Pressure-Swing Distillationa Process And Dynamics For Ethanol-Chloroform/N-Heptane Azeotrope

Rigorous steady-state and dynamic simulation of pressure-swing distillation for the separation of ethanol-chloroform and ethanol-n-heptane binary azeotropic system on the base of pressure-sensitive properties were completed by Aspen Plus and Aspen Plus Dynamics. The optimal sequences and operating parameters for different heat-integration processes were achieved by taking minimization of an objective function of the total annual cost (TAC). The effective control structures of different distillation processes were also obtained according to the performances of various control schemes.As for the pressure-swing distillation for separating the binary system containing 90% chloroform, the optimal configuration parameters of the high-pressure column were determined by the effects of pressure on the azeotropic characteristics. The optimal conditions are summarized as below:the separating scheme is HP-LP, the pressures of two columns are 13 and 1 atm, and the minimal TACs of no, partial and full heat-integration pressure-swing distillation are 140,807.22 $/y,130,955.75 $/y, and 111,067.775 $/y respectively. For the pressure-swing distillation for separating the binary system containing 30% n-heptane, the best distillation sequence of LP-HP and the optimal operating pressures of 10 and 0.5 atm for two columns are obtained using to the sequential iterative method. TAC of the partial heat-integration is the smallest among the three process.Dynamic control schemes of the pressure-swing distillation with different heat integration were further studied on the base of the steady-state results for ethanol-chloroform and ethanol-n-heptane systems. The composition/temperature cascade control structure show effective control performace in the pressure-swing distillation with no and partial heat-integration. The pressure-compensate temperature control structure was adopted in the full heat-integration pressure-swing distillation to conquer the problems of the decreased degree of freedom. For the control of pressure-swing distillation for separating binary mixture of ethanol-n-heptane, the improved control structure can deal with the ±20% disturbances of feed flowrate and feed composition. The pressure-compensate temperature control structure has some superiorities in the aspect of handling with the disturbances occurred in the full heat-integration pressure-swing distillation.Separation method and control scheme of ethanol-chloroform/n-heptane system were provided in this study. The results can provide guidance to the steady-state economic optimization and dynamic characteristics for the separation of similar azeotropic system.