MONTE-CARLO SIMULATION STUDIES OF HEATS OF ADSORPTION IN HETEROGENEOUS SOLIDS

We present calculations of heats of adsorption for molecular models of adsorption in heterogeneous porous solids via grand canonical Monte C arlo simulations. The molecular models treat the adsorbent as a matrix of particles arranged in a predefined microstructure, and the paramet ers are chosen to represent the adsorption of simple molecules in sili ca gel. Three different adsorbent microstructures have been considered , allowing us to study the role of translational order and connectivit y among the matrix particles in determining the heat of adsorption. We have calculated separately the contributions from the adsorbate-solid and adsorbate-adsorbate interactions to the heat of adsorption A comp arison with experimental data for methane in silica gel is made. Durin g the course of the work we have revisited the derivation of expressio ns used to determine heats of adsorption and we present a new derivati on which is free from some unnecessary assumptions used previously. In addition we test our results for thermodynamic consistency, and the a ccuracy of different methods for obtaining the isosteric heat from the Monte Carlo simulations is also investigated.