Introduction - Principles of Chemical Separations with Environmental Applications - page 6

soil clean-up (solvent contamination, heavy metals, etc.)
continuing discharges to the environment
automobiles
industries (chemical, nuclear, electronics, engineering, etc.).
2 Pollution prevention
Examples:
chemically benign processing
hybrid processing
use of water instead of hydrocarbon/fluorocarbon solvents
alternative chemical synthesis routes
use of separation step(s)
reduction in downstream processing steps
eliminate solvent use (membranes instead of extraction, for example)
eliminate purge streams (internally remove contaminants so purge stream is not
needed)
recovery and recycle instead of discharge (organics, water).
Figure 1.1 portrays a hierarchy for pollution prevention [5]. It is apparent that the diffi-
culty of implementation decreases from top to bottom. Note that, the first four approaches
on the hierarchy involve chemical separations (mass transfer operations).
The Chemical Manufacturers Association has published a strategy [6] for addressing
pollution minimization or elimination in chemical processing facilities very similar to
Figure 1.1. They suggest, in priority order:
1 Source reduction . Process changes to eliminate the problem.
These process changes can include:
Reducing by-product formation through changes in processing and/or catalyst usage.
This step can include changes in raw materials used.
Better process control to minimize processing variations which lead to additional
discharges.
New processing flowsheets to minimize unwanted product generation and/or release.
2 Recycle. If source reduction is not feasible, then recycle
within the process
within the plant
off-site.
3 Treatment . Post-process waste treatment prior to discharge to minimize the environ-
mental impact.
A recent article [7] describes more than 50 pollution prevention strategies that do not
require large investment costs.
The use of chemical separations is already very important in many industries. These
include biotechnology, metals recovery and purification, fuels, chemical processing plants
and feedstocks, municipal sewage treatment, and microelectronics. For these and other
industries, the efficiency of the separation steps is often the critical factor in the final cost
of the product.