Free, glass-box, GPL-3.0 — steady, batch, dynamic, control and properties
The process simulator that shows its work.
Choupo is a free and open-source chemical process simulator written in C++17. Build steady, batch and controlled processes; inspect thermodynamics; fit property models; and follow the balances and nonlinear solves all the way to the answer.
EduTools — nothing to install, no case to open
Each tool builds and solves its own worked example in your browser, so none of them needs a case open first. Pick one and it opens in Choupo, drawn beside the engine's own answer.
Loading the EduTools…
… live tools, generated from the application's own tool registry — this page cannot list a tool the app does not have, or miss one it does.
What is inside Choupo
Every number here is generated from the published Choupo-2608 tree, not written by hand. See the full model catalogue for names, status and source.
Counts exclude READMEs, templates, generated outputs and private data — only what is active and distributed in the release. Regenerate with bin/curate/release_inventory.py.
The glass-box contract
Choupo keeps equations, inputs, iterations, balances and provenance close together. A model is not merely a name in a dropdown: the run tells you which correlation was selected, where its parameters came from and whether the numerical problem closed.
Cases remain plain-text dictionaries on disk. The browser runs the same C++ engine through WebAssembly; it is a runner and visualiser, not a second source of process physics.
isothermalFlash | benzene / toluene | 370 K, 1 bar (flash01) Rachford-Rice Newton it V/F |g(V)| 0 0.50000000 3.76e-02 1 0.30001863 7.82e-04 2 0.30398070 5.66e-07 3 0.30398357 2.95e-13 converged K_benzene 1.6514 from Psat / P K_toluene 0.6735 from Psat / P material balance CLOSED energy balance reported
Capabilities
The breadth is now larger than the old landing page suggested. These are implemented workflows with runnable cases, not a roadmap.
Recycle networks, balances, design specifications and non-ideal separations, from first flash to multi-unit plants.
Evaluate, compare and regress pure-fluid and mixture models with provenance and validity visible beside the result.
Detailed workflows in areas usually compressed into opaque blocks, with inventories and transport assumptions exposed.
Recipe-driven campaigns and continuous dynamics with fixed or adaptive integration, controllers and energy ledgers.
Representative workflows
Each case is runnable, readable and designed around a question that can be checked in its output.
Move beyond shortcut columns into stagewise material, equilibrium, summation and heat equations, including azeotropic and reactive systems.
Combine electrolyte speciation, activity-based saturation indices, concentration polarisation and module-by-module recovery.
Carry one adsorption record from measured-data regression into working capacity, batch uptake and conservative fixed-bed transport.
Compare MSMPR moments and finite-volume crystal-size distributions while closing dissolved, solid and campaign inventories.
See adaptive integration through a thermal event, then distinguish the plant integration grid from a fixed digital-controller sampling grid.
Evidence, not badges
Choupo separates numerical convergence, conservation, model validation and data provenance. They are different questions and receive different verdicts.
Most tutorial cases ship an expected golden-master file (383 of 393 in this release); the rest are sweeps, deliberate refusal cases and composite sub-sectors, which are still run and still guarded against NaN/inf. bin/runTests re-runs the whole suite and flags any KPI drift, across all 4 engines.
A passing golden proves an answer has not moved, never that it is right. Agreement with published measurement is claimed only where a case carries an explicit anchor row citing its primary source — a separate and much smaller set.
Choupo is educational and research software, not certified process-design or safety software. Engineering use requires independent validation of models, data and results.
No installation required
The browser application executes the C++ engine locally through WebAssembly. Choose a tutorial, inspect its files, run it and read the results.
Run it
The browser needs nothing installed and works everywhere. Build from source when you want the native binaries, custom cases and the regression suite.
The C++ solver is compiled to WebAssembly and runs locally in your browser tab. Nothing is installed, no account is needed and no case data leaves your machine.
Recommended way to start on any operating system.
# Nothing to install. Open: https://www.choupo.org/app/ # The same C++ engine as the native build, # executed in your browser via WebAssembly.
1 · Browser — recommended to start. Just open the app; nothing to install.
2 · WSL2 — recommended for the native build, development and the regression tests.
There is no published native .exe installer. The Unix commands below run inside WSL2 (Ubuntu), not in PowerShell or CMD.
# In PowerShell (admin), then reboot: wsl --install -d Ubuntu # Inside the Ubuntu (WSL2) shell: sudo apt update && sudo apt install -y git build-essential git clone https://github.com/choupo-admin/choupo.git cd choupo make all source etc/bashrc runCase tutorials/steady/flash/flash01_benzene_toluene bin/runTests
1 · Browser — nothing to install; open the app.
2 · Native build from source — the standard C++17 toolchain, no external libraries.
A native macOS build is not yet part of the automated test matrix; treat it as unverified (both Apple Silicon and Intel) until a workflow confirms it.
# Command Line Tools (clang + make):
xcode-select --install
git clone https://github.com/choupo-admin/choupo.git
cd choupo
make all
source etc/bashrc
runCase tutorials/steady/flash/flash01_benzene_toluene
bin/runTests
The native target. Only a C++17 compiler and GNU make are required — zero external libraries.
# Debian / Ubuntu deps:
sudo apt install -y git build-essential
git clone https://github.com/choupo-admin/choupo.git
cd choupo
make all
source etc/bashrc
runCase tutorials/steady/flash/flash01_benzene_toluene
bin/runTests
The browser app runs in Safari and can be added to the Home Screen (Share → Add to Home Screen) to open full-screen.
Reading cases, running tutorials and inspecting results work on iPad. Building or editing flowsheets is not recommended on small phone screens.
There is no native iOS app. Choupo on iPhone and iPad means the WebAssembly build in Safari — the same engine, in the browser.
# iPad / iPhone — open in Safari: https://www.choupo.org/app/ # Share -> Add to Home Screen for a # full-screen, offline-capable launcher.
Documentation
Run, organise and understand Choupo cases, reports and workflows.
Open the User Guide (Choupo-dev)Select, evaluate and curate property models without hiding uncertainty.
Open the Property Guide (Choupo-dev)Inspect every implementation or report a reproducible problem.
Open GitHubThese guides track the development line. Documentation matching the stable release is the tag's own: docs at v2608.
Cite Choupo
Geraldes, V. (2026). Choupo — Open-source Chemical Process Simulator (version 2608) [Computer software]. https://www.choupo.org/
People and governance
Choupo was conceived and created by Vítor Geraldes, chemical engineer and process-modelling researcher. The Properties Guide and Theory Guide are coauthored with Pedro Mendes and Miguel Rodrigues. Their authorship and copyright are preserved in those two works.
Suggestions, bug reports, validation evidence and data corrections are welcome. Choupo is centrally developed; external code contributions and pull requests are not accepted. Suggestions do not imply acceptance, priority or an implementation timeline.