Elsevier

Fluid Phase Equilibria

Volume 478, 25 December 2018, Pages 75-81
Fluid Phase Equilibria

Measurement and correlation of the isobaric vapor-liquid equilibria of methanol + methyl carbonate + Bis(trifluoromethylsulfonyl)imide-based ionic liquidsat 101.3 kPa

https://doi.org/10.1016/j.fluid.2018.09.005Get rights and content

Highlights

  • The VLE data for methanol + methyl carbonate + [BMIM][NTf2]/[HMIM][NTf2] were studied.

  • The experimental and correlated, using NRTL model, data were in good agreement.

  • Compared to other ILs, [HMIM][NTf2] had the better separation capacity.

Abstract

Isobaric vapor-liquid equilibria (VLE) for the azeotropic system of methanol + methyl carbonate and the ternary systems of methanol + methyl carbonate + 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([BMIM][NTf2]) and methanol + methyl carbonate + 1-hexyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([HMIM][NTf2]) have been obtained using an Othmer Still. Methyl carbonate could be separated from the azeotropic system with [BMIM][NTf2] and [HMIM][NTf2] due to the existence of cross-salt effect. The experimental data were in good agreement with the correlated data using the NRTL model. The model results indicated that the minimum mole fractions required for [BMIM][NTf2] and [HMIM][NTf2] to eliminate azeotropes were 0.048 and 0.043, respectively. The separation capacity of [HMIM][NTf2] was much higher than that of [BMIM][NTf2]. This work provided a general method to understand the effect of ionic liquids (ILs) on the isobaric VLE behavior of methanol + methyl carbonate, and a promising way to the industrial application of ILs in extractive distillation.

Introduction

The specific distillation is a typically utilized industrial method to solve the azeotropic issues in the separation and purification of chemical products. During the specific distillation, an appropriate entrainer plays an essential role in improving the distillation efficiency, which makes the extractive distillation more competitive than other similar methods [[1], [2], [3]]. Compared to the traditional entrainers, such as typical organic solvents, inorganic salts, and organic-inorganic hybrid mixture, ILs with designable chemical structures are environmental friendly and can be recycled in the extractive distillation with less energy-consuming [[4], [5], [6], [7], [8], [9], [10]]. Furthermore, the phase equilibrium data of ILs-based system is an important theoretical basis for extractive distillation. Therefore, the effect of ILs on the azeotropic system has been a research hotspot in the fields of ILs and extractive distillation.

The non-toxic and non-irritating methyl carbonate is extensively used as a methylation reagent to replace the carcinogenic dimethyl sulfate in organic synthesis [[11], [12], [13], [14]]. During the industrial preparation of methyl carbonate, methanolis employed as the raw reaction material. Under local atmosphere pressure, the mixture of methanol and methyl carbonate can form an azeotrope which makes the separation between methyl carbonate and methanol-methyl carbonate azeotrope difficulty by ordinary distillation.

In order to deal with this problem, many efforts have been made. Chen et al. [15,16] applied three kinds of ILs ([BMIM][DBP], [MMIM][DMP] and [EMIM][DEP]) in separating methanol + methyl carbonate system. The azeotropic point could be eliminated when the ILs molar concentration was up to 0.15 due to the existence of salt-in effect. After that, [OMIM][BF4] [17], [EMIM][OTf] [18] and [BMIM][OTf] [18] were also studied as an entrainer to separate the azeotrope. Particularly, ILs ([OMIM][BF4], [EMIM][OTf] and [BMIM][OTf]) remarkably presented a cross-salt effect. The ILs molar concentrations eliminating the azeotropic point of [BMIM][OTf] and [OMIM][BF4] were 0.10 and 0.20, respectively. However, for the [EMIM][OTf] system, the azeotropic point only moved up but not eliminated. As a consequence, ILs possesses the capacity to separate the methanol-methyl carbonate azeotrope and could be applied in the purification of methyl carbonate. It is significant to investigate the application of ILs in the separation of azeotropes and to understand the function and separation principle of ILs in the extraction distillation.

Herein, the isobaric VLE data for binary system of methanol + methyl carbonate, ternary systems of methanol + methyl carbonate + [BMIM][NTf2] and methanol + methyl carbonate + [HMIM][NTf2] were measured at 101.3 kPa. Furthermore, the effects of ILs with different concentrations and species on the thermodynamic behavior of methanol + methyl carbonate were contrasted and discussed. The experimental data are correlated with NRTL model. This work can help understand the role of ILs in the separation of methanol + methyl carbonate azeotropic system.

Section snippets

Materials

Methanol (analytical grade) and methyl carbonate (analytical grade) were supplied by Beijing Chem. Works and Tianjin Guangfu Research Institution, respectively. No impurities were detected by gas chromatography (GC), so they were used without further purification.

[BMIM][NTf2] and [HMIM][NTf2] were bought from Shanghai Chengjie Co. Ltd., China, and they were reused in a vacuum rotary evaporator for 20 h (T = 433.15 K). The purities of ILs were checked by liquid chromatography (LC) and their mass

VLE results

The experimental VLE data for methanol (1) + methyl carbonate (2) binary system are listed in Table 2. After the comparison between this experimental results and the data reported in the previous references [15,17], they are in good agreement with the previous works as illustrated in Fig. 1. In terms of molar fractions, the mean deviations of the used method and previous reports are 0.004 [15] and 0.005 [17], respectively. Therefore, these results indicate that the experimental apparatus and

Conclusions

As discussed above, the VLE data for the binary system of methanol + methyl carbonate and the ternary system of methanol + methyl carbonate + [BMIM][NTf2] and methanol + methyl carbonate + [HMIM][NTf2] were obtained under 101.3 kPa. The addition of ILs ([BMIM][NTf2] or [HMIM][NTf2]) could effectively separate methyl carbonate from the azeotropic system due to the existence of a cross-salt effect. The azeotropic point could be eliminated when the ILs mole fraction was 0.05, which has great

Acknowledgements

This work was supported by the Fundamental Research Funds for the Central Universities (No. 2-9-2017-145).

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