Using External Recycle for Design of Reactive Distillation Columns

Abstract

Although reactive distillation column represent a promising technology of process intensification, it is difficult to use for the separation of reaction systems with the lightest and heaviest reactants producing the light and heavy products. In order to overcome the difficulty, we propose novel reactive distillation columns with a top-bottom external recycle. The direction of the external recycle should be determined according the thermodynamic characteristics of the reaction operation involved. The process configurations favor considerably internal mass integration and internal energy integration between the reaction operation and the separation operation involved and help to enhance the thermodynamic efficiencies of the reactive distillation column. An effective procedure for process synthesis and design is developed, and three examples, i.e., an ideal quaternary exothermic reaction, an ideal quaternary endothermic one, and the esterification of lactic acid with methanol, are chosen to evaluate the configurations proposed. The obtained results show that they are definitely superior to those with two or one reactive sections at their both or either ends in the aspect of capital investment and operating cost. They are also demonstrated to be highly competitive alternative to the conventional reactor/separator system.