IngentaConnect A simulation study of the pore size dependence of transport selec...

Author: Nicholson D.

Source: Molecular Physics, Volume 100, Number 13, 10 July 2002 , pp. 2151-2163(13)

Abstract:

The equilibrium adsorption and transport properties of mixtures of methane and carbon dioxide, modelled as spherical molecules, have been studied in cylindrical model pores with graphitic properties over a range of cylinder radii. The equilibrium isotherms exhibit packing transitions similar to those observed for single adsorbates; as a consequence, optimum separation factors are found at particular radii, depending on the fugacity (or pressure) in the system. The equations of non-equilibrium thermodynamics have been developed so as to represent the flux of each component in a Fickian form, as a coefficient multiplying the gradient of the total density. Diffusion coefficients were calculated from streaming velocity correlations and NEMD was used to obtain the "apparent" viscous component. The results show that diffusion coefficients from equlibrium molecular dynamics and viscous diffusion coefficients from nonequilibrium calculations are identical within the errors of the calculation. It follows that equilibrium and dynamic separation factors have the same values over a range of pore sizes.

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A simulation study of the pore size dependence of transport selectivity in cylindrical pores