Thermodynamic Inhibition of Carbon Dioxide Hydrate with Magnesium Chloride and Methanol: Comparative Phase Equilibrium and PXRD Study

Clathrate hydrates of carbon dioxide represent a subject of considerable interest in both fundamental science and the development of promising technologies. The phase behavior of CO₂ hydrate in the presence of concentrated aqueous solutions remains poorly understood. In this study, we conducted a comprehensive investigation into the impact of magnesium chloride (0-24 mass%) and methanol (0-40 mass%) on the thermodynamic stability of CO₂ hydrate. New experimental data on the three-phase gas-aqueous solution-gas hydrate equilibrium in the temperature range 243-283 K and pressure range 1-4.5 MPa were obtained. A correlation is proposed for the precise representation of equilibrium pressure-temperature lines. A comparison of the anti-hydrate effect, as indicated by the parameter ∆<i>T</i>_h, of these substances demonstrated that ionic MgCl₂ exhibits a stronger thermodynamic inhibitory effect on CO₂ hydrate formation than nonionic MeOH. The results of measuring the melting point of ice at 0.1 MPa for aqueous solutions of MgCl₂ and MeOH confirmed the thermodynamic consistency of the hydrate equilibrium data. A detailed comparison of the anti-hydrate effect of MgCl₂ and MeOH in a wide concentration range was performed on hydrates of different gases (CO₂ and CH₄). The phase composition of CO₂ hydrate samples obtained from water and aqueous solutions of MgCl₂ and MeOH was examined using powder X-ray diffraction (PXRD) at 133 K. The PXRD results indicate the formation of sI CO₂ hydrate with a cell parameter of 11.86 ± 0.04 Å in all cases.