Formation and Melting of Hydrate with Binary CO2/C2H6 Mixtures in Silica Sand: Comparison Between Dissociation Data and Phase Equilibrium of Pure CO2 and C2H6 Hydrates

The present study deals with hydrate formation with binary gaseous mixtures consisting of carbon dioxide mixed with ethane at varying concentrations. Since the production of hydrates is recognised as a stochastic process and also due to the marked influence that experimental apparatuses often have on the results, the continuous updating of the literature with new experimental data is needed. Hydrates were produced and dissociated in excess water and in unstirred conditions. The dissociation values were collected and tabulated. Each test was plotted and compared with the phase boundary equilibrium conditions of pure ethane and pure carbon dioxide hydrates. The results confirmed the lowering of pressures required for hydrate formation with the increase in ethane concentration in the gas mixture. In detail, the dissociation condition for CO2/C2H6 hydrates was tested within the following thermodynamic ranges: 0.1–13 °C and 11.26–36.75 bar for the 25/75 vol% mixture, 0.1–13 °C and 9.74–35.07 bar for the 50/50 vol% mixture and 7.0–12.9 °C and 17.36–30.05 bar for the 75/25 vol% mixture. When 75 vol% ethane was used, the dissociation of hydrates occurred at conditions corresponding to the phase equilibrium of pure ethane hydrates, denoting that the system reached the most favourable thermodynamic conditions possible despite the presence of 25 vol% CO2.