Adsorption of humid air in compacted montmorillonite: A Monte Carlo simulation study

Compacted montmorillonite (the most significant constituent of bentonite) was employed as a proxy for bentonite in atomistic Monte Carlo simulations in the grand canonical ensemble. Air, described in this study as a mixture of nitrogen, oxygen, argon, and carbon dioxide, was considered near ambient conditions, and with absolute humidity (i.e. total water content) varying from 0% up to 5% on a molar basis. The adsorption of each species constituting the mixture was computed under these conditions and the selectivity relative to nitrogen was considered. The species of particular interest in this study were water and oxygen, due to their role in the spoilage of foodstuffs. The results of the simulations suggest that molecular shape plays about as much of a role in sorption as dipole moment, with argon and oxygen displaying favourable uptake in bentonite as compared to all other species in the system. Water was somewhat more likely to be adsorbed in bentonite than nitrogen, although the disparity was less marked than for oxygen. The results suggest that bentonite may selectively separate oxygen from noble gases, which can have an impact on its use in packaging materials.