Bifurcation analysis for TAME synthesis in a reactive distillation column: comparison of pseudo-homogeneous and heterogeneous reaction kinetics models

Abstract

This paper presents a bifurcation analysis for synthesis of tertiary amyl ether (TAME) in a reactive distillation (RD) column. Two different methods for describing the reaction kinetics are explored and compared: (A) pseudo-homogeneous models: here the intra-particle diffusion and reaction is simplified by the use of catalyst effectiveness factors and pseudo-homogeneous rate expressions, and (B) heterogeneous models: here detailed account is taken of intra-particle diffusion, using the dusty fluid model, and reaction within the catalyst particles. Both pseudo-homogeneous and heterogeneous reaction models show the possibility of multiple steady states. The bifurcation characteristics obtained with the two models are similar in nature and the essential features of the heterogeneous model can be captured with the pseudo-homogenous model by defining an appropriate value for the catalyst effectiveness factor, the value of which depends on the particular branch of the bifurcation diagram. The pseudo-homogeneous model was then applied to study the dynamics of a TAME synthesis RD column. Starting at the low conversion steady state, a feed composition perturbation is shown to lead to a transition to the high conversion steady state, in qualitative agreement with the experiments of Mohl et al. (Chem. Eng. Sci. 54 (1999) 1029). The quantitative differences in the dynamic responses are to be ascribed to imprecise knowledge of hydrodynamics, especially as concerns the static liquid hold-up in the RD column.