Measurement of Excess Molar Enthalpies of Binary and Ternary Systems Involving Hydrocarbons and Ethers

The study of excess thermodynamic properties of liquid mixtures is very important for designing the thermal separation processes, developing solution theory models and to have a better understanding of molecular structure and interactions involved in the fluid mixtures. In particular, heat of mixing or excess molar enthalpy data of binary and ternary fluid mixtures have great industrial and theoretical significance. In this connection, the experimental excess molar enthalpies for seventeen binary and nine ternary systems involving hydrocarbons, ethers and alcohol have been measured at 298.15K and atmospheric conditions for a wide range of composition by means of a flow microcalorimeter (LKB 10700-1). The binary experimental excess molar enthalpy values are correlated by means of the Redlich-Kister polynomial equations and the Liebermann - Fried solution theory model. The ternary excess molar enthalpy values are represented by means of the Tsao-Smith equation with an added ternary term and the Liebermann-Fried model was used to predict ternary excess molar enthalpy values. The Liebermann-Fried solution theory model was able to closely represent the experimental excess enthalpy data for most of the binary and ternary systems with reasonable accuracy. The correlated and predicted excess molar enthalpy data for the ternary systems are plotted in Roozeboom diagram

Excess molar enthalpies of binary and ternary systems involving hydrocarbons and ethers

In modern separation design, an important part of many phase-equilibrium calculations is the mathematical representation of pure-component and mixture enthalpies. Mixture enthalpy data are important not only for determination of heat loads, but also for the design of distillation units. Further, mixture enthalpy data, when available, are useful for extending vapor-liquid equilibria to higher (or lower) temperatures, through the use of the Gibbs-Helmholtz equation. In this connection excess molar enthalpies for several binary and ternary mixtures involving ethers and hydrocarbons have been measured at the temperature 298.15 K and atmospheric pressure, over the whole mole fraction range. Values of the excess molar enthalpies were measured by means of a modified flow microcalorimeter (LKB 10700-1) and the systems show endothermic behavior. The Redlich-Kister equation has been used to correlate experimental excess molar enthalpy data of binary mixtures. Smooth representations of the excess molar enthalpy values of ternary mixtures are accomplished by means of the Tsao-Smith equation with an added ternary contribution term and are used to construct excess enthalpy contours on Roozeboom diagrams. The values of the standard deviations indicate good agreement between experimental results and those calculated from the smoothing equations. The experimental excess enthalpy data are also correlated and predicted by means of solution theories (Flory theory and Liebermann-Fried model) for binary and ternary mixtures, respectively. These solution theories correlate the binary heats of mixing data with reasonable accuracy. The prediction of ternary excess molar enthalpy by means of the solution theories are also presented on Roozeboom diagrams. The predictions of ternary excess enthalpy data by means of these theories are reasonably reliable

Derived thermodynamic properties of [o-xylene or p-xylene + (acetic acid or tetrahydro-furan)] at different temperatures and pressures

Thermal expansion coefficients α, their excess values , isothermal coefficient of pressure excess molar enthalpy , partial molar volumes and excess partial molar volumes , were calculated from experimental densities. The isothermal coefficients of pressure excess molar enthalpy for binary mixtures {o-xylene or p-xylene + acetic acid} at temperatures 313.15-473.15 K and pressure 0.2-2 MPa are negative and for binary mixtures {o-xylene or p-xylene + tetrahydrofuran (THF)} at temperatures 278. 15 K to 318.15 K and pressure 81.5 kPa are negative and with increasing temperature become more negative. The excess thermal expansions coefficient , for binary mixtures {o-xylene or p-xylene + acetic acid} at temperatures 313.15-473.15 K and pressure 0.2 MPa and 2 MPa are positive. The excess thermal expansions coefficient for binary mixtures {o-xylene or p-xylene + tetrahydrofuran (THF)} at temperatures 278.15-318.15 K and pressure 81.5 kPa are positive and with increasing temperature become more positive. The excess molar volumes were correlated with a Redlich–Kister type equation.KEY WORDS: Thermal expansion coefficients, Isothermal coefficient, Excess partial molar volumes Bull. Chem. Soc. Ethiop. 2011, 25(2), 273-286.

Density and Acidic Solution Calorimetry Studies of the 0.333CaO-0.667[xSiO2-(1-x)P2O5] Glassy System

Glassy samples of the 0.333CaO-0.667[xSiO2-(1-x)P2O5] system are prepared by the melt quenching technique. Accurate density and solution enthalpy measurements were performed by pycnometry at 296.15 K and acid solution calorimetry at 298.15 K, respectively. Excess molar volume and mixing enthalpy from the ideal behavior over the entire mole fraction range were calculated. These excess thermodynamic properties are negative over the whole composition range showing attractive and contraction behavior with the increase in the silica content. Excess properties were fitted to the Redlich-Kister type equation. Examination of the behavior of the excess properties indicates that deviations from ideality can be attributed mainly to the formation of mixed association complexes

A macroscopic model that connects the molar excess entropy of a deeply supercooled liquid near its glass transition temperature to its viscosity

For a deeply supercooled liquid near its glass transition temperature, we suggest a possible way to connect the temperature dependence of its molar excess entropy to that of its viscosity by constructing a macroscopic model, where the deeply supercooled liquid is assumed to be a mixture of solid-like and liquid-like micro regions. In this model, we assume that the mole fraction x of the liquid-like micro regions tends to zero as the temperature T of the liquid is decreased and extrapolated to a temperature Tg*, which we assume to be below but close to the lowest glass transition temperature Tg attainable with the slowest possible cooling rate for the liquid. Without referring to any specific microscopic nature of the solid-like and liquid-like micro regions, we also assume that near Tg, the molar enthalpy of the solid-like micro regions is lower than that of the liquid-like micro regions. We then show that the temperature dependence of x is directly related to that of the molar excess entropy. Close to Tg, we assume that an activated motion of the solid-like micro regions controls the viscosity and that this activated motion is a collective motion involving practically all of the solid-like micro-regions so that the molar activation free energy for the activated motion is proportional to the mole fraction, 1-x, of the solid-like micro regions. The temperature dependence of the viscosity is thus connected to that of the molar excess entropy through the temperature dependence of the mole fraction x. As an example, we apply our model to a class of glass formers for which the molar excess entropy at temperatures near Tg is proportional to 1-T/TK with TK < Tg \sim Tg* and find their viscosities to be well approximated by the Vogel-Fulcher-Tamman equation for temperatures very close to Tg. We estimate the values of three parameters in our model for three glass formers in this class.Comment: 29 pages. Extensively revised in sections I, II, III.G, III.H, IV, VI, and VI

Thermodiffusion in binary liquids: the role of irreversibility

We study thermal diffusion in binary mixtures in the framework of non-equilibrium thermodynamics. Our formal result displays the role of partial enthalpies and Onsager's generalized mobilities. The mobility ratio provides a measure for the irreversible character of thermal diffusion. Comparison with experimental data on benzene, cyclohexane, toluene and alkanes shows that irreversibility is essential for thermal diffusion, and in particular for the isotope effect.Comment: 7 pages, 2 figure

Microwave dielectric relaxation & polarization study of binary mixture of methylethylketone with nitrobenzene

Present paper reveals detailed study of dielectric relaxation and dielectric polarization and physicochemical study of binary polar-polar liquid mixture i.e. dielectric constant, relaxation time, viscosity, density of methylethylketone (MEK) with nitrobenzene (NB) at 303 K. The measured dielectric and physicochemical parameters employed to acquire additional derived properties like Bruggeman factor, molar refraction and excess properties like static dielectric constant, excess inverse relaxation time, excess molar volume, excess viscosity, excess molar refraction, Gibbs free energy, and enthalpy of activation. The variation of this parameters with composition of these quantities has been used to explain the type, strength and nature of intermolecular interactions between MEK+NB binary mixture. Attained results authenticate that there are strong hydrogen-bond interactions between unlike molecules of different groups of MEK+NB mixtures and that 1:1 complexes are produced and strength of intermolecular interaction rises with rise in concentration of MEK.               KEY WORDS: Bruggeman factor, Excess inverse relaxation time, Dielectric polarization Bull. Chem. Soc. Ethiop. 2019, 33(2), 349-358.DOI: https://dx.doi.org/10.4314/bcse.v33i2.1