Phase equilibrium for ozone-containing hydrates formed from an (ozone plus oxygen) gas mixture coexisting with gaseous carbon dioxide and liquid water

The paper reports the three-phase (gas + aqueous liquid + hydrate) equilibrium pressure (p) versus temperature (T) data for a (O-3 + O-2 + CO2 + H2O) system and, for comparison, corresponding data for a (O-2 + CO2 + H2O) system for the first time. These data cover the temperature range from (272 to 279) K, corresponding to pressures up to 4 MPa, for each of the three different (O-3 + O-2)-to-CO2 or O-2-to-CO2 mole ratios in the gas phase, which are approximately 1: 9, 2: 8, and 3: 7, respectively. The mole fraction of ozone in the gas phase of the (O-3 + O-2 + CO2 + H2O) system was from similar to 0.004 to similar to 0.02. The modified pressure-search method, developed in our previous study [S. Muromachi, T. Nakajima, R. Ohmura, Y.H. Mori, Fluid Phase Equilib. 305 (2011) 145-151] for p-T measurements in the presence of chemically unstable ozone, was applied, having been further modified for dealing with highly water-soluble CO2, for the (O-3 + O-2 + CO2 + H2O) system, while the conventional temperature-search method was used for the (O-2 + CO2 + H2O) system. The measurement uncertainties (with 95% coverage) were +/- 0.11 K for T, +/- 6.0 kPa for p, and +/- 0.0015 for the mole fraction of each species in the gas phase. It was confirmed that, at a given CO2 fraction in the gas phase, p for the (O-3 + O-2 + CO2 + H2O) system was consistently lower than that for the (O-2 + CO2 + H2O) system over the entire T range of the present measurements, indicating a preference of O-3 to O-2 in the uptake of guest-gas molecules into the cages of a structure I hydrate. (C) 2012 Elsevier Ltd. All rights reserved.