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Comment by philipkglass | Hacker News Reader

The atmosphere is approximately 78% nitrogen and 0.04% carbon dioxide. That means that separating pure nitrogen from the atmosphere is relatively simple while separating pure CO2 is more complex and energy intensive. The additional complexity and energy requirements are such that it may be worthwhile developing ways to use ammonia as a fuel, as in this work, even though methane is more well established.

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> separating pure CO2 [from the atmosphere] is more complex and energy intensive

Maybe we could find some kind of existing organism with the right chemistry to do this? Seems like such a beast would be very successful if that trick could be accomplished.

No, seriously, this is what plants do. Just ask them for help; we've done it before, we have their number in the rolodex.

Grow plants > feed to goats > collect menure > anerobic decay (aka methane digester) > natural gas (pretty close anyway) + good fertilizer.

That's the system I'm interested in. The only real issue is needing to filter out a sulfer based gas (forgetting the exact thing off the top of my head, but it's corrosive to metal)

Hydrogen sulfide (H2S) is pretty easy to clean from biogas.

Have you heard about the (possible) Azolla Event? https://en.wikipedia.org/wiki/Azolla_event

I bought some to grow in an unused tub in my yard until I figure out what to do with it. Not exactly a major CO2 vacuum, but I like the idea. I've wondered if there's something to using such plants as a way to reduce CO2 emissions from various plants. What to do with the plants is not clear since sequestration is the important part.

Here is a lab working on something like what you described. https://www.azollahs.com/research

You can use the NaOH/CaO cycle to scrub carbon dioxide at atmospheric conditions and even regenerate the calcium carbonate with a (fairly cheap) methane + pure oxygen lime kiln (electric lime kilns are currently in testing).

I'm fact, as long as we still use mined limestone to feed kilns, one can just switch them over to burn with pure oxygen (possibly diluted with it's own exhaust to reduce flame temperatures) and get a pure CO₂/H₂O exhaust. Usage in construction partially reacts back to limestone using atmospheric CO₂.

The issue with plants is just that they are really inefficient compared to solar panels, to the point where scientists have some success feeding solar-industrial synthetic acetate to plants [0] and ending up substantially more efficient per solar-capturing area than outdoor plants.

[0]: https://news.ycombinator.com/item?id=31957068

Did this person lie or something? Why the downvotes? HN is bizarre sometimes.

There's that "HN Egg Cup" picture someone shows, if the person hits their site from HN.

I have a couple of downvote stalkers. It's really cute. One of them even went and wrote a pretty much embarrassingly childish one-star review on one of my Apple App Store apps. It was so bad that Apple hid it.

Sometimes, we deal better with machines, than with other people.

I'm sure some people would consider me a troll, while I think I'm just writing honestly when I see things I don't agree with. Yet reading what you just wrote makes me want to quit this site forever. On most sites we know not to reveal enough to get doxxed. Here we reveal a lot thinking we're dealing with serious people. Stupid mistake. Thanks for the warning about the stalkers.

I’m not too concerned about it. I’m a fairly tough old coot (I’m a reformed troll, myself). I’ve dealt with much worse. As you can tell, more folks seem to value what I have to say, than have issues with it. I make a sincere effort not to bring negativity (and boy, oh boy, is that something I can do).

I’m pretty sure that the ones that have problems with me, consider me to be an arrogant old “OK boomer.” Maybe they’re right. I don’t think so, but, as they say, if your feet are wet, and you see pyramids, you’re in de Nile (or a fountain in Vegas). I don’t attack folks, or try to intimidate them. My worst crime is to be annoying.

This is a professional venue. It may not always seem like it, but people can get and lose careers, by their behavior, hereabouts. I’m done with mine. I don’t really need to impress anyone, but if I fight with someone, it could have severe consequences for them. I know how to draw the worst out in people, and make them show their ass. They may “win” their fight, here, and lose everything else. A pyrric victory.

Even if I don’t like someone, I don’t actually want to cause them damage. I would sincerely like to be a positive influence, if at all possible. As I said, I used to be a rather nasty troll, and one of the reasons I participate here, is as recompense. I believe amends need to be made.

This site is Disneyland. Maybe it can’t last, but it has, so far. I like it here. Most folks here have some truly great stuff to share, and I learn something every day. I am truly humbled by some of the participants, here. I make a point of hanging out with people smarter than I am. I’ve done that, all my life. I participate, because I want to be a good citizen, and it’s actually kind of an honor to be here.

If it gets bad, I can always hightail it outta here. I have done that many times, in the past.

Please don't criticize the downvoting system, you will get in trouble.

It only talks about separating gas from the atmosphere. You then have to split up the molecules to do useful things with the atoms, and nitrogen in the air is triple bonded diatomic N2.

N2 gas takes 945 kilojoules per mole to split, while CO2 takes 393 kJ/mol. Since the thermodynamics aren't as favorable, the difference in concentration cost needs to be pretty good. Which it probably would be, (LN2 has been produced at scale for a century via cryogenic air separation and costs about a buck a liter) but green NH4 v green CH4 synthesis is not a slam dunk and it's not clear yet which one will be cheaper at the "replacing all transport oil consumption worldwide" megascale.

thanks

I have a very naive assumption that the amount of energy needed to break apart molecules for fuel, is roughly the energy we get back when burning them.

Is there any truth to that?

Approximately. Burning H2, you have to separate the H2 to cram an oxygen in between.

You don't even need to purify N₂ that much, as you can just add air to H₂ and feed that to the reactor, wasting some H₂ on O₂ but AFAIK it's quite cheap to enrich air to low-purity N₂ via pressure-swing adsorption, and it's just O₂ that's cheaper to get high concentration of via cryogenic distillation. [Upon further reading, iron-based catalysts in Haber-Bosch synthesis are fairly sensitive to water as it promotes recrystallization of the high-surface-area needle geometry into more clumpy structures with less surface area and thus less catalytic activity; apparently it's thus preferable to cryogenically distill the oxygen out of the air to get by without a water-condenser-trap between the nitrogen feed and the catalytic reactor (ammonia condensing happens between reactor outlet and re-compressing to reactor inlet pressure).]

The bigger issue is that NH₃ (there is the ammonium cation NH₄⁺, but it's charged and thus needs an anion nearby to cancel the charge as coulomb repulsion would otherwise strongly limit the density of your (bulk) substance) is fairly toxic to inhalation when spilled, due to absorbing into water on the surfaces of your mucous membranes, eyes, and lungs.

It is technically also slightly toxic once in your bloodstream, but it's hard to experience that toxicity if you follow "GTFO once you smell" as most non-fish (mammals, sharks, amphibians, birds, reptiles, and terrestrial (i.e., non-aquatic) snails) have fairly capable metabolic excretion pathways due to protein "burning" (breaking down protein from old cells and food for energy) having ammonia as a waste product.

NH₃ is fairly toxic to fish because most assume they can just dump their own ammonia waste into the surrounding water and therefore rely on the surrounding water having concentrations far enough below what would be toxic inside the fish, as there needs to be some gradient to support the waste production/excretion rate.

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