Methane cracking
Methane cracking Note: the word 'cracking' has nothing to do with physical cracks in any material. is a process that converts methane (usually from natural gas) into hydrogen gas and solid carbon. The hydrogen can be burned for energy, and the carbon could be buried in the ground or used for something else. The carbon does not become CO2 (unlike normal combustion of methane).
Energy viability
Every methane-cracking method invented so far is a net loss of energy. Meaning that it takes more energy to crack the methane than you ultimately get from burning the hydrogen.
But in theory, this need not be true:
- Cracking the methane:
- CH4 → C + 2 H2 (energy in:endothermic reaction 74.850 kJ/mol)
- CH4 → C + 2 H2 (energy in:endothermic reaction 74.850 kJ/mol)
- Burning the hydrogen:
- 2 H2 + O2 → 2 H2O (energy out:exothermic reaction 285.820 kJ/mol)
Hydrogen production efficiency comparison
| Type | Method | Energy out / energy in |
|---|---|---|
| Methane cracking | Theoretical best case | 382% from the chemistry equations above |
| Not methane cracking | Electrolysis of water | 80% |
| Methane cracking | Best technologies so far | __ to be filled in soon |
| Not methane cracking | Heat -> turbine -> electrolysis of water | 25% |
There have been some green initiatives to use non-fossil-fuel energy to crack methane to make hydrogen gas. However, this is only worthwhile if the efficiency is better than non-methane-cracking ways to make hydrogen (see table).
Above 100%, you don't need any non-fossil-fuel energy for it to be green. Just burn some of the hydrogen to keep cracking the methane. Sadly, this has never been achieved.
In the ideal case, fossil fuels could power the entire world with zero carbon emissions. At least, until oil and gas reserves run out.