Heat Integration Process For Separating System Of Toluene And N-Butyl Alcohol With Pressure With Pressure Swing Distillation

Toluene and n-butyl alcohol can form an azeotrope, which can not achieve effective separation by ordinary distillation. Based on the consideration of technical feasibility and energy saving, pressure-swing distillation and heat integration technology were used to systematically study for separating the system of toluene and n-butyl alcohol.Based on the Aspen Plus simulation platform, the property method of NRTL was used to simulate the azeotropic data of toluene and n-butyl alcohol under different pressure. Through the study of deviation degree of azeotropic composition under different pressure, we determined the pressure sensitivity of the system and chose the pressure-swing distillation process. The pressure-swing distillation process under different operating pressure were simulated and the results show that the optimal operating pressure of low pressure column and high pressure column was 0.2atm and 1.0atm, respectively.The partially heat integrated and fully heat-integratied process without heat pump was studied. The heat integration scheme was determined by the quantitative relation of the heat duty of the top condenser in high pressure column and the heat duty of the bottom reboiler in low pressure column, if the former is smaller than the latter, the partial heat integration will be chosen, otherwise, the fully heat integration will be chosen. Taking the minimum TAC as the objective function and the optimization scheme is given, the results show that the saving TAC of the partially and fully heat integrated process were 11.8% and 18.0% compared with traditional PSD, respectively. The fully heat integration process has more advantages.Integrated process with heat pump was simulated and researched. Based on a minimum TAC, we systematically optimized three integrated process of pressure-swing - closed heat pump distillation, pressure-swing-bottom throttle heat pump distillation and pressure-swing-top vapor compression heat pump distillation, the influence of the operating parameters of distillation column (feed location, reflux ratio, theoretical stage number) and the operating parameters of heat pump process (top steam recovery, outlet pressure of the compressor,outlet pressure of the throttle valve) on the TAC was investigated, finally the optimum operating parameters and equipment parameters were determined. According to the optimal process, the composition, temperature and vapor-liquid flow rate distribution curve in the distillation column were used to investigate the rationality of the process. The results were indicated from the economic view and the economic sequence was pressure-swing-top vapor compression heat pump distillation, pressure-swing-bottom throttle heat pump distillation and pressure-swing - closed heat pump distillation, the saving TAC was 18.2%,14.0%,5.5% compared with traditional PSD, respectively.The heat integrated process of separating toluene and n-butyl alcohol in this paper can provide reference for separating similar azeotrope and has some guiding significance on the actual production process.