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Role of Fine Solids in Solvent Recovery from Reconstituted Alberta Oil Sands Gangue Open Access


Other title
Non-aqueous extraction
Oil sands
Fine solids
Solvent recovery
Type of item
Degree grantor
University of Alberta
Author or creator
Ejike, Lawrence I
Supervisor and department
Dr Phillip Choi, Chemical and Material Engineering
Examining committee member and department
Dr Qi Liu, Chemical and Material Engineering
Dr Lianne Lefsrud, Chemical and Material Engineering
Department of Chemical and Materials Engineering
Chemical Engineering
Date accepted
Graduation date
2016-06:Fall 2016
Master of Science
Degree level
Non-aqueous solvent extraction of bitumen from oil sands has the potential to replace the existing hot-water extraction process. The benefit of non-aqueous extraction process includes high bitumen recovery, reduction of fresh water demand for extraction and the elimination of resulting tailing ponds associated with the use of water. Other advantages include a significant reduction in energy consumption as well as greenhouse gas emission that are associated with ozone depletion and global warming. In the non-aqueous extraction process, bitumen is recovered from the ore using an organic solvent, leaving behind a gangue (solid waste) that contains residual bitumen, solvent, and water initially present in the ore. Despite its numerous advantages, a major limitation to NAE process is in minimizing the loss of solvent to the gangue. Recovery of solvent from the gangue is important to the economics of the non-aqueous extraction process and for environmental impact. Solvent recovery from the gangue involves a drying process in which the volatile solvent is evaporated from the porous gangue matrix in the presence of the water. Fine solids in oil sands are known to have a detrimental effect on water-based extraction. Their role in non-aqueous extraction process has not been fully investigated. In this study, we examine the effect of fine solids content on the recovery of solvent from the gangue. Results from the compositional analysis of extracted gangue revealed that the composition of the gangue varies with each extraction. This presented a challenge to studying the interaction of solvent with other gangue components. A proper analysis of the effect of gangue components on solvent recovery from the gangue required well-defined parameters and a systematic control of the gangue composition. As such, a protocol was developed to make synthetic sample (reconstituted gangue) whose drying behaviour (fluid transport mechanism) simulated that of the extracted gangue. The reconstituted gangue was important as samples whose composition could be controlled to enable analysis and a definitive assessment of the effect of the components on solvent recovery from the gangue. Thus, the reconstituted gangues served as perfect substitutes for the extracted gangue. Rich-grade solids (10% fines) and Low-grade solids (~20% fines) were used to prepare reconstituted gangue containing (i) 12% cyclohexane and (ii) 12% cyclohexane and 3.7 %* water (solvent free basis). Drying experiments were conducted on the samples in a fume hood at ambient temperature and pressure. All the drying experiments for samples containing only cyclohexane displayed a two stage drying process, with a fast initial rate drying stage and second slower drying stage. The first stage corresponded to the stage 1 evaporation of the solvent, in which liquid films maintain capillary connectivity to the external surface. In the slower second stage, liquid films had receded below the surface, and mass transfer occurred by diffusion within the porous media. For samples containing water, a third stage dominated by water diffusion followed the solvent-dominated drying stage. A comparison of drying curves for samples with similar liquid composition revealed that solvent removal was slower in low-grade samples compared to rich-grade samples. The particle size distribution and wettability of gangue solids were analyzed, and it was found that fine solids are more hydrophilic than coarse solids for each gangue. The effect of particle size distribution and wettability of solids of solids on the drying of porous media was investigated. Further experiments were performed for reconstituted gangue containing (i) 12% cyclohexane and (ii) 12% cyclohexane and 3.7% water (solvent free basis) for 0%, 10%, and 20% fines solids in each gangue grade. Results indicated that wettability of the fine solids had a dominant role on the drying of the gangue. An increase in fine solids content corresponded to a reduction in the solvent recovery and thus, an increase in solvent retention.
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