Sustainable Solvents

Perspectives from Research, Business and International Policy

James H Clark, Andrew Hunt, Corrado Topi, Giulia Paggiola, James Sherwood

• Publisher: Royal Society of Chemistry
• Year: 2017
• Edition: 1
• eBook ISBN:
  9781788011556
• Topic: Sciences physiques
• Subtopic: Chimie industrielle et technique

Solvents are ubiquitous throughout the chemical industry and are found in many consumer products. As a result, interest in solvents and their environmental impact has been steadily increasing. However, in order to achieve maximum integration of new green solvents into the relevant chemical sectors, clarification of the social, economic, and environmental implications of solvent substitution are needed. This book explores the solvent life cycle, highlighting the challenges faced at various points, from production, through the supply-chain and downstream use to end-of-life treatment. It also discusses the potential benefits that a green chemistry and bio-based economy approach could bring. The current state-of-the-art of green solvents is evaluated along these lines, in addition to reviewing their applications with an appreciation of sustainability criteria. Providing a critical assessment on emerging solvents and featuring case studies and perspectives from different sectors, this is an important reference for academics and industrialists working with solvents, as well as policy-makers involved in bio-based initiatives.

CHAPTER 1

Introduction to Solvents and Sustainable Chemistry

1.1 Sustainable Solutions

As with all products, it is a matter of urgency that the necessary feedstocks, manufacturing processes and habits of end-users become sustainable. Solvents are an important type of chemical product, with a multi-million tonne annual market. The reputation of solvents is strongly linked to their association with volatile organic compound (VOC) emissions. This book offers an insight into the sustainable use of solvents, through discussion of relevant sustainability issues, and by providing data for many different solvents that the reader can take forward into their own sustainability assessments. Case studies illustrate sustainable solvent developments and applications, and methods of solvent selection are also described to help explain a way to introduce sustainable solvents and motivate users to embrace these products.

This book explains how sustainability is applied to solvents (Chapter 3), and how the philosophy of green chemistry can help manage solvent use in a sustainable manner (Chapter 5). Chapter 6 provides extensive data to satisfy sustainability criteria for bio-based solvents and neoteric solvents, which are described in Chapter 4. Trends in solvent use are explained in Chapter 2. A general introduction to solvents and sustainability is provided in this chapter for those readers less familiar with these topics.

1.2 Solvents

1.2.1 Definition

The term solvent is applied to a vast number of different substances. They are unified by their role as inert fluids with the purpose of dissolving another substance (the solute). Solvents may be reactive under certain conditions, which must be avoided when applying the substance as a solvent. There are several alternative descriptions available, some of which are summarised below (Table 1.1). In this discussion it is also helpful to pinpoint the conditions that define a liquid as separate from other fluids (gases and supercritical fluids) and different from solids. Definitions of solvents usually specify that they are a liquid. Gases are not solvents because they do not have intermolecular bonds, but supercritical fluids are considered to be solvents. A supercritical fluid is a state of matter achieved when the temperature and pressure both equal or exceed a critical point, where the liquid and vapour phases reach the same density and become a single (supercritical) phase. The substance then has properties intermediate of a liquid and a gas, with intermolecular forces, which is why it is capable of acting as a weak solvent.

Table 1.1 Definitions of solutions and solvents.

Definition	Source
Solvent: “Substances that are liquid under the conditions of application and in which other substances can dissolve, and from which they can be recovered unchanged on removal of the solvent”	The Properties of Solvents, by Y. Marcus^103
Organic solvent: “Any volatile organic compound (VOC) which is used for any of the following: alone or in combination with other agents, and without undergoing a chemical change, to dissolve raw materials, products or waste materials; as a cleaning agent to dissolve contaminants; as a dissolver; as a dispersion medium; as a viscosity adjuster; as a surface tension adjuster; as a plasticiser; as a preservative”	EU Industrial Emissions Directive (2010/75/EU)^104
Solvent: “A substance that dissolves other material(s) to form [a] solution. Common solvents are liquid at room temperature but can be solid (ionic solvents) or gas (carbon dioxide). Solvents are differentiated from plasticizers by limiting their boiling point to a maximum of 250 °C. To differentiate solvents from monomers and other reactive materials, a solvent is considered to be non-reactive”	Handbook of Solvents, edited by G. Wypych^105
Solution: “A liquid or solid phase containing more than one substance, when for convenience one (or more) substance, which is called the solvent, is treated differently from the other substances, which are called solutes”	IUPAC definition^106

The United Nations (UN) Globally Harmonized System of Classification and Labelling of Chemicals (GHS),¹ and the subsequent European Regulation 1272/2008 for the Classification, Labelling and Packaging (CLP) of substances,² state that a liquid is a substance with a melting point (meaning the initial melting point if relevant) of no more than 20 °C at standard pressure. Also, a liquid is not completely gaseous at 20 °C, and at 50 °C a liquid has a vapour pressure of 300 kPa (3 bar) or less. Clearly this links to the definition of a gas, which is completely gaseous at 20 °C and at 50 °C has a vapour pressure above 300 kPa. For completeness, a solid is a substance that does not meet the criteria for either a liquid or a gas.

The definition offered by Marcus,¹⁰³ relies on our understanding of the liquid state as was previously discussed (Table 1.1). The more specific definition within the EU Industrial Emissions Directive 2010/75/EU,¹⁰⁴ uses applications to establish what an organic solvent is. Although the inertness of the solvent is maintained, some of the applications listed do not require that the solvent is actually dissolving anything. We are also required to appreciate the meaning of VOC, which is also defined in the Industrial Emissions Directive as “any organic compound … having at 20 °C a vapour pressure of 0.01 kPa or more, or having a corresponding volatility under the particular conditions of use”. Wypych differentiates between solvents and plasticisers in his definition,¹⁰⁵ while the Industrial Emissions Directive includes plasticisers as an application of solvents. Several of the solvents that will be discussed in this book have boiling points in excess of 250 °C (a plasticiser according to Wypych) and so it is more advantageous to follow the definitions of Marcus and the Industrial Emissions Directive. Also note that other formal definitions of a plasticiser exist without reference to boiling point, which only consider the context in which the substance is used (as a plasticiser).³ Wypych also suggests that certain solids and gases are solvents, and in doing so stretches the meaning of a solvent beyond what is useful.

The International Union of Pure and Applied Chemistry (IUPAC) decide upon the authoritative nomenclature and descriptions of chemicals and chemical phenomena. The definition of a solution offered by IUPAC alludes to the meaning of the term solvent, but it is not clearly stated.¹⁰⁶ Instead, IUPAC defines different types of solvent separately. For instance, according to IUPAC a dipolar aprotic solvent is “a solvent with a comparatively high relative permittivity (or dielectric constant), greater than ca. 15, and a sizable permanent dipole moment, that cannot donate suitably labile hydrogen atoms to form strong hydrogen bonds”,⁴ and an amphiprotic solvent is a “self-ionizing solvent possessing both characteristics of Brønsted acids and bases”.⁵

1.2.2 Types of Solvent and Their Origins

The history of solvents is nicely described by Estévez.⁶ Before the advent of the petrochemical industry, solvents were limited to water, naturally occurring oils and substances that could be easily fermented or distilled from biomass. By contrast the number of solvents available now is quite overwhelming. In order to provide satisfactory performance in the variety of processes, formulations, and cleaning applications that solvents are needed for, many different types of solvent are required. Large differences in boiling point, polarity, viscosity and several other physical properties can be found between solvents, and are documented in specialised texts.⁷ Fundamentally the solvent must dissolve the relevant substrates, sometimes selectively, and not react or decompose within the system. Hence many different chemical functionalities are found in both historically important solvents and contemporary examples. Protic solvents (in a hydrogen bonding sense) include water, alcohols, primary and secondary amines, acids, and multi-functional solvents containing any of these chemical groups. Glycol ethers would be one example. Aprotic solvents are more diverse, including aliphatic, olefinic, and aromatic hydrocarbons, halogenated hydrocarbons, ethers, esters, ketones, carbonates, nitriles, tertiary amines, nitrohydrocarbons, organophosphates, amides and sulphur containing compounds.

All the above solvents (with the exception of water) are routinely made from the major chemical building blocks of the petrochemical industry. These are syngas, ethylene, propylene, the butenes, butadiene, benzene, toluene, and xylenes, as produced from crude oil and natural gas (Figure 1.1). These bas...

Table of contents

• Title
• Copyright
• Contents
• Cover
• Chapter 1 Introduction to Solvents and Sustainable Chemistry
• Chapter 2 Modern Trends in Solvent Use
• Chapter 3 Sustainability Applied to Solvents
• Chapter 4 Alternative Solvents
• Chapter 5 Green Chemistry Concepts and Metrics for Solvent Selection
• Chapter 6 An Appendix of Solvent Data Sheets
• Subject Index