Separation of isopropyl acetate + isopropanol azeotropic mixture using ionic liquids with acetate anion as entrainers
Introduction
Isopropanol is an important industrial raw material, and has been used in many areas such as pharmaceutical, pesticides, paints, and so forth. Moreover, isopropanol can replace ethanol due to its low synthesis cost [[1], [2], [3]]. Isopropyl acetate has been widely employed as solvent and extractant in coating and ink industry. In addition, isopropyl acetate is an important solvent for making flavors and spices due to its unique fragrance [4,5].
Isopropyl acetate is manufactured through esterification reaction between isopropanol and acetic acid in industrial [6,7]. In this process, the separation of isopropanol and isopropyl acetate is necessary in order to obtain the target product isopropyl acetate with high purity and to recycle isopropyl alcohol. However, it is difficult to effectively separate the mixture of isopropyl acetate and isopropanol by a conventional distillation method due to the minimum-boiling azeotrope formed at 101.3 kPa. In recent years, extractive distillation process is widely used to separate such mixtures because of its high separation efficiency [[8], [9], [10], [11]]. Selecting a highly effective entrainer is the core of extractive distillation. Up to date, organic solvents [12,13] and inorganic salts [14] have been extensively employed in extractive distillation process as entrainers, but these entrainers are not optimal due to environmental pollution of organic solvents and equipment corrosion and pipeline blockage induced by inorganic salts. Therefore, developing an optimal entrainer is urgent.
In recent years, ionic liquids (ILs) have become the outstanding alternatives to conventional organic solvents and inorganic salts due to their merits of negligible vapor pressure, high thermal chemical stability and outstanding design ability, being liquid at room temperature [[15], [16], [17]]. Moreover, Ionic liquids have been widely employed as entrainers to separate the alcohol-ester azeotrope [[18], [19], [20]]. In terms of the isopropyl acetate and isopropanol azeotrope system, Alfonsina et al. [21,22] investigated the effects of two ionic liquids, namely 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([BMIM][NTf2]) and 1-octyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([OMIM][NTf2], on the VLE behavior of isopropyl acetate and isopropanol at 101.32 kPa, and correlated the VLE data with NRTL, Wilson, and UNIQUAC equations.
In this work, [HMIM][Ac], [OMIM][Ac] and [DMIM][Ac] were utilized to separate the isopropyl acetate and isopropanol system as entrainers and the VLE data were determined at 101.3 kPa. Then, the influence of the structures of ILs on the vapor-liquid phase equilibrium behavior of isopropyl acetate and isopropanol system was analyzed. Finally, the experimental VLE data for the binary system (isopropyl acetate and isopropanol) and the ternary systems containing ILs were correlated by the NRTL model.
Section snippets
Materials
Analytical grade isopropyl acetate and isopropanol were both supplied by Sinopharm Group. No impurities were measured with gas chromatography (model 7890 A, Agilent Technologies), thus they were used directly without further purification. [HMIM][Ac], [OMIM][Ac] and [DMIM][Ac] (YuLu Fine Chemical) were desiccated at 353 K for 24 h with Vacuum drying oven (DZF-6020) prior to use due to their hygroscopic characteristic. The water contents of the three ILs after purification detected by Karl Fisher
Experimental data
The isobaric VLE data for isopropyl acetate and isopropanol system were determined at 101.3 kPa, and compared with the reported data [22,24]. In order to inspect the property of our apparatus, the VLE data of binary system are listed in Table 2, where x1 and y1 are the mole fraction of isopropyl acetate in liquid and vapor phase, respectively. γi is the activity coefficient of component i, T is the system temperture. The comparison diagram is shown in Fig. 1. It can be seen that the
Conclusions
The isobaric vapor-liquid equilibrium data for the ternary systems of isopropyl acetate + isopropanol containing [HMIM][Ac] or [OMIM][Ac] or [DMIM][Ac] were gauged at 101.3 kPa, which indicated that all these ILs could enhance the relative volatility of isopropyl acetate to isopropanol and thereby eliminate the azeotropic point with a specific amount of IL. The separation effect of ILs follows this order: [DMIM][Ac] < [OMIM][Ac] < [HMIM][Ac]. The experimental results agreed well with the NRTL
Acknowledgments
This work is financially supported by National Science Foundation of China (Project No. 21076126), National Science Foundation of China (Project No. 21576166), and Liaoning Province Science Foundation of China (Project No. 2014020140).
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