Bio-Based Solvents

List of Contributors

Paula Bracco Biocatalysis, Department of Biotechnology, TU Delft, The Netherlands

Fergal Byrne Green Chemistry Centre of Excellence, Department of Chemistry, University of York, UK

James H. Clark Green Chemistry Centre of Excellence, Department of Chemistry, University of York, UK

Annelies Dewaele Centre for Surface Chemistry and Catalysis, KU Leuven, Belgium

Pablo Domínguez de María Sustainable Momentum SL, Las Palmas de Gran Canaria, Spain

Thomas J. Farmer Green Chemistry Centre of Excellence, Department of Chemistry, University of York, UK

Amandine Foulet Institut des Sciences Moléculaires, Université de Bordeaux, France

Joaquín García-Álvarez CSIC, Laboratorio de Compuestos Organometálicos y Catálisis, Centro de Innovación en Química Avanzada, Universidad de Oviedo, Spain

Eskinder Gemechu Institut des Sciences Moléculaires, Université de Bordeaux, France

Yanlong Gu School of Chemistry and Chemical Engineering, Huazhong University of Science and Technology, China

Andrew J. Hunt Green Chemistry Centre of Excellence, Department of Chemistry, University of York, UK

François Jérôme CNRS, Institut de Chimie des Milieux et Matériaux de Poitiers, Université de Poitiers, ENSIP, France

Saimeng Jin Green Chemistry Centre of Excellence, Department of Chemistry, University of York, UK

Yuhe Liao Centre for Surface Chemistry and Catalysis, KU Leuven, Belgium

Philippe Loubet Institut des Sciences Moléculaires, Université de Bordeaux, France

Rafael Luque Departamento de Química Orgánica, Universidad de Córdoba, Campus de Rabanales, Spain

C. Rob McElroy Green Chemistry Centre of Excellence, Department of Chemistry, University of York, UK

James Mgaya Chemistry Department, University of Dar es Salaam, Tanzania

Egid B. Mubofu Chemistry Department, University of Dar es Salaam, Tanzania

Joan J. E. Munissi Chemistry Department, University of Dar es Salaam, Tanzania

Karine de Oliveira Vigier CNRS, Institut de Chimie des Milieux et Matériaux de Poitiers, Université de Poitiers, France

Palanisamy Ravichandiran School of Chemistry and Chemical Engineering, Huazhong University of Science and Technology, China

Bert F. Sels Centre for Surface Chemistry and Catalysis, KU Leuven, Belgium

James Sherwood Green Chemistry Centre of Excellence, Department of Chemistry, University of York, UK

Guido Sonnemann Institut des Sciences Moléculaires, Université de Bordeaux, France

Michael Tsang Institut des Sciences Moléculaires, Université de Bordeaux, France

Danny Verboekend Centre for Surface Chemistry and Catalysis, KU Leuven, Belgium

Series Preface

Renewable resources, their use and modification are involved in a multitude of important processes with a major influence on our everyday lives. Applications can be found in the energy sector, chemistry, pharmacy, the textile industry, paints and coatings, to name but a few.

The area interconnects several scientific disciplines (agriculture, biochemistry, chemistry, technology, environmental sciences, forestry …), which makes it very difficult to have an expert view on the complicated interaction. Therefore, the idea to create a series of scientific books, focusing on specific topics concerning renewable resources, has been very opportune and can help to clarify some of the underlying connections in this area.

In a very fast changing world, trends are not only characteristic for fashion and political standpoints; also, science is not free from hypes and buzzwords. The use of renewable resources is again more important nowadays; however, it is not part of a hype or a fashion. As the lively discussions among scientists continue about how many years we will still be able to use fossil fuels – opinions ranging from 50 to 500 years – they do agree that the reserve is limited and that it is essential not only to search for new energy carriers but also for new material sources.

In this respect, renewable resources are a crucial area in the search for alternatives for fossil-based raw materials and energy. In the field of energy supply, biomass and renewable-based resources will be part of the solution alongside other alternatives such as solar energy, wind energy, hydraulic power, hydrogen technology and nuclear energy.

In the field of material sciences, the impact of renewable resources will probably be even bigger. Integral utilization of crops and the use of waste streams in certain industries will grow in importance, leading to a more sustainable way of producing materials.

Although our society was much more (almost exclusively) based on renewable resources centuries ago, this disappeared in the Western world in the nineteenth century. Now it is time to focus again on this field of research. However, it should not mean a ‘retour à la nature’, but it should be a multidisciplinary effort on a highly technological level to perform research towards new opportunities, to develop new crops and products from renewable resources. This will be essential to guarantee a level of comfort for a growing number of people living on our planet. It is ‘the’ challenge for the coming generations of scientists to develop more sustainable ways to create prosperity and to fight poverty and hunger in the world. A global approach is certainly favoured.

This challenge can only be dealt with if scientists are attracted to this area and are recognized for their efforts in this interdisciplinary field. It is, therefore, also essential that consumers recognize the fate of renewable resources in a number of products.

Furthermore, scientists do need to communicate and discuss the relevance of their work. The use and modification of renewable resources may not follow the path of the genetic engineering concept in view of consumer acceptance in Europe. Related to this aspect, the series will certainly help to increase the visibility of the importance of renewable resources.

Being convinced of the value of the renewables approach for the industrial world, as well as for developing countries, I was myself delighted to collaborate on this series of books focusing on different aspects of renewable resources. I hope that readers become aware of the complexity, the interaction and interconnections, and the challenges of this field and that they will help to communicate on the importance of renewable resources.

I certainly want to thank the people of Wiley's Chichester office, especially David Hughes, Jenny Cossham and Lyn Roberts, in seeing the need for such a series of books on renewable resources, for initiating and supporting it and for helping to carry the project to the end.

Last, but not least, I want to thank my family, especially my wife Hilde and children Paulien and Pieter-Jan, for their patience and for giving me the time to work on the series when other activities seemed to be more inviting.

Christian V. Stevens, Faculty of Bioscience Engineering

Ghent University, Belgium

Series Editor ‘Renewable Resources’

June 2005

Foreword

The present-day solvent market is of the order of 20 million tonnes and worth tens of billions of US dollars annually to the global economy. European solvent production provides about one-quarter of the worldwide market. The sheer volumes involved, the diversity of applications and the prevalence of small, functional compounds that often contain heteroatoms helps make the solvent sector a top candidate for switching to safer and more sustainable alternatives under the pressure of regional and global chemical regulation, notably REACh (Registration, Evaluation, Authorisation & restriction of Chemicals). A critical stage in the REACh process is imminent as the small- to medium-volume chemicals are registered in time for the 2018 deadline. As several commonly used solvents like NMP (N-methyl-2-pyrrolidone) are under close scrutiny at the time of writing, we can assume that the number of problematic solvents identified under REACh (and possibly other legislation) will be far greater at the time of reading.

The search for greener solvents is not new. If we go back to the early days of green chemistry in the 1990s, alternative solvents was one of the most popular research areas, with more and more articles reporting uses for known alternatives, including liquid and supercritical carbon dioxide, and an ever-increasing number of newly reported ionic liquids. These represented potentially positive step changes to chemical manufacturing technologies. Supercritical CO2 enables rapid and easy separation after reaction (since separations are commonly a major contributor to the low environmental impact of many chemical processes) and ionic liquids can avoid the critical environmental concerns around using volatile organic compounds (these being threats to human health and causes of atmospheric damage). Research in these areas has continued, though few industrial processes have changed to incorporate these step-change technologies. The costs of such major changes to the processes, the added energy and capital expenditure costs of working with supercritical fluids, and the toxicity, separation and purification challenges associated with some ionic liquids have inhibited progress. Among the most likely ionic liquids to have a future in industrial chemistry are deep eutectic mixtures as well as other low-melting mixtures that are constructed from bio-based compounds. These are the subject of a book chapter here. Other green solvent approaches including greater use of water as a reaction solvent; and no-solvent processes have had some impact, but the vast majority of solvent applications have remained essentially unchanged. In the meantime, the rapidly growing number of synthetic transformations used by the pharmaceutical industry have effectively increased the breadth and complexity of the problems (e.g. more metal-catalysed processes and more processes that need polar aprotic solvents). Other, newer industries, such as advanced materials, are creating additional problems (e.g. the current use of solvents like NMP to process graphene). The need for safer, cost-effective solvents has never been greater.

Bio-based organic solvents are another way to make chemical processes more sustainable, and despite the infancy of the area of bio-based chemicals, the annual bio-based solvent use in the European Union is projected to grow to over one million tonnes by 2020.

In the European Union, for example, a strategy for implementing and encouraging a bio-based economy has been launched and a mandate issued specifically addressing the development of standards relating to bio-based solvents. As a tool to support and enhance the bio-based economy, the purpose of standards is to increase market transparency and establish common requirements for products in order to guarantee certain characteristics, such as a minimum value of bio-based content. Bio-based solvents must also compete economically with established petrochemical solvents in order to gain a significant market share. It is also important to note that standards for bio-based products will increasingly include considerations of feedstocks – their renewability and sustainability, as well as end-of-life issues, potentially extending to the recovery of resources consistent with the circular economy. Life cycle assessments for greener solvents are described in a chapter in this book.

But what should future bio-based solvents look like? Is it sufficient for them to provide the advantages of sustainability and biodegradability? The problem with replacing petroleum-derived solvents with the same bio-based solvent is that any safety or toxicity issues are not resolved. Environmental issues occurring at the end of use will also persist. With the REACh European regulation starting to influence solvent selection, manufacturers will be forced to investigate alternative solvents. At least bio-based solvents are compatible with the development of environmentally sustainable processes. We must assume that new solvents will be needed to meet the highly demanding requirements of the current breadth of solvent properties. Nature provides few naturally occurring compounds that can act as solvents, though modern biotechnology enables access to large volumes of a number of useful small molecules, some of which can be directly used as solvents (e.g. ethanol) and others that can be easily converted into solvents (e.g. lactates from lactic acid). But the creation of new bio-based solvents with properties similar to many existing solvent types, including aromatics, halogenated solvents and amides, will be challenging. In this book we look at bio-based aromatic solvents in some detail.

Regarding the origin of bio-based solvents, it is important that bio-waste streams, including forestry wastes and food supply chain wastes (from farm to fork), should be the source of chemical products where at all possible. This is because two substantial issues detract from the advantages of solvent substitution in favour of first-generation sugar-derived bio-based solvents, especially those made by fermentation. This feedstock competes with our food supply, therefore creating a strongly objectionable conflict. Extending this argument, non-food crops for use in the chemical feedstock or biofuel sectors also require arable land, thus still creating pressure on food production (as well as biodiversity and other sustainability issues). Nonetheless, biofuels have quickly become a major part of the bio-economy, in regions from the Americas to Europe as well as in Asia and beyond. The success of the petrochemical industry is largely based on the availability of large quantities of inexpensive feedstock, and this has been enabled by the emergence and continued strength of the (petroleum) oil industry. We must learn to do the same in the bio-economy. The chapter on glycerol illustrates this by considering this major by-product from bio-diesel manufacturing as a solvent, while the broader coverage in Solvents from waste addresses the wider issue of waste valorization to make sustainable solvents.

When we consider wastes as feedstocks, it is important that we do not forget carbon dioxide. This major natural chemical that is a vital part of our life cycles and of the critical interaction between animal and plant life, has become regarded as a threat to civilization through its overproduction resulting from our uncontrolled burning of fossil fuels. From a biorefinery perspective, CO2 is a potential C1 feedstock, and a number of synthesis pathways have been developed to make compounds from it. In particular, organic carbonates can be synthesized using CO2 and alcohols, making them potentially 100% bio-based, at least for those small alcohols that are currently made from biomass. The resulting carbonates are considerably more attractive, at least from an environmental perspective, than those made using phosgene. The use of organic carbonates as solvent is the subject of a chapter in this book.

Solvents continue to play a key role in almost every industry sector. In the last 50 or so years we have built up an impressive array of solvents that offer a remarkable diversity of properties to suit an equally diverse range of applications. The challenge for green chemistry is to find safe, sustainable and effective replacements so that we can continue to enjoy the benefits of solvents without the environmental harm. Bio-based solvents will play an essential role in this quest, and this book helps to show us how.

James Clark

University of York Green Chemistry Centre of Excellence

April 2017

Chapter 1

Glycerol as Eco-Efficient Solvent for Organic Transformations

Palanisamy Ravichandiran and Yanlong Gu

School of Chemistry and Chemical Engineering, Huazhong University of Science and Technology, Wuhan, China

1.1 Introduction

Organic solvents are used in the chemical and pharmaceutical industries [1]. The global demand for these solvents has reached 20 million metric tons annually [2]. Solvents are unreactive supplementary fluids that can dissolve starting materials and facilitate product separation through recrystallization or chromatographic techniques. In a reaction mixture, the solvent is involved in intermolecular interactions and performs the following: (i) stabilization of solutes, (ii) promoting the preferred equilibrium position, (iii) changing the kinetic profile of the reaction, and (iv) influencing the product selectivity [3]. Selection of appropriate solvents for organic transformations is important to develop green synthesis pathways using renewable feedstock. In the past two decades, green methodologies and solvents have gained increasing attention because of their excellent physical and chemical properties [4–6]. Green solvents should be non-flammable, biodegradable and widely available from renewable sources [7].

Biodiesel production involves simple catalytic transesterification of triglycerides under basic conditions (Figure 1.1) [8]. This process generates glycerol as a by-product (approximately 10% by weight). The amount of glycerol produced globally has reached 1.2 million tons and will continue to increase in the future because of increasing demand for biodiesel [9]. Glycerol has more than 2000 applications, and its derivatives are highly valued starting materials for the preparation of drugs, food, beverages, chemicals and synthetic materials (Figure 1.2) [10].

Figure 1.1 Reaction for biodiesel production.

Figure 1.2 Commercial consumption of glycerol (industrial sectors and volumes).

The biodiesel industries generate large amounts of glycerol as a by-product. As such, the price of glycerol is low, leading to its imbalanced supply. Currently, a significant proportion of this renewable chemical is wasted. This phenomenon has resulted in a negative feedback on the future economic viability of the biodiesel industry and adversely affects the environment because of improper disposal [11]. In this regard, the application of glycerol as a sustainable and green solvent has been investigated in a number of organic transformations (Table 1.1). Glycerol is a colourless, odourless, relatively safe, inexpensive, viscous, hydroscopic polyol, and a widely available green solvent. Glycerol acts as an active hydrogen donor in several organic reactions. Glycerol exhibits a high boiling point, polarity and non-flammability and is a suitable substitute for organic solvents, such as water, dimethylformamide (DMF) and dimethylsulfoxide (DMSO). Thus, glycerol is considered a green solvent and an important subject of research on green chemistry. This review provides new perspectives for minimizing glycerol wastes produced by biomass industries.

Table 1.1 Physical, chemical and toxicity properties of glycerol

Our research group has contributed a comprehensive review on green and unconventional bio-based solvents for organic reactions [12]. However, enthusiasm for using glycerol as a green solvent for organic transformations in particular continues to increase. The present paper thus summarizes recent developments on metal-free and metal-promoted organic reactions in glycerol between 2002 and 2016.

1.2 Metal-Free Organic Transformations in Glycerol

The synthesis of complex organic molecules utilizes harsh reaction conditions, expensive reagents and toxic organic solvents. Most organic transformations use expensive metal catalysts, such as Pd(OAc)2, PdCl2, PtCl2 and AuCl2. The drawbacks of metal-promoted organic reactions are categorized into the following: (i) isolation and reuse of catalysts, (ii) lack of catalytic efficiency in the second usage, and (iii) disposal of metal catalysts. Over the past three decades, both industrial and academic chemists have continuously explored suitable methodologies, such as the use of green solvents. The chemical synthesis of glycerol as a sustainable solvent has gained wide attention because it provides valuable chemical scaffolds. Sugar fermentation produces glycerol either directly or as a by-product of the conversion of lignocelluloses into ethanol. Glycerol promotes this reaction without requiring any metal catalysts because of its excellent physical properties. Moreover, glycerol is widely available from renewable feedstock and is thus an appropriate green solvent for various reactions [13].

Scheme 1.1 Catalyst-free selective synthesis of 2-phenylbenzoxazole.

Scheme 1.2 Green synthesis of benzimidazoles and benzodiazepines in glycerol.

Quinoxaline, benzoxazole and benzimidazole derivatives can be synthesized using different methods; these molecules are commonly prepared through the condensation reaction of aryl 1,2-diamine with 1,2-dicarbonyl compounds [14, 15]. Bachhav et al. [16] developed an efficient, catalyst-free and straightforward method for synthesis of quinoxaline, benzoxazole and benzimidazole ring systems in glycerol; the yield is higher than those of conventional methods. The substrates 2-aminophenol and benzaldehyde are used as counter-reagents for the preparation of 2-arylbenzoxazoles (1).