Simultaneous Optimal Design of an Extractive Column and Ionic Liquid for the Separation of Bioethanol-Water Mixtures

Recently renewed interest in the optimal design of sustainable processing systems has emerged as consequence of pollution issues and global climate changes. The replacement of hazardous industrial solvents widely used for azeotropic separations is clearly a challenging research area for new products design. However, as important as product design is, the design of the optimal processing configuration where the azeotropic separation will take place is also a key issue. As a matter of fact, the strong interaction between product and process design indicates that better optimal processing conditions can be attained by solving both problems simultaneously rather than sequentially. In the present work, we take advantage of this natural interaction for the optimal simultaneous design of both ionic liquids and an extractive distillation column for the high purity separation of the ethanol/water azeotropic mixture for deploying ethanol as a biofuel. The problem is formulated as a steady-state disjunctive mixed-integer nonlinear programming (MINLP) problem. The results indicate that new green solvents constitute a good replacement for hazardous solvents. Because ionic liquids are expensive solvents, it is worth it to explore the deployment of advanced optimization tools for profit maximization of sustainable processing systems. Through the use of the proposed MINLP formulation, improved ethanol/water separation configurations deploying ionic liquids were attained. Because ethanol features high purity, it can be used for biofuel applications.