SUPERCRITICAL-FLUID EXTRACTION OF BITUMENS FROM UTAH OIL SANDS

The supercritical fluid extraction (SFE) of bitumens from four major U inta Basin (Utah) oil sand deposits was studied with propane solvent. The deposits studied included Whiterocks, Asphalt Ridge, PR Spring and Sunnyside. The bitumens from these deposits differed widely in physic al and chemical properties. The volatilities (components with boiling point < 811 K) were 46.6, 53.5, 45.4 and 40.9 wt.%; the molecular weig hts were 653, 426, 670 and 593 kg/kg mel; and the asphaltene contents (n-pentane insolubles) were 2.9, 6.8, 19.3 and 23.6 wt.% for the White rocks, Asphalt Ridge, PR Spring and Sunnyside bitumens, respectively. The SFE experiments were carried out at five conditions, combinations of three different pressures (5.6 MPa, 10.4 MPa, and 17.3 MPa) and thr ee temperatures (339 K, 380 K and 422 K). The cumulative extraction yi eld increased with increase in solvent density at all operating condit ions for the four bitumens. A maximum yield of 45 wt.% was obtained at the highest solvent density with the Whiterocks bitumen. The extracti on products were significantly upgraded liquids relative to the bitume ns. Comparatively lighter fi actions were extracted in the earlier sta ges of extraction for all the four bitumens, whereas heavier extracts were obtained at higher extraction-solvent densities. The asphaltene c ontents of the residual fractions were significantly higher than the a sphaltene contents predicted on a prorated basis for all four bitumens . This trend was due to the extraction of cosolubilizing components th at kept the asphaltenes in suspension in the bitumen. It was concluded that solute polarity played a significant role in the extraction yiel ds of the four bitumens. The Whiterocks bitumen, which was the least p olar bitumen based on asphaltenes content, gave higher extraction yiel ds compared to the bitumens from the other three deposits at all five operating conditions. The Sunnyside bitumen with the highest asphalten e content gave the lowest extraction yield at all five conditions. The Asphalt Ridge and PR Spring bitumens with intermediate polarity (base d on asphaltene content) gave intermediate extraction yields with the Asphalt Ridge bitumen extraction yields higher than the PR Spring bitu men. Preliminary modeling of the extraction process using the Peng-Rob inson cubic equation of state and a pseudocomponent lumping scheme pro vided a reasonable match with the experimental data for Whiterocks and PR Spring bitumens. (C) 1998 Elsevier Science B.V. All rights reserve d.