ICI uses a rough indicator of environmental impact called the environmental load factor (ELF) to choose the reaction route that is best for the environment. The ELF equals the net weight of raw materials, solvents, catalysts, and
other chemicals used to make a unit weight of product. Subtracting the weight of the finished product from the weight of all material fed to the process and dividing that difference by the weight of the finished product calculates the ELF. Therefore, pollution prevention dictates that researchers minimize the use of additives. Additives must be separated from a product, and at some point, they too become waste. In addition, installations designed to protect the environment are also invariably sources of waste (Hileman 1992).
The waste ratio is an indicator used at the 3M Company to measure the progress of the waste-reduction strategies. This ratio is defined rather simply as:
The quantities are measured by weight. Total output includes good output plus waste. Good output includes finished goods, semifinished goods, and by-products (however, by-product material that is beneficially burned for fuel counts as waste). Waste is the residual from the manufacturing site before it is subjected to any treatment process. The material that is recycled is not included as waste (Benforado, Riddlehover, and Gores 1991).
At 3M, the waste ratio varies from 10 to 20% for batch polymerizations to 99% for products that are not favored by reaction kinetics or that require multistep purification operations. New products undergo special screening if the initial waste ratio exceeds 50%. This screening is important not only for meeting waste-reduction targets but also for assessing the economic viability of the product as treatment and disposal costs escalate.
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