Analysis of Complex Separation Schemes in the Presence of Chemical Reactions

Abstract

A key feature in the analysis of extractive distillation columns is the use of difference points representing the flow rate and composition difference between the cascade section end-product and the extractive side feed(s). Also referred to as a Δ-point, it may be used to assess feasibility for complex cascades with highly non-ideal VLE behavior. We have recently generalized the concept of difference points to systems where chemical reactions take place. We have also shown that the analytical insights are independent of the actual configuration of physical equipment and apply to any partial or complete flowsheet. This paper will demonstrate how the theory of generalized difference points may be applied to the design of complex separation cascades with reaction. Two example designs with integrated reaction and separation will be presented and analyzed for 3 and 4 components, respectively: (a) reactive distillation for the production of acetic acid from acetic anhydride and water and (b) reactive extractive distillation for the production of methyl acetate from acetic acid and methanol with water as a side product. The acetic acid example will illustrate how composition space can be divided into regions where feasibility with respect to distillate placement and internal reaction distribution can be performed using difference point theory. The methyl acetate design will show how a complex column can be divided into sections and analyzed using difference points to expose the role each section plays in making a feasible design.