Role of the Composition of Cyclohexane-extracted gangue on its drying at ambient conditions

• Author / Creator

  Khalkhali, Reza

• Non-aqueous extraction (NAE) of bitumen from oil sands has recently regained interest as a replacement for the commercial, water-based extraction method. NAE has the potential to alleviate all the current water-induced extraction challenges such as high fresh water consumption, high heat consumption and carbon emissions, and the issue of ever-growing tailing ponds. Recovery of solvent from the “gangue,” the mixture of solids, connate water, residual bitumen, and residual solvent (cyclohexane in this study) after the extraction, is the biggest environmental and economical challenge of NAE.
  Drying of the gangue, like any other porous materials, consists of two general stages: the initial cyclohexane-dominated stage with a fast, constant, and linear drying rate and the final water-dominated stage which is almost an order of magnitude slower compared to the initial stage. The fast, constant drying rate of the initial stage is due to the presence of “liquid cyclohexane film flow” which occurs in the corners of pores as a result of capillary forces being dominant over viscous and gravity forces. The dominance of capillary forces is also demonstrated in this work through the estimation of capillary and Bond numbers developed for a square pore channel.
  The initial stage of drying consists of two processes: liquid transfer by film flow to the top surface of the drying bed and evaporation through a diffuse layer from the surface. Measurements of evaporation flux showed that it is much slower (approximately two orders of magnitude) than the film flow rate which is estimated using a model developed for a square pore channel.
  To study the effect of gangue’s composition on its initial drying rate, different sets of gangue samples with controlled compositions were artificially prepared and they are called “reconstituted gangue.” Drying of various reconstituted gangue samples with different bituminous carbon (Bit.C), water, and fine solids (solid particles <45µm) content were studied. Moreover, to further investigate the role of water on cyclohexane liquid film formation, the drying of different samples with 1 M solution of NaCl as well as n-butanol instead of water were also studied. The effect of each component on the initial drying rate was explained by its effect(s) on the film flow rate.
  Increasing Bit.C content from 0.0 to only 1.0 wt% remarkedly decreased the initial drying rate (more than 30%) by increasing the viscosity of cyclohexane/bitumen solution. Bitumen can also significantly contribute to cyclohexane retention by absorbing an equilibrium concentration of cyclohexane.
  Increasing water content from 6 to 12 wt% significantly slowed down the initial drying stage by more than 60%, while completely removing water also resulted in slower initial drying rate compared to samples with 3.88 and 6.0 wt% water. The role of water was explained by looking into the pore saturation by water and cyclohexane. Water content higher than a certain amount starts to fully cover the solid’s surface, not allowing the formation of cyclohexane liquid films. Moreover, the lower initial drying rate as a result of removing water can be related to a cyclohexane liquid film with a lower average thickness. Moreover, adding NaCl to water had almost no effect on drying. However, replacing water with n-butanol resulted in a much slower initial drying rate. Like the effect of bitumen, this was attributed to the reduction in viscosity due the miscibility of n-butanol and cyclohexane.
  Increasing fines content had no significant effect on the initial drying rate. This was unexpected since samples with higher fines content have a smaller mean pore size and thus were expected to show a lower initial drying rate. However, the samples with higher fines contents showed higher hydrophobicity and consequently, higher affinity to cyclohexane which is in favor of film flow rate. Higher hydrophobicity of samples with higher fines is attributed to the much higher carbon content of fines compared to that of coarse solids.

• Subjects / Keywords

  • oil sands
  • solvent extraction
  • liquid film
  • gangue
  • solvent recovery

• Graduation date

  Spring 2020

• Type of Item

  Thesis

• Degree

  Master of Science

• DOI

  https://doi.org/10.7939/r3-6wqn-4481

• License

  Permission is hereby granted to the University of Alberta Libraries to reproduce single copies of this thesis and to lend or sell such copies for private, scholarly or scientific research purposes only. Where the thesis is converted to, or otherwise made available in digital form, the University of Alberta will advise potential users of the thesis of these terms. The author reserves all other publication and other rights in association with the copyright in the thesis and, except as herein before provided, neither the thesis nor any substantial portion thereof may be printed or otherwise reproduced in any material form whatsoever without the author's prior written permission.