Separating an azeotropic mixture of toluene and ethanol via heat integration pressure swing distillation

•The optimized sequence of two pressure columns is determined by using Aspen Plus.•The optimization achieves the minimum TAC for separation of toluene and ethanol.•The control structures for partial and the full heat-integration pressure swing distillation based on steady state simulation. A procedure is suggested to separating a minimum-boiling azeotrope of toluene and ethanol via heat integration pressure swing distillation (PSD), and an optimized separation configuration is obtained via taking the minimization of the total annual cost (TAC) as an objective function. The result demonstrates that PSD with heat integration is more economical than conventional PSD without heat integration. Based on steady-state simulation results, several control structures were explored using Aspen Dynamics. The results indicate that the composition/temperature cascade control structure and the pressure-compensated temperature control of a PSD process with partial heat integration with stage 21 selected as the control stage in the low pressure column can handle disturbances well. As for the PSD with full heat integration, stage 20 of the low pressure column can act as the control stage because of its more efficient controllability under feed flow rate and feed composition disturbances.