MTBE decomposition in reactive distillation columns is investigated based on numerical simulations. Special emphasis is on the undesired side reactions. Quasi-homogeneous as well as heterogeneous column models are applied for a packed column. In the latter, the multi-component intra-particle mass transport phenomena are accounted for. Continuation methods are used to study the influence of the design and operating parameters in order to determine optimal conditions. One finding is that the catalyst holdup should be very low in order to fully convert MTBE with high selectivity into the desired products isobutene and methanol. The results from the heterogeneous model illustrate the role of mass transport inside the catalyst particles, especially at larger size and higher pressure.