An environmentally benign, energy intensified single-column side stream extractive distillation (SC-SSED) process for Acetone/n-heptane separation

Abstract

The single-column, side-stream extractive distillation (SSED) process has been proposed as a simple, novel, and energy-saving configuration for separating azeotropic mixtures, using an intermediate-boiling entrainer. However, within limited progress in separating the mixture of acetone (ACE) and n-heptane (HEP) through such processes, benzene (BEN), a human carcinogen, was frequently used as an entrainer. In view of this, our study aims to propose an environmentally benign SSED process to separate the same mixture. In the proposed process, 1-chlorobutane (CHL) is used as an entrainer. With thorough analysis, the economic performance of this process was found to outperform the other process using heavy entrainers (i.e. p-xylene and butyl propionate), while being economically comparable to the process using BEN as an entrainer. In addition, limited improvement is achieved by employing the SSED configuration for heavy entrainer-based processes, since a higher-grade steam is required at the reboiler of the extractive distillation column. Subsequently, a suitable control strategy with two temperature loops and three measurements (i.e. a side-stream temperature control loop, and a temperature difference control loop in the extractive section of the SSED column) was established. It can satisfactorily reject the specified feed disturbances (i.e. ±20% change in flowrate and composition). Compared to all other existing studies, the currently proposed control structure does not require any composition loop and, at the same time, is able to handle disturbances to a greater extent.