[johnpool]

It is expected that as a result of climate change, the permafrost in Siberia will thaw. This will release large amounts of methane into the atmosphere. Methane is a strong greenhouse gas, even stronger than carbon dioxide.
 
Question: is it theoretically possible to let methane and carbon dioxide react so that pure carbon and water are formed? (CO₂+CH₄ -> 2C+2H₂O). If this could be done on a large scale, it could help solve the greenhouse gas problem.

If this is a stupid proposal/question (which is probably the case): I'm not a chemist, just a computer scientist from the Netherlands.

Regards, John Pool

[Borek]

To "let" them react? No.

To use a lot of energy to produce carbon and water from these gases? Yes.

But when we have plenty of cheap energy we can just stop burning fuels and stop CO₂ emissions. Which may (or may not, if we are beyond some tipping point) stop the climate changes.

[Corribus]

Just because you can write a reaction equation does not mean it is thermodynamically or kinetically favorable. Neither methane nor carbon dioxide are particularly reactive gasses. A quick analysis by heats of formation and standard entropies yields an estimated ΔH° and ΔS° under standard conditions to be on the order of -15 kJ/mol and -13 J/molK respectively (for the products being solid carbon and water vapor). This would imply a reaction that is thermodynamically spontaneous at room temperature (ΔG° ~ -11 kJ/mol) but gets progressively less so at higher temperatures due to an unfavorable entropy contribution. Nevertheless, we don't see solid carbon falling out the sky everywhere so it would seem to suggest some kinetic barrier, possibly a high energy intermediate. Maybe one would come up with some kind of selective catalyst to increase the reaction rate. But then one must contend with the fact that water vapor is also a potent greenhouse gas.

[Enthalpy]

Such spontaneous reactions stop at CO.

When the conditions push for it, you get a mix of H₂, CO and more exotic things. C forms only if oxygen is too scarce for CO, then H₂O is much more rare.

In fact, opposite reactions exist and serve to produce gaseous and liquid fuels from coal (...which isn't quite carbon) and water.

Other difficulty: capturing anything from the atmosphere. Not only are the amounts of CO₂ (and CH₄) colossal, one must treat air amounts even much bigger.

[billnotgatez]

... Maybe one would come up with some kind of selective catalyst to increase the reaction rate. But then one must contend with the fact that water vapor is also a potent greenhouse gas.

green plants and sunshine?

[Borek]

But then one must contend with the fact that water vapor is also a potent greenhouse gas.

That's actually not something I would care about. Water levels in the atmosphere are not limited by the amount of water on the surface, it is already in a huge excess.

[Enthalpy]

Green plants and sunshine?

That would be the most natural and green response to the CO₂ excess, but serious difficulties exist.

Plants absorb CO₂ and release O₂ when the biomass grows and absorbs the C. At steady state, a constant amount of vegetals absorbs no net CO₂. That is, the dying plants release in some molecular combination the C they absorbed during growth.

One must follow the C to grasp the balance of CO₂. Vegetals are a "carbon well" in that they store C. To remove CO₂ from the atmosphere, we would need to increase the amount of vegetals, or perhaps prevent the release of C molecules when the vegetals have grown, say by using their methane instead of natural gas, and by burying the rests.

The amount of CO₂ injected by humans in the atmosphere is huge. We have burnt a significant proportion of coal, oil, gas deposits that were created during the Carboniferous period, when more continental area was tropical and coated with tall forests, and this took eons. I don't imagine forests on Antarctica, nor replacing crops in Europe.

I'd be happy to read a credible plan to remove the excess CO₂. Even actions as simple as:
"Connect a pipe to the CO₂ exhaust of a power plant, inject it at deep silicates for stable storage"
stopped every time CO₂ emissions got a bit cheaper.

We would need to remove the excess CO₂, but I fear it won't happen. Not even will we stop the emissions. The best we can hope is to limit further emissions, that is, limit a little bit the damage.

My message to the engineers and inventors: don't rely on politicians for that. They only want the status quo, the huge bribes and taxes they get from fossil energies, and the cheap fossil fuels that boost the economy and increase the taxes. Very few governments push towards green alternatives presently (not even Germany builds wind turbines) and they will favor fossil fuels again as soon as their price drops. Individuals like Elon Musk have done more for the climate than all politicians together.