Residue curve maps for heterogeneously catalysed reactive distillation of fuel ethers MTBE and TAME

Abstract

The liquid-phase synthesis of octane enhancing ethers like methyl tertiary butyl ether (MTBE) or tertiary amyl methyl ether (TAME) is increasingly realized as a reactive distillation process catalysed by ion exchange resins. To study the occurring physical and chemical phenomena of those systems, the present paper deals with a reactive batch distillation process in a heated still. The model is based on phase equilibrium between the liquid and the vapour phase and an adequate kinetic formulation of the heterogeneously catalysed etherification by application of the generalized Langmuir-Hinshelwood rate expressions. To describe the non-ideal mixture behaviour, liquid-phase activities are introduced. Simulation results show that the shape of residue curves depends on two essential parameters, the Damköhler number Da and the operating pressure p. The values of these parameters influence the existence and the position of stable nodes, saddles and separatrices in the residue curve map. The evaluated trajectories deviate quantitatively from those recently reported for homogeneous catalysis. The most interesting result lies in the fact that the lightest boiling component can be enriched in the still.