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Author: Subject: Building a mechanism capable of capturing/neutralizing H2SO4, HNO3 and HCl droplets and vapors
Johnny Cappone
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[*] posted on 18-11-2022 at 01:36
Building a mechanism capable of capturing/neutralizing H2SO4, HNO3 and HCl droplets and vapors

Hi guys.

I've been thinking about building something that can handle acidic fumes, neutralizing or capturing them in a filter that can be conveniently disposed of later.

Sometimes I need to boil sulfuric acid to concentrate it (dealing with the H2SO4 mist would be the main function of this apparatus) and sometimes I deal with nitration mixtures which naturally produce some HNO3 fumes. I can't afford a fume hood and, even if I could, I have nowhere to store it when it's not in use.

The attached image should give you an idea of the type of system I'm considering. A 100mm fan positioned directly above the reaction flask would capture the vapors. These would be conducted by flexible ducts to the "neutralization/absorption unit". Once purified, the resulting air would be discharged through a second in-line tube.

I'm confident I have the skills to make something like this work, but I'm not sure what kind of material or technique I could use in the "neutralization unit" to deal with the acid fumes. It must be something capable of rendering inert H2SO4, SO2, SO3, HNO3, NO2 and HCl.
Any idea?

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[Edited on 18-11-2022 by Johnny Cappone]

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[*] posted on 18-11-2022 at 01:48

Google "gas scrubber". Basically a vertical tube with a bottom inlet, a filler media to increase surface area and a liquid to absorb the gas in question. For acids the simplest would probably be a sodium carbonate solution.

We're not banging rocks together here. We know how to put a man back together.
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[*] posted on 1-12-2022 at 05:47

Scrubbing can be case sensitive, depending what and how much you need to scrub. I had my bad days when doing reactions that produced nitric oxide, as it goes clean through NaOH solution, and forms NO2 with atmospheric oxygen, so you would have needed a booster unit with air pump feeding air into a middle chamber to oxidize it prior absorption, however for full absorption multiple stages would've needed.

Activated carbon is good at absorbing a lot of different fumes, and it can hold quite a lot of them until losing effectiveness. Some stuff like ammonia goes straight through it, though, and same appears to be the case with formaldehyde fumes.

For basic fumes, I wonder what could be the cheapest and best absorbent solution? Sulfuric acid is too valuable to be wasted for scrubbing in my eyes, HCl is volatile on it's own, but stuff like phosphoric, citric and acetic acids could be an option?
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[*] posted on 1-12-2022 at 19:44

Venturi scrubber just use aquarium pump with air inlet as your scrubber then fill it with water and optional put a mesh screen over with wet rocks so you have a hybrid packed bed and venturi scrubber.
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violet sin
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[*] posted on 1-12-2022 at 21:32

I may be overthinking things, but there seems to be a number of choices to make based on the components you have and how long you want them to live.

-does the fan go in the front of the noxious fumes pushing, towards the rear pulling from the safe side or both?
-are you forcing the air through the scrubber/solution to a depth or narrow constrictions for small bubbles, or are you misting the solution through a chamber the air passes through?
-catching the mist afterward with inline air flow or attempting reverse flow with large drops and a reservoir?

the place across from my work prints color ceramic photos for grave headstones. they use lead chromate for the red color or something like that and have a scrubber system for it; I did inquire after a while. had to pack boxes staring out a large roll up door and witnessed a few redesigns on their system over the last few years. Hazmat suits with a PAPR are hard to miss for a guy like me. it must have been inline fans for a while, but became very clear they moved on to a positive displacement pump, perhaps a couple. the repetitious screeching of a metal on metal piston was undeniable. it required work a few times and ducting changes, cleaning, repair. someone got really sick at some point, thus the beginning of all the filter optimization.

having to stare at that for a long time and many hours of just cardboard, cardboard, cardboard, had me thinking about the same thing as the OP. I was hoping to set up a PVC tower of sorts. mist head at top/mid in some synthetic plastic fluff to hopefully guide it downward with maximal surface area, reservoir at bottom. a separate finishing staged of silica adsorbent(kitty litter) for ammonia if I needed it. (you can heat the adsorbent to retrieve a measure of ammonia. don't remember where that research paper is saved tho.)

only ever got around to starting the silica gel scrubber parts, my needs, free time and chem goals changed.

take away, make it cheap unless you foresee doing that for a long time. think about what methods will work best for the parts you have, and needs. maybe do rough check on methodology before going all in.

best of luck, I hope at least some of this mess of thoughts helps on some level.
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