Selectivity Effect of Oxygenates in Hydrocracking of Fischer—Tropsch Waxes

摘要

The potential effect of oxygenates on the hydrocracking of iron-based Fischer-Tropsch (FT) wax was investigated using bifunctional amorphous silica—alumina base metal and noble metal catalysts. Hydrogenation of the FT wax resulted in higher hydrocracking activity and increased conversion compared to unhydrogenated wax, but contrary to expectations, a higher diesel selectivity was obtained with the untreated wax. Experiments with a hydrogenated FT wax fraction whereby oxygenate model compounds such as tetradecanol and lauric acid were added to the wax showed that the oxygenates selectively affected the product spectrum by competitive adsorption with hydrocarbons on the active sites. Analyses of the product spectrum led to the conclusion that the oxygenates impacted the catalyst's metal—acid balance, which subsequently changed the bifunctional behavior of the original catalyst. The presence of the alcohol in the hydrogenated FT wax improved the hydrocracking selectivity to diesel. Addition of the acid led to more secondary cracking and as a result a higher selectivity to lower-boiling hydrocarbons. The hydrocracking product spectrum of a hydrogenated FT wax can consequently be successfully manipulated by the selective addition of oxygenates.