Fuel purpose hydrocracking of biomass based Fischer-Tropsch paraffin mixtures on bifunctional catalysts

摘要

Two biomass-based Fischer-Tropsch paraffins comprising of 16-46 and 11-45 carbon number range alkanes were hydrocracked over zeolite mordenite and tungstated-zirconia-supported platinum catalysts. The reaction was carried out in the temperature range of 300-350 degrees C, at 40 bar pressure and hydrogen/hydrocarbon volume ratio of 600. The liquid hourly space velocity was varied in the range of 0.5 and 2.0 h(-1). The yields and the compositions of gas, gasoline, jet and gas oil fractions were studied as function of process parameters and catalyst properties. The conversion of paraffin components having more than 21 carbon atoms was determined. Under identical reaction conditions near the same conversions were obtained over the two catalysts. However, the feedstock composition significantly influenced the result of the hydrocracking process. Regularly lower conversions and higher middle distillate yields (jet + gas oil) were obtained for feedstock characterized by 11-45 carbon number range. The weaker acidic tungstated-zirconia-supported platinum catalyst was more suitable for production of engine fuels than the stronger acidic mordenite catalyst. Over platinum/tungstated-zirconia catalyst lower gas (0.5-15.0 wt%) and higher middle distillate yields (14.7-43.0 wt%) were obtained than over platinum promoted mordenite catalyst. The formation and diffusion of isoparaffins is more favored in mesopores than in micropores, therefore more isoparaffin was formed over the mesoporous tungstated-zirconia-supported platinum catalyst than over the microporous mordenite. In the micropores diffusion constraints prevailed promoting the formation of gaseous products.