Elsevier

Fluid Phase Equilibria

Volume 458, 25 February 2018, Pages 142-152
Fluid Phase Equilibria

Liquid densities for n-decane + p-xylene mixtures from 293.15 K to 363.15 K at pressures up to 60 MPa

https://doi.org/10.1016/j.fluid.2017.11.021Get rights and content

Abstract

The experimental measurements for liquid densities of n-decane and p-xylene binary mixtures were performed over the entire composition with a high-pressure vibrating-tube densimeter. The temperature ranges for the present measurement were from 293.15 K to 363.15 K and the pressures were reached to 60 MPa. The experimental uncertainty is estimated to be 0.001 with 0.95 confidence level. Experimental density values were fitted by the modified Tammann–Tait equation. The PC-SAFT equation of state and Cibulka's equation was used to predict the densities of n-decane and p-xylene and its mixtures. In addition, derived volumetric properties, such as the excess molar volumes, the isothermal compressibility, and isobaric thermal expansivity, were calculated from the experimental density data. The effects of pressure and temperature on the derived properties were also discussed.

Introduction

Hydrocarbons (for example, n-alkanes, iso-alkanes, naphthenes and aromatics) are the main components of crude oil. Densities of hydrocarbons and its mixtures at reservoir conditions are indispensable for accurate assessment of the recoverable petroleum amount within a reservoir. Furthermore, the knowledge of accurate pρTx data of mixtures allows calculating the derived properties, including excess molar volumes, isothermal compressibility, isobaric thermal expansivity, and internal pressure. These properties can provide a good understanding the nature of molecular interactions of the mixtures.

Literature survey shows that there has a great deal of density data for alkane mixtures and alkane/naphthene mixtures [1], [2], [3], [4], [5], [6], [7], [8], [9], [10], [11]. However, pρTx properties of alkane/aromatics mixtures are still scarce in the literature, especially at high pressures. Kapoor and Rattan reported densities for n-decane/p-xylene mixtures from 303.15 K to 313.15 K at 0.1 MPa [12]. Mosteiro et al. measured experimental density data for the same mixtures in the temperature range from 288.15 K to 308.15 K at atmospheric pressure [13]. Chevalier et al. [14] obtained the density data of n-decane/p-xylene mixtures (0.5:0.5) at 298.14 K at ambient pressure. In addition, Caceres and Nunez reported the excess volumes of n-decane/p-xylene binary mixtures at 298.15 K [15]. For high pressures, only Gayol et al. reported densities of n-decane/p-xylene binary mixtures from 288.15 K to 308.15 K and pressures up to 40 MPa [16].

In order to extend the database of thermophysical properties of alkane/aromatics mixtures, liquid densities of n-decane/p-xylene mixtures were measured at temperatures from 293.15 K to 363.15 K and pressures up to 60 MPa over the whole range of composition. The density data were correlated to a modified Tammann–Tait equation and modeled using PC-SAFT equation of state. Additionally, derived volumetric properties, e.g. excess molar volumes, isothermal compressibilities, and isobaric thermal expansivity, were calculated and analyzed.

Section snippets

Samples

The samples of n-decane and p-xylene were purchased from Aladdin Chemistry with a mass purity better than 0.99. The two substances were used without further purification. Table 1 shows the information of the samples.

Experimental apparatus

The liquid densities of the mixtures were measured by Anton Paar vibrating-tube densimeter (DMA-HPM). Fig. 1 shows the schematic diagram of the system. Details of the apparatus have been described in our previous work [17], [18]. The main parts of the densimeter are the measuring

Results and discussion

Density results of pure n-decane, p-xylene and its binary mixtures were presented in Table 2. Due to the higher melting point of p-xylene (Tm = 286.4 K at atmospheric pressure), liquid densities of the mixtures were measured from 293.15 K. It should be noted that the phase of p-xylene or n-decane/p-xylene mixtures will be changed at high pressures. The liquid-solid transition behavior of p-xylene has been investigated in the literature and the results showed that the solidification pressure at

Conclusion

High-pressure density data are reported for n-decane, p-xylene and its binary mixtures over the entire composition range from 293.15 K to 363.15 K and at pressures up to 60 MPa. The experimental densities were fitted with a modified Tammann–Tait equation. The PC-SAFT equation is used to predict the densities of the studied compounds. The ARD between the experimental data and predicted results for n-decane, p-xylene and its mixtures is 0.51%, 1.57%, and 0.94%, respectively. Furthermore, the

Acknowledgements

This research was supported by the National Natural Science Foundation of China (Grant 51476129).

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