Graphical methods for reaction distribution in a reactive distillation column

Abstract

Visual methods of determining how to distribute reaction zones within a binary reactive distillation column were studied using both the Ponchon-Savarit and McCabe-Thiele methods modified to account for the reaction. Two types of reactions are compatible with a totally binary system: isomerization and dimerization. For isomerization with a heavy reactant and a light product, both diagrams indicate the potential for a pinch point if the reaction zone is in the stripping section and no such potential if the zone is in the rectifying section. These same diagrams show that the column will have fewer stages and less usage of utility to yield the same final top and bottom products with the reaction in the rectifying section. The situation reverses if the reactant is the light species for isomerization, suggesting reaction should then take place in the stripping section. The heat effect from the isomerization reaction is considered for four cases depending on whether the reaction is endothermic or exothermic. Even if the heat of the isomerization is dominant, the results do not change: with a heavy reactant and a light product, the separation performance is better when the reaction takes place in the rectifying section. In the dimerization reaction, where two light reactants form a heavy product, the light reactant enriches as we go down the column and the composition profile is reversed in a Ponchon-Savarit diagram with the reaction in the rectifying section even if there is no pinch point. Results on the location of reaction zones are confirmed by rigorous simulations.