Inhibition effect of 1-ethyl-3-methylimidazolium chloride on methane hydrate equilibrium. (December 2015) - Chu, Che-Kang
Highlights: Inhibition effect of an ionic liquid on methane hydrate formation was examined. The ionic liquid 1-ethyl-3-methylimidazolium chloride was investigated. DSC measurement was performed to determine methane hydrate dissociation temperature. The experiments were performed at pressure ranging from (5.00 to 35.00) MPa. A predictive thermodynamic model was applied to describe the experimental data. Abstract: The dissociation conditions of methane hydrate in the presence of 0.1, 0.2, 0.3 and 0.4 mass fraction of 1-ethyl-3-methylimidazolium chloride (abbreviated by EMIM-Cl hereafter) were experimentally determined. A high pressure micro-differential scanning calorimeter equipped with a motorized pump was applied to measure the dissociation temperature of the (hydrate + liquid water + vapor) three-phase equilibrium under a constant pressure process with a pressure ranging from (5.0 to 35.0) MPa. The addition of EMIM-Cl would inhibit the methane hydrate formation. The most significant inhibition effect was observed at 0.4 mass fraction of EMIM-Cl in aqueous solution to lower the dissociation temperature by 12.82 K at 20.00 MPa in comparison to that of the (methane + water) system. 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 applied to evaluate the fugacity of vapor and liquid phase. A modified van der Waals and Platteeuw model with an explicit pressure dependence of the Langmuir adsorption constant was applied to determine the fugacity of hydrate phase. The predictive thermodynamic model successfully describes the tendency of phase behavior of methane hydrate in the presence of EMIM-Cl in the range from 0.1 to 0.4 mass fraction with absolute average relative deviation in predicted temperature of 0.70%.