Determination of Micropore Size Distribution from Grand Canonical Monte Carlo Simulations and Experimental CO₂ Isotherm Data

A method for the determination of micropore size distribution is developed based on grand canonical Monte Carlo (GCMC) simulations and measured isotherm data. The technique is applied in the case of a microporous carbon membrane for which the CO2 isotherm at 195.5 K has been experimentally obtained. Simulations in slit-shaped graphitic pores of various sizes have been run offering insight to the structure of the CO2 molecules packing in the individual pores at different pressure levels. On the basis of these results and a postulated pore size distribution (PSD) function, the isotherm can be reconstructed and compared with its experimental counterpart. The PSD that gives the best match between measured and computed isotherm data is thus determined. The most probable pore size agrees with that found by conventional nitrogen porosimetry and the Dubinin−Radushkevich (DR) approach. The present method exhibits high sensitivity to changes in the range or mean value of the resulting optimal PSD. The GCMC simulations have also provided useful evidence about the effect of including the quadrupole moment in the model and the densification process in the micropores.