An improved column-chromatographic separation for polycyclic aromatic compounds in petroleum

The separation and preparation process of petroleum group components is the basis for the subsequent molecular composition and isotopic analysis. Due to the complex composition of isomers, the components of aromatic compounds prepared by traditional techniques still cannot meet the isotopic analysis requirements of specific compounds. Two different separating methods were used to finely separate and prepare polycyclic aromatic hydrocarbons in crude oils. The "one-step method" was to directly pass the de-asphalted crude oil samples through an alumina/silica gel chromatography column, and elute them with different ratios of petroleum ether/dichloromethane mixed solvent. The "two-step method" firstly used conventional separation methods to obtain aromatic fraction from crude oils, and then applied the aromatic fraction to a column filled with alumina and sub-fractions with different ring numbers then eluted with mixed solvent with different ratios of petroleum ether/dichloromethane. Gas chromatography-mass spectrometry (GC-MS) analysis for the sub-fractions were carried out for the comparison between the two separation methods. Results show that the "two-step method" can better realize the separation and preparation of monocyclic, bicyclic and tricyclic aromatic compounds. The mixed solvents of petroleum ether/dichloromethane of V/V: 99/1, 9/1 and 8/2 can obtain monocyclic, bicyclic and tricyclic aromatic compounds respectively.