Characterization of Microporous Carbons Using Adsorption at Near Ambient Temperatures

The adsorption isotherms of CF 4 and SF 6 measured at various temperatures near ambient are used to obtain information about micropore structure of two commercial carbons. This information is extracted from the comprehensive analysis of the data on three levels of assumptions. First from the temperature dependence of adsorption the isosteric heats of adsorption are calculated using nonparametric regression. Heats of adsorption allow for qualitative comparison of adsorption energetics between different carbons. The more detailed description of this energetics is given in terms of the adsorption energy distributions. Finally the micropore size distributions are calculated from the adsorption energy distributions assuming that the adsorption energy of molecules confined in micropores is determined by their sizes and geometry. No assumptions are made about the analytical form of the distribution. Effects of model assumptions, such as gas−solid interaction parameters or the pore wall thickness, on the calculated micropore size distributions are discussed. In order to obtain better insight on pore size distribution and geometry of actual carbons the results of this work are compared with the results of an independent chromatographic method based on the exclusion effect.