Optimization of Pathways for Biorefineries Involving the Selection of Feedstocks, Products, and Processing Steps

This paper presents a systematic approach to identify the optimal pathway configurations of a biorefinery while incorporating technical, economic, and environmental objectives. This problem is formulated as a generalized disjunctive programming model which accounts for the simultaneous selection of products, feedstocks, and processing steps. The optimal solution can involve multiproduct and multifeedstock biorefineries. The optimization model takes into account two potentially conflicting objectives, the maximization of the net profit and the minimization of the greenhouse gas emissions, while considering the number of processing steps. The environmental criterion is measured using the life cycle assessment methodology. The epsilon-constraint method is used to determine the Pareto curves of this multiobjective optimization problem and to show the trade-offs between the competing objectives. A case study is presented to illustrate the applicability of the proposed methodology for the optimal selection of the biorefinery configuration for the conditions of Mexico under several scenarios. The results show that the optimal combination of different feedstocks and products allows for proper trade-off between the economic and environmental objectives. Results also show that bioethanol, biodiesel, and biohydrogen usually appear as products, whereas sugar cane, jatropha, and microalgae appear as feedstocks in the optimal pathways.