Heat Of Mixing Data Research Articles

Excess enthalpy of mixing of mineral solid solutions derived from density-functional calculations

Calculations using the density-functional theory (DFT) in combination with the single defect method were carried out to determine the heat of mixing behaviour of mineral solid solution phases. The accuracy of this method was tested on the halite–sylvite (NaCl–KCl) binary, pyrope–grossular garnets (Mg3Al2Si3O12–Ca3Al2Si3O12), MgO–CaO (halite structure) binary, and on Al/Si ordered alkali feldspars (NaAlSi3O8–KAlSi3O8); as members for coupled substitutions, the diopside–jadeite pyroxenes (CaMgSi2O6–NaAlSi2O6) and diopside–CaTs pyroxenes (CaMgSi2O6–CaAlAlSiO6) were chosen for testing and, as an application, the heat of mixing of the tremolite–glaucophane amphiboles (Ca2Mg5Si8O22(OH)2–Na2Mg3Al2Si8O22(OH)2) was computed. Six of these binaries were selected because of their experimentally well-known thermodynamic mixing behaviours. The comparison of the calculated heat of mixing data with calorimetric data showed good agreement for halite–sylvite, pyrope–grossular, and diopside–jadeite binaries and small differences for the Al/Si ordered alkali feldspar solid solution. In the case of the diopside–CaTs binary, the situation is more complex because CaTs is an endmember with disordered cation distributions. Good agreement with the experimental data could be, however, achieved assuming a reasonable disordered state. The calculated data for the Al/Si ordered alkali feldspars were applied to phase equilibrium calculations, i.e. calculating the Al/Si ordered alkali feldspar solvus. This solvus was then compared to the experimentally determined solvus finding good agreement. The solvus of the MgO–CaO binary was also constructed from DFT-based data and compared to the experimentally determined solvus, and the two were also in good agreement. Another application was the determination of the solvus in tremolite–glaucophane amphiboles (Ca2Mg5Si8O22(OH)2–Na2Mg3Al2Si8O22(OH)2). It was compared to solvi based on coexisting amphiboles found in eclogites and phase equilibrium experiments.

\u03b1-Tocopherol/AOT/alkane/water system

In this paper the calorimetric studies on α-tocopherol/AOT/alkane/water systems are presented. Structural representations of surfactant AOT (a) and α-tocopherol (b) are shown below. α-Tocopherol (antioxidant) is a form of vitamin E that is preferentially absorbed and accumulated in humans. AOT is an anionic type of surfactant. Its molecule contains two non-polar hydrocarbon tails connected to the polar head. The paper contains new experimental data of heat of mixing (Q) for heterogeneous system α-tocopherol/AOT/n-alkane with and without water measured at 309.2 K. The heat of mixing for AOT (sodium bis (2-ethylhexyl) sulfosuccinate) and α-tocopherol solutions in n-alkane (heptane, decane, hexadecane) as the function of surfactant concentration and parameter R given as the water to surfactant molar ratio R = [H2O]/[AOT] was measured. It can be seen that the Q values grow significantly with temperature increase which indicates on entropic origin of this process. The significant influence of surfactant concentration on Q values was noticed. Unexpectedly, the water presence in the reverse micelles did not have any noticeable influence on the heat of mixing values measured at 309.2 K. There was not noticed the significant hydrocarbon chain length influence on the thermal effect of mixing α-tocopherol and AOT solutions. The thermodynamic parameters: the binding constant (K) and the molar enthalpy of transition (ΔHtr0) of α-tocopherol between solvent and AOT reverse micelles, were calculated from the heat of mixing data as a function of surfactant concentration using the nonlinear regression method. The new calorimetric data measured at 309.2 K were compared to results obtained earlier at 298.2 K, as well as have been discussed in the context of the hydrocarbon chain length and water presence influence on α-tocopherol solubility in AOT reverse micelles. Generally in all investigated systems have been not found a significant influence of water concentration in AOT reverse micelles on α-tocopherol molecules distribution between organic phase and micellar phases. The exothermic values of α-tocopherol molecules transition from organic to micellar phase indicate on spontaneous motion of α-tocopherol towards AOT aggregates. For the systems with n-heptane and n-decane as a solvent, the (ΔHtr0) values are between −51 and −52 kJ mol−1 whereas for n-hexadecane around −43 kJ mol−1. Such tendency can be explained through hydrocarbon chains orientation effect existing in hexadecane which probably is responsible for a α-tocopherol molecules freedom motion limitation. Moreover, the solubility of the α-tocopherol in AOT reverse micelles measured with calorimetric technique has been compared to the literature data obtained, respectively, with UV spectrophotometer for reverse micelles, and for phospholipids bilayer by other techniques. Finally, transferring of α-tocopherol from solvent to AOT reverse micelles, intermolecular interactions between α-tocopherol and AOT micelles were discussed, and a privileged place of α-tocopherol in the palisade layer of AOT reverse micelle has been deduced.

Heat of mixing and liquid–liquid-equilibrium of water + polypropylene glycol (PPG) with different molecular weights and water + propylene glycol dimethyl ether

Polypropylene glycols (PPG) are widely used in a large variety of different fields, e.g. polyurethane formulations, rheology, surfactant, wetting agent, dispersant in leather finishing, pharmacy, and tissue engineering, where polymers with different molecular weights are employed. Therefore, the phase behavior in aqueous solutions plays an important role. For thermodynamic models able to describe the phase behavior, especially the liquid–liquid equilibria (LLE), the occurring association phenomena are very significant. The purpose of this work is the analysis of detailed association models taking into account self-association of water, self-association of polymer and cross-associations. Starting from a general association scheme of hydrogen bonds two models (model 2 and model 3) were derived and investigated with regard to the performance of correlating LLE data as well heat of mixing data, simultaneously. In model 2 identical associations between water to ether-oxygen and water to hydroxyl end-group are considered and in model 3 identical associations between water to hydroxyl end-group and hydroxyl end-group to water are established. The extrapolation power related to phase equilibria or heat of mixing data not involved in the parameter fitting procedure of the two models were analyzed carefully. Finally, the prediction power were studied by application of the adjusted parameters to a slightly different system, namely the LLE of 1,2-dimethoxypropane and water mixtures. It turns out, that the model can predict the LLE of 1,2-dimethoxypropane and water in fair agreement with new data measured in this work.

Thermodynamic assessment of LaBr 3 unary and LiBr–LaBr 3 binary system

Experimental data for the system LiBr–LaBr 3 was subjected to a critical thermodynamic assessment using the CALPHAD approach. To reach a self-consistent thermodynamic description for the constituent phases in the system, it appeared to be necessary to reassess the experimental heat capacity data of the stoichiometric compound LaBr 3. A two-sublattice ionic solution model for the liquid, denoted as ( Li + ) P : (Br −,LaBr 6 −3,LaBr 3) Q, was employed to represent the phase diagram and heat of mixing data. Our assessment resulted in a Gibbs energy formation covering the temperature range between 300 and 1100 K. To give our assessment of LiBr–LaBr 3 a wider application to higher-order alkali–bormide–LaBr 3 systems, additional assessments of the binaries NaBr–LaBr 3 and KBr–LaBr 3 were carried out. By modelling the liquid phase with the two-sublattice ionic solution model, a thermodynamic description, compatible in the three binary systems, was obtained for these systems covering the temperature range between 300 and 1100 K.

Vapor Pressure, Vapor−Liquid Equilibrium, and Excess Enthalpy Data for Compounds and Binary Subsystems of the Chlorohydrin Process for Propylene Oxide Production

Vapor−liquid equilibrium (VLE), excess enthalpy (HE), and vapor pressure (Pis) data for eight binary systems containing cis-1-chloropropene, trans-1-chloropropene, 1,2-dichloropropane, 1,2-propanediol, 1,2-propylene glycol diacetate, propylene oxide, and water are presented in a temperature range from 276 to 368 K. The VLE and vapor pressure data were obtained by means of a computer-controlled static apparatus, and the heat of mixing data were measured using an isothermal flow calorimeter. Temperature-dependent NRTL interaction parameters were regressed by a simultaneous correlation of the experimental VLE and HE data. These parameters are required for a proper simulation of the different separation steps in the chlorohydrin process for the production of propylene oxide.

Vapor−Liquid Equilibria and Excess Enthalpy Data for the Binary Systems 2-Methyltetrahydrofuran with 2,2,4-Trimethylpentane (Isooctane), Ethanol, Toluene, Cyclohexane, and Methylcyclohexane

Isothermal P−x data (vapor−liquid equilibrium (VLE)) and excess enthalpy data (HE) for the five binary systems 2-methyltetrahydrofuran with 2,2,4-trimethylpentane (isooctane), ethanol, toluene, cyclohexane, and methylcyclohexane are presented. The VLE data were obtained experimentally, in a computer-controlled static apparatus, and the heat of mixing data were measured in an isothermal flow calorimeter. Also presented are linear temperature-dependent interaction parameters for the NRTL and UNIQUAC models which were fitted simultaneously to the experimental VLE and HE data. These data and the correlation parameters should be useful for predicting properties, e.g., volatility (Reid vapor pressure (RVP), etc.) of blends of alternative automotive fuels which contain ethanol, 2-methyltetrahydrofuran, and light hydrocarbons.

Calculations of multicomponent phase equilibria with a new group contribution method

The present paper introduces a new group contribution model (GTASQUAC) for calculations of multicomponent phase equilibria of organic compounds. The method is based on the concept of quasi-chemical equilibrium using the TASQUAC formalism for determination of contact numbers in the liquid mixture. GTASQUAC has two adjustable parameters for describing the temperature dependent interchange energy and was applied to the description of VLE and heat of mixing data. The results are compared to those of other '‘local composition models'' like UNIFAC, ASOG or mod. UNIFAC using two, four or six adjustable parameters, respectively. GTASQUAC can also be applied for true prediction of thermodynamic excess properties. A comparison with simulated heat of mixing data shows good agreement. Moreover, the method provides a high flexibility.

The phase behavior of tetramethyl bisphenol-A polyarylate/aliphatic polyester blends

The phase behavior of blends of tetramethyl bisphenol-A polyarylate (TMPAr) with various linear aliphatic polyesters characterized by the ratio of aliphatic carbons to ester groups in the repeating unit, CH2/COO = 3 ∼ 9, was examined by differential scanning calorimetry and dynamic mechanical analysis. TMPAr/aliphatic polyester blends prepared by solvent casting were found to be miscible when the CH2/COO ratio of aliphatic polyesters was larger than 4 and up to 9. The thermodynamic interaction parameter, B for the miscible blends was determined by the analysis of the depression of the melting point of polyester using the Hoffman-Weeks method. From the analysis of the heat of mixing data using a binary interaction model, it was concluded that strong unfavorable intramolecular interaction exists between the CH2 and COO units in aliphatic polyesters and that four substituted methyl groups produces more favorable effects on the miscibility TMPAr with aliphatic polyesters. © 1998 John Wiley & Sons, Inc. J Polym Sci 36: 201–212, 1998

Thermodynamics of the System MgCl2–NaCl–H2O to 573 K: New Measurements of Heat of Mixing and Heat of Dilution

Heats of mixing of NaCl(aq) with MgCl2(aq) at 373.15, 423.15, 473.15, 523.15, and 573.15 K for ionic strengths of 0.5 to 3.8 mol·kg−1, and heats of dilution of MgCl2(aq) at 523.15 and 573.15 K for ionic strengths of 0.3 to 4.6 mol·kg−1, have been measured at 20.5 MPa. These experimental data are combined with published heat of mixing data at 298 and 373 K to provide a comprehensive Pitzer ion-interaction treatment for the thermodynamic properties of the \({\text{NaCl}}{\kern 1pt} {\kern 1pt} - {\text{MgCl}}_{\text{2}} {\kern 1pt} ---{\kern 1pt} {\text{H}}_{\text{2}} {\text{O}}\) system to 573 K. The treatment includes a general equation valid to 523 K, incorporating the published equations for NaCl(aq) and MgCl2(aq), and equations for MgCl2(aq) and the mixed system valid at 573 K.

Excess Molar Enthalpies for the Propan-2-OL + Methylacetate + Dichloromethane System at 298.15 K

Abstract Heat of mixing data for the ternary liquid system propan-2-01 + methylacetate + dichloromethane at 298.15 K are reported along with data for the constituent binary systems. Different expressions published in the literature were used to calculate excess enthalpies from the corresponding binary data. The empirical correlation of Tanaka and Tamura gives the best prediction for this system. The UNIFAC group contribution is applied to predict enthalpies, in this case only for binary systems and compared with experimental data.

Thermodynamic properties of transition metals in aqueous solution: 3. The heats of mixing aqueous solutions of CdCl2, NiCl2 and ZnCl2 with NaCl at varying ionic strength at 25°C

Many fields, including oil recovery, require aqueous electrolyte data under relevant conditions. The heat of dilution of aqueous solutions of ZnCl[sub 2] and the heats of mixing [Delta]H[sub m] of aqueous solutions of CdCl[sub 2], NiCl[sub 2], and ZnCl[sub 2] with NaCl solutions were measured at 25[degrees]C. The heats of mixing were made at constant ionic strengths of 0.5, 1.0, and 3.0 molal. The excess enthalpy equations of Pitzer were then fitted to the resulting heats of dilution and heats of mixing data. The resulting parameters are the temperature derivatives of the activity coefficient mixing parameters in the Pitzer system. 38 refs., 5 tabs.

Thermodynamic properties of transition metals in aqueous solution. 2. The enthalpies of mixing of aqueous solutions of CoCl2, CuCl2, and MnCl2 with NaCl at varying ionic strength at 25�C

The heat of dilution of aqueous solutions of ZnCl2 and the heats of mixing ΔHm of aqueous solutions of CdCl2, NiCl2, and ZnCl2 with NaCl solutions were measured at 25°C. The heats of mixing were made at constant ionic strengths of 0.5, 1.0, and 3.0 molal. The excess enthalpy equations of Pitzer were then fitted to the resulting heats of dilution and heats of mixing data. The resulting parameters are the temperature derivatives of the activity coefficient mixing parameters in the Pitzer system.

Enthalpy of dissociation of water at 325�C and LogK, ?H, ?S, and ?C p values for the formation of NaOH(aq) from 250 to 325�C

The aqueous reactions H++OH−=H2O at 325°C and Na++OH−= NaOH(aq) at 250–325°C, were studied using a flow calorimeter. Heats of mixing of aqueous NaOH and HCl solutions were measured at 325°C. The enthalpy of water formation (ΔH=95.9 kJ-mol−1, valid at 12.4 MPa and infinite dilution) was obtained at this temperature from the heat of mixing data but differs significantly from that calculated from the Marshall-Franck equation. This calorimetric ΔH at 325°C was used in combination with literaturelog K and ΔH values at lower temperatures to derive equations representinglog K, ΔH, ΔS, and ΔCp for the formation of water from 250 to 325°C. Heats of dilution of aqueous NaOH solutions were measured at 250, 275, 300, and 325°C. Log K, ΔH, and ΔS for the formation of NaOH(aq) were determined at these temperatures from the fits of the calculated and measured heats while ΔCp values were calculated from the variation of ΔH with temperature. No previous experimental results have been reported for the formation of NaOH(aq). The isocoulombic reaction principle is tested using thelog K values obtained in this study. The plot oflog K vs. 1/T for the isocoulombic reaction NaOH(aq) +H+=H2O+Na+ is approximately linear.

Calorimetric determination of thermodynamic quantities for chemical reactions in the system CO2?NaOH?H2O from 225 to 325�C

The phase equilibrium CO2(g)=CO2(aq) and the aqueous reactions CO32−+H+=HCO3−, HCO3−+H+=CO2(aq)+H2O, and Na++CO32−=NaCO3− were studied from 225 to 325°C using a flow calorimetric technique. Heats of mixing of gaseous CO2 with liquid H2O and with aqueous NaOH solutions were measured at these temperatures. Log K, ΔH, ΔS, and ΔCp values were determined for these reactions from the heat of mixing data. Equations for these thermodynamic quantities valid at infinite dilution (I=0) and 12.4 MPa are given as a function of temperature from 225 to 325°C. The log K and ΔH values agree well with literature values at these temperatures for the first and third reactions, but not for the second reaction. No previous results have been reported for the fourth reaction at high temperatures. The isocoulombic reaction principle is tested using the log K values determined in this study. This principle is found to be valid for the reactions where each charge on one side of the equation is balanced on the other side by a charge of the same sign and magnitude, but not for the reaction where two single negative charges (HCO3− and OH−) are balanced by one double negative charge (CO32−).

Thermodynamics of electrolyte mixtures. Activity and osmotic coefficients consistent with the higher-order limiting law for symmetrical mixing

The parameters for symmetrical mixing of ions of the same sign in the virial-coefficient (Pitzer) system are evaluated from literature data for 25°C in a manner consistent with the higher-order limiting law of Friedman. Twenty-four systems involve cation mixing with a common anion and fourteen involve anion mixing with a common cation. Heat of mixing data were similarly treated in a recent publication; the results give the temperature coefficients of some of these same parameters. The combined results yield the mixing parameters as functions of temperature on a basis both self-consistent and in accord with the limiting law. The results also yield, for a few systems without a common ion, predicted values in good agreement with experimental data.

Polymer blends, 3. Preparation and evaluation of the blends of shellac with polyamideimide from rosin

AbstractPolymer blends were prepared from shellac and polyamideimide. The polyamideimide was synthesized by reacting rosin maleic anhydride Diels‐Alder adduct with 4,4′‐diamino diphenylmethane. The compatibility of these blends was studied by solubility parameter, heat of mixing data, solution viscosity, and differential scanning calorimetry. It was found that the composition of 40 : 60, shellac : polyamideimide produces a compatible blend. The thermal behaviour of the blends was investigated.

Polymer blends—4: Blends of resole with polyamideimide synthesized from rosin

Polymer blends were prepared by the solution blending method from a polyamideimide synthesized from rosin and resole resin. The polyamideimide was synthesized by reacting rosin maleic anhydride Diels-Alder adduct with 4,4′-diaminodiphenyl methane. The compatibility of these blends was studied by solubility parameter, heat of mixing data, solution viscosity and differential scanning calorimetry. It was found that the composition of resole/polyamideimide at and near 40/60 would form a compatible blend. Thermal behaviour of the blends has been investigated. The insolubility of the blends on heating to 150°C and above is explained on the basis of crosslinking.

Polymer blends—2: Compatibility and thermal behaviour of blends of novolac and polyamideimide from rosin

Polymer blends were prepared from a polyamideimide synthesized from rosin with novolac. The polyamideimide was synthesized by reacting rosin maleic anhydride Diels-Alder adduct with 4,4′-diaminodiphenylmethane. The compatibility of these blends was studied by solubility parameter, heat of mixing data, solution viscosity, and T g. It was found that there is a compatibility window ranging in composition from 40:60 to 60:40 novolac-polyamideimide. Thermal behaviour of the blends was also investigated by TGA, DTG and DSC. The insolubility of the blends on heating to 200° and above was explained on the basis of crosslinking.

Interactions in polymer blends‐relationship between thermodynamic and scattering measurements

AbstractMethods of preparation and of determining miscibility limits for partially miscible binary polymer blends are described. An equation‐of‐state, theoretical description of this behavior is introduced and the terms describing interactions within the system discussed, Values of these interaction terms are obtained by fitting the models to measured cloud point curves, heats of mixing data, etc. The use of neutron scattering experiments to obtain molecular conformation and interaction parameters is described and a comparison made with values extracted from the thermodynamic measurements.

An improved group method for hydrocarbon-hydrocarbon systems arising from a comparative study of asog and unifac

A comparison of the formalism of ASOG, in the version of Kojima and Tochigi, and of UNIFAC shows the total formal equivalence of both empirical group methods for calculating activity coefficients in mixtures. The most advantageous features of each method are taken into account in the formulation of an improved method for hydrocarbon-hydrocarbon systems. Parameters for CH 2/ArCH, CH 2/CyCH, CH 2CH, ArCH/CyCH, ArCH/CH and CyCH/CH are evaluated from total pressure- liquid composition and heats of mixing data using the SIGMA procedure. The results obtained with the three empirical group methods are compared with experimental data. The ability to predict activity coefficients at infinite dilution is discussed.