3,024
edits
Methane cracking: Difference between revisions
→Energy viability
No edit summary |
|||
| (6 intermediate revisions by the same user not shown) | |||
| Line 1: | Line 1: | ||
Methane cracking{{x|Note: the word 'cracking' has nothing to do with physical cracks in any material.}} is a process that converts methane (usually from [[fossil fuels|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 [[climate change|CO<sub>2</sub>]]''' (unlike normal combustion of methane). | |||
==Energy viability== | ==Energy viability== | ||
{{sum|'''Not''' viable - but could work in theory}} | |||
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. | 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. | ||
| Line 5: | Line 8: | ||
But '''in theory''', this need not be true: | But '''in theory''', this need not be true: | ||
: Cracking the methane: | : Cracking the methane: | ||
:: | :: CH<sub>4</sub> → C + 2 H<sub>2</sub>     ({{p2|energy in:|'''endo'''thermic reaction}}   74.850 kJ/mol)<br /> | ||
: Burning the hydrogen: | : Burning the hydrogen: | ||
:: 2 | :: 2 H<sub>2</sub> + O<sub>2</sub> → 2 H<sub>2</sub>O   ({{p2|energy out:|'''exo'''thermic reaction}} 571.640 kJ/mol) | ||
===Hydrogen production efficiency comparison=== | ===Hydrogen production efficiency comparison=== | ||
| Line 18: | Line 21: | ||
|Methane cracking | |Methane cracking | ||
|Theoretical best case | |Theoretical best case | ||
| | |764% {{p|from the chemistry equations above}} | ||
|- | |- | ||
|'''Not''' methane cracking | |'''Not''' methane cracking | ||
|Electrolysis of water | |Electrolysis of water | ||
|80% | | 80% | ||
|- | |- | ||
|Methane cracking | |Methane cracking | ||
|Best technologies so far | |Best technologies so far | ||
| | | . . . {{p|To be filled in soon.<br />It's almost certainly less than 80%.}} | ||
|- | |- | ||
|'''Not''' methane cracking | |'''Not''' methane cracking | ||
|Heat -> turbine -> electrolysis of water | |Heat -> turbine -> electrolysis of water | ||
|25% | | 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). | 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. | 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 [[peak oil|oil and gas reserves run out]]. | In the ideal case, fossil fuels could power the entire world with zero carbon emissions. At least, until [[peak oil|oil and gas reserves run out]]. | ||