Studies of structure II propane clathrate hydrate: Formation, composition, and potential for storage of methane and carbon dioxide

Gas clathrate hydrates are crystalline solids with structures consisting of a lattice of water encaging small diameter gas molecules. Propane hydrate was studied to investigate its use as a possible storage medium for gases. For practical purposes, hydrate formation needs to be efficient at near ambient conditions. Ice particles exposed to varying mixtures of propane and methane gas are found to form the double hydrate efficiently and may be quite effective for storing methane. For instance, exposure of ice particles to a 2/1 methane/propane gas mixture for 18 hours converts 66% of the ice to hydrate with 77% occupancy of the 512 cages and a final dissociation temperature of 287 K. Compositions of the double hydrates were determined after dissociation via gas chromatography. Additional experiments were performed in which the ice particles were sequentially exposed to propane and then methane to make the double hydrate. However, this technique did not prove to be as efficient as exposure to the mixed gas.;Heats of hydrate dissociation were calculated through the use of thermodynamics and phase equilibrium data. The enthalpy of dissociation for Structure II hydrate for temperatures between 272 and 279 K was determined from experimental data for methane-propane hydrate double hydrate. This data indicates that dissociation occurred near equilibrium at 1 K/hr. Also, the DeltaH values were found to be quite sensitive to cage occupation below 273 K.;Propane-carbon dioxide double hydrate was synthesized. Simultaneous addition of gases to ice showed a quicker initial gas uptake rate compared to sequential addition of gases. In the simultaneous addition of gases, the final gas ratio of carbon dioxide to propane was 1.2/1 with a final decomposition pressure reached of 1.2 MPa, while the sequential addition of gases produced a final gas ratio of 0.49/1 carbon dioxide to propane and final decomposition pressure of 0.75 MPa. The simultaneous addition method stores the most CO2 + C3H8 gas, as well as greater carbon dioxide uptake.;Lastly, preliminary 1H spectra were collected on propane hydrate and propane-methane hydrate by utilizing solid-state NMR. Techniques for preparing hydrates for solid-state NMR analysis are developed.