On the determination of diffusivities of volatile hydrocarbons in semi‐solid bitumen

Abstract

Residual volatile hydrocarbons in bitumen constitute a potential source of air pollution. Diffusivities of volatile components in bitumen are needed to assess the extent of environmental damages that could result from bitumen spill or working loss of vapour to the atmosphere. Knowledge of solvent dispersion is also required in the recovery of viscous bitumen by solvent displacement. This paper discussed the de‐coupled transfer model developed by Tang and Zhang and its limiting solution. Fu and Phillips' diffusion data were re‐interpreted based on the limiting solution with delay time correction. The diffusion coefficients of hexane iso‐hexane, cyclo‐hexane and toluene at 25°C were found to be 8.6 × 10−8 cm2/s, 6.3 × 10−8 cm2/s, 2.4 × 10−8 cm2/s and 6.8 × 10−8 cm2/s, respectively. Improper use of the limiting solution could lead to 25% over‐estimates of diffusion coefficients.

Critical review of mutual diffusion coefficient measurements for liquid solvent + bitumen/heavy oil mixtures

“…Consequently, the value of mutual diffusion coefficients is strongly dependent on the composition and spatial resolution of such profiles, forcing many researchers to smooth composition profiles before analysing them. 1.25 Average value (SOR ¼ 20%) [10] Athabasca bitumen 295 17 AE 4 1 0 -90% by mass solvent [13] N-hexane bitumen: m ¼ 56.5 Pa s @ 295.15 K 296.15 AE 1.5 1.07 Solvent finite dilution [3] bitumen: m ¼ 56.5 Pa s @ 298.15 K 296.15 AE 1.5 0.086 Solvent finite dilution [16] Cold Lake: m ¼ 130 Pa s @ 298.15 K 303.15 83.2 Average value (SOR ¼ 20%) [9] heavy oil: m ¼ 12 Pa s @ 298.15 K 295.15 AE 2 35.2 Average value (SOR ¼ 72%) [12] Cold Lake: m ¼ 130 Pa s @ 298.15 K 303.15 (?) Incorporation of density changes in calculations of mutual diffusion coefficients appears to be of little importance with respect to concentration dependency.…”

“…4. 1.62 Average value (SOR ¼ 20%) [10] heavy oil: m ¼ 6 Pa s @ 298.15 298.15 4-85 $0-80% by volume solvent [14] N-heptane bitumen: m ¼ 56.5 Pa s @ 295.15 K 296.15 AE 1.5 1.07 Solvent finite dilution [3] bitumen: m ¼ 56.5 Pa s @ 298.15 K 296.15 AE 1.5 0.086 Solvent finite dilution [16] Cold Lake: m ¼ 130 Pa s @ 298.15 K 303.15 83.2 Average value (SOR ¼ 20%) [19] heavy oil: m ¼ 12 Pa s @ 298.15 K 295.15 AE 2 35.2 Average value (SOR ¼ 72%) [12] Cold Lake: m ¼ 130 Pa s @ 298.15 K 303.15 (?) More accurately, at later diffusion times where density gradients are low, Equation (14) can be safely employed, provided that the gradients are experimentally detectable outside the error of measurement.…”

“…Tang [16] also re-examined the original data of Fu and Phillips [3] to find the source of the error that had caused the shift from the origin. By converting the reported experimental run-times of Fu and Phillips [3] to dimensionless times, they found that the concentration measurements were truly in the linear late-time region; therefore, the shift from the origin was due to the delay time, or time-lag error.…”

“…He found the delay times (t) for each experiment through a trial-and-error regression procedure, as they were not measured by Fu and Phillips. Reproduced from Reference [16] Copyright 2001, with permission from Wiley. ffiffi t p plot for hexane.…”

Propagation of Phenol in Aquifer With Reversible Adsorption

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Previous study [1][2][3] indicated that phenol transport from spilled bitumen into flowing aquifer was controlled by slow molecular diffusion of phenol in bitumen as the ratedetermining step. This simplified de-coupled transfer mechanism has led to a 2 dimensional planar flow analytical solution, which described the time-dependent phenol concentration in a flowing stream 4 .

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