Solvent Extraction of Bitumen from Oil Sands

In the present study, solvent extraction of bitumen from Xinjiang oil sands was investigated using solvents, such as alkanes, toluene, and chloroform, and mixed solvents, such as n-hexane ethyl acetate and cyclohexane methyl ethyl ketone (MEK). The n-heptane asphaltene content in the extracted bitumen was measured by saturate, aromatic, resin, and asphaltene (SARA) analysis, and the average molar mass of asphaltene was tested by vapor pressure osmometry (VPO). The average molar mass of asphaltene was 2850, and the calculated Hansen solubility parameter (HSP) of asphaltene was 20.1 MPa1/2. The operating conditions were well-investigated using cyclohexane as the extraction solvent, and the effect of the volume fractions of the mixed solvents on bitumen recovery was studied. The extraction processes were most appropriate at a stirring velocity of 500 revolutions/min for 30 min at a temperature of 50-60 degrees C using a ratio of cyclohexane/oil sands of 5:3 (mL/g) based on a high bitumen yield and low extraction cost. Under such conditions, bitumen recovery of about 75% was obtained for cyclohexane extraction, comparable to that of naphtha (78%). Considering the bitumen yield and extraction cost, the appropriate volume fractions of polar solvents were found to be at 0.33 and 0.2 for n-hexane ethyl acetate and cyclohexane MEK extractions, respectively. On the basis of the above research and theoretical analysis, a solvent with a high solubility parameter close to that of asphaltene and a parameter distribution close to that of toluene is appropriate for the bitumen extraction of Xinjiang oil sands. The specific parameters were about 18.0-19.0 MPa1/2 for HSP, 65-92 for the dispersion force parameter fraction (f(d)), 0-15 for the polar force parameter fraction (f(p)), and 4-22 for the hydrogen-bonding force parameter fraction (f(h)). The asphaltene content in the extracted bitumen generally has a positive relationship with the bitumen recovery, which is likely due to the mechanism that it is the extracted fuel oil and not the solvent that extracts the asphaltene into the solvent phase.