Employing Top-Bottom Recycled Reactive Distillation Column To Two-Stagea Cascade Reaction

As a hybrid of reaction operation and separation operation, reactive distillation can solve many problems in reaction process and separation process and lead to improvement of process efficiency and reduction of capital investment and operating cost. It is the convincing success of the reactive distillation in industrial applications with enormous economic benefits that drives many researchers to focus on it.Compared to conventional structure, although the reactive distillation column can improve the performance of chemical process, the obtainable improvement depends heavily on thermodynamic properties. For the separations of reacting mixtures with the most unfavorable ranking of relative volatilities (i.e., the reactants are the lightest and heaviest components with the products as the intermediate ones), the capital investment and operating cost of reactive distillation column will increase since inadequate contact of reactants leads to low reaction conversion. In order to overcome this problem, our team has proposed a reactive distillation column with top-bottom external recycle (RDC-TBER) which is advantageous over currently available process schemes in terms of the separations of various ternary or quaternary reacting mixtures with the most unfavorable ranking of relative volatilities. In order to examine its feasibility and applicability, this paper employs the RDC-TBER to the separations of more complicated reacting mixtures with the most unfavorable ranking of relative volatilities and designs the RDC-TBER on the basis of plant-wide process.In the present study, the RDC-TBER is to be employed to the separations of adipic acid and glutaric acid esterifications and then is evaluated based on plant-wide process. The outcomes show that the RDC-TBER leads to sharply reduced capital investment and operating cost in comparison with the conventional reactive distillation column. Moreover, the reduction of the total annual cost tends to increase in case that the two-stage cascade reaction involved becomes difficult to proceed, which can be detected by comparison between adipic acid and glutaric acid esterifications. In plant-wide process, the RDC-TBER has influence on follow-up distillation column and the reduction of total annual cost is presented by the follow-up distillation column instead of the RDC-TBER itself. These outcomes indicate that the arrangement of a top-bottom external recycle helps to enhance internal mass integration and/or internal energy integration between the reaction operation and the separation operation involved and leads to improvement in performance of reactive distillation column. Therefore, the RDC-TBER is a favorable option for the separations of complicated two-stage cascade reaction kinetics besides the most unfavorable ranking of relative volatilities (i.e., the reactants are the lightest and heaviest components while the products are light and heavy componets).