Experimental high pressure speed of sound and density of (tetralin + n-decane) and (tetralin + n-hexadecane) systems and thermodynamic modeling

doi:10.1016/j.jct.2014.09.020

The Journal of Chemical Thermodynamics

Volume 81, February 2015, Pages 77-88

https://doi.org/10.1016/j.jct.2014.09.020 Get rights and content

Highlights

•
High pressure speed of sound and density for C₁₀H₁₂, n-C₁₀H₂₂, n-C₁₆H₃₄ mixtures.
•
High pressure density and excess properties provided.
•
PFP model better than SAFT but misled pressure effect on speed of sound.
•
PFP model correlates well excess properties.

Abstract

In this work, speed of sound for n-decane, n-hexadecane and tetralin, as well as for binary mixtures involving these hydrocarbons, were determined at pressures of (0.1, 5, 10, 15, 20 and 25) MPa at temperatures of (313.15, 323.15 and 333.15) K at different compositions. Density data at atmospheric pressure for these same systems were measured experimentally at temperatures of (313.15, 323.15 and 333.15) K. From these results and thermodynamic definitions, the following properties were calculated: density at high pressures, excess molar volume and excess isentropic compressibility. Tetralin, n-decane and n-hexadecane are chemicals asymmetrical in shape, length and chemical nature that can be found in naphtha and kerosene fractions. The influence of these differences on the physical properties of these mixtures was then evaluated. Density and speed of sound data were correlated with Prigogine–Flory–Patterson (PFP) equation of state. The PFP model correlated well experimental densities for pure components but did not correlate so well the speed of sound dependency with pressure. The model calculated well excess properties, with correct signs, magnitudes, and the qualitative effect of pressure and temperature on these properties.

Introduction

In many areas of Chemical Engineering, like process development and petroleum fractions characterization, the accurate estimate of density of liquid mixtures as a function of composition and temperature are particularly important [1]. The knowledge of density, along a sufficient number of isotherms and isobars can be used to determine the isothermal compressibility and the thermal expansion coefficient of fluids [2].

The accurate measurement of ultrasonic velocity plays an important role in the characterization of the effect of pressure on thermodynamic properties of liquids if it coincides perfectly with the speed of sound within the low frequency limit [3]. For the systems studied in this investigation, this condition is satisfied because the hydrocarbons present in the mixtures do not present dispersive effects in the frequency domain concerned by the experiments [4], [5].

In petroleum research, tetralin is a reference aromatic compound used as a surrogate to naphtha and kerosene fractions [6]. In this context, studies of speed of sound and density at high pressures of binary mixtures of tetralin with n-decane or n-hexadecane can be used to simulate the properties of kerosene and naphtha fractions. These substances are asymmetrical in shape, length and chemical nature so the binary mixture should not present ideal solution behavior [7]. Despite of this complexity, no speed of sound data at high pressure for (tetralin + n-decane) and (tetralin + n-hexadecane) mixtures are available in open literature.

In this work, speed of sound, c, for n-decane, n-hexadecane and tetralin, as well as for binary mixtures involving these hydrocarbons, were determined at pressures, P, of (0.1, 5, 10, 15, 20 and 25) MPa at temperatures, T, of (313.15, 323.15 and 333.15) K at different compositions. Density (ρ) measurements for the systems at atmospheric pressure were performed in the same temperatures. From these data and some thermodynamic definitions the following properties were calculated: density at high pressures, excess molar volume, V^E, and excess isentropic compressibility, $k_{S}^{E}$ _, in the same temperature interval and pressure range of the speed of sound measurements. Density and speed of sound data were used to estimate the parameters of Prigogine–Flory–Patterson (PFP) equation of state [8], [9].

Section snippets

Experimental section

The suppliers and weight fraction purities of the chemicals used in the study are shown in table 1. All chemicals were used without further purification. Distilled water was used for calibration of the speed of sound apparatus. The speed of sound measurements were carried out in a modified version of the high pressure equilibrium apparatus described in Rocha et al. [10]. The main modification was made in the pressure cell.

Density at high pressures

From density (ρ) at atmospheric pressure and speed of sound (c) at high pressures, a computational routine based on a modification of the methodology proposed by Daridon et al. [14] and González-Salgado et al. [15] was written to evaluate the density at high pressures. The method is based on the Newton–Laplace equation [16], [17], which relates speed of sound, isentropic compressibility (k_S) and density (equation (1)). $k_{S} = \frac{1}{ρ c^{2}} .$

The thermodynamic relation which correlates k_S to the isothermal

Results and discussion

The speed of sound measuring system and procedure were evaluated reproducing data from literature for pure n-hexadecane [22] at temperatures of (313.15 and 333.15) K and pressures of (0.1, 5, 10, 15, 20 and 25) MPa. The deviations (literature minus our data) were calculated for speed of sound and density and results are presented in figure 2. According with the results presented in Fig. 2(a), the deviations between our data and those presented by Ye et al. [22] are lower than the expanded

Conclusions

In this paper we have experimentally determined density at atmospheric pressure and speed of sound at atmospheric and high pressures for the binary systems {tetralin (1) + n-decane (2)} and {tetralin (1) + n-hexadecane (2)}. High pressure densities were calculated as pseudo-experimental data. Data are reported at T = (313.15, 323.15 and 333.15) K. In order to analyze the experimental results, we have calculated the excess molar volume and excess isentropic compressibility over the temperature,

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Experimental high pressure speed of sound and density of (tetralin + n-decane) and (tetralin + n-hexadecane) systems and thermodynamic modeling

Highlights

Abstract

Introduction

Section snippets

Experimental section

Density at high pressures

Results and discussion

Conclusions

J. Chem. Thermodyn.

Fluid Phase Equilib.

J. Chem. Thermodyn.

J. Supercrit. Fluids

J. Chem. Thermodyn.

J. Chem. Thermodyn.

J. Chem. Thermodyn.

J. Chem. Thermodyn.

J. Chem. Thermodyn.

Physica

Characterization and Properties of Petroleum Fractions

Int. J. Thermophys.

J. Chem. Eng. Data

Nature

J. Chem. Eng. Data

Molecular Thermodynamics of Fluid-Phase Equilibria

J. Thermodyn.