Elsevier

Fluid Phase Equilibria

Volume 383, 15 December 2014, Pages 182-187
Fluid Phase Equilibria

Separation of acetone and methanol azeotropic system using ionic liquid as entrainer

https://doi.org/10.1016/j.fluid.2014.10.011Get rights and content

Highlights

  • Capability of three ILs to break the acetone–methanol azeotrope was examined.

  • Isobaric VLE data of the acetone + methanol + IL systems was detected.

  • [EMIM][OAC] was proposed as a new entrainer to separate acetone + methanol system.

  • Ternary VLE data was well correlated by NRTL model.

  • Hydrogen bond was discussed to disclose the interaction operating between components and ionic liquid.

Abstract

In this work, three ionic liquids (ILs), namely monoethanolamine chloride ([HMEA][Cl]), monoethanolamine acetate ([HMEA][OAC]) and 1-ethyl-3-methylimidazole acetate ([EMIM][OAC]), were studied as entrainers to separate acetone + methanol azeotropic mixture by extractive distillation. Isobaric vapor liquid equilibrium of ternary systems containing ILs was investigated to examine the effect between the structure of ionic liquids and separation performance on acetone + methanol. The measurements were carried out at 101.3 kPa and the headspace chromatograph was employed to analyze the VLE data. From the experimental results, it is found that the addition of ILs can remarkably increase the separation factor (relative volatility) of acetone to methanol. The azeotropic point is pulled up and the azeotropy is even eliminated eventually. Comparison of the separation effect of ILs is that [EMIM][OAC] outperforms [HMEA][Cl] and [HMEA][OAC]. The experimental VLE data are well correlated using nonrandom two-liquid model (NRTL).

Introduction

The separation of azeotropic mixtures has conventionally been one of the most challenging tasks in industrial processes due to the fact that their separation by common distillation is almost impossible. Extractive distillation as a special distillation is the most widely used method to separate azeotropes. With the addition of a third solvent (entrainer), the relative volatility can be altered which makes the azeotropy broken. Thus, the selection of optimal entrainer is a significant step. Organic solvents [1], solid salts [2] and hyper-branched polymers [3] as traditional entrainers have been investigated before. However, the traditional entrainer comprises some disadvantages such as solvent loss, highly corrosive, difficulty in recycling, which has been a handicap for further application of extractive distillation.

Efforts to make existing separation method of extractive distillation more efficient and eco-friendly will get a boost from the use of a new class of compounds known as ILs. The addition of ILs can offer technologically and environmentally favorable alternatives to traditional entrainers in separation of organic substances. As new and potential solvents, IL has attracted much attention because of the unique chemical and physical merits, such as: no effective vapor pressure, less corrosive, high selectivity and solubility, high thermal stability and distinctive design-ability. Plenty of imidazole [4] and pyridine based [5] ILs as entrainers used in the extractive distillation have been investigated and the superiorities they displayed were uplifting.

The vapor liquid equilibrium of acetone and methanol system may be one of the most studied binary systems owing to its industrial importance and promising applications. To the best of our knowledge, Seiler et al. [6], and Kurzin et al. [7] have reported the isothermal VLE data of 1-ethyl-3-methylimidazolium tetrafluoroborate ([EMIM][BF4]) and N-butylpyridinium hexafluorophosphate ([BPY][PF6]) presented in acetone + methanol mixture at temperature of 328.15 K and 313.15 K, respectively. Meanwhile, Vincent Liebert studied the influence of two sulfate-based anion ionic liquids 1-ethyl-3-methylimidazole hydrogensulfate ([EMIM][HSO4]) and 1-ethyl-3-methylimidazolemethylsulfate ([EMIM][MeSO4]) [8] on vapor-liquid equilibrium of the system and compared the separation effect. A. Vicent Orchilles reported isobaric VLE data of ternary systems containing 1-ethyl-3-methylimidazolium dicyanamide ([EMIM][DCA]) [9], 1-butyl-3-ethylimidazolium trifluoromethanesulfonate ([beim][triflate]), 1-butyl-1-methylpyrrolidinium trifluoromethanesulfonate ([bmpyr][triflate]) [10] and 1-ethyl-3-methylimidazolium trifluoromethanesulfonate ([emim][triflate]) [11] at a pressure of 101.3 kPa. In this paper, [HMEA][Cl], [HMEA][OAC] and [EMIM][OAC] have been selected as entrainer to separate acetone + methanol azeotropic system and to determine, if any [HMEA][Cl], [HMEA][OAC] or [EMIM][OAC] are capable of breaking the azeotropy. The separation effect is compared among the three ILs to select the potential entrainer. Finally the effect of potential entrainer for separating acetone from methanol is compared with the reported effect of ILs in the previous literature.

Section snippets

Material

The ILs [HMEA][Cl], [HMEA][OAC] and [EMIM][OAC] were synthesized in our own laboratory with mass purity greater than 99% checked by liquid chromatography. Besides, the ILs were dried in a vacuum desiccator at 393 K for 48 h before the experiments. The mass fraction of water in ILs, measured by Karl Fisher titration, is less than 0.005. The volatile chemicals used in this study were acetone (Sinopharm Group, minimum Wt 99.5%) and dried methanol (Sinopharm Group, minimum Wt 99.5%). The organic

Result and discussion

In the process of extractive distillation, two indicative quantities, relative volatility (or separation factor) α12 [13] and selectivity S12 [14] are conventionally used to describe the separation effect of entrainer. The relative volatility of component 1 respect to component 2 is defined as:α12=y1/x1y2/x2where x1 (x2) and y1 (y2) are the mole fractions of component 1 and 2 in the liquid and vapor phase, respectively. That is to say, the higher the value of α12, the more effective the

Conclusions

Isobaric VLE data for the ternary systems of acetone (1) +methanol (2) containing [EMIM][OAC] (3), [HMEA][Cl] (3) or [HMEA][OAC] (3) were measured at 101.3 kPa to select a optimal IL as entrainer for the separation of acetone and methanol. From the result of the experiments, it can be seen that [EMIM][OAC] shows a greater increase on separation factor than [HMEA][Cl] and [HMEA][OAC]. The conclusion that [EMIM][OAC] has the potential as an entrainer for the separation of the system can also be

Acknowledgements

This work is financially supported by the National Science Foundation of China (Project No. 21076126), Program for Liaoning Excellent Talents in University (LR2012013) and Liaoning Province science foundation of China (Project No. 2014020140).

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