Induction Phenomena at the Dissociation of Gas Hydrate Freon-12

About the authors:

Aleksey G. Zavodovsky, Cand. Sci. (Phys.-Math.), Senior Researcher, Earth Cryosphere Institute, Tyumen Scientific Center of the Siberian Branch of the RAS; zag-2-57@yandex.ru

Marat Sh. Madygulov, Junior Researcher, Earth Cryosphere Institute, Tyumen Scientific Center of the Siberian Branch of the RAS; marat747@gmail.com

Vladimir P. Shchipanov, Dr. Sci. (Chem.), Professor, Department of General and Physical Chemistry, Tyumen Industrial University

Abstract:

This paper presents the results of differential thermal analysis (DTA) studies of the dissociation of Freon-12 gas hydrate on ice, supercooled water, and gas at temperature below 273 K. The experiments involved two types of samples, which differed by state phase of the water that had not transformed into the gas hydrate. Due to the specificity of the experiments with the DTA method, the phase state of water in the samples of the gas hydrate was constantly monitored. The results show an induction effect related to the delay in the onset of dissociation of Freon-12 gas hydrate to ice and gas in the region of thermodynamic parameters located on the phase P-T diagram below the “ice-hydrate-gas” phase equilibrium line.

It was established that, in the presence of unreacted ice in the samples under study, Freon-12 gas hydrate decomposes at pressures significantly lower than the corresponding equilibrium pressures in the “ice-hydrate-gas” system. In the presence of unreacted ice in the samples, Freon-12 gas hydrate decomposes at pressures significantly lower than the corresponding equilibrium pressures in the ice-hydrate-gas system. The experiment results show that the case pressure of the gas hydrate’s dissociation onset depends on rate lower in gas pressure: the higher this rate, the greater the depth of approach to pressure in the area instability of the gas hydrate. Moreover, at this temperature of sample, delay time of the onset of dissociation of the gas hydrate to ice and gas decreases as the pressure deepens into the area of instability of Freon-12 gas hydrate. In the presence of liquid water in the sample, dissociation of the gas hydrate on the water and gas starts at the moment crossing by the metastable equilibrium line “supercooled water-hydrate-gas”. The induction effect (found in this study) allows to correct the methodology for determining the equilibrium line ice-hydrate-gas and water-hydrate-gas.

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