Biodiesel: alkali-catalysed transesterification with methanol recovery — a PENG-ROBINSON process flowsheet
Continuous base-catalysed (NaOH/methoxide) transesterification of a refined vegetable oil to fatty acid methyl esters — the classic FAME biodiesel process. The oil is modeled as a 70/30 triolein/tripalmitin blend (the C₁₈:1 and C₁₆:0 triglycerides that dominate soy, canola and rendered-fat feedstocks); each is transesterified with methanol at a 6:1 molar ratio and 60 C in a two-reactor cascade at 97% conversion per stage, the standard industrial staging that drives the equilibrium toward the esters. Excess methanol is then vacuum-flashed overhead for recycle, and the wash/settling step splits the heavy glycerol phase from the ester product. The FAME product comes out at 96.9 wt% ester content — just over the EN 14214 minimum of 96.5 wt% — and the crude glycerin at ~85 wt% glycerol, typical of the crude co-product that goes on to a glycerin refining column.
Modeling assumptions & limitations
- 1The deliverable here is the material balance (conversion, ester yield, product specifications, methanol recovery), which is exact. The energy balance is NOT: the triglyceride and methyl-ester records in the databank carry no ideal-gas heat-capacity correlation, so they are injected as pseudocomponents whose Cp comes from the Kesler-Lee petroleum correlation, and their acentric factors (omega ~2.2-2.3) sit far outside the range Peng-Robinson's alpha function was fitted to. Reported duties and any adiabatic mixing temperature are therefore indicative only, which is why every unit here is temperature-specified rather than solved adiabatically, and why the reactor feed is given as one combined specified stream. Two further simplifications: the NaOH catalyst and the soap (sodium palmitate) that free fatty acids would form with it are not carried, so this is a refined, low-FFA feedstock; and the glycerol/ester split is a specified wash-section recovery rather than a rigorous liquid-liquid flash. That is now a modelling choice and no longer a data limit: every species reaching that step — the methyl esters, glycerol, the unconverted triglyceride and the free fatty acid — carries a predictive-UNIFAC group decomposition, and a liquid-liquid flash on this stream does split into an ester phase and a glycerol phase with the excess methanol partitioning into the glycerol, as it does industrially. Solving it here rather than specifying it would still inherit the pseudocomponent-Cp caveat above for the phase enthalpies.
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- Rigorous PENG-ROBINSON thermodynamics, solved by the same engine every simulation runs on.
- 3 unit operations modeled: 2× RX2, MEOH Flash, WASH.
- Focus areas: Biodiesel, Transesterification, FAME, Renewable fuels, Oleochemicals.
- Thermodynamics
- PENG-ROBINSON
- Components
- triolein_ooo, tripalmitin_ppp, methanol, methyl_oleate, methyl_palmitate, glycerol
- Unit operations
- 2× RX2MEOH FlashWASH
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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("biodiesel-transesterification")
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
Enzymatic biodiesel from high-FFA waste oil (lipase)
Immobilised-lipase (e.g. Novozym 435) production of FAME from a waste feedstock — used cooking oil / rendered fat carrying ~17 mol% free fatty acid. This is the feed slate a renewable-fuels producer actually buys, and it is exactly where the conventional alkali route breaks down: NaOH or methoxide saponifies free fatty acid into soap (the databank even carries sodium palmitate), which destroys yield and emulsifies the glycerol settling step, so a high-FFA feed needs an acid-esterification pretrain before it can be base-catalysed at all. A lipase does both reactions at once and at 40 C: it transesterifies the triglyceride to esters plus glycerol, and it esterifies the free fatty acid into more product rather than losing it to soap. Both reactions are carried explicitly here, so the FFA ends up as methyl palmitate instead of as a loss. The result: 97.9 wt% ester content (EN 14214 requires >= 96.5 wt%) with the free fatty acid taken down to under 0.1 mol% of the product, i.e. a low acid value, from a feed the alkali route could not process directly. Esterification also makes one mole of water per mole of FFA converted, which is why the vacuum flash takes methanol and water overhead together — water inhibits the enzyme and has to leave the loop.
Fatty-ester vacuum fractionation
Biodiesel methyl esters (C₁₆ / C₁₈) split at 0.05 bar — vacuum keeps the bottoms under 515 K; near-total C₁₆ recovery overhead and ~98% C₁₈ in the bottoms (the two components' relative volatility caps bottoms purity there — more stages/reflux do not push it further). From the ChemSep casebook (Fatty_Acids, as methyl esters).
Fat splitting: fatty acids from palm kernel oil
Continuous high-pressure countercurrent fat splitting (Colgate-Emery process): triglyceride oil hydrolyzed with excess water at ~260 C / 55 bar to free fatty acids plus glycerol. The databank has no lauric/myristic acid or their triglycerides (palm kernel oil's actual dominant fatty acids), so the feed is modeled as tripalmitin/triolein hydrolyzing to palmitic/oleic acid instead — the same reaction chemistry and process conditions, a different (available) fatty-acid slate. The real unit gravity-settles the fatty-acid and glycerol-water phases downstream; that decanting step is not modeled here (scope note), so the product stream is the full reactor effluent.
Fatty alcohols from methyl ester hydrogenolysis
High-pressure hydrogenolysis of a fatty acid methyl ester over a copper-chromite catalyst to the corresponding fatty alcohol plus methanol byproduct, the route used by natural-fatty-alcohol producers such as Oxiteno. Modeled with methyl palmitate as the ester feed (the C₁₆ member of the coconut/palm-kernel-derived ester slate these plants actually run); a flash removes unreacted hydrogen for recycle and a partial-condenser column recovers methanol overhead from the crude fatty alcohol. The column runs a vapor distillate because the flash liquid still carries dissolved hydrogen, and its distillate rate is set to the feed's light-component fraction — ask for more overhead than there is light material and the column can only meet the spec by dragging fatty alcohol up with it.
Butyl acetate synthesis via reactive distillation
Methyl acetate transesterifies with n-butanol over the reactive stages of a column into butyl acetate (a common paint/coatings solvent) and methanol, which is pulled overhead as it forms while high-boiling butyl acetate collects in the bottoms. Luyben et al., Ind. Eng. Chem. Res. 2011, 50, 1247.
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.