Recovery of Bitumen by Vacuum Pyrolysis of Alberta Tar Sands

A bench-scale study was undertaken to investigate the potential of vacuum pyrolysis for the production of upgraded bitumen from Alberta tar sands. Vacuum pyrolysis limits the secondary decomposition reactions which results in high yield of transportable oil and low yield of gas. The objectives of this study were (i) to study the influence of the reaction conditions on the nature of the bitumen, and (ii) to gain some insight into the asphaltene decomposition and recovery of bitumen from tar sands. A batch of 3 kg of tar sands was heated to 500 °C under a total pressure of 1 kPa. The oil yield was 10.8% by wt. CO2 (the most abundant), CO, H2S, and CH4, and C2−C8 hydrocarbons were the major pyrolysis gases produced during pyrolysis. Elemental analysis was conducted to gain further insight into the composition of each fraction. The pyrolysis oil was deasphalted and yielded about 97.8% by wt of maltene. Maltene fractions from both Soxhlet extracted and pyrolysis bitumens were separated into various fractions by column chromatography, analyzed, and compared. The distribution of n-alkanes, n-alkenes, and triterpenoid hopanes was interpreted in terms of biological markers. Potential merit of the vacuum pyrolysis concept over other extraction techniques was also discussed. Significant differences were observed in the distribution of various maltene components obtained from the Soxhlet extraction and pyrolysis bitumens. The pyrolysis-derived maltene had a lower viscosity than the Soxhlet-derived maltene. A 13% naphtha fraction was obtained after distillation of the pyrolysis maltene. The absence of n-alkanes indicated the biologically degraded oil source.