MICROPORE STRUCTURE AND INTRAPORE DIFFUSION OF OXYGEN AND NITROGEN IN A MOLECULAR-SIEVING CARBON

Both micropore size and volume in molecular sieving carbon (MSC) were controlled by heat treating of a hydrocarbon-impregnated MSC precursor, consisting of coconut-husk charcoal having various pore size distributions, in nitrogen at 1023, 1123 and 1223 K after heating at 10 K/min. The hydrocarbon mixtures used were guaiacol-naphthalene, diphenyl-naphthalene, fluorene-naphthalene and coal tar. The micropore size in the heat-treated MSC could be controlled to 0.28-0.4 nm through the proper combination of hydrocarbons, their concentrations and heat-treatment conditions, to give a high selectivity of separation of oxygen and nitrogen. The separation performance of the heat-treated MSC was evaluated in terms of the micropore volume W0* with pore size of 0.28-0.4 nm and the diffusivity ratio of oxygen and nitrogen D(O)2/D(N)2 to obtain the following correlation: D(O)2/D(N)2 = 29(W0*/W(T))5.7 It was found that the selectivity, D(O)2/D(N)2 increases with increasing micropore volume W0* (pore size: 0.28-0.4 nm) for the limiting volume of adsorption space with pore size larger than 0.28 nm, W(T).