Elsevier

Fluid Phase Equilibria

Volume 309, Issue 1, 15 October 2011, Pages 102-107
Fluid Phase Equilibria

Separation of propylbenzene and n-alkanes from their mixtures using 4-methyl-N-butylpyridinium tetrafluoroborate as an ionic solvent at several temperatures

https://doi.org/10.1016/j.fluid.2011.06.036Get rights and content

Abstract

Liquid–liquid extraction is the most common method for separation of aromatics from their mixtures with n-alkanes hydrocarbons. An ionic liquid (IL), 4-methyl-N-butylpyridinium tetrafluoroborate [(mebupy)(BF4)], was evaluated as solvent for this separation. Liquid equilibria (LLE) for 2 ternary systems comprising tetradecane, or hexadecane + propylbenzene + [(mebupy)(BF4)] were measured over a temperature range of 313–333 K and atmospheric pressure. The reliability of the experimental data was evaluated using the Othmer–Tobias correlation. The effect of temperature, n-alkane chain length and solvent to feed ratio upon solubility, selectivity, and distribution coefficient were investigated experimentally. In addition, the experimental results were regressed to estimate the interaction parameters between each of the 3 pairs of components for the UNIQUAC and the NRTL models as a function of temperature. Both models satisfactorily correlate the experimental data, however the UNIQUAC fit was slightly better than that obtained with the NRTL model.

Highlights

► 4-Methyl-N-butylpyridinium tetrafluoroborate [(mebupy)(BF4)] was evaluated as an ionic solvent for the separation of aromatics from their mixtures with n-alkanes hydrocarbons. ► The reliability of the experimentally measured tie line data can be ascertained by applying the Othmer–Tobias correlation. ► The effect of temperature, n-alkane chain length and solvent to feed ratio upon solubility, selectivity, and distribution coefficient were investigated experimentally. ► The UNIQUAC and the NRTL models as a function of temperature satisfactorily correlate the experimental data.

Introduction

The separation of aromatic and aliphatic compounds from their mixtures is an important goal in chemical operations that produce both types of compounds. On the other hand, smoke point of kerosene, cetane index of diesel, and viscosity index of lubricating oil can be improved by removing aromatic hydrocarbons. Ternary phase equilibrium data are essential to the proper understanding of the solvent extraction processes.

Over the past few years, research about ionic liquids (ILs) has increased greatly, mainly in 2 directions: as reaction media and as a solvent for separation processes. Ionic liquids properties, such as a negligible vapour pressure and stability at high temperatures allow them to substitute classic organic solvents with improving performance and less damage to the environment [1], [2], [3].

The knowledge of the liquid–liquid equilibria (LLE) for the ternary systems (aliphatic hydrocarbons + aromatic hydrocarbons + ILs) is essential to evaluate the feasibility of using ILs as extractive solvents in the separation of aromatic and aliphatic hydrocarbons [4], [5], [6], [7], [8], [9], [10], [11], [12], [13], [14], [15], [16].

The 4-methyl-N-butylpyridinium tetrafluoroborate [(mebupy)(BF4)] has been one of the few ILs that has shown both higher selectivity and extractive capacity than those of sulfolane for the extraction of aromatic hydrocarbons [1]. Nevertheless, LLE data are still quite scarce for systems containing ionic liquids. Currently, there are only a few experimental liquid–liquid equilibrium data have been published for [(mebupy)(BF4)] + aromatic + n-aliphatic (C5–C9) and hardly any for systems containing carbon number greater than nine for the aliphatic and/or aromatics [1], [3], [17], [18], [19].

This article is a continuation of our study on the liquid–liquid phase equilibria for dearomatization of Kuwait middle distilled fraction [20], [21]. Our interest in IL is focused on providing experimental LLE data. The purpose of this work is to study LLE of 2 ternary systems; system-I {tetradecane (1) + propylbenzene (2) + [(mebupy)(BF4)] (3)}, and system-II {hexadecane (1) + propylbenzene (2) + [(mebupy)(BF4)] (3)}. The LLE data for the studied ternary systems were measured at 313, 323, and 333 K and atmospheric pressure. The reliability of the experimentally measured tie line data was ascertained by the Othmer–Tobias correlation [22], and the distribution coefficient as well as the selectivity was calculated from these data. Finally, the UNIQUAC and the NRTL models [23], [24] were used to correlate our experimental data.

Section snippets

Chemicals

The [(mebupy)(BF4)] and propylbenzene were stored under 4 nm molecular sieve. The purities of the n-alkanes and propylbenzene were determined by gas chromatography. All chemicals were used without further purification. The purities and refractive indices of all chemicals used in this study are presented in Table 1.

Apparatus and procedure

The experimental apparatus used for extraction consists of a 60 mL glass cells with a water jacket in order to maintain a constant temperature. The temperature was controlled with an

Experimental data

The measured equilibrium mole fractions over a temperature range 313–333 K for the ternary systems; I and II are reported in Table 2, Table 3 respectively. As shown in these tables, the temperature has no effect on the solubility of [(mebupy)(BF4)] in n-alkane rich phase, while it has a little effect upon the solubility of n-alkane in ionic solvent rich phase. On the other hand, the concentration of propylbenzene has no effect on the solubility of [(mebupy)(BF4)] in n-alkane rich phase, while it

Conclusions

An experimental investigation of equilibrium behavior of liquid–liquid, tetradecane, or hexadecane + propylbenzene + [(mebupy)(BF4)] ternary systems were carried out at temperatures of 313 to 333 K and at atmospheric pressure. While the temperature has no effect on the solubility of [(mebupy)(BF4)] in n-alkane rich phase increases, it has a little effect upon the solubility of n-alkane in ionic solvent rich phase. The solubility of n-alkane in the ionic solvent rich phase increased as the

Acknowledgements

The authors thank the Public Authority for Applied Education and Training (PAAET-TS-08-012) for the financial support of this work.

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