Prediction of Phase Equilibrium of Methane Hydrates in the Presence of Ionic Liquids

Abstract

In this work, a predictive method is applied to determine the vapor–liquid-hydrate three-phase equilibrium condition of methane hydrate in the presence of ionic liquids and other additives. The Peng–Robinson–Stryjek–Vera Equation of State (PRSV EOS) incorporated with the COSMO-SAC activity coefficient model through the first order modified Huron–Vidal (MHV1) mixing rule is used to evaluate the fugacities of vapor and liquid phases. A modified van der Waals and Platteeuw model is applied to describe the hydrate phase. The absolute average relative deviation in predicted temperature (AARD-T) is 0.31% (165 data points, temperature ranging from 273.6 to 291.59 K, and pressure ranging from 1.01 to 20.77 MPa). The method is further used to screen for the most effective thermodynamic inhibitors from a total of 1722 ionic liquids and 574 electrolytes (combined from 56 cations and 41 anions). The valence number of ionic species is found to be the primary factor of inhibition capability, with the higher valence leading to stronger inhibition effects. The molecular volume of ionic liquid is of secondary importance, with the smaller size resulting in stronger inhibition effects.

Inhibition effect of 1-ethyl-3-methylimidazolium chloride on methane hydrate equilibrium

“…A predictive method was applied to predict the vapor-liquid-hydrate three-phase equilibrium condition of methane hydrate in the presence of the ionic liquid EMIM-Cl [17][18][19][20]. At equilibrium, the fugacity of water is equal in all coexisting phases (vapor, liquid, and hydrate phase).…”

“…The measurements were performed in the concentration ranging from 0.1 to 0.4 mass fraction of EMIM-Cl aqueous solution and pressure ranging from 5.00 to 35.00 MPa. A predictive thermodynamic model with an explicit pressure dependence of the Langmuir adsorption constant [17][18][19][20] was applied to describe the experimental results of dissociation conditions of methane hydrates in the presence of EMIM-Cl, even at high pressures (up to 350 bar), in this work.…”

“…Filled symbols represent experimental results of this study and open symbols stand for literature data[7; 16]. Solid lines are the predicted methane hydrate boundary from the predictive thermodynamic model[17][18][19][20].…”

An improved model for the phase equilibrium of methane hydrate inhibition in the presence of ionic liquids

“…Partoon et al [15] used electrolyte solution model to predict phase equilibrium conditions for methane hydrate-IL-water system, where water activity is computed from Pitzer-Mayorga activity model which showed an AARD in predicted temperature less than 0.6% in comparison with their own experimental data. Chin et al [17] screened inhibition power of 1722 ILs and 574 electrolytes based on key factors consideration such as valance number and molecular size of ILs and electrolytes. This simulated model is based on the hydrate phase computed from modified van der Waals and Platteeuw model, Peng-Robinson-Stryjek-Vera EoS (PRSV-EoS) incorporated with the COSMO-SAC activity coefficient model through the first order modified Huron-Vidal (MHV1) mixing rule which are used to evaluate the fugacity of vapor and liquid phases, respectively.…”

“…b ð1Þ and h are dependent upon the temperature and pressure (H-L-V data).A ' is the Debye-Hückel constant for water as reported by Eq. (17)[40].A ' ¼ 4:0 Â 10 À6 T À 273:15 ð Þ 2 þ 5:0 Â 10 À4 ðT À 273:15Þ þ 0:3769(17) …”