Methanol Synthesis¶

In this tutorial you will model the industrial synthesis of methanol from synthesis gas (CO + 2 H2 → CH3OH) in DWSIM's Classic UI. This is the capstone tutorial: it combines compression, equilibrium reaction, separation, and (optionally) a recycle loop.

What you will learn

How to design a complete synthesis loop with multiple unit operations
How to model methanol synthesis at high pressure
How to balance per-pass conversion with overall conversion via recycle

Prerequisites

Completed Ammonia Synthesis and Recycle Loops

Process Overview¶

Methanol from syngas (CO + CO2 + H2):

CO + 2 H2 → CH3OH (exothermic, equilibrium-limited)

Industrial conditions: 50-100 bar, 200-300 °C, copper-zinc-alumina catalyst. In an industrial reactor the per-pass conversion is only 15-25% (the syngas carries CO2 and inerts, and the catalyst does not reach equilibrium), so unconverted syngas must be recycled. The equilibrium reactor of this tutorial gives the thermodynamic ceiling for a clean 2:1 feed, which is much higher.

We start with single-pass model; recycle is an exercise.

Process Flow Diagram¶

graph LR
    F["Syngas<br/>2:1 H2:CO<br/>30 bar"] --> C["C-1<br/>Compressor<br/>80 bar"]
    C --> H["H-1<br/>Heater<br/>525 K"]
    H --> R["R-1<br/>Eq. Reactor"]
    R --> CL["CL-1<br/>Cooler<br/>308 K"]
    CL --> SEP["SEP-1<br/>Separator"]
    SEP -->|Gas| PG["Recycle Gas"]
    SEP -->|Liquid| MeOH["Crude Methanol"]

Key Design Parameters¶

Parameter	Value
Compounds	Hydrogen, Carbon monoxide, Methanol
Property Package	Peng-Robinson
Feed	3 mol/s (2 H2 + 1 CO), 300 K, 30 bar
Compressor outlet	80 bar, 75% efficiency
Reactor T	525 K (252 °C), isothermal
Cooler outlet	308 K
ln(Keq)	`11833/T - 29.07`

Step-by-Step in the Classic UI¶

1. Set up¶

File > New Chemical Process Model:

Compounds: Hydrogen, Carbon monoxide, Methanol
Property Package: Peng-Robinson

Why Peng-Robinson for syngas?

PR handles high-pressure light gases and the supercritical-like behavior of H2 well. Methanol's hydrogen-bonding contribution is weaker at the elevated reactor temperature, so PR's accuracy is acceptable for this synthesis loop.

2. Define the methanol synthesis reaction¶

Edit > Simulation Settings > Reactions → Add Equilibrium:

Name: MeOH_Synth
Stoichiometry: Carbon monoxide = -1, Hydrogen = -2, Methanol = +1
Base compound: Methanol, Phase: Vapor, Basis: Activity
ln(Keq): 11833/T - 29.07

Create Reaction Set MeOHSet containing it.

Where the Keq expression comes from

This is the correlation of Graaf et al. (1986), Kp = 10^(5139/T - 12.621) in bar⁻², written in natural logarithms. With the Vapor phase and the Activity basis, DWSIM evaluates it on fugacities relative to 1 atm, so a pressure-based Kp is the right input. At 525 K it gives Kp = 1.5 × 10⁻³.

Why an Equilibrium Reactor?

Like ammonia synthesis, MeOH synthesis is equilibrium-limited at industrial T,P. The Equilibrium Reactor gives the thermodynamic ceiling on yield; real reactors approach but do not reach it, and recycling unreacted syngas is what drives overall conversion above 95%.

Why high pressure (80 bar)?

CO + 2 H2 → CH3OH reduces 3 mol of gas to 1 mol; high P shifts the equilibrium toward MeOH per Le Chatelier. Industrial low-pressure methanol plants run at 50-100 bar, balancing yield improvement against compression cost.

3. Build the train¶

Drag and configure (mirroring the ammonia synthesis tutorial pattern):

Material Stream Syngas: T=300 K, P=30 bar, total molar flow=3 mol/s, mole fractions: H2=0.667, CO=0.333, MeOH=0
Compressor C-1: Adiabatic, outlet=80 bar, η=75%
Material Stream Comp-Out (empty)
Heater H-1: outlet T=525 K
Material Stream Hot (empty)
Equilibrium Reactor R-1: Isothermal, Reaction Set=MeOHSet
Material Stream Reactor-Out (vapor outlet, empty)
Material Stream Reactor-Liq (liquid outlet, empty)
Cooler CL-1: outlet T=308 K
Material Stream Cooled (empty)
Separator Vessel SEP-1
Material Stream Recycle-Gas (empty)
Material Stream Crude-Methanol (empty)

Wire all connections with appropriate energy streams (W_comp, Q_rx, Q_cool).

Methanol synthesis flowsheet

4. Solve¶

F6 ON → Solve.

5. Inspect results¶

R-1 Results: CO conversion about 68% (extent 0.68 mol/s); this is the equilibrium ceiling at 525 K and 80 bar
Crude-Methanol stream Results: 0.68 mol/s at 0.99 methanol mole fraction (because of MeOH's much higher BP than H2/CO)
Recycle-Gas Results: 0.95 mol/s of unreacted H2 and CO, still at 2:1 (the reaction consumes them in the feed ratio), with 0.6% methanol
W_comp Energy: compression power (11.5 kW); Q_rx removes 69 kW, Q_cool 39 kW

Results and Validation¶

Variable	Expected
CO conversion at equilibrium	about 68%
Crude methanol purity	0.99 mole frac
Recycle gas H2/CO ratio	2.0 (a stoichiometric feed keeps its ratio)

Expected results

About 68% of the CO reacts at equilibrium at 525 K and 80 bar; an industrial reactor, with CO2 and inerts in the feed and finite kinetics, stays at 15-30% per pass. Cooled liquid is high-purity methanol due to BP differences.

Understanding the Results¶

Methanol synthesis is a textbook equilibrium-limited reactor design:

Le Chatelier: 3 mol gas → 1 mol product, so high P shifts equilibrium toward products
Temperature: low T favors equilibrium, but catalyst needs ~250 °C
Recycle: per-pass conversion is low; recycling unreacted syngas pushes overall conversion above 95%

In a real plant: recycle compressor + small purge to remove inerts, then distillation to remove water and light ends from the crude methanol.

Automating This Tutorial¶

Files in this repository

Python script: examples/advanced/07_methanol_synthesis.py
Pre-built flowsheet: examples/saved/methanol_synthesis.dwxmz
In DWSIM: Samples list on the welcome screen, Tutorial 13 - Methanol Synthesis

FluentAPI (Python)MCP Server (JSON-RPC)LLM Prompt

See examples/advanced/07_methanol_synthesis.py in the DWSIM.Tutorials repository.

dwsim.reaction.define_equilibrium, then dwsim.unitop.add for each operation in sequence.

Output may vary

Results depend on the LLM's reasoning quality and tool-use accuracy. Always verify the simulation matches your intent before relying on the numbers.

Use DWSIM (via the MCP server) to build the following simulation:

- Create a flowsheet called "MethanolSynthesis"
- Add Hydrogen, Carbon monoxide and Methanol as compounds; set the
  property package to "Peng-Robinson"
- Define an equilibrium reaction "MeOH_Synth" with stoichiometry
  CO = -1, H2 = -2, Methanol = +1; base compound = Methanol,
  phase = Vapor, basis = Activity, ln(Keq) = 11833/T - 29.07; add it
  to a new reaction set "MeOHSet"
- Add a material stream "Syngas" at 300 K and 30 bar with total molar
  flow = 3 mol/s and mole fractions H2 = 0.667, CO = 0.333, MeOH = 0
- Add a Compressor "C-1" (adiabatic, outlet P = 80 bar, efficiency
  = 75%) with energy stream W_comp
- Add a Heater "H-1" with outlet T = 525 K
- Add an Equilibrium Reactor "R-1" in isothermal mode using reaction
  set MeOHSet, with energy stream Q_rx
- Add a Cooler "CL-1" with outlet T = 308 K, energy stream Q_cool
- Add a Separator Vessel "SEP-1" with vapor outlet "Recycle-Gas" and
  liquid outlet "Crude-Methanol"
- Connect: Syngas → C-1 → H-1 → R-1 → CL-1 → SEP-1
- Solve the flowsheet
- Report the per-pass CO conversion in R-1, the methanol mole
  fraction in Crude-Methanol, the H2/CO ratio in Recycle-Gas, and
  the energy flows W_comp, Q_rx and Q_cool

Exercises

Lower reactor T to 475 K. How does the conversion change? Look at Reactor-Liq too: at 475 K and 80 bar part of the methanol already condenses inside the reactor.
Increase pressure to 120 bar. Is the additional compression cost justified?
Add a Recycle logical operation: connect Recycle-Gas back to a Mixer at the Compressor inlet (with a small purge stream via a Splitter for inerts).
Add CO2 (10 mol%) to the feed and a second equilibrium reaction (CO2 + 3 H2 → CH3OH + H2O) for a more realistic syngas.

Next Steps¶

In Divided-Wall Column, you will separate three products in a single shell and compare its energy use with two conventional columns.