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-methyl-imidazolium 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.

Thermodynamic Assessment of the Suitability of the Limiting Selectivity to Screen Ionic Liquid Entrainers for Homogeneous Extractive Distillation Processes

“…In Table 2, we compare the calculated minimum mole frac of IL (x 3 ) needed to break the azeotrope using reference calculations to that using Equation (17). We again find the values are in excellent agreement.…”

“…Following our discussion (Equations (8) and (17)), for a binary system that exhibits a minimum boiling azeotrope, the addition of IL will break the azeotrope if…”

“…For all of the systems studied, we use binary interaction parameters for the NRTL (non-random, two-liquid) equation provided in the original publications [28]. All of the binary interaction parameters for the binary systems were fit directly to binary vapor/liquid equilibrium data, and the parameters involving the ionic liquids were fit to ternary vapor/liquid equilibrium data [11][12][13][14][15][16][17]. All of the vapor pressures at the temperatures of interest were taken from ref.…”

“…Room temperature ionic liquids (ILs) have received tremendous attention for use as replacement solvents in a wide range of industrial processes [8,9], and are particularly well-suited to use an entrainers in extractive distillation processes [5,[10][11][12][13][14][15][16][17][18][19][20][21][22][23]. The cation and anion may be changed and modified to tune their chemical and physical properties, and can thus be used to tune S. Additionally, due to their ionic nature, ILs have negligible vapor pressures facilitating recovery.…”

“…As a result, in the present study, we investigate the ability to use S ∞ (or limiting activity coefficients) to screen ILs as entrainer candidates for homogeneous extractive distillation processes. We analyze four recently studied systems which all exhibit a minimum boiling azeotrope: ethanol(1)/water(2), tetrahydrofuran(1)/ethanol(2), methyl acetate(1)/methanol(2) and ethyl acetate(1)/ethanol(2) [11][12][13][14][15][16][17]. For all of the systems studied, we use binary interaction parameters for the NRTL (non-random, two-liquid) equation provided in the original publications, allowing us to calculate both composition dependent and limiting activity coefficients for the MVC and LVC in the ternary mixture formed by the addition of IL [28].…”