Global Solvents Report: Opportunities for Greener Solvents

The overall solvents market has been diminishing somewhat in the developed countries, mainly as a result of regulatory pressures to reduce emissions that tend to cause lower-atmospheric smog and that, in some cases, pose health threats. The opportunity to develop and market solvents with lower ecological and toxicological profiles is excellent, especially with the strong global "green" movement.

However, the perfect solvent is not available. Tradeoffs have to be made regarding efficiency, cost and environmental impact. In recent years, there has been a movement toward the use of solvents that are more benign to humans and to the environment. Several bio-based materials (e.g., methyl soyate, ethyl lactate and D-limonene) have been available for ten or fifteen years, and have enjoyed some commercial success in niche markets. Other novel solvents, like ionic liquids, that focus as much on their environmental impact as on their cost and technical feasibility, are being developed. There will be increased use of supercritical carbon dioxide in solvent applications. Despite these efforts, traditional petroleum-based materials currently account for 99% of the solvent market.

Besides technical feasibility, environmental and toxicological considerations are vitally important. In recent years, there has been a movement toward the use of solvents that are more benign to humans and to the environment. Many solvents have the potential to cause harm if not used properly. Some of the newer criteria being used to determine the feasibility of a potential solvent include the following:

• Inherent toxicity
• Flammability
• Explosivity
• Stratospheric ozone depletion
• Atmospheric ozone production
• Global warming potential

Many large industrial users are under regulatory pressure to reduce or even eliminate the use of certain solvents. Often, users will decide to install engineering controls to reduce or eliminate solvent emissions rather than making a switch to a solvent that is more environmentally benign, but that has a higher cost or that compromises product quality. In the dry cleaning industry, for example, solvent use has dropped significantly as users have switched to equipment that minimizes fugitive emissions. In coatings, adhesives, ink and other industries, users have switched to technologies that consume less solvent such as high-solids coatings, powder coatings, or waterborne formulations.

The following pie charts show world consumption of solvents by region and by type of solvent.

Consumption in paints and coatings accounts for 40–50% of solvent use. Despite the trend over the last thirty years toward technologies that contain less solvent, there is still significant use of solvents. An estimated 40–50% of the coatings used are still low-solids and solvent-based. However, this percentage will likely continue to decrease as more restrictive coatings regulations are scheduled to come into effect in Southern California, the Northeast United States and the European Union in the next five years.

Other important markets, which each account for less than 10% of the use of solvents, are adhesives, inks, pharmaceuticals, chemical processing, household use, personal care, dry cleaning, metal cleaning and agriculture.

Most industries are actively trying to reduce or eliminate the use of hazardous solvents. For example, in the pharmaceutical industry, an industry-sponsored roundtable group (the ACS GCI Pharmaceutical Roundtable) has urged its members to reduce or eliminate the use of solvents that pose high toxicological or environmental concerns in favor of more benign solvents. Work practices should be modified to restrict solvent use. Laboratory chemists should be coached in early research work to avoid non-green solvents so that large quantities of undesirable materials do not have to be treated in production scale-up efforts. If solvent use is minimized, capital costs for manufacture and waste treatment can be reduced.

With solvents, "green chemistry" can be regarded as using a variety of techniques to design new solvents, solvent systems and new ways of using known solvents to reduce or eliminate the intrinsic hazard associated with the traditional solvents and solvent systems. In some cases, new substances are being designed and developed for use as solvents, while in other cases, some of the best known substances in the world are finding new applications as solvents. Of course, using no solvent at all in certain circumstances can be the ultimate solution to minimizing solvent-associated hazards.

The use of solvents that are more benign to health and the environment is part of the "green chemistry" movement. In fact, many solvents are prime examples of "dirty chemistry." There is no universal definition of a "green solvent." Several authors have described some of the attributes of green chemistry. Twelve principles have been suggested by Anastas and Warner*:

• Prevention. It is better to prevent waste than to treat or clean up waste after it has been created.
• Atom Economy. Synthetic methods should be designed to maximize the incorporation of all materials used in the process into the final product.
• Less Hazardous Chemical Synthesis. Whenever possible, synthetic methods should be designed to use and generate substances that possess little or no toxicity to human health and the environment.
• Designing Safer Chemicals. Chemical products should be designed to effect their desired function while minimizing their toxicity.
• Safer Solvents and Auxiliaries. The use of auxiliary substances (e.g., solvents, separation agents, etc.) should be made unnecessary wherever possible and innocuous when used.
• Design for Energy Efficiency. Energy requirements of chemical processes should be recognized for their environmental and economic impacts and should be minimized. Ifpossible, synthetic methods should be conducted at ambient temperature and pressure.
• Use of Renewable Feedstocks. A raw material or feedstock should be renewable rather than depleting whenever technically and economically practicable.
• Reduce Derivatives. Unnecessary derivatization (use of blocking groups, protection/deprotection, temporary modification of physical/chemical processes) should be minimized or avoided if possible, because such steps require additional reagents and can generate waste.
• Catalysis. Catalytic reagents (as selective as possible) are superior to stoichiometric reagents.
• Design for Degradation. Chemical products should be designed so that at the end of their function they break down into innocuous degradation products and do not persist in the environment.
• Real-Time Analysis for Pollution Prevention. Analytical methodologies need to be further developed to allow for real-time, in-process monitoring and control prior to the formation of hazardous substances.
• Inherently Safer Chemistry for Accident Prevention. Substances and the form of a substance used in a chemical process should be chosen to minimize the potential for chemical accidents, including releases, explosions, and fires.

This updated 331-page Safe & Sustainable Chemicals report provides an in-depth study of the global solvents market and examines the potential for replacement of harmful solvents by green solvents in fifteen major market areas and for nearly thirty major solvents in use today.

* Paul T. Anastas and John C. Warner, Green Chemistry: Theory and Practice, Oxford University Press, 1998.

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