Ionic liquid breaks the ethanol-water azeotrope

The ethanol-water azeotrope is a wall: at 89.4 mol% ethanol the vapour and the liquid have the SAME composition, relative volatility is 1, and no number of trays gets you past it. This flowsheet walks through it by adding an involatile ionic liquid, [EMIM][BF4], which binds water preferentially and pulls the two apart. The numbers are the demonstration. NRTL puts the relative volatility at the azeotrope at 0.996 — that is the wall, computed, not asserted. Add the IL and it climbs to 2.10 at 10 mol%, 2.98 at 20%, and 3.66 at 30%. Flash the IL-laden mixture here and the vapour comes off at an ethanol:water ratio of 22.6 against the azeotrope's 8.43 — decisively across. Run the same feed with no IL and there is nothing to separate: the mixture goes straight from all-liquid to all-vapour with no useful two-phase band, which is precisely what an azeotrope means. Why an IL rather than the usual glycol entrainer (see 'anhydrous-ethanol-extractive-distillation'): an ionic liquid has effectively no vapour pressure, so it never contaminates the distillate and it regenerates by flashing rather than by a second column. Bounded, and this is why the example is a flash and not a column: the IL package models the phase behaviour — which is what decides whether an entrainer works — but omits the IL's own pure-component enthalpy, so a rigorous column energy balance is a follow-up. The separation shown here needs only the phase equilibrium. The IL also carries no molar mass in the databank, so mass-basis readouts show a dash; the mole-basis flash is exact.