Assessment of dominant factors affecting hydroisomerization on bifunctional zeolites

The hydroisomerization of n-octane in the liquid phase was investigated over beta, USY and mordenite zeolites loaded with I wt% Pt in a stirred semi-batch microautoclave. The total pressure ranged form 5 to 9 MPa and the temperature from 523 to 563 K with all initial catalyst/n-octane ratio of 7 g(catalysts)/mol(n-Cg). PtBETA was the most active catalyst at all operating conditions, followed by PtMOR and PtUSY. The isomer yields oil PtMOR were somewhat lower than oil PtBETA and PtUSY. Increasing the total pressure always resulted in a decrease in the n-octane conversion, which is indicative of so-called ideal hydroisomerization. The n-octane hydroisomerization experiments were simulated with a kinetic model based on a parallel/consecutive reaction scheme involving reversible mono- and multibranching and irreversible cracking from mono- as well as multibranched isomers. The model fitted adequately the experimental data on PtBETA and PtUSY. However, more dispersion was observed with catalyst PtMOR. The ratio of the composite rate coefficients for cracking to that for monobranching was significantly higher oil PtMOR than on PtUSY and PtBETA. The composite activation energy for monobranching was 20 kJ mol(-1) higher on USY if compared to that of mordenite and beta. These modelling results were related to pore sizes and geometry and average acid strength. (c) 2008 Elsevier B.V. All rights reserved