Synthesis, Design, and Control of an Azeotropic Distillation System for Methanol-Isopropyl Acetate Separation

The existence of a minimum boiling homogeneous azeotrope precludes the separation of a methanol-isopropyl acetate (MeOH-IPAc) binary mixture into its constituent pure components using simple distillation. In this work, alternative separation processes for recovering pure MeOH and pure IPAc are synthesized. Three promising flowsheet alternatives, denoted as FS3a-c, are further analyzed for energy-efficient operation. The analyzed flowsheets use water as an entrainer for MeOH and consist of a liquid liquid extractor (LLX) and three columns. The flowsheets differ in where the fresh feed is fed. The dominant design variables for the process are the entrainer (water) recirculation rate to the LLX and the number of extractive trays. A design steady state is obtained by adjusting these dominant variables for (near) minimum total reboiler duty. For the nominal equimolar binary fresh feed, FS3a is found to be significantly more energy efficient than the other two variants. A decentralized plantwide control system is synthesized for its recommended process design and is shown to reject large throughput and fresh feed composition changes. It is also shown that the flowsheet recommendation can change for extreme fresh feed compositions. Thus, for a MeOH-lean feed, FS3b is clearly superior, while, for a MeOH-rich feed, FS3c is superior. The recommended flowsheet, FS3a, is more energy-efficient over a large fresh feed composition range.