Effect of glycine,dl-alanine and dl-2-aminobutyric acid on the temperature of maximum density of water

The effect of glycine, dl-alanine and dl-2-aminobutyric acid on the temperature of maximum density of water was determined from density measurements using a magnetic float densimeter.Densities of aqueous solutions were measured within the temperature range from T = (275.65 to 278.65) K at intervals of T = 0.50 K over the concentration range between (0.0300 and 0.1000) mol · kg⁻¹. A linear relationship between density and concentration was obtained for all the systems in the temperature range considered.The temperature of maximum density was determined from the experimental results. The effect of the three amino acids is to decrease the temperature of maximum density of water and the decrease is proportional to molality according to Despretz equation. The effect of the amino acids on the temperature of maximum density decreases as the number of methylene groups of the alkyl chain becomes larger. The results are discussed in terms of (solute + water) interactions and the effect of amino acids on water structure.     

The vapour pressures over saturated aqueous solutions of cadmium chloride,cadmium bromide,cadmium iodide,cadmium nitrate,and cadmium sulphate

Vapour pressures of water over saturated solutions of cadmium salts (chloride, bromide, iodide, nitrate, and sulphate) were determined over the temperature range 280 K to 322 K and compared with the literature data. The vapour pressures determined were used to obtain the water activities, osmotic coefficients and the molar enthalpies of vaporization in the (cadmium salt + water) systems.     

The vapour pressures over saturated aqueous solutions of sodium and potassium acetates,chlorates, and perchlorates

Vapour pressures of water over saturated solutions of sodium acetate, potassium acetate, sodium perchlorate, and potassium perchlorate were determined over the (278 to 318) K temperature range and compared with available in the literature data. The cases of saturated solutions of sodium chlorate and potassium chlorate are also considered. The determined vapour pressures were used to obtain the water activities, the osmotic coefficients, and the molar enthalpies of vaporization in considered systems.     

Solubilities of magnesium-l-ascorbate,calcium-l-ascorbate,magnesium-l-glutamate,magnesium-d-gluconate,calcium-d-gluconate,calcium-d-heptagluconate,l-aspartic acid,and 3-nitrobenzoic acid in water

The solubility in water of magnesium-l-ascorbate, calcium-l-ascorbate, magnesium-l-glutamate, magnesium-d-gluconate, calcium-d-gluconate, calcium-d-heptagluconate, l-aspartic acid, and 3-nitrobenzoic acid was determined in the 278.15 K to 343.15 K temperature range. The solubility of these compounds served to permit the evaluation of the apparent molar enthalpies of solution.     

Volumetric properties of itaconic acid aqueous solutions

Densities of itaconic acid aqueous solutions were measured at 5 K intervals from T = (278.15 to 343.15) K. From the determined densities, the apparent molar volumes, the cubic expansion coefficients and the second derivatives of volume with respect to temperature which are interrelated with the derivatives of isobaric heat capacities with respect to pressure were evaluated. These derivatives were qualitatively correlated with the changes in the structure of water when itaconic acid is dissolved in it.     

Solubilities of oleanolic acid and ursolic acid in (ethanol + water) mixed solvents from T = (292.2 to 328.2) K

The solubility of oleanolic acid and of ursolic acid in (ethanol + water) mixed solvents was measured over the temperature range of (292.2 to 328.2) K. The solubility of oleanolic acid and of ursolic acid in the (ethanol + water) mixed solvent systems increase with increasing the mole fraction of ethanol in mixed solvents. The experimental solubility data are correlated by a simplified thermodynamic equation and the modified Apelblat equation.     

Vapour pressures of selected organic compounds down to 1 mPa,using mass-loss Knudsen effusion method

A recently developed Knudsen effusion apparatus was improved and used for measurements of vapour pressures of selected organic compounds. Calorimetric studies were conducted using a Calvet-type calorimeter, complementing the information obtained for the vapour pressures and facilitating the modelling and analysis of the data.Vapour pressures of benzoic acid, a reference substance, were determined at temperatures between 269 K and 317 K, corresponding to a pressure range from 2 mPa to 1 Pa, extending the range of results available in the literature to lower pressures. Benzanthrone was studied between temperatures 360 K and 410 K (5 mPa–1 Pa) in order to test the apparatus at higher temperatures.Values presented in the literature for the vapour pressure of solid n-octadecane, one of the most promising compounds to be used as “phase change material” for textile applications, were found inconsistent with the triple point of the substance. Sublimation pressures were measured for this compound between T = 286 K and 298 K (2–20 mPa) allowing the correction of the existing values. Finally, vapour pressures of diphenyl carbonate, a compound of high industrial relevance for its use in the production of polycarbonates, were determined from T = 302 K to 332 K (0.02–1 Pa).     

Bubble points of the systems isopropanol–water,isopropanol–water–sodium acetate and isopropanol–water–sodium oleate at high pressure

Supercritical water oxidation (SCWO) is a powerful technology for destroying organic wastes with high removal efficiencies. Corrosion and salt deposition are the main challenges for the industrial development of the SCWO process. In SCWO heteroatoms are oxidized until high oxidation states: oxides, acids or salts. If there are enough cations, the heteroatoms precipitate as salts and eventually can be recovered. Cations can be introduced in the system by adding organic salts to the feed. The organic part of the salt is oxidized to CO₂ and water, and the cations remain free to join the free anions and precipitate as inorganic salts. The thermodynamic study of this system it is very interesting for future modeling of the SCWO process.Bubble points of the systems isopropanol (IPA)–water, IPA–water–sodium acetate and IPA–water–sodium oleate were determined in the temperature range (396 and 460 K), pressures higher than 0.35 MPa, with IPA concentrations lower than 5 mol% and salt concentrations of 5 and 8.2 mol% for sodium acetate, and 0.11 and 0.25 mol% for sodium oleate. Bubble points were determined using a Cailletet apparatus that operates with the synthetic method.As expected, the vapor pressure of the system increases as IPA concentration is increased, and in general decreases when salt concentration increases. The measured vapor pressures of mixtures of water and IPA were consistent with literature data.The experimental data were correlated using the Anderko–Pitzer EoS, which was specially developed for water–salt systems at high temperatures and pressures. Densities and vapor pressures of IPA and the experimental data presented in this work were used for obtaining the parameters of the EoS in the range of pressure and temperature of the data. In the range of temperature and concentration considered, the average deviations between experimental and calculated vapor pressures were %ΔP = 1.18% for the system IPA–water, %ΔP = 4.03% for the system IPA–water–NaAc and %ΔP = 2.77% for the system IPA–water–NaOl.     

Phase equilibrium measurements and modelling of ternary system (carbon dioxide + ethanol + palmitic acid)

This work reports phase equilibrium measurements for the ternary system (palmitic acid + ethanol + CO₂). The motivation of this research relies on the fact that palmitic acid is the major compound of several vegetable oils. Besides, equilibrium data for palmitic acid in carbon dioxide using ethanol as co-solvent are scarce in the literature. Phase equilibrium experiments were performed using a high-pressure variable-volume view cell over the temperature range of (303 to 343) K and pressures up to 20 MPa and mole fraction of palmitic acid from 0.0199 to 0.2930. Vapour–liquid and solid–fluid transitions were visually observed for the system studied. The Peng–Robinson equation of state, with the classical van der Waals quadratic mixing rule was employed for thermodynamic modelling of the system investigated with a satisfactory agreement between experimental and calculated values.     

Measurement of densities and excess molar volumes for (1,2-propanediol,or 1,2-butanediol + water) at the temperatures (288.15, 298.15, and 308.15) K and at the pressures (0.1, 20, 40, and 60) MPa

Excess molar volumes V_m^Eof (1,2-propanediol  +  water) and (1,2-butanediol  +  water) were measured at temperatures of (288.15, 298.15, and 308.15) K and at pressures of (0.1, 20, 40, and 60) MPa with a densimeter, model DMA 512p from Anton Paar. Values of V_m^Ewere negative for all the mixtures studied over the whole concentration range and for all temperatures and pressures. Results were correlated by polynomial equations of Redlich and Kister and of Myers and Scott.     

Solubilities of l-glutamic acid, 3-nitrobenzoic acid,p-toluic acid,calcium-l-lactate,calcium gluconate,magnesium-dl-aspartate,and magnesium-l-lactate in water

Solubilities of l -glutamic acid, 3-nitrobenzoic acid, p -toluic acid, calcium-l -lactate, calcium gluconate, magnesium- dl -aspartate, and magnesium- l -lactate in water were determined in the temperature range 278 K to 343 K. The apparent molar enthalpies of solution at T =  298.15 K as derived from these solubilities areΔ_solH_m (l -glutamic acid,m_sat =  0.0565 mol · kg ^− 1)  =  30.2 kJ · mol ^− 1,Δ_solH_m (3-nitrobenzoic acid, m =  0.0188 mol · kg ^− 1)  =  28.1 kJ · mol ^− 1, Δ_solH_m( p - toluic acid, m =  0.00267 mol · kg ^− 1)  =  23.9 kJ · mol ^− 1,Δ_solH_m (calcium- l -lactate tetrahydrate,m =  0.2902 mol · kg ^− 1)  =  25.8 kJ · mol ^− 1,Δ_solH_m (calcium gluconate, m =  0.0806 mol · kg ^− 1)  =  22.1 kJ · mol ^− 1, Δ_solH_m(magnesium-dl -aspartate tetrahydrate, m =  0.1469 mol · kg ^− 1)  =  11.5 kJ · mol ^− 1, andΔ_solH_m (magnesium- l -lactate trihydrate,m =  0.3462 mol · kg ^− 1)  =  3.81 kJ · mol ^− 1.     

Simultaneous determination of dopamine,ascorbic acid and uric acid with electrospun carbon nanofibers modified electrode

A novel carbon-nanofiber-modified carbon-paste electrode (CNF-CPE) was employed for the simultaneous determination of dopamine (DA), ascorbic acid (AA) and uric acid (UA) with good selectivity and high sensitivity. The CNFs were prepared by combination of electrospinning technique with thermal treatment method and were used without any pretreatment. In application to determination of DA, AA and UA in the ternary mixture, the pristine CNF-CPE exhibited well-separated differential pulse voltammetric peaks with high catalytic current. Low detection limits of 0.04 μM, 2 μM and 0.2 μM for DA, AA and UA were obtained, with the linear calibration curves over the concentration range 0.04–5.6 μM, 2–64 μM and 0.8–16.8 μM, respectively.     

Determination of chlorogenic acid by flow injection irreversible biamperometry

A flow injection irreversible biamperometric method for the determination of chlorogenic acid is described.The proposedmethod is based on the electrochemical oxidation of chlorogenic acid at pretreated platinum electrode and the reduction ofpermanganate at another electrode to form an irreversible biamperometric detection system.Under the external potential difference(△E)of 0 V,in the 0.05 mol/L sulfuric acid,chlorogenic acid can be determined over the range 0.8-120 mg/L with a samplemeasurement frequency of 80 samples/h.The detection limit is 0.18 mg/L.The proposed method exhibits the satisfactoryreproducibility with a relative standard derivation(R.S.D.)of 2.21%for 19 successive determinations of 40 mg/L.     

Phase transitions on (liquid + liquid) equilibria for (water + 1-methylnaphthalene + light aromatic hydrocarbon) ternary systems at T = (563, 573, and 583) K

Phase transitions for (water + 1-methylnaphthalene + light aromatic hydrocarbon) ternary systems are observed at their (liquid + liquid) equilibria at T = (563, 573, and 583) K and (8.6 to 25.0) MPa. The phase transition pressures at T = (563, 573, and 583) K were measured for the five species of light aromatic hydrocarbons, o-, m-, p-xylenes, ethylbenzene, and mesitylene. The measurements of the phase transition pressures were carried out by changing the feed mole fraction of water and 1-methylnaphthalene in water free, respectively. Effects of the feed mole fraction of water on the phase transition pressures are very small. Increasing the feed mole fraction of 1-methylnaphthalene results in decreasing the phase transition pressures at constant temperature. The slopes depending on the feed mole fraction for 1-methylnaphthalene at the phase transition pressures are decreased with increasing temperature for (water + 1-methylnaphthalene + p-xylene), (water + 1-methylnaphthalene + o-xylene), and (water + 1-methylnaphthalene + mesitylene) systems. For xylene isomers, the highest and lowest of the phase transition pressures are obtained in the case of p- and o-xylenes, respectively. The phase transition pressures for ethylbenzene are lower than those in the case of p-xylene. The similar phase transition pressures are given for p-xylene and mesitylene.     

Phase behavior of (CO2 + methanol + lauric acid) system

In this study the phase equilibrium behaviors of the binary system (CO₂ + lauric acid) and the ternary system (CO₂ + methanol + lauric acid) were determined. The static synthetic method, using a variable-volume view cell, was employed to obtain the experimental data in the temperature range of (293 to 343) K and pressures up to 24 MPa. The mole fractions of carbon dioxide were varied according to the systems as follows: (0.7524 to 0.9955) for the binary system (CO₂ + lauric acid); (0.4616 to 0.9895) for the ternary system (CO₂ + methanol + lauric acid) with a methanol to lauric acid molar ratio of (2:1); and (0.3414 to 0.9182) for the system (CO₂ + methanol + lauric acid) with a methanol to lauric acid molar ratio of (6:1). For these systems (vapor + liquid), (liquid + liquid), (vapor + liquid + liquid), and (solid + fluid) transitions were observed. The phase equilibrium data obtained for the systems were modeled using the Peng–Robinson equation of state with the classical van der Waals mixing rule with a satisfactory correlation between experimental and calculated values.     

(Liquid + liquid) equilibria in ternary aqueous mixtures of phosphoric acid with organic solvents at T = 298.2 K

(Liquid + liquid) equilibrium (LLE) data for the ternary mixtures of {water (1) + phosphoric acid (2) + organic solvents (3)} were determined at T = 298.2 K and atmospheric pressure. The organic solvents were cyclohexane, 2-methyl-2-butanol (tert-amyl alcohol), and isobutyl acetate. All the investigated systems exhibit Type-1 behaviour of LLE. The immiscibility region was found to be larger for the (water + phosphoric acid + cyclohexane) ternary system. The experimental LLE results were correlated with the NRTL model, and the binary interaction parameters were obtained. The reliability of the experimental tie-line results was tested through the Othmer–Tobias and Bachman correlation equations. Distribution coefficients and separation factors were evaluated over the immiscibility regions and a comparison of the extracting capabilities of the solvents was made with respect to these factors. The experimental results indicate the superiority of cyclohexane as the preferred solvent for the extraction of phosphoric acid from its aqueous solutions.     

Thermodynamic study on the sublimation of succinic acid and of methyl- and dimethyl-substituted succinic and glutaric acids

The Knudsen mass-loss effusion technique was used to measure the vapour pressures at different temperatures of the following crystalline dicarboxylic acids: succinic acid, between T =  360.11 K and T =  375.14 K; methylsuccinic acid, between T =  343.12 K and T =  360.11 K; 2,2-dimethylsuccinic acid, between T =  350.11 K, and T =  365.11 K; 2-methylglutaric acid, between T =  338.38 K and T =  347.63 K; and 2,2-dimethylglutaric acid between T =  342.18 K and T =  352.66 K. From the temperature dependence of the vapour pressure, the standard molar enthalpies of sublimation were derived by the Clausius–Clapeyron equation and the molar entropies of sublimation at equilibrium pressures were calculated. Using estimated values for the heat capacity differences between the gas and the crystal phases of the studied compounds, the standard, p^o =  10⁵Pa, molar enthalpies, entropies and Gibbs energies of sublimation at T =  298.15 K, were derived:     

Phase equilibrium properties of binary aqueous solutions containing ethanediamine, 1,2-diaminopropane, 1,3-diaminopropane,or 1,4-diaminobutane at several temperatures

The vapour pressures of {ethanediamine (EDA) + water}, {1,2-diaminopropane (1,2-DAP) + water}, {1,3-diaminopropane (1,3-DAP) + water} or {1,4-diaminobutane (1,4-DAB) + water} binary mixtures, and of pure EDA, 1,2-DAP, 1,3-DAP, 1,4-DAB, and water components were measured by means of two static devices at temperatures between (293 and 363) K. The data were correlated with the Antoine equation. From these data, the excess Gibbs function (G^E) was calculated for several constant temperatures and fitted to a fourth-order Redlich–Kister equation using the Barker’s method. The {ethanediamine (EDA) + water}, and {1,2-diaminopropane (1,2-DAP) + water} binary systems show negative azeotropic behaviour. The aqueous solutions of EDA, 1,2-DAP, or 1,3-DAP exhibit negative deviations in G^E for all investigated temperatures over the whole composition range whereas the (1,4-DAB + water) binary mixture shows negative G^E for temperatures (293.15 < T/K < 353.15) and a sinusoidal shape for G^E at T = 363.15 K.     

Solid–liquid equilibria measurements for binary systems comprising (butyric acid + propionic or pentanoic acid) and (heptanoic acid + propionic or butyric or pentanoic or hexanoic acid)

Solid–liquid equilibria (SLE) measurements have been undertaken for carboxylic acid systems comprising (butyric acid + propionic or pentanoic acid) and (heptanoic acid + propionic or butyric or pentanoic or hexanoic acid) via a synthetic method using two complementary pieces of equipment. The measurements have been obtained at atmospheric pressure and over the temperature range of (225.6 to 270.7) K. All the acid mixtures exhibit a eutectic point in their respective phase diagrams, which have been determined experimentally. The estimated maximum uncertainties in the reported temperatures and compositions are ±1 K and ±0.0006 mole fraction, respectively. The experimental data have been satisfactorily correlated with the Wilson and NRTL activity coefficient models.     

Thermodynamic study on the sublimation of 3-phenylpropionic acid and of three methoxy-substituted 3-phenylpropionic acids

The Knudsen mass-loss effusion technique was used to measure the vapour pressures at different temperatures of the following compounds: 3-phenylpropionic acid, between T =  305.17 K and T =  315.17 K; 3-(2-methoxyphenyl)propionic acid, between T =  331.16 K and T =  347.16 K; 3-(4-methoxyphenyl)propionic acid, between T =  341.19 K and T =  357.15 K; 3-(3,4-dimethoxyphenyl)propionic acid, between T =  352.18 K and T =  366.16 K. From the temperature dependence of the vapour pressure, the standard molar enthalpies of sublimation Δ_cr^gH_m^owere derived by the Clausius–Clapeyron equation and the molar entropies of sublimation at equilibrium pressures were calculated. On the basis of estimated values for the heat capacity differences between the gas and the crystal phases of the studied compounds the standard, p ^∘  =  10⁵Pa, molar enthalpies, entropies and Gibbs energies of sublimation at T =  298.15 K, were derived: