Packed column SFC of gas oils part I: Hydrocarbon group separation using pure carbon dioxide

In this paper, the critical application of the ASTM method to hydrocarbon group separation in gas oils using conventional packed column SFC coupled to FID is described. Resolution of model compounds is studied using a recent commercial apparatus and the chromatographic conditions such as pressure, temperature, and density of the mobile phase and the nature of the stationary phase after FID detection conditions have been selected to give the best sensitivity. Three gas oils differing in composition (ratio arimatic/non-aromatic hydrocarbons)have been selected to evaluate the method for separation of the non-aromatic hydrocarbon group from mono-, di-, and polyaromatic hydrocarbons groups (sub-aromatic groups). The ASTM requiements for this analysis are very easy to obtain in adsorption chromatography. However, in adsorption or normal phase chromatography, SFC results cannot be perfect either for the quantification of aromatic and non-aromatic hydrocarbon fractions because there is still an overlap between the two groups (the separation is better in adsorption chromatography than in normal phase chromatography) or for sub-aromatic fractionation (the separation is better in normal phase chromatography than in adsorption chromatography); combination of both separation techniques only improves the sub-aromatic group fractionation. Thus, further enhancement of resolution for group and sub-group separation is needed.