Solvent Use and Waste Issues

Stewart Slater, Mariano J. Savelski, William A. Carole, and David J.C. Constable 

The waste generated by pharmaceutical companies have increased concerns about environmental and human safety. Direct releases of treated solvent wastes, hazardous work conditions, and accidental releases of toxic chemicals into the environment have led to the implementation of many laws and regulations 

Edited by Peter J. Dunn, Andrew S. Wells and Michael T. Williams 2010 WILEY-VCH Verlag GmbH Co. KGaA, Weinheim ISBN 978-3-527-32418-7 

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Purification can also be achieved in other ways, through precipitation with salts, crystallization, and through aqueous two-phase extraction. Some of these methods are associated with substantial capital cost, low throughput, low yields, or waste issues. Fractional precipitation, one of the oldest protein separation technologies, can be surprisingly effective to separate a compound of interest from a complex broth. For instance, the process of fractional solvent precipitation of blood plasma components has been used since World War II. 

In HPLC, a semiprep column might be operated at 25 mL/min, using up solvent and generating waste at a rate of up to 36 L/24-h day, or just under two 20-L containers of solvent in and two 20-L containers out as waste. Each week, the user needs to have available at least 10-14, 20-L containers of new solvent and must dispose of about 10-14 20-L containers of toxic, mixed waste for each chromatograph. Most jurisdictions limit the amount of solvent allowed in a lab at any given time as a fire safety issue. The limit is usually 50 L. A whole lot of barrel rolling occurs. 

Students are also very environmentally aware. Adding the microwave component has provided the opportunity to introduce many of the concepts of green chemistry. The role of solvents in a reaction can be exemplified by having students compare changes in reactions that under traditional microscale procedure used toluene or DMF as solvents but are now run in ethanol and water. The issues of solubility and boiling point properties are compared to enviromnental impact and waste management. For example, water need not necessarily be the optimal solvent for a reaction. Not only does the reaction step itself have to be considered but also the enviromnental impact of product workup and waste disposal in order to make an informed decision on the benefits of a particular solvent. 

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