Effects of solvent on microstructure and proton conductivity of organic-inorganic hybrid membranes

Effects of solvent on the microscopic structure and proton conductivity of organic-inorganic hybrids containing heteropolyacid are reported. The organic-inorganic hybrids were prepared by sol-gel synthesis of 1,8-bis(triethoxysilyl)octane (TES-Oct) in the presence of phosphotungstic acid (PWA). The proton conductivity of the membranes prepared under different solvents exhibited greater values in the order methanol < 1-butanol < 2-propanol < ethanol < 1-propanol < 2-butanol. The conductivity strongly correlated to the amount of incorporated PWA in the membranes, which was determined by titration of the solutions containing PWA leaked from the membrane. Small-angle X-ray scattering (SAXS), atomic force microscopy (AFM) and thermogravimetric analysis (TGA) were employed to reveal the relationship between the proton conductivity and microscopic structure of the TES-Oct/PWA membranes. It was found that there is an optimal condition for the formation of the condensed domain structure, indicating the important role of the structures in the membrane conductivity.     

Prediction and measurement of the lower flash points for flammable binary solutions by using a setaflash closed cup tester

The flash point is one of the most important physical properties used to determine the potential for fire and explosion hazards of industrial materials. The purpose of this study was to measure and predict the lower flash points for the binary mixtures to aid in evaluating the safety of flammable liquid mixtures. The lower flash points for the flammable binary systems, n-hexanol+propionic acid, n-butyric acid+m-xylene and n-pentanol+n-butanol, were measured by Setaflash closed cup tester. The experimentally derived data were correlated with the Wilson and UNIQUAC (UNIversal QUuasi Chemical) equations using the binary interaction parameters. Both equations correlated with a good accuracy.     

Measurement and prediction of high-pressure vapor-liquid equilibria for binary mixtures of carbon dioxide + n-octane, methanol, ethanol, and perfluorohexane

We report the measurement of high-pressure vapor-liquid equilibrium data for binary mixtures of carbon dioxide + n-octane, +methanol, and +ethanol systems at 313.14 K and carbon dioxide + perfluorohexane at 303.15-323.15 K. The experimental data were collected using a new simple apparatus for measuring high-pressure vapor-liquid equilibria and correlated using a modified SRK equation with the three-parameter conventional mixing rule proposed by Adachi and Sugie. The SAFT-VR equation of state has also been used to predict the phase behavior and found to be in good agreement with experimental data. For the carbon dioxide + methanol, carbon dioxide + ethanol and carbon dioxide + perfluorhexane systems simple Lorentz-Berthelot combining rules can be used to determine the cross interactions and predict the phase behavior. For the carbon dioxide + n-octane system cross interaction parameters fitted to experimental data are needed in order to capture the non-ideal phase behavior exhibited by this system.     

Feasibility of 1,3-butanediol as solvent for limonene and linalool separation

Liquid–liquid equilibrium of the system limonene + linalool + 1,3-butanediol has been studied at two different temperatures. The obtained data were satisfactorily correlated with the NRTL activity coefficient model, in order to obtain the binary interaction parameters of the mixture. Later on, an extraction column was simulated with ASPEN PLUS^® software, to ascertain the feasibility of 1,3-butanediol as solvent for limonene and linalool separation and to determine the advantages of this solvent over the employed previous ones in this process. The influence of the number of theoretical stages and the solvent/feed ratio over the amount and purity of the recovered limonene and linalool were also studied.     

Equation of state modeling of high-pressure, high-temperature hydrocarbon density data

Experimental densities are reported for n-pentane, n-octane, cyclooctane, 2,2,4-trimethylpentane, n-decane, and toluene to ∼280 MPa and ∼250 °C. These densities are in good agreement with available literature data that typically cover lower pressure and temperature ranges than those reported here. The data are modeled with the Peng-Robinson (PR) and Soave-Redlich-Kwong (SRK) cubic equations, the temperature-dependent, volume-translated SRK equation, the temperature- and density-dependent SRK equation, and the SAFT and PC-SAFT equations. Mean absolute percentage deviation (MAPD) values between densities calculated with the PR equation and literature data are 4.55 for n-pentane, 2.91 for n-octane, 3.68 for cyclooctane, 3.98 for 2,2,4-trimethylpentane, 5.58 for n-decane, and 1.99 for toluene. With the exception of 2,2,4-trimethylpentane, these MAPD values are substantially better than those obtained with the SRK and modified SRK equations. Although both SAFT-based models have MAPD values significantly lower than those with the PR equation, the PC-SAFT equation provides the lowest MAPD values.     

Laminar burning velocities of n-heptane, iso-octane, ethanol and their binary and tertiary mixtures

Measurements of the adiabatic laminar burning velocities of n-heptane, iso-octane, ethanol and their binary and tertiary mixtures are reported. Non-stretched flames were stabilized on a perforated plate burner at 1 atm. The Heat Flux method was used to determine burning velocities under conditions when the net heat loss from the flame to the burner is zero. Initial temperatures of the gas mixtures with air were 298 and 338 K. Uncertainties of the measurements were analyzed and assessed experimentally. The overall accuracy of the burning velocities was estimated to be better than ±1 cm/s. These new measurements were compared with the literature data when available. Experimental results in lean ethanol + air mixtures are systematically higher than previous measurements under similar conditions. Good agreement for n-heptane + air flames and for iso-octane + air flames was found with the experiments performed in counter-flow twin flames with linear extrapolation to zero stretch.     

Isobaric vapor–liquid equilibria for mixtures of tetrahydrofuran, 2-propanol, and 2,2,4-trimethylpentane at 101.3 kPa

Vapor–liquid equilibrium (VLE) at 101.3 kPa have been determined for a ternary system (tetrahydofuran + 2-propanol + 2,2,4-trimethylpentane) and its constituent binary systems (tetrahydrofuran + 2-propanol, tetrahydrofuran + 2,2,4-trimethylpentane, and 2-propanol + 2,2,4-trimethylpentane). The activity coefficients of liquid mixtures were calculated from the modified Raoult's law. Thermodynamic consistency tests were performed for all VLE data. The VLE data of the binary mixtures and ternary mixtures were correlated using the Margules, Wilson, NRTL, and UNIQUAC activity-coefficient models. The models with their best-fitted interaction parameters of the binary systems were used to predict the ternary vapor–liquid equilibrium. All VLE data are also used to calculate the reduced excess molar Gibbs free energy g^E/RT and the deviations in the boiling point ΔT. The calculated quantities of g^E/RT and ΔT were fitted to variable-degree polynomials in terms of liquid composition.     

Vapor-liquid equilibrium of polymer + solvent systems: Experimental data and thermodynamic modeling

In this work, experimental vapor-liquid equilibrium (VLE) data for binary systems polymer + solvent were obtained using a gravimetric sorption apparatus. The studied systems were benzene + polystyrene, hexane + polystyrene, benzene + poly(methyl methacrylate), benzene + poly(ethyl methacrylate), hexane + poly(vinyl chlorate) and water + poly(vinyl chlorate), in the range of 30-40 °C.The experimental data were modeled with two group contribution models for the activity coefficient, Elbro-FV and UNIFAC-Zhong; the latter method considers the free-volume of molecules of high molecular weight, such as polymers. UNIFAC groups in the literature as well as new groups that were proposed for the monomers were used. The necessary energy interaction parameters between these groups were estimated. There were observed mean deviations between experimental and calculated mass fractions of about 8.5% with Elbro-FV, and about 17% with UNIFAC-Zhong when original groups were used, while there were observed mean deviations of about 7% with Elbro-FV and about 16% with UNIFAC-Zhong when new groups were used. The Elbro-FV model represents the experimental data with better precision in both cases; on the other hand, the data were better correlated with both models when new groups were used.     

Equilibrium solubilities of a p-toluenesulfonamide and sulfanilamide mixture in supercritical carbon dioxide with and without ethanol

Supercritical separation processes for a multi-component mixture of solutes are of practical interest. In this study, the experimental equilibrium solubilities of two solute mixtures, p-toluenesulfonamide (p-TSA) and sulfanilamide (SNA), in supercritical carbon dioxide (SC CO₂) were measured at temperatures of 308, 318 and 328 K and pressures in the range of 11.0-21.0 MPa using a dynamic flow method. The effect of cosolvent on the multi-component system was investigated by the addition of a 3.5 mol% ethanol. In the ternary system (p-TSA + SNA + CO₂), the solubility of SNA increased as compared to its binary system (SNA + CO₂), while the solubility of p-TSA decreased. In the quaternary system (p-TSA + SNA + ethanol + CO₂), a significant solubility enhancement was observed for both p-TSA and SNA. The selectivity, which is thought to imply the intermolecular interactions between p-TSA and SNA, was also enhanced by the presence of ethanol so that the two solutes could be separated by a max. purity of 99.4%. The influence of the hydrogen bond interaction on solubility was discussed. The equations of Chrastil, Méndez-Santiago and Teja, and their modified forms were used to correlate the experimental data.     

Solubility of supercritical gases in organic liquids

Chrastil (1982) [6] demonstrated that the solubility of a substance in a supercritical fluid (SCF) can be correlated with the density of the pure supercritical gas. Therefore, Chrastil's equation permits calculation of the supercritical phase composition of binary SCF + substance mixture based on the knowledge of the supercritical gas density and avoiding the use of equation of state based models.In this work, it is demonstrated that the supercritical fluid density also defines the liquid phase composition of binary systems; a density-dependent relationship is presented to calculate the solubility of supercritical gases in organic liquids. The isothermal solubility of several gases commonly employed in supercritical processing, such as carbon dioxide, methane, and ethane, in different organic liquids, including alkanes, alkenes, alcohols, acids, ketones, esters, terpenes and aromatic compounds, was successfully correlated as a function solely of the pure supercritical fluid density. As an application, pressure vs. composition phase diagrams of binary SCF + substance mixtures were obtained circumventing the use of equation of state models.     

High-pressure phase equilibria for the binary system carbon dioxide + benzyl alcohol

The phase equilibria of the carbon dioxide + benzyl alcohol system were measured at 298.15, 306.35 and 313.15 K, under pressures from 1.03 to 16.15 MPa. An upper critical end point (UCEP) of the binary system was identified at 307.45 K and 7.77 MPa and three-phase equilibria were observed along the liquid-liquid-vapor (LLV) equilibrium line between 279.75 and 307.45 K. The experimental data were correlated well by the Peng-Robinson equation of state with two binary parameters. According to the experimental results, the phase behavior of the carbon dioxide + benzyl alcohol system appears to belong to Type-III according to the classification of van Konynenburg and Scott.     

Measurement and correlation of the solid-liquid-gas equilibria for carbon dioxide + normal chain saturated aliphatic hydrocarbon systems

The pressure p-temperature T projections of solid-liquid-gas (S-L-G) three-phase coexistence lines for the carbon dioxide + tetradecanoic acid (C₁₄H₂₈O₂) system, the carbon dioxide + hexadecanoic acid (C₁₆H₃₂O₂) system, and the carbon dioxide + 1-hexadecanol (C₁₆H₃₄O) were measured by the first melting point method in which the initial appearance of the liquid phase was observed. The profiles of the p-T projections of the S-L-G lines for the carbon dioxide + acid systems are similar to each other, the S-L-G equilibria for the carbon dioxide + acid systems are, however, different from that for the carbon dioxide + 1-hexadecanol systems. The experimental p-T projections of the S-L-G lines were also correlated by the Peng-Robinson equation of state and the van der Waals type mixing rules with two binary interaction parameters introduced into attraction term and size terms, respectively. The present model gave good correlation results for all of the experimental S-L-G lines with maximum average absolute relative deviations of 0.075% for the carbon dioxide + tetradecanoic acid system, 0.14% for the carbon dioxide + hexadecanoic acid system and 0.28% for the carbon dioxide + 1-hexadecanol system, respectively.     

Open-circuit-potentials of gas/electrode/YSZ boundary versus molten carbonate reference electrode at medium temperatures: II. Potential response of Au, Pt and Ni-cermet electrodes in CH4 + O2 and H2 + O2 gas mixtures

Values of open-circuit-potentials (OCP) have been determined for pairs of electrodes: Au and Pt, Ni-Ce_0.8Sm_0.2O_1.9 cermet and Au, Pt and Sm_0.5Sr_0.5CoO₃ composite at the YSZ electrolyte, in the uniform atmospheres of xCH₄ + yO₂ + (1 − x − y)Ar gas mixtures with variable x and y coefficients, at 600 °C. The determined dependencies of OCP values on the initial gas mixture compositions have been compared with the respective dependencies calculated for equilibrium or quasi-equilibrium compositions of these gas mixtures. The OCP values for the pair of Pt and Au electrodes have been measured also in the xH₂ + yO₂ + (1 − x − y)Ar uniform gas mixtures but no distinct difference of the OCP values has been observed in this atmosphere. For some pairs of electrodes investigated in xCH₄ + yO₂ + (1 − x − y)Ar atmospheres the measured OCP values have shown differences up to ca 0.9-1.0 V. These differences were stable within large range of compositions of this gas mixture. Within this gas composition range one of the electrodes conserves the potential of oxygen electrode determined by oxygen partial pressure in the initial gas mixture and is insensitive to reaction occurring in the gas phase. These results are discussed on the basis of equilibria or some quasi-equilibria, that establish in the C-H-O gas mixture and the solid carbon deposition is considered. For a given pair of dissimilar electrodes, their selective sensibility to the electrochemical process of oxygen electrode has been confirmed. Within large range of gas mixture concentrations, in the Pt-Au electrode pair Au has shown behavior of the oxygen electrode, whereas the OCP values of the Pt electrode are within the range of hydrogen electrode, also at gas compositions corresponding to the solid carbon stability. With this pair the OCP differences of ca. 600 mV have been obtained. Among three electrodes studied the cermet Ni-Ce_0.8Sm_0.2O_1.9 electrode shows the best electrocatalytic properties resulting in the OCP values following exactly the respective equilibrium dependence. In the pair Ni-Ce_0.8Sm_0.2O_1.9 and Au a stable potential difference of ca. 900 mV have been established. Unexpectedly, Pt electrode in the pair with the Sm_0.5Sr_0.5CoO₃ composite electrode plays role of the oxygen electrode quite insensitive to other components of the equilibrated initial gas mixture. This surprising fact seems indicate that in conditions of the experiments performed the electrocatalytic behavior of the electrode depends not only of the material of this electrode but also on the properties of the second electrode in the given pairs of electrodes.     

Correlation of measured excess enthalpies of binary systems composed of n-alkane+1-alkanol

The excess enthalpies of the binary mixture composed of n-alkane (n-octane, n-nonane, n-decane) and 1-alkanol (ethanol, 1-propanol, 1-butanol) have been measured by using a flow-type isothermal microcalorimeter (model CSC 4400, Calorimetry Science Corp., USA) at 313.15 K under atmospheric pressure. The measured excess enthalpy data were correlated by the Redlich-Kister equation and the nonrandom lattice fluid with hydrogen bonding (NLFHB) equation of state. Hydrogen bonding type specific parameters were introduced in the NLF-HB equation of state framework, and the effects of those parameters were investigated for excess enthalpy calculations. With two adjustable temperature-dependent interaction parameters, the NLF-HB equation represents the excess enthalpies for nine binary systems qualitatively. This article is dedicated to Professor Chul Soo Lee in commemoration of his retirement from Department of Chemical and Biological Engineering of Korea University.     

Solubility of carbon dioxide in pentaerythritol ester oils. New data and modeling using the PC-SAFT model

In this work, the solubility of carbon dioxide, CO₂, in pentaerythritol tetraheptanoate (PEC7) and in pentaerythritol tetranonanoate (PEC9) has been performed from 283 to 348 K and pressures up to 7.5 MPa in an isochoric high-pressure gas solubility apparatus. The solubility values are very similar in terms of mole fractions of CO₂ in both pentaerythritol esters. The experimental gas solubility data, together with those available in the literature for other CO₂ + pentaerythritol tetraester systems, were satisfactorily correlated with the PC-SAFT equation of state. The average absolute deviations of the gas solubility correlations were less than 3.9% for all the systems. In addition, PC-SAFT model was applied in a semi-predictive manner: the pure component's molecular parameters and the binary interaction parameter optimized from solubility data were used to calculate the types of the phase diagram as well as the densities and excess molar volumes in broad temperature and pressure ranges. The results obtained show the robustness of the model and these parameters to calculate properties not included in the fitting procedure.     

High pressure phase behavior of carbon dioxide + nitrobenzene binary system at 298.15, 310.45 and 322.75 K

The phase behavior of the carbon dioxide + nitrobenzene binary system has been studied in a high-pressure variable-volume view cell using an analytical method. The phase boundaries were measured at temperatures of 298.15, 310.45 and 322.75 K under pressures between 2.76 and 12.83 MPa, and it was found that three-phase equilibria existed over a temperature range from 303.60 to 313.65 K. The experimental data could be correlated with the Peng-Robinson equation of state (PR EoS) and two binary parameters. The phase behavior of the carbon dioxide + nitrobenzene system appears to belong to Type-V according to the classification of van Konynenburg and Scott.     

Thermodynamic modeling of dealcoholization of beverages using supercritical CO2: Application to wine samples

The supercritical removal of ethanol from alcoholic beverages (brandy, wine, and cider) was studied using the GC-EoS model to represent the phase equilibria behavior of the CO₂ + beverage mixture. Each alcoholic drink was represented as the ethanol + water mixture with the corresponding ethanol concentration (35 wt% for brandy, 9-12 wt% for different wines and 6 wt% for cider). The thermodynamic modeling was based on an accurate representation of the CO₂ + ethanol and CO₂ + water binary mixtures, and the CO₂ + ethanol + water ternary mixture.The GC-EoS model was employed to simulate the countercurrent supercritical CO₂ dealcoholization of the referred beverages; the results obtained compared good with experimental data from the literature. Thus, the model was used to estimate process conditions to achieve an ethanol content reduction from ca. 10 wt% to values lower than 1 wt%. The model results were tested by carrying out several extraction assays using wine, in a 3 m height packed column at 308 K, pressures in the range of 9-18 MPa and solvent to wine ratio between 9 and 30 kg/kg.     

A molecular model for correlating vapor-liquid equilibrium of propane+hydrocarbon mixtures

Simple analytical expressions are proposed for the calculation of the equilibrium pressure and the mole fractions of both liquid and vapor phases of propane+hydrocarbon binary mixtures. The new proposed expressions are based on a simple analytical expression for the vapor pressure of pure non-polar fluids, which, for a given temperature, only requires as input the values of the Lennard-Jones molecular parameters and the acentric factor. A properly modified Lorentz-Berthelot mixing rule is used, the interaction parameters being given as simple functions of the temperature and concentration with eight constants for each binary mixture. A different model is proposed to calculate the vapor mole fraction in which four appropriate constants are needed for each mixture. Here, it is shown how the models can reproduce accurately and straightforwardly the vapor liquid equilibrium properties (pressure, liquid mole fraction, and vapor mole fraction) of binary mixtures containing propane.     

Water chemical potential: A key parameter to determine the thermodynamic stability of some hydrated cement phases in concrete?

The CaO-Al₂O₃-SO₃-H₂O system at 25 °C under 1 bar of pressure has been investigated with phase diagrams software (Zen + k) based on chemical potentials (or activities). The reported invariant points are similar to those obtained previously using equilibrium calculations. However Zen + k enables us to calculate systems at different relative humidities, and in conditions where water is not in excess, calcium monosulfoaluminate could be a stable phase and thus, as observed experimentally, remain for long times in an ordinary Portland cement paste.