THE MOLECULAR-SIEVING MECHANISM IN CARBON MOLECULAR-SIEVES - A MOLECULAR-DYNAMICS AND CRITICAL PATH-ANALYSIS

We have investigated the molecular sieving mechanism in carbon molecul ar sieves (CMSs), by a combination of molecular dynamics simulations a nd pore network theory, using the separation of air into oxygen and ni trogen as a prototype. Molecular dynamics simulations of diffusion in individual pores show that the diffusion coefficients for oxygen and n itrogen are strong functions of pore width and that the degree of kine tic separation (expressed as the ratio of the species diffusion coeffi cients) observed experimentally can be reproduced at the level of indi vidual pores. A critical path analysis of diffusion in the pore networ k of the CMS shows that this degree of kinetic separation can also be obtained with pore networks having a range of pore sizes, even where t he width of the pore size distribution is large.