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We are looking at doing planet changing work, and removing CO2 from the atmosphere. The issue is storing the CO2. Please let us know the best ways to compress millions of tons of CO2, as we have limited storage space. For example, how much could we compress a ton of CO2 gas? What size container would a ton of CO2 fit in, when fully compressed? Also, would turning tons of CO2 into liquid be more space effective? How much space would a ton of CO2 gas that has been turned into liquid take up?

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closed as too broad by Mithoron, M. Farooq, Mathew Mahindaratne, Poutnik, Nilay Ghosh Oct 13 at 10:53

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  • $\begingroup$ Compression of CO2 mens also CO2 generation unless everything is green powered. People looks for sequestration, as in the answer. Or to some kind of fuel production, that again must be green to be effective. $\endgroup$ – Alchimista Oct 12 at 10:36
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    $\begingroup$ To remove 100ppm CO2 from the atmosphere of Earth would require removing about 1800 billion tons of CO2. If you solidified this CO2 into dry ice you would be producing 1200 billion cubic meters of CO2, or about 1200 km^3. This would be enough to fill half of Lake Victoria, or cover the entire land area of Hong Kong in a meter thick layer of dry ice. So... good luck with that. $\endgroup$ – J... Oct 12 at 16:17
  • $\begingroup$ The global average $CO_2$ in the atmosphere is around 400 ppm. $\endgroup$ – M. Farooq Oct 12 at 17:33
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    $\begingroup$ @M.Farooq And we certainly don't want to remove all of it. That would be catastrophic. $\endgroup$ – J... Oct 12 at 20:42
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    $\begingroup$ 7z a CO2Storage.7z "Tons of CO2" $\endgroup$ – Sean Oct 12 at 22:26
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Poor carbon dioxide has been unnecessarily defamed as a greenhouse effect. This is not only gas in the atmosphere which is an infrared absorber. Guess what, water vapor is a major culprit as well along with methane (recall cows digestive system). Nature has a very delicate balance, carbon dioxide is plant's food as well.

I recall some people doing PhDs on carbon dioxide remediation in chemical engineering. One of options is to pump carbon dioxide into deep rocks with a hope that it will convert into carbonates, mainly calcium carbonate in deep layers. One can then study all types of phase diagram of carbon dioxide etc.

One green solution is a massive drive for the plantation of trees. This option is far better than more expensive options.

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    $\begingroup$ The plantation approach is a great way to restore Earth, but is there any more land left that can sustain vegetation... Nearly every bit appears to have been claimed for construction or housing purposes. $\endgroup$ – Priyanshu Das Oct 12 at 3:01
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    $\begingroup$ At least the forests which have been destroyed by humans should be re-grown. There is a trend of roof top gardening in some developed areas. And every tree/plant one person grows counts even in a medium sized pot in a balcony. $\endgroup$ – M. Farooq Oct 12 at 3:12
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    $\begingroup$ Just for precision and independent of any debate. Removal of water from the atmosphere happens continuously and fast by rain cycle. CO2 is also fixated but on more slow rate. A quick fixation is done by diatoms rather than plants. But it seems that more CO2 means less diatoms. That is why CO2 is at focus. That CO2 is plant food is not a mechanism of fixation. CO2 → plant→ digestion → CO2 & CH4. It only works if we let forests grow up. $\endgroup$ – Alchimista Oct 12 at 10:50
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    $\begingroup$ This does not answer the question whatsoever. $\endgroup$ – J... Oct 12 at 15:56
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    $\begingroup$ The fact that $H_2O$ and $CH_4$ are both also infrared absorbers does not mean $CO_2$ is being "unnecessarily defamed". E.g., $CO_2$ is a forcing agent, $H_2O$ is not. (see: grist.org/article/… ) $\endgroup$ – theorist Oct 12 at 18:11
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In case you're actually trying to design a serious scheme for extracting and storing carbon dioxide, you might want to start by reading the Wikipedia articles on carbon capture and storage and carbon sequestration.

For the impatient, the summary is that it's simply not practical to store that much $\ce{CO2}$ in containers of any kind. Instead, you either:

  • react it with minerals to form carbonates (which are stable, but require you to first mine lots of suitable minerals and then somehow deal with the fact that the reactions are very slow under typical conditions);

  • try to do something useful with it, such as:

    • making plants grow faster (which works up to a point, but would require huge greenhouses to do on a large scale, and isn't that much more efficient than simply releasing the $\ce{CO2}$ into the atmosphere and growing the same amount of plants outdoors would be) or

    • using it as a chemical feedstock (which typically requires you to spend considerable energy to drive off most of the oxygen from the $\ce{CO2}$, as there's not much you can do with $\ce{CO2}$ without de-oxidizing it first — more energy, in fact, than you obtained by burning the carbon with oxygen in the first place); or

  • pump it underground and hope and pray really hard that it stays there (which isn't that much of a stretch if you e.g. pump it into a seam that previously held oil or natural gas, since clearly that hadn't leaked in the past; of course, your seam now has a borehole in it that it didn't have before, which introduces an extra leak risk — also, when done with oil or gas fields, this isn't so much a way of removing $\ce{CO2}$ from circulation as it is a way of offsetting the $\ce{CO2}$ emissions from burning the extracted oil or gas).

Pumping the $\ce{CO2}$ into the ocean and letting it dissolve there as carbonate ions is also an option that some have considered, but comes with some serious risks like acidifying the ocean (since carbonic acid is, surprise surprise, an acid), disrupting deep-sea ecosystems and potentially creating dead zones on the ocean floor, and of course the risk of the $\ce{CO2}$ coming out of solution and bubbling back up into the atmosphere over time (or, if you're really unlucky, all at once).

Another option that the Wikipedia articles (currently) only mention in passing is storing the carbon not as $\ce{CO2}$ but as elemental carbon, a.k.a. charcoal. This is most easily done before you burn the fuel, by pyrolyzing it to split it into carbon-rich charcoal and hydrogen-rich syngas. You can then bury the charcoal underground (where it's pretty stable and even makes a decent soil additive) and burn the syngas for energy (which releases $\ce{CO2}$, but nearly not as much as if you'd burnt the original fuel directly; if the original fuel was from a non-fossil source, you can even end up with negative net carbon emissions).

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As in how much you could compress $\ce{CO2}$ would be the point when it gets converted to dry ice. Surely a solid would take even lesser space than liquid. As for liquid, you need to maintain a pressure of approx 5 atm at 31.1 °C to liquify $\ce{CO2}.$

If you want, you can have a look at the article World can ‘safely’ store billions of tonnes of CO2 underground on carbonbrief.org (accessed 2019-10-13). They here speak about how we can store large amounts of $\ce{CO2}$ in depleted oil fields, natural gas reserves or other such underground storage reserves. Even MIT has a PDF on carbon storage and sequestration. Have a look!

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