Effect of Chain Length of Ionic Liquid On the Formation of Methane Hydrate

The dissociation conditions for methane hydrates in the presence of ionic liquid 1–carbonyl–3–methylimidazolium chloride were experimentally measured within the pressure range from 10 to 35 MPa. A homologous series of ionic liquid 1-carbonyl-3-methylimidazolium chloride: 1-ethyl-3-methylimidazolium chloride, 1-hexyl-3-methylimidazolium chloride and 1-decyl-3-methylimidazolium chloride, with different chain lengths were used as methane hydrate inhibitors. The hydrate phase dissociation conditions were measured by using a differential scanning calorimetry operated at constant high pressure. It was found that the addition of 1-carbonyl-3-methylimidazolium chloride has an inhibition effect on the formation of methane hydrate. In addition, the longer the chain is, the weaker the inhibition is. In other word, the inhibition effect of three ionic liquids is in the order of 1-ethyl-3-methylimidazolium chloride > 1-hexyl-3-methylimidazolium chloride > 1-decyl-3-methylimidazolium chloride. In addition, a predictive method was applied to predict the vapor-liquid-hydrate three-phase equilibrium condition of methane hydrate in the presence of ionic liquids. The Peng-Robinson-Stryjek-Vera equation of state incorporated with  COSMO-SAC activity coefficient model and the first order modified Huron-Vidal mixing rule were chosen to evaluate the fugacity of vapor and liquid phase. A modified van der Waals and Platteeuw model was applied to describe the hydrate phase. This predictive method can successfully describe the inhibition effect of these ionic liquids on the methane hydrate formation.