Heterogeneous azeotropic distillation — a NRTL process flowsheet
An n-hexane entrainer carries water overhead as a ternary heteroazeotrope; the condensed overhead splits in a three-phase flash into an organic layer and an aqueous layer, while dry ethanol leaves in the bottoms — the three-phase separation ordinary distillation cannot do.
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- Rigorous NRTL thermodynamics, solved by the same engine every simulation runs on.
- 2 unit operations modeled: COL, COND.
- Focus areas: Azeotropic, Three-phase, Decanter, Entrainer.
- Thermodynamics
- NRTL
- Components
- ethanol, water, n_hexane
- Unit operations
- COLCOND
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("heterogeneous-azeotropic-distillation")
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
Ethanol-water-benzene column (multiplicity study)
The ethanol/water/benzene heteroazeotropic column — one of the most-studied systems in distillation modeling for exhibiting multiple steady states at the same specifications (Magnussen et al. 1979; Prokopakis & Seider, AIChE J. 29, 49, 1983; Venkataraman & Lucia, Comput. Chem. Eng. 12, 55, 1988). Benzene entrains water overhead as a heteroazeotrope, decanted into organic/aqueous layers, leaving dry ethanol in the bottoms. This flowsheet reports the single steady state the MaximaLabs solver converges to from its initial guess — it does not sweep initial guesses to map the full multiplicity map the cited studies performed.
Dilute acetic acid recovery by extractive distillation
Recovering acetic acid from a dilute aqueous stream (e.g. cellulose acetate or terephthalic acid plant wastewater) using diisobutyl ketone (DIBK) as an extractive entrainer. Because acetic acid and water form no azeotrope but have a relative volatility that flattens toward 1 as the mixture concentrates, straight distillation needs an impractically tall column and heavy reboil duty; the entrainer raises water's relative volatility so the extractive column takes water overhead in far fewer stages, and a second column then strips the entrainer from the acid bottoms for recycle.
Butanol/water separation via LLE-assisted distillation
Butanol and water form a heterogeneous azeotrope: overhead vapor condenses into two liquid phases (a butanol-rich organic layer and a water-rich aqueous layer). A decanter splits the condensed reflux by liquid-liquid equilibrium, returning the water-rich phase to strip more butanol while the organic phase is drawn as a near-pure butanol product — the phase split does the separating work an ordinary VLE column can't past the azeotrope. Luyben et al., Energy Fuels 2008, 22, 4249.
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.
Polymerization reactor comparison: CSTR cascade vs. tubular (PFR)
The same monomer feed, split 50/50 into two trains at equal total reactor volume: a 3-stage CSTR cascade (each stage blending its own new polymer with the MWD already carried by the stream from the stage before it) versus a single tubular (PFR) reactor. Both converge to a real, different Mn/Mw/PDI — the PFR reaches higher conversion at the same total volume, but its cumulative polydispersity is measurably broader than the cascade's, because chain length drifts continuously with conversion along the tube while each CSTR stage makes its own local production under one fixed monomer concentration. See the 'Polymerization Reactors' docs page for the full reasoning.
Helium liquefaction (Linde-Hampson cycle)
A Joule-Thomson liquefaction loop: helium is compressed, aftercooled, precooled well below its ~40-51 K JT-inversion temperature, then throttled through a valve into a flash drum that draws off liquid helium while the cold vapor recycles back to the compressor suction — the same JT-cycle physics as the platform's LNG/refrigeration loops, run on a fluid whose inversion curve makes precooling mandatory before the throttle can cool it at all.