Synthesis of Reactive Distillation Systems with Multiple Equilibrium Chemical Reactions

The authors describe a procedure to determine the feasibility of separating mixtures with multiple equilibrium chemical reactions by reactive distillation. The method involves describing the system in terms of new composition coordinates which represent the reactive system in a lower dimensional composition space. The justification for these new variables is that when equilibrium chemical reactions occur in a mixture, the phase diagrams and fractionation diagrams are confined to be on surfaces embedded within the mole fraction coordinate space, and are normally difficult, if not impossible to visualize and interpret. The new variables represent these surfaces in a simpler way, thus giving an easier visualization of the diagrams. The new variables sum to unity and they take the same numerical values before and after reaction. In view of these properties, the new variables behave like mole fractions in nonreactive mixtures and can be thought of as reaction-invariant compositions. Therefore, the standard procedures used to determine the feasibility and sequencing for nonreactive distillations can be applied, provided the transformed composition variables are used. The procedure is demonstrated on the methyl tert-butyl ether process with the presence of inert, and on the separation of p- and m-xylene using di-tert-butylbenzene as a reactive entrainer.