Experiment and thermodynamic modeling of methane hydrate equilibria in the presence of aqueous imidazolium-based ionic liquid solutions using electrolyte cubic square well equation of state

Methane hydrate dissociation conditions in the presence of imidazolium based aqueous ionic liquid solutions including 1-buthyl-3-methylimidazolium methyl sulfate ([BMIM][MeSO4]), 1-ethyl-3-methylimidazolium hydrogen sulfate ([EMIM][HSO4]), 1-ethyl-3-methylimidazolium ethyl sulfate ([EMIM][EtSO4]), 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIM][BF4]) and 1-(2-hydroxyethyl)-3-methylimidazolium tetrafluoroborate ([OH-EMIM][BF4]) are investigated. Isochoric method is used to measure experimental data in temperature range of 281.9-287.4K and in pressure range of 7.08-12.16 MPa. The studied ionic liquids present a thermodynamic inhibition behavior on methane hydrate and cause to shift the hydrate equilibrium dissociation conditions to the higher pressures/lower temperatures. It is found that the most effective thermodynamic inhibitor is [OH-EMIM][BF4] and among alkylsulfate-containing ionic liquids, the thermodynamic inhibition effects of two ionic liquids such as [EMIM][HSO4] and [BMIM][MeSO4] are better than that of [EMIM][EtSO4]. Furthermore, the electrolyte cubic square-well equation of state (eCSW EoS) is coupled with the van der Waals-Platteuw model and applied to predict the hydrate dissociation pressures of the methane + ionic liquid + water systems. A good agreement between the results of the model with the experimental data indicates the reliability of this model to predict the hydrate equilibrium conditions. (C) 2013 Elsevier B.V. All rights reserved.