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.
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