Using Ionic Liquids To Break the Ethanol−Ethyl Acetate Azeotrope

Abstract

Systems that form azeotropes or have relative volatilities close to 1.0 represent very little energy and capital intensive separations. Ionic liquids (ILs) can serve as nonvolatile entrainers to break azeotropes and enable a more energy efficient and environmentally friendly process. Here, six ILs have been investigated for their ability to break the ethanol + ethyl acetate azeotrope at 313.15 K. Three of the ILs investigated, 1-ethyl-3-methylimidazolium methanesulfonate [emim][MeSO3], 1-ethyl-3-methyl-imidazolium methylsulfate [emim][MeSO4], and 1-butyl-3-methyl-imidazolium trifluoromethanesulfonate [bmim]- [CF3SO3] are excellent entrainer candidates. In fact, the ethanol + ethyl acetate azeotrope can be broken over the entire composition range by adding as little as 2.5 mol percent of either [emim][MeSO3] or [emim][MeSO4] to the binary organic mixture, which is less IL than what is needed to break any azeotropic system discussed in literature to date. The other three ILs, 1-ethyl-3-methyl-imidazolium bis(trifluoromethylsulfonyl)imide [emim][Tf2N], 1- hexyl-3-methyl-imidazolium bis(trifluoromethylsulfonyl)imide [hmim][Tf2N], and 1-butyl-1- methyl-pyrrolidinium bis(trifluoromethylsulfonyl)imide [bmpyrr][Tf2N], are limited in their ability to break this azeotrope. The difference between these two groups correlates with the infinite dilution activity coefficients of the ethyl acetate and ethanol in each of the ILs. Both polarity and hydrogen bonding are important in determining the preferential affinity of the ethanol for the ILs, which raises the ethyl acetate/ethanol relative volatility. In addition, the experimental binary and ternary vapor−liquid equilibrium data have been fit to the Non Random Two Liquid (NRTL) activity coefficient model, which is able to predict and correlate the amount of IL needed to break the azeotrope in these ternary vapor− liquid equilibrium systems.