Multi-objective optimization approach for green design of methanol plant based on CO2-efficeincy indicator

Abstract The aim of the present work is to propose an eco-design method for sustainable development of methanol production by implementing a multi-objective optimization model based on CO2-efficiency. Two different approaches for the methanol production, i.e. a conventional reference methanol case (RMC) and proposed green integrated methanol case (GIMC) were compared from the view point of eco-design. Using life cycle assessment and process simulation, the environmental features as well as operational decision variables of the RMC and GIMC were assessed. Based on the inventory analysis of LCA, it was found that carbon dioxide is the major emitted pollutant from methanol production. Thus the multi-objective model in the proposed GIMC was formulated as maximizing methanol production (which refers to a classical objective in process design) and minimizing CO2 emission (which refers to an environmental objective in process design) and the set of Pareto frontier was obtained. In order to achieve single optimal solution, the multi-objective model is transformed to a single objective optimization problem by weighted product method and the single optimum point is found by using genetic algorithm. Comparing obtained results showed that the optimal condition of the RMC which is based on a classical objective is a local optima from the view point of environmental benign design, whereas by involving the environmental objective in the design stage, a lower CO2 emission with respect to the RMC could be achieved at the expense of a small decrease in the methanol production.