Kinetics of hydroisomerization of C 5–C 7 alkanes and their mixtures over platinum containing mordenite

Abstract

The hydroisomerization of n-pentane ( n-C 5), n-hexane ( n-C 6), n-heptane ( n-C 7), cyclohexane (c-C 6) and their binary mixtures, n-C 5/ n-C 6, n-C 6/ n-C 7, n-C 6/c-C 6, was investigated over platinum loaded hydrogen mordenite catalyst at 180–220 °C, 5–40 bar total pressure and hydrogen to hydrocarbon molar ratios 1–20. The apparent activation energies of isomerization are 147, 123, 118 and 114 kJ/mol in case of n-C 5, n-C 6, n-C 7 and c-C 6, respectively. The reaction orders in alkane up to 4 bar are 0.33, 0.39, 0.15 and 0.18, as well as the reaction orders in hydrogen up to 36 bar are −0.81, −0.65, −1.08 and −0.57 for n-C 5, n-C 6, n-C 7 and c-C 6, respectively. Rate equations were derived and parameters involved determined for the isomerization of pure paraffins. Kinetic results of n-C 5, n-C 6 and c-C 6 in lower pressure range ( p alkane, p H 2 ≤4 bar) suggest that the isomerization reaction on acid sites is rate-determining step. But in the case of n-C 7 or at higher pressures of n-C 6 and c-C 6 ( p H 2 ≥20 bar, p alkane>5 bar approximately), the zeolite micropore is getting filled with reactants resulting in diffusional inhibition. Experimental data for binary mixtures showed that the reaction rate of both components decreased on mixing. The component having higher boiling point exerts higher inhibiting effect on the hydroisomerization of more volatile alkane than inversely. Kinetic equations for binary mixtures were also proposed.