(242e) Solvent Extraction for Bitumen Recovery from Oil Sands Ores

Unconventional oils, including oil/tar sands, shale oil, heavy oil, etc., have been considered as an alternative of traditional crude oils due to their huge reserves (about two thirds of the total oils) buried around the world. It is estimated that there are about 1700 trillion barrels of bitumen contained in the oil sands ores in Alberta, Canada(Chew, 2014; Gray et al., 2009). To release this kind of petroleum, hot water-based extraction (HWBE) has been proposed and applied in industry which creates large volumes of wet tailings with fine solids. To avoid this environment pollution, the solvent extraction has been attracting increasing attention from industry due to its high extraction efficiency, less water and energy consumption, and high compatibility for different kinds of ores.

In the present study, solvent extraction of oil sands has been investigated using pure organic solvents, including toluene, tetrahydrofuran (THF), cyclohexane, n-heptane, n-hexane, ethyl acetate, and etc. Results of bottle tests showed that the bitumen recovery increased with the increase of the number of carbon and the cyclic hydrocarbons (toluene, THF and cyclohexane) performed better than alkane hydrocarbons (n-heptane, n-hexane, ethyl acetate and acetone). To analysis the bitumen in the extracted phase more detailedly, it has been divided into four fractions, named as saturates, aromatics, resins, and asphaltenes (SARA). Results show that increasing the aromaticity of the solvent is beneficial for the recovery of heavy fractions (e.g., resins and asphaltenes) of bitumen from the oil sands.

To further explore the solvent extraction process, solubility simulation in COSMOtherm software was applied and four typical molecules were selected as the representatives of SARA. A similar trend of bitumen recovery with different solvents was obtained as an order of: THF â?¥ toluene > cyclohexane > n-heptane > n-hexane > ethyl acetate. Firstly, the efficiency of solvent extraction is found to be highly dependent on the polarity of the solvent. The solvents with too low (i.e. n-hexane and n-heptane) or too high (i.e. acetone and methanol) polarity had a poor solubility to bitumen. The polarity of the solvent will cause certain effect to the bitumen recovery because some special polar groups (i.e. groups containing oxygen, nitrogen, sulfur, and etc.) affected the properties of bitumen components. Secondly, the enhancement of solvent aromaticity makes the recovery of aromatics, resins and asphaltenes increase. The reason for these may be that the heavy bituminous constituents contain aromatic or cyclic structures. From the solubility point of view, the more similarity of microstructure between bitumen components and solvent, the more bitumen was recovered. Finally, after careful analysis, it is found that the dispersion force of the solvent plays a dominate role (weight > 55%) in dissolving bitumen fractions, followed by hydrogen-bonding force (weight at 0~26%) and polar force (weight at 0~18%). This finding allows us to consider more detailed influence factors when selecting the potential solvents for bitumen recovery process and solubility simulation may be a relatively efficient and accurate previous prediction of solvents screening.

Accordingly, the solvent extraction process would be a promising method for the recovery of unconventional oil from the ores. This study would improve the knowledge base for bitumen recovery mechanism and serve for future work on the solvent extraction technology applications.

References:

Chew, K.J., 2014. The future of oil: unconventional fossil fuels. Philos Trans A Math Phys Eng Sci 372, 20120324.

Gray, M., Xu, Z., Masliyah, J., 2009. Physics in the oil sands of Alberta. Phys. Today 62, 31-35.