Stability and Growth of Methane Hydrates in Confined Media for Carbon Sequestration
Shurraya Denning, Ahmad A. A. Majid, Carolyn A. Koh
Abstract
Methane hydrates pose potential as both an energy resource and an environmental risk, as a significant amount of the Earth’s carbon is sequestered in naturally occurring gas hydrates in deep-water porous oceanic sediments. More research into understanding the thermodynamic stability and kinetic growth in confined spaces like pores is needed to find ways to efficiently extract methane and prevent destabilization. Although effects of pore diameter on methane hydrates have been studied in the literature, very little is known about the effect of pore shape. This study investigated how the shape of a pore affected both stability and nucleation of methane hydrate and ice using two mesoporous silica materials: SBA-15 (cylindrical channels) and SBA-16 (cubic pores with interconnecting channels). Both SBAs destabilized the structure of methane hydrates and ice, with SBA-16 on average decreasing the thermodynamic equilibrium temperature to a greater extent than SBA-15 relative to pore size, as the interconnecting channels of SBA-16 choke growth due to its narrower size. The pore shape also affected hydrate growth. SBA-15 favored hydrate growth within the cylindrical channels, and SBA-16 showed differing behavior with methane hydrate growth in the cubic pore, yet ice freezing in the interconnecting channels. The two SBAs also showed interesting inhibition of ice freezing, yet promoting methane hydrate formation. In comparison to experiments at ambient pressure, the addition of 8 MPa of methane resulted in the liquid water to hydrate conversion increasing by 72 ± 14% for SBA-15 and 67 ± 19% for SBA-16. Methane at relatively high pressures (>1 MPa) disrupts the water adsorption on the hydrophilic silica surfaces of SBA-15 and SBA-16, leading to an increase in water activity. Overall, this study found that the pore shape may not significantly influence how much methane hydrate forms, yet greatly impacts methane hydrate stability and nucleation.