Thermodynamic and Kinetic Effects on the Feasible Products of Reactive Distillation

During the last decade, Reactive Distillation has emerged as one of the most successful reactive separation technologies. For the design of countercurrrent reactive distillation columns Doherty and coworkers [1], introduced the concept of reactive flash cascades to predict feasilbe top and bottom products of fully reactive distillation columns. In the first part of the present contribution, an alternative columns design concept is proposed which is based on a reactive batch reboiler, whose stable singular points represent possible bottom product of a countercurrent column, and a reactive condenser, whose stable singular points represent possible top products [2]. This concept can be applied to phase equilibrium controlled systems with thermodynamically or kinetically controlled chemical reactions. The corresponding singular points represent reactive azeotropes and kinetic azeotropes, respectively. In the second part, it is shown how singular points of reactive distillation processes can be shifted or circumvented by means of interfacial mass transfer resistances. Based on this idea, some years ago Schlünder and coworkers developed the process of "diffusion distillation" to separate non-reactive azeotropic mixtures and thereby mew singular points, called "reactive arheotropes", can be achieved. As demonstrated in the final section, arheotropic mextures can be also attained in a desired region of the composition space by application of selective membranes to be installed between the reactive liquid bulk phase and the vopour phase [4]. The principle can be realized in reactive pervaporation processes. Simple reactions in ideal liquid phase and real reaction examples in non-ideal liquid phase are used for illustration of the most important membrane effects