(313e) Sustainability Indicators in Computer-Aided Process Evaluation and Design

Sustainability indicators provide an approach to evaluating process sustainability that integrates with computer-aided process methods.  As processes are developed, their design determines input and output flows responsible for resource use and releases (i.e., a process life cycle inventory).  These flows are the bases for process indicators, which can be evaluated with the U.S. Environmental Protection Agency’s GREENSCOPE methodology and tool. GREENSCOPE indicators, placed in context with best-target and worst case limits, can be used in the evaluation and design of chemical processes, representing nearly 140 indicators in four basis areas: environment, economics, energy, and (mass) efficiency.  Computer-aided process methods are one avenue for using these indicators.   In this work, GREENSCOPE indicators for the oxidation of toluene are calculated, and an optimization is performed across a range of conversions.  Intermediate conversions realize the maximum total utility, as lower conversions increase toluene emissions and higher conversions increase byproduct formation.  Tradeoffs are resolved using marginal rates of substitution, allowing for the calculation of total utility in terms of only GREENSCOPE indicator scores, best-target / worst-case ranges for the indicators, and marginal rates of substitution.  With the indicator ranges being constant and marginal rates of substitution set by user choices, the results depend on indicator scores, providing an intuitive method for connecting process attributes to the optimized results.