Separation of ternary mixture with double azeotropic system by a pressure-swing batch distillation integrated with quasi-continuous process

Abstract

Two pressure-swing batch distillation processes, which are double-column batch stripper process and its integration with quasi-continuous process named triple-column process, were designed and investigated to separate the tetrahydrofuran/methanol/water ternary system. There are two azeotropes in the system and previous studies about batch distillation to separate such mixtures are insufficient. Based on the residue curve maps, the feasibility of the processes was analyzed. Control structures were explored to implement efficient separation and ensure the safety and stability of the process. The minimum total annual cost was used to optimize the processes. The double-column batch stripper process can separate the tetrahydrofuran and water well but the methanol purity is only 99.4 mol%. To improve the separation effect, a third column was integrated in the batch distillation process to separate the methanol/water mixture directly. The new triple-column process has the characteristics of batch distillation and continuous distillation. The results show that the minimum TAC of double-column batch stripper process is 147,815 $/y which is a little lower than that of triple-column process by only 3.2%. The final compositions of tetrahydrofuran and water are same in the two processes, which are 99.9 mol% for water and 99.85 mol% for tetrahydrofuran, but the methanol purity is different. The methanol is 99.4 mol% in the double-column process while 99.9 mol% in the triple-column process. The improved methanol purity reflects the high separation efficiency and it is beneficial for the environmental protection.