Hydroisomerization of N-hexadecane using metal-promoted tungstate-modified zirconia catalysts.

摘要

The use of environmentally benign metal-promoted tungstated zirconia (Metal/WO₃/ZrO₂) catalysts for n-hexadecane hydroisomerization was investigated with the object of producing high yields of branched isomers of hexadecane with minimal cracking. Reactions were carried out in a small trickle bed reactor. The maximum yield (about 71 wt%) of isohexadecanes was obtained with a catalyst (Pt/WO₃/ZrO₂) containing 6.5 wt% tungsten and 0.5 wt% platinum at a temperature of 218°C and pressure of 160 psig with a hydrogen to hexadecane mole ratio of 2 at a space velocity of 1 h−1.; The two most commonly used catalyst preparation procedures in the literature were chosen for study. The procedure with separate calcinations after tungstate and platinum impregnations yielded a catalyst which was more active and selective for n-hexadecane hydroisomerization. Six Pt/WO₃/ZrO ₂ catalysts with tungsten contents from 3 to 15 wt% were evaluated and the highest activity and selectivity were found at 6.5–8 wt% tungsten; the catalyst containing 6.5 wt% W was selected for further work.; A run of 72 h and a run of 93.5 h were carried out to investigate the catalytic activity and stability of this catalyst. The robustness of the catalyst to changes in operation conditions was evaluated by calcination at a high temperature (450°C), shutdowns and restarts, and changes of reaction variables. In every case, the catalyst regained the high activity, isomerization selectivity and isohexadecane yield after returning to standard conditions.; A continuous run of 100 h carried out at a pressure of 160 psig and a temperature about 220°C without interruption showed no sign of catalyst deactivation.; The effect of metal promoters was studied by treating tungstated zirconia supports with Ni, Pd and Pt. Pt is a better promoter than Ni or Pd. Moderate reduction with hydrogen near reaction temperatures is beneficial.; The results of n-hexadecane hydroisomerization using the 6.5 wt% tungstated zirconia catalyst and a platinum-promoted sulfated zirconia catalyst, prepared in this laboratory, were also compared. The former was an active isomerization catalyst; the latter was an active hydrocracking catalyst.; Hydroisomerization of n-hexadecane and Fischer-Tropsch waxes, carried out in 27 ml microautoclaves, is reported.