Fatty-ester vacuum fractionation — a PENG-ROBINSON process flowsheet
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).
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- Rigorous PENG-ROBINSON thermodynamics, solved by the same engine every simulation runs on.
- 1 unit operations modeled: Vaccol.
- Focus areas: Vacuum distillation, Biodiesel, Oleochemicals.
- Thermodynamics
- PENG-ROBINSON
- Components
- methyl_palmitate, methyl_stearate
- Unit operations
- Vaccol
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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("fatty-ester-fractionation")
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
Biodiesel: alkali-catalysed transesterification with methanol recovery
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.
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.
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.
Patent benchmark: methyl lactate synthesis (CN104628563A)
Real patent replication, not an invented process: CN104628563A's acid-catalyzed lactate-ester route — lactic acid esterified with excess methanol, then purified by vacuum distillation — reproduced here as a continuous flowsheet. The patent's own worked methyl-lactate example reports 98.8% esterification conversion and 99.6% product purity at 120 degC/3h. This flowsheet's reactor conversion is set directly to the patent's reported 98.8% (not fitted); the vacuum column (0.2 atm, matching the patent's vacuum-distillation purification step) then splits the methanol and reaction water off the ester completely — zero methyl lactate leaves overhead — and delivers 97.8 mol% methyl lactate in the bottoms at 389.9 K. The property method is the whole story here, exactly as it was on the sulfolane extractive column. Written on Peng-Robinson, this example did not converge at all: every pair in a methanol / water / lactic-acid / methyl-lactate mixture is hydrogen-bonding, which van der Waals mixing cannot represent, and the column returned a partial profile carrying 2.60 mol/s of methyl lactate out of a column fed 1.98 — 32% more product than the reactor made, a 0.26 component-balance residual. (That wrong profile is where this example's previously-published 98.75% purity was read from; the number was retracted at the test level and is now corrected here.) A plain activity model cannot be used either, for a data reason rather than a physics one: neither lactic acid nor methyl lactate carries a regressed ideal-gas-Cp correlation, and the gamma-phi enthalpy path raises on that where a cubic quietly falls back to a corresponding-states estimate. PSRK is a cubic whose mixing is driven by UNIFAC, so it has both — and it converges to a 2.7e-06 component-balance residual, with methyl lactate and lactic acid each leaving in exactly the amount the reactor made.
Bio-acrylic: glycerol to acrylic acid and butyl acrylate
Biodiesel glycerol (5 mol% in water, the dilute crude a transesterification plant actually sells) is vaporised and dehydrated over an acid catalyst at 553 K to acrolein, oxidised with air at 573 K to acrylic acid, quenched, dewatered in a vacuum column, and esterified with n-butanol to n-butyl acrylate: the two-step route from a renewable C₃ to the acrylic monomer, written out so its water, oxygen and carbon bookkeeping can be checked end to end. Each reaction is a conversion reactor with an exact element balance: dehydration (glycerol → acrolein + 2 H₂O), the competing C-C cleavage that every gas-phase dehydration catalyst shows (glycerol → acetaldehyde + CO + H₂ + H₂O), selective oxidation (acrolein + 1/2 O₂ → acrylic acid), over-oxidation (acrolein + 3/2 O₂ → acetic acid + CO₂), and esterification (acrylic acid + n-butanol → n-butyl acrylate + H₂O). A knock-out flash after dehydration rejects most of the water before the oxidiser; the quench liquid goes to a 0.15 atm acrylic-acid column (vacuum because acrylic acid polymerises when hot, which is also why its inhibitor profile is the question the column-inhibition analysis answers on this column); a caustic wash takes the unreacted acids out of the ester before a 0.2 atm butyl-acrylate column. What the flowsheet shows is where the water goes: 102 mol/s of it arrive with 5 mol/s of glycerol, the dehydration makes two more per acrolein, and nearly all of it has to be removed before the acid is concentrated, which is the energy cost that decides whether a bio-acrylic plant is viable. Solved: the vacuum column delivers a crude acid of 87 mol% acrylic acid (11% water, 2% acetic) and loses about 7% of the acid overhead with the water; the ester column delivers 94 mol% n-butyl acrylate, the balance unreacted butanol.