Remarks on Kinetic Arheotropes

As demonstrated by means of residue curve analysis, selective mass transfer through a membrane has a significant effect on the location of the singular points of a batch reactive separation process. The singular points are shifted, and thereby the topology of the residue curve maps can change dramatically. Depending on the structure of the matrix of effective membrane mass transfer coefficients, the attainable product compositions are shifted to a desired or to an undesired direction. 

A singular point of reactive membrane separation should be denoted as kinetic arheotrope because it is a process phenomenon rather than a thermodynamic phenomenon. The condition for arheotropy can be elegantly expressed in terms of new transformed variables, which are a generalized formulation of the transformed composition variables first introduced to analyze reactive azeotropes. 

The determination of feasible products is very important for conceptual process design and for the evaluation of competing process variants. In this chapter, methods have been discussed to identify feasible products as singular points of residue curve maps (RCM). RCM-analysis is a tool which is well established for nonreactive and reactive distillation processes. Here, it is shown how RCM can also be used for reactive membrane separation processes. 

In order to denote singular points, a clear terminology is needed. The well-known term a-zeo-trope should only be used for phase equilibrium-controlled singular points, whilst the newer term, a-rheo-trope, is proposed for mass transfer-controlled processes. Translated, the latter term means that the composition is not changing with flux . The different types of azeotropes and arheotropes, together with the names of those investigators who were the first to deal with these singular points, are summarized in Tab. 4.4. 

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