Selectivity of N2–CH4 Mixed Clathrate Hydrates: A Grand Canonical Monte Carlo Study

Abstract

In this article, we report the results of a grand canonical Monte Carlo simulation study aiming at characterizing the competitive trapping of N₂ and CH₄ molecules into the same clathrate hydrate structure. Simulations have been performed at temperature conditions typical of those encountered at the surface of, e.g., Titan, and in accordance with recent experiments. Various compositions of the fluid in contact with the clathrate hydrate phase, i.e., various nitrogen/methane ratios, have been considered in the simulations. The results of these simulations reveal that, although the ratio between the number of enclathrated methane and that of nitrogen molecules strongly varies with the composition of the fluid phase, the clathrate hydrate lattice remains always selective for methane. This means that the relative proportion of methane with respect to nitrogen is always larger in the clathrate phase than in the fluid phase, with the mixed clathrate hydrate thus acting as a methane concentrator, irrespective of the fluid composition. These features indicate that the formation of clathrate hydrates can strongly influence the composition of the nitrogen–methane fluid phase, which may thus be impoverished in methane, as already inferred from the experimental results.