Determination of the thermodynamic correction factor of fluids confined in nano-metric slit pores from molecular simulation

A procedure to find thermodynamic equilibrium constants for CO2 and CH4 adsorption on activated carbon

Thermodynamic equilibrium for adsorption means that the chemical potential of gas and adsorbed phase are equal. A precise knowledge of the chemical potential is, however, often lacking, because the activity coefficient of the adsorbate is not known. Adsorption isotherms are therefore commonly fitted to ideal models such as the Langmuir, Sips or Henry models. We propose here a new procedure to find the activity coefficient and the equilibrium constant for adsorption which uses the thermodynamic factor. Instead of fitting the data to a model, we calculate the thermodynamic factor and use this to find first the activity coefficient. We show, using published molecular simulation data, how this procedure gives the thermodynamic equilibrium constant and enthalpies of adsorption for CO2(g) on graphite. We also use published experimental data to find similar thermodynamic properties of CO2(g) and of CH4(g) adsorbed on activated carbon. The procedure gives a higher accuracy in the determination of enthalpies of adsorption than ideal models do.

Calculation of the chemical potential and the activity coefficient of two layers of CO2 adsorbed on a graphite surface

Thermodynamics of two layers of CO₂ on a graphite surface obtained directly from the simulations and the Small System Method.