How to simulate ethanol-water rectifier (uniquac)
The ethanol-water rectifier on UNIQUAC — Abrams and Prausnitz's local-composition model with its surface and volume parameters, here on the one binary the package carries regressed parameters for (every other pair falls back to UNIFAC, which the package description says). 30 mol% feed, 20 stages, reflux 2.5, 40% distillate: 75 mol% ethanol overhead and ethanol-free water in the bottoms at 5.7 MW. The cut is kept at 0.40 on purpose: at 0.32 the spec asked for a 94% distillate past the 89.4% azeotrope and the column reported exactly that, and at 0.36 it pinched a hair short of it (balance 5e-3). Compare with the same column on NRTL and Wilson to see how much three regressed models agree on one well-measured pair — a few tenths of a percent in the distillate.
- 1Open the ready-made model
Open the "Ethanol-water rectifier (UNIQUAC)" 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 UNIQUAC property package over ethanol, water — already selected, so the phase equilibrium and enthalpy are physically consistent from the first run.
- 3Review the flowsheet
The flowsheet chains COL. 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
- UNIQUAC
- Components
- ethanol, water
- Unit operations
- COL
Opens live on the canvas — free, no install.
Explore the model & flowsheetFrequently asked questions
- What does the Ethanol-water rectifier (UNIQUAC) model simulate?
- The ethanol-water rectifier on UNIQUAC — Abrams and Prausnitz's local-composition model with its surface and volume parameters, here on the one binary the package carries regressed parameters for (every other pair falls back to UNIFAC, which the package description says). 30 mol% feed, 20 stages, reflux 2.5, 40% distillate: 75 mol% ethanol overhead and ethanol-free water in the bottoms at 5.7 MW. The cut is kept at 0.40 on purpose: at 0.32 the spec asked for a 94% distillate past the 89.4% azeotrope and the column reported exactly that, and at 0.36 it pinched a hair short of it (balance 5e-3). Compare with the same column on NRTL and Wilson to see how much three regressed models agree on one well-measured pair — a few tenths of a percent in the distillate.
- Which thermodynamic method does it use?
- The UNIQUAC 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 COL. 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. Ethanol-water rectifier (UNIQUAC) 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
Beer column: 8% ethanol to 53% (Wilson)
The first column of a distillery on the Wilson equation — the oldest local-composition model, fine for a fully miscible pair like ethanol-water and unable by construction to represent a liquid-liquid split, which is why it is offered for this pair and not as a default. An 8 mol% fermenter beer, 12 stages with the feed near the top (stage 3) as a beer column is run, reflux 1, 15% distillate: 53 mol% ethanol overhead and a stillage bottoms with no ethanol left, 1.37 MW on the reboiler for 100 mol/s of beer. Ethanol-water is the one binary the package carries regressed Wilson parameters for; everything else falls back to UNIFAC.
Ethanol–water distillation
An 8-stage column concentrating ethanol overhead toward the azeotrope (the headline demo).
Ethanol-water column at 6 atm (SRK + MHV1)
The ethanol-water column everyone knows, run at 6 atm on the Gᴱ-mixing-rule package: Soave-Redlich-Kwong whose mixture energy parameter comes from NRTL's excess Gibbs energy through the MHV1 rule (Michelsen 1990) instead of a kij — the package built for polar, hydrogen-bonding mixtures at pressure, where a γ-φ activity model is past its ~10 bar ceiling and a plain cubic with van der Waals mixing has no hydrogen bonding at all. A 10 mol% ethanol feed through 16 stages at a reflux ratio of 2.5 gives a 66.7 mol% distillate and an ethanol-free bottoms, 2.6 MW on the reboiler. Read it against NRTL, which at 6 atm is still inside its own range: the two packages put the pressure-shifted azeotrope in different places — 0.88 mol fraction ethanol here, 0.84 on NRTL at 6 atm (0.97 against 0.89 at 1 atm) — so this card shows where the MHV1 rule sits, not a number to prefer over the fitted binary at low pressure. The cut is kept well short of the azeotrope on purpose: at a distillate ratio of 0.12 the profile pinched against it and the column reported exactly that. Each solve is about a minute, because every stage K-value is a Gᴱ mixing-rule evaluation.
n-Hexane / 1-butanol column with no fitted binary (UNIFAC)
A binary the databank has no regressed NRTL parameters for, so the column runs on predictive original UNIFAC from the two molecules' groups alone: 50/50 n-hexane and 1-butanol, 20 stages, reflux 2, 45% distillate. UNIFAC predicts the minimum-boiling azeotrope at 97 mol% hexane and 341.7 K, and the column lands its distillate exactly there (96.7%) with an 88% butanol bottoms — the azeotrope, not the stage count, is what caps the overhead purity, and that is a prediction from group contributions with no data on this pair behind it. Read it as a screening result: original UNIFAC's mean error against fitted binaries in this tree is 0.08 in ln gamma, and an alkane/alcohol pair is in its well-behaved range.
Toluene removal from 1-butanol solvent (modified UNIFAC, Dortmund)
A recovered 1-butanol solvent contaminated with 5 mol% toluene, redistilled to send the toluene overhead: 24 stages, reflux 3, an 8% distillate. There is no fitted toluene/1-butanol binary, so this runs on modified UNIFAC (Dortmund) — the variant that cuts infinite-dilution error from 42% to 16% in this tree, and a dilute contaminant in a solvent is exactly the infinite-dilution regime. Dortmund puts the toluene/butanol azeotrope at 67 mol% toluene (original UNIFAC: 70%), which is why the overhead comes out at 43% toluene rather than pure, and the bottoms at 1.7% toluene — two-thirds of the contaminant removed per pass. The 3-point azeotrope difference between the two variants is the size of the model choice on this pair.
Ethanol-water heat-and-flash (Van Laar)
The simplest separation there is, on the simplest activity model that still gets a non-ideal pair right: a 40 mol% ethanol-water stream heated to 356 K at 1 atm and flashed adiabatically, on the two-constant Van Laar equation — the oldest of the family, temperature-independent, cheap to fit from a single azeotrope point. What it computes: 55% of the feed vaporizes at 356 K, the vapour at 54 mol% ethanol against 22% left in the liquid, on 2.75 MW of preheat. Ethanol-water is the one pair the package carries regressed constants for; other pairs fall back to UNIFAC.