How to implement environmental considerations in chemical process design: An approach to multiobjective optimization for undergraduate students

This paper expects to give some guidelines for undergraduate students about how to implement environmental considerations in chemical process design and how the introduction of these issues could have an important effect on the results obtained in the multiobjective problem optimization when economic and environmental aspects are considered simultaneously.For this work, a representative flowsheet of many chemical and petrochemical processes has been considered. This processing scheme works with a feedstock containing some inert and with not very high conversion per pass in the reactor.Therefore, the influence of the quality of raw materials, the installation of additional stages for treating effluents, the environmental impact and the optimum conversion of the chemical process are evaluated, attending both environmental and economic criteria.Our goals were, first to show how to identify the tradeoffs of a representative chemical process when environmental and economic considerations are included simultaneously in the design and its optimization. Secondly, how feedstock quality and additional waste treatment stages affect to the results obtained in the multiobjective optimization: minimize the total cost of the installation and its environmental impact.As a result, the final objective of this paper is to teach undergraduate students how multi-objective optimization could be used to make better decisions in the design of chemical processes, taking into account both economic (minimum total cost) and environmental (minimum environmental impact) performances.For each case study proposed, a detailed optimization was performed to determine Pareto curves using the ɛ-constraint method to identify the tradeoffs of this multiobjective optimization and ultimately determine the best alternatives, and even their optimum operational conditions attending to both criteria.It is important to remark that this problem could be solved in Excel so that it could be a good example to undergraduate students.

► This work shows how to introduce environmental aspects in chemical process design. ► A representative flowsheet of many chemical processes has been considered. ► Raw materials, effluent treatment, environmental impact and costs are evaluated. ► Better decisions are taken in process design using multiobjective analysis.