Upgrading and extraction of bitumen from Nigerian tar sand by supercritical carbon dioxide

The current experimental study describes the recovery of bitumen from Nigerian tar sand by the supercritical carbon dioxide method, which has the advantages of a substantial reduction in water consumption, an absence of chemicals, and an upgrading of the bitumen through the rejection of solids, petcokes and asphaltenes. The bitumen extraction from 50g piece of tar sand was carried out at 50, 60 and 65MPa and 110°C by pure carbon dioxide and with the addition of 10mL of fresh or salty water. The recovery decreased in the following order: with salty water, with fresh water, pure CO₂. The maximum recovery of 29.6% was obtained at 50MPa with the addition of salty water declining at higher pressures. The heaviest fractions were extracted by pure carbon dioxide at 60 and 65MPa. The presence of bisnorhopane, a biomarker typical for source rocks formed in marine depositional environment, was detected in crude bitumen and all extracts by GC-MS TIC analysis.