Isothermal vapor–liquid equilibria and excess molar volumes for the ternary mixtures containing 2-methyl pyrazine

Isothermal vapor–liquid equilibrium (VLE) data at 353.15 K and excess molar volumes (V^E) at 298.15 K are reported for the binary systems of ethyl acetate (EA)+cyclohexane and EA+n-hexane and also for the ternary systems of EA+cyclohexane+2-methyl pyrazine (2MP) and EA+n-hexane+2MP. The experimental binary VLE data were correlated with common g^E model equations. The correlated Wilson parameters of the constituent binary systems were used to calculate the phase behavior of the ternary mixtures. The calculated ternary VLE data using Wilson parameters were compared with experimental ternary data. The experimental excess molar volumes were correlated with the Redlich–Kister equation for the binary mixtures, and Cibulka’s equation for the ternary mixtures.     

Bubble points of hydrogen chloride–water–isopropanol and hydrogen chloride–water–isopropanol–benzene systems and liquid–liquid equilibria of hydrogen chloride–water–benzene and hydrogen chloride–water–isopropanol–benzene systems

Bubble points of the HCl–water–isopropanol and the HCl–water–isopropanol–benzene systems and liquid–liquid equilibria (LLE) of the HCl–water–benzene and the HCl–water– isopropanol–benzene systems were measured at 25–85°C and 30–70°C, respectively. The electrolyte nonrandom two-liquid model proposed by Chen et al. [C.-C. Chen, H.I. Britt, J.F. Boston, L.B. Evans, AIChE J. 28 (1982) 588–596] can satisfactorily correlate bubble points and liquid–liquid equilibria of the present mixed-solvent electrolyte systems over the entire range of temperature and concentrations using only binary adjustable parameters.     

Phase separation of gas–liquid and liquid–liquid microflows in microchips

Phase separation of gas–liquid and liquid–liquid microflows in microchannels were examined and characterized by interfacial pressure balance. We considered the conditions of the phase separation, where the phase separation requires a single phase flow in each output of the microchannel. As the interfacial pressure, we considered the pressure difference between the two phases due to pressure loss in each phase and the Laplace pressure generated by the interfacial tension at the interface between the separated phases. When the pressure difference between the two phases is balanced by the Laplace pressure, the contact line between the two phases is static. Since the contact angle characterizing the Laplace pressure is restricted to values between the advancing and receding contact angles, the Laplace pressure has a limit. When the pressure difference between the two phases exceeds the limiting Laplace pressure, one of the phases leaks into the output channel of the other phase, and the phase separation fails. In order to experimentally verify this physical picture, microchips were used having a width of 215 μm and a depth of 34 μm for the liquid–liquid microflows, a width of 100 μm and a depth of 45 μm for the gas–liquid microflows. The experimental results of the liquid–liquid microflows agreed well with the model whilst that of the gas–liquid microflows did not agree with the model because of the compressive properties of the gas phase and evaporation of the liquid phase. The model is useful for general liquid–liquid microflows in continuous flow chemical processing.     

2-Methoxyethanol–Tetrahydrofuran–Binary Liquid System. Viscosities,densities, excess molar volumes and excess Gibbs activation energies of viscous flow at various temperatures

Densities (d ₁₂) and viscosities (η₁₂) have been measured for 2-methoxyethanol (ME) with tetrahydrofuran (THF) binary liquid mixtures over the whole composition range at various temperatures ranging from 291.15 to 308.15 K. The experimental data were used to test some empirical equations of the type: y ₁₂=y ₁₂(t) and y ₁₂=y ₁₂(X ₁) [where: y ₁₂−d ₁₂ or η₁₂]. From all these data, the excess molar volumes (V ₁₂ ^E), the excess viscosities (η₁₂ ^E) and excess Gibbs activation energies (ΔG ^*) of viscous flow were calculated. These structural parameters as a function of concentration suggest the formation of 3ME⋅THF and 2ME⋅THF types of intermolecular complexes. This revised version was published online in August 2006 with corrections to the Cover Date.     

An investigation of a separation process involving liquid—water—coal systems

A liquid—liquid—solid separation procedure wherein a water—oil—coal—mineral matter slurry is allowed to come to equilibrium through mechanical agitation has for many years been applied to the separation of coal from mineral matter. The product is a black “cottage cheese”-like mass of agglomerated coal particles and oil suspended in the excess water which supports the dispersed mineral matter particles. A liquid “bridge” model was proposed by earlier investigators which is reviewed critically and used to estimate the free energy per unit area of the separation of coals of different ranks. Observations of the kinetics of the process suggest that the simple liquid “bridge” model is insufficient, probably due to the heterogeneous surfaces of the coal. An alternative model is proposed.     

Volumetric properties of binary liquid mixtures: Application of the Prigogine–Flory–Patterson theory to excess molar volumes of dichloromethane with benzene or toluene

The values of the density were measured for binary liquid mixtures of benzene and toluene with dichloromethane over entire range of concentration using a vibrating-tube densimeter at T = (288.15, 293.15, 298.15, and 303.15) K and atmospheric pressure. The excess molar volumes, calculated from the density results, are positive for the systems of dichloromethane with benzene over the whole concentration range and present an approximate sigmoid curve for the dichloromethane with toluene. The $V_{\text{m}}^{\text{E}}$ values have been fitted to the Redlich–Kister polynomial equation, and other volumetric properties such as the partial molar volumes, $\overline{V_i}$, the apparent molar volume, V_?i, and the partial molar excess volumes at infinite dilution, $(\overline{V_i^{\text{E}}}{)}^{\infty }$, were calculated over the whole composition range. The Prigogine–Flory–Patterson (PFP) theory and its applicability in predicting $V_{\text{m}}^{\text{E}}$ at T = 298.15 K are tested. Good agreement was found for the mixtures dichloromethane with benzene. For the mixtures dichloromethane with toluene, which shows an approximate S-shaped $V_{\text{m}}^{\text{E}}$ behaviour, the correlation fails.     

The liquid–liquid coexistence curves of {benzonitrile + n-pentadecane} and {benzonitrile + n-heptadecane} in the critical region

Liquid + liquid coexistence curves for the binary solutions of {benzonitrile + n-pentadecane} and {benzonitrile + n-heptadecane} have been measured in the critical region. The critical exponent β and the critical amplitudes have been deduced and the former is consistent with the theoretic prediction. It was found that the coexistence curves may be well described by the crossover model proposed by Gutkowski et al. The asymmetries of the diameters of the coexistence curves were also discussed in the frame of the complete scaling theory.     

Interfacial tension in polyelectrolyte systems exhibiting associative liquid–liquid phase separation

A continued interest in polyelectrolyte phase diagrams guides the study of interfacial phenomena driven by polyelectrolyte complexation. The liquid–liquid interfaces formed by associative phase separation of oppositely charged synthetic and natural polyelectrolytes provide measurement challenges addressed by force-sensitive methods and deformed droplet retraction. The ultralow interfacial tension, typical of these systems, is sensitive to salt concentration and temperature and displays universal features described by mean-field theory. Several areas of fundamental development and novel applications of charge complexation for interfacial study and examples from membraneless organelles and biomolecular condensates are described.     

Liquid densities and excess molar volumes for water + diethylene glycolamine,and water,methanol, ethanol, 1-propanol + triethylene glycol binary systems at atmospheric pressure and temperatures in the range of 283.15–363.15 K

Liquid densities and excess molar volumes (V^E) are reported for the binary water+diethylene glycolamine, and water, methanol, ethanol, 1-propanol+triethylene glycol systems at atmospheric pressure and temperatures between 283.15 and 363.15 K in 10 K intervals. Negative V^E were found for all investigated systems. At given temperature, the most negative V^E is for the water+diethylene glycolamine system. For water containing systems, V^E increase with temperature while the inverse effect was observed for alcoholic systems, i.e. V^E became more negative with increasing temperature. For the triethylene glycol systems at constant temperature, absolute value of V^E decreases in the series: water>methanol>ethanol>1-propanol within the whole composition range. The experimental results have been correlated using the three parameter Redlich–Kister equation.     

Influence of temperature on excess molar volumes for butyl acetate + aromatic hydrocarbons

Excess molar volumes dependence with temperature for the mixtures butyl acetate?+?aromatic hydrocarbons (toluene, ethylbenzene, p-xylene, mesitylene, isopropylbenzene, butylbenzene, isobutylbenzene, and t-butylbenzene) were determined from density measurements by a vibrating-tube densimeter. The excess molar volumes are positive or slightly negative in the studied mixtures over the whole composition range, attending to the solvent molecular weight, only the isobutylbenzene showing a sigmoid trend. Steric hindrance in these mixtures was analyzed in the light of partial excess molar volumes behavior. The experimental data were used to test semiempirical procedures of density prediction, and compute the binary interaction parameters of the Soave–Redlich–Kwong (SRK) and Peng–Robinson (PR) equations of state, which are of general interest in multicomponent thermodynamic functions estimation. The obtained results point out the interest of the equations of state to study complex mixtures and as a tool for predicting other magnitudes of general application for theoretical studies or processes calculations.     

Salt effects on liquid–liquid equilibria in the partially miscible systems water+2-butanone and water+ethyl acetate

Liquid–liquid equilibrium data for the partially miscible systems of water+2-butanone+salt and water+ethyl acetate+salt were measured at 298.15 K. The salts used were potassium iodide, sodium bromide and lithium chloride. The systems were compared in terms of salting effect. The three-contribution electrolyte NRTL model is used to perform the data regression of the experimental data. New binary parameters are obtained. The calculated results are compared with the experimental data.     

Correlation and prediction of salt effects on vapor–liquid equilibrium in alcohol–water–salt systems

A modification of the solvation model of Ohe is proposed for the calculation of vapor–liquid equilibria (VLE) in alcohol–water–salt systems. The modified method employs the Bromley equation to calculate the activity of water in salt solutions, and a one-parameter empirical expression to calculate the activity of the alcohol. The single parameter is obtained by fitting ternary alcohol–water–salt data. The method is simple to use and does not require data on the vapor-pressures of alcohol–salt mixtures that are seldom available in the literature. Experimental data for 17 salts in 36 alcohol–water–salt systems, covering a temperature range from 298 to 375 K, and salt concentrations up to about 8 m, were correlated using the new approach. In all, 69 data sets and 1045 data points were correlated satisfactorily. The method was also used to predict VLE in four ternary alcohol–alcohol–salt systems and one quaternary alcohol–alcohol–water–salt system with satisfactory results.     

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.     

Densities and excess molar volumes for mixtures of methanol with other alcohols at temperatures (288.15–313.15 K)

Densities have been measured for the binary mixtures of methanol with ethanol, isomers of propanol and butanol over the entire composition range at 288.15, 293.15, 298.15, 303.15, 308.15, 313.15 K. The density data have been used to calculate the molar volumes, thermal expansion coefficients and their excess values. The excess parameters have been fitted to the Redlich–Kister polynomial equation. The values of the molar volumes, excess molar volumes, thermal expansion coefficients and excess thermal expansion coefficients have been analyzed as a function of the mole fraction and the carbon chain length.     

Liquid–liquid equilibria of two binary systems: water+1-pentanol and water+2-methyl-2-butanol and two ternary systems: water+1-pentanol+2-butyloxyethanol and water+2-methyl-2-butanol+2-butyloxyethanol

Liquid–liquid equilibrium phase diagrams for two binary systems: water+1-pentanol and water+2-methyl-2-butanol and two ternary systems: water+1-pentanol+2-butyloxyethanol and water+2-methyl-2-butanol+2-butyloxyethanol at 20°C and 30°C are presented in this paper. The experimental results were correlated with the UNIQUAC model by fitting the effective UNIQUAC binary interaction parameters as a function of temperature. Agreement between the calculated and experimental data was very good.     

Bulk properties and hydration numbers of components of water–salt,water–urea,and water–urea–salt systems

With an increase in the concentration of additives, the hydration numbers of compounds decrease. Thus, in a saturated 54.6% solution, urea loses approximately 3/4 of the initial amount of water, forming an aquacomplex of the composition (NH₂)₂CO?H₂O. In a supersaturated 44% solution, the sodium chloride aquacomplex is dehydrated by 2/3, and in a supersaturated 67% solution, sodium sulfate is dehydrated by 5/6. The density of these solutions is 1.354÷1.360 g/cm³ (44% NaCl) and 1.800÷1.849 g/cm³ (67% Na₂SO₄). In a saturated urea solution, NaNO₃, NaCl, and Na₂SO₄ complexes lose 53÷55% of hydration water. It is shown that the interactions in the binary water–urea system somewhat increase the hydration number of the salts (structural hydration). The hydration water density, a structurally important characteristic, increases in the series of solutions of urea, NaNO₃, NaCl, and Na₂SO₄. In the same series of additives, the excess volume of binary water–urea and water–salt systems becomes more negative.     

Thermodynamic Model for BiPO4(cr) and Bi(OH)3(am) Solubility in the Aqueous Na+–H+–\mathrm{H}_{2}\mathrm{PO}_{4}^{-}–\mathrm{HPO}_{4}^{2-}–\mathrm{PO}_{4}^{3-}–OH−–Cl−–H2O System

Prior to this study no data for the solubility product of BiPO₄(cr) or the complexation constants of Bi with phosphate were available. The solubility of BiPO₄(cr) was studied at 23±2?°C from both the over- and under-saturation directions as functions of a wide range in time (6–309 days), pH values (0–15), and phosphate concentrations (reaching as high as 1.0 mol?kg^?1). HCl or NaOH were used to obtain a range in pH values. Steady state concentrations and equilibrium were reached in <6 days. The data were interpreted using the SIT model. These extensive data provided a solubility product value for BiPO₄(cr) and an upper limit value for the formation of BiPO₄(aq). Because the aqueous system in this study involved relatively high concentrations of chloride, reliable values for the complexation constants of Bi with chloride were required to accurately interpret the solubility data. Therefore as a part of this investigation, existing Bi–Cl data were critically reviewed and used to obtain values of equilibrium constants for various Bi–Cl complexes at zero ionic strength along with the values for various SIT ion interaction parameters. Predictions based on these thermodynamic quantities agreed closely with our experimental data, the chloride concentrations of which ranged as high as 0.7 mol?kg^?1. The study showed that BiPO₄(cr) is stable at pH values <9.0. At pH values >9.0, Bi(OH)₃(am) is the solubility controlling phase. Reliable values for the Bi(OH)₃(am) solubility reactions involving Bi(OH)₃(aq) and $\mathrm{Bi}(\mathrm{OH})_{4}^{-}$ and the formation constants of these aqueous species are also reported.     

Dispersive liquid–liquid microextraction and spectrophotometric determination of cobalt in water samples

A new simple and rapid dispersive liquid–liquid microextraction has been applied to preconcentrate trace levels of cobalt as a prior step to its determination by spectrophotometric detection. In this method a small amount of chloroform as the extraction solvent was dissolved in pure ethanol as the disperser solvent, then the binary solution was rapidly injected by a syringe into the water sample containing cobalt ions complexed by 1-(2-pyridylazo)-2-naphthol (PAN). This forms a cloudy solution. The cloudy state was the result of chloroform fine droplets formation, which has been dispersed in bulk aqueous sample. Therefore, Co-PAN complex was extracted into the fine chloroform droplets. After centrifugation (2 min at 5000 rpm) these droplets were sedimented at the bottom of conical test tube (about 100 µL) and then the whole of complex enriched extracted phase was determined by a spectrophotometer at 577 nm. Complex formation and extraction are usually affected by some parameters, such as the types and volumes of extraction solvent and disperser solvent, salt effect, pH and the concentration of chelating agent, which have been optimised for the presented method. Under optimum conditions, the enhancement factor (as the ratio of slope of preconcentrated sample to that obtained without preconcentration) of 125 was obtained from 50 mL of water sample, and the limit of detection (LOD) of the method was 0.5 µg L^?1and the relative standard deviation (RSD, n = 5) for 50 µg L^?1 of cobalt was 2.5%. The method was applied to the determination of cobalt in tap and river water samples.