The link between the kinetics of gas hydrate formation and surface ion distribution in the low salt concentration regime

Inorganic salts can thermodynamically inhibit gas hydrate formation. However, some inorganic salts at low concentration can act as a kinetic hydrate promoter. The mechanism of kinetic hydrate promotion in the presence of low concentration of inorganic salts is still unknown. This paper presents an experimental study into methane hydrate formation in an impeller-agitated vessel in the presence of sodium halides and alkali metal chlorides at low concentrations. It is shown that alkali metal chlorides and sodium halides at low concentration can reduce the induction time and kinetically promote gas hydrate formation. It has been proposed that bubbles form inside the agitated vessel as a result of the gas pocket break-up. Simulated gas pocket break-up studies show a smaller gas bubble formation in the salts solution with low concentrations in comparison with in the pure water. The small bubbles formation leads to an increase in the gas-water interface area and gas hold-up of the vessel. Consequently, there will be an increase in the mass transfer for gas hydration formation. In addition, the strength of hydrogen bonds at the gas/water interface affect the gas dissolution rate into the aqueous phase. Ions that have more affinity for the interface order water molecules weakly and improve the gas hydrate formation. Bubbles zeta potential measurements also confirm the ion-specific effect of the applied salts at the gas-water interface. Ultimately, gas-water interfacial area and ion-specific effect play critical roles in the gas hydrate formation.