PACKED-COLUMN SFC OF GAS OILS .1. HYDROCARBON GROUP SEPARATION USING PURE CARBON-DIOXIDE

In this paper, the critical application of the ASTM method to hydrocar bon 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 th e nature of the stationary phase after the FID detection conditions ha ve been selected to give the best sensitivity, Three gas oils differin g in composition (ratio aromatic/non-aromatic hydrocarbons) have been selected to evaluate the method for separation of the non-aromatic hyd rocarbon group from mono-, di-, and polyaromatic hydrocarbons groups ( sub-aromatic groups). The ASTM requirements for this analysis are very easy to obtain in adsorption chromatography. However, in adsorption o r normal phase chromatography, SFC results cannot be perfect either fo r the quantification of aromatic and non-aromatic hydrocarbon fraction s because there is still an overlap between the two groups (the separa tion is better in adsorption chromatography than in normal phase chrom atography) or for sub-aromatic fractionation (the separation is better in normal phase chromatography than in adsorption chromatography); co mbination of both separation techniques only improves the sub-aromatic group fractionation, Thus, further enhancement of resolution for grou p and sub-group separation is needed.