Eugeny Ya. Aladko

Phase Diagram and High-Pressure Boundary of Hydrate Formation in the Carbon Dioxide−Water System

Experimental investigation of the phase diagram of the system carbon dioxide-water at pressures up to 2.7 GPa has been carried out in order to explain earlier controversial results on the decomposition curves of the hydrates formed in this system. According to X-ray diffraction data, solid and/or liquid phases of water and CO2 coexist in the system at room temperature within the pressure range from 0.8 to 2.6 GPa; no clathrate hydrates are observed. The results of neutron diffraction experiments involving the samples with different CO2/H2O molar ratios, and the data on the phase diagram of the system carbon dioxide-water show that CO2 hydrate of cubic structure I is the only clathrate phase present in this system under studied P-T conditions. We suppose that in the cubic structure I hydrate of CO2 multiple occupation of the large hydrate cavities with CO2 molecules takes place. At pressure of about 0.8 GPa this hydrate decomposes into components indicating the presence of the upper pressure boundary of the existence of clathrate hydrates in the system.

Solubility of helium in ice Ih at pressures up to 2000 bar: experiment and calculations.

The solubility of helium in ice Ih has been examined both experimentally and theoretically. It has been demonstrated that the calculations are in good accord with the experimental data. The tested calculation method has been used for deriving the helium solubility in ice Ih at pressures up to 2000 bar and at temperatures of 0-50 °C. Obtained data may be useful in some practical applications (storage of enriched with helium natural gas in permafrost, extraction of helium from natural gas).

Phase Diagrams of the Ternary Gas Hydrate Forming Systems at High Pressures. Part 1. Propane–Methane–Water System

Abstract Cross sections of the ternary system propane–methane–water at pressure up to 15 kbar have been investigated by means of differential thermal analysis. It is stated that a double gas hydrate of the cubic structure II is formed in the system. It is stable within the whole pressure range investigated. It is most likely that at pressures above 3.4 kbar one more double hydrate exists in the system. The possibility of the formation of solid solutions of methane in propane hydrates and of propane in methane hydrates existing under different P–T conditions is discussed on the basis of P–T curves corresponding to monovariant equilibria in the system.