Thermodynamic Stability, Spectroscopic Identification, and Gas Storage Capacity of CO_2-CH_4-N_2 Mixture Gas Hydrates: Implications for Landfill Gas Hydrates

摘要

Landfill gas (LFG), which is primarily composed of CH_4, CO_2, and N_2 is produced from the anaerobic digestion of organic materials. To investigate the feasibility of the storage and transportation of LFG via the formation of hydrate, we observed the phase equilibrium behavior of CO_2-CH_4-N_2 mixture hydrates. When the specific molar ratio of CO_2/CH_4 was 40/55, the equilibrium dissociation pressures were gradually shifted to higher pressures and lower temperatures as the mole fraction of N_2 increased. X-ray dim-action revealed that the CO_2-CH_4-N_2 mixture hydrate prepared from the CO_2/CH_4/N_2 (4O/55/5) gas mixture formed a structure I dathrate hydrate. A combination of Raman and solid-state ~(13)C NMR measurements provided detailed information regarding the cage occupancy of gas molecules trapped in the hydrate frameworks. The gas storage capacity of LFG hydrates was estimated from the experimental results for the hydrate formations under two-phase equilibrium conditions. We also confirmed that trace amounts of nonmethane organic compounds do not affect the cage occupancy of gas molecules or the thermodynamic stability of LFG hydrates.