Phenomena-based analysis of fixed points in reactive separation systems

Abstract

Integrated systems for reaction and separation offer promising technology for less expensive and more energy-efficient chemical processes. In this paper, we show how to view reactive separation processes as a vector combination of reaction, separation and mixing. In composition space, vector directions are calculated from physical and chemical data only; thus they are independent of design. On the other hand, vector lengths reflect design decisions which are at our disposal, allowing us to manipulate resultant moves in composition space by how we design and operate the equipment. Of particular interest is the discovery of a reaction difference point. We show that this mathematical artifact is found outside the feasible composition space. It determines the underlying structure of linear composition changes by reaction in mole fraction space. Using the proposed vector notation and the reaction difference point, we provide a simple and visual explanation for the term `reactive azeotrope', herein referred to as a reactive fixed point. The potential for such points arises from collinearity among reaction, separation and mixing as individual phenomena and is independent of operating conditions. We discuss the possible impact of such points on limiting behaviour in systems featuring simultaneous reaction and separation.