SYNTHESIS OF REACTIVE DISTILLATION SYSTEMS WITH MULTIPLE EQUILIBRIUM CHEMICAL-REACTIONS

We describe a procedure to determine the feasibility of separating mix tures with multiple equilibrium chemical reactions by reactive distill ation. The method involves describing the system in terms of new compo sition coordinates which represent the reactive system in a lower dime nsional composition space. The justification for these new variables i s that when equilibrium chemical reactions occur in a mixture, the pha se diagrams and fractionation diagrams are confined to be on surfaces embedded within the mole fraction coordinate space, and are normally d ifficult, if not impossible, to visualize and interpret. The new varia bles 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 nonr eactive mixtures and can be thought of as reaction-invariant compositi ons. Therefore, the standard procedures used to determine the feasibil ity and sequencing for nonreactive distillations can be applied, provi ded the transformed composition variables are used. The procedure is d emonstrated on the methyl tert-butyl ether process with the presence o f inert, and on the separation of p- and m-xylene using di-tert-butylb enzene as a reactive entrainer.