Evolution of sulfur compounds and hydrocarbons classes in diesel fuels during hydrodesulfurization.: Combined use of thin-layer chromatography and GC-sulfur-selective chemiluminescence detection

A straight run gas oil has been hydrotreated with a commercial COMO/Al2O3 catalyst, under variable conditions of severity, in order to yield processed products containing a variable amount of residual sulfur. These products have been characterized by simulated distillation, gas chromatography with sulfur-selective detection (GC-SCD), and thin-layer chromatography. The sulfur compounds have been grouped into distinct representative families. The rate constants for the reaction of desulfurization of the considered groups and the apparent rate order with respect to some individual sulfur compounds have been determined. The following hydrocarbon groups have been determined in the hydrotreated products by analytical thin-layer chromatography-densitometry: alkanes, cycloalkanes, total aromatics, and polyaromatic compounds (PACs). The straight run gas oil has been submitted to fractionation by preparative thin-layer chromatography, and the resulting fractions of alkanes, cycloalkanes, and aromatics have been characterized by simulated distillation and GC-SCD. It has been observed that the sulfur compounds concentrate in the aromatic fraction. In the hydrotreated samples, the content of total aromatics decreases as sulfur is eliminated. Heavy cycloalkanes and PACs remain constant, while the alkanes content increases. The combined use of TLC and GC-SCD allows one to obtain useful information on the gas oil composition and its behavior in the HDS process.