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 0.167 MPa ≤ p ≤ 0.361 MPa and 275.6 K ≤ T ≤ 277.3 K 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.

► Describes phase-equilibrium measurements for O3-containing hydrate-forming systems. ► Presents a new PE-measuring technique applicable for chemically unstable guests. ► The PE data for the O3 + O2 + CCl4 hydrate show a linear ln p versus T−1 relation.