Elsevier

Fluid Phase Equilibria

Volume 492, 15 July 2019, Pages 80-87
Fluid Phase Equilibria

Separation abilities of three acetate-based ionic liquids for benzene-methanol mixture through vapor-liquid equilibrium experiment at 101.3 kPa

https://doi.org/10.1016/j.fluid.2019.03.022Get rights and content

Abstract

Three ionic liquids (ILs) with acetate anion (1-hexyl-3-methylimidazolium acetate, [HMIM][OAC]; 1-octyl-3-methylimidazolium acetate, [OMIM][OAC]; and 1-decyl-3-methylimidazolium acetate, [DMIM][OAC]) were studied as entrainers for separating the benzene-methanol binary azeotrope. Isobaric vapor-liquid equilibrium (VLE) data for the ternary systems of benzene + methanol + IL were measured at 101.3 kPa. The VLE data were well correlated by using the nonrandom two-liquid (NRTL) model. The relative volatility of benzene to methanol is enhanced with the increase in IL content. The azeotropic phenomenon of benzene-methanol mixture can be completely eliminated when IL content reaches a specific value. After the azeotropy of benzene-methanol mixture is completely eliminated, the separation ability of the three ILs follows the order [HMIM][OAC] > [OMIM][OAC] > [DMIM][OAC]. The separation abilities of the three ILs were further analyzed with the help of their σ-profiles.

Introduction

Benzene and methanol are important solvents. The mixture of benzene and methanol is common in fine chemical industries [1,2]. However, benzene and/or methanol can't be completely recovered from their waste mixture by traditional distillation method because of the formation of benzene-methanol azeotrope. A few special distillation methods have been utilized to separate the azeotrope such as azeotropic distillation, extractive distillation, and pressure swing distillation [[3], [4], [5], [6], [7], [8], [9]]. Extractive distillation is widely used because of its advantages of simple operation, high separation ability, and flexible selection of entrainer. Entrainer is the core of extractive distillation. More and more attentions are paid to the selection of entrainer [[10], [11], [12]]. Compared with the traditional entrainer (solid salt [13,14] and organic solvent [15,16]), ionic liquids (ILs) have many advantages such as stable property, negligible vapor pressure, and easy recovery [[17], [18], [19]]. In recent years, many publications have been devoted to ILs for the application as entrainer of extractive distillation [17,[19], [20], [21], [22], [23]].

In the reports on the inorganic or organic salt entrainers [1,[24], [25], [26], [27]], the benzene-methanol system could only be completely separated by LiI [27]. The separation effect of IL on the benzene + methanol mixture was investigated through a series of isobaric VLE experiments by Li Q. S et al. [2,28,29]. 1-octyl-3-methylimidazolium tetrafluoroborate ([OMIM][BF4]) showed the best salting out effect. The azeotropy was eliminated by increasing the mole concentration of [OMIM][BF4] to 0.3. The isothermal VLE data of benzene and methanol containing tetraphenylphosphonium chloride ([PH4P]Cl) IL were studied by Kurzin, A. V. et al. [30]. The azeotropy was eliminated when the concentration of [PH4P]Cl was 0.5 mol kg−1.

The purpose of this study is to obtain some useful data for the separation of the benzene-methanol mixtures. Three acetate-based ILs (1-hexyl-3-methylimidazolium acetate [HMIM][OAC], 1-octyl-3-methylimidazolium acetate [OMIM][OAC], and 1-decyl-3-methylimidazolium acetate [DMIM][OAC]) were selected by a molecular design method. The VLE data for the ternary systems of the benzene + methanol + IL were measured at 101.3 kPa. The VLE data were correlated by NRTL model. The separation abilities of the three ILs for the benzene-methanol system were analyzed.

Section snippets

Chemicals

[HMIM][OAC], [OMIM][OAC], and [DMIM][OAC] were provided by Yulu Group with claimed purity ≥99.0 (wt)%. Prior to the experiment, IL was dried at 353 K and 2 kPa for 36 h to remove the volatile compounds. The ILs were checked by liquid chromatography. Benzene and methanol were purchased from Sinopharm group with claimed purity ≥ 99.9 (wt)%. The water contents in IL, benzene, and methanol were measured by Karl Fischer titration. The specifications of all the chemicals are shown in Table 1.

Apparatus and procedure

The VLE

Binary data

To test the dependability of the equilibrium apparatus, the binary VLE data of the benzene (1) + methanol (2) mixture were measured at 101.3 kPa and are shown in Table 3 and Fig. 1. The correlated curve and the reported data [2] are also listed in Fig. 1. Where T presents the VLE temperature. The ARD between the correlated curve and the experimental data is 0.73% and that between the correlated curve and the reported data is 2.0%. In addition, the experimental data are consistent with

Conclusions

Isobaric VLE data for benzene + methanol + ILs ([HMIM][OAC], [OMIM][OAC], or [DMIM][OAC]) systems were obtained at 101.3 kPa. The relative volatility of benzene to methanol can be enhanced by rising the IL mole fraction. The minimum mole fractions of [HMIM][OAC], [OMIM][OAC] and [DMIM][OAC] needed to eliminate azeotropy are 0.145, 0.136, and 0.132 on the basis of the NRTL model. The minimum mass fractions of [HMIM][OAC], [OMIM][OAC], or [DMIM][OAC] needed to eliminate azeotropy are 0.329,

Acknowledgments

This work is financially supported by the National Science Foundation of China (Project No. 21576166), Program for Liaoning Excellent Talents in University (LR2012013) and Liaoning Province Science Foundation of China (Project No. 2014020140).

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