SAP fractions from light, medium and heavy oils: Correlation between chemical profile and stationary phases

The chemical composition of oil samples is fundamentally important for planning the recovery, transportation and refining processes of the oil industry. In this work, we examined how stationary phase affects the recovery of non-retained substances and the separation of saturated, aromatic and polar fractions from different density oils by column chromatography. We evaluated four stationary phases: silica gel, alumina, strong anion exchange (SAX) and C-18 silica gel, the latter being the only nonpolar one. The experiment was carried out in quintuplicate and the fractions obtained were analyzed by gas chromatography coupled with mass spectrometry and positive-ion mode electrospray ionization FT-ICR mass spectrometry (ESI(+)-FT-ICR MS). The influence of the stationary phase on the separation of the various classes of substances found in petroleum was observed by chemometrics. For saturated compounds, light and medium oils presented n-paraffins, iso-paraffins, naphthenes, terpanes and steranes, while heavy oil presented intense biodegradation, with a higher concentration of terpanes and steranes. When heavy oil was fractionated with C-18 silica gel, the presence of n-paraffins could also be observed. Alumina generated a saturated fraction, that was less contaminated with aromatics, and it showed a separation capacity similar to that of silica gel and SAX. For aromatics, all stationary phases generated fractions contaminated with saturated compounds, and polar fractions showed a greater presence of basic heteroaromatics compounds containing predominantly one nitrogen. A more reliable SAP separation of crude oil fractions depends on their density.