Selectivity of the Binary CO2-N2 and CO2-CO Clathrate Hydrates: A Grand Canonical Monte Carlo Simulation Study

In this paper, we report the results of grand canonical Monte Carlo simulations, aiming at characterizing the competitive trapping between CO2 and either CO or N-2 molecules into clathrate hydrates under moderate thermodynamic conditions (i.e., 270 K and 25 bar) corresponding to those considered in recent Raman spectroscopy experiments. Various compositions of the binary CO2/CO or CO2/N-2 fluid in contact with the clathrate phase have been taken into account in the simulations, which have been focused on the corresponding selectivity process. The simulation results reveal a strong preferential trapping of the CO2 molecules in both CO2/CO and CO2/N-2 mixed clathrate hydrates, at the expense of the other species, in excellent agreement with the experimental results. This selectivity is mainly due to the large cages of the clathrate hydrates, into which the CO2 molecules are much more favorably trapped than the two other species, which exhibit a clear preference for the fewer in number, small cages. These features indicate that clathrate hydrates may be efficient selective traps for the CO2 molecules when in contact with CO2/CO and CO2/N-2 mixtures and may thus strongly influence their compositions.