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How to pull carbon dioxide out of seawater

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Re: How to pull carbon dioxide out of seawater

#21

Post by mrguyorama »

L_226 wrote: post #3
version_five wrote: post #2

Had to read most of the way through to get to what I was most interested in: The process could be more efficient than air-capture systems, Hatton says, because the concentration of carbon dioxide in seawater is more than 100 times greater than it is in air. In direct air-capture systems it is first necessary to capture and concentrate the gas before recovering it. Sounds like a promising area to explore. I wonder how…

Seawater CO2 reactions are quite complex, because various compounds form from dissolved gaseous CO2 in the water and the molecules interact in ways that are difficult to quantify (I am not a chemist). My layperson understanding is that carbonic acid ("normal" dissolved CO2) can break down into bicarbonate ions, which themselves can further break down into single carbonate ions. Then depending on what other ions are p…

What do you do with the resulting algae? What's a good way to sequester that captured carbon? I guess on industrial scales we should really just pump an algae sludge right back into the holes we pumped them out of.

Re: How to pull carbon dioxide out of seawater

#22

Post by zamalek »

hedora wrote: post #15
zamalek wrote: post #10

Earlier quoted context omitted.

> Sounds like a promising area to explore. It's so completely obvious in hindsight. It's amazing how many great ideas share that property.

This isn't a new idea. It's possible it was also obvious in hindsight a few decades ago when it was first proposed.

It's a new idea to me, and is completely obvious to me in hindsight.

Re: How to pull carbon dioxide out of seawater

#23

Post by DennisP »

Cheetah26 wrote: post #14

This article makes no mention of the power required for a process like this. A few days ago there was a post describing the older seawater method which stated that to remove as much carbon from the ocean as we are putting in would require ~70% of current global electricity production. Unless the improvements made here are really significant, I don't see how this actually solves anything until we have moved to truly c…

The linked paper says this uses 122 kJ/mol. I translated that into more familiar units, and it came out to 770 kWh per metric ton CO2.

If you were dumb enough to power it with coal then you'd have net emissions, but put it someplace sunny, power it with solar at 2 cents/kWh and you're paying just $15.40 in energy cost per ton of CO2 absorption. One gallon of gasoline produces 20 pounds of CO2, and there are 2204 pounds in a metric ton, so you could pay for this by adding a surcharge of just 7 cents/gallon.

Of course that's just energy cost, there's also capital cost, and I don't have an estimate for that. But it's not obviously unworkable. Reducing emissions is usually better but I could see this being pretty helpful for cleaning up things that are hard to decarbonize, and once we hit net zero we'll need tech like this already scaling to bring CO2 back down.

Re: How to pull carbon dioxide out of seawater

#24

Post by boringg »

version_five wrote: post #2

Had to read most of the way through to get to what I was most interested in: The process could be more efficient than air-capture systems, Hatton says, because the concentration of carbon dioxide in seawater is more than 100 times greater than it is in air. In direct air-capture systems it is first necessary to capture and concentrate the gas before recovering it. Sounds like a promising area to explore. I wonder how…

I mean comparing to direct air capture is A comparison. I wouldn't call direct air capture efficient by any stretch.

Re: How to pull carbon dioxide out of seawater

#25

Post by eppp »

mrguyorama wrote: post #21
L_226 wrote: post #3

Earlier quoted context omitted.

Seawater CO2 reactions are quite complex, because various compounds form from dissolved gaseous CO2 in the water and the molecules interact in ways that are difficult to quantify (I am not a chemist). My layperson understanding is that carbonic acid ("normal" dissolved CO2) can break down into bicarbonate ions, which themselves can further break down into single carbonate ions. Then depending on what other ions are p…

What do you do with the resulting algae? What's a good way to sequester that captured carbon? I guess on industrial scales we should really just pump an algae sludge right back into the holes we pumped them out of.

Pump it into old oil wells

Re: How to pull carbon dioxide out of seawater

#26

Post by Zagill »

immmmmm wrote: post #11

> in places such as fish farms, which tend to acidify the water, so this could be a way of helping to counter that effect. so basically overeating fish is to be offset by miracle technology. brilliant.

Similar to efforts to reduce methane from cows instead of actually facing the fact that industrialized meat production is, y'know, really wasteful and bad for the environment (and us, given how bad eating too much red meat is)

Re: How to pull carbon dioxide out of seawater

#27

Post by malfist »

Aperocky wrote: post #7
malfist wrote: post #4

Earlier quoted context omitted.

> concentration of carbon dioxide in seawater is more than 100 times greater than it is in air This is straight up wrong. Unless they mean alkalinity, which is carbonate, but not dissolved CO2. I keep both reef and freshwater aquariums. I have to inject CO2 into my freshwater aquariums to keep the plants happy, and the maximum I can go without killing off the fish is ~30ppm. Given that the PPM of CO2 in air is 4, are…

> PPM of CO2 in air is 4 This is wrong, CO2 is currently 420PPM in Earth's atmosphere.

Wow, how did I manage that. My numbers are all off by 100x.

So that means they're saying the ocean is 4% CO2? That would mean the ocean has more CO2 than salt (3.5% or 35 ppt)

Re: How to pull carbon dioxide out of seawater

#28

Post by L_226 »

mrguyorama wrote: post #21
L_226 wrote: post #3

Earlier quoted context omitted.

Seawater CO2 reactions are quite complex, because various compounds form from dissolved gaseous CO2 in the water and the molecules interact in ways that are difficult to quantify (I am not a chemist). My layperson understanding is that carbonic acid ("normal" dissolved CO2) can break down into bicarbonate ions, which themselves can further break down into single carbonate ions. Then depending on what other ions are p…

What do you do with the resulting algae? What's a good way to sequester that captured carbon? I guess on industrial scales we should really just pump an algae sludge right back into the holes we pumped them out of.

You can sink it in the ocean - beneath around 500m it just gets compressed and sinks to the bottom. So that would be "permanent" sequestration. The other option is to make it into "biochar" which is basically anaerobically combusting it to leave carbon residues, that you can then bury in the ground. This is scientifically accepted as also being permanently sequestered. This has the benefit of acting as a soil amendment also, increasing water retention and facilitating microorganism development.

Re: How to pull carbon dioxide out of seawater

#29

Post by Aperocky »

malfist wrote: post #27
Aperocky wrote: post #7

Earlier quoted context omitted.

> PPM of CO2 in air is 4 This is wrong, CO2 is currently 420PPM in Earth's atmosphere.

Wow, how did I manage that. My numbers are all off by 100x. So that means they're saying the ocean is 4% CO2? That would mean the ocean has more CO2 than salt (3.5% or 35 ppt)

Ocean is also about 1000x as dense as air, so it only needs 40ppm of CO2 to be 100x more concentrated as air.

Re: How to pull carbon dioxide out of seawater

#30

Post by pfdietz »

hedora wrote: post #17

Here is some more context on related technologies: https://www.american.edu/sis/centers/carbon-removal/fact-she... The MIT article presents an expensive strawman alternative, but ignores simpler, cheaper technologies that already exist. In particular, since CO2 acidifies the ocean, dumping alkaline chemicals into sea water converts the CO2 to inert solids, which precipitate out. At least, that's the theory. Caveats i…

Or, adding limestone converts CO2 and CO3(-2) into 2 HCO3(-1).
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