Elsevier

Fluid Phase Equilibria

Volume 381, 15 November 2014, Pages 77-82
Fluid Phase Equilibria

Excess molar enthalpies for binary mixtures of n-propanol, acetic acid, and n-propyl acetate at 313.15 K and atmospheric pressure

https://doi.org/10.1016/j.fluid.2014.08.022Get rights and content

Highlights

  • Excess molar enthalpies, HE, data for the binary mixtures of acetic acid + n-propanol, acetic acid + n-propyl acetate, and n-propanol + n-propyl acetate have been measured at 313.15 K.

  • The mixing processes are endothermic for acetic acid + n-propanol and n-propanol + n-propyl acetate, and acetic acid + n-propyl acetate presents S-shaped HE behavior.

  • The experimental data have been correlated using Redlich–Kister equation and its modified version.

  • The use of NRTL model gives satisfactory agreement between experimental and calculated HE data.

Abstract

Excess molar enthalpies, HE, for the binary mixtures of acetic acid (AcOH) + n-propanol (n-PrOH), acetic acid (AcOH) + n-propyl acetate (n-PrOAc), and n-propanol (n-PrOH) + n-propyl acetate (n-PrOAc) have been measured at 313.15 K and atmospheric pressure using the Setaram C80 calorimeter. The experimental results are presented and correlated with the Redlich–Kister polynomial equation and its modified version. Modeling of the excess enthalpies has been performed using the UNIFAC and NRTL models.

Introduction

The aim of present work is to study excess enthalpies of binary mixtures of n-PrOH, AcOH, and n-PrOAc. The knowledge of excess thermodynamic properties is very important for a number of reasons. For example, they quantify the deviations from ideality of the thermodynamic functions of mixtures, which result essentially from energetic interactions between the molecules present in a mixture, such as van der Waals forces, hydrogen bonding interactions, etc. The data sets on enthalpy are necessary in many engineering applications, such as process simulation or distillation design. The knowledge of enthalpy values allow to extend vapor–liquid equilibrium data to higher or lower temperatures using the Gibbs–Helmholtz equation.

The choice of the experimental object was caused by our studies of quaternary systems with n-PrOAc synthesis reaction. Recently we published some experimental data and results of the modeling of solubility, liquid–liquid equilibrium, vapor–liquid equilibrium and chemical equilibrium for the system AcOH + n-PrOH + n-PrOAc + H2O at few temperatures [1], [2], [3], [4]. The study of excess thermodynamic properties of some binary subsystems of this quaternary system had been carried out by various authors [5], [6], [7].

The most widely studied system is n-PrOH + H2O. The excess enthalpies of mixing data were obtained at various temperatures (for example, at 273.15, 293.15, 298.15, 303.15, 323.15 K and others) using different types of calorimeters, such as Tian–Calvet calorimeter, flow-mixing calorimeter, solution calorimeter, etc. [8], [9], [10], [11], [12], [13], [14], [15], [16], [17], [18], [19]. A little less studied binary mixture is AcOH + H2O, its heats of mixing were measured at, for example, 296–298, 298.15, 313.15, 333.15, 353.15 K [20], [21], [22], [23], [24]. There were investigated two binary systems with n-PrOAc: H2O + n-PrOAc and n-PrOH + n-PrOAc at three temperatures (300.15, 323.15, and 348.15 K) [25]. As concerns the ternary mixtures, H2O + n-PrOAc + n-PrOH is a single system, which was studied calorimetrically; the excess molar enthalpies were obtained at 300.15, 323.15, and 348.15 K [26].

The goal of this research is to obtain reliable data on the excess molar enthalpies for three binary systems, AcOH + n-PrOH, AcOH + n-PrOAc, and n-PrOH + n-PrOAc, at T = 313.15 K, which are also the subsystems of the quaternary system AcOH + n-PrOH + n-PrOAc + H2O. The experimental results have been represented and correlated with the Redlich–Kister equation and its modified version. The experimental HE data have been used to test the suitability of the UNIFAC molecular group-contribution method and the NRTL model, based on local composition theory.

Section snippets

Materials

All chemicals have been supplied by “Vekton” (Russia). The species used in experiments have been additionally purified by distillation (the details have been described previously in, for instance, [4]). The purity of the substances, checked by gas chromatography, has been not less than 0.997 mole fraction. Evidence of chemical purity was also provided by comparison of the measured refractive indexes, nD, with the literature values. The refractive indexes were determined with the IRF-454B2M

Results and discussion

Experimental values of excess enthalpies at 313.15 K and atmospheric pressure are given in Table 2, Table 3, Table 4 and presented in Fig. 1, Fig. 2, Fig. 3.

The excess enthalpies for binary systems AcOH + n-PrOH and n-PrOH + n-PrOAc are quite large and positive over the entire range of mole fractions. The curves vary almost symmetrically with compositions with maximum HE = 409 J mol−1 at xn-PrOH = 0.4001 in AcOH + n-PrOH and HE = 1482 J mol−1 at xn-PrOAc = 0.4996 in n-PrOH + n-PrOAc. This shape of the curves can be

Conclusions

The excess enthalpies, HE, have been measured for three binary systems, AcOH + n-PrOH, AcOH + n-PrOAc, and n-PrOH + n-PrOAc at T = 313.15 K and atmospheric pressure. It has been found that mixing processes are endothermic for AcOH + n-PrOH and n-PrOH + n-PrOAc, and AcOH + n-PrOAc presents S-shaped HE behavior.

The Redlich–Kister equation and its modified version have successfully correlated the experimental excess enthalpy data. UNIFAC and NRTL models have been also used to predict and to correlate the excess

Acknowledgments

The authors acknowledge St. Petersburg State University for a research grant (12.38.257.2014). The investigations experimental study has been carried out using the equipment of the Center of Thermal Analysis and Calorimetry of St. Petersburg State University. We are grateful to the NIST ThermoData Engine group for the data on the properties of considered system.

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      Solubility, liquid-liquid and vapor-liquid phase equilibria, chemical equilibrium of this system and its subsystems were studied by our scientific group earlier [1,2,16–19]. The excess molar enthalpies of the binary and ternary constituent subsystems were studied at different temperatures [20–22], but there is no a uniform database with multi-temperature data [23–25]. In our research we compare the excess molar enthalpies of the mentioned above binary systems predicted with the origin UNIFAC model and the modified UNIFAC (Dortmund) model with the obtained experimentally at T = 313.15 K.

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      The present work reports the experimental excess molar enthalpies for the ternary system n-PrOH + AcOH + H2O at 313.15 K and atmospheric pressure. The HEm experimental data for appropriate binary systems are given in the literature [11,13–15]. The excess molar enthalpy data were fitted using Redlich–Kister, Cibulka, Singh et al., Nagata–Tamura and Morris et al. equations.

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