Modeling of Gas Solubility Using the Electrolyte Cubic Plus Association Equation of State

Abstract

The prediction of the solubilities of carbon dioxide and methane in aqueous solutions of inorganic salts is important for geological carbon storage, enhanced oil recovery, gas hydrate formation and seawater desalination. Few electrolyte equations of state can be used for accurate gas solubility calculations over wide ranges of temperature, pressure and salt molality. This work presents a thermodynamic modeling study on the solubilities of carbon dioxide and methane in aqueous solutions of several inorganic salts with the electrolyte Cubic-Plus-Association equation of state. The binary interaction parameters between ion and gas are obtained by fitting the experimental data of gas solubility in single-salt solutions. It is shown that the equation of state can satisfactorily correlate the gas solubility over a wide range of conditions, with deviation less than the reported experimental uncertainties (7%) for most systems. The equation of state is then used to predict the gas solubility in multi-salt solutions, and a satisfactory performance is achieved. The saltingout effects resulting from ion size, charge density, and salt concentration are also extensively discussed.

Predicting activity coefficients with the Debye–Hückel theory using concentration dependent static permittivity

“…In this way, DHFULL still presents a thermodynamically consistent approach, and it can be integrated into a thermodynamic model, for example, an equation of state, 29 with other molecular interactions considered. The integrated model shall then offer the capability to describe various experimental data over a wide range of temperature, pressure and concentration 30,38,49,51,69,70 . It also provides the flexibility to adjust the size parameters together with other model parameters to the experimental data if this becomes necessary.…”

Thermodynamic modeling of gas solubility in aqueous solutions of quaternary ammonium salts with the e-CPA equation of state

“…the model parameters are by nature ion specific, while in order to minimize the number of parameters, a series of assumptions have been made. For more details of e-CPA and how the parameters are set, the reader is referred to the Section A of Support Information, Maribo-Mogensen et al [23] or particularly Sun et al [27,28]. The temperature dependency parameter ( ) was respectively set to 340 K and 350K for chloride salts and bromide salts in the work of Maribo-Mogensen et al [23].…”

“…The temperature dependency parameter ( ) was respectively set to 340 K and 350K for chloride salts and bromide salts in the work of Maribo-Mogensen et al [23]. In this work, three fitting approaches have been investigated for the regression of the ion-gas binary interaction parameters, as in our previous works [27,28]. Approaches A, B and C have respectively three, two and one adjustable parameters, and more details are given in the Table S1 The physical properties and pure component e-CPA parameters are summarized in Tables S2 and S3 of Supporting Information.…”

Evaluating the Performance of the PC-SAFT and CPA Equations of State on Anomalous Properties of Water

“…Thus, this model achieves a balance between accuracy due to the inclusion of the association term and simplicity, as all physical interactions are represented by SRK . The CPA can be expressed in terms of residual Helmholtz free energy as where a SRK is the Helmholtz free energy contribution of the SRK equation of state, which contains the contribution of repulsive and dispersive interactions, and a assoc is the contribution of association. These terms can be expressed as where n is the total number of moles, b is the co-volume parameter, v is the molar volume, a ( T ) is the temperature dependent energy parameter of the mixture, and X A i is the monomer fraction (eq ).…”