Phase equilibria and kinetics of clathrate solutions containing multiple guest molecules

Abstract

Clathrates are non-stoichiometric inclusion compounds formed by a lattice of host molecules, strongly hydrogen bonded under certain conditions of pressure and temperature, which encage low molecular weight gases or volatile liquids in different cavities within the lattice. While the guest molecule is enclosed within the lattice, there is no chemical union between the guest and host molecules. Application of clathrates had been tried to several technologies such as desalination, food concentration, bio-material separation, carbon dioxide deposit in ocean floor, and natural gas production from gas hydrate field. It was believed that reported hydrate formation and dissociation rate in methane gas, pure water, and aqueous solution containing clay mineral and sodium chloride, major ingredient in the sea water, in this thesis. Three-phase (hydrate-liquid water-vapor) equilibrium dissociation conditions for simple and mixed hydrates of carbon dioxide, nitrogen, and hydrocarbons were measured. Depending on composition of gas mixture, equilibrium dissociation pressure were varied between two pure lines of carbon dioxide and nitrogen. Equilibrium dissociation pressures were also affected by adding hydrocarbons, and hydrates stability increased. And hydrate structures were changed to structure H by adding hydrocarbons. That is; striking decrease of the equilibrium pressure at a temperature. Difference of hydrate stability was changed according to a kind of hydrocarbons. New thermodynamic model was suggested as the hydrate phase changing. Hydrate formation and dissociation kinetics of methane gas with and without clay mineral (bentonite) and NaCl. It was observed that hydrate formation occurred in the bulk liquid water if supersaturation existed as a result of the dissolution process and that the formation rate was very fast at the early stage of the whole period of hydrate formation. In clay mineral added system, hydrate formation rate decreased and dissociation rat...