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This is just law of conservation of energy (1st law of thermodynamics). If burning carbon to CO2 produces certain amount of energy (part of which then can be us

by js8 8y ago

This is just law of conservation of energy (1st law of thermodynamics). If burning carbon to CO2 produces certain amount of energy (part of which then can be used to do useful work), then the reverse of that process, breaking up CO2 to carbon and oxygen, will require at least the amount of energy that was produced in burning it. So yeah, it's nice to have the technology to take CO2 from the air and create C and O2, however, the catch is, it requires energy. If that energy comes from fossil fuels, you will be better off not to do this thing at all, because you will end up creating a bit more CO2 in the process.

DougN7 8y ago
If the energy to do the reverse is not from carbon fuels (solar, wind) then it gets interesting though, right?
mhandley 8y ago
If we're going to depend on renewables for almost all electricity generation, this will require both energy storage, and installing more renewables than are needed for typical usage. This wouldn't be true if we had cheap energy storage that could supply load for weeks at a time through unusual dips in generation, but that seems unlikely. In practice it's cheaper to install excess generation than excess storage. Now, if you've got excess generation for electricity, then at times of good generation, you want to use that electricity for something, as otherwise the electricity price will be negative. Using it to produce synthetic fuels for aviation seems like a really good match, as that electricity would be effectively free.
jbay808 8y ago
The second law makes it much worse. If you take concentrated oxygen and concentrated carbon (soot), you can burn them in a sealed chamber into pure CO2. If you are very careful about extracting the energy, you might get most of it. But already the entropy has increased, because now the carbon and oxygen have mixed together. Attempting to reverse the reaction will need extra energy to deal with that. It gets much worse though, if you open up our chamber and vent the gas into the atmosphere. The entropy goes through the roof as the CO2 concentration drops to a few hundred PPM, and the cost of reversing the reaction goes up even more.
SilasX 8y ago
>If burning carbon to CO2 produces certain amount of energy (part of which then can be used to do useful work), then the reverse of that process, breaking up CO2 to carbon and oxygen, will require at least the amount of energy that was produced in burning it. Except that you don't have to do the exact reverse of the process, you just have to extract it from the atmosphere (or emission point) and contain it somehow, which could be any number of mechanisms that may or may not require significant energy (beyond the cost of distillation). Edit: Your argument is like saying that garbage collection (in the municipal sense) can never be economical because because it has to cost at least as much as making the products-to-be-disposed.
SubiculumCode 8y ago
I do not think all methods of CO2 capture require an active energy source. I believe there are sequestration methods involving volcanic rock.

by js8 8y ago

DougN7 8y ago

If the energy to do the reverse is not from carbon fuels (solar, wind) then it gets interesting though, right?

mhandley 8y ago

If we're going to depend on renewables for almost all electricity generation, this will require both energy storage, and installing more renewables than are needed for typical usage. This wouldn't be true if we had cheap energy storage that could supply load for weeks at a time through unusual dips in generation, but that seems unlikely. In practice it's cheaper to install excess generation than excess storage. Now, if you've got excess generation for electricity, then at times of good generation, you want to use that electricity for something, as otherwise the electricity price will be negative. Using it to produce synthetic fuels for aviation seems like a really good match, as that electricity would be effectively free.

jbay808 8y ago

The second law makes it much worse. If you take concentrated oxygen and concentrated carbon (soot), you can burn them in a sealed chamber into pure CO2. If you are very careful about extracting the energy, you might get most of it. But already the entropy has increased, because now the carbon and oxygen have mixed together. Attempting to reverse the reaction will need extra energy to deal with that. It gets much worse though, if you open up our chamber and vent the gas into the atmosphere. The entropy goes through the roof as the CO2 concentration drops to a few hundred PPM, and the cost of reversing the reaction goes up even more.

SilasX 8y ago

>If burning carbon to CO2 produces certain amount of energy (part of which then can be used to do useful work), then the reverse of that process, breaking up CO2 to carbon and oxygen, will require at least the amount of energy that was produced in burning it. Except that you don't have to do the exact reverse of the process, you just have to extract it from the atmosphere (or emission point) and contain it somehow, which could be any number of mechanisms that may or may not require significant energy (beyond the cost of distillation). Edit: Your argument is like saying that garbage collection (in the municipal sense) can never be economical because because it has to cost at least as much as making the products-to-be-disposed.

SubiculumCode 8y ago

I do not think all methods of CO2 capture require an active energy source. I believe there are sequestration methods involving volcanic rock.