Kinetic Studies on the Dimerization of Isobutene with Ion-Exchange Resin in the Presence of Water as a Selectivity Enhancer

The dimerization of isobutene (IB) followed by hydrogenation is looked upon as an important route to produce the octane booster isooctane (IO), because of doubts being raised about methyl tert-butyl ether (MTBE) being a clean fuel additive because of its substantial solubility in water. In the present work, the dimerization of IB has been carried out in a batch reactor over a temperature range of 65-95 °C in the presence of ion-exchange resin as a catalyst and isooctane as a solvent. The influence of various parameters such as temperature, catalyst loading, concentration of water, and initial concentration of IB was examined. Because several side reactions are involved in this reacting system, the selectivity of IB toward the dimers is an important issue. The presence of a polar compound in the reaction mixture plays a vital role as an inhibitor to the side reactions and improves the selectivity toward the dimers. In the present system, water was used as an inhibitor, which leads to the formation of tert-butyl alcohol (TBA) through the hydration of IB. A rigorous kinetic model is proposed to explain the experimental data. All of the reactions such as the reversible dehydration of TBA, dimerization, trimerization, and oligomerization of IB are considered explicitly in the kinetic models. The developed kinetic models would be versatile enough to design a commercial reactor such as a fixed-bed reactor or a reactive distillation column.