Sorption equilibrium and kinetics for cyclohexane, toluene, and water on Athabasca oil sands solids

Abstract

The sorption of solvents from the vapour phase to solid substrates is important in producing heavy oil and bitumen, particularly from the oil sands. We investigated the sorption and desorption equilibrium and kinetics of cyclohexane, toluene, and water on kaolinite, fine solids, and organic‐rich fine solids isolated from Athabasca oil sands over a wide range of solvent vapour concentrations using a gravimetric method. The isotherms for both adsorption and desorption of solvent vapour were determined, and the Brunauer‐Emmett‐Teller equation was used to fit the experimental data. The initial kinetic rate constants for the adsorption and desorption of solvent vapour were determined with the linear driving force model. The results were compared and discussed in terms of the type of solvent, the content of organic materials, and the surface area of the solid substrates. The results suggest that, in addition to the adsorption of solvent on mineral surfaces, the contribution from solvent partitioning in the organic materials and the porosity resulting from high amounts of organic materials are significant factors for solvent uptake and kinetic rate constants. In mixed solvent vapours, the competitive sorption of water and cyclohexane was observed in the solid substrates. However, the degree of competitiveness decreased with an increase in the content of organic materials in the substrates.

Solvent removal from cyclohexane‐extracted oil sands gangue

“…At low relative humidity, most of the water evaporates, while at 90 % relative humidity about 2/3 of the water is removed after 60 min. All of the water concentrations reported in Figure are well above equilibrium levels, based on the data of Tan et al, ranging from 1.5 times the equilibrium concentration at 40 % relative humidity to 6 times at 90 % relative humiduty. Despite the higher vapour pressure of cyclohexane, its residual concentrations did not drop significantly as the water evaporated.…”

“…Interestingly, in the second stage, the average drying rate of cyclohexane (∼1.7 mg/kg/min) is much lower than the average drying rate of water (470 mg/kg/min, from total sample mass loss between 20 and 70 min at 30 % RH in the fume hood). All of the residual cyclohexane concentrations in Table and Figure are far in excess of equilibrium levels, based on the desorption isotherms reported by Tan et al for oil sands solids. Even if all of the mass loss at 20 min of drying (Figure ) was due to cyclohexane, the concentration in the vapour phase would be so low that the equilibrium concentration in the gangue would be ∼3 mg/kg.…”

Recent Advances in Nonaqueous Extraction of Bitumen from Mineable Oil Sands: A Review

“…Also, the increase of cation exchange capacity and layer charge density was reported to increase both the clay–organic interactions and the amount of organics retained. The results suggested a role for clays in enhancing solvent retention by trapping solvent in the adsorbed bitumen components and a correlation between solid surface characteristics and the amount of organics retained. − …”

“…Although fines are a minority constituent, they have high surface-to-volume ratios and retain organic materials (e.g., residual bitumen), making solvent recovery problematic. A couple of studies observed that solvent vapor had a higher sorption rate and quantities on bare kaolinite than on bare quartz sand, due the larger specific surface area of kaolinite compared to quartz. − Osacky et al stated that the nonswelling clays retained 20–58% of solvent-insolvable organic materials of the total content, mainly on the basal planes and edges of clays in the form of patches . The amount of organic materials retained after extraction and solvent removal from the tailings correlated well with specific surface area of clays.…”

“…Tan et al reported a more remarkable solvent sorption capacity on bitumen- or asphaltene-coated fine solids than on the virgin fine solids. High bitumen residue content produced decreased sorption and desorption rate due to solvent partitioning into the organic component . In addition to the residual bitumen, the interaction between the potential solvent and bitumen should be considered.…”