Which thermodynamic method does it use?

The PR-MHV1 property package, over ethanol, water — already selected. You can switch the method on the canvas before running.

Which unit operations are in the flowsheet?

It chains PUMP, Hpcol. 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. Pressure-swing ethanol dehydration (Gᴱ mixing rule) runs entirely in your browser on MaximaLabs — free, no install, no license. Open the model to load it live and run the deterministic solver.

All guides

Fuel-ethanol dehydration, Pekin, Illinois, USA

How to simulate 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.

AZEO FEED

PUMP

feed

dist

btms

Hpcol

Recycle TO LP

Ethanol

1
Open the ready-made model
Open the "Pressure-swing ethanol dehydration (Gᴱ mixing rule)" model in the MaximaLabs workspace — no install, no license. It loads live on the canvas, ready to edit and run.
2
Confirm the thermodynamics
This process is modeled with the PR-MHV1 property package over ethanol, water — already selected, so the phase equilibrium and enthalpy are physically consistent from the first run.
3
Review the flowsheet
The flowsheet chains PUMP, Hpcol. Every block is a real, solvable unit op you can reconfigure on the canvas.
4
Run 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.
5
Read 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.

What you'll build

Thermodynamics: PR-MHV1
Components: ethanol, water
Unit operations: PUMPHpcol

Open this model in the workspace

Opens live on the canvas — free, no install.

Explore the model & flowsheet

Modeling assumptions & limitations

What this model captures, and what it deliberately does not — from the engineers who built it.

1`pr-mhv1` is *less* accurate than NRTL at 1 atm (0.949 vs 0.891) — MHV1 is the right tool for the pressurized column, not a replacement for a fitted activity model at ambient pressure; multi-package flowsheets (`thermo_overrides`) let a real pressure-swing pair use each where it belongs.
2Only the high-pressure column is drawn here — the low-pressure column and the recycle that close the loop are left out to keep the thermodynamic point legible.

Frequently asked questions

What does the Pressure-swing ethanol dehydration (Gᴱ mixing rule) model simulate?: 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.
Which thermodynamic method does it use?: The PR-MHV1 property package, over ethanol, water — already selected. You can switch the method on the canvas before running.
Which unit operations are in the flowsheet?: It chains PUMP, Hpcol. 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. Pressure-swing ethanol dehydration (Gᴱ mixing rule) 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

Pekin, Illinois, USA

Ethanol–water distillation

An 8-stage column concentrating ethanol overhead toward the azeotrope (the headline demo).

Reference model (ChemSep / IECR 2009)

Ethanol dehydration (pervaporation)

A hydrophilic pervaporation membrane pulls water out of near-azeotropic ethanol — crossing the 89 mol% ethanol-water azeotrope that ordinary distillation cannot. Permeate is ~95% water; the retentate is dried past the azeotrope.

Reference model (Luyben 2006)

Extractive distillation (ethanol/water with ethylene glycol)

Near-azeotropic ethanol/water (85 mol% ethanol) can't be pushed past the 89 mol% azeotrope by ordinary distillation. A heavy, high-boiling entrainer (ethylene glycol) fed near the top of the column raises water's relative volatility enough to pull overhead ethanol past the azeotrope in one pass; a second column then strips water overhead from the glycol, regenerating it as the bottoms product. The classic extractive-distillation textbook case (Luyben, Ind. Eng. Chem. Res. 2006, 45, 4625).

Reference model (Luyben 2008)

Pressure-swing azeotropic distillation (methanol/acetone)

Methanol and acetone form a minimum-boiling azeotrope whose composition shifts noticeably with pressure — enough that two ordinary columns run at different pressures can cross the azeotrope without an entrainer. Column 1 (low pressure) takes pure acetone bottoms and a near-azeotropic overhead; that overhead is compressed into Column 2 (high pressure), whose new, shifted azeotrope composition lets pure methanol come off the bottoms (the recycle of Column 2's now off-azeotrope overhead back to Column 1 is reported as a product here rather than closed, the same open-loop simplification the acetone-water example already uses). Luyben, Ind. Eng. Chem. Res. 2008, 47, 2696.

Puerto Rico (pharmaceutical manufacturing corridor)

Waste solvent recovery — extractive distillation (IPA/water)

A pharmaceutical waste isopropanol/water stream (near the ~68 mol% IPA azeotrope) is fed to an extractive column with a high-boiling entrainer feeding in a few stages above it; a second column strips the entrainer back out of the bottoms for reuse.

Fuel-ethanol dehydration unit, Pekin, Illinois, USA

Anhydrous ethanol — extractive distillation past the azeotrope (NRTL)

Producing fuel-grade anhydrous ethanol from a near-azeotropic ethanol/water feed using ethylene glycol as the extractive entrainer. Ordinary distillation is capped at the 89.4 mol% ethanol azeotrope; the high-boiling glycol raises water's relative volatility so ethanol crosses its azeotrope and leaves the extractive column essentially pure, while a vacuum solvent-recovery column strips the water and recycles the glycol. This is modeled with the NRTL activity package on pinned DECHEMA binaries for every pair (ethanol/water, ethanol/glycol, water/glycol) — the non-ideal, azeotrope-crossing VLE a cubic equation of state structurally cannot reproduce (Peng-Robinson stays trapped at the ~89% azeotrope).