Hydrogenation and deactivation kinetics in the liquid-phase hydrogenation of isooctenes on Pt/Al2O3

Isooctenes (2,4,4-trimethyl-1-pentene, TMP-1, and 2,4,4-trimethyl-2-pentene, TMP-2) were hydrogenated to isooctane (2,2,4-trimethylpentane) using a commercial Pt/Al2O3 catalyst in a three-phase laboratory-scale reactor. The terminal double bond in TMP-1 was hydrogenated substantially faster than the internal double bond in TMP-2, and double bond isomerization was found to be of no importance. Furthermore, strong catalyst deactivation through the formation of carbonaceous deposits was observed under the applied reaction conditions. Kinetic models, which were formulated on the basis of the Horiuti-Polanyi mechanism, described the experimental data accurately and with physically reasonable parameter values (E-a 49 kJ/mol for TMP-1 and 65 kJ/mol for TMP-2). Catalyst deactivation was successfully described with the first-order equation, in which the deactivation constant was dependent on the alkene-to-hydrogen ratio. Features in which the studied Pt catalyst deviates from Ni and Co include higher activation energies, stronger hydrogen adsorption, and more severe catalyst deactivation.