Phase equilibrium for clathrate hydrates formed from an ozone+oxygen gas mixture coexisting with carbon tetrachloride or 1,1-dichloro-1-fluoroethane

This paper reports an attempt at acquiring phase-equilibrium pressure (p) versus temperature (T) data for ozone-containing clathrate hydrates formed from an ozone+oxygen gas mixture, a hydrophobic hydrate-forming liquid, and water in the liquid state. For dealing with ozone (O₃), a chemically unstable material continuously decaying to oxygen (O₂) in the gas phase, we devised a new method, i.e., a modified pressure-search method, to determine the equilibrium p-T conditions while maintaining the ozone concentration in the gas phase nearly constant by repeatedly replacing the contents of the gas phase with a freshly generated O₃+O₂ mixture. Using carbon tetrachloride (CCl₄) as the hydrophobic hydrate-forming liquid, we obtained equilibrium p-T data in the range of 0.167MPa≤p≤0.361MPa and 275.6K≤T≤277.3K in the presence of a gas phase containing O₃ at the molar concentration of 6.9±0.8%. We also obtained, for comparison, the corresponding p-T data, using pure O₂ gas, instead of the O₃+O₂ mixture, and the conventional pressure-search method. The two data groups obtained from the O₃-containing and O₃-free systems, respectively, show simple, mutually consistent p-T relations each well fitted by the Clausius-Clapeyron equation assuming a constant enthalpy of hydrate dissociation. The paper also describes our additional attempt at obtaining equilibrium p-T data using 1,1-dichloro-1-fluoroethane (R141b) as a substitute for CCl₄. Because of the partial decomposition of R141b due to the coexistence of O₃ and water, however, we obtained only limited data which are tentative in nature.