Abstract
Oil upgrading due to the decrease of metal, asphaltene and sulfur content improves the quality and value of oil. The three-step sequential extraction from Nigerian oil sand samples by supercritical carbon dioxide (SC-CO2) was carried out by the addition of ethanol, isopropanol, fresh water and salty water as co-solvents at (50, 60 and 65) MPa and 110°C. The objective of this work was to increase both the recovery and the quality of the extracted liquid oil product. The change in color of the oil samples from black to orange observed after extraction could be attributed to the reduction in coke and asphaltene contents of the oil. The total oil recovery varied from 27% by pure carbon dioxide to 73.3% with the addition of salty water. Addition of water in the amount three times more than of ethanol facilitated similar or higher liquid recovery. The composition of oil samples gets heavier after each subsequent step while pressure has a lower effect as observed from the changes of refractive indices. Total sulfur content in extracted oil samples was reduced significantly up to (0.6–1.1) % compared to its content in the crude bitumen of 1.95%.
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