Gravimetric Study of Cyclohexane Transport in Nanoscale Bitumen Films

• Author / Creator

  Kislitsin, Vadim

• In view of the increasing environmental concerns about the current water-based bitumen extraction process, there have been numerous efforts to develop a non-aqueous extraction (NAE) method for the recovery of bitumen from oil sands. The research reported in this thesis was carried out to study the fundamentals of the NAE process with the hope of obtaining a better understanding of the solvent recovery step.
  Firstly, the initial estimation of the bitumen contents adsorbed on the residual solid particles made up of sand and clay was made and it was found that the bitumen film thickness appeared to be in the range of 10 to 102 nm (i.e., nano-scale films). Then, the decision to recreate the gangue with controlled composition was made, first with the glass particles of a single size and then by adding fine clay particles. In the first experimental study, the mass uptake of cyclohexane vapor by three different samples at two different relative saturations was evaluated. The gravimetric data from three samples (the two mentioned above and one actual residual solids sample) was collected, the shape of mass uptake curves was analysed, and the equilibrium solvent concentrations and initial stage diffusion coefficients were calculated. Comparison of the mass uptake curves to different models was made and it was found that the double-first-order kinetics model fits the experimental data best, which suggested that there are two (at least) different mechanisms with different rate constants involved in the uptake and transport of cyclohexane in bitumen. Also, it was observed a linear positive thickness dependence of diffusion coefficient on the bitumen film. The equilibrium concentration of cyclohexane was higher for the higher cyclohexane relative saturation in the carrier gas but did not significantly depend on the film thickness. Owing to the heterogeneous chemical nature of the bitumen films (each film is composed of different types of molecules with different polarities), there existed a gradient of polar and nonpolar molecules established prior to the cyclohexane uptake.
  In the substrate properties study, two types of samples were considered. Both had the same large particle size distribution as the actual residual solids after bitumen extraction, while the fraction of fine particles varied from 5 to 20 wt%. One sample was made up only of glass spherical particles, while the other was made up of glass spherical particles with a fine fraction made up of kaolin clay particles with an irregular shape. It turned out that the chemical composition of the substrate significantly affected the initial rate of relative mass uptake. The rate of initial mass uptake exhibited a negative film thickness (bitumen content) dependence. The diffusion coefficient values were lower for the particles with a higher fine particle content due to a decreased thickness. The rate of initial mass uptake was not affected by this parameter.
  Lastly, the mass uptake and mass release processes were compared. The same samples as in the first two set of experiments were made. The absorption rate was observed to be up to two times faster than that of the desorption rate. The absorption rate exhibited a linear negative film thickness dependence, while for the desorption process this negative dependence was exponential. The diffusion coefficient values had a positive linear thickness dependence in all the cases and were higher in the absorption than in the desorption experiment. One interesting observation was that in the early stages of the desorption experiment, mass uptake rather than mass release was observed in the early stage of the process. The data show that this unexpected phenomenon would probably occur in the case of nanoscale bitumen films.

• Subjects / Keywords

  • mass transport
  • cyclohexane
  • diffusion
  • oil sands
  • desorption
  • Absorption
  • nonofilm

• Graduation date

  Fall 2020

• Type of Item

  Thesis

• Degree

  Doctor of Philosophy

• DOI

  https://doi.org/10.7939/r3-jtxh-1d64

• License

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