Skeletal isomerization kinetics of 1-pentene over an HZSM-22 catalyst

Synthesis of the oxygenate fuel additive TAME (tertiary amyl methyl ether) is based on the reaction between reactive isopentene compounds (2-methyl-1-butene and 2-methyl-2-butene) and methanol. Skeletal isomerization of n-pentenes is an important reaction route in production of the raw material for TAME synthesis. In this work the kinetics of skeletal isomerization of 1-pentene was studied using HZSM-22 as a catalyst, and the effect of temperature (523–598 K) and WHSV (weight hourly space velocity) on product composition were investigated. The observed main reaction products were cis- and trans-2-pentenes, 2-methyl-2-butene, 2-methyl-1-butene and 3-methyl-1-butene. Minor products found in the output stream were C₂, C₃, C₄, C₆, C₇, C₈ and C₁₀ – alkenes and – alkanes. Only traces of methane and C₉ compounds were detected. Two different reaction mechanisms have been proposed in literature for skeletal isomerization of n-pentenes and their side reactions (dimerization and fragmentation); the monomolecular and the bimolecular skeletal isomerization mechanisms. In the current work a pseudohomogeneous reaction model for both mechanisms is fitted to experimental data. The fitting results show that both reaction mechanisms explain the skeletal isomerization of 1-pentene to isopentenes well. However, the monomolecular reaction mechanism explained the formation of dimerization and fragmentation products slightly better. The reliability of the estimated Arrhenius parameters was analyzed using Bayesian inference and Markov chain Monte Carlo methods (MCMC) which are rarely used in chemical engineering.