Effect of Lower Alcohols on the Formation of Methane Hydrate at Temperatures Below the Ice Melting Point

This work revealed that most water-soluble compounds have a dual nature (thermodynamic promotion or hydrate inhibition) depending on thermobaric conditions. Indeed, by lowering the melting point of ice, water-soluble organic compounds expand the region of water-containing liquid phase existence below 0 degrees C. This work considered typical thermodynamic hydrate inhibitors as alcohols (methanol, ethanol, and 2-propanol). It turned out that even methanol does not exhibit inhibitory properties below the ice crystallization line, and it does not affect the equilibrium conditions of methane hydrate formation. In this case, the observed four-phase hydrate-ice-solution-gas equilibrium either corresponds to the hydrate-ice-gas line for the water-methane system (in the case of methanol) or lies at higher temperatures (in the case of ethanol and 2-propanol). This allowed us to assume that practically any water-soluble organic compounds will either exhibit the properties of thermodynamic hydrate promoters in a specific temperature range below 0 degrees C or will not affect the hydrate-ice-gas equilibrium. In addition, the presence of the ice and an aqueous liquid mixture in the system accelerates the hydrate growth (compared to the hydrate growth from the bulk phase of ice). It should also be noted that, unlike conventional thermodynamic promoters, methanol does not alter the methane hydrate's structure and gas capacity, which is more favorable. The data obtained can contribute to developing hydrate-based technologies for gas storage and separation of gas mixtures.

Automated summary

This work shows that water-soluble compounds can either promote or inhibit hydrate formation depending on the thermobaric conditions. Alcohols like methanol, ethanol, and 2-propanol are commonly used as thermodynamic hydrate inhibitors, but this study found that even methanol does not inhibit hydrate formation below the ice crystallization line. Additionally, the presence of ice and liquid mixture accelerates hydrate growth compared to growth from the bulk phase of ice. These findings have implications for developing gas storage and gas mixture separation technologies based on hydrates.