The importance of proper economic criteria and process modeling for single- and multi-objective optimizations

• Appropriate application of economics for process optimization problems is provided.
• Suitable economic criteria for single- and multi-objective optimizations are defined.
• NPV generates operationally, economically and environmentally efficient processes.
• The composed LCA-based objective functions produce less profitable process designs.

This paper provides an overview of the influences that different economic objectives have on the efficiencies of those optimal process designs obtained by using single- and multi-objective optimizations. Optimizations of monetary criteria, like the profit, lead to operationally and environmentally more efficient but economically less attractive designs than optimization of non-monetary economic objectives, like the internal rate of return. The net present value produces compromise designs with intermediate efficiencies and environmental impacts. These differences are significant only if the processes’ mathematical models are sufficiently accurate for establishing appropriate trade-offs between investment and cash flow. The Pareto curves obtained by different economic objectives vary regarding the maximum environmental impacts and in the intervals of the environmental indicators. The composed criteria that combine the economic and environmental indicators into one single objective produce smaller differences between optimum designs that are closer to those designs with minimum possible environmental impacts.