Application of dynamic supercritical fluid extraction to the recovery and upgrading of complex hydrocarbon mixtures

A supercritical fluid extraction system was used to study the extraction of hexadecane, a paraffinic crude oil, a bitumen-derived liquid and the native Whiterocks bitumen with solvents such as C02 and propane. The hexadecane-C02 experiments were intended to refine experimental procedures and to ascertain attainment of thermodynamic equilibrium during extraction. The amount extracted and compositions of the extracted phases were monitored continuously to determine the nature of the extract and residual fractions as the extraction proceeded. The compositions of the feedstocks and selected extract fractions were determined by simulated distillation and gas chromatography-mass spectrometry. Carbon dioxide was used as a solvent for the extraction of all three feedstocks. Propane was used as a solvent with the bitumen-derived liquid and native bitumen. In general, the propane yields were significantly higher than the C02 yields. The influence of three process variables- extraction time, pressure and temperature- was investigated. As the pressure increased at constant temperature for the paraffinic crude and the native bitumen, the amount extracted increased and relatively heavier compounds were extracted. The nondiscriminatory extraction of the bitumen-derived liquid was attributed to the presence of olefins and aromatic moieties. The extractions were most efficient in the vicinity of the critical temperatures of the solvents. The residual fractions produced when the native bitumen was extracted with propane contained more asphaltenes (pentane-insolubles) than the original feedstock. The asphaltene content of the residual fractions increased with pressure and in the vicinity of the critical temperature. Thus the co-solubilizing lighter compounds (which were extracted) have a profound influence on the "asphaltene" content of complex hydrocarbon mixtures. The results from the extraction of the native bitumen with propane indicated the upgrading potential of the solvent extraction process and provided insight to the use of propane as an additive in the in-situ recovery of oil sand bitumen. The compositions were predicted using the Peng-Robinson equation-of-state and a component lumping procedure for selected data sets. The agreement between experimental and calculated data was reasonable considering the uncertainties involved in modeling such complex processes.