A comprehensive model for calculating phase equilibria and thermophysical properties of electrolyte systems (original) (raw)
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A speciation-based model for mixed-solvent electrolyte systems
Fluid Phase Equilibria, 2002
A comprehensive model has been developed for the calculation of speciation, phase equilibria, enthalpies, heat capacities and densities in mixed-solvent electrolyte systems. The model incorporates chemical equilibria to account for chemical speciation in multiphase, multicomponent systems. For this purpose, the model combines standard-state thermochemical properties of solution species with an expression for the excess Gibbs energy. The excess Gibbs energy model incorporates a long-range electrostatic interaction term expressed by a Pitzer-Debye-Hückel equation, a short-range interaction term expressed by the UNIQUAC model and a middle-range, second virial coefficient-type term for the remaining ionic interactions. The standard-state properties are calculated by using the Helgeson-Kirkham-Flowers equation of state for species at infinite dilution in water and by constraining the model to reproduce the Gibbs energy of transfer between various solvents. The model is capable of accurately reproducing various types of experimental data for systems including aqueous electrolyte solutions ranging from infinite dilution to fused salts, electrolytes in organic or mixed, water + organic, solvents up to the solubility limit and acid-water mixtures in the full concentration range.
Speciation and Phase Behavior in Mixed Solvent Electrolyte Solutions: Thermodynamic Modeling
A comprehensive mixed-solvent electrolyte (MSE) model has been applied to provide a thermodynamic foundation for crystallization studies. The model can be used to calculate phase equilibria, speciation, and other thermodynamic properties of multicomponent solutions containing electrolytes (salts, acids, or bases) in water, organic, or mixed solvents. The thermodynamic framework has been design to reproduce the properties of both aqueous and mixed-solvent electrolyte systems ranging from dilute solutions to solid saturation or pure-solute limit. The model combines an excess Gibbs energy model with detailed speciation calculations. The excess Gibbs energy model consists of a long-range interaction contribution represented by the Pitzer-Debye-Hückel expression, a short-range term expressed by the UNIQUAC model and a second-virialcoefficient type term for specific ionic interactions. The model accurately represents the solubility behavior of aqueous, non-aqueous and mixed-solvent electrolyte mixtures that are of interest in crystallization. The accuracy of the model has been demonstrated for the CaO -P 2 O 5 -H 2 O, Na -HCO 3 -CO 3 -H 2 O and Na -K -Mg -Ca -Cl -SO 4 -methanol -H 2 O systems. Of particular importance is the model's capability of reproducing the solubilities in multicomponent systems based on parameters obtained from binary data and its accuracy of predicting the correct solid phases in systems with widely varying solvent and ionic compositions.
Modeling acid–base equilibria and phase behavior in mixed-solvent electrolyte systems
Fluid Phase Equilibria, 2007
A comprehensive thermodynamic framework for mixed-solvent electrolyte systems has been applied to the simultaneous computation of phase behavior and acid-base equilibria. The computational approach combines an excess Gibbs energy model with a formulation for standard-state properties of individual species and an algorithm for speciation calculations. Using this framework, a consistent methodology has been established to calculate the pH of mixed-solvent solutions using a single, aqueous reference state. It has been shown that solid solubilities, vapor-liquid equilibria, solution pH and other properties can be reproduced for mixed solvents ranging from pure water to pure non-aqueous components and for solutes ranging from infinite dilution to the fused salt limit. In particular, the model has been shown to be accurate for mixtures containing hydrogen peroxide and ethylene glycol as solvents and various salts, acids and bases as solutes.
Iranian Journal of Oil and Gas Science and Technology, 2017
In this work, the performance of four electrolyte models for prediction the osmotic and activity coefficients of different aqueous salt solutions at 298 K, atmospheric pressure and in a wide range of concentrations are evaluated. In two of these models, (electrolyte Non-Random Two-Liquid e-NRTL and Mean Spherical Approximation-Non-Random Two-Liquid MSA-NRTL), association between ions of opposite charges for simplification purposes is ignored and in the other two ones, (Associative Mean Spherical Approximation-Non-Random Two-Liquid AMSA-NRTL and Binding Mean Spherical Approximation BiMSA) association and solvation effects are considered. The predictions of these four models for the osmotic and activity coefficients of electrolyte solutions at 298 K and atmospheric pressure are compared with the experimental data reported in the literature. This comparison includes, 28 different aqueous salt solutions including thio-cyanates, perchlorates, nitrates, hydroxides, quaternary ammonium sal...
A New Gibbs Energy Model for Obtaining Thermophysical Properties of Aqueous Electrolyte Solutions
Journal of Solution Chemistry, 2008
In this paper, a new Gibbs energy model is proposed to study the thermophysical properties of aqueous electrolyte solutions at various temperatures. The proposed model assumes that the electrolytes completely dissociate in solution. The model also has two temperature-independent adjustable parameters that were regressed using experimental values of the mean ionic activity coefficients (MIAC) for 87 electrolyte solutions at 298.15 K. Results from the proposed model for the MIAC were compared with those obtained from the E-Wilson, E-NRTL, Pitzer and the E-UNIQUAC models, and the adjustable model parameters were used directly to predict the osmotic coefficients at this temperature. The results showed that the proposed model can accurately correlate the MIAC and predict the osmotic coefficients of the aqueous electrolyte solutions better on the average than the other models studied in this work at 298.15 K. Also, the proposed model was examined to study the osmotic coefficient and vapor pressure for a number of aqueous electrolyte solutions at high temperatures. It should be stated that in order to calculate the osmotic coefficients for the electrolyte solutions, the regressed values of parameters obtained for the vapor pressure at high temperatures were used directly. The results obtained for the osmotic coefficients and vapor pressures of electrolyte solutions indicate that good agreement is attained between the experimental data and the results of the proposed model. In order to unequivocally compare the results, the same experimental data and same minimization procedure were used for all of the studied models.
Ion-specific thermodynamics of multicomponent electrolytes: A hybrid HNC/MD approach
Chemical Physics, 2009
Using effective infinite dilution ion-ion interaction potentials derived from explicit-water molecular dynamics (MD) computer simulations in the hypernetted-chain (HNC) integral equation theory we calculate the liquid structure and thermodynamic properties, namely the activity and osmotic coeffcients of various multicomponent aqueous electrolyte mixtures. The electrolyte structure expressed by the ion-ion radial distribution functions is for most ions in excellent agreement with MD and implicit solvent Monte-Carlo (MC) simulation results. Calculated thermodynamic properties are also represented consistently among these three methods. Our versatile HNC/MD hybrid method allows for a quick prediction of the thermodynamics of multicomponent electrolyte solutions for a wide range of concentrations and an efficient assessment of the validity of the employed MD force-fields with possible implications in the development of thermodynamically consistent parameter sets.
Fluid Phase Equilibria, 2002
Recent advances in modeling thermodynamic and transport properties of electrolyte solutions are reviewed. In particular, attention is focused on mixed-solvent electrolyte models, equations of state for high-temperature and supercritical electrolyte systems and transport property models for multicomponent, concentrated solutions. The models are analyzed with respect to their capability of computing thermodynamic and transport properties in wide ranges of conditions and composition (i.e. for aqueous or mixed-solvent, dilute or concentrated solutions). Various frameworks for the development of electrolyte models are discussed, i.e. models that treat electrolytes on a completely dissociated or undissociated basis and those that take into account the speciation of solutions. A new mixed-solvent electrolyte model is developed for the simultaneous calculation of speciation and phase equilibria. The role of speciation is discussed with respect to the representation of the thermodynamic properties of mixed-solvent electrolyte solutions and diffusion coefficients in aqueous systems.
Thermodynamic Model for Aqueous Electrolyte Solutions with Partial Ionization
Industrial & Engineering Chemistry Research, 2013
An equation of state has been developed to describe the thermodynamic properties of single electrolytes in water within a wide range of temperatures from 25 °C to near the critical point of the solvent. The new equation of state was obtained from an analytical expression of the Helmholtz free energy containing three major contributions: (1) a discrete-solvent term to account for short-range interactions between uncharged particles based on the Peng-Robinson equation of state, (2) an ion charging term described by the continuum-solvent model of Born, and (3) a charge-charge interaction term given by the explicit mean-spherical-approximation (MSA) expression. The thermodynamic model proposed here incorporates chemical equilibrium for the dissolved electrolyte allowing the calculation of the corresponding degree of dissociation of the salt at different temperatures. The present equation of state was applied to the representation of mean ionic activity coefficients, osmotic coefficients, standard free energies of hydration of ions, and densities for NaCl, CaCl 2 , K 2 SO 4 , and MgSO 4 salts in water over a wide range of temperatures and salt molalities. The results indicated a good agreement between the experimental data and those calculated using the present equation of state.