HmE Values Research Articles

Excess molar enthalpies of binary mixtures of formamide with butanol at 298.15 K: Application of Prigogine–Flory–Patterson theory and Treszczanowicz–Benson association model

Excess molar enthalpies (HmE) of formamide (1)+1-butanol or 2-methyl-1-propanol or 2-methyl-2-propanol (2) mixtures have been measured at 298.15K over the entire composition range using flow micro calorimeter. The excess enthalpy data along with previously published excess volumes data (VmE) (M. Rani, S. Maken, J. Ind. Eng. Chem. 18 (2012) 1694) have been utilised to study the thermodynamics of molecular interactions in terms of Prigogine–Flory–Patterson theory and Treszczanowicz–Benson association model with a Flory contribution term. The Treszczanowicz–Benson model was developed for alkane+alkanol systems considering Mecke–Kempter type of association in alkanol. In this paper the Treszczanowicz–Benson association model was applied, for the first time, to binary mixtures containing both components associated (butanol and formamide) through hydrogen bonding. In both the cases, when either of formamide or butanol was assumed to be associated, the calculated HmE and VmE values compared reasonably well with the corresponding experimental data, but the agreement is not very impressive for excess enthalpy in formamide+2-methyl-2-propanol mixtures. Extent of inter-molecular H-bonding in formamide and butanols in their binary mixtures was also reflected in their molar enthalpy of association of H-bonding ΔhH0.

Excess molar enthalpies and excess molar volumes of formamide + 1-propanol or 2-propanol and thermodynamic modeling by Prigogine–Flory–Patterson theory and Treszczanowicz–Benson association model

Excess molar enthalpies (HmE) at 298.15K and 308.15K and excess molar volumes (VmE) at 308.15K for formamide (1)+1-propanol or 2-propanol (2) mixtures have been measured over the entire composition range. The excess enthalpies and excess volumes data have been utilized to study the thermodynamics of molecular interactions in terms of Prigogine–Flory–Patterson theory and Treszczanowicz–Benson association model with a Flory contribution term. In this paper, this Treszczanowicz–Benson association model was applied, for the first time, to binary mixtures containing both components associated (propanol and formamide) through hydrogen bonding. In both the cases, when either of formamide or propanol was assumed to be associated, the calculated HmE and VmE values compared well with corresponding experimental data. Extent of inter-molecular H-bonding in formamide and propanol in their binary mixtures was also reflected in their molar enthalpy of association of H-bonding ΔhH0 and association constant KH.

Thermodynamics of ketone + amine mixtures. Part IX. Excess molar enthalpies at 298.15 K for dipropylamine, or dibutylamine + 2-alkanone systems and modeling of linear or aromatic amine + 2-alkanone mixtures in terms of DISQUAC and ERAS

Excess molar enthalpies, HmE, at 298.15K and atmospheric pressure, have been measured, over the entire mole fraction range, by means of a Tian–Calvet microcalorimeter, for the systems: dipropylamine (DPA), or dibutylamine (DBA)+2-propanone,+2-butanone,+2-pentanone, or+2-heptanone. These data, together with those available in the literature for aniline or N-methylaniline+2-alkanone systems, or for 2-alkanone, or amine+heptane mixtures have been used to determine ΔHNCO, the enthalpy of the amine–ketone interactions. For solutions with a given aromatic amine, ΔHNCO values are large and decrease with the increasing of the ketone size. The corresponding HmE values are large and negative. Mixtures with DPA or DBA are characterized by much weaker interactions between unlike molecules and ΔHNCO is nearly independent of the ketone. The HmE values are positive and decrease when the chain length of the 2-alkanone is increased, which has been ascribed to a decreasing positive contribution to HmE from the disruption of the ketone–ketone interactions upon mixing. Excess molar internal energies at constant volume, UVmE, have been obtained from HmE data using our previous volumetric measurements for the studied mixtures. Similar trends that for HmE are observed. Differences between UVmE and HmE are about 15% for DPA or DBA solutions and are ranged between 35% and 45% for mixtures with aromatic amines. The excess molar volume, VmE, changes in line with HmE and both magnitudes are usually of the same sign, which reveals that the main contribution to the former is the interactional one. In systems including linear secondary amines, structural effects increase with the chain length of the ketone. Amine+2-alkanone systems have been also investigated in terms of the DISQUAC, UNIFAC and ERAS models. DISQUAC and ERAS interaction parameters are reported. As in other many applications, the quasichemical interchange coefficients for l=1 (Gibbs energy), 3 (heat capacity) remain constant along each homologous series considered. DISQUAC improves meaningfully ERAS results on HmE, while UNIFAC results are slightly better. This suggests that physical interactions are more relevant than those related to association/solvation effects.

Thermodynamics of alkanone + aromatic hydrocarbon mixtures

Linear alkanone or cyclohexanone+aromatic hydrocarbon mixtures have been studied using DISQUAC and the Kirkwood–Buff formalism. The aromatic compounds considered are: benzene, toluene, 1,4-dimethylbenzene, 1,2,4-trimethylbenzene and ethylbenzene. Vapour–liquid equilibria (VLE), molar excess Gibbs energies, GmE, molar excess enthalpies, HmE, and isobaric molar excess heat capacities, CpmE, of the binary systems studied are well represented by DISQUAC. There is a good agreement between experimental HmE values of related ternary mixtures, and DISQUAC predictions obtained by means of binary interaction parameters only DISQUAC improves very meaningfully UNIFAC results on HmE, CpmE, properties which are closely related to the molecular structure of the mixture components. The enthalpy (HintCO-S) of the ketone–aromatic hydrocarbon interactions has been evaluated. These interactions become weaker when the alkanone size increases in mixtures with a given aromatic hydrocarbon, or when the aliphatic surface of the alkylbenzene is increased in systems with a given ketone. Steric effects are more relevant in 1,4-dimethylbenzene mixtures than in those with ethylbenzene. The application of the Kirkwood–Buff formalism to mixtures including toluene or ethylbenzene shows that orientational effects, related to ketone–ketone interactions, exist in solutions with the shorter 2-alkanones. Such effects are weakened when the chain length of the 2-alkanone increases. The opposite behaviour is observed when increasing the aliphatic surface of the alkylbenzene in systems with a given 2-alkanone. The cyclohexanone+benzene mixture shows a structure close to random mixing.

Experimental study on the calorimetric data of cyclohexanol with alkanols (C1–C4) and correlation with the Wilson, NRTL and UNIQUAC models at T = 300 K

Excess molar enthalpies, HmE for the binary mixtures of cyclohexanol with methanol, ethanol, propan-1-ol, propan-2-ol, butan-1-ol and butan-2-ol have been calculated from calorimetric data at T=300K and atmospheric pressure. Calorimetric measurements were performed with a Parr 1455 solution calorimeter. All the binary mixtures show endothermic behaviour over the entire range of compositions. The HmE values become more positive with increasing the steric factors. With increasing the chain length of the alkanols, the HmE values become less positive. The maximum HmE values were observed about 0.4–0.6 mole fraction of cyclohexanol. The results were interpreted on the basis of the polarity, size and shape of alkanols. The experimental data were correlated by the Redlich–Kister equation and three thermodynamics models (Wilson, NRTL and UNIQUAC).

Excess molar enthalpies for mixtures of supercritical CO2 and ethyl acetate and their role in supercritical fluid applications

Mixtures of supercritical CO2 and ethyl acetate (EA) are very often involved in supercritical fluid applications and their thermodynamic properties are required to understand and design these processes. Excess molar enthalpies (HmE) for (CO2+EA) mixtures were measured using an isothermal high-pressure flow calorimeter under conditions of temperature and pressure typically used in supercritical processes: pressures from (9.00 to 18.00)MPa and temperatures from (313.15 to 333.15)K. Mixtures showed exothermic mixing; excess molar enthalpies exhibited a minimum in the CO2-rich region. The effects of pressure and temperature on the excess molar enthalpy of (CO2+EA) are large. The most exothermic HmE values were observed for a coincident CO2 mole fraction value of 0.737 at T/K=(323.15 and 333.15) and P/MPa=9.00: (−4489 and −4407)J·mol−1, respectively. Two-phase splitting was observed in the CO2-rich region at T/K=333.15 and P/MPa=9.00; in this region HmE varies linearly with CO2 mole fraction. For a given mole fraction and temperature, mixtures become more exothermic as pressure decreases. These trends were analyzed in terms of molecular interactions, phase equilibria, density and critical parameters previously reported for (CO2+EA). Excess molar enthalpies here reported were correlated using the Soave–Redlich–Kwong and Peng–Robinson equations of state, and the classical mixing rule with two binary interaction parameters. The influence of the thermal effects on the phase behavior of (CO2+EA) mixtures formed in supercritical antisolvent precipitation experiments was discussed.

Thermodynamics of Ketone + Amine Mixtures. Part VIII. Molar Excess Enthalpies at 298.15 K for n-Alkanone + Aniline or + N-Methylaniline Systems

Molar excess enthalpies, HmE, at 298.15 K and atmospheric pressure have been determined over the entire mole fraction range, using a Tian-Calvet microcalorimeter, for the systems: propanone, 2-butanone, 2-pentanone, or 2-heptanone + aniline or + N-methylaniline. The negative HmE values obtained for all of the mixtures reveal that interactions between unlike molecules are prevalent. Aniline solutions show more negative HmE values due to stronger amine-ketone interactions compared to those in N-methylaniline solutions. In addition, HmE increases with the size of the alkanone, which may be interpreted in terms of a weakening of interactions between unlike molecules. HmE varies somewhat differently in N-methylaniline solutions, probably due to the positive contribution to HmE is here more important. Molar excess internal energies at constant volume, UVmE, have been determined from the present HmE data using our previous measurements on molar excess volumes, compressibilities, and isothermal expansion coeffici...

Application of the extended real associated solution (ERAS) theory to excess molar enthalpies of benzaldehyde + 1-alkanols (C1 to C5) at T = 298.15 K

This paper reports excess molar enthalpies, HmE, for the binary mixtures of {1-alkanols (2), namely, {methanol, ethanol, 1-propanol, 1-butanol, and 1-pentanol} with benzaldehyde (1)} at T=298.15K at ambient pressure over a whole range of mole fraction. The sign of HmE for all systems are positive and the magnitude of HmE values with increasing of chain length, increase. The Redlich–Kister polynomial equation was used to correlate HmE. The excess partial molar enthalpies of benzaldehyde, Hm,1E, excess partial molar enthalpies of 1-alkanols (C1 to C5), Hm,2E, and excess partial molar enthalpies at infinite dilution, Hm,iE,0, are calculated according to experimental excess molar enthalpies and Redlich–Kister polynomial equation. The extracted date were used to evaluated the so-called intermolecular interaction functions ∂Hm,iE/∂xi and ∂Hm,iE/∂xj in terms of enthalpy. The ERAS, Wilson and NRTL models have been applied for describing the HmE.

Excess molar enthalpy for methanol, ethanol, 1-propanol, 1-butanol + n-butylamine mixtures at 288.15 and 308.15 K at atmospheric pressure

Experimental data of excess molar enthalpy (HmE) of binary liquid mixtures containing (methanol or ethanol or 1-propanol, or 1-butanol) + n-butylamine mixtures have been determined as a function of composition at temperatures 288.15 and 308.15 K, at atmospheric pressure, using a modified 1455 PARR mixture calorimeter. The HmE values are negative for both systems over the whole composition range. The applicability of the ERAS Model to correlate HmE of mixtures studied is tested, and the agreement between experimental and theoretical results is satisfactory. The model results are discussed in terms of the cross-association interactions with temperature variation as well as in terms of the variation of the carbon chain in the alcohols presents in the mixtures.

Excess molar enthalpies for mixtures of supercritical carbon dioxide and limonene

Excess molar enthalpies (HmE) for mixtures of supercritical CO2 and limonene were measured at 308.15, 313.15 and 323.15K and 7.64 and 10.00MPa using an isothermal high-pressure flow calorimeter. The effects of pressure and temperature on the excess molar enthalpy of [CO2(x)+limonene(1−x)] are large. Mixtures at 308.15K and 10.00MPa show slightly endothermic mixing in the limonene-rich region and moderately exothermic mixing for x>0.5. Mixtures at the other conditions of temperature and pressure studied show exothermic mixing, excess molar enthalpies exhibit a minimum in the CO2-rich region. The lowest HmE values (≈−4500Jmol−1) are observed for mixtures at 313.15K and 7.64MPa. On the other hand, HmE at 7.64MPa and 308.15, 313.15 and 323.15K varies linearly with CO2 mole fraction in the two-phase region where a gaseous and a liquid mixture of fixed composition, for a given condition of temperature and pressure, are in equilibrium. These data are examined together with phase equilibria and critical parameters previously reported for CO2+limonene. Excess molar enthalpies are simultaneously correlated using the Peng–Robinson equation of state and the classical mixing rule with one binary interaction parameter.

Volumetric properties of binary mixtures of N, N- dimethylformamide with water or water- d2 at temperatures from 277.13 K to 318.15 K

Densities of binary mixtures of N, N -dimethylformamide (DMF) with water (H2 O) or water- d2(D 2O) were measured at the temperatures from 277.13 K to 318.15 K by means of a vibrating-tube densimeter. The excess molar volumes VmE, calculated from the density data, are negative for the (H 2O + DMF) and (D 2O + DMF) systems over the entire range of composition and temperature. TheVmE curves exhibit a minimum at x (H 2O or D 2O) ∼= 0.6. At each temperature this minimum is slightly deeper for the (D 2O + DMF) than for the corresponding (H 2O + DMF). The difference between D2 O and H 2O systems becomes smaller when the temperature increases. TheVmE results were correlated using a modified Redlich–Kister expansion. The partial molar volume of DMF plotted against x (H 2O or D 2O) goes through a sharp minimum in the water-rich region around x (H 2O or D 2O) ∼= 0.92. This minimum is more pronounced the lower the temperature and is deeper in D 2O than in H 2O at each temperature. Again, the difference becomes smaller as the temperature increases. The excess expansion factor αE plotted against x (H 2O or D 2O) exhibit a maximum in the water rich region of the mole fraction scale. At each temperature, this maximum is higher for the (D 2O + DMF) than for the corresponding (H2 O + DMF). At T= 277.134 K, the maximum is located at x (H2 O or D 2O) ∼= 0.8 and is shifting slightly towards lower x (H2 O or D 2O) with increasing temperature. At its maximum, αE can be even more than 25 per cent of total value of the cubic expansion coefficient α in the (H 2O + DMF) and (D 2O + DMF). The experimental data ofVmE and the literature data ofHmE were used to test the applicability of the extended real association solution (ERAS) model for describing the both excess properties. For all the mixtures theVmE and HmE values, calculated by ERAS, are of the same sign as the experimental values. Small deviations in the symmetry of the predicted curves are, however, observed.

Application of different group contribution models and empirical methods to excess enthalpies of ternary mixtures

Studies were previously made of the excess molar enthalpies, HmE, at 298.15 K and normal atmospheric pressure of the ternary mixtures (ethyl propanoate or 3-pentanone) + (n-hexane) + (n-decane, n-dodecane or n-tetradecane) and (1-propanol) + (3-pentanone) + (n-hexane, n-heptane, n-octane, 1-hexanol or 1-heptanol). In the present work, experimental values of HmE were correlated through use of the Cibulka and Nagata equations, and a new correlation equation is proposed. Experimental data were compared with the predictions of the UNIFAC I (version of Tassios), UNIFAC II (version of Larsen) and Nitta-Chao group contribution models. HmE values were used to test several empirical predictive methods, both symmetric (Kohler, Jacob-Fitzner, Colinet and Knobeloch-Schwartz), and asymmetric (Tsao-Smith, Toop, Scatchard, Hillert and Mathieson-Tynne).

The excess enthalpies of (carbon dioxide + n-hexane + toluene) at 573.15 K and 7.50 and 12.50 MPa

The excess molar enthalpies HmE{x1CO2 + x2C6H14+ (1 − x1 − x2)C6H5CH3} were measured at 573.15 K and 7.50 and 12.50 MPa with an isothermal flow calorimeter. All mixings were endothermic with maximum HmE values of 7120 J · mol−1 and 7.50 MPa and 4300 J · mol−1 at 12.50 MPa. The relation between the ternary HmEs and the HmEs for the three related binary mixtures is discussed. Toop's equation was found to provide accurate predictions of ternary HmEs. Correlations methods are also discussed. Results are compared with those previously obtained for the same mixture at lower temperatures.

Excess enthalpies of {x(CH3)2CO+(1–x)C6H14} in the supercritical region

Excess molar enthalpies HmE of acetone–n-hexane mixtures have been measured at the critical temperature 493.2 K of the x= 0.5 mixture, and at the supercritical temperatures 510.2, 523.2 and 548.2 K. The HmE measurements for {x(CH3)2CO+(1–x)C6H14} were made at fixed mole fractions x at pressures up to 7.94 MPa. At 510.2 K measurements were made at x= 0.25, x= 0.50 and x= 0.75, but at all other temperatures the measurements were made at x= 0.50 only. The HmE values measured at 493.2 K have been combined with the enthalpies of acetone and n-hexane to obtain the enthalpy vs. pressure isotherm at the critical temperature Tc(x= 0.5) of the mixture. The HmE values in the supercritical region exhibit double maxima similar to those observed for carbon dioxide–ethane mixtures at supercritical temperatures. The double maxima fade as the temperature increases. The shape of the HmE against p graphs is well reproduced by the Patel–Teja equation of state using k12= 0.14 in the combining rule a12=(1 –k12)(a11a22)1/2. Density-dependent local composition mixing rules were found not to improve the fit to the measurements. The Patel–Teja equation has been used to explore the shape of the HmE(x,p,T) surfaces in the supercritical region. The surfaces are similar to those for carbon dioxide–ethane mixtures.

Thermodynamic properties of (a xylene + an n-alkanol) II. Excess molar enthalpies at 298.15 K for 1-propanol, 1-butanol, and 1-pentanol

Excess molar enthalpies H m E were measured as a function of the mole fraction x at 298.15 K and atmospheric pressure for the nine mixtures [ xo-C 6H 4(CH 3) 2 + (1 − x)C n H 2 n+1 OH], ( n = 3, 4, and 5); [ xm-C 6H 4(CH 3) 2 + (1 − x)C n H 2 n+1 OH], ( n = 3, 4, and 5); and [ xp-C 6H 4(CH 3) 2 + (1 − x)C n H 2 n+1 OH], ( n = 3, 4, and 5). The instrument used was a Calvet microcalorimeter. The H m E values for all these mixtures are large and positive. The results complete H m E( T = 298.15 K, x, n) for the three series with n = 3, 4, 5, 6, 7, and 8.

Thermodynamic properties of binary and ternary systems XII. Excess enthalpies of cyclohexane + p-xylene, p-xylene + dimethylsulfoxide, and dimethylsulfoxide + cyclohexane + p-xylene

Excess molar enthalpies HmE of (cyclohexane + p-xylene) and (p-xylene + dimethylsufloxide), and of (dimenthylsulfoxide + cyclohexane + p-xylene) at mole fractions along lines through the apices of the triangular diagram were determined at 313.15 K. The HmE values remain positive over the whole mole-fraction region examined.