(790c) Decision Making for Sustainable Processes

Multi-objective decision support tools aim to represent the thought process of decision makers in the development and design of chemical processes.  These tools often use calculations that mathematically describe preferences to combine various utility scores with weighting factors.  Once utility scores are combined into a single objective, the alternative solutions for process development and design can be ranked.  The creation of a single objective for a multi-attribute decision necessarily generates tradeoffs (except in the simplest win-win scenarios).  While the intention in choosing (equal) weighting factors may be to make them value free, this contribution will show how combining utility scores is always a statement of a relationship between the weighted scores.  The relationships between utility scores can be rewritten as a series of equations in terms of the weighting factors.  Calculations can be used to determine the weighting factors for different sets of relationships, allowing for explicit representation of the implied tradeoffs for decision makers.  In addition, a method will be described for using marginal rates of substitution between utility scores to calculate total utility.  This method will simplify the relationships between the utility scores and present a powerful and intuitive way to calculate total utility. 

The methods presented will be demonstrated in an example utilizing indicators derived from EPA’s sustainability evaluation and design tool, GREENSCOPE (Gauging Reaction Effectiveness for the Environmental Sustainability of Chemistries with a multi-Objective Process Evaluator).  GREENSCOPE has 140+ indicators in four basis areas: environment, economics, energy, and efficiency.  Previous work has developed absolute sustainability limits for these indicators and provided data needs and solutions for calculations.  The combination of GREENSCOPE with weighting / marginal rate of substitution methods and explicit representations of implied tradeoffs will provide users with tools to support multi-objective decisions.