Ilmenite Reduction with H2

Ilmenite (FeTiO₃) is a relatively common Lunar mineral. This process heats up ilmenite powder and passes hydrogen gas over it. The hydrogen gas strips off oxygen molecules, becoming water vapor. The water vapor is condensed into water and split through electrolysis. The oxygen is stored and the hydrogen is sent back into the process.

Operation

• Chemical reaction
  • FeTiO3 + H2 <–> FeO + Ti02 + H20 [1, pg 186]

Continuous Fluid-Bed Reduction

• Continuous feeding of fresh ilmentite.
• Withdrawal of spent ilmenite.
• Recirculation of hydrogen gas (reducing and fluidizing medium).
  • One possible electrolyte (used to split water) is zirconium oxide stabilized with calcium oxide or yttrium oxide (1, pg 186).
    • The problem is that these are not common Lunar materials.
• It is expected that the high heat-transfer coefficients between the fluidized solid ilmenite powder and the gas will make this an efficient process [1, pg 187].
• This is a fairly complex process. However, it could have a large oxygen output.
• Operational steps [1, pg 188]
  • Ilmenite is concentrated from lunar regolith and processed into a powder.
  • Ilmenite powder is fed into a three-stage fluidized bed.
    • First stage – Ilmenite is preheated by hot hydrogen gas
    • Second stage – This is the main reactor bed. Maximum temperature hydrogen gas reacts with the ilmenite powder. This forms water vapor (H2O), metallic iron (Fe), and titanium oxide (TiO2).
      • The water vapor and excess hydrogen are extracted and fed into an electrolyzer.
      • The free oxygen is sent to storage.
    • Third stage – Heat is recovered from the spent ilmenite by hydrogen gas.
  • The spent ilmenite is dumped from the reactor.
    • The spent ilmenite could be pressed into blocks or bricks. Additional heat may be necessary. [1, 189]

Advantages

• Relatively low operating temperatures
• Straightforward chemistry
• Hydrogen is rather benign compared to other reagents

Disadvantages

• Ilmenite must be physically separated from the raw material.
  • Additional equipment, energy, time, space.
• Low equilibrium conversion
  • Relatively small water vapor pressures will stop the reduction and cause it to reverse [1, pg 187].
  • Potential solution – create a pressure gradient that moves (diffusion) the water vapor from the reaction chamber to a cold trap where it then condenses [1, pg 187].
  • Diffusion and heat removal rates have to exceed the rate of water vapor formation but not be large enough to hamper water vapor formation [1, pg 187].
  • Diffusion calculations indicate that it may not be possible to reduce water vapor pressure in large scale systems [1, pg 187]. This is OK for LH though since our systems are all small-scale.

Parameter priorities

1. Able to be constructed/maintained locally
   1. UNKNOWN
2. Minimal reliance on Earth for reagents
   1. Hydrogen will probably have to be imported from Earth.
   2. The hydrogen should be able to be recovered. Unknown how much might be lost.
3. Operable in 1 SLHA
   1. UNKNOWN
   2. Hydrogen gas is flammable. But I doubt Homesteaders will store hydrogen as a gas because the molecule is so “slippery”. That means hydrogen gas molecules are so small that they can escape through solid materials.
   3. A much better way to store hydrogen is as water. Just split the water when you need hydrogen (or oxygen)
4. Ease of maintenance
   1. UNKNOWN
5. Simple
   1. UNKNOWN
6. Durable
   1. UNKNOWN
7. Energy input
   1. UNKNOWN
8. Heat output
   1. UNKNOWN
9. No hazardous materials are produced
   1. UNKNOWN
10. Efficiency
    1. UNKNOWN
11. Processes that extract more than just oxygen are preferred
    1. Iron and titanium oxide are byproducts.
12. Weight/mass/volume
    1. UNKNOWN
13. Other uses for the reagents
    1. UNKNOWN

Resources

1. Processing Lunar Soils for Oxygen and Other Materials. Knudsen, C. and Gibson, M. Space Resources (NASA SP-509) Vol 3 Resources

Need to read

Oxygen Extraction from Lunar Materials: an Experimental Test of an Ilmenite Reduction Process (http://adsabs.harvard.edu/full/1985lbsa.conf..551W)