Design and control of fully heat-integrated pressure swing distillation with a side withdrawal for separating the methanol/methyl acetate/acetaldehyde ternary mixture

In the industrial manufacturing process of polyvinyl alcohol, there is inevitably a small amount of acetaldehyde in the alcoholysis solution (methyl acetate/methanol mixture), the accumulation of which may decrease the purity of product. The effect of acetaldehyde on the separation of homogeneous azeotrope of methyl acetate and methanol via fully heat-integrated pressure swing distillation (FHI-PSD) is investigated. A PSD process with a side withdrawal is proposed and proved to avoid the accumulation of acetaldehyde in the system effectively. The optimum separation configuration conditions are based on the minimum total annual cost (TAC) analysis. In the steady-state design, the simulation reveals that the process has the minimal TAC when operating pressure of the HPC is 10 atm. A conventional pressure-compensated temperature control (CS3) and a new temperature difference control (CS4) are compared in Aspen Dynamics. Both of them can eliminate the influence of pressure fluctuation on bubble points at the sensitive plates and perform well even for large feed disturbances. However, it is easier to design CS4 as CS4 doesn't require complex bubble point temperature calculation compared with CS3. Therefore, CS4 is suggested to be another favorable and viable control scheme for PSD process, which may show superiority in industrial application.