Control of Benzene–Cyclohexane Separation System via Extractive Distillation Using Sulfolane as Entrainer

Benzene and cyclohexane (CYH) can be separated via extractive distillation using sulfolane (SULF) as entrainer. In this Article, the steady state of an extractive distillation system has been simulated using the RadFrac model in Aspen plus, and the controllability of this system with feed flow rate and feed composition disturbances has been studied in Aspen Dynamics. Sensitivity analysis is used to obtain optimal operation conditions. The common control scheme for extractive distillation is infeasible. Two control structures are demonstrated in this Article. Each control structure has three main temperature controllers, two in the extractive distillation column and one in entrainer recovery column. Although both control structures can solve all disturbance issues and maintain the product purities very close to the set points, the dynamic responses of initial control structure have large transient deviation when +20% feed flow rate disturbance is introduced, while the improved control structure can overcome this obstacle.