(Liquid + liquid) equilibria for (benzene + cyclohexane + dimethyl sulfoxide) system at T = (298.15 or 303.15) K: Experimental data and correlation

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Highlights

  • The highest selectivity coefficient is beyond 14 of DMSO at T = (298.15 or 303.15) K.

  • The data’s reliability is approved by the correlation of Othmer–Tobias equation.

  • NRTL model is in good agreement with the experimental data.

Abstract

(Liquid + liquid) equilibrium (LLE) data were measured experimentally at T = (298.15 or 303.15) K and atmospheric pressure for the (benzene + cyclohexane + dimethyl sulfone (DMSO)) system. The Othmer–Tobias equation was applied to verify the reliability of the data. Based on the data, the selectivity of DMSO was estimated and compared with that of ionic liquids. The highest selectivity coefficient of DMSO can reach beyond 14, which means it is able to compete with some ionic liquids and it would be a good extractant to separate benzene from cyclohexane. At the same time, the NRTL model was used to correlate the data and the results show that the model agrees on the experimental data very well.

Graphical abstract

The selectivity of DMSO, is usually high. At 25 °C and atmospheric pressure, the selectivity coefficient can reach beyond 14, which means that DMSO can compete with some ionic liquids for extracting benzene from cyclohexane. So, DMSO has large potential to separate benzene from cyclohexane as a new extractant.

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Introduction

Separating benzene from cyclohexane is very difficult. Traditional distillation cannot be used for this separation because of their close boiling points and the binary azeotrope. Therefore, azeotropic or extractive distillation is usually applied for this separation process in industry. But both of these processes are complex and high energy-consuming [1], [2], [3]. Hence it is necessary to develop an alternative separation process.

Extraction is an alternative to the conventional techniques from an economic and technical point of view [4]. Recently, because ionic liquids have low volatility and can be regenerated easily, several kinds of them are investigated to extract benzene from cyclohexane including [Mim]DBP [1], [MMim]DMP [5], [EMim] DEP [5], [BMim]MSO4 [6],[BMim]NTf2 [6], [BMim]SCN [4], [EMim]ESO4 [7], [Cn Mim]PF6 (n = 4,5,6) [8], [BMim]BF4 [4], [Bpy]BF4 [4], [BMpy]BF4 [9] and [EMpy]ESO4 [10]. The results show that ionic liquids can be good extracting solvents. But ionic liquids are difficult to be applied industrially for they are usually too expensive. So it is necessary to look for a more economical solvent for the separation. We have reported that the complex solvent consisted of N,N-dimethylformamide (DMF) + thiocyanate (potassium thiocyanate, ammonium thiocyanate or sodium thiocyanate) may be good extractant for the high selectivity and it is less costly than ionic liquids [11], [12], [13].

However, if an organic solvent can extract benzene, it may be more competitive than a complex solvent. Dimethyl sulfoxide (DMSO) is a very common solvent and in this work, (liquid + liquid) equilibrium (LLE) data are measured for (benzene + cyclohexane + DMSO) at T = (298.15 or 303.15) K and atmospheric pressure to prove that it has potential to separate benzene from cyclohexane. Also, the NRTL model is applied to correlate the LLE data and the parameters are obtained by our programmes based on artificial bee colony algorithm [14], [15].

Section snippets

Materials

The chemicals in the experiments were benzene, cyclohexane and DMSO. Benzene, cyclohexane and DMSO with a nominal minimum mass fraction of 0.995 were used, which were purchased from Tianjin Kemiou Chemical Reagent Company. Their purity was analyzed by gas chromatography (GC) and the results were listed in table 1. All chemicals were used without further purification.

Apparatus and procedures

(Liquid + liquid) equilibrium experiments were carried out in a conical flask in a thermostat controlled at T = (298.15 or 303.15) K

Experimental data and selectivity coefficients

The LLE data of (benzene + cyclohexane + DMSO) are listed in TABLE 2, TABLE 3 at T = (298.15 or 303.15) K in mass fraction. The corresponding triangular diagram are displayed in figures 1 and 2 in mole fraction.

The selectivity is important to evaluate the solvent in extraction, defined as follow:S=ω1,E/ω1,Rω2,E/ω2,R,where ω1,E and ω2,E represent the mass fraction of benzene and cyclohexane in the extract phase and ω1,R and ω2,R the raffinate phase. The selectivity coefficients are shown for

Conclusions

LLE data of the ternary system, (benzene + cyclohexane + DMSO), were obtained at T = (298.15 or 303.15) K under atmospheric pressure and the selectivity coefficients were calculated. The highest selectivity coefficient is 14.68 at T = 298.15 K and 14.06 at T = 303.15 K, which is high and close to those of some ionic liquids. Because of its high selectivity and relatively low price, DMSO has large potential to serve as a good solvent to extract benzene from cyclohexane.

The Othmer–Tobias equation is applied

Acknowledgments

The authors would appreciate the financial support of National Natural Science Foundation of China (No. 21076049), Natural Science Foundation of Heilongjiang Province of China (No. QC2013C011) and Fundamental Research Funds for the Central Universities (No. HEUCF201403013).

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