PρT measurements and modelling of (n-decane + m-xylene) mixtures from 293.15 K to 363.15 K at pressures up to 60 MPa

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Highlights

  • High pressure density data of n-decane and m-xylene mixtures were reported.

  • The sPC-SAFT and CPA EoSs were applied to predict the densities of n-decane and m-xylene and their mixtures.

  • The effects of pressure and temperature on the excess molar volume were discussed.

Abstract

In this work, the experimental measurements for liquid densities of n-decane and m-xylene binary mixtures were performed over the entire composition range with a high-pressure vibrating-tube densimeter. The range of temperatures for the present measurements was from 293.15 K to 363.15 K and the pressures were up to 60 MPa. The combined expanded uncertainty of the density measurements is estimated to be 0.001ρ with 0.95 confidence. Experimental density values were correlated by the modified Tammann-Tait equation. The simplified Perturbed Associating Fluid Theory (sPC-SAFT) and Cubic Plus Associated (CPA) equations of state (EoS) were applied to predict the densities of n-decane and m-xylene and their mixtures. Reasonably results were observed between the experimental data and calculated results for the two equations, and the deviation is less than 0.48% and 0.89% with sPC-SAFT and CPA EoS, respectively. In addition, excess molar volumes were determined from the experimental density data as well as from sPC-SAFT and CPA models. The effects of pressure and temperature on the excess molar volume were also discussed.

Introduction

Density data for hydrocarbons (for instance, n-alkanes, iso-alkanes, naphthenes and aromatics) and their 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 is also needed for testing the performance of equations of state (EoS). The development of EoS is of particular significance as, when sufficiently accurate, they constitute a convenient way to obtaining results compared to the time-consuming measurements of gas-crude-oil reservoir-fluid samples.

There are limited density data of asymmetric hydrocarbon mixtures under high-pressure conditions in the open literatures. To the best of our knowledge, only Hamzehlouia et al. [1] reported densities of the n-decane/m-xylene binary mixtures at 308.15 K and 313.15 K under atmospheric pressure. As a continuation of our work to investigate PρTx properties of mixtures containing n-decane [2], the vibrating-tube densimeter is used here to provide experimental densities of n-decane/m-xylene binary system over the entire composition range at pressures up to 60 MPa and at temperatures from 293.15 K to 363.15 K. The obtained density data were correlated as a function of temperature and pressure with the modified Tammann-Tait equation. In addition, excess molar volumes were determined from the experimental densities. Moreover, the capabilities of two EoS, i.e. cubic plus association (CPA) [3] and simplified perturbed-chain statistical associating fluid theory (sPC-SAFT) [4], [5] to calculate the densities and the excess molar volume were analysed.

Section snippets

Samples

The samples of n-decane and m-xylene were supplied by Aladdin Chemistry without further purification. The information of the samples is presented in Table 1.

Experimental apparatus

The PρTx properties of the mixtures were measured with the Anton Paar vibrating-tube densimeter (DMA-HPM). Figure 1 shows the schematic diagram of the apparatus. Detailed descriptions of the system have been presented in our previous work [2], [6], [7], [8]. The main parts of the densimeter consist of the measuring cell and interface

Equations of state

In this section, the CPA and sPC-SAFT EoS, used as tools for describing PρTx properties of samples considered, are introduced in brief. CPA is a convenient equation of state, proposed by Kontogeorgis et al.[3], which combines the simple cubic equation of state (SRK) [11] and an association term, the latter from the Wertheim theory [12], [13], [14], [15], similar to that used in the well-known SAFT models [4], [5], [16], [17], [18], [19], [20], [21], [22], [23]. Of particular note is that CPA

Density data and correlations

Experimental density results of pure m-xylene and the binary mixtures of m-xylene and n-decane are shown in Table 3. For all samples, measurements of density were carried out along isotherms spaced at 10 K intervals from 293.15 K to 363.15 K in the pressure range from 0.1 to 60 MPa. Meanwhile, the density data were correlated as a function of both temperature and pressure using the modified Tammann-Tait equation.

The correlation parameters of the modified Tammann-Tait equation, Ai, Bi and C, are

Conclusion

High-pressure liquid densities are reported for m-xylene and n-decane/m-xylene 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 the modified Tammann-Tait equation with absolute relative deviation in comparison with available literature data less than 0.2% in most cases. Densities of the studied system were predicted with CPA and sPC-SAFT EoS with ARD of 0.89% and 0.48%, respectively. Furthermore, the

Notes

The author declare no competing financial interest.

Funding sources

This work was supported by National Key R&D Program of China (Grant No. 2016YFE0204200) and National Natural Science Foundation of China (No. 51776170).

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