Vapour-liquid coexisting curves and hysteresis of simple adsorbate in complex porous systems

A unified approach for simulation of the vapour-liquid coexisting curves on phase diagrams and hysteresis phenomena for simple adsorbates in various type porous adsorbents was developed on the basis of the lattice-gas model. The ideas of this model in complex porous systems were used twice: for a construction of the over-molecular structure for high-dispersed bodies and for a description of the molecular distribution within the complex porous space. The supramolecular structure of these systems is modelled by sections with a simple regular geometry (slit-like, cylindrical and spherical) with additional inclusion of junctions between different pore sections. At the description of the adsorbate distribution, the lateral interactions between the fluidic molecules were included through the quasi-chemical approximation (QCA) that takes into account direct pair correlations between interacting molecules. The knowledge of phase diagrams allows improving a description of the adsorption hysteresis phenomena. The lattice-gas model enables explaining the experimental data for MCM-41 like sample in which the hysteresis is absent, when the pore size is narrowed more than ∼4 nm.