Heterogeneous Models of Tubular Reactors Packed with Ion-Exchange Resins: Simulation of the MTBE Synthesis

Abstract

The study of the behavior of fixed-bed reactors using ion-exchange resins as catalysts was carried out by making use of a complete bidimensional heterogeneous model for the reactor, which included the resistances inside the ion-exchange resin particles, considered with a macroreticular structure. The active sites were located inside the gel phase of the resin, represented by microspheres, and on the macropores walls. The overall efficiency of such heterogeneous catalyst particles was defined by the macroeffectiveness and microeffectiveness factors accounting for the process behavior on the macropores and inside the microspheres. The synthesis of methyl tert-butyl ether, MTBE, a liquid-phase reversible exothermic reaction between methanol and isobutene, was considered as a reference case. This system was studied in the temperature range of 313-338 K, and the effect of the thermodynamic equilibrium conditions was examined. The results predicted by the complete heterogeneous model were compared with those obtained with the simple pseudohomogeneous model, which revealed higher hot spots. Moreover, a comparison between bidimensional and unidimensional models was also performed. The orthogonal collocation method was used for the discretization of the differential equations inside the catalyst particles, which were reduced from three (corresponding to the three mass balances for the three compounds, isobutene, methanol, and MTBE) to only one differential equation, by using the concept of the generalized variable.