Correlation of the prigogine-flory theory with isothermal compressibility and excess enthalpy data for benzene +n-alkane mixtures

Isothermal compressibilitiesκ _T for benzene + n-alkane systems at 25, 35, 45, and 60°C have been used to check the Prigogine-Flory theory using the van der Waals and Lennard-Jones potentials in order to study the energy-volume dependence. The Flory interaction parameter χ₁₂ has also been calculated for those set of systems at four temperatures. The variation of χ₁₂ with the number of carbon atoms in the n-alkane was studied. Three excess functions have been obtained from χ₁₂ for the equimolecular mixture: (?V ^E/?p)_T which is related toκ _T ^E , the excess enthalpy H ^E , and the excess volume V ^E . Except for H ^E theoretical predictions using a Lennard-Jones potential are in good agreement with the experimental data. A similar treatment has been performed for the same set of systems but using H ^E data at 25°C. The theory, using a van der Waals potential, predicts correctly the variation of the three excess functions with the chain length of the n-alkane but using a Lennard-Jones potential results in better agreement for the order in the magnitude of these excess functions.     

Excess molar volumes and viscosities of binary mixtures of cyclohexane and n-alkane at 298.15 K

Awwad, A.M. and Salman, M.A., 1986. Excess molar volumes and viscosities of binary mixtures of cyclohexane and n-alkane at 298.15 K. Fluid Phase Equilibria, 25: 195-208.Excess molar volumes, viscosities, excess molar viscosities, and excess molar activation energies of viscous flow were determined for binary mixtures of cyclohexane + n-pentane, + n-hexane, + n-heptane, + n-octane, + n-nonane, + n-decane, + n-dodecane, + n-tetradecane and + n-hexadecane at 298.15 K. The effect of orientational order of n-alkane on solution molar volumes and viscosities is investigated as well as the adequacy of the Flory theory and free volume theories used to predict solution molar volumes and viscosities. For longer n-alkanes V^E, η^E and ΔG*^E are positive and associated with the orientational order.     

Solid + liquid equilibria of (n-alkane + cyclohexane) mixtures at high pressures

Solid+liquid equilibria (SLE) of [n-alkanes (tridecane, hexadecane, octadecane, or eicosane) + cyclohexane] at very high pressures up to about 1.0 GPa have been investigated in the temperature range from 293 to 363 K using a thermostated apparatus for the measurements of transition pressures from the liquid to the solid state in two component isothermal solutions. The freezing temperature of each mixture increases monotonously with increasing pressure. The eutectic point of the binary systems shifts to a higher temperature and to a higher n-alkane concentration with increasing pressure. The pressure–temperature–composition relation of the high-pressure solid–liquid equilibria, a polynomial based on the general solubility equation at atmospheric pressure, was satisfactorily used. Additionally, the SLE of the binary system (tridecane+cyclohexane) at normal pressure was measured by the dynamic method. The results at high pressure for all systems were compared to that at normal pressure.     

Relative permittivities of binary mixtures of 1-butanol + n-alkane AT 298.15 k

A previous study on the physical properties of 1-alkanol + n-alkane has establised a correlation between dielectric permittivity at 1 GHz and excess molar volumes for all binary systems that were studied. In order to determine whether this behaviour is similar at lower frequencies, relative permittivity was measured at 100 kHz. The refractive index was measured to explore the effects at higher frequencies. Mixtures under study are in particular the systems (1-butanol + n-hexane, or n-octane, or n-decane) at the temperature of 298.15 K and atmospheric pressure, over the entire composition range. This revised version was published online in July 2006 with corrections to the Cover Date.     

Prediction of viscosities of hydrocarbon mixtures

A new model for prediction of the viscosities of hydrocarbons including oil and gas mixtures is presented. The model is based on the principle of corresponding states with methane and decane as reference components. The viscosity of a given component or mixture is determined from the reduced viscosities of the reference components using the molecular weight as an interpolation parameter.

The model has been used for prediction of viscosities of both pure components and mixtures over large pressure ranges and for reduced temperatures above 0.476. The results are in good agreement with the experimental data. The new model compares favorably with earlier published methods, which use only one reference component.

Finally, the model has been tested on data for 6 oil mixtures from the North Sea. The mean deviation based on 34 experimental points was 6.4 %.     

Thermodynamics of binary mixtures containing aldehydes. excess enthalpies of n-alkanals + benzene and + tetrachloromethane mixtures

Molar excess enthalpies H^E have been measured as a function of mole fraction at atmospheric pressure and 298.15 K for the binary liquid mixtures of ethanal, propanal, butanal and pentanal + benzene or + tetrachloromethane. The results show that the excess enthalpies decrease with increasing the n-alkanal chain length, with negative values for n-pentanal.     

Modeling the phase behavior of H2S+n-alkane binary mixtures using the SAFT-VR+D approach

A statistical associating fluid theory for potential of variable range has been recently developed to model dipolar fluids (SAFT-VR+D) [Zhao and McCabe, J. Chem. Phys. 2006, 125, 104504]. The SAFT-VR+D equation explicitly accounts for dipolar interactions and their effect on the thermodynamics and structure of a fluid by using the generalized mean spherical approximation (GMSA) to describe a reference fluid of dipolar square-well segments. In this work, we apply the SAFT-VR+D approach to real mixtures of dipolar fluids. In particular, we examine the high-pressure phase diagram of hydrogen sulfide+n-alkane binary mixtures. Hydrogen sulfide is modeled as an associating spherical molecule with four off-center sites to mimic hydrogen bonding and an embedded dipole moment (micro) to describe the polarity of H2S. The n-alkane molecules are modeled as spherical segments tangentially bonded together to form chains of length m, as in the original SAFT-VR approach. By using simple Lorentz-Berthelot combining rules, the theoretical predictions from the SAFT-VR+D equation are found to be in excellent overall agreement with experimental data. In particular, the theory is able to accurately describe the different types of phase behavior observed for these mixtures as the molecular weight of the alkane is varied: type III phase behavior, according to the scheme of classification by Scott and Konynenburg, for the H2S+methane system, type IIA (with the presence of azeotropy) for the H2S+ethane and+propane mixtures; and type I phase behavior for mixtures of H2S and longer n-alkanes up to n-decane. The theory is also able to predict in a qualitative manner the solubility of hydrogen sulfide in heavy n-alkanes.     

Predictions of solvation and vaporization enthalpies. 1.n-alkane +n-alkane solutions

A simple method for the calculation of the enthalpy of solvation is presented and demonstrated for 35 n-alkane + n-alkane solutions at 25°C. There is a good agreement between the predicted and experimental values. The calculation was based on the separation of the solvation enthalpy into the cavity formation and solute-solvent interaction contributions. The former term was determined from the activation enthalpy of the solvent viscous flow and solute molar volume while the latter on the basis of the dispersion energy using van der Waals diameters for n-propyl group. The procedure was also successful in prediction of the vaporization enthalpy of C₅–C₁₇ n-alkanes.     

Excess molar quantities of (a halogenated n-alkane + an n-alkane) A comparative study of mixtures containing either 1-chlorobutane or 1,4-dichlorobutane

Excess molar volumes V_m^E at 298.15 K were obtained, as a function of mole fraction x, for series I: {x1-C₄H₉Cl + (1 ? x)n-C_lH_{2l + 2}}, and II: {x1,4-C₄H₈Cl₂ + (1 ? x)n-C_lH_{2l + 2}}, for l = 7, 10, and 14. 10, and 14. The instrument used was a vibrating-tube densimeter. For the same mixtures at the same temperature, a Picker flow calorimeter was used to measure excess molar heat capacities C_{p, m}^E at constant pressure. V_m^E is positive for all mixtures in series I: at x = 0.5, V_m^E/(cm³ · mol^?1) is 0.277 for l = 7, 0.388 for l = 10, and 0.411 for l = 14. For series II, V_m^E of {x1,4-C₄H₈Cl₂ + (1 ? x)n-C₇H₁₆} is small and S-shaped, the maximum being situated at x_max = 0.178 with V_m^E(x_max)/(cm³ · mvl^?1) = 0.095, and the minimum is at x_min = 0.772 with V_m^E(x_min)/(cm³ · mol^?1) = ?0.087. The excess volumes of the other mixtures are all positive and fairly large: at x = 0.5, V_m^E/(cm³ · mol^?1) is 0.458 for l = 10, and 0.771 for l = 14. The C_{p, m}^Es of series I are all negative and |C_{p, m}^E| increases with increasing l: at x = 0.5, C_{p, m}^E/(J · K^?1 · mol^?1) is ?0.56 for l = 7, ?1.39 for l = 10, and ?3.12 for l = 14. Two minima are observed for C_{p, m}^E of {x1,4-C₄H₈Cl₂ + (1 ? x)n-C₇H₁₆}. The more prominent minimum is situated at x′_min = 0.184 with C_{p, m}^E(x′_min)/(J · K^?1 · mol^?1) = ?0.62, and the less prominent at x″_min = 0.703 with C_{p, m}^E(x″_min)/(J · K^?1 · mol^?1) = ?0.29. Each of the remaining two mixtures (l = 10 and 14) has a pronounced minimum at low mole fraction (x_min = 0.222 and 0.312, respectively) and a broad shoulder around x = 0.7.     

Thermodynamic behavior of water-acetonitrile mixtures excess volumes and viscosities

Densities of water+acetonitrile mixture have been measured from 308.15 to 278.15 K over the entire composition range. Partial molal volumes of both components of the mixed system have been calculated and deviations from ideal volumes of mixing have been evaluated. Literature data on viscosity have also been treated by a least square method and activation thermodynamic functions of viscous flow computed. Structural correlations have been made with previous results on acid-base properties; they allow to distinguish several interaction regions between components of binary systems.     

Prediction of vapor-liquid equilibrium from excess enthalpy data for binary ether +n-alkane or cyclohexane mixtures

Vapor liquid equilibrium (VLE) is successfully predicted from excess enthalpy H^E data for binary ether + n-alkane or cyclohexane mixtures. Parameters for the continuous linear association model (CLAM) and for the UNIQUAC Model for the excess Gibbs energy G^E were determined from H^E data measured at a low temperature (ambient temperature). These parameters are used to predict VLE data at low and high temperatures. The dependence of the accuracy of predictions on the set of H^E data chosen to evaluate the parameters and on the model for G^E are discussed.     

Experimental measurements and prediction of liquid densities for n-alkane mixtures

We present experimental liquid densities for n-pentane, n-hexane and n-heptane and their binary mixtures from (273.15 to 363.15) K over the entire composition range (for the mixtures) at atmospheric pressure. A vibrating tube densimeter produces the experimental densities. Also, we present a generalized correlation to predict the liquid densities of n-alkanes and their mixtures. We have combined the principle of congruence with the Tait equation to obtain an equation that uses as variables: temperature, pressure and the equivalent carbon number of the mixture. Also, we present a generalized correlation for the atmospheric liquid densities of n-alkanes. The average absolute percentage deviation of this equation from the literature experimental density values is 0.26%. The Tait equation has an average percentage deviation of 0.15% from experimental density measurements.     

Spinodal phase separation of unstable solid-state binary n-alkane mixtures

Two mixtures of unequal chain length n-alkanes in which one component is deuterated have been investigated by infrared spectroscopy as they demixed. The measurements followed the band shapes of the scissors vibrations as a function of time. The band envelopes are analyzed as composites of a number of reference mixtures of known concentration. The unequal-chain mixtures separate into phases that slowly change their composition toward pure alkane phases. The method of analysis, which reveals local concentrations, should be generally applicable to polymethylene systems.     

Solid-fluid and solid-solid phase equilibrium in a model of n-alkane mixtures

Solid-fluid and solid-solid phase equilibrium for binary mixtures of hard sphere chains modeling n-hexane, n-heptane, and n-octane has been calculated using Monte Carlo computer simulations. Thermodynamic integration was used to calculate the Gibbs free energy and chemical potentials in the solid and fluid phases from pure component reference values. A multiple stage free energy perturbation method was used to calculate the composition derivative of the Gibbs free energy. Equation of state and free energy data for the fluid phase indicate ideal solution behavior. Nonideality is much more significant in the solid phase with only partial solubility of shorter chains in the longer chains and essentially no solubility at the other end of the composition range. The miscibility decreases with increasing chain length difference between the components. For the model of n-hexane/n-octane mixtures solid--solid phase separation has been observed directly in some of the simulations, with the components segregating between the layers of the solid structure. The behavior is similar to that seen in some binary n-alkane mixtures with longer chain lengths but comparable chain length ratios between the components. Such phase separation, although indicated thermodynamically, is not seen directly in the simulations of the n-heptane/n-octane mixture due to the difference in the pure component crystal structures.     

Excess enthalpies for n-alkane/ -carotene+n-alkane/AOT/water systems

The experimental data of excess enthalpies for β-carotene/n-alkane+n-alkane/AOT/water systems at 298.15 K are reported. The H_E dependence on AOT (sodium bis(2-ethylhexyl) sulfosuccinate) concentration and hydrocarbon chain length was investigated. The excess enthalpy was measured using the flow microcalorimeter UNIPAN type 600.     

Volumes and heat capacities of anionic-nonionic surfactant mixtures

Density, heat capacity and surface tension measurements of sodium decylsulfate (NaDeS)-dodecyldimethylamine oxide (DDAO)-water mixtures were carried out as functions of the surfactants total molality m_t at fixed stoichiometric mixture compositions X_NaDeS. From the surface tension data, the critical micelle concentration of NaDeS-DDAO mixtures as a function of X_NaDeS were obtained. From density and heat capacity data, the apparent molar volume V_,2 and heat capacity C_,2 of NaDeS-DDAO mixtures in water were calculated, respectively. At a given mole fraction, V_,2 and C_,2 monotonically increases and decreases, respectively, with increasing mt. However, anomalies were observed at X_NaDeS=0.1 and 0.3 for both V_,2 and C_,2 vs. mt curves. The nonideal contributions to the thermodynamic properties for the formation of surfactant-surfactant mixed micelles in water by mixing aqueous solutions of pure NaDeS and DDAO micelles were calculated at 0.3 mol-kg^–1 for the micellized surfactants mixture. The excess volume V^exc and heat capacity as functions of X_NaDeS are concave and S-shaped curves, respectively. All the properties are compared to those for sodium dodecylsulfate-DDAO mixture. In addition, to clarify the effect of the change in the hydrophobicity of the surfactants mixtures V^exc for the dodecyltrimethylammonium bromide-decyltrimethylammonium bromide mixture were calculated from literature data.     

The effect of keto-enol tautomerism on the properties of methylethylketone + benzene mixtures

Ratkovics, F. and Palágyi-Fényes, B., 1984. The effect of keto-enol tautomerism on the properties of methylethylketone + benzene mixtures. Fluid Phase Equilibria, 16: 99–116.The density, viscosity, static relative permittivity, conductivity and refractive index of methylethylketone + benzene mixtures have been measured in the interval 293.15–313.15 K. Vapor-liquid equilibrium data for the same mixtures were measured between 313.15 and 333.15 K. The results obtained indicate the formation of an association complex between benzene and methylethylketone in the enolic form, and the keto-enol equilibrium is shifted accordingly towards formation of the latter. Electrolytic dissociation of the benzene-enol association complex contributes to the conductivity of the benzene-ketone mixtures. In addition to concentration, the relative permittivity also has a considerable influence on the conductivity, since a considerable number of nondissociated ion pairs are formed (in the sense of Bjerrum theory). Comparison of the model based on the physical picture outlined and the experimental results indicates that ions deriving from the benzene-enol association complex are solvated in the region of higher benzene molar ratios. The model is also suitable for the interpretation of results obtained for mixtures containing other ketones and proton acceptors.     

A novel approach to the modelling of the fluid multiphase behaviour of ternary mixtures of carbon dioxide + n-alkane + 1-alkanol

In this work, modelling of the phase behaviour in ternary systems composed of CO₂ + n-alkanes + 1-alkanols is described. The model assumes that the ternary system is congruent to binary systems composed of CO₂ + n-alkanes and that the phase behaviour of the ternary system can be related to the average molecular size of the solute molecules. The average molecular size of the solute molecules is calculated taking into account alkanol aggregation. Although some crude assumptions have been made, the model is able to describe experimental results qualitatively. Values for model parameters like the degree of aggregation and the equilibrium constant of the aggregation reaction correspond very well to values for these parameters obtained from IR-spectroscopy.