Liquid–liquid equilibrium for binary and ternary systems containing di-isopropyl ether (DIPE) and an imidazolium-based ionic liquid at different temperatures
Introduction
Oxygenates raise gasoline combustion temperatures and can improve overall engine efficiencies. They also lower the levels of carbon monoxide and unburned hydrocarbons in auto exhaust. Methyl tert-butyl ether (MTBE) by far dominates the market for fuel oxygenates. However, heavier ethers have received increased interest due to an insufficient supply of MBTE and the concern over groundwater contamination. Di-isopropyl ether (DIPE), ethyl tert-butyl ether (ETBE), and tert-amyl methyl ether (TAME) could all be suitable gasoline additives [1].
Phase equilibriums and mixture properties must be examined to design an effective DIPE synthesis and separation process and properly analyze DIPE as a fuel additive. Thus, we have systematically reported the phase equilibriums and mixture properties for oxygenated ether compounds inclusive DIPE [2], [3]. DIPE is gained by a reaction of propylene with isopropyl alcohol, which is initially produced by hydration of propylene. The ether purification involves extraction of alcohol with water. Arce et al. reported therefore ternary phase equilibria for DIPE with alcohol and water [4], [5].
Ionic liquids are an unusual class of nonvolatile chemical compounds with interesting properties. They are therefore studied in several fields. Ionic liquids possess high ionic conductivity, electrochemical stability, and variable physical and chemical properties. They typically contain large organic cations and smaller inorganic or organic anions. The lattice energy of their crystal structure is therefore generally reduced and results in a lower melting point. This is the reason why ionic liquids usually remain liquid at room temperature. Unlike molecular liquids, ionic liquids have negligible vapor pressures at room temperature and high solvating capacity for organic, inorganic, and organometallic compounds. Thus, they can effectively be used as environmentally friendly solvents in liquid–liquid extractions and can be designed for particular applications [6], [7]. However, the solubility between ionic liquids and a second liquid phase is still unknown. Thus, new data concerning phase equilibrium and mixture properties would be of great use to the field of ionic liquids.
In this paper, we present data concerning the liquid–liquid equilibriums (LLE) of two binary systems {di-isopropyl ether (DIPE) + 1-ethyl-3-methylimidazolium-ethylsulfate (EMISE)} and {DIPE + 1-butyl-3-methylimidazolium-tetrafluoroborate ([Bmim][BF4])} and six ternary systems {DIPE + water + EMISE} and {DIPE + water + [Bmim][BF4]} at several temperatures: 293.15 K, 303.15 K and 313.15 K. These data were determined at atmospheric pressure using stirred and thermo-regulated cells. Data for the binary and ternary systems were correlated using two activity coefficient models: NRTL and UNIQUAC. In addition, the extraction properties (distribution coefficients and selectivity) of the ionic liquids EMISE and [Bmim][BF4] for water in a DIPE phase were measured.
Section snippets
Materials
Commercial grade of di-isopropyl ether (DIPE, C6H14O, M = 102.18 g mol−1, CAS-RN 108-20-3) was obtained from Aldrich, 1-ethyl-3-methylimidazolium-ethylsulfate (EMISE, C8H16N2O4S, M = 236.29 g mol−1, CAS-RN 342573-75) was obtained from Fluka Co. and 1-Butyl-3-methylimidazolium-tetrafluoroborate ([Bmim][BF4], C8H15BF4N2, M = 226.02 g mol−1, CAS-RN 174501-65-6) was supplied from CTRI Chemical Co. (Korea). Water was distilled twice in our laboratory. EMISE and [Bmim][BF4] were dried using molecular sieves
Results and discussion
The LLE data measured for the binary systems {DIPE + EMISE} and {DIPE + [Bmim][BF4]} at several temperatures (293.15 K, 298.15 K, 303.15 K, 308.15 K, 313.15 K) and atmospheric pressures are listed in Table 2. The mutual solubility curves are plotted in Fig. 1, Fig. 2. As can be seen, the solubility is enlarged in each dilute region. The solubility of DIPE in EMISE was very small (less than 0.2 mol%) over the range of tested temperatures. In contrast, the solubility of DIPE in [Bmim][BF4] was significant:
Conclusion
The LLE data for binary systems consisting of DIPE and the imidazolium-based ionic liquids EMISE and [Bmim][BF4] and for ternary systems consisting of DIPE, water, and either EMISE or [Bmim][BF4] were measured. The solubility of DIPE in EMISE or [Bmim][BF4] was negligible over the tested temperature range, while the solubility of EMISE and [Bmim][BF4] in DIPE was significant and increased with increasing temperatures. The data obtained for ternary systems were classified as Treybal's type II
Acknowledgement
This work was supported by a Korea Research Foundation Grant that was funded by the Korean Government (MOEHRD) (KRF-2008-313-D00182).
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