Distribution and Diffusion of Sara Fractions in Bituminous Layer of Athabasca Oil Sands: Instrumental Measurements and Molecular Dynamic Simulation
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The bitumen liberation and recovery of oil sands have been well known affected , to some extent , by the bitumen physical properties , especially the surface properties , such as the interfacial tensions. Previous research showed that the interfacial tension of bitumen-water system was dependent on the composition of the bitumen (Mehrotra et al. , 1985). Therefore , the understanding of the composition of the surface materials on the sand grains is important and necessary for the oil sands processing and technology improvement. In this study , a conceptual model was proposed to illustrate the composition and distribution of SARA (saturate , aromatic , resin and asphaltenes) fractions in the bituminous layer on the surface of Athabasca oil sands , which was verified by elemental analysis , X-ray photoelectron spectroscopy , field emission scanning electron microscopy with energy dispersive spectrometer , and Fourier-transformed infrared spectrometer. The contents of S , N , and the ratios of C/S and C/N were characterized as potential indicators for evaluating the distribution of SARA fractions in the bituminous layer. The results indicated that the light fractions such as saturates tend to deposit at the outer bituminous layer , while the asphaltenes and resins were inclined to distribute at the inner layer. It is also suggested that the distribution of SARA fractions was thermodynamic dependent and was susceptible to thermal treatment. These findings came to support our simulation results with molecular dynamic (MD) simulation (Wu et al. , 2013). Results of simulation showed the sorption of saturates on quartz decreased by 31% when temperature increased from 298 to 398 K while opposite trend was observed for resins , but insigniﬁcant changes were found in asphaltenes and aromatics. It was found that the main contribution of interactions was van der Waals energy (>90%) irrespective of molecular components and temperatures. The diffusion coefﬁcient of saturates was predicted as10.8×10-10 m2s-1 while that of the remaining fractions was about 4×10-10m2s-1at 298 K. This work provides experimental evidences and simulation supports for validating the distribution patterns of SARA fractions on the surface of Athabasca oil sands. The proposed distribution model is expected to serve a basis for future studies on the liberation of bitumen from oil sands and the operation conditions for oil sands processing , especially for the solvent extraction and water-based extraction with chemical addition prior to the extraction. Also , it will provide insights to understand the oil remediation in oil fields or oil polluted fields.