Molecular Selectivity in Supercritical CO2 Extraction of a Crude Oil

Supercritical CO, flooding has been considered as a promising enhanced oil recovery (EOR) method because it can effectively improve the oil recovery and promote greenhouse gas sequestration. However, the solubility of different petroleum components in supercritical carbon dioxide (SC-CO2) has not been well investigated. This paper presents the molecular selectivity of SC-CO2 extraction on crude oil under different pressures and temperatures. The crude oils were loaded on the surface of kieselguhr and extracted by SC-CO2. The extracts and residues from SC-CO2 extraction were analyzed by gas chromatography mass spectrometry and Fourier transform ion cyclotron resonance mass spectrometry. Our results showed that the operating pressure (20-30 MPa) affected the extraction yields more than the temperature (50-70 degrees C). SC-CO2 preferentially extracted small molecules with relatively low aromaticity and polarity. Compound classes containing multiple heteroatoms had lower extraction yields than hydrocarbons. The carbon number distribution ranges of various compound classes in the residues were largely different. Carboxylic acids and phenolic compounds were found to have poor solubility in SC-CO2. The risk of asphaltene precipitation in CO2, EOR is also discussed.