Slightly offtopic, what's the easiest way to scrub CO2 from air (e.g. in a house) without using up consumable materials? Some form of pressure swing absorption?
If you are concerned about indoor CO2 concentration, the answer is to ventilate the place.
No reasonable amount of plants will keep a house stable.
If it's just really curiosity, well, people have been scrubbing CO2 since space travel is a thing. Wikipedia was completely unhelpful to me, but I remember there is a mineral with high CO2 selectivity that you can simply push the air though it.
98% curiosity, 2% lack of faith in our long term ability to keep CO2 levels down to healthy levels (1000ppm is enough that we can detect minor negative effects... I have to wonder if really minor ones exist even at 400 ppm).
Wikipedia was similarly not useful for me. Scuba divers and the like apparently use a one-time-use non-regenerative mineral that absorbs CO2. The space station has something that regenerates but I haven't been able to figure out what.
I know older spacecraft didn’t have a regenerative material, this is the first I’ve heard about the space station.
You’d have to reduce the CO2 pretty far (I’m betting reducing to CO like in TFA isn’t what you’re looking for.) I think a lot of people underestimate how much energy this takes.
Re ISS, I've been clicking around on this a bit more, and
> While cabin air processing, one carbon dioxide removal bed is in the process of regeneration. Regeneration is accomplished using pressure/thermal swing methodology. First, the two-stage pump removes the free air from the adsorbent bed and returns it to the cabin, reducing oxygen ullage. Then Kapton heaters integrated within the adsorbent bed raise the zeolite temperature, and space vacuum creates a low, partial pressure driving the carbon dioxide gas overboard. Daylight and continuous day power cycle is overlapped with the operating cycle. In the daylight power cycle, the carbon dioxide adsorbent bed heaters are only allowed to be powered on during the day portion of the cycle
> [...]
> The CDRA continuously removes 6 person-equivalents of CO, when operating with both C02 removal beds (dual beds) functioning.
Converting CO2 into CO would be rather counterproductive (absent a reliable and efficient mechanism to remove CO), I suspect an efficient setup will involve "mechanical" filtration not chemical reactions.
If you figure out some concrete setup, let me know. I am fairly certain that there are measurable cognitive effects at "just" 500 ppm, and good luck staying below that when you can't just sit at an open window outside of a city.
1000 ppm is btw. enough to feel uncomfortable. Cognitive impairment will be much more subtle.
Indoors that's problematic today, outdoors we have "awhile" if you make 500 your cutoff, we're only growing at ~2.4 ppm per and the yearly peak is at roughly 420 right now, we can probably count on 20 years before we hit 500 outdoors.
Not really without consumables, unfortunately. But it's easy and costs about 50-200$ per human and month when you just buy the required substance, granular CaOH treated with 1~2 NaOH (by pouring a concentrated solution of it over the CaOH), from Alibaba once a year. That stuff is e.g. used for re-breathers in anesthesia. CAS 8006-28-8 is the "magic" word/number.
The potential alternative, which would not use consumables, would be to just freeze it out. It's not _that_ hard, I believe an ammonia-based single-stage chiller should still suffice. Make sure to use counter-flow heat exchangers to not loose insane amounts of power. Handling the water condensation might not be that trivial, though.
Get a large amount of calcium hydroxide in a watery slurry. That absorbs CO2 to form calcium carbonate. Take the carbonate outside and heat it up sufficiently to form calcium oxide and carbon dioxide. Add water to go back to calcium hydroxide.
Be careful with alkali metal hydroxides! They tend to be caustic and mixing them with water is exothermic (it can boil if you do it fast enough.) They will also react with aluminum, potentially violently and can ruin glass.
No reasonable amount of plants will keep a house stable.
If it's just really curiosity, well, people have been scrubbing CO2 since space travel is a thing. Wikipedia was completely unhelpful to me, but I remember there is a mineral with high CO2 selectivity that you can simply push the air though it.