Dehydroisomerization of n-Butane over Pt–ZSM5: II. Kinetic and Thermodynamic Aspects

A kinetic model is applied to describe the dehydroisomerization of n-butane to isobutene over Pt–ZSM5. It is compared with experimental data and used to show how a combination of kinetics and thermodynamics affects the obtained yields. High temperatures reduced the selectivity to by-product formation by oligomerization/cracking of butenes. However, the stability of the catalyst decreased. This is attributed to the enhanced formation of butadiene, poisoning metal and acid sites. Lowering the pressure also reduced the selectivity to by-products and the thermodynamic constraints and was, thus, favorable for dehydroisomerization. The H2/n-butane ratio mainly affected the selectivity to hydrogenolysis, which increased with hydrogen partial pressure, while catalyst stability did not improve significantly. An optimum with respect to selectivity and stability was found for a H2/n-butane ratio of 2.