis historical 1 – acceleration of dissolution reactions 1933 7

311

– activation of an immersed sodium cube 1957 9 – ammonia synthesis 1950 7 – book by Isaak El’piner “Ultrasound: Physical, Chemical, and Biological Effects” 1964 8 – first use of the term sonochemistry 1951 1 – hydrogen peroxide formation 1929 6 – the renaissance of sonochemistry 1987 1 – Weissler “ultrasonics in chemistry” 1948 1 – Weissler reaction 1950 6 synthesis mechanisms 2 – acceleration due to high temperatures in cavitation bubbles 1968 4 – can sonochemistry take place in the absence of cavitation 5 – change in the solvation of species 5 – effect of different frequencies 8 – hot spot chemistry 1956 2 – Luche rules 3 – no direct interaction between ultrasound and chemical bonds 1927 2 – physical effects of cavitation 3 synthesis organometallic – Barbier reaction 10 – coupling of organic halides using lithium 11 – cyclopropanation large-scale reactor 11 – Grignard reaction 12 – Simmons–Smith cyclopropanation 10, 25 – Ullmann condensation 13 – Ullmann coupling of aryl halides 13 Textbooks – Utrasound in food processing, 1998 193 textile fabrics – woven and compacted 221 textile fibres 214 textile impregnation with nanoparticles – alternative throwing the stones method 240 – Coventry method 241 textile treatment – carbonizing for wool 227 – chemical bleaching 229 – desizing to prepare surface for special coatings 228 – dyeing 230 – improvement in enzyme performance 229 – mercerization 216, 228 – processes involved 222 – processing chain 213

312

Index

– scouring to remove oil and waxes 226 – sizing for protective coating 227 therapeutic ultrasound – controlled release drug delivery 120 – magnetic capsules 149 – polyelectrolyte capsules 147 – cutting and drilling 118 – definition 117 – International Society for Therapeutic Ultrasound (ISTU) 145 – removal of blood clots 120 – tissue removal via aspiration 119 total energy input 26 transesterification 262 – continuous ultrasound process 271 – dual-feed reactors 283 – dual-frequency reactor 285 – fish oil 280 – scale up to continuous ultrasound process 273 – the chemistry involved 265 – to determine the chemical structure of stearine 1862 263

– use of calcium oxide as base 282 – use of colliding sprays 287 – use of refrigerating liquid (1,1,1,2tetrafluoroethane) 286 UK research programmes – Advanced and Hygienic Food Manufacture, 1994 183 Ultrasonic companies – Advanced Sonic Processing Systems 285 – FFR Ultrasonics 164 – Langford Ultrasonics 91 – MPI Ultrasonics 289 – Sonic Process Technologies 184 – Sonics and Materials 291 – Undatim Ultrasonics 22 ultrasonic degassing of glass 95 ultrasonic fabric cleaning – combined ultrasound and conventional 226 – mass transfer effects 221 – vibrating plate 223 ultrasound in medicine general overview 118