Oxidative dehydrogenation of ethane to ethylene + acetic acid (EDHOX concept) — a PENG-ROBINSON process flowsheet
Linde's EDHOX technology co-produces ethylene AND acetic acid from ethane and oxygen in one catalytic step (a proprietary mixed-metal catalyst in a multi-tubular salt-cooled reactor), with combined ethylene+acetic-acid selectivity published above 93% and the CO2 by-product of over-oxidation recovered pure (no nitrogen dilution, since the oxidant is pure O2, not air). Modeled here as three chained fixed-conversion reactors on real, exactly mass-balanced reactions: the main dehydrogenation (C2H6 + 0.5 O2 -> C2H4 + H2O), the acetic-acid co-production path (C2H6 + 1.5 O2 -> CH3COOH + H2O), and a minor full-oxidation loss path (C2H6 + 3.5 O2 -> 2 CO2 + 3 H2O) accounting for the un-selective balance -- the same 'illustrative, not fitted' posture as the naphtha cracker's furnace, since Linde's catalyst kinetics are proprietary and not published. The per-reaction conversions here are tuned to reproduce the one real published number (>93% combined selectivity: this flowsheet computes ~96%), not an assumed per-pass ethane conversion, which Linde doesn't publish. Honesty note: the acetic acid/water co-product is reported as one crude liquid stream (recovered via a simple cold knockout, ~98% of the acetic acid produced) -- the real downstream acetic-acid/water dehydration column is not modeled, matching this codebase's convention of disclosing every unmodeled downstream separation rather than implying a purity that wasn't computed.
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- Rigorous PENG-ROBINSON thermodynamics, solved by the same engine every simulation runs on.
- 4 unit operations modeled: MIX, 3× ODH COX, COOL, Knockout.
- Focus areas: EDHOX, Oxidative dehydrogenation, Ethylene, Acetic acid, CCUS.
- Thermodynamics
- PENG-ROBINSON
- Components
- ethane, ethylene, oxygen, acetic_acid, water, co2
- Unit operations
- MIX3× ODH COXCOOLKnockout
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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("edhox-oxidative-dehydrogenation")
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
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Dilute acetic acid recovery by extractive distillation
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Dense-phase CO₂ pipeline transport
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Ethane steam cracker
A simplified thermal-cracking train: an equilibrium reactor converts ethane to ethylene + H2 at furnace conditions (1100 K), then a quench, compression, and a cold flash strip the H2 tail gas before a C2 splitter separates ethylene product from unconverted ethane. An equilibrium reactor is used here rather than the kinetic reactor because the latter's concentration term always uses a liquid-phase density (a real gap for a vapor-phase reaction at 1100 K) -- noted, not fixed, out of scope for this example. The C2 splitter needs many stages and high reflux since ethylene/ethane relative volatility is modest. From the ChemSep casebook (ethane cracker).
Acetic acid recovery — NRTL with vapor-phase dimerization
Concentrating dilute aqueous acetic acid (30 mol%) to a 99.8% acetic-acid bottoms product by distillation, modeled with the NRTL activity package and chemical-theory vapor-phase association (acetic acid dimerizes, 2 A -> A2, in the vapor). This is the physics a cubic equation of state gets wrong: the pinned NRTL acetic-acid/water binary (DECHEMA) plus the cited dimerization constants (Nagy et al., Molecules 2020) give the real bubble curve and latent heat, so the close-boiling acid/water pair actually separates and converges where Peng-Robinson does not. Honesty note: acetic acid and water are close-boiling with no azeotrope, so the water distillate is only ~87% water (the acid product is the concentrated, high-purity stream); a sharper water cut needs more stages / reflux than this screening case uses.
Naphtha steam cracker: furnace, quench, compression, cryo train
The full ethylene-plant process shape (steam-methane-cracking's headline technology, e.g. Linde's steam cracking line): a fired-heater convection preheat, a three-reactor lumped pyrolysis furnace, a transfer-line-exchanger quench, a primary fractionator pulling off pyrolysis gasoline, two-stage compression with interstage knockouts, selective acetylene hydrogenation, and a cryogenic cold train (cold-flash light-gas rejection, deethanizer, C2 splitter, depropanizer) delivering four real products -- ethylene, propylene, a butadiene-rich C4 cut, and a pygas/heavy-ends byproduct -- plus an H2/CH4-rich tail gas and two knockout condensate streams. Honesty notes: (1) naphtha is modeled as a single n-heptane surrogate (no fitted radical-chain kinetics exist in this codebase for real naphtha pyrolysis, so the furnace is three chained fixed-conversion reactors on real, exactly mass-balanced cracking/dehydrogenation stoichiometry -- C7H16 -> C2H4+C2H6+C3H6, C7H16 -> CH4+C2H4+C4H6+H2, and C2H4 -> C2H2+H2 for a trace acetylene impurity -- tuned to a representative, not literature-fitted, product distribution, the same 'illustrative, not fitted' posture already disclosed for saf-hefa-renewable-jet's hydrocracking lump). (2) The demethanizer is a single cold flash stage, not a rigorous multi-tray column: H2 is permanently supercritical at any realistic column pressure (Pc~13 atm vs. the ~20+ atm this train runs at), which was found during this build to corrupt the MESH solver's initial temperature-profile guess (fixed in unitops/distillation.py -- see its CLAUDE.md entry -- but even after that fix a genuine ~15 mol% H2 feed to a sharp-cut demethanizer is a hard column this solver doesn't converge on cleanly); a single flash stage rejects H2/CH4 in bulk instead, consistent with the 'cold-box front-end flash' some real designs use, but with materially worse light-key rejection than a real 20+ tray demethanizer. That carries through honestly to the ethylene product: it converges at ~77 mol% ethylene (the balance methane and H2), not polymer-grade purity -- the real number the solver computes, not an assumed spec. Propylene fares much better (~96%) since it isn't competing with as light a contaminant. (3) No BTX/aromatics extraction -- the pygas cut is reported as a single lumped heavy stream, matching saf-hefa's precedent of not resolving every real product cut.