Calculation of diffusion coefficients for aqueous organic species at temperatures from 0 to 350 °C

Details Calculation of diffusion coefficients for aqueous organic species at temperatures from 0 to 350 °C Calculation of diffusion coefficients for aqueous organic species at temperatures from 0 to 350 °C

Dec 1991

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1991gecoa..55.3515o&link_type=abstract

Geochimica et Cosmochimica Acta, vol. 55, Issue 12, pp.3515-3529

Computer Science

1

Scientific paper

Evaluation of hydrocarbon transport through the pore spaces of saturated rock in the subsurface as a function of time and distance requires accurate values of diffusion coefficients for aqueous organic species. Analysis of aqueous tracer diffusion coefficients ( D 0 ) for normal alkanes, alcohols, amides, carboxylic acids, alkylbenzenes, and alkylnaphthalenes reported in the literature indicates that diffusional activation energies decrease with increasing temperature, reaching a constant limiting value of ~3300 cal mol -1 at temperatures a: 00°C. This observation is consistent with the modified Arrhenius expression reported by and (1988). The Kirkwood-Riseman equation is used to predict D 0 values as a function of the polymer chain length of hydrocarbons. Regression of experimental D 0 data with a combined expression of the Kirkwood-Riseman and modified Arrhenius equations yields parameters which permit calculation of tracer diffusion coefficients for over 50 aqueous organic species at temperatures from 0° to 350°C and P sat . ( p sat refers to pressures corresponding to the liquid-vapor equilibrium curve for H 2 O at temperatures greater than 100°C and 1 bar at lower temperatures.) Resulting values of D 0 permit evaluation of the extent of diffusional mass transfer in both contaminated near-surface environments and in the porewater adjoining oil field reservoirs. The computed tracer diffusion coefficients, which are qualitatively similar to D 0 values previously calculated for aqueous ions, increase substantially with increasing temperature. For example, the tracer diffusion coefficient of aqueous toluene increases from 0.36 to 27.1 × 10 -5 cm 2 sec -1 in response to increasing temperature from 0 to 350°C.

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