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 50 g piece of tar sand was carried out at 50, 60 and 65 MPa and 110 °C by pure carbon dioxide and with the addition of 10 mL 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 50 MPa with the addition of salty water declining at higher pressures. The heaviest fractions were extracted by pure carbon dioxide at 60 and 65 MPa. 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.