Phase behavior of methane hydrate in the presence of imidazolium ionic liquids and their mixtures

The phase equilibrium conditions of methane hydrate in single ionic liquid aqueous solutions containing low dosage 1-ethyl-3-methylimidazolium nitrate ([Emim][NO3]) at mass fractions of 0.01, 0.025, 0.05 are measured in a pressure range of 3.50-15.0 MPa via an isochoric step-heating pressure search method. The thermodynamic inhibition effect of mixed ionic liquids containing [Emim][NO3] in conjunction with 1-ethyl-3-methylimidazolium chloride ([Emim][Cl]) at low and high concentrations on methane hydrate formation is also investigated for the possible presence of synergistic effects. It is observed that for all the inhibitor systems containing [Emim][NO3] or [Emim][Cl], the inhibition effect increases progressively with the increased concentration and pressure. In addition, the mixture of [Emim][NO3] and [Emim][Cl] does not always exhibit synergetic effect on the thermodynamic inhibition of methane hydrate at higher concentrations up to 0.2 mass fraction. The higher concentrations are, the positive interactions between [Emim][NO3] and [Emim][Cl] possibly happen at higher pressures.