Kinetics of Liquid-Phase 1-Butene Hydroisomerization over Pd/Al2O3 Catalysts

Liquid-phase 1-butene hydroisomerization to 2-butene is an important approach to utilize cheap and abundant C4 olefins (normally as by-products from refinery processes), and the reaction kinetics is critical to the development of its reactors and catalysts. Herein, kinetics experiments are performed to understand the characteristics of liquid-phase 1-butene hydroisomerization over a commercial Pd/Al2O3 catalyst, and three intrinsic kinetics models are proposed to describe the rates of the hydro-isomerization and hydrogenation reactions. The results show that the selectivity toward 2-butene increases with temperature, indicating the hydrogenation reactions are suppressed due to the low partial pressure of hydrogen under high temperature. The fraction of hydrogen in reactants significantly affects 1-butene conversion and 2-butene selectivity, and thus, this effect should be included in kinetics models. Comparing the proposed power-law, dual-site Langmuir-Hinshelwood, and single-site Langmuir-Hinshelwood models, the single-site Langmuir-Hinshelwood model is the best in predicting the experiments, implying that hydroisomerization and hydrogenation reactions may occur at the same type of active sites under the reaction conditions in this work. The activation energies of the hydroisomerization reactions are lower than those of the hydrogenation reaction, and the adsorption enthalpy of butenes is smaller than that of hydrogen.