Reverse Water-Gas Shift Reaction
The synthesis of carbon monoxide is readily achieved using the Reverse Water-Gas Shift Reaction.
CO2 + H2 → CO + H2O (deltaH = +9 kcal/mole) The Hydrogen must be obtained from Electrolysis of water.
High temperature electrolysis
Carbon monoxide can also be produced by high-temperature electrolysis of carbon dioxide with solid oxide electrolyzer cells:
- 2 CO2 → 2 CO + O2
Liquid carbon monoxide and liquid oxygen can be burned as a fuel producing only carbon dioxide and unreacted oxygen and carbon monoxide in the exhaust. This is especially suitable for utility vehicles on Mars because carbon monoxide and oxygen and can be readily produced from the Martian atmosphere. Carbon monoxide and oxygen can readily be produced anywhere on Mars while fuels containing hydrogen need water as a raw material, which may be scarce in tropical Mars.
The lower energy density per unit weight of this fuel compared to liquid methane and liquid oxygen should not be a problem in Mars' low gravity unless the requirement is for a long range vehicle. A disadvantage of this fuel is that carbon monoxide is a poison. For safety reasons the engine of such a vehicle must be isolated from the passenger compartment. Repair and maintenance en route would require the driver to put on a Mars suit and exit the vehicle.
Carbon monoxide can be used to fill rocket launching silos on Mars. This would prevent Carbon dioxide (which has a much higher freezing point) from condensing as a frost on cryogenic tanks and piping.
A blast furnace is loaded with iron ores, usually hematite Fe2O3 or magnetite Fe3O4, together with coke . Air pre-heated to 900 °C is blown through the mixture, in sufficient amount to turn the carbon into carbon monoxide:
- 2 C + O2 → 2 CO
This reaction raises the temperature to about 2000 °C The carbon monoxide reduces the iron ore to metallic iron
- Fe2O3 + 3 CO → 2 Fe + 3 CO2
Some iron in the high-temperature lower region of the furnace reacts directly with the coke:
- 2 Fe2O3 + 3 C → 4 Fe + 3 CO2
The direct production of carbon monoxide from atmospheric CO2 using the using the Reverse Water-Gas Shift Reaction might be used to smelt iron. This avoids the need for coke, that is not available on Mars.
Carbon monoxide is toxic to humans and many other species. It bonds readily to hemoglobin molecules in blood, preventing the transfer of oxygen within the body. Symptoms begin at concentrations as low as 100 ppm. The potential release of incidental amounts of carbon monoxide outside need not be a worry on Mars because carbon monoxide is already a component of the atmosphere, and that atmosphere is already 100% fatal for short term exposures of people whether carbon monoxide has been released or not. Release of carbon monoxide in the sealed environment of a Mars colony must be avoided rigorously.