Effect of Supercritical Water on Desulfurization Behavior of Oil Sand Bitumen

The desulfurization behavior of oil sand bitumen in supercritical water (SCW) was examined to evaluate the possibility of desulfurization using SCW. Athabasca bitumen was treated with water, nitrogen, or toluene at 430-450 °C and 23-30 MPa using a batch autoclave. SCW showed the same trends in sulfur content, liquid and coke yields as high-pressure nitrogen. Furthermore, liquid products obtained using SCW had the same distributions of sulfur-containing compounds as high-pressure nitrogen and showed no specific results, whereas supercritical toluene was involved in desulfurization as a reactant. However, the reaction media influenced the sulfur distribution to coke with the variations of desulfurization ratio and sulfur conversion: that using SCW was higher than using toluene and lower than using nitrogen. SCW showed dispersion effect against the desulfurization reaction, whereas toluene showed radical scavenging and dispersion effects. The dispersion of reactant enhances intramolecular dehydrogenation and keeps the product toluene-soluble rather than coke. Because SCW retained heavy fraction as liquid product than high-pressure nitrogen, the desulfurization of bitumen using SCW was not evaluated to be practically promising.