Reboot
Hazard to Others
Posts: 141
Registered: 8-8-2017
Member Is Offline
Mood: No Mood
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Filter media for a ductless hood/scrubber?
I'm hoping to build a small ductless hood for low-risk work (essentially for nuisance smells and vapors.) A ductless fume hood poses some real
potential dangers (you need to be sure everything you use and create in reactions is compatible with the filter materials) but I think it makes the
most sense for me right now.
So far I haven't seen a commercial filter that was sanely priced, so I'm looking at building my own, which begs the question of materials to use as
adsorbents/neutralizers.
Activated carbon seems like the obvious place to start since it will remove most non-polars and organics (but is less effective on lighter organics
like methanol.) But that leaves (at the least) acid vapors and ammonia/volatile amines.
The most interesting suggestion I've seen is to use a permanganate filter bed to oxidize organics, but that could be a lot sketchier to handle than
carbon.
Since I don't want to deal with liquid scrubber media, that seems to leave either dry chemicals or some sort of absorbent such as (maybe) ion exchange
resins.
For ammonia/amines, I wonder if a dry weak acid (like citric acid) wouldn't work well. Zeolite (as an adsorbent) seems more traditional, but I don't
know if one makes more sense than the other.
For acid vapors I'm thinking sodium carbonate. (Hydroxides will react with CO2 in the air and convert to carbonates anyway.)
One possibility that comes to mind is using commercial ion exchange resins, which are typically small plastic beads coated with either H+ or OH- ions.
They should provide a significant absorbent/neutralizing capacity for stray acids and ammonia while being easy to handle (and regenerate.)
I'm definitely at the 'making this up as I go along' stage, so any suggestions/advice would be appreciated. :-)
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SWIM
National Hazard
Posts: 970
Registered: 3-9-2017
Member Is Offline
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Back in WWI, gas masks used activated charcoal backed up by a mixture of soda-lime (I think this is calcium hydroxide which has been treated with NaOH
leaving Naoh on the surface to react with the acids and the calcium hydroxide to act as a reserve to regenerate the NaOH), and permanganate.
Magpie has put some posts on here about a vapor scrubber which has a large PVC tube with lots of high surface area low volume inert plastics in it
which has a pump that sprays water in at the top and recirculates it from the bottom.
Obviously something like that could be charged with some carbonate or acid to make the spray absorb acids or bases better when you're working with one
of those, or even thiosulfate or something to neutralize halogens.
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