Ethanol dehydration (pervaporation) — a NRTL process flowsheet
A hydrophilic pervaporation membrane pulls water out of near-azeotropic ethanol — crossing the 89 mol% ethanol-water azeotrope that ordinary distillation cannot. Permeate is ~95% water; the retentate is dried past the azeotrope.
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- Rigorous NRTL thermodynamics, solved by the same engine every simulation runs on.
- 1 unit operations modeled: PV.
- Focus areas: Pervaporation, Membrane, Azeotrope, Ethanol dehydration.
- Verified fast convergence — a real, measured solve time, not an estimate.
- Thermodynamics
- NRTL
- Components
- ethanol, water
- Unit operations
- PV
Opens in a new tab, loaded straight into the app — no setup.
Read the step-by-step guideReproduce this exact result from Python — the real client.get_example() → run_and_wait() path, not a mockup.
from flowsim.sdk import FlowSimClient
client = FlowSimClient()
example = client.get_example("ethanol-dehydration-pervaporation")
sim = client.create_simulation(example["title"], example["flowsheet"])
result = client.run_and_wait(sim["id"])
print(result["status"]) # "converged"
streams = client.streams(sim["id"])Related models
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.
Ethanol–water distillation
An 8-stage column concentrating ethanol overhead toward the azeotrope (the headline demo).
Pressure-swing ethanol dehydration (Gᴱ mixing rule)
Ethanol–water is the classic azeotrope, and pressure-swing distillation breaks it without an entrainer: the azeotrope moves with pressure, so a low-pressure column and a high-pressure column pass each other's azeotropic distillate and each recovers a pure product. The whole process only works if the property package tracks that shift — which is exactly where a conventional package choice falls between two chairs. This flowsheet runs the high-pressure column at 15 bar on pr-mhv1: Peng-Robinson with an MHV1 excess-Gibbs mixing rule, so the cubic equation of state gets its attraction parameter from NRTL's excess Gibbs energy instead of from a single binary interaction constant. Switch the thermo package (Solver menu) and compare the predicted azeotrope: | package | 1 atm | 15 bar | valid at 15 bar? | |---|---|---|---| | NRTL | 0.891 | 0.802 | no — γ-φ is a low-pressure formulation (~10 bar) | | Peng-Robinson (kij) | 0.586 | 0.613 | yes, but a kij cannot represent this azeotrope | | pr-mhv1 | 0.949 | 0.798 | yes | (mole fraction ethanol; the repo's DECHEMA-validated 1 atm anchor is 0.894.) At 15 bar pr-mhv1 lands within 0.005 of NRTL while remaining a genuine equation of state, whereas plain Peng-Robinson is off by ~0.19 and puts the azeotrope in the wrong place entirely. Selecting nrtl here also trips the applicability guard, which warns that the activity model is past its pressure ceiling and names the fix. The flowsheet demonstrates the mechanism on itself. Drop the column pressure to 1 atm and re-run, changing nothing else: the solve fails with SPEC_THERMODYNAMICALLY_IMPOSSIBLE, because at atmospheric pressure the requested bottoms purity sits beyond the azeotrope and no column can reach it. At 15 bar the same specification converges and the bottoms leaves at x_EtOH ≈ 0.924 — past the atmospheric azeotrope of 0.894, which is precisely the composition an atmospheric column cannot cross.
Extractive distillation (ethanol/water with ethylene glycol)
Near-azeotropic ethanol/water (85 mol% ethanol) can't be pushed past the 89 mol% azeotrope by ordinary distillation. A heavy, high-boiling entrainer (ethylene glycol) fed near the top of the column raises water's relative volatility enough to pull overhead ethanol past the azeotrope in one pass; a second column then strips water overhead from the glycol, regenerating it as the bottoms product. The classic extractive-distillation textbook case (Luyben, Ind. Eng. Chem. Res. 2006, 45, 4625).
Pressure-swing azeotropic distillation (methanol/acetone)
Methanol and acetone form a minimum-boiling azeotrope whose composition shifts noticeably with pressure — enough that two ordinary columns run at different pressures can cross the azeotrope without an entrainer. Column 1 (low pressure) takes pure acetone bottoms and a near-azeotropic overhead; that overhead is compressed into Column 2 (high pressure), whose new, shifted azeotrope composition lets pure methanol come off the bottoms (the recycle of Column 2's now off-azeotrope overhead back to Column 1 is reported as a product here rather than closed, the same open-loop simplification the acetone-water example already uses). Luyben, Ind. Eng. Chem. Res. 2008, 47, 2696.
Waste solvent recovery — extractive distillation (IPA/water)
A pharmaceutical waste isopropanol/water stream (near the ~68 mol% IPA azeotrope) is fed to an extractive column with a high-boiling entrainer feeding in a few stages above it; a second column strips the entrainer back out of the bottoms for reuse.