Thermophysical and volumetric study of mixtures {p-cymene + propan-1-ol} at several temperatures and atmospheric pressure. Modeling with COSMO-RS

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Highlights

  • Cp,m, of the binary mixture {p-cymene (1) + propan-1-ol (2)}, have been determined in the temperature range (298.8–328.5) K.

  • Experimental densities were measured at the same temperatures in the whole composition range.

  • Cp,mE are positive in the whole composition range and increase as temperature rises.

  • COSMO-RS were tested to predict Cp,mE showing acceptable deviations from experimental data.

Abstract

Experimental isobaric molar heat capacities at atmospheric pressure have been determined for the mixture {p-cymene + propan-1-ol} every 10 K in the temperature interval (298.8–328.5) K and over the entire composition range with a Calvet type calorimeter. Densities, necessary for calculating heat capacities, have been also measured in similar conditions. Excess molar volumes have been calculated from densities. They are positive at (318.15 and 328.15) K and sigmoidal at (298.15 and 308.15) K with negative values in the zone very rich in propan-1-ol. Excess molar heat capacities have been calculated from the molar heat capacities and show positive values. Both excess molar properties increase as the temperature rises at a given molar fraction. Excess properties are discussed in terms of intermolecular interactions. The solvation model COSMO-RS has been applied to predict the excess molar heat capacities, being the quantitative predictions rather poor.

Introduction

The thermodynamic study of binary mixtures of short chain alkanols such as ethanol or propan-1-ol with the main component of a vegetable extract results interesting for the design of extraction processes with supercritical CO2 as those alkanols are added as cosolvents to CO2 for increasing the polarity of the final solvent [1]. For this reason, in an earlier paper [2] we reported values of isobaric heat capacities and densities at atmospheric pressure for the binary mixtures of p-cymene with ethanol. In this respect, it would be interesting to extend these studies to the mixture of p-cymene with propan-1-ol.p-Cymene (1-methyl-4-(1-methyl-ethyl)benzene) is a monocyclic monoterpene that is present in volatile oils from over 100 vegetal species being a major component in the extracts of certain plants such as cumin and thyme. p-Cymene also occurs naturally in more than 200 foodstuffs, such as orange juice, grapefruit, carrots, raspberries, butter, nutmeg, tangerine, oregano, and most any other spice [3]. At present the main economic importance of this compound lies in its use as an intermediate in the industrial syntheses of fragrances, flavours, herbicides and, principally, pharmaceuticals. Besides, some studies have recently proven that p-cymene possesses antinociceptive as well as anti-inflammatory activity [4], a fact which can widen its field of applications.

In addition to the interest of thermodynamic properties for the extraction processes mentioned above, there are several studies in the literature about the thermodynamic behavior of binary mixtures of an alkanol with alkylbenzenes. So, for binary mixtures of propan-1-ol with benzene or alkylbenzenes (toluene or cumene or xylene isomers) excess molar enthalpies [5], [6], [7], [8], [9], [10], [11], [12], [13], excess molar volumes [6], [14], [15], [16], [17], [18], [19], [20], [21], [22], excess molar Gibbs energies [5], [9] and isobaric molar heat capacities [9] have been determined. New data for the mixture of p-cymene with propan-1-ol would provide a more complete knowledge about this kind of mixtures.

Therefore, in this work values of experimental isobaric molar heat capacities for the binary mixtures of p-cymene with propan-1-ol, at four temperatures (298.8, 308.7, 318.6 and 328.5) K and atmospheric pressure over the entire composition range are reported. Besides, densities have been measured at (298.15, 308.15, 318.15 and 328.15) K and atmospheric pressure also over the entire composition range. Then, excess molar volumes and excess molar heat capacities have been calculated for the mixture. The solvation model COSMO-RS [23], [24], [25] has been applied in order to evaluate its ability to predict the excess molar heat capacity. In this way useful information would be added for practical purposes as well as for basic knowledge of mixtures of alkylbenzene with alkanol.

Section snippets

Materials

The chemicals used were p-cymene and propan-1-ol. Also, water (milliQ quality) was used to perform the measurements. Their descriptions are shown in Table 1. Experimental values of density for the pure components at the working temperatures are reported in Table 2 and compared with available bibliographic values [26], [27], [28], [29], [30], [31], [32]. In general, a good agreement can be observed between both sets of data. As pointed out in a previous paper [2] for p-cymene there are

Results and discussion

Experimental values of densities, in the entire composition range, for the mixture {p-cymene (1) + propan-1-ol (2)} are reported in Table 3.

Excess molar volumes, VmE were obtained from these densities by means of the equationVmE(p,T)=x1M11ρ-1ρ1+x2M21ρ-1ρ2being xi the mole fraction of pure component i and their values appear represented in Fig. 1. The estimated expanded uncertainty (k ≈ 2) for VmE is ±0.008·106 m3·mol−1. This excess quantity was fitted to the Redlich–Kister equationVmE=x1(1-x1)i

Conclusions

The molar heat capacity at atmospheric pressure of the mixture {p-cymene (1) + propan-1-ol (2)} has been determined in the temperature interval (298.8–328.5) K and the whole composition range. Densities have been also experimentally measured for the mixture in the same temperature interval for the entire composition range. From densities and molar heat capacity data, the excess molar volumes and the excess molar heat capacities have been calculated, respectively. Excess molar volumes are

Acknowledgements

The authors are grateful for the financial support of MINECO-FEDER (Project CTQ2015-64049-C3-2-R) and of Departamento de Ciencia, Tecnología y Universidad del Gobierno de Aragón-Fondo Social Europeo (Grupo E52).

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