Application of Life Cycle Assessment to the Structural Optimization of Process Flowsheets

This work proposes a novel framework for the optimal design of chemical processes whose main novelty lies
in the incorporation of environmental concerns based on the principles of the Life Cycle Assessment (LCA)
methodology. The approach presented applies mixed-integer modeling techniques to the superstructure
optimization of sustainable chemical process flowsheets. As such, the resulting mathematical formulation
simultaneously accounts for the minimization of the environmental impact and the cost. The environmental
impact is measured through the Eco-indicator 99, which reflects the advances in the damage-oriented method
recently developed for Life Cycle Impact Assessment. The incorporation of this environmental performance
measure at the modeling stage causes a multiobjective mixed-integer nonlinear problem (moMINLP) that
can be addressed by standard techniques for multiobjective optimization. The main advantages of our approach
are highlighted through its application to a well-known design problem (the hydrodealkylation (HDA) of
toluene), for which the set of trade-off solutions, in terms of cost and environmental criteria, is computed.
The obtained results show that an inherent tradeoff naturally exists between both objectives and also suggest
that significant environmental improvements can be achieved if decision makers are willing to compromise
the economic benefit of the process.