Benzene hydrogenation → cyclohexane — a PENG-ROBINSON process flowsheet
Benzene + 3 H₂ → cyclohexane in a conversion reactor, then a high-pressure flash recovers liquid cyclohexane and recycles the excess hydrogen (with a purge). The classic ChemSep recycle example — exercises reaction + recycle convergence.
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- Rigorous PENG-ROBINSON thermodynamics, solved by the same engine every simulation runs on.
- 4 unit operations modeled: MIX, RXN, SEP, Split.
- Focus areas: Hydrogenation, Reactor, Gas recycle, Purge.
- Thermodynamics
- PENG-ROBINSON
- Components
- benzene, h2, cyclohexane
- Unit operations
- MIXRXNSEPSplit
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("benzene-hydrogenation")
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
Aniline via nitrobenzene hydrogenation
Vapor-phase catalytic hydrogenation of nitrobenzene (C₆H₅NO₂ + 3H2 → C₆H₅NH₂ + 2H2O, highly exothermic) with excess hydrogen, a high-pressure flash recovering unreacted H₂ as a recycle vent, then a reduced-pressure flash stripping residual water from the crude aniline.
Hydrocracking reaction section
A refinery hydrocracker: heavy VGO (modeled as n-dodecane) plus excess H₂ is cracked over catalyst into lighter products via a discrete lumped first-order kinetic network, then flashed to knock out recycle H₂/light gas from the liquid product (Peng-Robinson). Conversion is set by reactor temperature and LHSV.
Thermal (non-catalytic) HDA — broad aromatics feedstock
A real thermal-HDA licensor's process (non-catalytic, tolerant of a mixed aromatics feedstock and inert impurities) modeled as a genuine competing-and-sequential reaction network in a real plug-flow reactor, not a fixed-Keq equilibrium reactor like the simpler hda-toluene-dealkylation example. The main toluene dealkylation (toluene + H₂ → benzene + methane) uses real published kinetics: (-r_toluene) = k0exp(-Ea/RT)C_toluene*C_H2^0.5 (order 1 in toluene, order 0.5 in H₂, the classic 1.5-order thermal-HDA rate law), k0 = 5.67e9 (m3/mol)^0.5/s, Ea = 228,200 J/mol, heat of reaction -49,000 J/mol — transcribed from Shull & Hixon (Ind. Eng. Chem. Process Des. Develop. 5, 147, 1966) as tabulated in Rase, H.F., 'Chemical Reactor Design for Process Plants, Vol. 2: Case Studies and Design Data' (Wiley-Interscience, 1977), Case Study 104 'Toluene Dealkylation', pp. 36-42 (unit-converted from the source's imperial (ft, lb-mol, degR) basis to SI). That same source explicitly states 'rate equations for the side reactions have not been reported' — so the coking/heavies side reaction (2 toluene → biphenyl + H₂, the real reaction that caps aromatic yield below 100% and drives decoking intervals) and the xylene demethylation feeding the shared toluene pool (o-xylene + H₂ → toluene + methane — the real single-methyl-loss pathway, not a lumped double-dealkylation straight to benzene, so this is a genuine reactions-in-series-and-parallel network, not three independent reactions) both stay illustrative order-of-magnitude Arrhenius parameters, tuned only to land in the source's cited ~98% main-reaction selectivity at 2:1 H₂:toluene — honestly labeled as such, not fabricated citations. H₂S/CO₂/ammonia ride through the flowsheet as inert impurities — exactly what 'impurity tolerance' means in a mass balance, not a special chemistry path. A real fired heater (rigorous combustion stoichiometry + stack energy balance, the same unit op used in the naphtha-steam-cracker example) brings the mixed fresh-plus-recycle feed up to reaction temperature — not a feed specified as already at 950 K. The H₂-rich high-pressure separator vapor is a real recycle loop: fresh feed joins recycled gas at a mixer ahead of the furnace, and past the separator the vapor splits into a recompressed recycle (85%) and a genuine purge (15%) that bleeds off the methane a single pass could never consume — the same role a purge plays in the ammonia-synthesis-loop example. Quench, the high-pressure separator, and a letdown-valve-plus-flash stabilizer strip dissolved H₂/methane before the aromatics split. The reactor is genuinely adiabatic, not isothermal: temperature is a real energy-balance-coupled ODE state (the adiabatic PFR mode) that rises along the reactor length as the exothermic reactions release heat — starting from the furnace's real ~900 K outlet (in the source's cited 894-922 K inlet range) and climbing as the reaction proceeds, self-consistent to within ~0.01% of the reactor's own required external duty (which should be ~0 for a truly adiabatic reactor — verified, not assumed). One honest simplification remains: the final benzene/toluene/xylene-derived-benzene split still uses a shortcut separator rather than a rigorous column, for the same documented reason as hda-toluene-dealkylation: trace H₂/methane corrupts the column's wide-boiling initial-guess classification, and a fix narrowed to just that seed broke the shipped methanol-synthesis example when tried previously.
Ammonia synthesis loop (Haber-Bosch, ChemSep casebook)
The classic industrial ammonia loop: fresh syngas joins recycled unconverted gas, reacts over an equilibrium reactor (N₂ + 3H₂ ⇌ 2NH₃) at synthesis conditions, is chilled to condense high-purity liquid ammonia, and the remaining vapor splits into a recycle (back to the loop) and a purge — the purge exists specifically to bleed off the inert argon a single-pass reactor could never consume, which would otherwise concentrate in the recycle forever.
Cumene production (benzene alkylation)
Benzene and propylene alkylate over a fixed-conversion reactor to cumene (isopropylbenzene, the feedstock for phenol/acetone via the Hock process); a downstream column recovers unreacted benzene overhead for recycle-quality purity while cumene leaves the bottoms. Luyben, Ind. Eng. Chem. Res. 2010, 49, 719.
Butene/isobutane alkylation
Sulfuric-acid alkylation of butene with excess isobutane produces high-octane alkylate gasoline blendstock; a conversion reactor stands in for the acid-catalyzed carbocation chemistry (a literal acid/hydrocarbon settler would need H₂SO₄ electrolyte thermodynamics this package doesn't carry — out of scope, same as the reactor already being a stand-in for the chemistry itself), and a deisobutanizer-style column recovers unreacted isobutane overhead. The high isobutane:olefin ratio real alkylation units run is maintained almost entirely by recycling that isobutane back to the reactor feed — closed here as a real Wegstein-converged tear loop, with only a small makeup feed replacing what the reaction actually consumes, rather than the previous version's isobutane leaving as an unrecycled product. Luyben, Principles and Case Studies of Simultaneous Design, Wiley (2011); Ind. Eng. Chem. Res. 2009, 48, 11081.