Contribution to study of the thermodynamics properties of mixtures containing 2-methoxy-2-methylpropane, alkanol, alkane
Graphical abstract
Introduction
This work contributes to the systematic knowledge of several thermodynamic properties of ternary and binary mixtures containing 2-methoxy-2-methylpropane (MTBE), alkanols and alkanes as components. It is the continuation of previous papers [1], [2], [3], [4], [5], [6], [7], [8], [9], [10], [11], [12], [13], [14], [15], [16] which are part of the scientific project entitled “Study on physical properties of mixtures hydrocarbon + alcohol + ether like alternative fuels”. The main objective of this project has been the characterization of non-electrolyte liquids, and their mixtures, through experimental determination of thermophysical properties on mixing.
The series including the ternary systems {2-methoxy-2-methylpropane (MTBE) + 1-pentanol + alkane (decane [15], nonane [14], octane [9])} and {2-methoxy-2-methylpropane (MTBE) + 1-alkanol (ethanol [11], propanol [13], butanol [5]) + hexane}, are continued, considering hexane and 1-pentanol as components in this case.
This should help to study the molecular interactions of these mixtures and to examine the effect of the enlargement of the CH2 unit in the alkanol or alkane. So, as an extension of these earlier investigations, the aim of this research was to measure, using a Calvet microcalorimeter, experimental excess molar enthalpies, over the whole composition range, for the ternary mixture {x1 2-methoxy-2-methylpropane (MTBE) + x2 1-pentanol + (1 − x1 − x2) hexane}, at the temperature of 298.15 K and atmospheric pressure. Additionally, experimental data for the binary mixture {x 1-pentanol + (1 − x) hexane} are reported. To correlate adequately the binary experimental data, a variable degree polynomial due to Myers–Scott [17] was used. The ternary contribution to the excess enthalpy was fitted on the basis of an equation proposed by Verdes et al. [15].
The experimental values were compared with the estimates obtained by applying the group contribution model of UNIFAC, the latter in the versions introduced by Larsen [18] and Gmehling et al. [19].
As the number of components in the mixture increases, the determination of thermodynamic properties becomes more laborious. Therefore, the applicability of predictive methods is of great interest for estimating ternary properties from the experimental data of the binaries involved. These methods allow us to estimate excess properties of generalised multi-component mixtures from the experimental correlated values of the binary mixtures.
So, deviations of the ternary enthalpies calculated on the basis of several empirical methods were also listed. The symmetric equations used were those introduced by Kohler [20], Jacob and Fitzner [21], Colinet [22], Knobeloch and Schwartz [23], and the asymmetric ones those due to Tsao and Smith [24], Toop [25], Scatchard et al. [26], Hillert [27], and Mathieson and Tynne [28].
Section snippets
Experimental
The chemical substances employed were commercial products of the best quality grade. Their sources and purities (stated by the supplier) are listed in Table 1. All products were used as supplied, no further purification being applied. In order to avoid hydration and to eliminate residual traces of water, the chemicals were dried over Union Carbide 0.4 nm molecular sieves. In addition, they were degassed by an ultrasound technique. The handling and disposal of the chemicals used have been done
Theoretical predictions
The UNIFAC group contribution model was originally developed by Fredenslund et al. [35], from the UNIQUAC equation developed by Abrams and Prausnitz [36] for a multi-component mixture. In this model, the activity coefficient is calculated as the sum of two terms. The first term is combinatorial and takes into account the differences of the shape and size of the molecules; the second one is a residual term that includes the energetic interactions present in the mixture. The adjustable parameters
Results and discussion
The excess molar enthalpies, , for the binary mixture {x 1-pentanol + (1 − x) hexane} are listed in table 3.
The experimental data of excess molar enthalpies for the binary mixture {x 2-methoxy-2-methylpropane + (1 − x) 1-pentanol} and {x 2-methoxy-2-methylpropane + (1 − x) hexane} were reported in early papers [16], [13]. These sets of data were fitted to the variable-degree polynomial suggested by Redlich–Kister [37].
The set of data measured in this work for the
Acknowledgements
We are thankful for the financial support provided by the projects EM2012/141, and XUGA PGIDT99PXI30103B by “Xunta de Galicia” and the project CGL2008-03668 funded by Ministry of Science and Innovation of Spain.
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Present address: Departamento de Física Aplicada, Facultad de Ciencias, Universidade de Vigo, E-36310 Vigo, Spain.