What's going on with mining carbon from the atmosphere?

[Khatti]

<Mentor moved thread to Science Fiction>

Hello one and all. I'm fascinated by the idea of breaking down methane and carbon dioxide and using the carbon as a building material (graphene being the preferred material rendered from this process). Can anyone tell me anything on where the current state of mining the atmosphere is?

 

[russ_watters]

Hello one and all. I'm fascinated by the idea of breaking down methane and carbon dioxide and using the carbon as a building material (graphene being the preferred material rendered from this process). Can anyone tell me anything on where the current state of mining the atmosphere is?

We occasionally hear kitschy stories in the news about projects people are doing to demonstrate such ideas, but they really are complete non-starters from a thermodynamics standpoint. Other than getting published in a non-science news outlet, there's really no point to it.

 

[Keith_McClary]

It seems to be called Direct Air Capture.
The other step, transforming CO2 to C requires at least as much energy as was produced by burning the C. As @russ_watters typed (faster than me), carbon is cheap - it would make more sense to make carbon from coal and sequester the captured CO2.
Although, I think there is a $million prize for finding a use for CO2.
EDIT - Two of them:
https://carbon.xprize.org/prizes/carbon
https://ec.europa.eu/info/research-...ties/prizes/horizon-prizes/co2-reuse-prize_en

 

[Keith_McClary]

non-science news outlet

I ran across this recently:
https://phys.org/news/2020-07-rwanda-methane-lake-kivu-electricity.html

"The reason for this concentration of gases is that the lake sits in a highly volcanic area; carbon dioxide enters the lake from the volcanic rock beneath it, and is converted into methane gas by the bacteria and fermentation of biogenic sediments in the lake. It has been likened to a bottle of fizzy drink that, when shaken, releases gas."
https://www.dlapiper.com/en/uk/insi...ity-generation-through-methane-gas-in-rwanda/

https://www.osti.gov/biblio/1041046

 

[256bits]

and is converted into methane gas by the bacteria

Actually not bacteria, nor archaebacteria, but archaea.

Some more on methanogens, which are everywhere.
https://en.wikipedia.org/wiki/Methanogen

 

[TeethWhitener]

A lot of the focus is on electrochemical CO₂ fixation directly to commodity chemicals (like ethylene or ethanol) using some sort of renewable energy source. CO₂ is free, and going directly to a valuable chemical might be economically feasible (currently, most electrochemical fixation methods give a mixture of many different compounds which is uneconomical to purify).

 

[Khatti]

It seems to be called Direct Air Capture.
The other step, transforming CO2 to C requires at least as much energy as was produced by burning the C. As @russ_watters typed (faster than me), carbon is cheap - it would make more sense to make carbon from coal and sequester the captured CO2.
Although, I think there is a $million prize for finding a use for CO2.
EDIT - Two of them:
https://carbon.xprize.org/prizes/carbon
https://ec.europa.eu/info/research-...ties/prizes/horizon-prizes/co2-reuse-prize_en

What I find so intriguing about this idea is, if we could figure out a way to mine carbon from CO/2 and Methane, it would be one of the few elements that could be mined and processed in low-Earth orbit. Yeah I know, that would involve a couple of technologies that exist only one paper.

 

[Vanadium 50]

Whoa, whoa, whoa, whoa, whoa...nice shootin', Tex!

We're all going off in the wrong direction. There is no serious thought about turning CO2 back into C. As pointed out, this is energetically a non starter. Where there is research is binding CO2 into carbonates (and of course, the biological version of this "planting trees"). This happened on Earth billions of years ago. To do it today, one would use silicate minerals and CO2 as inputs and get carbonate minerals and SiO2 as output. This reaction is exothermic for some minerals.

There are a few issues with this. One is that the reaction goes slowly at room temperatures (c.f. "billions of years" above) so you need to heat it up (perhaps by burning coal somewhere else?) or find a suitable catalyst. Another is that there is a lot of carbon in the atmosphere. We'd want to take out something like a trillion tons of carbon. Where do you put it? To compare, that's about 1000x the annual world wide solid waste production. Finally, environmentalists hate, hate, hate this. If you see how much they hate nuclear power, it is nothing compared to this. It is a complete political non-starter.

 

[Khatti]

Environmentalists may hate this, but I have lot more faith in fifty very smart guys (or gals, or transsexuals or whatever else may be interested in this) solving global warming by trying to make money at it than I do any Environmentalist dream of arranging the societies of the world to their tastes.

 

[Rive]

Can anyone tell me anything on where the current state of mining the atmosphere is?

So far the only viable method to get anything really useful, new and worthy out of this would be through some heavily modified (GMO) plants.
As things are, it would stir up more hatred than nuclear.

 

[Keith_McClary]

Adam Marblestone's Climate Technology Primer (via John Baez) outlines the possibilities.

 

[Vanadium 50]

So far the only viable method to get anything really useful, new and worthy out of this would be through some heavily modified (GMO) plants.

You could do this with trees. You need to forest about 1% of the Earth's land area (i.e. raise the forested fraction from 30 to 31%) over a decade. And of course, to ensure that the wood doesn't get it carbon returned to the atmosphere. That turns out to be the trickier part.

 

[Khatti]

You could do this with trees. You need to forest about 1% of the Earth's land area (i.e. rais the forested fraction from 30 to 31%) over a decade. And of course, to ensure that the wood doesn't get it carbon returned to the atmosphere. That turns out to be the trickier part.

This is why I wanted to ship the carbon upwards and use it to build O'Neil Colonies.

 

[Vanadium 50]

Let' see - a trillion tons, $5000/kg, that's $5 x 10¹⁸ or about 60,000 years worth of world GDP.

 

[DaveE]

It makes no economic sense to do this as long as we are still putting lots of CO₂ into the air. Reduction is cheaper than removal.

Capture is also cheaper than removal. There is a much higher concentration of CO₂ in smokestacks than the atmosphere and you can tell who made it and why.

 

[Keith_McClary]

There is a much higher concentration of CO2 in smokestacks than the atmosphere

But it may not make much difference. Search within this page for "stack":
https://longitudinal.blog/co2-series-part-2-co2-removal/

 

[russ_watters]

What I find so intriguing about this idea is, if we could figure out a way to mine carbon from CO/2 and Methane, it would be one of the few elements that could be mined and processed in low-Earth orbit.

What? It isn't clear to me that you know what the word "mined" means, or regardless, why you would want to do the processing in orbit, or why you think "is is one of the few..."

That whole sentence/idea sounds like technobabble.

 

[Vanadium 50]

I did some searching, and we've gone around this particular block before.

 

[jim mcnamara]

This discussion seems to have delved into Science Fiction. It does not belong in the Earth Science Forums - moved

 

[Vanadium 50]

I don't think the SF forum should become the wastebasket for low quality threads. The OP has shown no indications that they are writing SF. There's a difference between SF and pretend science.

 

[hmmm27]

Bluntly, the only reason this thread belongs in "science fiction" - if it does at all - is the lack of quality in responses, not the question.

Is direct capture of C (from atmospheric CO2) an excuse not to obviate/mitigate C(O2) release in the first place ? No, and "duh".

Is direct capture of CO2 a best option, compared with creating it from scratch (ie: burning C), for processes that rely on CO2 as feedstock ? Yes ; also "duh".

Other than that, by all means somebody(s) argue that - given a surplus of ("clean") energy - a condition not currently being met on a global basis - yanking carbon out of the atmosphere isn't a good idea.

What I find so intriguing about this idea is, if we could figure out a way to mine carbon from CO/2 and Methane, it would be one of the few elements that could be mined and processed in low-Earth orbit. Yeah I know, that would involve a couple of technologies that exist only one paper.

I'm not sure any facility close enough to make extraction worthwhile wouldn't be so close as to waste all the saved energy and more trying to keep from falling down. (Also, bear in mind that CO2 is heavier than air in the first place). [edit : actually it's worse than that - you have to get the stuff up to orbital velocity before you even start]

 

[Khatti]

I'm not sure any facility close enough to make extraction worthwhile wouldn't be so close as to waste all the saved energy and more trying to keep from falling down. (Also, bear in mind that CO2 is heavier than air in the first place)

Point Taken.

 

[Khatti]

Is direct capture of C (from atmospheric CO2) a best option, compared with mitigating C(O2) release in the first place ? No, and "duh".

Is direct capture of CO2 a best option, compared with creating it from scratch (ie: burning C), for processes that rely on CO2 as feedstock ? Yes ; also "duh".

Other than that, by all means somebody(s) argue that - given a surplus of ("clean")energy: a condition not currently being met on a global basis - yanking carbon out of the atmosphere isn't a good idea.

The other problem is the consensus that there is already too much CO2 in the atmosphere, and there needs to be some way to remove at least some of it. Admittedly, I go for the most romantic solution.

 

[hmmm27]

... hmm... I was actually trying to say that it's a good idea as long as it isn't being used as an excuse to continue fossil-fuel abuse.

Interesting paradigm : even with benign use (carbon-fibre, terra preta, etc), is the amount of damage leaving a ton of C in the atmosphere worth the extra energy it takes to directly extract, as compared with coal or petroleum mining.

Carbon in space is a neat idea : could grow bamboo for structural members, the ingredients taking up less room on the shuttle.

 

[Khatti]

Interesting paradigm : even with benign use (carbon-fibre, pret de nigra, etc), is the amount of damage leaving a ton of C in the atmosphere worth the extra energy it takes to directly extract, as compared with coal or petroleum mining.

As you might have figured out, what interests me is building O'Neil structures. Don't get me wrong, I like the idea of the Earth cooling down a lot, but it isn't the only thing I'm thinking of. Carbon, being the lightest and strongest of materials to build with, is the logical material to build these structures from. That being (in my mind anyway) a given, it is a matter of getting the Carbon up where it can be used.

 

[Khatti]

... hmm... I was actually trying to say that it's a good idea as long as it isn't being used as an excuse to continue fossil-fuel abuse.

I have no love affair with oil or coal, if we can get rid of them so much the better. Conversely, even though I live out in the sticks and only need to drive a few miles south in order to see wind turbines, I don't have a great deal of faith in renewables filling our energy needs. I see wind and solar filling boutique functions in any plan to combat climate change. If you want to make use of wind energy produced in North Dakota to power your factory, the best idea is to move your factory (and your workers) to North Dakota. North Dakotans are my neighbors, I love the idea for their sakes but, if you're from say Boston or New York or Los Angeles, how excited are you to move your operations and home to the cold, cold north?

 

[hmmm27]

what interests me is building O'Neil structures

I think, by the time we get around to building really massive facilities, we'll be mining asteroids, so that'll save the trouble of hoisting the material up and around.

But, of course, carbon-fibre is much lighter than steel.

 

[hmmm27]

As far as "renewables" are concerned, I dunno... Sure, you could power the entire world's current energy needs by rimming Greenland with wind turbines a couple of hundred kilometers deep... but that's likely to be short-term expensive.

In regards off-peak energy, I'd be more inclined to go with producing ammonia to replace fossil-fuels, but the direct-capture/cracking option has the distinct advantage of not having to wait for infrastructure to catch up with new paradigms... and the distinct disadvantage of not being very impressive-looking for the media.

 

[Khatti]

In regards off-peak energy, I'd be more inclined to go with producing ammonia to replace fossil-fuels, but the direct-capture option has the distinct advantage of not having to wait for infrastructure to catch up with new paradigms.

Again, point taken.

 

[mfb]

Harvesting carbon from CO2 in low Earth orbit is awfully inefficient. The highest-altitude data I could find is 100 km, with a concentration of ~240 ppm (extrapolated). You need at least twice that height for a reasonable orbit, which should drop the concentration significantly more, but let's use 250 ppm. At 10^-10 kg/m³ your giant 1000 m² scoop collects 750 mg of gas per second or 60 kg per day. Out of that ~20 gram is CO2, which means 6 g of carbon per day or 200 grams per year.

Sure, make the scoop larger... but we also need to keep this thing in orbit. Re-accelerating mass needs an average power of 20 kW at 100% efficiency, and you won't reach 100% efficiency with a nitrogen/oxygen gas mixture. And of course making it larger increases its mass. I doubt that there is a point where you ever collect more carbon than the mass of the spacecraft . For nitrogen and oxygen this is different, and collecting gas in the upper atmosphere has been discussed seriously. You could fuel e.g. interplanetary spacecraft with it. If you just have to launch the hydrogen then you save most of the mass.

 

[stefan r]

As you might have figured out, what interests me is building O'Neil structures. Don't get me wrong, I like the idea of the Earth cooling down a lot, but it isn't the only thing I'm thinking of. Carbon, being the lightest and strongest of materials to build with, is the logical material to build these structures from. That being (in my mind anyway) a given, it is a matter of getting the Carbon up where it can be used.

Build O'Neil cylinders using asteroids. The raw materials are already up there. Trying to get anything out of Earth's gravity well is going to be a huge energy drain.

https://periodictable.com/Properties/A/MeteoriteAbundance.html
Calcium is 1.1% of the mass of asteroids. Calcium is not very useful as a construction material. Magnesium is 12% of the mass of asteroids. Magnesium is extremely useful as construction material. However, we might be able to sacrifice some of it. Calcium and Magnesium react with carbon dioxide in the air. This ultimately creates limestone and dolomite. This material can be made into artificial islands. Sort of like what China is doing in the Spratly Islands. Or perhaps you could just let it burn up on reentry.

For power supply use orbital ring systems. The kinetic energy contained in objects in low Earth orbit LEO is roughly equivalent to the energy in hydrocarbons like butane. This is not including the oxygen mass. We have well developed magnetic braking technology. Some of it is deployed in electric cars. You need an elliptical orbital ring system that contacts Earth's surface in order to de-orbit objects while delivering power. The electric supply is much better than crude oil because magnetic brakes recover better than 90% of the energy. Power plants are limited by the Carnot cycle.

Lime (calcium oxide) is a major component of Lunar highlands (~15%). This should be sent to Earth's orbital ring system and then used as for concrete and mortar in construction projects. Concrete is labeled as a CO2 source but that is only in the production of portland cement. Concrete absorbs carbon dioxide during its lifetime.

If there is no ring system the mass can still be used by space stations with momentum exchange tethers. Catapulting the calcium into a lower orbit boosts the station to a higher orbit. The gives us momentum that can be used to catapult missions out of Earth's orbit. Most of the fuel used in launching deep space missions is wasted lifting fuel to LEO. It does not matter what sort of material you send down from Luna. Only the total mass matters. You could build mass into a useable products and use the products and then de-orbit when you are done with it.

Magnesium is weaker than steel by cross section but is about equal by weight. Magnesium is stiffer. That would be a defect in some cases like automobiles but for space applications like huge telescopes or frames for solar farms it is a feature.

I'm not certain what effects calcium (or magnesium) particles in the upper atmosphere would have on climate. They should rain out fairly quickly once they sink to cloud level. While the particles are up in the stratosphere they help cool things down. May also cause havoc in the ozone and most agriculture. Should do more research before trying this.

 

[DrStupid]

There is no serious thought about turning CO2 back into C.

Where does the black stuff comes from that burns in your barbecue?

 

[Khatti]

Harvesting carbon from CO2 in low Earth orbit is awfully inefficient. The highest-altitude data I could find is 100 km, with a concentration of ~240 ppm (extrapolated). You need at least twice that height for a reasonable orbit, which should drop the concentration significantly more, but let's use 250 ppm. At 10-10 kg/m3 your giant 1000 m2 scoop collects 750 mg of gas per second or 60 kg per day. Out of that ~20 gram is CO2, which means 6 g of carbon per day or 200 grams per year.

Would it be possible to drop a large tube or hose into the atmosphere from low orbit down to--say-- seventy kilometers and cycle atmosphere up into orbit where the oxygen and carbon could be separated? In theory cheap power would be more feasible in orbit than on Earth. I can see stability issues with a free hanging tube, but it may not matter at that height. I'm sure there are other technical issues, but then if we knew how to do it we wouldn't be having this conversation in the first place.

 

[DrStupid]

Would it be possible to drop a large tube or hose into the atmosphere from low orbit down to--say-- seventy kilometers and cycle atmosphere up into orbit where the oxygen and carbon could be separated?

The bottom end of the tube would get quite hot if it dives through the atmosphere with a speed of 7.8 km/s.

How does that "cycling" works?

In order to keep the speed of the orbiter, you would need to compensate drag and coriolis force (in the co-rotating frame). How are you going to do that? Maybe waste oxygen can be used as reaction mass for a rocket motor. But I don't think that would be trivial.

Maybe the drag and heat problem can be solved if the tube is not hanging straight down but rotating around the orbiter and diving into the atmosphere with almost zero relative velocity. But that would bring some other problems (e.g. the required strength of the material).

 

[Rive]

Would it be possible to drop a large tube or hose into the atmosphere from low orbit down to--say-- seventy kilometers and cycle atmosphere up into orbit where the oxygen and carbon could be separated?

Any place dense enough would mean significant atmospheric drag what you must compensate with fuel.
But if you have fuel (mass) at hand already then you don't need atmosphere anymore.