Comparison of extractive distillation separation sequences for acetonitrile/methanol/benzene multi-azeotropic mixtures

BackgroundThe extractive distillation-based separation of a multi-azeotropic mixture has several optional solvents and schemes. The screen of a suitable solvent was performed and diverse extractive distillation sequences were compared for separating the specified mixture of acetonitrile/methanol/benzene. ResultAs a solvent breaking all binary azeotropes, chlorobenzene was selected over aniline on the basis vapor-liquid equilibrium diagrams and infinite dilution factors. Four separation sequences were optimized by the sequential iterative procedure on the basis of minimal total annual cost (TAC), and CO2 emissions were calculated. Among four sequences, sequence III, composed of two extractive distillation columns and one solvent recovery column, is the best scheme from environmental and economic viewpoints. Simple partial heat integration was further implemented and can save 20.08% and 8.86% in terms of energy cost and TAC. ConclusionThe results demonstrate that the separation of acetonitrile/methanol/benzene is fully achievable using common extractive distillation with chlorobenzene as solvent. Moreover, there is a trade-off between heat transfer in the reboiler-condenser and corresponding energy consumption variations due to pressure changes when considering heat integration. (c) 2018 Society of Chemical Industry