Predicting Multiple Steady States in Equilibrium Reactive Distillation. 1. Analysis of Nonhybrid Systems

Abstract

During the last few years, multiple steady states (output multiplicities) have been discovered for reactive distillation processes, for example, for the production of fuel ethers and for some esterification processes. Using the transformation of Ung and Doherty (Chem. Eng. Sci. 1995e, 50 (1), 23−48), a method is presented to predict the existence of output multiplicities based on the reactive vapor−liquid equilibrium for the limiting case of reactive columns of infinite length operated at infinite internal flows. This graphical method rests upon the ∞/∞ analysis for azeotropic distillation columns by Bekiaris et al. (Ind. Eng. Chem. Res. 1993, 32 (9), 2023−2038). It is directly applicable to systems where the reactions take place in the entire column (“nonhybrid” columns). When all possible profiles and products are located through a bifurcation analysis, qualitative and quantitative predictions are obtained. The region of feed compositions leading to multiple steady states can be constructed graphically by applying a necessary and sufficient geometrical condition. The prediction results are shown to carry over to finite columns by application to the methyl tert-butyl ether process and are verified by simulation.