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.