Kinetics of liquid‐phase hydrogenation of isooctenes on a Pd/γ‐alumina catalyst

Abstract

AbstractThe kinetics of liquid‐phase hydrogenation of isooctenes [2,4,4‐trimethyl‐1‐pentene (1‐TMP) and 2,4,4‐trimethyl‐2‐pentene (2‐TMP)] was studied on a Pd/γ‐Al2O3 catalyst in a semibatch reactor. Experimental results revealed that palladium was highly active for the hydrogenation of isooctenes and did not show any significant deactivation like that of the nickel, cobalt, or platinum catalysts reported in the literature. The internal double bond of 2‐TMP was hydrogenated faster than the terminal double bond of 1‐TMP. In addition to the hydrogenation reactions, double‐bond isomerization was observed between 1‐TMP and 2‐TMP. A kinetic model was developed based on the Horiuti–Polanyi mechanism, involving a half‐hydrogenated surface intermediate and the rate‐limiting step was the first hydrogen addition. Isomerization was assumed to take place via the partly hydrogenated intermediates because no isomerization was observed in the absence of hydrogen. The dynamic reactor model consisted of material balances for the gas and the liquid phases, as well as for the porous catalyst particles. A resulting coupled ordinary differential equation–partial differential equation system was solved by Newton's method simultaneously with the minimization of the objective function from the kinetic model. The estimated model parameters with 95% confidence intervals accurately described the experimental data. The hydrogenation of both isomers was found to be strongly dependent on internal diffusion inside the catalyst particle. © 2005 American Institute of Chemical Engineers AIChE J, 2006