How to simulate 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.
- 1Open the ready-made model
Open the "Bio-acrylic: glycerol to acrylic acid and butyl acrylate" model in the MaximaLabs workspace — no install, no license. It loads live on the canvas, ready to edit and run.
- 2Confirm the thermodynamics
This process is modeled with the NRTL property package over glycerol, water, acrolein, acetaldehyde, co, h2, o2, n2, co2, acrylic_acid, acetic_acid, n_butanol, n_butyl_acrylate — already selected, so the phase equilibrium and enthalpy are physically consistent from the first run.
- 3Review the flowsheet
The flowsheet chains 2× OX Preheat, 5× Esterify, 2× Quench, 2× Ester MIX, 2× BA COL, AA PUMP, Neutralize. Every block is a real, solvable unit op you can reconfigure on the canvas.
- 4Run the simulation
Click Run. The deterministic solver converges the material and energy balances (recycles included) and fills the live stream table — the AI never invents a number.
- 5Read the results and iterate
Inspect the converged streams, tweak a spec, and re-run — or ask the AI copilot to explain a result or diagnose a failed solve in plain English.
- Thermodynamics
- NRTL
- Components
- glycerol, water, acrolein, acetaldehyde, co, h2, o2, n2, co2, acrylic_acid, acetic_acid, n_butanol, n_butyl_acrylate
- Unit operations
- 2× OX Preheat5× Esterify2× Quench2× Ester MIX2× BA COLAA PUMPNeutralize
Opens live on the canvas — free, no install.
Explore the model & flowsheetModeling assumptions & limitations
What this model captures, and what it deliberately does not — from the engineers who built it.
- 1The conversions are stated screening INPUTS, not predictions: 75% of the glycerol to acrolein (with the C-C cleavage taking most of the rest), 90% of the acrolein to acid with half the remainder over-oxidised, 95% esterification. They sit inside the ranges reviewed by Katryniok et al., Green Chem. 12
- 22079 and Ullmann's 'Acrylic Acid and Derivatives', and are not a fit to any one catalyst. The real byproduct slate (hydroxyacetone, propanal, allyl alcohol, formaldehyde, phenols, coke) is lumped into acetaldehyde + CO + H₂: hydroxyacetone has no ideal-gas Cp in the bundled data and formaldehyde has no NRTL binaries here, so writing them in would have meant inventing properties.
- 3No heats of reaction are given: the reactors are isothermal and their duties carry sensible heat only, so the oxidiser's large exotherm (and the salt-bath cooling it needs) is not in the reported duty.
- 4The acid section runs on NRTL with the permanent gases as Henry's-law solutes; the esterification, wash and ester column run on Peng-Robinson, because n-butyl acrylate has no ideal-gas heat capacity the activity-model enthalpy path can use.
- 5The caustic wash is a fixed-recovery separator, not a reactive extraction, and the esterification is a single pass with no water removal, so the ester column carries the unreacted butanol and water overhead rather than recycling them.
- 6The acrylic-acid column's product is the crude a real plant would still finish in a separate glacial column. No acrylic polymerisation kinetics ship; the inhibitor analysis takes them as an input.
Frequently asked questions
- What does the Bio-acrylic: glycerol to acrylic acid and butyl acrylate model simulate?
- 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.
- Which thermodynamic method does it use?
- The NRTL property package, over glycerol, water, acrolein, acetaldehyde, co, h2, o2, n2, co2, acrylic_acid, acetic_acid, n_butanol, n_butyl_acrylate — already selected. You can switch the method on the canvas before running.
- Which unit operations are in the flowsheet?
- It chains 2× OX Preheat, 5× Esterify, 2× Quench, 2× Ester MIX, 2× BA COL, AA PUMP, Neutralize. Every block is a real, solvable unit operation you can reconfigure, add to, or remove.
- Do I need to install software or buy a license?
- No. Bio-acrylic: glycerol to acrylic acid and butyl acrylate runs entirely in your browser on MaximaLabs — free, no install, no license. Open the model to load it live and run the deterministic solver.
More guides like this
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.
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).
Methyl acetate esterification via reactive distillation
Acetic acid and methanol esterify over the reactive stages of a column into methyl acetate and water — a genuine quadruple-azeotrope system where reactive distillation intensifies what would otherwise need several conventional columns. Reactive Distillation Design and Control, Luyben & Yu, Wiley (2006), pp. 147-164.
Batch campaign: a batch step inside a continuous flowsheet
Fine chemicals and pharma run batches, but a flowsheet is written in mol/s. These two unit ops reconcile that: they integrate the real batch physics over the batch, then report the products as the RATE that campaign delivers, so a batch step sits inside a continuous flowsheet the way a plant actually runs one. The batch reactor esterifies ethanol with acetic acid to ethyl acetate and water. It reaches 63.2% conversion and stops, and that number is not a specification — it is the equilibrium. The reaction is reversible with an equilibrium constant of 4 (the forward and reverse pre-exponentials are given as 5.0e4 and 1.25e4), and solving K = x(0.10+x)/(0.45-x)^2 = 4 for an equimolar charge carrying 10% water gives an extent of 0.285, which is 63.3% of the acid. Fischer esterification really does plateau there; a model that ran to completion would be describing a different reaction. Turnaround time costs throughput exactly as reaction time does. Two hours of reaction plus one hour of turnaround is a 3-hour cycle and 2922 batches a year, and the reactor is only reacting for 67% of the time it is occupied. That fraction is the number that decides whether you need a second reactor, and it is invisible to a steady-state model. The batch still then takes the crude and recovers the ethyl acetate — the distillate comes off essentially pure, from a pot that started at 28.5 mol% ester — on its own longer 4-hour cycle, so the two units run at genuinely different campaign rates. Bounded: the flowsheet sees each unit's CYCLE AVERAGE, not the transient. A real plant has a surge tank between these two smoothing the pulses, and neither the concentration profile during the batch nor the still's changing overhead composition is visible downstream.
Ethylene glycol plant: closed water loop + multi-effect evaporator dehydration
The water-integrated evolution of the fiber-grade MEG plant. Two changes turn the once-through EO/glycol chain into a real, water-economical process: (1) the recovered process water is RECYCLED back to the hydration reactors through a purge splitter. A pure recycle is inventory-singular (reactors are keyed on the shrinking EO pool, so water consumption is fixed regardless of how much water circulates), so an 8% purge pins the loop and makes it well-posed, cutting fresh water makeup from 10 to ~1.75 mol/s (a >80% reduction). (2) The bulk dehydration is done by a genuine TWO-EFFECT EVAPORATOR TRAIN (forward-feed, real steam economy: effect 1's low-temperature vapor is the heating steam for effect 2) doing rigorous (P,H)-flash water removal, rather than a single spec-based split. The recycle converges through the solver's Wegstein tearing (~15 outer passes) and MEG still comes out fiber-grade (>=99.9%). HONEST SCOPE: the reaction chemistry is rigorous stoichiometry (real atom balances, ~90/9/1 selectivity) and the evaporators are real energy-balanced flash effects — but flash evaporation CANNOT reach glycol dryness without slipping glycol into the overhead vapor (MEG has a real vapor pressure at 90 C), so the evaporators run cool and only pre-concentrate. An overhead knockout returns the ~1-2% slipped glycol to the product (no yield loss), and a final vacuum-refining polish (still a spec-based split, representing the refluxed dehydration column a flash cannot replicate) removes the last water. This mirrors a real MEG plant's multi-effect-evaporator + vacuum-refining dehydration section. The product columns remain spec-based (a converged 99.9% fiber-grade MEG column is not tractable under Peng-Robinson here — the MEG/DEG relative volatility is too narrow for the wide-boiling MESH path).
Pressure-swing ethanol dehydration (Gᴱ mixing rule)
Ethanol–water is the classic azeotrope, and pressure-swing distillation breaks it without an entrainer: the azeotrope moves with pressure, so a low-pressure column and a high-pressure column pass each other's azeotropic distillate and each recovers a pure product. The whole process only works if the property package tracks that shift — which is exactly where a conventional package choice falls between two chairs. This flowsheet runs the high-pressure column at 15 bar on pr-mhv1: Peng-Robinson with an MHV1 excess-Gibbs mixing rule, so the cubic equation of state gets its attraction parameter from NRTL's excess Gibbs energy instead of from a single binary interaction constant. Switch the thermo package (Solver menu) and compare the predicted azeotrope: | package | 1 atm | 15 bar | valid at 15 bar? | |---|---|---|---| | NRTL | 0.891 | 0.802 | no — γ-φ is a low-pressure formulation (~10 bar) | | Peng-Robinson (kij) | 0.586 | 0.613 | yes, but a kij cannot represent this azeotrope | | pr-mhv1 | 0.949 | 0.798 | yes | (mole fraction ethanol; the repo's DECHEMA-validated 1 atm anchor is 0.894.) At 15 bar pr-mhv1 lands within 0.005 of NRTL while remaining a genuine equation of state, whereas plain Peng-Robinson is off by ~0.19 and puts the azeotrope in the wrong place entirely. Selecting nrtl here also trips the applicability guard, which warns that the activity model is past its pressure ceiling and names the fix. The flowsheet demonstrates the mechanism on itself. Drop the column pressure to 1 atm and re-run, changing nothing else: the solve fails with SPEC_THERMODYNAMICALLY_IMPOSSIBLE, because at atmospheric pressure the requested bottoms purity sits beyond the azeotrope and no column can reach it. At 15 bar the same specification converges and the bottoms leaves at x_EtOH ≈ 0.924 — past the atmospheric azeotrope of 0.894, which is precisely the composition an atmospheric column cannot cross.