Comprehensive study on the dynamic action mechanism of methanol inhibiting hydrate formation and decomposition in simulated seawater

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Natural gas hydrate is one of the main clean energy sources. It has abundant reserves and high exploitation value in the world. At present, the injection inhibitor decomposition method is the most effective extraction method. In order to further clarify the mechanism of thermodynamic inhibitors for methanol, this paper combines experimental and molecular simulation methods to study the dynamic influence mechanism of methanol on hydrate formation and decomposition in simulated seawater. The specific mechanism of how salt ions and alcohol molecules affect hydrate growth is analyzed, and an explanation is given accordingly. The results show that: ① Methanol at a concentration of 1 wt% has a promoting effect of 9.91% on the formation of methane hydrates. At lower concentrations of 3 wt% and 5 wt%, methanol shows a weak inhibitory effect on hydrates. At a concentration of 10 wt%, the formation of hydrates is completely inhibited. ② From the perspective of kinetics analysis, methanol has no effect on the decomposition of hydrate, but can effectively inhibit the secondary formation of hydrate. ③ The salt ions in simulated seawater have hydration and salt-expulsion effects, which continuously reduce the solubility of methane, leading to an extended growth period of hydrate and inhibiting the formation of hydrate. ④ The molecular simulation results show that when the simulation step size lasts for 30 ns, methane gas exhibits different existential states in simulated seawater and fresh water. The former shows obvious gas-liquid stratification, and the latter appears in the form of nanobubbles, and an increase in methanol concentration will prolong the formation time of methane nanobubbles. ⑤ According to the simulation results from the perspective of molecular dynamics, when methanol molecules enter the crystal cavity of the hydrate, the hydroxyl groups will disturb the formation of the hydrogen bond network of the hydrate, resulting in the inability of the hydrate cage structure to close, which inhibits the formation of the hydrate. The above research results are helpful for field personnel to deepen the understanding of the mechanism of methanol inhibitors.