Effect of solvent-to-bitumen ratio on the pyrolysis properties of precipitated athabasca asphaltenes

The first stage in the conventional hot water process for extracting bitumen from mined oil sand produces a bitumen froth containing substantial amounts of emulsified water and fine solids. Dilution of the froth with a sufficient quantity of a paraffinic solvent, such as hexane, causes the aggregation and rapid settling of water droplets, solid particles, and precipitated asphaltenes. The fraction of asphaltenes precipitated from the bitumen increases with the solvent-to-bitumen ratio (SIB). This paper reports the results of thermogravimetric measurements of asphaltenes precipitated from Athabasca bitumen using hexane at SIB values ranging from 1.1 to 3.5. For all samples, approximately 60 wt % of the hydrocarbons was volatilized below 525 degrees C, and most of the remainder was transformed into coke. Pyrolysis-gas chromatography and photoacoustic Fourier transform-infrared spectroscopy support the conclusion that varying SIB does not greatly alter the chemical composition of the precipitated asphaltenes and their pyrolytic products.