Methane Hydrate Structure I Dissociation Process and Free Surface Analysis.

Methane hydrates are crystalline solids of water that contain methane molecules trapped inside their molecular cavities. Gas hydrates with methane as a guest molecule form structure I hydrates with two small dodecahedral cages and six tetra decahedral large cages. This study assesses the influence of occupation and the behavior of methane release from the molecular perspective during the dissociation process, particularly for the purpose of testing a series of molecular dynamics simulations. The dissociation cases conducted include an ideal 4 × 4 × 4 and 2 × 2 × 2 supercell methane hydrate system while inducing dissociation with two different types of temperature-rising functions for understanding the limitation and capability. These temperature-rising functions are temperature ramping and a single temperature step simulating in 5-7 various conditions. Temperature step results showed the earliest dissociation starting 50 ps into the simulation at an ΔT of 100 K, while at an ΔT of 80 K, dissociation was not observed. There was not a distinct dissociation preference observed between large and small cages, so it appears that the dissociation affects the entire structure uniformly when temperature increases are applied throughout the system rather than transport from a boundary. Temperature ramping simulations showed that the dissociation temperature increased with a higher heating rate. The mean-squared displacement results for the oxygen atoms in the water molecules at a high heating rate of 400 TK/s showed behavior similar to that for methane gas. As in the temperature step simulation, there were no clear differences in dissociation between large and small cages, which suggested homogeneous dissociation in all cases. Finally, a coordination analysis was performed on a 3 × 4 × 4 structure I methane hydrate with two free surfaces to demonstrate clear free surface boundaries and its location.

Dataset for SO2, SO3, H2SO4 and H2O infrared absorption spectra at 300° C and 350° C temperatures.

The data presented here consists of library spectra obtained for use with a laser absorption spectroscopy gas sensor. The spectra include absorbance data for SO2, SO3, H2O and H2SO4 at 300° C and 350° C temperatures in two wavelength bands, 7-8 µm and 8-9 µm. Datasets were collected in a heated multi-pass absorption Herriott cell using two tunable external cavity quantum cascade laser sources, with the resulting transmission signal measured using a thermoelectrically cooled MCT detector. The absorbance was calculated from measurements taken with and without gas samples and scaled for the length of the multi-pass cell. The data will be useful for scientists and engineers building SO3 and H2SO4 gas sensing equipment for emission monitoring, process control, and other applications.

Experimental studies on combined production of CH4 and safe long-term storage of CO2 in the form of solid hydrate in sediment.

The production of the confirmed enormous resources of CH4 trapped in permafrost and deep ocean sediments in the form of hydrates has been hampered by the lack of an extraction procedure that is both effective and environmentally sensitive. This research explores experimentally the dynamic rate limiting steps in the dissociation of methane hydrates and the formation of CO2 hydrates in a sediment matrix. The use of CO2 injection and substitution for hydrate extraction takes advantage of novel thermodynamics and also provides a safe storage option for greenhouse gas. This experimental work incorporates a high-pressure facility dedicated for CH4 hydrates exchange with CO2 that replicates creation of natural gas hydrate from incoming gas below water in the pore space. The hydrate formation/exchange chamber follows the state-of-art hydrate science and is equipped with sensors distributed in several sections: the top section for gas release, a CH4 hydrate section, and a subsequent injection of CO2 from the bottom section, which also mimics hydrate dissociation towards incoming seawater through fracture systems connected from the seafloor. Four experimental conditions were examined. They comprise pure CO2 injection, and 10, 20, and 30 mole% N2 added to the CO2. We observed an increase in CH4 release from pure CO2 injection to 10 mole% N2 addition. A significant extra release of CH4 occurred by stepping up to 20 mole% N2 addition but no significant change was observed from 20 to 30 mole% N2 addition. Maximum conversion in this study is 34 mole% of CO2, and 2 mole% N2 taking the place of methane hydrate in large and small cavities. The results also show that effective substitution for hydrate production cannot rely on pure carbon dioxide injection.