Adsorption Behaviors and Phase Equilibria for Clathrate Hydrates of Sulfur- and Nitrogen-Containing Small Molecules

NX Qiu and XJ Bai and JQ Xu and NR Sun and JS Francisco and MH Yang and Q Huang and SY Du, JOURNAL OF PHYSICAL CHEMISTRY C, 123, 2691-2702 (2019).

DOI: 10.1021/acs.jpcc.8b05962

In order to understand the role for different components of flue gases in the replacement of CH4 from natural gas hydrates, in this work, the cage occupancies of SO2, H2S, N2O, NO, and CS2 gases in the structure I (sI) and structure II (sII) hydrates have been investigated by grand canonical Monte Carlo + molecular dynamics simulations. The results show that SO2 and N2O molecules prefer to occupy the large cages (LCs) of sI and sII hydrates, and H2S and NO molecules almost have no preference to cage types, whereas the CS2 molecule can only enter the LCs of the sII hydrate. The adsorption isotherms are used to predict the gas hydrate phase equilibria by statistical thermodynamics, which are in good agreement with the experimental measurements. The dissociation pressures of these clathrate hydrates at given temperatures are in the order: NO > N2O > H2S > SO2. Moreover, it is found that the SO2, H2S, N2O, and even CS2 gases have the ability to replace the CH4 gas from natural gas hydrates. Results from this study suggest that some components in flue gases may assist in the displacement of CH4. This implies that it is probably not necessary to remove all impurities in flue gases when performing replacement of CH4 gas in natural gas hydrates with the CO2 gas.

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