Lecture 10

Question 1

Ilmenite reduction with H2

Answer 1

• product: Oxygen
• feedstock: Ilmenite (FeTiO3) from high-Ti mare basalts
• Reduction (step 1, at 700-1000°C) -> FeTiO3 + H2 -> Fe + TiO2 + H2O
• Electrolysis (step 2) -> H2O -> H2 + 1/2 O2
• mildly endothermic
• mole fraction of water needs to remain < 10% to maintain the reaction
• shrinking core type process

Question 2

Ilmenite reduction with H2 - Pro/Con

Answer 2

• Pro
  
  • single reaction step already yields water
  • Mild reaction T
  • Ilmenite is an abundant resource in Mare regions
• Con
  
  • Beneficiation of ilmenite is recommended & greatly affects process efficiency
  • only low oxygen yield is possible (5wt%)

Question 3

Shrinking core type process

Answer 3

1. Diffusion of the reactant through product TiO2 layer
2. Reaction with the ilmenite core -> core shrinks
3. Diffusion of iron out of the TiO2 pores (more porous material after reaction)
4. Formation of metallic iron outside the ilmenite grains

Question 4

Glass reduction with H2

Answer 4

• product: O2
• Feedstock: Glass (w. up to 20wt% FeO)
  
  • from mare basalts, either produced by impacts or volcanic activity
  • faster reaction kinetics compared to silicates
• Reduction: FeO + H2 -> Fe + H20
• Electrolysis: H2O -> H2 + 1/2 O2
• Glass found in agglutinates abundant but mixed with silicates -> beneficiation required
• Glass found in pyroclastic deposits is comparably pure, but not as abundant

Question 5

Glass reduction with H2 - Pro/Con

Answer 5

• Pro
  
  • Single reaction step already yields water
  • Mild reaction temperatures
  • Glass is an abundant resource across the lunar surface
• Con
  
  • Beneficiation of glass is required of not taken from a pyroclastic deposit
  • Process has not yet been demonstrated on a plant scale

Question 6

Ilmenite reduction with CO

Answer 6

• product: oxygen
• feedstock: Ilmenite from high-Ti mare basalts
• 1. Step: Reduction: FeTiO3 + CO -> Fe + TiO2 + CO2
• 2. Step: CO2 cracking: CO2 -> Co + 1/2 O2
• similar to reduction with H2 but slower (higher activation energy)
• follows the shrinking core model
• CO2 cracking is highly endothermic

Question 7

Ilmenite reduction with CO - Pro/Con

Answer 7

• Pro
  
  • Mild reaction T
  • Ilmenite is an abundant resource in Mare regions
• Con
  
  • Beneficiation of ilmenite is recommended & greatly affects process efficiency
  • Cracking of CO2 requires much energy
  • Reduction rate is slower c compared to using hydrogen

Question 8

Ilmenite Reduction with CH4

Answer 8

• product: O2
• feedstock: Ilmenite from high-Ti mare basalts
• Step 1: Reduction: FeTiO3 + CH4 -> Fe + TiO2 + CO + H2
• Step 2: Hydrogenation: CO + 3 H2 -> CH4 + H2O
• Step 3: Electrolysis: H2O -> H2 + 1/2 O2
• similar process as for reduction with hydrogen
• reaction T starts around 1000°C & involves decomposition of CH4 into C & H2
• SW implanted H2/C could be used to replenish

Question 9

Ilmenite reduction with CH4 - Pro/Con

Answer 9

• Pro
  
  • Medium reaction T
  • Ilmenite is an abundant resource in Mare
• Con
  
  • Beneficiation of ilmenite is recommended & greatly affects process efficiency
  • Hydrogenation as additional process step
  • Additional reactant needed (H2)

Question 10

Carbothermal reduction

Answer 10

• product: oxygen
• feedstock: any kind of silicate or oxide minerals
• Step 1:
  
  • Reduction (v1): Mg2SiO4 + 2CH4 -> 2MgO + Si + 4H2 + 2CO
  • Reduction (v2): FeTiO3 + C -> Fe + TiO2 + CO
• Step 2: Hydrogenation: CO + 3H2 -> CH4 + H2O
• Step 3: Electrolysis: H2O -> H2 + 1/2 O2
• Carbothermal includes all processes involving molten reactant & carbon in some form
• as CH4 decomposes prior to reacting C/CO/CO2 can be used
• melt required for highest efficiency
• No beneficiation
• process was demonstrated with simulants

Question 11

Carbothermal reaction - Pro/Con

Answer 11

• Pro
  
  • Higher oxygen yield possible ( ~10wt%)
  • No beneficiation required & applicable to various minerals
• Con
  
  • High reaction T
  • Added system complexity & material handling challenges
  • Considerable reactant makeup requires resupply or compensation from SWIP

Question 12

Extraction with Fluorine

Answer 12

• product: O2
• Feedstock: all minerals
• MxyOy + y F2 -> xy MF(2/x) + y/2 O2
• large variety of feedstock
• Fluorine is a strong oxidiser
• Silicates combine with fluorine to build fluorides, oxygen is liberated
• has been demonstrated in the 90s

Question 13

Extraction with Fluorine - Pro/Con

Answer 13

• Pro
  
  • About 80% of the total oxygen can be released
  • Moderate T required
• Con
  
  • Experiments have only been done with small sample quantities
  • Fluorine needs to be recycled to a high degree or imported
  • Fluorine is toxic to humans

Question 14

Sabatier process

Answer 14

• product: oxygen
• Feedstock: CO2 in the atmosphere (96% on Mars)
• Step 1: Reaction: CO2 + H2 -> CH4 + 2 H2O
• Step 2: Electrolysis: H2O -> H2 + 1/2 O2
• T = 300-400°C; ~30 bar
• Nickel or ideally ruthenium acts as catalyst
• residual H2 is fed back into reaction
• process is used on the ISS to support recovery of oxygen
• CH4 & O2 can be used as fuel -> Methalox engine

Question 15

Sabatier process - Pro/Con

Answer 15

• Pro
  
  • Well-known process, part of Life Support System (LSS) on the ISS
  • Exothermic reaction, excess heat can be used to drive reactor
• Con
  
  • H2 needs to be imported from Earth
  • Excess heat might require radiators or heat sinks