No abstract

Improved separation and quantitative determination of hydrocarbon types in gas oil by normal phase high-performance TLC with UV and fluorescence scanning densitometry Improved methods for separation and quantitative determination of hydrocarbon types from gas oil have been developed, which were based on high-performance thin-layer chromatography with ultraviolet and fluorescence scanning densitometry using horizontal elution. One of the methods allows the separation, detection, and determination of alkanes and naphthenes to be carried out, using berberine-impregnated silica gel HPTLC plates, elution with n-hexane, and berberine-induced fluorescence detection at 365 nm. Another developed method allows total aromatics to be determined using silica gel HPTLC plates by elution with n-hexane and acetone, and UV detection. In turn, PACs over three aromatic rings can be determined on either silica gel or caffeine-impregnated silica gel HPTLC plates, elution with n-hexane, and selective detection using native fluorescence at 365 nm. Concentrations lower than 5 wt% can be determined using this technique. In addition, a technique for an efficient, baseline-resolved separation of a gas oil according to the number of aromatics rings (mono + di-, tri-, and polyaromatic compounds with more than three rings) is presented here. This technique involves a multistep elution on a mixed (silica gel and caffeine-impregnated silica gel HPTLC plate) using a counter-elution device, and UV 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.