Thermodynamic behaviour of alkyl lactate–alkanol systems

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Highlights

  • Densities and speeds of sound of methyl (or ethyl) lactate + alkanol systems have been measured.

  • The alkanols involved were: methanol, ethanol, 1-propanol, and 1-butanol.

  • From experimental data, excess volumes and excess isentropic compressibilities were calculated.

  • The thermal effect of the mixing process was evaluated through the determination of excess enthalpies.

Abstract

This work reports densities and speeds of sound of some alkyl lactates + alkanols binary mixtures over the whole composition range at T = 298.15 K and p = 0.1 MPa. The studied systems were methyl lactate or ethyl lactate with methanol, ethanol, 1-propanol, or 1-butanol. From experimental results, excess molar volumes and excess isentropic compressibilities have been calculated. Furthermore, excess molar enthalpies were experimentally determined at T = 298.15 K and p = 0.1 MPa. Finally, the excess properties were correlated with composition and discussed taking into account the associated character of both components, alkyl lactates and alkanols. From this analysis it has been concluded that excess properties values depend mainly on the length of the alkyl chain of the alkanol.

Introduction

In the last years, our research group has characterized the thermophysical behaviour of different families of compounds derived from biomass that have been proposed as green solvents [1], [2]. Between the compounds studied, organic esters can be used in a wide range of applications in the chemical industry, including the production of less contaminant solvents. In particular, previous studies [3] have shown that methyl lactate and ethyl lactate present lower vapour pressures, higher densities and viscosities than many volatile organic compounds (VOCs) commonly used nowadays. In order to explore the applications of alkyl lactates it is also relevant to investigate their mixtures with other traditional solvents, like alcohols, that are used in many industrial processes.

In this contribution, we present experimental densities and speeds of sound for eight binary mixtures formed by an alkyl lactate (methyl or ethyl) and a n-alkanol (from methanol to 1-butanol) at T = 298.15 K and at p = 0.1 MPa. The isentropic compressibilities have been also calculated along with excess molar volumes and excess isentropic compressibilities. The thermal effect of the mixing process has been also determined through the excess molar enthalpies, these excess molar enthalpies were experimentally measured at T = 298.15 K and p = 0.1 MPa.

Mixtures of alkanols and alkyl esters have been deeply investigated in the scientific literature [4], [5], [6] because these compounds can be found together in many systems of interest, since esters are generally obtained by direct esterification of a carboxylic acid with the corresponding alcohol [7]. However, there are few studies about the thermophysical properties of the binary mixtures analysed in this contribution. As far as we know, there are only three previous references reporting isobaric vapour-liquid equilibrium of the following mixtures: methyl lactate + methanol [8] ethyl lactate + ethanol [9] and ethyl lactate + methanol or 1-propanol [10]. In the first two references densities were measured, while in the last reference densities, refractive indices and speeds of sound were also determined.

Section snippets

Experimental

Table 1 summarizes the information about the compounds used in this study. As it can be seen in this Table the impurities are in low concentration, so the chemicals can be employed without further purification. The water content was measured by using an automatic titrator Crison KF 1S-2B.

The thermophysical properties of the pure compounds at T = 298.15 K and at p = 0.1 MPa are collected in Table 2 along with literature density and speed of sound values [3], [8], [10], [11], [12], [13], [14],

Results and discussion

The experimental densities and speeds of sound together with calculated isentropic compressibilities are collected in Table S1 of the Supplementary material, the isentropic compressibility can be calculated from density and speed of sound supposing that the ultrasonic absorption is negligible by means of the Newton-Laplace equation, KS = 1/(ρu2). In this Table S1 calculated excess molar volumes and excess isentropic compressibilities are also provided. On the other hand, the excess molar

Conclusions

Densities, speeds of sound and heats of mixing have been obtained for the binary mixtures lactate (methyl lactate or ethyl lactate) + 1-alkanol (methanol, ethanol, 1-propanol or 1-butanol) at T = 298.15 K and p = 0.1 MPa. From experimental data, excess molar volumes, excess isentropic compressibilities and excess molar enthalpies have been determined and correlated using Redlich-Kister polynomial expansions.

Compared to other alkyl esters + alkanols binary mixtures studied in the scientific

Acknowledgement

Authors are indebted by financial support from Gobierno de Aragón (grant E31_17R).

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