Melting heat transfer in squeezing flow of basefluid (water), nanofluid (CNTs + water) and hybrid nanofluid (CNTs + CuO + water)

Journal of Thermal Analysis and Calorimetry - Unsteady squeezed flow of hybrid nanofluid is investigated in this analysis. Comparison of hybrid nanofluid (using CNTs?+?CuO) and...     

Solubility of minoxidil in binary mixture of ethanol + water at various temperatures

ABSTRACT

The solubility of minoxidil in the aqueous binary mixtures of ethanol at different temperature are investigated and the obtained solubility data are fitted by using some cosolvency models including van’t Hoff equation, Yalkowsky model, Jouyban–Acree model and Jouyban–Acree–van’t Hoff model. The mean relative deviations (MRD%) are used to illustrate the models performance. Moreover, the apparent entropy, enthalpy, and Gibbs free energy of minoxidil dissolution process in the investigated solvent mixtures are computed using van’t Hoff and Gibbs equations. Finally, by means of the inverse Kirkwood–Buff integrals preferential solvation of minoxidil by water is observed in water-rich and ethanol-rich mixtures.     

Complexing properties of nitrilotri(methylenephosphonic) acid with various transition and heavy metals in a 10:90 ethanol—water medium

The nature and stability of some transition- and heavy-metal cation complexes of nitrilotri(methylenephosphonic) acid have been determined in 0.1 M NaClO₄ 10:90 ethanol—water solutions by means of pH metric measurements. In this medium stable 1:1 complexes and protonated species were found.     

Molecular thermodynamics of salt effect in vapor–liquid equilibrium of ethanol–water systems

Scaled particle theory was used to derive a general expression for the salt effect parameter, K, of isobaric vapor–liquid equilibrium for ethanol–water-1-1 type electrolytic systems, which appears in the Furter equation. This expression was essentially a sum of two terms: 1, the hard sphere interaction term calculated by Masterton–Lee's equation, 2, the soft sphere interaction term calculated by Y. Hu's molecular thermodynamical model, in which the diameters of nacked ions were replaced by that of solvated ions, the solvation coefficients (i.e., in the radio of the latter to the former) were taken to be adjustable parameters, their magnitude implies the ionic solvation rules. A correlation equation for the local dielectrical constant around central ions with liquid concentration was obtained by mapping out experimental points. The calculated salt effect parameters of 9 ethanol–water-1–1 type electrolytic systems were in good agreement with the literature values within the wide range of liquid concentration.     

Potentiometric determination of ascorbic acid in water–acetonitrile solution using pyrite and chalcopyrite electrodes

Journal of Solid State Electrochemistry - Performance characteristics of the solid-state potentiometric sensors, based on natural sulfide minerals pyrite and chalcopyrite, are assayed in aqueous...     

The thermodynamics of ionization of α-alanine in methanol + water mixtures and the determination of single ion thermodynamics

In order to understand the effect of solvents on the thermodynamic parameters of amino acids, the thermodynamic dissociation constants, k₁ and K₂, for the reactions

and

(where RH^± = α-alanine) have been determined pH-metrically in methanol + water mixtures. The measurements were carried out in dilute solutions and in the absence of neutral electrolytes to minimize the “salt effect” as far as practicable so that the “medium effects” on the dissociation constants of the α-alanine can be properly understood.The enthalpy values for reactions (1) and (2) (up to 44.14 wt% of methanol) have been determined calorimetrically. It has been observed that the conversion of α-alanine into cations and anions is favourable both from enthalpic and entropic considerations, so that the reverse reactions of (1) and (2) are spontaneous. Attempts have been made to interpret the thermodynamics properties of α-alanine in terms of hydrophilic and hydrophobic interactions and other structural changes of the solvent molecules.In order to get a better insight into the nature of specific solute-solvent interactions, we have analysed the results in terms of single ion values using the thermodynamic values from the present work and other relevant data from previous work in our laboratory.     

Solubility behavior,dissolution thermodynamics and solute–solvent intermolecular interactions of a solid antioxidant product in water + isopropanol liquid mixtures from 298.15 to 320.15 K

The solid–liquid equilibria of a poorly water-soluble antioxidant agent namely naringoside were assayed to determine solubility in binary liquid mixtures of water?+?isopropanol (iso-PrOH) between 298.15 K and 320.15 K under atmospheric pressure. The mole fraction solubilities of naringoside in the saturated solution were determined using a combination of static shake-flask and ultraviolet spectrophotometry techniques. The dissolution behavior of naringoside was correlated with three solution models consisting of the van’t Hoff equation, the modified Apelblat equation and the Buchowski-Ksiazczak λH equation. The modified Apelblat equation was more consistent than the two other correlation models. Apparent thermodynamic analysis of naringoside dissolution was also performed at the mean harmonic temperature using the model parameters of the modified Apelblat equation. Furthermore, the Kamlet, Abboud and Taft Linear Solvation Energy Relationship (KAT-LSER) model was applied to analyze the effect of the solute–solvent intermolecular interactions on the solubility of this natural bioactive product.     

Solubility and dissolution thermodynamics of tetranitroglycoluril in organic solvents at 295–318 K

The solubility data of tetranitroglycoluril in acetone, methanol, ethanol, ethyl acetate, nitromethane and chloroform at temperatures ranging from 295–318 K were measured by gravimetric method. The solubility data of tetranitroglycoluril were fitted with Apelblat semiempirical equation. The dissolution enthalpy, entropy and Gibbs energy of tetranitroglycoluril were calculated using the Van’t Hoff and Gibbs equations. The results showed that the Apelblat semiempirical equation was significantly correlated with solubility data. The dissolving process was endothermic, entropy-driven, and nonspontaneous.     

Solvation Behaviors of Poly(acrylic acid) in Mixed Solvents of 2-Butoxyethanol + Water

Poly(acrylic acid) (PAA) is a well known weak polyelectrolyte in water but little is known about the solvation behavior of PAA in the mixtures of alcohol?+?water. In this study, the solvation behavior of PAA in the mixed solvents composed of 2-butoxyethanol (2BE)?+?water were investigated by measurements of volumetric properties, electrical conductivity, resonance light scattering and dynamic light scattering. All the measured experimental properties showed extrema or abrupt changes at a 2BE mole fraction of about 0.017 in 2BE?+?water. This may be explained by the formation of aggregates of 2BE and water, which is a poor solvent for PAA and results in cononsolvency of PAA in the mixture of the two good solvents, 2BE and water. We found that the volumetric property is sensitive to the occurrence of the specific aggregate of 2BE and water and the interactions in the complex fluid mixtures.     

Solubility and dissolution thermodynamics of phthalic anhydride in organic solvents at 283–313 K

The solubility of phthalic anhydride was measured at 283–313 K under atmospheric pressure in ethyl acetate, n-propyl acetate, methyl acetate, acetone, 1,4-dioxane, n-hexane, n-butyl acetate, cyclohexane, and dichloromethane. The solubility of phthalic anhydride in all solvents increased with the increasing temperature. The Van’t Hoff equation, modified Apelblat equation, λh equation, and Wilson model were used to correlate the experimental solubility data. The standard dissolution enthalpy, the standard entropy, and the standard Gibbs energy were evaluated based on the Van’t Hoff analysis. The experimental data and model parameters would be useful for optimizing of the separation processes involving phthalic anhydride.     

Formation constants and coordination thermodynamics for binary complexes of Cu(II) and some α-amino acids in aqueous solution

In this study, the formation constants of 1?:?1 binary complexes of Cu(II) with L-glutamic acid, L-aspartic acid, glycine, L-alanine, L-valine, and L-leucine and 1?:?2 binary complexes of L-glutamic acid, glycine and the protonation macro- and microconstants of all these amino acids were determined potentiometrically in aqueous solutions at 5.0, 20.0, and 35.0°C at a constant ionic strength of I?=?0.10?mol?L^?1 (NaClO₄). The thermodynamic parameters ΔG _f°, ΔH _f°, and ΔS _f° were determined for the protonation of all amino acids used in this study and for the complex formation reactions of them with Cu(II). The results were analysed by means of Principle of hard and soft [Lewis] acids and bases. Additionally, in order to confirm the complex formation and determine the stability constants of complexes, UV-Vis spectroscopic studies were carried out. The stability constants obtained by spectrophotometrically are confirmed by those determined potentiometrically.     

Study of equilibrium solution and thermodynamic models in correlation with solubility data of rivastigmine tartrate in (H2O + isopropanol), (H2O + ethanol), and (H2O + acetonitrile) binary solvent mixtures

Millions of people around the world have been suffering from Alzheimer’s disease (AD) everyday. Rivastigmine tartrate is a potential AD drug. A crystallization process can enhance purities of rivastigmine tartrate properly. Predictive models for solubilities of rivastigmine tartrate will improve subsequent industrial crystallization process design. In this work, the solubility of rivastigmine tartrate in (H₂O?+?isopropanol), (H₂O?+?ethanol), and (H₂O?+?acetonitrile) binary solvent systems in the temperature range of 278.15–333.15 K under atmospheric pressure was measured and investigated by employing the analytical stirred-flask method. Binary solvent systems of rivastigmine tartrate overcame drawbacks of mono-solvent crystallization systems, such as high viscosity. Three thermodynamic models, including modified Apelblat equation, the general cosolvency model, and the Jouyban–Acree model, were employed to correlate with the obtained experimental solubility data. Moreover, the calculations of apparent thermodynamic properties of rivastigmine tartrate dissolution process involving the Gibbs free energy, enthalpy, and entropy were accomplished by using the van’t Hoff analysis. Among the three models, the modified Apelblat equation is the most suitable one for predicting the solubility behavior of rivastigmine tartrate in binary solvent systems. Based on the data from modified Apelblat equation, a crystallization process of (H₂O?+?ethanol) binary solvent mixture was developed.

     

Interactions of some α-l-glutamic acid oligomers and polymers with Cu(II) in aqueous solution

The interactions between copper ions and various α-l-glutamic polyacids (DP 6,27,50,300) has been studied, in aqueous solution with an external salt NaClO₄ 0.1 M at 25°C. Both measurements of pH and pCu allow, according to Bjerrum's and Marinsky's methods, the display of MA and MA₂ species and the calculation of their formation constants. These last are depending on the DP and, concerning DP 300, the formation constants vary with the respective metallic and polyacid concentrations. The formation of polynuclear species has been demonstrated for this DP only.     

Solubility and thermodynamics of dissolution of helium in water at gas partial pressures of 0.1–100 MPa within a temperature range of 278–353 K

The tables of recommended numerical values for the water solubility of helium at gas partial pressures of 0.1–100 MPa within a temperature range of 278.15–353.15 K are given. The thermodynamic characteristics of dissolution of helium in water at the mentioned parameters of state have been calculated. The independence of the dissolution enthalpy on the pressure has been recognized and explained.     

Phase and extraction equilibria in water–polyethyleneglycol ethers of monoethanolamides of synthetic fatty acid–ammonium chloride systems

Phase equilibria in layering systems of water, polyethyleneglycol ethers of monoethanolamides of synthetic fatty acids (SFAs) (synthamide-5), and ammonium chloride are studied. The possibility of using such systems for the liquid extraction of metal ions is evaluated. The effect the nature of salting-out agents has on the processes of segregation of the systems has been considered.     

Solvation thermodynamics of benzene,nitrobenzene, and aniline in water–acetonitrile mixtures

The enthalpies of dissolution of benzene, nitrobenzene, and aniline in water–acetonitrile mixtures are determined via calorimetry. The concentration dependences of the standard enthalpies of solvation of solutes are calculated. It is found that the concentration dependences of the standard enthalpies of solvation pass through maxima. The height of the observed maxima is shown to depend largely on the nature of the substituent. In the presence of a hydrophilic amino group capable of forming strong hydrogen bonds with water molecules, the value of a maximum falls; in the presence of a nitro group, it rises. The enthalpy parameters of pair interaction between molecules of water and benzene and its derivatives are calculated.