Water gas is a synthesis gas, containing carbon monoxide and hydrogen. It is a useful product but requires careful handling because of the risk of carbon monoxide poisoning. The gas is made by passing steam over a red-hot carbon fuel such as coke:
- H2O + C → H2 + CO (ΔH = +131 kJ/mol)
The reaction is endothermic so the fuel must be continually re-heated to keep the reaction going. In order to do this, an air stream, which alternates with the vapor stream, is introduced for the combustion of carbon to take place.
- O2 + C → CO2 (ΔH = −393.5 kJ/mol)
Theoretically to make 6 L of water gas, 5 L of air is required.
Or alternatively to prevent contamination with nitrogen, energy can be provided by using pure oxygen to burn carbon into carbon monoxide.
- O2 + 2 C → 2 CO (ΔH = −221 kJ/mol)
In this case 1 L of oxygen will create 5.3 L of pure water gas
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