Vapour–liquid equilibrium and extractive distillation for separation of azeotrope isopropyl alcohol and diisopropyl ether
Introduction
Isopropyl alcohol (IPA) is an important chemical, which is widely applied as good solvent and raw material for preparation of pharmaceuticals [1], [2], [3], [4]. Generally, isopropyl alcohol can be produced by hydration of propylene catalysed by acids [5]. During the production, diisopropyl ether (DIPE) is obtained as a byproduct, which can be used as a gasoline additive and as a solvent to extract nicotine in tobacco production [6], [7], [8], [9]. Therefore, it is of significance to separate IPA and DIPE from the reaction product. Since IPA and DIPE can form a homogeneous azeotrope at atmospheric pressure, it is difficult to separate such an azeotrope by conventional distillation. Recently, some special distillation processes, such as pressure-swing distillation and extractive distillation are adopted to separate azeotropic mixture or close boiling mixture [10].
Luo et al. explored the possibility to separate IPA and DIPE by pressure-swing distillation and extractive distillation and made a comparison [11]. In their work, the extractive distillation process shows better controllability compared with the pressure-swing distillation in maintaining the purities of IPA and DIPE with the feed flow rate disturbances, where 2-methoxyethanol was selected as extractive solvent. In this work, the extractive distillation was adopted to separate the azeotrope IPA and DIPE. Based on the extractive solvent selection criteria proposed by Gmehling and Möllmann [12], 2-ethoxyethanol and butyl acetate were selected as the extractive solvent candidates.
Up to now, the isobaric vapour–liquid equilibrium (VLE) data for the system IPA and DIPE at atmospheric pressure have been reported by Lladosa [13] and Arce [14]. Villamañãn [15] and Chamorro [16] reported the VLE data for IPA and DIPE at different pressures. By retrieving from the NIST [17] and Dortmund Data Bank [18], the isobaric VLE data for the binary systems of (IPA + 2-ethoxyethanol), (IPA + butyl acetate), (DIPE + 2-ethoxyethanol) and (DIPE + butyl acetate) have not been found.
Therefore, in this work, the isobaric VLE data for the systems (IPA + 2-ethoxyethanol), (IPA + butyl acetate), (DIPE + 2-ethoxyethanol) and (DIPE + butyl acetate) were measured at 101.3 kPa. The thermodynamic consistency of the experimental data was validated by the Herington test [19] and van Ness test [20]. The NRTL [21], UNIQUAC [22] and Wilson [23] activity coefficient models were adopted to correlate the VLE data. Based on the above, a conceptual extractive distillation process is proposed to separate the azeotrope of IPA and DIPE.
Section snippets
Chemicals
Analytical reagents IPA, DIPE, 2-ethoxyethanol and butyl acetate were purchased commercially. The purities of the reagents were checked by GC, and the reagents were used directly. The boiling temperature of the reagents were measured and compared with the literature data as listed in Table 1. The detailed information of the reagents is presented in Table 1.
Apparatus and procedure
The isobaric VLE measurements for the systems (IPA + 2-ethoxyethanol), (IPA + butyl acetate), (DIPE + 2-ethoxyethanol) and (DIPE + butyl
Validation of the apparatus
To validate the VLE measurement apparatus, the VLE data for the system {DIPE (1) + IPA (2)} were measured at pressure of 101.3 kPa, which are listed in Table 2. The measured VLE results were compared with the literature data reported by Lladosa et al. [13], Arce et al. [14], Miller et al. [41] and Zhang et al. [30], which are plotted in Fig. 1. As shown in Fig. 1, the measured VLE data agree with the literature data.
Experimental results
The isobaric VLE data for the binary systems for (IPA + 2-ethoxyethanol),
Effects of extractive solvent
Generally, the relative volatility (α12) is used to examine the suitability of the solvent and it is defined as follows [48]:where xi and yi represent the equilibrium mole fraction of component i in the liquid phase and the vapour phase, respectively.
The relative volatility diagram for the systems is presented in Fig. 8. As shown in Fig. 8, the values of relative volatility for the systems (IPA + 2-ethoxyethanol), (IPA + butyl acetate), (DIPE + 2-ethoxyethanol) and (DIPE + butyl
Conclusions
The isobaric VLE data for the systems of (IPA + 2-ethoxyethanol), (IPA + butyl acetate), (DIPE + 2-ethoxyethanol) and (DIPE + butyl acetate) were measured at 101.3 kPa. The Herington and van Ness consistency methods were used to check the thermodynamic consistency for the experimental data. Meanwhile, the NRTL, UNIQUAC and Wilson models were applied to correlate the measured VLE values, and the binary parameter of the thermodynamic models was regressed. The RMSD values of the vapour-phase
Acknowledgements
This work was financially supported by the Shandong Provincial Key Research & Development Project (2018GGX107001), the National Natural Science Foundation of China (Grant 21776145) and Scientific Research Foundation of Shandong University of Science and Technology for Recruited Talents.
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