r/IsaacArthur • u/Opcn • Aug 06 '20

Turning carbon dioxide into liquid fuel. Scientists have discovered a new electrocatalyst that converts carbon dioxide (CO2) and water into ethanol with very high energy efficiency, high selectivity for the desired final product and low cost.

https://www.anl.gov/article/turning-carbon-dioxide-into-liquid-fuel
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u/Opcn Aug 07 '20

Storing hot CO2 exhaust from a car is hard to do. Recapturing carbon from the atmosphere is also hard to do.

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u/synocrat Aug 07 '20

This technology sounds like it might be able to pull carbon out of the air and store it.

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u/Opcn Aug 07 '20

You have to pull the carbon out with a compressor to have a high enough concentration to do anything.

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u/MiloBem Aug 13 '20

You don't sequester carbon by compressing and liquifying/distilling it from the atmosphere. The most likely industrial process in my opinion is Mineral carbonation.

You blow air through a solution that reacts with CO2, like Calcium Oxide, the resulting Calcium Carbonate is insoluble so you can remove it from the tank by simply letting it drop down, or maybe some cheap filter/centrifuge. It is then heated in a different chamber to release pure Carbon Dioxide and return Calcium Oxide powder into the tank where it is dissolved and ready to absorb.

The cycle uses some energy in blowing air into the tank, and a lot of energy in heating Calcium Carbonate. Then of course there is the energy of transporting Carbon Dioxide through some pipe into the other reactor that produces the fuel out of it.

The whole process is quite well developed, but like all reversible reactions it will cause losses of energy at different stages. So it only makes sense to use really green energy in it, like nuclear or maybe space solar.

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u/Opcn Aug 13 '20

That’s all well and good, but the device you use to blow the air through the solution is a compressor. So is the device that pulls the CO2 from the oven where you are reforming the CaO (which is the same step if you are relying on granules of Calcium Oxide passively gathering CO2). There are lots of options but none of them are going to be super energy efficient.

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u/MiloBem Aug 13 '20

I think we are talking different grades of compressors.

Yes, you obviously need to apply some pressure/force to move gases and liquids around, but you don't need very high pressure differential at any stage of the mineral carbonation process, as opposed to high pressure required in liquefaction and fractional distillation of air.

And yes, they all are inefficient. That's why they only make industrial sense when we have a cheap and abundant source of green energy, like modern fission, or ideally fusion plans.