Experimental Measurements and Thermodynamic Modeling of Hydrate Dissociation Conditions for Methane + TBAB + NaCl, MgCl₂, or NaCl-MgCl₂ + Water Systems

Abstract

Much attention has been made to solidified natural gas (SNG) technology via clathrate hydrates in recent years. Tetra-n-butyl ammonium bromide (TBAB) is known as a promising promoter to tackle hydrate technology limitations. This research focuses on investigating the effect of NaCl, MgCl2, and the mixture of NaCl + MgCl2 (two major soluble salts in naturally occurring water are NaCl and MgCl2) on hydrate stability conditions of methane in the presence of TBAB aqueous solution. An isochoric pressure search method was employed to generate the dissociation/equilibrium data in the temperature, pressure, and TBAB composition ranges of 275–291 K, 0.5–5.5 MPa, and 5–20 wt %, respectively. The experimental results reveal that in the case of wTBAB = 5%, NaCl and MgCl2 with the low concentration of 5% have a promotion effect for the systems of CH4 + TBAB + NaCl + H2O, CH4 + TBAB + MgCl2 + H2O, and CH4 + TBAB + NaCl + MgCl2 + H2O and shift the dissociation curve toward milder region (higher temperature and lower pressure). However, in the case of wTBAB = 20%, NaCl and MgCl2 play an inhibition role in all of the aforementioned systems. A thermodynamic model was developed based on the van der Waals–Platteeuw (vdWP) solid solution theory, to predict the behavior of methane in the presence of the promoter in saline water. The Peng–Robinson equation of the state (PR EOS) is used to describe the thermodynamic properties of the gas phase, and the electrolyte non-random two-liquid (e-NRTL) activity coefficient model is employed to determine the activity coefficient of water and promoter in the electrolyte solution. The presented model results are in satisfactory agreement with the experimental data generated in this work. The discrepancy of the model results with experimental is 10.78%.

Hydrate Phase Equilibria of Methane + TBAC + Water System in the Presence and Absence of NaCl and/or MgCl2

“…NaCl and MgCl 2 promote the methane + TBAC (0.05 mass fraction) system by about 2.7 K. It means that the synergism of salt + TBAC promotes the thermodynamic stability conditions of semiclathrate hydrates of the methane + salt + TBAC systems in the mentioned concentration. Such an effect was observed in the presence of NaCl in conjunction with TBAB . As reported, the hydrate stability conditions of the methane + TBAB + NaCl (0.05 + 0.05 mass fraction) + water system are in lower pressures and higher temperatures compared to the methane + TBAB (0.05 mass fraction) + water system.…”

“…Lv et al reported the effects of different ions of seawater on the phase behavior of the methane + cyclopentane hydrate system . The influences of NaCl and/or MgCl 2 on the hydrate phase behaviors of CH 4 + TBAB and CH 4 + TBAB + THF systems were investigated in our previous works. , Mech and Sangwai reported the hydrate phase equilibrium data for methane + low THF mass fractions of 0.005 and 0.010 in the presence of NaCl with the mass fractions of 0.03, 0.05, and 0.10 in aqueous solutions in the pressure range of 2.17–6.43 MPa . In another study, they investigated the effects of mixed promoters of THF + TBAB on the phase equilibrium of methane hydrate in the presence of some inhibitors like NaCl .…”

Liquid–Liquid Equilibrium in the Nitric Acid + Calcium Nitrate + Water + Tri-n-octylamine System

“…It can calculate activity coefficients for ionic species and molecular species in aqueous electrolyte systems as well as in mixed solvent electrolyte systems. In recent years, this model is widely used for correlating the salting effect in VLE and LLE. − The main mathematical expression of this model is where is the excess Gibbs energy of electrolyte systems; is the long rang ion–ion interaction contribution; and is the short-range van der Waals interactions, which are only effective within the local domain of the species Equation leads to the following expression for the activity coefficient: where superscript * denotes an unsymmetric reference state; subscript i refers to molecular (m), cation (c), and anion (a); M s is the mixed solvent molecular weight; A ϕ is the Debye–Hückel constant; ρ is the closest approach parameter fixed at 14.9; Z i is the charge number of species i ; and I x is the ionic strength.…”

Effects of Graphene Oxide Nanosheets and Al2O3Nanoparticles on CO2Uptake in Semi‐clathrate Hydrates

“…Different thermodynamic and kinetic promoters have been proposed to modify the gas hydrate equilibrium conditions and the rate of hydrate formation. Thermodynamic promoters, including tetra-n-butyl ammonium bromide (TBAB) and tetra-hydrofuran (THF) modify the conditions for stable hydrate phases to higher temperatures and lower pressures [21][22][23][24]. Several studies have confirmed that CO 2 could probably be separated from flue gases under the effect of TBAB hydrates [5,25,26].…”