Kinetics of Simultaneous Isomerization and Cracking of the Five Hexane Isomers by Use of the Wei-Prater Method

Abstract

The kinetics of simultaneous isomerization and cracking of normal and isohexanes on a bifunctional 0.35 wt % Pt-Al203 catalyst has been studied at 435 °C, a total pressure of 10.5 bar and a hydrogen/hydrocarbon partial pressure ratio of 20 in a fixed bed reactor. At these reaction conditions the reaction system-interconversion of -hexane, dimethylbutanes, and methylpentanes and C-C bond rupture of the hexane isomers-can be assumed to be pseudomonomolecular, and the Wei-Prater method was used to evaluate isomerization and cracking rate constants. Reaction paths in the composition space calculated on the basis of these rate constants reveal good agreement with experimental reaction paths and fit the experimental data better than reaction paths computed on the basis of initial reaction rate constants. The individual conversion rates of the hexane isomers correspond to predictions from a bifunctional mechanism in which alkyl shift rearrangements of carbocations are considered to be the rate-determining steps.

NETWORK OF n-HEXANE ISOMERIZATION OVER Pt/Al2O3AND Pd/HM CATALYSTS

“…Christoffel studied kinetic models for n-hexane isomerization and hydrocracking o n P t / A120, reforming catalysts, where dimethyl butane (DMB) appeared only in trace amounts (Christoffel, 1982(Christoffel, , 1979. Bryant calculated the overall conversion of n-hexane o n Pt-H-form mordenite ( P t / H M ) in kinetic models (Spiner, 1982).…”