Ability of ionic liquids to inhibit the formation of methane hydrate: Insights from molecular dynamics simulations

Ionic liquids can both thermodynamically and kinetically inhibit the formation of solid hydrates in oil and gas pipelines, and thus are a new class of dual-function inhibitors of the formation of hydrates. In this study, the ability of six ionic liquids with different functional groups to inhibit the formation of methane hydrate was investigated using molecular dynamics simulations. The alkyl chains in ionic liquids strengthen the tetrahedral arrangement of water molecules by forming pentagonal and hexagonal ring structures with water molecules. In contrast, anionic groups weaken the tetrahedral arrangement of water molecules. The longer alkyl chain of the 1-butyl-3-methylimidazolium ion) (BMIM) substantially enhanced the tetrahedral arrangement of water molecules, and thus BMIM exhibited less inhibition of the formation of methane hydrate than did the 1-ethyl-3-methylimidazolium ion (EMIM). In general, the relative abilities of the various components of the studied ionic liquids to inhibit the formation of methane hydrates were found to be as follows: BMIM < EMIM < tetrafluoroborate ion ≈ bromide ion ≈ chloride ion. The findings of this study provide insights into mechanisms by which ionic liquids inhibit the formation of methane hydrate and have potential applications in the petroleum pipeline industry.