Kaj Thomsen

Modeling of vapor-liquid-solid equilibrium in gas-aqueous electrolyte systems

Abstract A thermodynamic model for the description of vapor–liquid–solid equilibria is introduced. This model is a combination of the extended UNIQUAC model for electrolytes and the Soave–Redlich–Kwong cubic equation of state. The model has been applied to aqueous systems containing ammonia and/or carbon dioxide along with various salts. Model parameters valid in the temperature range 0–110°C, the pressure range from 0–100 bar, and the concentration range up to approximately 80 molal ammonia are given. The model parameters were evaluated on the basis of more than 7000 experimental data points.

Correlation and Prediction of Thermal Properties and Phase Behaviour for a Class of Aqueous Electrolyte Systems

Abstract An extended UNIQUAC model is used to describe phase behaviour (VLE, SLE) and thermal properties (heat of mixing, heat capacity) for aqueous solutions containing ions like (Na + , K + , H + ) (Cl − , NO 3 − , SO 4 2− , OH − , CO 3 2− , HCO 3 − ). A linear temperature dependence of the binary interaction parameters allows good agreement with experimental data in the temperature range 0–110°C.

Extended UNIQUAC model for correlation and prediction of vapour–liquid–solid equilibria in aqueous salt systems containing non-electrolytes. Part A. Methanol–water–salt systems

Abstract The Extended UNIQUAC model has previously been used to describe the excess Gibbs energy for aqueous electrolyte mixtures. It is an electrolyte model formed by combining the original UNIQUAC model, the Debye–Huckel law and the Soave–Redlich–Kwong equation of state. In this work the model is extended to aqueous salt systems containing non-electrolytes in order to demonstrate its ability in representing solid–liquid–vapour (SLV) equilibrium and thermal property data for these strongly non-ideal systems. The model requires only pure component and binary temperature-dependent interaction parameters. The calculations are based on an extensive database consisting of salt solubility data in pure and mixed solvents, VLE data for solvent mixtures and mixed solvent–electrolyte systems and thermal properties for mixed solvent solutions. Application of the model to the methanol–water system in the presence of several ions (Na + , K + , NH 4 + , Cl − , NO 3 − , SO 4 2− , CO 3 2− and HCO 3 − ) shows that the Extended UNIQUAC model is able to give an accurate description of VLE and SLE in ternary and quaternary mixtures, using the same set of binary interaction parameters. The capability of the model to predict accurately the phase behaviour of methanol–water–three salts systems is illustrated.

Simulation and optimization of fractional crystallization processes

A general method for the calculation of various types of phase diagrams for aqueous electrolyte mixtures is outlined. It is shown how the thermodynamic equilibrium precipitation process can be used to satisfy the operational needs of industrial crystallizer/centrifuge units. Examples of simulation and optimization of fractional crystallization processes are shown. In one of these examples, a process with multiple steady states is analyzed. The thermodynamic model applied for describing the highly non-ideal aqueous electrolyte systems is the Extended UNIQUAC model.

Modeling electrolyte solutions with the extended universal quasichemical (UNIQUAC) model

The extended universal quasichemical (UNIQUAC) model is a thermodynamic model for solutions containing electrolytes and nonelectrolytes. The model is a Gibbs excess function consisting of a Debye–Hückel term and a standard UNIQUAC term. The model only requires binary ion-specific interaction parameters. A unique choice of standard states makes the model able to reproduce solid–liquid, vapor–liquid, and liquid–liquid phase equilibria as well as thermal properties of electrolyte solutions using one set of parameters.

Modeling of Dielectric Properties of Aqueous Salt Solutions with an Equation of State

The static permittivity is the most important physical property for thermodynamic models that account for the electrostatic interactions between ions. The measured static permittivity in mixtures containing electrolytes is reduced due to kinetic depolarization and reorientation of the dipoles in the electrical field surrounding ions. Kinetic depolarization may explain 25-75% of the observed decrease in the permittivity of solutions containing salts, but since this is a dynamic property, this effect should not be included in the thermodynamic modeling of electrolytes. Kinetic depolarization has, however, been ignored in relation to thermodynamic modeling, and authors have either neglected the effect of salts on permittivity or used empirical correlations fitted to the measured static permittivity, leading to an overestimation of the reduction in the thermodynamic static permittivity. We present a new methodology for obtaining the static permittivity over wide ranges of temperatures, pressures, and compositions for use within an equation of state for mixed solvents containing salts. The static permittivity is calculated from a new extension of the framework developed by Onsager, Kirkwood, and Fröhlich to associating mixtures. Wertheims association model as formulated in the statistical associating fluid theory is used to account for hydrogen-bonding molecules and ion-solvent association. Finally, we compare the Debye-Hückel Helmholtz energy obtained using an empirical model with the new physical model and show that the empirical models may introduce unphysical behavior in the equation of state.

Vapor–liquid–solid equilibria of sulfur dioxide in aqueous electrolyte solutions

Abstract The Extended UNIQUAC model for electrolyte systems, combined with the Soave–Redlich–Kwong equation of state is used to describe the complex vapor–liquid–solid equilibria of sulfur dioxide in electrolyte solutions. Model parameters based on 1500 experimental data points are presented. The parameters are applicable in the temperature range 0–110°C, concentrations up to saturation and pressures up to 30 bar. This validity range corresponds to the experimental data used for the evaluation of parameters.

Predictive screening of ionic liquids for dissolving cellulose and experimental verification

In this work, 357 ionic liquids (ILs) formed from 17 cations and 21 anions were selected for evaluation of their ability to dissolve cellulose by COSMO-RS. In order to evaluate the predictive model and method, experimental measurements of the solubility of microcrystalline cellulose (MCC) in 7 of these ILs were also conducted. Predicted results from logarithmic activity coefficients were generally in good agreement with the experimental results. Three different models were used for describing cellulose, and the mid-monomer part of the cellotriose model was found to be closer to the experimental results than a neat glucose model and the model of the mid-dimer part of cellotetraose. Excess enthalpy calculations indicated that hydrogen-bond (H-bond) interactions between cellulose (i.e. the three cellulose models) and the 7 studied ILs are key factors for the solubility of cellulose, and the anions play a crucial role in the cellulose dissolution process. Importantly, the cations of methylimidazolium+, pyridinium+, ethylmorpholinium+ and methylpyrrolidinium+ structured with functional groups including ethyl, allyl, 2-hydroxylethyl, 2-methoxyethyl and acryloyloxypropyl, combined with anions Ac−, Dec−, HCOO−, Cl−, BEN−, DMPO4−, DEP−, DBP− and Br− were predicted to be the best for dissolving cellulose.

Modeling of Dielectric Properties of Complex Fluids with an Equation of State

The static permittivity is a key property for describing solutions containing polar and hydrogen bonding compounds. However, the precise relationship between the molecular and dielectric properties is not well-established. Here we show that the relative permittivity at zero frequency (static permittivity) can be modeled simultaneously with thermodynamic properties. The static permittivity is calculated from an extension of the framework developed by Onsager, Kirkwood, and Fröhlich to associating mixtures. The thermodynamic properties are calculated from the cubic-plus-association (CPA) equation of state that includes the Wertheim association model as formulated in the statistical associating fluid theory (SAFT) to account for hydrogen bonding molecules. We show that, by using a simple description of the geometry of the association, we may calculate the Kirkwood g-factor as a function of the probability of hydrogen bond formation. The results show that it is possible to predict the static permittivity of complex mixtures over wide temperature and pressure ranges from simple extensions of well-established theories simultaneously with the calculation of thermodynamic properties.

Review and recommended thermodynamic properties of FeCO3

Abstract An extensive review of entropy, enthalpy of formation and Gibbs energy of formation, heat capacity, aqueous solubility and solubility constant of FeCO3 is given. A consistent set of thermodynamic properties for FeCO3 and relevant aqueous species is selected and recommended for use. Speciation schemes for aqueous FeCO3 are reviewed and evaluated. Issues related to supersaturation of FeCO3 are discussed. Works on the thermal decomposition of FeCO3 are presented and an overview of measured solubility and synthesis of FeCO3 is given.