Recovery of Cyclohexane from Oil Sands Gangue Using Microwave: Influence of Fine Particles

Abstract

The extraction of bitumen from oil sands using non-aqueous extraction (NAE) techniques has the potential to replace currently used water-based extraction techniques. High bitumen recovery rates, lower freshwater requirements, and elimination of afterward tailing ponds are all advantages of non-aqueous extraction. Other benefits include a significant reduction in energy use and greenhouse gas emissions related to global warming and ozone depletion. Using an organic solvent, bitumen is extracted from the oil sands ore during the nonaqueous extraction process, leaving behind a mixture of coarse and fine solids containing water, residual bitumen, and residual solvent (cyclohexane in this study), or “gangue”. Regardless of its numerous advantages, a significant environmental and economical drawback of the NAE method is the removal of solvent from the gangue post extraction. A well-defined procedure to control the gangue composition was necessary in order to accurately analyze the impact of gangue components on solvent recovery from the gangue. Reconstituted gangue samples were prepared to create a synthetic sample whose drying behavior represented that of the non-aqueous extraction gangue. The utilization of reconstituted gangue was necessary because it represented samples whose composition could be precisely controlled for analysis. This research demonstrated the effect of varying the content of fine particles at constant residual bitumen, water, and cyclohexane contents on the removal of cyclohexane from reconstituted gangue using two different solvent removal mechanisms: microwave-only in and air-drying followed by microwave. Heat was generated internally within the reconstituted gangue during the microwave experiment upon the interaction of the dipolar molecules with microwave radiation. iii For reconstituted gangue samples undergoing only microwave heating, cyclohexane required more time to go through phase change, regardless of fine particles content. The temperature at which cyclohexane underwent phase change was significantly depressed for all samples undergoing microwave heating for all contents of fine particles. There was no apparent difference between the duration of cyclohexane evaporation in samples with 10% and 20% fine particles. The time required for cyclohexane to be removed from the gangue becomes independent of fine particles content at increased contents of fine particles. The maximum temperature reached by the Soxhlet solids remained unchanged for gangue samples with 10 wt.% fine particles but somewhat increased upon the addition of 20 wt.% fine particles, relative to samples containing 0 wt.% fine particles. For reconstituted gangue samples undergoing air-drying prior to microwave heating, the duration at which cyclohexane underwent phase change reached its maximum at 10 wt.% fine particles content. This duration was similar for samples containing 0 wt.% and 20 wt.% fine particles. The temperature at which cyclohexane underwent phase change was comparable to cyclohexane’s normal boiling point for all contents of fine particles. The duration of cyclohexane evaporation in reconstituted gangue samples containing 10% and 20% fine particles was doubled and tripled, respectively, relative to reconstituted gangue samples containing no fine particles. The time required for cyclohexane to evaporate from the reconstituted gangue significantly increases at increased contents of fine particles. The average maximum temperature reached by the Soxhlet solids was independent of the content of fine particles. Finally, fine particles accelerated the recovery of cyclohexane using microwave and lowered the evaporation onset temperature.