Coefficients Of Aqueous Solutions Research Articles

Understanding water behavior through activity coefficients in aqueous solutions: insights from experimental and modeled relative static permittivity

Understanding water behavior through activity coefficients in aqueous solutions: insights from experimental and modeled relative static permittivity

The SIT model parameters for interactions of carbonate compounds with sodium and potassium ions accounting for association

The current study is devoted to the determination of the SIT coefficients at 298.15 K for interactions, involving CO2(aq), HCO3−, and CO32‐, with mostly Na+ and K+ ions. The SIT model is a simple yet physically sound model for activity coefficients in aqueous solutions, that has just one parameter for each cation-anion or a dissolved gas – electrolyte interaction. Among the issues that were met for carbonate systems are the side reactions of hydrolysis and disproportionation in the carbonate solutions, that complicate the analysis of data and lead to unusually large difference, up to 9%, in the values of activity coefficients, determined in different authoritative laboratories. For Na2CO3 and K2CO3 solutions, it was necessary to take into account the reaction of formation of the ionic pair M++CO32‐=MCO3−, with the equilibrium constants β1o equal to log10β1o= 0.75 ± 0.08 for M+=Na+ and to log10β1o= 0.67 ± 0.11 for M+=K+. In all, there are values for more than 20 binary SIT interaction coefficients. All results are valid at 298.15 K, 0.1 MPa.

Modeling Osmotic Coefficients in Aqueous Solutions of 1-Alkyl-3-methylimidazolim Halides: A Theory That Reflects the Electrical Structure of Ions and ePC-SAFT

Modeling Osmotic Coefficients in Aqueous Solutions of 1-Alkyl-3-methylimidazolim Halides: A Theory That Reflects the Electrical Structure of Ions and ePC-SAFT

Analysis of Activity Coefficients in Aqueous Solutions of Alkali Metal Bromides Based on Dielectric Properties

Extended Debye–Hückel (EDH) theory was used to calculate activity coefficients in aqueous solutions of alkali-metal bromides at 298 K from experimentally determined values of their static permittivities. Calculations with non-optimized model parameters fit the nonmonotonic concentration-dependent trend of the activity coefficients and the cation radius–dependent trend of the activity coefficients. The latter is explained by hydration weakening and ion association strengthening in response to increasing cation radius in the salt series.

Modelling of Mean Ionic Activity and Osmotic Coefficients in Aqueous Solutions of Symmetrical Tetra alkyl Ammonium Halides

Modelling of Mean Ionic Activity and Osmotic Coefficients in Aqueous Solutions of Symmetrical Tetra alkyl Ammonium Halides

KINETICS OF OZONE REACTIONS WITH ADENINE AND CYTOSINE IN AQUEOUS SOLUTIONS

The ultraviolet spectroscopy method has been applied to study the kinetics of the ozone reactions with nitrogenous bases (NB), namely adenine and cytosine in aqueous solutions. At the first research stage, the range of NB working concentrations has been determined. It was found that linear dependences between optical densities and concentrations of nitrogenous bases aqueous solutions are quite reliable, with correlation coefficients r ≥ 0.998, are satisfied up to [NB] = 2.3 ∙ 10–4 mol/l. According to the Bouguer-Lambert-Beer law, adenine and cytosine extinction coefficients in aqueous solutions were determined and subsequently used to calculate their residual concentrations. At the next stage, the kinetics of nitrogenous bases ozonized oxidation was studied with equal initial concentrations of the starting substances ([NB]0 = [О3]0). The results revealed that the kinetic consumption curves of the starting reagents are fairly well linearized (r ≥ 0.996) in the second-order reaction equation coordinates. As found with the bubbling installation, 1 mol of the absorbed ozone falls on 1 mol of the used NB. Thus, the reactions of ozone with adenine and cytosine explicitly proceed according to the second-order kinetic laws (the first – according to О3 and the first – according to NB). The rate constants were calculated by the integral reaction equations, the values of which indicate a higher ozone reactivity in relation to nitrogen bases. The temperature dependences of the second-order rate constants was studied ranging 285-309 K, and the activation parameters (pre-exponential factors and activation energies) of the ozone reactions with adenine and cytosine in aqueous solutions were determined.

Relationship of the Permittivity with the Activity Coefficients of Water and Ions in Aqueous Solutions of Lithium and Sodium Sulfates

The activity coefficients in aqueous solutions of lithium and sodium sulfates at 298 K were calculated by the generalized Debye–Huckel theory using the experimental values of the static permittivity of the solutions. The effect of the hydration and ion association on the dielectric and thermodynamic properties of the electrolyte solutions was considered.

Anion-Specific Effects on Activity Coefficients in Aqueous Solutions of Sodium Salts: Modeling with the Extended Debye–Hückel Theory

The extended Debye–Huckel theory, which allows for concentration variation of electrolyte solution static permittivity, is employed to predict activity coefficients in aqueous solutions of sodium salts with various univalent anions (NaCl, NaBr, NaI, NaNO3, NaClO4 and NaSCN) at ambient conditions. Calculations without empirical adjustments reproduced the activity coefficients for NaI in the concentration range up to 6 mol·kg−1 and for NaSCN up to 2 mol·kg−1. In the case of other solutions, calculations underestimate water activity coefficients and overestimate mean ionic activity coefficients at concentrations beyond 0.5 mol·kg−1. In order to improve the representations, the model was extended to include ion pairing, which resulted in a better agreement between calculated activity coefficients and experimental data, especially for NaNO3. The ion pairing equilibrium constants were estimated and compared with available literature values. The extent of ion pairing was found to increase in the sequence NaI < NaSCN < NaBr < NaCl < NaClO4 < NaNO3, with violation of the Collins rule in the case of polyatomic oxygen-containing anions.

Novel solutions for closed-loop reverse electrodialysis: Thermodynamic characterisation and perspective analysis

Closed-loop Reverse Electrodialysis is a novel technology to directly convert low-grade heat into electricity. It consists of a reverse electrodialysis (RED) unit where electricity is produced exploiting the salinity gradient between two salt-water solutions, coupled with a regeneration unit where waste-heat is used to treat the solutions exiting from the RED unit and restore their initial composition. One of the most important advantages of closed-loop systems compared to the open systems is the possibility to select ad-hoc salt solutions to achieve high efficiencies. Therefore, the properties of the salt solutions are essential to assess the performance of the energy generation and solution regeneration processes. The aim of this study is to analyse the influence of thermodynamic properties of non-conventional salt solutions (i.e. other than NaCl-aqueous solutions) and their influence on the operation of the closed-loop RED. New data for caesium and potassium acetate salts, i.e. osmotic and activity coefficients in aqueous solutions, at temperature between 20 and 90 °C are reported as a function of molality. The data are correlated using Pitzer's model, which is then used to assess the theoretical performance of the whole closed-loop RED system considering both single and multi-stage regeneration units. Results indicate that KAc, CsAc and LiCl are the most promising salts among those screened.

Study of Aqueous Solutions of Surfactants in the Presence of Alcohols by Means of Ultrasonic Relaxation

Abstract Ultrasonic absorption coefficients in aqueous solutions of surfactants, octyltrimethylammonium bromide, dodecyltrimethylammonium bromide, and tetradecyltrimethylammonium bromide have been measured in the presence of 2-propanol or ethanol in the frequency range from 0.8 to 220 MHz at 25 °C. The frequency dependence of the observed absorption in solution of octyltrimethylammonium bromide has been characterized by a Debye-type relaxation equation with one single relaxation frequency which decreases with the surfactant concentration. On the other hand, the dependences in solutions of dodecyltrimethylammonium bromide and cetyltrimethylammonium bromide have been well fitted to the equation with two relaxation frequencies. One relaxation frequency decreases with the surfactant concentrations, and the other relaxation frequency shows concentration independence trend. The relaxation mechanisms have been considered on the basis of interaction between surfactant monomer and alcohol aggregate and of a conformational change of the surfactants with long hydrophobic groups to which plural alcohol molecules (dumpling cake) attract. The rate and thermodynamic parameters have been determined for aqueous solutions of octyltrimethylammonium bromide coexisting with 2.00 mol dm−3 2-propanol and 3.00 mol dm−3 ethanol. It has been speculated from the analysis that the dumpling cake of alcohols attaches and detaches on and from the alkyl chains of the surfactants. The number of alcohols in the aggregate is dependent on size of alcohol molecule although the forward and backward rate constants are not very dependent on coexisting alcohols. However, only the orders of the rate constants for the systems of dodecyltrimethylammonium bromide solution with 2.00 mol dm−3 2-propanol have been speculated because of too many parameters which should be determined. Following the proposed reaction model, the relation between the surfactant concentration dependence of adiabatic compressibility and the solution characteristics has been discussed.

Ranges of frequency dispersion for the shear viscosity coefficients of aqueous solutions of electrolytes

The range of frequency dispersion for dynamic coefficient of shear viscosity ηS(ω) of electrolyte solutions obtained through kinetic equations under the condition of recovering the steady-state structure of a liquid exponentially or according to the diffusion law is considered. Numerical calculations of ηS(ω) are performed for an aqueous solution of NaCl depending on density ρ, temperature T, concentration C, and frequencies ω to select the potential of intermolecular interaction Φab(|r|) and equilibrium radial distribution function gab(|r|). It is noted that the calculated theoretical results of ηS(ω) are in quantitative accordance with the experimental data. It is shown that the range of frequency dispersion ηS(ω) based on the diffusion mechanism is broad (∼105 Hz) and is narrow in the case of exponential attenuation of the viscous stress tensor (∼102 Hz); this corresponds to both acoustic measurements and results from phenomenological theory.

New Data on Activity Coefficients of Potassium, Nitrate, and Chloride Ions in Aqueous Solutions of KNO3 and KCl by Ion Selective Electrodes

Ion selective electrodes (ISEs) are used to measure the single-ion activity coefficients in aqueous solutions of KNO3 and KCl at 298.15 K against a double-junction reference electrode. The EMF responses of ISEs up to 0.01 m are plotted to obtain the slope and intercept values. The obtained slopes and intercepts are used in Nernst equation for higher concentrated solutions for calculation of individual ion activity coefficient. The mean ionic activity coefficients are estimated from single ion activity coefficient, and the obtained results are compared with the literature values.

Mean Activity Coefficients and Osmotic Coefficients in Aqueous Solutions of Salts of Ammonium Ions with Univalent Anions at 25 °C

The Hückel equation used in this study to describe the thermodynamic properties of dilute solutions of the ammonium salts of NH4Cl, NH4Br, NH4I, NH4NO3, NH4SCN, and NH4H2PO4 up to 1.5 mol·kg–1 is consisted of two electrolyte-dependent parameters B and b1. Parameter B is linearly related to the ion-size parameter a* in the Debye–Hückel equation, and parameter b1 is the coefficient of the linear correction term with respect to the molality. This coefficient is associated with the hydration numbers of the ions forming the electrolyte. For NH4ClO4 solutions, the estimated Hückel equation applies up to 2.1 mol·kg–1, and the equation was obtained from the isopiestic data measured by Esval and Tyree (J. Phys. Chem.1962, 66, 940–942) against KCl solutions. For molalities above 1.5 mol·kg–1 (in the best case up to 10 mol·kg–1), an extended Hückel equation was used. For this equation, the Hückel equation is supplemented with a quadratic term in molality, and the coefficient of this term is parameter b2. All of the parameters for the Hückel equations of NH4Cl and NH4NO3 solutions were estimated from isopiestic data of Wishaw and Stokes (Trans. Faraday Soc.1953, 49, 27–31). The former data were measured against KCl solutions and the latter against NaCl solutions. The Hückel parameters for NH4Br, NH4I, NH4SCN, and NH4H2PO4 solutions were estimated from the data measured by Covington and Irish (J. Chem. Eng. Data1972, 17, 175–176), Bonner (J. Chem. Eng. Data1976, 21, 498–499), Covington and Matheson (J. Solution Chem.1977, 6, 263–267), and Filippov et al. (J. Appl. Chem., U.S.S.R., 1985, 58, 1807–1811), respectively, using the same experimental technique against NaCl solutions. In all of these estimations, the Hückel parameters of a recent KCl and NaCl study (J. Chem. Eng. Data2009, 54, 208–219) were used for the solutions of the reference electrolyte. In the tests of the new parameter values, the cell potential difference, vapor pressure, and isopiestic data available in the literature were used. These data support well the tested Hückel parameters in most cases at least up to 3.5 mol·kg–1. Reliable thermodynamic activity quantities for ammonium salt solutions are, therefore, obtained using the new Hückel parameters. The activity coefficients, osmotic coefficients, and the vapor pressures obtained using these equations are tabulated here at rounded molalities. These values were compared to those suggested by Robinson and Stokes (Electrolyte Solutions, 2nd ed.; Butterworths Scientific Publications: London, 1959), to those obtained using Pitzer equations (Activity Coefficients in Electrolyte Solutions, 2nd ed.; CRC Press: Boca Raton, 1991; pp 100–101), and to those obtained using the extended Hückel equations presented by Hamer and Wu (J. Phys. Chem. Ref. Data1972, 1, 1047–1099).

Diffusion transport of magnesium nitrate aqueous solutions in membranes made of a porous glass

The diffusion coefficients of aqueous solutions of magnesium nitrate in a wide range of the concentrations upon transport in porous glass membranes (pore radius from 4.5 to 70 nm) were determined. The effect of magnesium nitrate concentration on the properties of the diffusion transport in the membranes was studied, based on ideas about the structuring of the boundary layers of water with the silica surface and their destruction under the action of ions.

Measuring and Modeling Activity Coefficients in Aqueous Amino-Acid Solutions

The perturbed-chain statistical association theory (PC-SAFT) is applied to simultaneously describe various thermodynamic properties (density, vapor-pressure depression, activity coefficient, solubility) of aqueous solutions containing an amino acid or an oligopeptide. The 28 organic compounds considered within this work are glycine, alanine, serine, proline, hydroxyproline, valine, leucine, arginine, lysine, threonine, asparagine, tyrosine, histidine, cysteine, methionine, aspartic acid, glutamic acid, α-ABA, α-isoABA, β-ABA, γ-ABA, α-AVA, γ-AVA, diglycine, triglycine, dialanine, Gly-Ala, and Ala-Gly. If not yet available in literature, amino-acid solubility data and activity coefficients were determined experimentally. To prove the predictivity of PC-SAFT, osmotic coefficients in aqueous solutions containing two amino acids (glycine/valine and alanine/valine) were measured and predicted without applying any additional model parameters.

Osmotic coefficients of aqueous solutions of potassium acesulfame, sodium saccharin, and ammonium and tetramethylammonium cyclohexylsulfamates at the freezing point of solutions

The osmotic coefficients of aqueous solutions of potassium acesulfame (0.67 mol kg−1), sodium saccharin (0.75 mol kg−1), and tetramethylammonium (0.55 mol kg−1) and ammonium (0.35 mol kg−1) cyclohexylsulfamates were determined up to the molality indicated in parentheses. The osmotic coefficients were fitted to the Pitzer equation, and the ion interaction parameters α 1, β (0), and β (1) were evaluated. The mean ionic activity coefficients of the solutes were calculated, and the non-ideal behaviour of the systems investigated were characterized by calculation of the excess Gibbs energy of the solution and the respective partial molar functions of solute and solvent. The partial molar excess Gibbs energies of the solutes are negative, as also are the corresponding excess Gibbs energies of their solutions, and the partial molar excess Gibbs energies of the solvent are positive and increase slightly with increasing concentrations of the solutes. The solvation ability of water was calculated from differences between the Gibbs energy of solution of water in the aqueous solutions and that of pure water, and are positive and small for all the solutes investigated, throughout the concentration ranges studied.

Measurement of Ion Activity Coefficients in Aqueous Solutions of Mixed Electrolyte with a Common Ion: NaNO3 + KNO3, NaCl + KCl and NaBr + NaCl

Measurement of Ion Activity Coefficients in Aqueous Solutions of Mixed Electrolyte with a Common Ion: NaNO₃ + KNO₃, NaCl + KCl and NaBr + NaCl

Measurement of Ion Activity Coefficients in Aqueous Solutions of Mixed Electrolyte with a Common Ion: NaNO3 + KNO3, NaCl + KCl, and NaBr + NaCl

This work reports individual ion activity coefficients in aqueous solutions of mixed 1:1 electrolytes with a common ion for the systems NaNO3 + KNO3, NaCl + KCl, and NaCl + NaBr at 298.15 K. These values were obtained from electrode potential measurements of ion-selective-electrodes (ISEs) of the common ion against an Ag−AgCl single-junction reference electrode filled with 4 mol·kg−1 KCl solution saturated with AgCl. For the NaNO3 + KNO3 and NaCl + KCl systems, experiments were carried out at cation molal fractions of sodium of 0.75, 0.5, and 0.25, and for the NaCl + NaBr system, experiments were carried out at an anion molal fraction of chloride of 0.5. For NaNO3 + KNO3, single ion activity coefficients were obtained up to 2.4 mol·kg−1 total nitrate concentration, and for the NaCl + KCl and NaCl + NaBr systems, up to 4 mol·kg−1 of total chloride and sodium concentrations, respectively. The Henderson equation was used to estimate the value of the liquid−junction potential.

Correlation of Activity Coefficients in Aqueous Solutions of Ammonium Salts Using Local Composition Models and Stochastic Optimization Methods

In this study, several local composition models and stochastic optimization methods have been used and compared in data fitting of activity coefficients in aqueous electrolytes. We have utilized the electrolyte-NRTL model of Chen et al. and the modified Wilson models proposed by Xu and Macedo, and Zhao et al. to fit the activity coefficients of several quaternary ammonium salts in water at 25°C. These electrolytes have interesting properties for their application as ionic liquids. However, the modeling of their thermodynamic behavior using local composition models is a global optimization problem. In this study, several stochastic optimization methods have been used to solve this optimization problem and their numerical performances have been compared. Specifically, we have tested the classical Simulated Annealing and the hybrid methods: Direct Search Simulated Annealing, Simplex Coding Genetic Algorithm, Simulated Annealing Heuristic Pattern Search, and Directed Tabu Search. Our results show that Simulated Annealing is a suitable tool for data fitting of the activity coefficients of aqueous electrolytes. Finally, the tested models can satisfactorily correlate the mean activity coefficients of electrolytes treated in this study, and are suitable for process design.

Gex-Model Using Local Area Fraction for Binary Electrolyte Systems

The correlation and prediction of phase equilibria of electrolyte systems are essential in the design and operation of many industrial processes such as downstream processing in biotechnology, desalination, hydrometallurgy, etc. In this research, the local composition non-random two liquid-nonrandom factor (NRTL-NRF) model of Haghtalab and Vera was extended for uni-univalent aqueous electrolyte solutions. Based on the assumptions of the NRTL-NRF model, excess Gibbs free energy (g E) functions were derived for binary electrolyte systems. In this work, the local area fraction was applied and the modified model of NRTL-NRF was developed with either an equal or unequal surface area of an anion to the surface area of a cation. The modified NRTL-NRF models consist of two contributions, one due to long-range forces represented by the Debye–Huckel theory, and the other due to short-range forces, represented by local area fractions of species through nonrandom factors. Each model contains only two adjustable parameters per electrolyte. In addition, the model with unequal surface area of ionic species gives better results in comparison with the second new model with equal surface area of ions. The results for the mean activity coefficients for aqueous solutions of uni-univalent electrolytes at 298.15 K showed that the present model is more accurate than the original NRTL-NRF model.