Fluid Phase Equilibria (v.244, #1)

José Tojo by A. Arce (1).

Critical points of adsorbed phases using a 2D lattice gas equation of state by Marcelo F. Alfradique; Papa M. Ndiaye; Marcelo Castier (2-10).
The types of critical phase diagrams for adsorbed binary mixtures that can be predicted by an equation of state (EOS) based on a two-dimensional lattice gas theory are investigated. The search for critical point conditions was done using the Hicks and Young algorithm, switching to the Heidemann and Khalil algorithm in the close of vicinity of a critical point. We observed that the model can predict critical points that represent the conditions in which a vapor-like and a liquid-like adsorbed phases collapse. The critical diagrams were classified using an analogy with the van Konynenburg and Scott scheme for classifying the critical behavior of binary bulk mixtures. The original classification scheme is based on the critical lines on the pressure–temperature plane; we used a straightforward extension based on the critical lines on the spreading pressure–temperature plane. Five of the six types of phase behavior classified by von Konynenburg and Scott were observed using this thermodynamic model. The transitions between the types of phase diagram were also observed in temperature–mole fraction projections. These results extend previous observations that suggested the possibility of very interesting phase behaviors for adsorbed mixtures. However, experimental data would be necessary to confirm the predicted types of critical diagrams.
Keywords: Adsorption; Critical points; Equations of state; Phase diagrams; Lattice models;

Prediction of the enthalpy of vaporization of metals and metalloids by S. Velasco; F.L. Román; J.A. White; A. Mulero (11-15).
A simple correlation equation without adjustable parameters is used to obtain the enthalpy of vaporization of 10 metals and 2 metalloids as a function of the temperature. Besides the critical temperature, this equation requires knowing of the enthalpy of vaporization at two reference temperatures: the lowest available temperature and the normal boiling temperature. Average relative deviations are less than 0.75% for the available ranges of temperature. A comparison is made with three other well-known empirical equations based only on the normal boiling point.
Keywords: Enthalpy of vaporization; Predictive models; Phase transitions; Metals; Metalloids;

In this work, the thermodynamic behavior of binary systems composed by one commercial biodegradable copolymer [poly(d,l-lactide-co-glycolide)] and supercritical fluids, SCF, (dimethyl ether, carbon dioxide, chlorodifluoromethane and trifluoromethane) was studied. The perturbed chain-SAFT (PC-SAFT) and the Sanchez–Lacombe (SL) non-cubic equations of state (EoS) were used to model the fluid–liquid equilibrium (FLE) for these binary systems, by fitting one temperature-dependent binary interaction parameter. For comparison, the same data were also modeled by using the traditional Peng–Robinson (PR) cubic EoS. The three PC-SAFT and SL pure-component parameters and two PR pure-component parameters were regressed by fitting pure-component data (liquid pressure–volume–temperature, PVT, data for copolymer and saturated liquid vapor pressure and molar volume for SCF). Liquid PVT data of PLAG copolymers were estimated by using a group contribution method, taken from literature. The estimation of pure-component and binary interaction parameters was performed by using the modified maximum likelihood method with an objective function that includes the cloud point pressure. An excellent agreement was obtained with the PC-SAFT EoS, while the performance of the SL and PR EoS were less satisfactory.
Keywords: Biodegradable; Copolymer; Fluid–liquid equilibrium; Equation of state;

Ultrasonic velocity U and viscosity η have been measured for the binary mixture of tetrahydrofuran with 1-propanol and 2-propanol at T  = 293 K, 303 K and 313 K over the entire composition range. Using these experimental data and previously reported values of density ρ, excess adiabatic compressibility β s E , excess viscosity Δη, excess energy of activation ΔG *E and excess internal pressure π i E have been evaluated. All these excess parameters were plotted against the mole fraction of tetrahydrofuran over the whole composition range. The strength and the nature of the interactions between like and unlike molecules have been discussed.
Keywords: Ultrasonic velocity; Viscosity; Excess thermodynamic parameters; Tetrahydrofuran; Propanol;

This work discusses the reasons why the activities of ions were considered to be impossible to measure using electrochemical cells with liquid junctions. The key steps followed to overcome the experimental and conceptual barriers are outlined and an overview of the successful method for measuring ionic activities is presented. The comparison of two approaches used for reducing the experimental emf data is used to emphasize the negligible effect introduced by errors in the estimate of junction potentials. The possible effects of underlying assumptions of the method on the accuracy of the activity coefficients obtained are discussed and evaluated. Two options of handling the independent equations relating the activity of a single ion to the junction potential are presented and it is demonstrated why Malatesta's procedure cannot provide ionic activities while our method can. Additional examples are presented demonstrating that ionic activities are real quantities. The robustness of the proposed method for their measurement is tested.
Keywords: Ions; activity; Activity coefficients; Electrolytes; Junction potential; Ion selective electrodes;

Vapor quality measurement by a discharging calorimeter by Abram Dorfman; Ella Fridman (46-51).
A theoretical development is presented showing that the quality of saturated mixture inside a heat-insulated discharging container may be expressed as a function of pressure and a parameter defined as instant flow work per unit flow mass, leaving the container. Since both the parameter and the pressure inside the container are easily measured, the derived relation may be used to create a device for measuring the vapor quality. Possible schemes and characteristics of such device as well as some properties of discharging process and accuracy are discussed.
Keywords: Quality; Mixture; Discharging calorimeter; Enthalpy; Flow work; Unsteady process;

Liquid–liquid equilibrium (LLE) data were obtained for the polyethylene glycol 2000–sodium citrate–water system at 298.15, 308.15 and 318.15 K. Experimental and analytical methods were described in the previous article [T. Murugesan, M. Perumalsamy, J. Chem. Eng. Data 50 (2005) 1392]. The UNIQUAC, NRTL, UNIFAC and ASOG models have been used to fit the experimental LLE data. The interaction parameters of the models were estimated. The Debye–Huckel equation was used to calculate the long-range electrostatic interaction of the ions. The predicted LLE data by the models show good agreement with the experimental data.
Keywords: Liquid–liquid equilibria; Polyethylene glycol; Sodium citrate; UNIQUAC; NRTL; ASOG; UNIFAC;

Experimental and predicted excess molar enthalpies for 1,4-dioxane + octane + cyclohexane at 303.15 K by Zehira Hamoudi; Farid Brahim Belaribi; Ahmed Ait-Kaci; Ghénima Boukais-Belaribi (62-67).
Excess molar enthalpies for the ternary system 1,4-dioxane (1) +  n-octane (2) + cyclohexane (3) and for the three constituent binary systems have been measured by a Calvet microcalorimeter at 303.15 K and ambient pressure. The experimental binary results were fitted by the Redlich–Kister equation. The excess molar enthalpies of the ternary system were correlated using the Cibulka equation. The DISQUAC group contribution model was applied to predict the excess molar enthalpy for this mixture.
Keywords: Ternary excess molar enthalpies; 1,4-Dioxane; n-Octane; Cyclohexane; DISQUAC model;

Heat capacities for nine ionic liquids (IL) have been determined with the “three-step” method using two different differential scanning calorimeters (DSC). In addition, the heat capacities of these ionic liquids have been studied by the modulated-temperature differential scanning calorimetry (MDSC™). The measurements cover a temperature range from 315 to 425 K.
Keywords: Ionic liquids; Heat capacity; DSC; MDSC™;

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.
Keywords: Isopropanol; Sodium acetate; Sodium oleate; LV equilibrium; Anderko–Pitzer EoS; Supercritical water oxidation;

Activity coefficients of the binary mixtures of o-cresol or p-cresol with C1–C4 aliphatic alcohols near ambient pressure by T.E. Vittal Prasad; Anupam Jaiswal; Suraj Prasad; G. Harish; N. Krupavaram; N.M. Sirisha; K. Ashok; Y. Naveen Kumar; N. Venkanna; D.H.L. Prasad (86-98).
Bubble point temperatures near ambient pressure, for the binary mixtures, formed by o-cresol or p-cresol with – methanol, ethanol, n- and iso-propanols and n-, iso-, sec- and tert-butanols – covering the whole composition range, are measured using a Swietoslawski-type ebulliometer. The liquid phase composition–bubble point temperature measurements are found to be well represented by the Wilson model. Values of the optimum Wilson parameters as well as the computed values of vapor phase mole fractions and activity coefficients are tabulated. The results are discussed in terms of isomerization with reference to the selected set of compounds, constituting the mixtures and the stearic effects in the cresols.
Keywords: Bubble point temperatures; o-Cresol; p-Cresol; Aliphatic alcohols; Vapor–liquid equilibria;

Athermal lattice chains compared with hard-sphere chains by Chul Soo Lee; Jung Won Kang (99-103).
The Guggenheim–Huggins–Miller approximation of athermal lattice fluids has been a basis for lattice fluid equations of state. For better understanding of GHM solution, it was compared with molecular simulation data of hard-sphere chains. Relations were developed between parameters of lattice and off-lattice chain fluids for the comparison. The Guggenheim–Huggins–Miller approximation was found in good agreements with molecular simulation data of fused-hard-spheres when compared using the developed relations. But the agreements of GHM solution with tangent-hard-sphere chain data were found less satisfactory and deviations increased as segment number increased. Average deviations of GHM solution from mixed tangent-hard-sphere chain data were found similar to those of pure components. Real fluid parameters fitted to a GHM-based lattice fluid equation of state and the first order thermodynamic perturbation theory-based SAFT were found optimized to give similar repulsive contributions.
Keywords: Equation of state; Athermal lattice chain; Hard-sphere chain; Fused-hard-sphere chain; Molecular simulation;