Design and control of side-stream extractive distillation to separate acetic acid and cyclohexanone from wastewater by varying pressure

Abstract

A large amount of wastewater containing acetic acid and cyclohexanone is produced during the production of ε-caprolactone. It is necessary to recycle acetic acid and cyclohexanone from wastewater. In this paper, the feasibility analysis for the separation of acetic acid/ cyclohexanone/ water with a near-azeotrope and an azeotrope which is pressure sensitive is carried out based on the residue curve map (RCM). And two sequences of conventional extractive distillation are determined. In order to prevent the remixing effect in conventional extractive distillation, four configurations of side-stream extractive distillation by varying pressure are proposed and optimized. The results show that the single liquid side-stream extractive distillation configuration SED1 is the optimal configuration in terms of economy, environmental protection, energy efficiency and safety. Compared with the optimal conventional extractive distillation configuration CED1, the total annual cost (TAC) of SED1 is reduced by 6.6%, and CO2 emissions are reduced by 11.9%. Subsequently, three proportion-integral (PI) control structures and a model predictive control (MPC) structure are proposed for SED1. The robustness and controllability of PI and MPC systems are compared by calculating integral absolute error (IAE). The findings indicate that the MPC structure has the best performance among all control structures.