Distillation of reactive mixtures

Abstract

In this dissertation, the influence of equilibrium chemical reactions on vapor-liquid equilibrium and distillation processes is studied. The theory of reactive-phase diagrams for two-phase systems, in which the components undergo one equilibrium chemical reaction, is developed, and the conditions for reactive-azeotropy are derived. It is shown that reactive-azeotropes do not necessarily correspond to stationary points in the chemical equilibrium surfaces. Reactive-phase diagrams, which illustrate the influence of chemical reactions on phase equilibria, are computed for some typical systems. These diagrams show that reactive-azeotropes can occur even for ideal mixtures.^ The effect of equilibrium reactions on distillation processes is illustrated by studying the simple distillation of homogeneous reactive mixtures. The residue curve maps for some typical systems show that by allowing the components of a mixture to react we can either create or eliminate simple distillation boundaries. Moreover, the addition of reaction may prevent some non-reactive azeotropes from being obtained as products of the distillation process.^ The study of the simple distillation of reactive mixtures led to the definition of a set of transformed composition variables that reduce the conservation equations for reactive mixtures to a form identical to that for non-reactive mixtures. These variables are used to simplify the design equations for single- and double-feed reactive distillation columns. These variables also allow the derivation of simple relationships between the dependent design variables, which are not evident when mole fractions are used.^ The new design equations are used to devise a technique for the calculation of minimum reflux ratios in single- and double-feed multicomponent reactive distillation columns. The design of reactive distillation columns for commercially important non-ideal mixtures is considered. The application of the results of this work to the synthesis of flow sheets for processes using reactive distillation is discussed.