Volumetric behaviour of binary liquid systems composed of toluene, isooctane, and methyl tert-butyl ether at temperatures from (298.15 to 328.15) K

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Abstract

The densities and speeds of sound of (toluene + isooctane), (MTBE + toluene), and (MTBE + isooctane) were measured at four temperatures from (298.15 to 328.15) K, and the respective values of excess volumes VmE and adiabatic compressibility κS were calculated. The VmE and κS values were fitted to the fourth-order Redlich–Kister equation. The VmE values for (MTBE + toluene) are negative and decreasing with increasing temperature. The other systems show positive VmE with comparatively small temperature dependence.

Introduction

Research activities of our laboratory comprise, among others, the systematic measurement of volumetric properties of different groups of organic compounds. Our present project is devoted to the systematic study of liquid systems modelling liquid engine fuels. After measuring (cyclohexane + alkane) at normal pressure and T = 298.15 K [1], (cyclohexane + nonane) at temperatures from (298.15 to 328.15) K and at pressures up to 40 MPa [2], (octane + benzene, or +toluene, or +1,3-xylene, or +1,3,5-trimethylbenzene) at temperatures between (298.15 and 328.15) K [3], and (octane + benzene) at temperatures from (298.15 to 328.15) K and at pressures up to 40 MPa [4], the binary and ternary systems containing methyl tert-butyl ether (MTBE) have been studied with the aim to decide what and how many ternary constants, in addition to the binary constants, are needed to fit the ternary data to Redlich–Kister equation within the error of experimental results. This measurement is also of practical importance with respect to use of MTBE as the liquid fuel antiknock additive.

The thorough literature search showed that there exist some limited binary data for these systems (for their detailed comparison with our results see Section 3). However, to be able to do the test, we needed more accurate and mutually consistent binary (and ternary) results. Not finding such data sets, we decided to measure the title binary systems as the first step.

The densities and excess volumes of the investigated liquids and their mixtures are required, for instance, for relating excess enthalpy and excess Gibbs free energy values. From a practical point of view, the data are useful for the design of mixing, storage, and process equipment. Last but not least, the measured results reflect interactions between the molecules of the mixtures studied and can serve for testing the theories of the liquid state.

Section snippets

Materials

The chemicals used in the experiments were the following products from Fluka: MTBE (methyl 1,1-dimethylethyl ether), puriss., g.c. mass fraction purity ⩾0.95, toluene, RdH, for chromatography, g.c. mass fraction purity ⩾0.995, isooctane (2,2,4-trimethylpentane), RdH puriss. p.a., g.c. mass fraction purity ⩾0.995. The substances were used without further purification and dried and stored over 0.4 nm molecular sieves. In order to check the purity of the substances, their density and refractive

Results and correlation

The results of the measurements of densities and sound velocities of the three binary systems are given in TABLE 2, TABLE 3, TABLE 4 together with the calculated values of VmE and adiabatic compressibility κS and illustrated in FIGURE 1, FIGURE 2, FIGURE 3 for the temperature dependence of VmE and in FIGURE 4, FIGURE 5, FIGURE 6 for the temperature dependence of κS. The adiabatic compressibility κS was calculated from the relationκS=1/(u2ρ),where u is the measured sound velocity. For fitting

Discussion

The VmE values for (MTBE + toluene) are negative and considerably decreasing with increasing temperature. The other systems show positive VmE with comparatively smaller temperature dependence. (Toluene + isooctane) exhibits VmE decreasing with increasing temperature, (MTBE + isooctane) shows the same trend up to T = 328.15 K, then the opposite trend seems to start.

The deviations from ideal behaviour of the systems studied can be discussed in terms of intermolecular interactions as follows. In (toluene + 

Acknowledgements

The authors acknowledge the partial support from the Grant Agency of the Czech Republic; the work has been carried out under Grants No. 104/06/0656 and No. 104/09/0666.

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