Liquid–liquid extraction of toluene from alkane with pyridinium based ionic liquid ([BPy][NO3] and [HPy][NO3]) at 298.15 K and atmospheric pressure

doi:10.1016/j.jct.2016.07.030

The Journal of Chemical Thermodynamics

Volume 102, November 2016, Pages 316-321

https://doi.org/10.1016/j.jct.2016.07.030 Get rights and content

Highlights

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Extraction of toluene from alkane with pyridinium based ionic liquid was studied.
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The ionic liquids [BPy][NO₃] and [HPy][NO₃] were used.
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The effect of alkane chain length on selectivity of toluene was evaluated.
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The effect of alkyl chain length of ionic liquids on toluene selectivity was investigated.
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The experimental data were correlated with the NRTL model.

Abstract

The focus of this paper is to study the liquid−liquid extraction process for the separation of toluene from alkane employing the ionic liquids N-butylpyridinium nitrate, [BPy][NO₃], and N-hexylpyridinium nitrate, [HPy][NO₃], as a new solvents. New experimental data for the ternary systems of {[BPy][NO₃] (1) + heptane, or octane, or decane (2) + toluene (3)} and {[HPy][NO₃] (1) + heptane, or octane, or decane (2) + toluene (3)} at T = 298.15 K and atmospheric pressure are reported. The Othmer-Tobias and Hand correlation are examined to check the reliability of the experimental LLE data. The toluene distribution ratios and selectivity were calculated form the experimental data. The selectivity values are higher than unity which indicates the ILs, [BPy][NO₃] and [HPy][NO₃], used in this work are potential solvents to separate toluene from alkane. Besides, the effect of the alkane chain length in the selectivity values was evaluated. In addition, the result of the NRTL thermodynamic modeling shows, the experimental data were satisfactorily correlated.

Introduction

The extraction or separation of aromatic hydrocarbons from alkanes by liquid–liquid extraction is commonly performed in the petrochemical industry. In liquid–liquid extraction processes, environmentally unfriendly solvents such as sulfolane, N-methyl pyrrolidone (NMP), N-formyl morpholine (NFM) and ethylene glycol or combinations of solvents are used for the extraction of aromatic compounds [1], [2], [3], [4], [5], [6], [7], [8], [9]. However, these classic solvents are basically toxic, volatile, flammable and crucial to be recycled. In the past decade, ionic liquids (ILs) were suggested as an environmentally friendly alternative to replace classical solvent for separation processes especially liquid extraction [10]. Because these solvents have unique properties like, negligible vapor pressure, non-flammability, easy to recycle and excellent solubility for organic and inorganic substances [11].

Numerous researches concerning separation of toluene from aliphatic hydrocarbons using ILs have been published [12], [13], [14], [15], [16], [17], [18], [19], [20], [21], [22], [23], [24], [25], [26], but most of the works were performed using 1-alkyl-3-methylimidazolium based ionic liquids. The purpose of this study is to investigate the potential of pyridinium based ionic liquids for separation of toluene from alkanes.

In this research, which is part of our ongoing work on the extraction of aromatic from their mixtures with alkane using ILs [14], [27], [28], [29], we analyzed the suitability of the ILs N-butyl pyridinium nitrate, [BPy][NO₃], and N-hexylpyridinium nitrate, [HPy][NO₃], as a new solvent in the ternary mixtures {[BPy][NO₃] (1) + heptane, or octane, or decane (2) + toluene (3)} and {[HPy][NO₃] (1) + heptane, or octane, or decane (2) + toluene (3)} at T = 298.15 K and atmospheric pressure. From these experimental results, the toluene distribution ratio (β) and the selectivity (S) were calculated and compared with data from other ionic liquids. The reliability of the experimental data was ascertained by applying the Othmer-Tobias [30] and Hand [31] equations. Finally, the non-random two liquid (NRTL) model [32] was used to correlate the experimental data for all studied ternary systems.

Section snippets

Chemicals

The suppliers, molecular weight, water content and mass fraction purity of the chemicals are represented in Table 1.

The ILs used in this study were synthesized and purified in our laboratory. [BPy][NO₃] was prepared from its corresponding [BPy][Br] that was synthesized according to the method described in the literature [33]. Alkylation was carried out in an inert atmosphere and T = 338 K by use of pyridine and a little excess of 1-Bromobutane without addition of solvent [33]. The desired [BPy][NO₃

Experimental data

The experimental data for the ternary system of {[BPy][NO₃] (1) + heptane, or octane, or decane (2) + toluene (3)} and {[HPy][NO₃] (1) + heptane, or octane, or decane (2) + toluene (3)} at T = 298.15 K are given in Table 2, Table 3. The corresponding triangular diagrams for each system in mole fraction, are schemed in Fig. 1. As the figure shows, toluene is more soluble in the tested ILs than alkane that indicates the ionic liquids used in this work are potential solvents for the separation of toluene

Conclusions

In order to evaluate the potential of pyridinium based ionic liquids for separation of toluene from alkanes, LLE data for the ternary mixtures of {[BPy][NO₃] (1) + heptane, or octane, or decane (2) + toluene (3)} and {[HPy][NO₃] (1) + heptane, or octane, or decane (2) + toluene (3)} were determined at T = 298.15 K and atmospheric pressure. The Othmer–Tobias and Hand equation were applied to test the reliability of the experimental LLE data and a good accuracy was observed. The ability of [BPy][NO₃] and

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