Micropore size distributions of activated carbons and carbon molecular sieves assessed by high-pressure methane and carbon dioxide adsorption isotherms

Experimental N-2 adsorption isotherms and high-pressure CO2 and CH4 adsorption isotherms have been obtained for a series of microporous carbon materials prepared for being used in gas separation and methane storage. The shape of the isotherms is very different, which is due in part to differences in the overall micropore volume but, additionally and importantly, to the significant differences in the micropore size distribution of those samples. Micropore size distributions (MPSDs) have been deduced from those N-2, CO2, and CH4 isotherms by application of the General Adsorption Isotherm (GAI), according to two different approaches proposed in previous independent works. The comparison of the results has shown that, despite the different characteristics of CH4 and CO2, and the different experimental temperatures and adsorption conditions (298 K, supercritical conditions, and 273 K, subcritical conditions, respectively), a quite good consistency between the MPSDs from these two gases has been obtained for all the samples studied. That suggests that both methods are suitable to analyze more sensibly the changes in the MPSDs of microporous samples. The fact that these MPSDs analysis are based on high-pressure adsorption isotherms and that CO2 is especially useful for characterizing the narrow microporosity not accessible to N-2 makes both techniques very useful for the characterization of microporous samples.