Supercritical extraction of crude oil by methanol- and ethanol-modified carbon dioxide

The effect of ethanol and methanol cosolvents on the extraction yield and kinetics of crude oil originating from the Halfdan field of the North Sea by supercritical carbon dioxide was investigated across a pressure range of 20–60 MPa under a fixed temperature of 60 °C. Results inform that the pure carbon dioxide recovery varied between 43 and 77% while the recovery of the liquid phase of oil ranged between 22 and 56% across the entire pressure range. Using ethanol- and methanol-modified CO₂, the total recovery yield increased significantly averaging an additional 18.2% and 19.4% respectively when compared to pure carbon dioxide. The ethanol addition improved the recovery of the liquid phase of oil averaging 9.6% while the methanol addition improved it to 7.3% across the entire pressure range.Study of the kinetics of extraction process indicated that heavier fractions were extracted faster with the ethanol- compared to the methanol-modified CO₂. GC–MS TIC chromatographic analysis of the extracted oil fractions showed that the extraction of C₁₉-C₃₀ single carbon number groups with the addition of methanol is more dependent on pressure. Predominantly, ethanol addition was more efficient in extraction of C₁₇-C₃₈ single carbon number groups while methanol contributed more in extraction of C₇-C₉ SCN groups.