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Publication list of Kaj Thomsen

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Papers, reports, and thesis

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 aqeous species is selected and recommended for use. Speciation schemes for aqeous 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.

Zheng Guo, Bena-Marie Lue, Kaj Thomsen, Anne Boye Strunge Meyer, and Xuebing Xu, Predictions of Flavonoid Solubility in Ionic Liquids by COSMO-RS: Experimental Verification, Structural Elucidation, and Solvation Characterization,  (Green Chemistry,  9(2007)1362-1373))

ABSTRACT: Predictions of the solubility of flavonoids in a large variety of ionic liquids (ILs) with over 1800 available structures were examined based on COSMO-RS computation. The results shows that the solubilities of flavonoids are strongly anion-dependent; and the ILs could be classified into 3 groups according to the values of esculin solubility. The predictions were experimentally verified by the measurement of the solubilities of esculin and rutin in 12 ILs with varying anion and cation parts. It is shown that predicted and experimental results generally have a good agreement, indicating the correctness of the physics of COSMO-RS as an experimentally independent approach, and the application potential to preselect favourable structures from a large pool of available ILs. Importantly, this work first systemically demonstrated that COSMO-RS derived parameters, electrostatic misfit, H-bonding, and van der Waals interaction energy, are capable of and effectively characterize the complicated multiple interactions in IL system. Force field analysis shows that H-bonding interaction is the most dominant interaction for ILs (followed by electrostatic misfit and van der Waals interactions) to determine the solubility of flavonoids, and anionic part has greater effect on the overall H-bonding capability of the IL. Based on solvation interaction energy with flavonoids and hydrogen bond basicity derived from COSMO-RS, ILs were scaled and categorized qualitatively and quantitatively, which may be of general value to better understand the solvation behaviors of ILs. Conversely, the improved understanding and knowledge of the correct association of specific interactions with defined groups of ILs may help to mix and match these moieties into an optimal structure for a particular application. Therefore, the data obtained in this study may be important for the tailoring of the desired structures of ILs used as the media for efficient enzymatic esterification of flavonoids.

Yi Lin, Kaj Thomsen and Jean-Charles de Hemptinne, Multi Component Equations of State for Electrolytes”,  (AIChE Journal, 53(4)(2007)989-1005)

ABSTRACT: Four equations of state have been implemented and evaluated for multi-component electrolyte solutions at different temperatures and pressures. The equations contain terms accounting for short-range and long-range interactions in electrolyte solutions. Short range interactions are described by one of the three equations of state, Peng-Robinson, Soave-Redlich-Kwong, or Cubic-Plus-Association (CPA). Long range interactions are described by either the simplified mean spherical approximation (MSA) solution of the Ornstein–Zernicke equation or the simplified Debye-Hückel term. An optional Born term is added to these electrostatic terms. The resulting electrolyte equations of state were tested by determining the optimal model parameters for the multi-component test system consisting of H₂O, Na⁺, H⁺, Ca²⁺, Cl^-, OH^-, SO₄^2-. In order to describe the thermodynamics of this multi-component system, ion specific parameters were determined. The parameters in the equations of state were fitted to experimental data consisting of apparent molar volumes, osmotic coefficients, mean ionic activity coefficients, and solid-liquid equilibrium data. The results of the parameter fitting are presented. The ability of the equations of state to reproduce the experimental data is demonstrated. The performance of the equations of state for multi-component systems is compared and analyzed in view of the various short range and long range terms employed.

Kaj Thomsen, Jørgen Peter Jensen, Peter Simonsen, Bo Sander, Reuse of Alkali from Fly Ash from Biomass Combustion,  Report written in Danish language on research project sponsored by PSO (Danish Power Plants).

ABSTRACT: Experiments to leach potassium salts from fly ash from straw combustion were performed. The fly ash was produced in the bio mass boiler at the Avedøre power plant in south western Copenhagen, Denmark. The fly ash contained approximately 90 mass percent water soluble material. When the fly ash was dissolved at low pH, a slightly higher solubility was found. 100 gram fly ash consisted typically of 9 gram insoluble material, 9 gram calcium phosphate, 29 gram potassium sulfate and 53 gram of potassium chloride. In addition, 100 gram of fly ash contained approximately 1 mg of cadmium, corresponding to a concentration of cadmium of 10 ppm in the fly ash. Fly ash from the bio mass boiler at the Avedøre power plant apparently has a significantly larger content of potassium salts than fly ash from other boilers.
The Extended UNIQUAC thermodynamic model was used for calculating relevant phase diagrams and calculations of the necessary amount of water required for dissolving all the KCl and all KCl + K2SO4 of the fly ash. This theoretical minimum amount of water was calculated at a range of temperatures between 10 and 100°C. The amount of water required at 100°C was less than half of that required at 10°C. Experiments were performed in order to find a feasible method for separating the potassium salts of the fly ash from the ash residue and especially from the soluble cadmium salts found in the fly ash.
Experiments with counter current leaching of fly ash in a fluid bed gave unsatisfactory results. Apparently there was a lack of contact between the wash water and the ash. In addition, sedimentation was very slow resulting in an incomplete separation of wash water and ash residue. Experiments with ion exchange by adding CaCl2 to the wash water and successive precipitation of gypsum or anhydrite gave unsatisfactory results. Process simulation had shown that by this method the necessary amount of washing water could be decreased. This is due to the higher solubility of potassium chloride compared to potassium sulfate. By using this reduced amount of washing water with CaCl2 a viscous, muddy slurry was obtained. It was not possible to separate this slurry into a liquid phase and a solid phase.
It was found that a good separation was obtained by intense stirring followed by centrifuging or by filtering the slurry in a filter press. The lab experiments were performed as a counter current leaching process in four stages. Depending on the applied amount of water relative to the theoretical minimum amount of water a complete separation could be obtained in two or more stages. More stages are required if less water is used. If the leaching is performed in less stages, a larger amount of water is required.
If the washing process was performed at pH 1, the phosphate fraction could successively be obtained as a fine, white powder of almost pure calcium phosphate by regulating pH to 12. If the washing process was conducted at a pH between 1 and 5 and pH was successively adjusted to 12, cadmium could not be detected in the brine by current analysis methods. All cadmium was precipitated as phosphate.

Kaj Thomsen, Duc Thoung Vu, Mette Stenby, Jørgen Peter Jensen, Peter Simonsen and Bo Sander, Leaching of Nutrient Salts from Fly Ash from Biomass Combustion, (Proceedings from 14th European Conference and Technology Exhibition on Biomass for Energy, Industry and Climate Protection, October 2005, p. 1273-1276)

ABSTRACT: Methods to selectively leach nutrient salts from fly ash, while leaving cadmium un-dissolved were studied. Temperature, pH, water to fly ash ratio are all expected to influence the kinetics and the equilibrium boundaries for this process. Three different leaching methods were investigated. The first method was a counter current moving bed process in four stages. The ash was kept in filter bags and leached with water that was introduced into the bags at 40-50°C. In the second method, fly ash and water was brought into contact in a partially fluidized bed. The third method was a counter current moving bed process with agitation/centrifugation. It was found that a satisfactory leaching of the nutrient salts could be achieved with the third method using only two or three stages, depending on the water to fly ash ratio. It is an advantage to perform the process at temperatures above 50°C as the amount of water used for leaching at this temperature can be reduced compared to the amount of water needed at 25°C.

Ada Villafáfila García, Kaj Thomsen, and Erling H. Stenby, Prediction of Mineral Scale Formation in Geothermal and Oilfield operations using the Extended UNIQUAC Model. Part II: Carbonate Scaling Minerals,  (Geothermics 35(2006)239-284)

ABSTRACT: Two additional parameters to account for the pressure dependency of solubility are added to the Extended UNIQUAC model presented by Thomsen and Rasmussen (1999). The improved model has been used for correlation and prediction of vapor-liquid-solid equilibrium for different carbonate systems (CaCO₃, MgCO₃, BaCO3 and SrCO₃) causing scale problems. The solubility of NaCl and CO₂ in pure water, and the solubility of CO₂ in solutions of different salts (NaCl and Na₂SO₄) have also been correlated. The temperature and pressure range covered is from 0 to 250°C and from 1 to 1000 bar, respectively. The results show that the Extended UNIQUAC model, with the proposed pressure parameters, is able to represent binary (NaCl-H₂O, MCO₃-H₂O and CO₂-H₂O), ternary (MCO₃-CO₂-H₂O, CO₂-NaCl-H2O and CO₂-Na₂SO₄-H₂O) and quaternary (CO₂-NaCl-Na₂SO₄-H₂O) solubility data within the experimental accuracy in the temperature range from 0 to 250°C, and the pressure range from 1 to 1000 bar. M stands for Ca²⁺, Mg²⁺, Ba²⁺ and Sr²⁺

Søren Gregers Christensen and Kaj Thomsen, Representation of volumetric data of electrolyte solutions at varying concentrations and temperatures,  (Internal report)

ABSTRACT: A modification of the Masson equation combined with Young’s rule based on ion specific parameters has been applied to volumetric data for mixtures of (H⁺, Na⁺, K⁺, NH₄⁺, Ca⁺⁺, Mg⁺⁺) (Cl^-,NO₃^-,SO₄^--). The parameters have been regressed from data in the temperature range 0 – 100°C and concentration range 0 – 11.8 mol/kg but are shown to be valid up to saturation. The model only requires 5 parameters per ion in the entire range of concentration and temperature. The model is easily applied to multi component mixtures, and it is shown that the relative errors of the predicted results in both ternary and quaternary systems are well within the experimental accuracy of the data.

Kaj Thomsen, Modeling Electrolyte Solutions with the extended universal quasichemical (UNIQUAC) Model, (Presented at the 11th ISSP in Aveiro, Portugal, 2004) (Journal of Pure and Applied Chemistry, 77(2005)531-542, issue 3 )

ABSTRACT: The extended universal quasichemical (UNIQUAC) model is a thermodynamic model for solutions containing electrolytes and non-electrolytes. 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.

Søren Gregers Christensen and Kaj Thomsen, Experimental measurement and modeling of the distribution of solvent and ions between an aqueous phase and an ion exchange resin, (Fluid Phase Equilibria, 228-229(2005)247-260).

ABSTRACT: The distribution of solutes and solvent between an aqueous solution of salt and an ion exchange resin has been measured at ambient temperature. The experiments have been performed for aqueous solutions of KNO₃, KCl, Ca(NO₃)₂ and CaCl₂ in the concentration range of 0-3N. The absorption has been measured for 3 gel type and 3 macroreticular resins with a degree of crosslinking varying from 10.5 to 18.5%. The experimental results have been modeled with the Extended UNIQUAC model combined with an elastic term taking the elastic properties of the resin structure into account. The model shows very good predictions with varying degree of crosslinking, and the deviations between model results and experimental data are all within the experimental error.

Ada Villafáfila García, Kaj Thomsen, Prediction of Mineral Scale Formation in Geothermal and Oilfield Operations using the Extended UNIQUAC Model. Part I: Sulphate Scaling Minerals, and Erling H. Stenby (Geothermics, 34(2005)61-97)

Pressure parameters are added to the Extended UNIQUAC model presented by Thomsen and Rasmussen (1999). The improved model has been used for correlation and prediction of solid-liquid equilibrium (SLE) of scaling minerals (CaSO4, CaSO4·2H2O, BaSO4 and SrSO4) at temperatures up to 300°C and pressures up to 1000 bar. The results show that the Extended UNIQUAC model, with the proposed pressure parameters is able to represent binary, ternary and quaternary solubility data within the experimental accuracy in the temperature range from -20 to 300°C, and the pressure range from 1 to 1000 bar.

Kaj Thomsen, Maria Iliuta, and Peter Rasmussen "Extended UNIQUAC model for correlation and prediction of vapor-liquid-liquid-solid equilibria in aqueous salt systems containing non-electrolytes. Part B. Alcohol (Ethanol, Propanols, Butanols) - water - salt systems". (Chemical Engineering Science 59(2004)3631-3647, issue 17)

ABSTRACT:  The Extended UNIQUAC model is an electrolyte model formed by combining the original UNIQUAC model, the Debye-Hückel law, and the Soave-Redlich-Kwong equation of state. The model only requires binary, temperature dependent interaction parameters. It has previously been used to describe the excess Gibbs energy for aqueous electrolyte mixtures and aqueous electrolyte systems containing methanol. It has been found to be an adequate model for representing solid-liquid-vapor equilibrium and thermal property data for strongly non-ideal systems. In this work the model is extended to aqueous salt systems containing higher alcohols. The calculations are based on an extensive database consisting of salt solubility data, vapor liquid equilibrium data, and liquid-liquid equilibrium data for solvent mixtures and for mixed solvent-electrolyte systems.
The application of this model to represent the vapor-liquid-liquid-solid equilibria in aqueous systems containing various non-electrolytes (ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, 2-methyl 1-propanol, 2-methyl 2-propanol) and various ions (Na⁺, K⁺, NH₄⁺, Cl^-, NO₃^-, SO₄^2-, SO₃^2-, HSO₃^-, CO₃^2-,and HCO₃^-) shows the capability of the model to accurately represent the phase behavior of these kinds of systems.