Kinetics and Mechanism of the Catalytic Hydroisomerization of n-Hexadecane in the Presence of a Pt/SAPO-11 Catalyst

A kinetic model of the catalytic hydroisomerization of n-hexadecane is developed. It is shown that the relevance of this process is attributed to the necessity to improve the low-temperature properties of diesel fuel and Group III and IV oils. The process is run for the selective isomerization of normal alkanes contained in the feedstock in the presence of a Pt/SAPO-11 catalyst based on platinum supported on SAPO-11 with a one-dimensional channel pore structure. The studies are conducted at temperatures of 300–360°C in increments of 20°C. Rate constants for the steps, preexponential factors, and activation energies for kinetic models for simplified and detailed n-hexadecane hydroisomerization schemes are calculated by solving the inverse kinetic problem. Numerical solution methods, in particular, the multistep variable-order Gear method and a genetic algorithm, are used. According to the calculated kinetic parameters, the dehydrogenation and protonation reactions that initiate the process are characterized by high activation energies. It is shown that an increase in temperature leads to an abrupt increase in the cracking rate relative to the isomerization rate.