Nonequilibrium modelling of reactive distillation: multiple steady states in MTBE synthesis

Abstract

We have developed a generic non-equilibrium (NEQ) model for packed reactive distillation columns. The important features of the model are the use of the Maxwell-Stefan equations for description of intraphase mass transfer and incorporation of a homotopy-like continuation method that allows for easy tracking of multiple steady states. The interesting features of the developed NEQ model are demonstrated with a case study for production of Methyl-tert-butyl-ether (MTBE). Multiple steady states behaviour is observed when the bottom product flow rate of MTBE is varied. The results of the NEQ model show significant quantitative differences from an equilibrium stage (EQ) model. Furthermore, for the NEQ model counter-intuitive effects are observed for the low-conversion “branch”. For example, increasing the mass transfer coefficient decreases the conversion of the low conversion branch. Decreasing the catalytic activity increases the conversion of the low conversion branch. The system is also found very sensitive to the amount of n-butenes (inerts) in the feed stream. With decreasing the n-butene feed, the phenomenon of multiple steady-states tends to disappear.