Adsorption and Diffusion of Supercritical Carbon Dioxide in Slit Pores

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A combination of grand canonical Monte Carlo and molecular dynamics methods has been used to investigate the adsorption and diffusion of carbon dioxide confined in seven slit carbon pores from 0.744 to 3.72 nm from subcritical to supercritical conditions. Adsorption isotherms and microstructures of carbon dioxide molecules in slit carbon pores are analyzed. The effects of pore size and operating conditions on the parallel and perpendicular diffusion coefficients are examined. The diffusion coefficients of CO2 molecules confined in a slit pore in supercritical conditions strongly depend on the pore fluid density. The parallel diffusion coefficients are on the magnitude of 10-9m2·s-1, a typical liquidlike value. For the pores of reduced width larger than 4.0, the parallel diffusion coefficients are generally 10−20 times greater than the perpendicular ones. When the pressure is in the range 2−10 MPa, the parallel diffusion coefficients are in the range (1.3−2.8) × 10-9 m2·s-1 at 323 K, while they are (2.0−5.3) × 10-9 m2·s-1 at 348 K. Diffusion coefficients parallel and normal to the walls at supercritical temperatures are both 5−15 times larger than those at subcritical temperatures.