Modeling Phase Behavior of Semi-Clathrate Hydrates of CO₂, CH₄, and N₂ in Aqueous Solution of Tetra-n-butyl Ammonium Fluoride

Abstract

Semi-clathrate hydrates are members of the class of clathrate compounds. In comparison with clathrate hydrates, where the networks are formed only by H2O molecules, the networks of semi-clathrate hydrates are formed by mixtures of H2O and quaternary ammonium salts (QASs). The addition of QASs to the solution enables to improve the formation of semi-clathrate hydrates at much milder conditions comparing to clathrate hydrates. In this work, we study the phase equilibria of semi-clathrate hydrates of CH4, CO2, and N2gas in an aqueous solution of tetra-n-butyl ammonium fluoride (TBAF). An extension of the Chen–Guo model is proposed as a thermodynamic model. The Peng–Robinson equation of state (PREOS) was applied to calculate the fugacity of the gas phase and in order to determine the water activity in the presence of TBAF, a correlation between the system temperature, the TBAF mass fraction, and the nature of the guest molecules has been used. These equations were solved simultaneously and through optimizing tuning parameters via the Nelder–Mead simplex algorithm. The results are compared to experimental data and good agreement is observed.

Minireview on the Thermodynamic and Kinetic Modeling of Ionic Liquid Promoted Inhibition of Gas Hydrate Formation

“…Link cavities adsorb gas molecules in the second step, and the adsorption process is described by Langmuir adsorption theory. The Chen–Guo thermodynamic model is primarily used to study the phase equilibrium of semiclathrate hydrates such as methane, carbon dioxide, and natural gas in an aqueous solution of tetrabutylammonium fluoride (TBAF) IL . Moreover, the dissociation of semiclathrate hydrate formation with noble gases such as krypton in the presence of tetrabutylammonium bromide IL has also been modeled by the Chen–Guo model .…”

“…The fugacity of the gas in the basic hydrate is given by f i 0 and can be calculated from eq . Mesbah et al use a parametric relation to compute the activity of water, and the expression is given below The values for the parameters χ 1 and χ 2 are obtained from the global optimization algorithms such as genetic algorithm . The objective function is given as Here, P exp and P p are the experimental and predicted pressure, respectively.…”

“…Therefore, ILs act as kinetic and thermodynamic inhibitors. Following the work, several classes of ILs such as imidazolium, ammonium, phosphonium, and pyrolidinium cation-based ILs are being explored as inhibitors to the gas hydrate. − Along with the experimental investigations, IL-assisted gas hydrate systems are modeled in the thermodynamic and kinetic framework. − However, unlike the other organic solvents, ILs have a wide liquidus range, negligible vapor pressure, and high thermal stability. The cations and anions of ILs can form numerous nonbonded interactions with the solute molecule in the solvent.…”

Semi-clathrate hydrate phase stability conditions for methane + TetraButylAmmonium Bromide (TBAB)/TetraButylAmmonium Acetate (TBAA) + water system: Experimental measurements and thermodynamic modeling

“…Long et al [38] measured the hydrate phase stability conditions of CH 4 /CO 2 + TBAB + water systems in the P and T ranges of 0.54-14.57 MPa and 273.6-294.2 K, respectively. Alongside the experimental studies, various thermodynamic modeling studies on gas + ammoniumbased salts + water systems have been presented [39][40][41][42][43][44][45][46][47].…”

Hydrates of Binary Guest Mixtures: Fugacity Model Development and Experimental Validation

“…Recently, Mesbah et al modeled phase behavior of CO 2 , CH 4 , and N 2 semiclathrates in the presence of TBAB using the Chen-Guo model [33]. Previously, Mesbah et al performed thermodynamic modeling of CO 2 , CH 4 , N 2 , and H 2 S in the presence of TBAF via the Chen-Guo model [34]. Other works include that by Pandey et al, who also used the Chen-Guo model for prediction of equilibrium conditions of CO 2 , CH 4 , and N 2 in the presence of NaCl as inhibitor [35].…”