Process Assessment of Distillation Using Intermediate Entrainer: Conventional Sequences to the Corresponding Dividing-Wall Columns

In extractive distillation, an intermediate entrainer that differently interacts with the azeotropic components can be introduced. In this work, the separation system of methanol toluene has been investigated to evaluate the performance of conventional extractive distillation (CED) and the corresponding dividing wall column (DWC) by using an intermediate entrainer. First, the conventional extractive distillation separation sequences including direct sequence (DS) and indirect sequence (IS) are investigated. It is indicated that DS provides much more energy saving and investment reduction, while DS exhibits an obvious remixing effect and IS has a problem with vaporizations of light product. Then, in order to deminish the remixing effect, two types of DWC, dividing wall column with the wall in the top (DWC-T) and that in the bottom (DWC-B), are further explored and investigated. It is found that, compared to DWC-T, DWC-B offers more energy savings and reduces the remixing effect. Moreover, a basic temperature control scheme for DWC-B is investigated when feed flow rate and composition disturbances are introduced. From the standpoint of both the optimum designs and fairly good dynamic performance, DWC-B is considered as a suitable selection for the methanol-toluene azeotrope separation.