We need to take CO2 out of the sky

Re:We need to take CO2 out of the sky by elihu on Tuesday October 05, 2021 @10:43PM (#28768579)

I don't know if there's any sane way to do this on a small scale and without concentrated CO2, but the first thing that comes to mind is to make synthetic methane using a Sabatier process. I think the way this works is you create hydrogen through electrolysis of water, and then react it CO2 to make methane.

Methane is a worse greenhouse gas than CO2, but if you burn it as fuel it's a carbon-neutral energy source.

Alternatively, you could use electrolysis to make hydrogen, but hydrogen is harder to store.

(I'm not a chemist, so I have no idea if this could work. And it probably wouldn't be very practical even if it did.)

I do like your idea of experimenting with a rock crusher. The article mentions that finding the least-energy means of crushing rocks to the appropriate size is something of an open problem.

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Re:We need to take CO2 out of the sky by IntrepidWorm on Wednesday October 06, 2021 @12:47AM (#28769309)

What purpose would the methane serve?

Assuming it's possible to use this process on a home scale with a decent solar grid and energy storage, it seems to me that you would be sequestering the carbon only very temporarily. Wouldn't the electrical energy used to produce the methane heat your home more efficiently (assuming you have an electric heating system) as you would be inviting energy losses through the Sabatier process?

Seems you would need to produce industrial levels of methane and distribute it (which would almost certainly be carbon expensive in it's own right) as substitute for naturally occuring methane being extracted from deposits.

It's a cool idea though. If there were a process to produce solid carbon, this would be much more promising (disclaimer: definitely not a chemist).

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Re:We need to take CO2 out of the sky by elihu on Wednesday October 06, 2021 @04:22AM (#28770523)

The general idea is you can make methane that's equivalent to the methane that comes out of the ground, but in a carbon neutral way. So it's a benefit if you can give it someone who was going to burn methane anyways, like to run their natural gas furnace.

That's not as satisfying as just plain sequestering the carbon somehow. I mean, it would almost certainly be better to just run an extension cord to a neighbors house and let them run an electric space heater or heat pump off of the excess electricity.

Maybe methane could be used as an ingredient to make something else that's possible to store or bury long term, like some kind of plastic or liquid? (Most of what I know about the processing of hydrocarbons is probably wildly inaccurate because I learned it from Factorio.)

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Re:We need to take CO2 out of the sky by nico_h on Wednesday October 06, 2021 @04:30AM (#28770570)

Time-shifting. If you have a good way of storing it you could generate methane during the months when you have surplus solar power and use it in winter after you've depleted your batteries and the sun is not bright enough.

Probably (over) insulating the house is the most efficient way of minimizing energy loss. But then does an over-insulated house get overly warm in summer or easier to cool?

The air-sourced methane could be used for things that are hard to electrify/de-carbonify, and could reduce the use of ground based sources.

I'm wondering at what level of carbon tax it makes more sense to extract the carbon from the air to turn it into plastic than to use ground-based oil.

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