Ilmenite Hydrogen Reduction — Lunar Oxygen ISRU

Reactor Conditions

Reduction temperature 950 °C

H₂ partial pressure 0.50 atm

Ilmenite content of feed 10.0 wt%

Grain size (d₅₀) 60 µm

Batch Progress

X = 0.0%X_eq ≈ 0%

Elapsed (batch time)

0.0 h

O₂ yield rate

0 g/h

Cumulative O₂ (100 kg regolith charge)

0.0 g

How it works

Roughly 3–10 wt% of mare regolith is ilmenite (FeTiO₃), the one common lunar mineral that reduces easily. Flowing hot hydrogen gas over it drives:

FeTiO₃(s) + H₂(g) ⇌ Fe(s) + TiO₂(s) + H₂O(g)

The water vapor is then split by solid-oxide electrolysis (2H₂O → 2H₂ + O₂), recovering breathable/propellant O₂ and recycling the H₂ back into the reactor — H₂ is a catalyst-like carrier, not consumed overall.

This sim tracks the ilmenite conversion fraction X(t) with a simplified rate law approaching a temperature/pressure-dependent equilibrium:

dX/dt = k(T)·(1 − X/X_eq)
k(T)  = k₀·exp(−Eₐ / R·T)         (Arrhenius rate constant)
X_eq  = K(T)·P(H₂) / (1 + K(T)·P(H₂))
K(T)  = exp(−ΔG° / R·T),  ΔG° = ΔH° − TΔS°

Temperature — raises both the rate constant k(T) and the equilibrium ceiling X_eq, matching why real reactors run near 900–1050 °C rather than lower.
H₂ pressure — pushes the equilibrium (Le Chatelier) toward more product, raising X_eq.
Grain size — finer grains expose more reactive surface area, so k(T) is scaled by a 1/d factor (shrinking-core intuition): halving grain size roughly doubles the rate.
Ilmenite content — sets what fraction of the 100 kg charge is reactive FeTiO₃; the rest is inert gangue (plagioclase, pyroxene) that never converts and stays dark in the drum.

O₂ mass is computed stoichiometrically: each mole of FeTiO₃ (151.7 g/mol) converted yields ½ mole O₂ (32 g/mol) once its H₂O is electrolyzed, so cumulative O₂ = moles ilmenite reacted × 16 g. Rate constants and thermodynamic terms here are illustrative, tuned to match the published order-of-magnitude (900–1050 °C, hours to reach 60–90% conversion) from NASA/JSC hydrogen-reduction ISRU studies — not a substitute for lab-measured kinetics of a specific regolith simulant.

Unreacted ilmenite Reduced (Fe + TiO₂) Inert gangue H₂ / H₂O gas flow

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