The Coupling Effect of Waxes and Asphaltenes in the Model Oil on the Supercritical CO2 Extraction

Supercritical CO2 (scCO2) extraction exerts a significant effect on the physicochemical characteristics of crude oil. This work focuses on the role that waxes and asphaltenes played in the scCO2 extraction effect. The extraction rate, hydrocarbon composition, wax precipitation characteristics, conductivity, and centrifugal stability are quantitatively characterized. It is found that the extraction rate of model oil without paraffin wax is the highest after scCO2 treatment, approximately 18.3%. When the paraffin wax content is enlarged from 5.0 to 15.0 wt %, the extraction rate decreases from 16.7% to 11.7%. It is indicated that the presence of wax inhibits the extraction effect of scCO2. In addition, with further addition of asphaltenes, the extraction rate increases and then decreases. This manifests that the addition of asphaltene promotes the extraction effect of scCO2, while the combined effect of waxes and asphaltenes inhibits the extraction effect with the further increase of the asphaltene concentration. Considering the wax precipitation characteristics, the wax appearance temperature (WAT) and wax precipitation amount (WPA) are both increased after scCO2 treatment. With the addition of asphaltene, the WAT and WPA of model oil are both decreased. As for wax crystal morphology, the wax crystals in paraffin wax oil become finer after the treatment, and the amount of wax crystals precipitated increases. Lastly, after scCO2 treatment, the conductivity and absorbance of model oil containing asphaltene decrease, while the light transmittance increases, due to the formation of asphaltene aggregates under scCO2.