Can I get carbon from the air?
December 6, 2005 10:20 AM   Subscribe

Theoretically, if I needed large amounts of carbon, could I extract it from the air? How could I do it?
posted by Mwongozi to Science & Nature (18 answers total)
If only there was some source of carbon available.
posted by jellicle at 10:23 AM on December 6, 2005

Best answer: The traditional method is to harvest vegetation.
posted by warbaby at 10:24 AM on December 6, 2005

Response by poster: OK, good answer. But what if I don't have the room to grow trees, or need the carbon quickly?

Could I get a tree-sized amount of carbon in, say, a few months? Or less?
posted by Mwongozi at 10:27 AM on December 6, 2005

Best answer: Cryogenic distillation of the atmosphere will get you N, O, CO2 and Ar in commercially useful amounts. Basically, all the carbon (even petrocarbons) circulated through the atmosphere at one time. There are a few exceptions such as diamonds, but those are rare and vegetables are plentiful. Are there no vegetables on your planet?
posted by warbaby at 10:33 AM on December 6, 2005

Looks like there are some people who have thought about this already.

Google: "carbon dioxide" sequestration.
posted by 5MeoCMP at 10:35 AM on December 6, 2005

AFAIK the best known way to fix carbon from the air is via the plant enzyme rubisco. Without a good enzyme, this is a hella slow reaction due to the fact that you've got little bits of CO2 buzzing around in the air and you've got to get it in just the right configuration before it will react to become a non-gas. Of course, you also need to add a bit of energy (e.g. in photosynthesis). Without real plants, you'd probably need some sci-fi-level contraption that worked as a rubisco-based bioreactor.
posted by rxrfrx at 10:39 AM on December 6, 2005

Best answer: If you want a mechanical process, the Amateur Scientist back in the 50's or early 60's had a project for Linde process gas liquification.

You can build it out of old refrigerator compressors, copper tube and Thermos bottles. The liquification rigs are arranged in a cascade, with the liquid gas in the warmer stages chilling the input to the next stage. It's easy enough (basic plumbing skills) that it shows up as science fair projects quite frequently.

You just let it run and run and run and run and after a while, the thermos bottles have amounts of liquified gas proportional to the atmosphere.
posted by warbaby at 10:49 AM on December 6, 2005

What 5MeoCMP said. Carbon dioxide sequestration is the name of the group of technologies that you are looking for.

As warbaby mentions, there is a significant industry of cryogenic air distillers. Liquid CO2 has thousands of commercial uses, including as a shield gas for welding, for chemical production, for oil and gas extraction and not least for making dry ice (which has hundreds of uses also). Typical plant sizes run up to 100s of tonnes of liquid CO2/day. There are probably a few hundred distillation plants in the world, if not more.
posted by bonehead at 10:55 AM on December 6, 2005

"The Amateur Scientist," Scientific American, p. 160, May 1957.
posted by warbaby at 11:03 AM on December 6, 2005

Cryogenic Engineering (Van Nostrand)
posted by warbaby at 11:52 AM on December 6, 2005

The best-marked answers refer to capture of liquefied CO2 from the air. By "get large amounts of carbon" I assumed you meant solid, reduced carbon compounds.
posted by rxrfrx at 12:12 PM on December 6, 2005

Best answer: OK, reduce it with hydrogen in an arc reactor. Extra points if you use a pressure high enough to yield diamonds.
posted by warbaby at 12:39 PM on December 6, 2005

Um, do you want carbon dioxide AKA Dry Ice? That's a compound with carbon in it, but it's no more like diamonds or graphite then table salt is too chlorine gas, and it's definitely not what people mean when they say "Carbon".

Carbon comes in many pure forms, from diamonds to graphite (like pencil lead). Purifying the CO2 in the air doesn’t get you much of anything, you have a chunk of dry ice or a bottle of CO2: something you're breathing out large quantities of already. You might as well just blow into a balloon (of course there are a lot more chemicals in your breath, but there's a lot more CO2 then you're breathing in)

Another easy way to get CO2 would be to burn some pure type of fuel, like gasoline with a good air mixture, you'd be left with exhaust containing mostly pure CO2.

But, beyond that? What are you going to do with it? stripping carbon from CO2 is difficult. You're better off burning with not enough oxygen so that it produces a lot of soot. Soot, by the way, is pure carbon

In any event, CO2 and pure Carbon are very easy to get.
posted by delmoi at 3:43 PM on December 6, 2005

Most gas vendors only separate O2, N2 and Ar from air. The concentration of CO2 is too low to be worthwhile. According to Airgas:
Because of its low concentration in the atmosphere, air is not a suitable feedstock for carbon dioxide production. Instead, CO2 is obtained from by-product streams from various manufacturing processes. Bulk quantities of carbon dioxide are usually stored and shipped as liquid under pressure and refrigeration.
So you can extract CO2 from the air, but it isn't easy to get large quantities.
posted by yarmond at 3:46 PM on December 6, 2005

Gas Name
Percent Volume
Nitrogen N2 78.08%
Oxygen O2 20.95%
*Water H2O 0 to 4%
Argon Ar 0.93%
*Carbon Dioxide CO2 0.0360%
Neon Ne 0.0018%
Helium He 0.0005%
*Methane CH4 0.00017%
Hydrogen H2 0.00005%
*Nitrous Oxide N2O 0.00003%
*Ozone O3 0.000004%

posted by warbaby at 5:50 PM on December 6, 2005

If you needed large amounts of elemental carbon, extraction from the air would be a terrible way to go about it. It isn't present in sufficient quantities, and extracting it is a pain, and very energy consuming. I mean sure, plants do it, but this is the sort of inefficiency you have to deal with when you have no cognitive processes and can't move. Air is pretty much all you've got to work with. But you don't have this problem! You have access to the internet and the international commodities markets!

What you want is a bulk commodities chemical supplier. You'll want to research in advance what type of carbon you're looking for, probably either amorphous carbon or graphite. Diamonds, white carbon (the birefringent "fourth allotrope" of carbon), Carbon-14, buckminsterfullerenes etc. are all probably too spendy for your needs.

Presume you're looking for bulk graphite (generally produced by oxygen-free oven treatment of petroleum coke, a byproduct of crude refinement). If you're looking for cheapness as the primary commodity, though, coke (the same process applied to soft coal), used primarily in steel manufacture, will probably fit the bill. Otherwise you're looking for graphite with some sort of technical properties, you know, purity and particle size and that kind of thing. Again, if cost is an object you might want to scope out suppliers in, say, China or India. It's the usual thing, you know, shop around, get some samples.

Spot price on coke, maybe $250 US per ton? Graphite will run you considerably steeper, maybe dollars per pound depending on the specific properties. Nevertheless, with careful shopping you should be able to fill your home with a "tree-sized amount of carbon" in no time.

What did you say this was for again?
posted by nanojath at 10:34 PM on December 6, 2005

What did you say this was for again? My guess, a work of fiction.
posted by Good Brain at 11:51 PM on December 6, 2005

I think it's a chemistry final take-home quiz.
posted by warbaby at 6:15 AM on December 8, 2005

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