Entrainer based economical design and plantwide control study for Tetrahydrofuran/Water separation process

Abstract

In this work, the control structure design for a continuous extractive distillation scheme using entrainers for separating THF–water azeotropic mixture into high purity product (THF) has been studied. The selection of suitable entrainer for the undertaken process was purely based on economical design criteria where total annualised cost (TAC) for different entrainers were first calculated and further compared. Once the suitable entrainer was selected based on the design economics, later the plantwide control structure was evaluated for disturbance rejection capabilities and smooth process operations in the face of feed throughput and composition change. For economical design operations, the recycle rate of entrainers has to be kept around a minimum recycle rate. However, operating below minimum entrainer recycle rate leads the product purity to fall sharply in conventional control structure designs due to THF–Water azeotropic constraints. The presented control structure design in this works ensures that product purity is not lost even in case of sever disturbances in feed throughput (by ±10%) or a changed feed composition (by ±5%).