Experimental Excess Enthalpies Research Articles

Thermodynamics of binary mixtures containing a very strongly polar compound — Part 3: DISQUAC characterization of NMP + organic solvent mixtures

Binary mixtures of 1-methyl pyrrolidin-2-one (NMP) with alkanes, benzene, toluene, 1-alkanol, or 1-alkyne have been investigated in the framework of the DISQUAC model. The reported interaction parameters change regularly with the molecular structure of the mixture components. The model consistently describes a set of thermodynamic properties, including liquid–liquid equilibria, vapor–liquid equilibria, solid–liquid equilibria, and molar excess enthalpies. A brief comparison of the DISQUAC results and those obtained from the UNIFAC and ERAS models is presented. The experimental excess enthalpies are better represented by DISQUAC than by UNIFAC because this quantity strongly depends on molecular structure. For NMP + alkane mixtures, the liquid–liquid equilibria data are also better represented by DISQUAC, while UNIFAC more accurately describes the vapor–liquid equilibria measurements at temperatures close to the critical point. This result suggests that a mean field theory is not able to represent simultaneously, with the same set of interaction parameters, liquid–liquid and vapor–liquid equilibria at the mentioned temperatures. ERAS fails when treating mixtures with 1-alkanols. This has been attributed to the strong dipole–dipole interactions between NMP molecules, characteristic of the investigated systems. Mixture structure is briefly studied in terms of the concentration–concentration structure factor.Key words: thermodynamics, NMP, organic solvent, self-association, dipole–dipole interactions.

Excess enthalpies of five pentanol isomer + n-heptane systems measured at 303.15 K and a model describing the behavior

Experimental excess enthalpy data are reported for mixtures of n-heptane with five pentanol isomers: 1-pentanol, 2-pentanol, 3-methyl-1-butanol, 3-methyl-2-butanol and 2-methyl-2-butanol. The data were obtained using isothermal flow calorimetry and are compared with previous studies. These new data are represented by a model that combines the physical interactions of the Scatchard–Hildebrand regular solutions model with classical hydrogen bonding of the Kretschmer–Wiebe model. The model includes an adjustable parameter that reflects physical interactions and a self-association equilibrium constant that represents hydrogen bonding.

Ammonia–carbon dioxide association. Second virial cross coefficients for (ammonia+carbon dioxide) derived from gas phase excess enthalpy measurements

A flow mixing calorimeter has been used to measure the excess molar enthalpy H E m of gaseous (ammonia + carbon dioxide) at the mole fraction y=0.5, at standard atmospheric pressure, and over the temperature range 343.15 to 443.15 K. Second virial coefficients B and isothermal Joule-Thomson coefficients φ for ammonia were fitted by the Stockmayer potential, and similar properties for carbon dioxide were fitted by the Kihara potential. Cross terms B 12 and φ 12 were calculated using the arithmetic mean rule for the collision diameter and the rule ε 12=(1− k 12)( ε 11· ε 22) 1/2 for the depth of the potential well. Values of H E m were predicted using the combining rule (1− k 12)=2( σ 11 3 σ 22 3) 1/2( σ 12 3)(I 1I 2) 1/2( I 1+ I 2) −1 which gave (1− k 12)=0.94. Correction for dipole-induced dipole effects increased this value by 5 per cent to 0.98. At T=353.15 K the calculated value of H E m was 14 J· mol −1 but the experimental value was found to be only 1.5 J· mol −1 . This, and the other experimental values of H E m, could all be fitted by (1− k 12)=1.47. The difference between the calculated and experimental values of H E m was analysed in terms of a quasi-chemical association model in which the second virial cross coefficient B 12 was written B 12= B 12 ns−( RTK 12)/2. The non-specific term B 12 ns was calculated using (1− k 12)=0.98, and values of the equilibrium constant K 12 were determined from the difference between the calculated and experimental excess enthalpies. A plot of ln K 12 against reciprocal temperature yielded the enthalpy of formation Δ H 12 of the ammonia–carbon dioxide complex and this was found to be ΔH 12=−(8.6±2) kJ· mol −1 . The sum of the specific and non specific contributions is −(11.5±3) kJ· mol −1 .

Ammonia–benzene association. Second virial cross coefficients for ammonia–benzene and ammonia–cyclohexane derived from gas phase excess enthalpy measurements

A flow mixing calorimeter has been used to measure the excess molar enthalpyHmE of gaseous (ammonia + benzene) and (ammonia + cyclohexane) at the mole fraction y= 0.5, at standard atmospheric pressure, and over the temperature range 363.15 K to 493.15 K. Second virial coefficients B and isothermal Joule–Thomson coefficients φ for benzene and cyclohexane were fitted by the Kihara potential, and similar properties for ammonia were fitted by the Stockmayer potential. Cross terms B12 andφ12 were calculated using the arithmetic mean rule for collision diameters and the ruleϵ12= (1 −k12 )(ϵ11·ϵ22 )1/2 for the depth of the potential well. TheHmE measurements on (ammonia + cyclohexane) were fitted to within experimental error by the choice (1 −k12) = 0.92. At the temperatures 363.15 K and 493.15 K the values ofHmE for (ammonia + benzene) were found to be 9J · mol−1 and 5 J·mol−1 less positive than the values calculated using (1 −k12 ) = 0.92. This difference was attributed to a specific interaction between ammonia and benzene. The difference was analysed in terms of a quasi-chemical association model in which the second virial cross coefficient B12 was written B12=B12ns− (RTK12)/2. The non-specific term B12ns was calculated using (1 −k12 ) = 0.92, and values of the equilibrium constant K12 were determined from the difference between the calculated and experimental excess enthalpies. A plot oflnK12 against reciprocal temperature yielded the enthalpy of formationΔH12 of the ammonia–benzene complex and this was found to beΔH12=−(4.6 ± 2)kJ· mol−1. The sum of the specific and non specific contributions is −(8.5 ± 3)kJ·mol−1 , and this is in reasonable agreement with values of the binding energy of the ammonia–benzene van der Waals complex computed by ab initio methods.

Sulfur dioxide–benzene association. Second virial cross coefficients for sulfur dioxide–benzene and sulfur dioxide–cyclohexane derived from gas phase excess enthalpy measurements

A flow mixing calorimeter has been used to measure the excess molar enthalpy HEm of gaseous (sulfur dioxide + benzene) and (sulfur dioxide + cyclohexane) at the mole fraction y = 0.5, at standard atmospheric pressure, and over the temperature range 363.15 K to 473.15 K. The measurements were analysed in terms of the virial equation of state. The cross coefficient B12 was calculated using the arithmetic mean rule for collision diameters and the rule e12 = (1 − k12)(e11e22)1/2 for the depth of the potential well. The HEm measurements on (sulfur dioxide + cyclohexane) were fitted to within experimental error by the choice (1 − k12) = 1.01 but this value did not fit the measurements on (sulfur dioxide + benzene). The difference was attributed to a specific interaction which was analysed in terms of a quasi-chemical association model in which B12 = Bns12 − (RTK12)/2. The non-specific term Bns12 was calculated using (1 − k12) = 1.01, and values of the equilibrium constant K12 were determined from the difference between the calculated and experimental excess enthalpies. A plot of ln K12 against reciprocal temperature yielded an enthalpy of formation ΔH12 of the sulfur dioxide–benzene complex and this was found to be −(8.7 ± 2) kJ mol−1. The sum of the specific and non-specific contributions is −(13.8 ± 3) kJ mol−1. As this energy is an average taken over all orientations it should be less than the binding energy of the van der Waals complex in the minimum energy configuration computed by ab initio methods. Taleb-Bendiab et al. (A. Taleb-Bendiab, K. W. Hillig and R. L. Kuczkowski, J. Chem. Phys., 1992, 97, 2996) computed an ab initio value of −12 kJ mol−1, which is smaller than our value. Grover et al. (J. R. Grover, E. A. Walters, J. K. Newman and M. G. White, J. Am. Chem. Soc, 1985, 107, 7329) used photoionisation spectroscopy and obtained −(16.7 ± 0.8) kJ mol−1, which is in better agreement.

Analog calorimetry and UNIQUAC group contributions approaches to the miscibility of pvc with eva copolymers

The miscibility of blends of poly(vinyl-chloride) (PVC) with poly(ethylene-co-vinyl acetate) (EVA) was investigated through analog calorimetry and a group contribution procedure based on the UNIQUAC model. The group contribution parameters quantifying the pair interactions between the structural features of the above polymers were calculated from experimental excess enthalpies of a series of binary mixtures of chlorocompounds, esters and hydrocarbons. Enthalpy data were also collected for the ternary mixtures (2-chloropropane+ethyl acetate+n-heptane) and (2-chlorobutane + methyl acetate+n-heptane), chosen as possible models for the studied macromolecular mixtures. The miscibility window of the PVC-EVA blends is fairly predicted by the group contribution method. It is also acceptably predicted by the enthalpic behaviour of the first ternary set, but only when the latter is calculated with binary data. A slightly narrower miscibility range is predicted by the binary interaction model. The results of these procedures are compared and the higher reliability of the group contribution procedure is emphasized in terms of its capability to reproduce the exact structure of the macromolecules and the non-univocal choice of the model molecules involved in the analog calorimetry approach.

Excess Enthalpy Data for Seven Binary Systems at Temperatures between 50 and 140 °C

Experimental excess enthalpies for the following seven systems have been determined with the help of isothermal flow calorimetry: benzene + cyclohexane at 50, 90, and 140 °C, heptane + diethyl carbonate at 100 and 140 °C, hexane + dimethyl carbonate at 90 °C, dimethyl carbonate + heptane at 90 and 140 °C, perfluoro-2-methylpentane + benzene at 50, 90, and 140 °C, 1,2-epoxybutane + methanol at 90 and 140 °C, and 1,2-expoxybutane + 2-ethyl-1-hexanol at 90 and 140 °C. The experimental HE values have been used for the revision and extension of the group contribution method Modified UNIFAC (Dortmund). The predicted results are in good agreement with the experimental data.

Benzene–polar fluid association. An analysis of measurements of the vapour phase excess molar enthalpy of mixtures of (cyclohexane, or benzene + polar and non-polar fluids)

A differential flow mixing calorimeter has been used to measure the excess molar enthalpy HmEof gaseous mixtures containing either cyclohexane or benzene mixed with 14 other gases. These are nitrogen, methane, carbon dioxide, dimethyl ketone, diethyl ketone, ether, dioxane, chloromethane, dichloromethane, chloroform, tetrachloromethane, water, methanol, and ethanol. For the mixtures with cyclohexane vapour, the excess enthalpy of the mixtures with nitrogen, methane, and carbon dioxide is in accord with values calculated by using the usual combining rules to obtain the interaction parameter (1 −k12) in the combining rule ϵ12= (1 −k12)(ϵ11ϵ22)1/2. For (cyclohexane + polar fluids) the interaction parameter is slightly larger than expected. The experimental values of (1 −k12) obtained from the HmEmeasurements on the cyclohexane mixtures were used to calculate HmEfor mixtures in which benzene rather than cyclohexane was used. However, with the exception of the mixtures of benzene with nitrogen and methane, the excess enthalpies of all the other 12 gases are smaller than predicted, and this suggests that there is a specific interaction between benzene and the polar component. The difference between the calculated and experimental excess enthalpies was fitted by an association model which describes the unlike molecular interaction in terms of an equilibrium constant K12, and an enthalpy ΔH12of dimer formation. No obvious relationship between the electrical properties of the polar molecule and the enthalpy of association was found, but when plotted against Pitzer’s acentric factor ω the values of K12and ΔH12were discovered to be in three groups: chlorocarbons, ketones and ethers, and alcohols. In each group the values of K12and ΔH12are a linear function of ω. The HmEmeasurements on (carbon dioxide + benzene) and (dioxane + benzene) make it clear that contributions to the pair potential due to quadrupolar forces must be included if benzene–polar fluid interactions are to be understood.

Vapor−Liquid Equilibria at 453.25 K and Excess Enthalpies at 363.15 K and 413.15 K for Mixtures of Benzene, Toluene, Phenol, Benzaldehyde, and Benzyl Alcohol with Benzyl Benzoate

Isothermal P−x data at 453.25 K and excess enthalpies at 363.15 K and 413.15 K are presented for binary systems of benzyl benzoate together with benzene, toluene, phenol, benzaldehyde, and benzyl alcohol. As pointed out previously (Nienhaus, B.; Limbeck, U.; Bolts, R.; de Haan, A. B.; Niemann, S. H.; Gmehling, J. J. Chem. Eng. Data 1998, 43, 941−948), information about the real behavior of systems including these components is very important, especially for the production of phenol by toluene oxidation. In addition, these data will be used for the introduction of a new aromatic ester group (AC−COO−) into modified UNIFAC (Dortmund), which is part of the revision, extension, and further development of this group contribution method. The vapor−liquid equilibrium (VLE) data of four systems were measured using a static apparatus. The corresponding experimental excess enthalpy (HE) data were determined with the help of an isothermal flow calorimeter. For the simultaneous description of VLE and HE data the NRTL ...

Thermophysical properties of methanol+some polyethylene glycol dimethyl ether by UNIFAC and DISQUAC group-contribution models for absorption heat pumps

Several group-contribution models including three different versions of UNIFAC, GC-UNIMOD and DISQUAC are tested for their capabilities of predicting vapour–liquid equilibria, excess enthalpies and viscosities of methanol+some polyethylene glycol dimethyl ethers over a wide range of temperature. Also, the literature experimental thermophysical property database of these serial systems are collected, and new experimental excess enthalpies of methanol+pentaethylene glycol dimethyl ether at 303.15 K and densities and kinematic viscosities of methanol with monoethylene glycol dimethyl ether, triethylene glycol dimethyl ether, or pentaethylene glycol ether at 303.15 K are reported as a supplement to this experimental database. The predictions for vapour–liquid equilibria and excess enthalpies from modified UNIFAC of Gmehling et al. are the best, yielding the average relative deviation around 3% for vapour pressure and 30% for excess enthalpy. GC-UNIMOD viscosity group-contribution model gives the average relative deviation around 20% for viscosity predictions of the studied systems

Vapor−Liquid Equilibria at 413.65 K and Excess Enthalpies at 323.15, 363.15, and 413.15 K for Mixtures of Benzene, Toluene, Phenol, and Benzaldehyde

Isothermal P, x data at 413.65 K, excess enthalpies at 323.15, 363.15, and 413.15 K, and azeotropic data are presented for binary systems containing benzaldehyde, benzene, toluene, and phenol. Reliable information about the real behavior of systems including these components is very important for various chemical processes, e.g., for the production of phenol by toluene oxidation. Furthermore, these data will be used for the revision, extension, and further development of the group contribution method modified UNIFAC (Dortmund). The vapor−liquid equilibrium (VLE) data of four systems were measured using a static apparatus. In the case of the system benzaldehyde + phenol, azeotropic data were determined by distillation. For all systems, the corresponding experimental excess enthalpy (HE) data were determined with the help of an isothermal flow calorimeter. For the simultaneous description of VLE and HE data, the NRTL model was used.

Thermodynamic study of the binary mixture trichloromethane–1,2-epoxybutane

A previously reported ‘chemical’ model proposes that most strongly non-ideal binary mixtures can be described as consisting of both simple chemical species and their associates. FTIR spectroscopy indicates that the title mixture can be considered to consist mainly of CHCl 3 , C 4 H 8 O, CHCl 3 ·C 4 H 8 O, and (CHCl 3 ) 2 . Comparison between experimental excess enthalpies and those calculated using the model indicates that such a composition provides a viable description of the mixture.

Excess Enthalpy HE of Binary Mixtures Containing Alkanes, Ethanol and Ethyl‐Tert. Butyl Ether (ETBE)

AbstractThe excess enthalpies of all possible binary mixtures of n‐heptane, isooctane (2,2,4‐trimethylpentane), ETBE (ethyl‐tert. butyl ether) and ethanol have been measured at 298.15 K and 313.15 K and atmospheric pressure using a quasi‐isothermal flow calorimeter. The experimental excess enthalpies HE and published excess heat capacities CEP and excess volumes VE are used to test the applicability of the ERAS (Extended Real Associated Solution)‐model.

Vapour pressures at several temperatures and excess functions of n-butanol with 2,2-dimethylbutane and with 2,3-dimethylbutane at 298.15 K

Vapour pressures of n-butanol with 2,2-dimethylbutane and with 2,3-dimethylbutane between 283.15 and 313.15 K were measured at 5 K intervals by a static method. At 298.15 K, experimental excess enthalpies and excess volumes of n-butanol with 2,3-dimethylbutane were also measured. Vapour pressures of both alkanes have been fitted to Antoine equations. At 298.15 K and x = 0.5, H E values calculated from the Gibbs-Helmholtz equation compare favourably with the experimental ones. The ERAS model gives a qualitative description of V E and reproduces quantitatively the experimental results of G E and H E, at 298.15 K.

Endothermicity or exothermicity of water/alcohol mixtures

Excess enthalpies of mixtures of water with methanol, ethanol, 1- and 2-propanol, 1-, 2- and tert-butanol were determined by dilution calorimetry in the accessible range of mole fractions at 25-degrees-C. Ab initio RHF calculations were performed on the alcohols, their dimers and complexes with water. A full optimisation at the 6-31G level was used to obtain the properties of interest of these systems. The calculated H-bond energies are similar for all the studied alcohols. Nevertheless, a systematic stabilisation of the mixed dimers is found, especially for the secondary and tertiary alcohols. The formation of mixed H-bond chains is exothermic and does not follow the rules of the geometric mean. To a first approximation, the experimental excess enthalpies DELTAH(e) for all the systems follow the equation DELTAH(e) = C6/1X(W)6X(A) + C1/1X(W)X(A) + C1/2X(W)X(A)2 The calorimetric results may be explained by the presence in water of two kinds of H-bonds differing by about 8.3 kJ mol-1 in energy. Upon dilution in water, the alcohol is inserted in a weak chain and renders the adjacent water-bond strong. As a consequence, the dilution of an alcohol in water is always exothermic. The dilution of water in an alcohol causes stabilisation of the H-bonds but has a negative effect on the non-specific cohesion. The effect of the non-specific forces increases in the homologous series, making the dissolution of water in the alcohols endothermic starting from propanol. The stabilisation of H-bonds formed by water at high dilution in the alcohols increases according to the sequence: primary < secondary < tertiary.

Excess molar enthalpies of some examples of (a dichloroalkane+a ket-2-one) at the temperature 298.15 K

Experimental excess enthalpies H E m at the temperature 298.15 and normal atmospheric pressure were obtained for (1,1-dichloropropane + hexan-2-one or heptan-2-one), (1,3-dichloropropane + propan-2-one, or hexan-2-one or heptan-2-one), and (1,4-dichlorobutane + propan-2-one or hexan-2-one or heptan-2-one) using a Calvet microcalorimeter. All the H E m values are negative except those of { xCH 2Cl(CH 2) 2CH 2Cl + (1- x)CH 3COCH 3}, which are positive for x > 0.65. The experimental results are compared with two versions of the UNIFAC group-contribution model.

Viscosity of binary mixtures. I. mono-, di-, and tri-n-butyl and -n-octylamine with cyclohexane

Viscosities for six binary mixtures of n-butylamine, di-n-butylamine, tri-n-butylamine, n-octylamine, di-n-octylamine, and tri-n-octylamine with cyclohexane have been measured at 303.15 K with an Ubbelohde suspendedlevel viscometer. Deviations of viscosities from a rectilinear dependence on mole fraction are attributed to H-bonding and to the size of alkylamine compounds. The application of the Eyring's theory of activation energy is examined. The free volume theory of Prigogine-Flory-Patterson (PFP) and the experimental excess enthalpy have been used to estimate excess viscosity Δ ln η = (ln η/η 1 0 − x2 ln η 2 0 /η 1 0 ) and corresponding free volume, enthalpy, and entropy contributions for five binary mixtures of tri-n-alkylamine: triethyl, tripropyl, tributyl, trihexyl, and trioctylamine with cyclohexane. A comparison of experimental and theoretical excess viscosities indicates a failure of the PFP theory when two components of the mixture differ considerably in size. The size difference contribution to excess viscosity is related to (V 2 *1/2 − V 1 *1/2 ), where V 1 * and V 2 * are hard-core volumes of two components of the mixture.

Prediction of the consolute curve for CH 4CF 4 with a WCA-type perturbation theory

The consolute curve for the mixture CH 4CF 4 at zero pressure is predicted using two mixture models, one modelling both components as spheres, the other modelling CH 4 as a sphere and CF 4 as a tetrahedron. Both models are treated by a Weeks—Chandler—Andersen-type perturbation theory for mixtures. Moreover, the sphere—sphere model is considered also by a one-fluid approach for which the pure component equation of state is again obtained from perturbation theory. With unlike interaction parameters fitted to the experimental excess enthalpy h E, a reasonable prediction of the consolute curve is obtained with all three approaches. It is concluded that a simultaneous description of vapour—liquid and liquid—liquid equilibria is possible on the basis of perturbation theory except for the non-analytic behaviour in the critical region.

Use of the modified Wilson equation for description of vapor-liquid equilibrium in the system 1-nonyne-1-propanol

A modified Wilson equation is reported describing the linear dependence of the parameters λ 12 - λ 11 and λ 21 - λ 22 on temperature. The expressions for 16 partial derivatives of the minimization function have been derived in order to calculate the Wilson equation parameters from isobaric experimental data using the Newton iteration method. The modified Wilson method has been applied to T-x measurements for the 1-nonyne-l-propanol system. Experimental T-x data at pressures 100, 200, 400, 600 and 760 mm Hg are reported. Using the temperature-dependent Wilson parameters, the excess Gibbs energy is calculated at a temperature of 313.15 K and considered together with experimental excess enthalpy data.

Excess thermodynamic properties of the 2-propanol + dichloromethane system at 25°C

Densities, viscosities, enthalpies, vapor-liquid equilibria, and surface tensions were determined at 25°C for the 2-propanol+dichloromethane system. From the experimental results excess volumes, viscosities, enthalpies, Gibbs energies, and excess surface tensions were calculated. An attempt has been made to explain the observed deviations from ideal behavior on the basis of intermolecular interactions.