Isobaric vapor–liquid equilibrium for the binary mixtures of nonane with cyclohexane, toluene, m-xylene, or p-xylene at 101.3 kPa
Highlights
► Isobaric binary vapor–liquid equilibrium (VLE) data were measured at 101.3 kPa. ► The studied systems are nonane with cyclohexane, toluene, m-xylene, or p-xylene. ► No azeotrope was formed and positive deviations from the Raoult's law were found. ► The UNIFAC and the COSMO-RS models were tested with the new VLE data. ► The Wilson, the NRTL, and the UNIQUAC models correlated well the VLE data.
Introduction
The separation of aromatic hydrocarbons (such as benzene, toluene, alkylbenzenes, and xylenes) from aliphatic hydrocarbons (such as hexane, heptane, octane, nonane, and decane) mixtures is commonly encountered in refinery and petrochemical industries. To develop the separation processes, vapor–liquid equilibrium (VLE) data of the related mixtures are fundamentally important. In the present study, we focus on the phase equilibrium properties for the mixtures containing nonane. Among several other studies [1], [2], [3], [4] on the physical properties of this class of mixtures, the isobaric VLE data at 101.3 kPa for the binary systems of cyclohexane + o-xylene, + p-xylene, + m-xylene and heptane + o-xylene, + p-xylene, + m-xylene were reported by Tojo et al. [5], [6] For the binary mixtures containing nonane, Calvar et al. [7] measured the densities of nonane + benzene at 313.15 K under atmospheric pressure and Aicart et al. [8] reported the isothermal density and compressibility data of the nonane + cyclohexane at temperatures from 298.15 K to 333.15 K. Using density measurements to determine liquid phase compositions, Chen et al. [9] and Lee et al. [10] reported the isothermal P-x data of nonane + benzene and nonane + cyclohexane at temperatures ranging from 313.15 K to 353.15 K. Since the vapor phase compositions were not measured, thermodynamics consistency test cannot be made for those VLE data.
In the present study, the isobaric VLE measurements were conducted for the binary systems of nonane with cyclohexane, toluene, m-xylene, or p-xylene at 101.3 kPa by using an Othmer-type recirculating still. The obtained VLE data were verified with the Herington [11] thermodynamic consistency test. These new VLE data are used to examine the validity of two predictive activity coefficient models, the UNIFAC [12] and the conductor-like screening model for realistic solvents (COSMO-RS) [13], [14], [15]. In the VLE calculation, the fugacity coefficient of each constituent compound in the vapor phase was estimated from the two-term virial equation together with the Hayden-O’Connell (HOC) model [16] for calculating the second virial coefficients. The new VLE data were also correlated with three correlative models, the Wilson [17], the NRTL [18], and the UNIQUAC [19].
Section snippets
Materials
The purity levels and sources of the chemicals used in this study are reported in Table 1. These all substances were checked with gas chromatography analysis. No impurity peak was detected. The purity of the chemicals was also assessed by comparing their measured density (ρ) and normal boiling point with literature values [20], [21], [22], [23], [24], [25] as shown in Table 2, where the density data were measured by using a digital vibrating-tube densimeter (DMA 4500, Anton Paar, Austria) with
Experimental results
To validate the experimental method, the VLE data of toluene (1) + benzene (2) at 101.3 kPa was measured and compared with the literature values [27], [28]. The experimental data (T, x1, and y1) is listed in Table 3 and the comparison is shown in Fig. 1. As can be seen, the agreement is satisfactorily well. The apparatus was then employed to measure the VLE data for four binary systems of nonane with cyclohexane, toluene, m-xylene, or p-xylene at 101.3 kPa. The VLE phase diagrams of nonane (1) +
VLE calculation
Based on the experimental VLE data, we test the predictive capability of a group-contribution based model: UNIFAC [12] and a quantum approach based model: COSMO-RS [13], [14], [15] for VLE calculations. The results of COSMO-RS are obtained by using the software of COSMOtherm. Fig. 2, Fig. 3 compare graphically the predicted results with experimental values. For nonane + cyclohexane and nonane + toluene, the predictions from both models generally agree well with the experimental values. As seen from
Conclusion
Isobaric VLE data were measured for the binary systems composed of nonane with cyclohexane, toluene, m-xylene, or p-xylene at 101.3 kPa over the entire composition range. All the experimental data were passed the Herington thermodynamic consistency test and exhibited positive deviations from the Raoult's law. No azeotrope was formed in these four binary systems. It was also found that the non-ideality in the liquid phase for these nonane-containing systems followed the order of m-xylene > toluene >
Acknowledgements
The authors are grateful for financing provided by the National Science Council, Taiwan, through grant no. NSC99-2221-E-011-079-MY3, and also thank for Dr. Ho-mu Lin for valuable discussions.
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