Steryl glucosides (SG) are minor components that dramatically modify the low temperature performance of fatty acid methyl esters (FAME) used as biodiesel. SG are naturally present in vegetable oils but they may also be the result of the transesterification of esterified steryl glucosides (ESG). These are present in vegetable oils at a level of a few hundred milligrams per kilogram, depending on the nature of the feedstock. We developed an analytical method to quantify SG and ESG in vegetable oils and in FAME. The purification of SG and ESG was performed by liquid chromatography on silica gel, and the analysis of the trimethylsilyl derivatives was achieved by gas chromatography and flame ionization detection. The filterability of biodiesel is affected when the SG content is higher than 20 mg/kg. Therefore, the sensitivity of this new method is adapted for this purpose since the quantification limit is 10 mg/kg of SG and ESG. The recoveries are acceptable, between 75% and 90% depending on the species and content, and the reproducibility relative standard deviation, evaluated at 10%, is comparable to other studies.

Although the Claus-reaction-based processes are widely used in industry to recover sulfur from sour gas or crude oil, the precise mechanism of this reaction remains unclear and controversial. The aim of this study was to determine the chemical species of the Claus reaction in an organic liquid phase [using polyethylene glycol 400 (PEG) as solvent] at 125-130 °C. A combined UV-vis and Raman spectroscopic approach is developed to monitor the sulfur speciation. In addition, ab initio molecular-modeling techniques lead to an exhaustive mapping of the Raman spectral properties of molecules. Several intermediate sulfur-containing species have also been identified, as a function of experimental conditions. These analytical results are required as preliminary data to describe the chemistry of the Claus reaction in the organic liquid phase. These data are helpful to improve the kinetic model for the subdew point Claus tail gas treatment, used in the refining and natural gas treatment industries.