Hydroisomerization of normal hexadecane with platinum-promoted tungstate-modified zirconia catalysts Original Research Article

The present work examines the activity, selectivity and long-term stability of platinum-promoted tungstate-modified zirconia (Pt/WO3/ZrO2) catalysts for the hydroisomerization of long-chain linear alkanes under relatively mild conditions, using n-hexadecane as a model compound. The preparation of catalysts is described. A trickle-bed reactor is used to compare the activities and selectivities of three Pt/WO3/ZrO2 catalysts prepared by different methods and to investigate the effects of tungsten loading and of reaction conditions for hydroisomerization of n-hexadecane. A run of 93.5 h was conducted using the most highly active Pt/WO3/ZrO2 catalyst which contains 0.5 wt.% well-dispersed Pt and 6.5 wt.% W. Reaction conditions were manipulated and five shutdown (feed stopped, reactor temperature lowered but H2 flow rate maintained) and restart operations were carried out. This catalyst showed high activity and stability. Considerable success has also been achieved in converting n-hexadecane to isohexadecanes for 100 h at temperatures of about 220°C and under H2 pressure as low as 160 psig (1 psig = 6.895 kPa). Our best results (highest i-C16 yield) are a 79.1 wt.% n-C16 conversion, 89.9 wt.% i-C16 selectivity and 71.1 wt.% i-C16 yield at 218°C, 160 psig H2, H2/n-C16 mole ratio = 2 and weight hour space velocity (WHSV) = 1 h−1. The Pt/WO3/ZrO2 catalyst is rugged and has properties which allow one to propose that it may attain commercial use after further study.