Novel temperature-control strategy for single column side-stream extractive distillation process with intermediate-boiling entrainer

A simple, novel, and energy-saving single column side-stream extractive distillation (SSED) process was recently proposed in literature, for separating the azeotropic mixture of methanol (MeOH) and toluene (TOL) using triethylamine (Et3N) as an intermediate boiling entrainer. However, within the limited progress regarding the control of this process, composition controllers were required to maintain stringent product specifications in the face of disturbances. In view of this, our work firstly uncovers the feasibility of establishing control strategies without using composition loops. The research scope also covers the revision of thermodynamic properties in between MeOH and Et3N, re-design of the process with systematic optimization, development and evaluation of four control schemes. With thorough analyses, a dual-temperature control structure with three measurement (i.e. a side-stream temperature control loop, and a temperature difference control loop in the extractive section of the SSED column) was found to satisfactorily reject the specified feed disturbances (i.e. ±20% change in flowrate and composition). Notably, the loop adjusting the makeup flowrate to control the side stream temperature, which has not been proposed to the single column SSED process, greatly reduced the settling time under disturbances. Comparing with other control structures in literature, the one proposed in this work provides good control performances, but in a manner that is more industrially maneuverable.