Search Results

The green chemistry movement that emerged among academic and applied chemists during the 1990s has grown into a significant international force for change within the field of chemistry. Green chemistry innovations are emerging in green reagents, alternative solvents, low-waste reactions, aqueous processing, biocatalysts, energy-conserving processes, safer chemical products, chemicals from renewable feedstocks, and chemicals modelled on natural systems. However, the chemical industry has been slow to embrace this new approach to chemistry and there has been little movement on the basic platform chemicals of the industry.

In this chapter the authors explore the role that the dominant discourse of risk has played in the processes of institutional change that have taken place in the field of chemistry as a result of the emergence and expansion of “green” chemistry. The aim of green chemistry is to replace hazardous substances with benign ones so as to eliminate chemical risks to human health and the environment. They show how significant institutional changes have occurred through two forms of “risk translation” that have changed the discursive landscape by constructing new kinds of “knowing subjects” who are able to act on different “known” objects.

The successful shift away from chemicals of concern requires the development of new and safer alternatives. This involves the synthesis of new chemicals and chemical processes. Nanotechnology and synthetic biology both offer novel routes to such alternatives if they are effectively guided by a drive for safety and ecological compatibility. Green engineering and nonchemical alternatives also offer safer substitutes. These innovations require a clear definition of the term “safer” and tools for assisting in such searches. However, there is now a growing market of safer chemical and nonchemical alternatives that could use either government of private investment assistance to get to the scale and competitive prices that are needed for effective market conversions.

This chapter presents three case studies of chemical risks to examine regulatory riskwork in three different risk scenarios. The first risk scenario concerns ‘established’ risks, which stem from hazards that are widely recognized and which have been causally linked to particular practices or products, usually through significant and mainly uncontroversial scientific study. The second scenario involves ‘emerging’ risks, which stem from hazards that are perceived to be novel or unfamiliar, and which are only starting to be recognized by some, but not all, members of scientific and other communities. The third scenario involves ‘eliminating’ risks altogether, by substituting practices or products understood as being hazardous with alternatives believed to be non-hazardous. For each scenario, the chapter identifies the riskworkers, the nature of riskwork and discursive work in which they engage, the implications of their work for how risk objects are conceptualized, and the likely effects of their riskwork.

Our economy is based on thousands of chemicals many of which have hazardous properties. For over 40 years the United States has relied on federal chemical control laws to manage the risks of these chemicals, however, many of these substances today show up as pollutants in our homes, workplaces and bodies. A growing movement among consumer and environmental organizations, product manufacturers, retailers, and governments is working to eliminate the use of many of these chemicals. This book documents that movement and offers a series of proposals on how to broaden the movement and make it more effective.

Developing a truly effective chemical management approach in the United States requires changing the way that the chemicals problem has been framed. Instead of controlling a few hundred truly dangerous chemicals, we should be focusing on all the chemicals on the market today and progressively shifting towards safer chemicals and non-chemical alternatives. This will require understanding chemicals as products of a massive chemical production, consumption and disposal system that needs to be restructured. A new safer chemical policy framework is needed and a comprehensive chemical conversion strategy that involves three strategic fronts; converting the chemical market, transforming the chemical industry and designing greener chemicals.

During the 1990s, the chemical industry has focused on ways to reduce and prevent pollution caused by chemical synthesis and manufacturing. The goal of this approach is to modify existing reaction conditions and/or to develop new chemistries that do not require the use of toxic reagents or solvents, or that do not produce toxic by-products. The terms “environmentally benign synthesis and processing” and “green chemistry” have been coined to describe this approach where the environmental impact of a process is as important an issue as reaction yield, efficiency, or cost. Most chemical reactions require the use of a solvent that may serve several functions in a reaction: for example, ensuring homogeneity of the reactants, facilitating heat transfer, extraction of a product (or by-product), or product purification via chromatography. However, because the solvent is only indirectly involved in a reaction (i.e., it is not consumed), its disposal becomes an important issue. Thus, one obvious approach to “green chemistry” is to identify alternative solvents that are nontoxic and/or environmentally benign. Supercritical carbon dioxide (sc CO2) has been identified as a solvent that may be a viable alternative to solvents such as CCl4, benzene, and chloroflurocarbons (CFCs), which are either toxic or damaging to the environment. The critical state is achieved when a substance is taken above its critical temperature and pressure (Tc, Pc). Above this point on a phase diagram, the gas and liquid phases become indistinguishable. The physical properties of the supercritical state (e.g., density, viscosity, solubility parameter, etc.) are intermediate between those of a gas and a liquid, and vary considerably as a function of temperature and pressure. The interest in sc CO2 specifically is related to the fact that CO2 is nontoxic and naturally occurring. The critical parameters of CO2 are moderate (Tc = 31 °C, Pc = 74 bar), which means that the supercritical state can be achieved without a disproportionate expenditure of energy. For these two reasons, there is a great deal of interest in sc CO2 as a solvent for chemical reactions. This chapter reviews the literature pertaining to free-radical reactions in sc CO2 solvent.

The use of compressed carbon dioxide as a reaction medium, either as a liquid or a supercritical fluid (sc CO2), offers the opportunity not only to replace conventional hazardous organic solvents but also to optimize and potentially control the effect of solvent on chemical synthesis. Although synthetic chemists, particularly those employing catalysis, may be relative latecomers to the area of supercritical fluids, the area of catalysis in carbon dioxide has grown significantly since around 1975 to the point that a number of excellent reviews have appeared (Baiker et al., 1999; Buelow et al., 1998; Jessop and Leitner, 1999; Jessop et al., 1995c, 1999; Morgenstern et al., 1996). Developing and understanding catalytic processes in dense-phase carbon dioxide could lead to “greener” processing at three levels: (1) solvent replacement, (2) improved chemistry (e.g., higher reactivity, selectivity, less energy), and (3) new chemistry (e.g., use of CO2 as a C-1 source). In this chapter, we will highlight a number of examples from the literature in homogeneous and heterogeneous transition-metal catalysis, as well as the emerging area of biphasic catalysis in H2O/sc CO2 mixtures. The intent is to provide an illustrative rather than a comprehensive overview to four classes of catalytic transformations: acid catalysis, reduction via hydrogenation, selective oxidation catalysis, and catalytic carbon–carbon bond-forming reactions. The reader is referred to other chapters in this book and other reviews (King and Bott, 1993) for discussion of uncatalyzed reactions, phase-transfer catalysis, polymerization, and radical reactions in sc CO2. From a synthetic chemist’s viewpoint, sc CO2 has a number of potential advantages that one would like to capitalize upon. • Solvent Replacement Carbon dioxide is a nontoxic, nonflammable, inexpensive alternative to hazardous organic solvents. Simple solvent replacement will not be a sufficient driver for all chemical reactions; however, as described below, the use of carbon dioxide could lead to better chemistry for certain reactions. • Gas Miscibility Gases such as H2, O2, and CO are sparingly soluble in liquid solvents but they are highly miscible with sc CO2.

Because of the recent emphasis on green chemistry, there has been interest in using supercritical carbon dioxide (sc CO2) as a solvent or swelling agent to aid in polymer processing and polymer chemistry (Adamsky and Beckman, 1994; DeSimone et al., 1992; Hayes and McCarthy, 1998; Kung et al., 1998; Mistele et al., 1996; Romack et al., 1995; Watkins and McCarthy, 1995). Supercritical CO2 is a very weak solvent for most polymers (some fluoropolymers and silicones are exceptions); however, it swells most polymers and dissolves many small molecules (Berens and Huvard, 1989). The density of a supercritical fluid (SCF), and thus its solvent strength, is continuously tunable as a function of temperature or pressure up to liquidlike values. This provides the ability to control the degree of swelling in a polymer as well as the partitioning of small-molecule penetrants between a swollen polymer phase and the fluid phase. The low viscosity and zero surface tension of SCFs allows for fast transfer of penetrants into swollen polymers. The lack of vapor/liquid coexistance in SCFs allows the sorption to proceed without the penetrant solution wetting the substrate surface. Since most of the common SCFs are gases at ambient conditions, the removal and recovery of the solvent from the final product is extremely facile. All of these factors aid in a new method we have developed for preparing polymer composites. This method involves the absorption of a supercritical solution of a monomer, initiator, and CO2 into a solid polymer substrate and subsequent thermal polymerization of the monomer to yield a composite system of the two polymers. We have focused on radical polymerization of styrene within various solid semicrystalline polymer substrates (Hayes and McCarthy, 1998; Kung et al., 1998; Watkins and McCarthy, 1995). Table 10.1 lists a number of systems that we have studied to make polymer–polystyrene composites. The method for preparing the polymer blends listed in Table 10.1 involves the soaking of the substrate polymer in a supercritical solution of styrene, a thermal radical initiator, and CO2 at a temperature where the initiator decomposes very slowly (half-lives of hundreds of hours).