Sciencemadness Discussion Board

Best way to absorb ammonia gas in an air filtration system

RogueRose - 4-5-2024 at 17:02

I'm trying to figure out a way to filter out or neutralize ammonia gas with an air circulation system that can use a filter to scrub the ammonia. From what I've found, sulfuric and phosphoric acid are supposedly what is used in larger ammonia scrubbing systems but I'm wondering if there is something that is more like CO2 scrubbers that use something like Ca(OH)2, NaOH, KOH or LiOH as they are solids which I think would be preferable to using something that is in liquid form. Also, I think sulfuric & phosphoric acid might be a little too strong (aggressive) for what I'm looking to do and I'm wondering if something like acetic acid (vinegar) or oxalic acid or even citric acid might work for this application if a liquid needs to be used.

If a liquid were to be used, I would use some kind of a synthetic fiber panel or cylindrical filter (similar to the small humidifiers) and drip the acid solution on top of the filter & recirculate it from a catch tray to the top of the filter.

What acid would you suggest for this application or is there something else I could use to do this?

bnull - 4-5-2024 at 17:42

Acetic acid is volatile and will be carried along with the air.

Is that for a homemade fume hood?

j_sum1 - 4-5-2024 at 18:35

Water is pretty good at absorbing ammonia. Not sure what your constraints are or how permanent a setup you want. But here are some ideas using water:
  • attach an air pump to your feed line to keep positive pressure and then bubble through a flask of water
  • spray a mist of water through your exhaust gases
  • pass you gas over or through some gamp cloths or paper towels. You could add an indicator too if you wish.

    If you want to go gaseous, then an open container of concentrated hydrochloric acid will quickly tell you if you have ammonia present and react pretty well. A small fan directed at the surface will increase effectiveness.

    Twospoons - 4-5-2024 at 19:01

    I built a gas scrubber using oxalic acid solution to remove the stink from rotting meat* - which I believe is largely due to amines from protein breakdown. It works extremely well for that, and would no doubt work even better with ammonia, given its solubility.

    * my daughter breeds flies to feed her frogs.

    RogueRose - 4-5-2024 at 19:47

    Quote: Originally posted by bnull  
    Acetic acid is volatile and will be carried along with the air.

    Is that for a homemade fume hood?


    Good point about the acetic acid, I guess I just thought about it b/c of it's saftey at lower concentrations like 5% vinegar, but the smell is strong which means it's evaporating in the air.

    I guess it's similar to a fume hood, but I don't vent of exhaust the air, but I can send the air from the reaction through an in-room air filtration system. The ammonia isn't always being evolved but if it starts, I want to be able to neutralize whatever is emmitted. Luckily it will never be at high volumes.

    RogueRose - 4-5-2024 at 19:52

    Quote: Originally posted by j_sum1  
    Water is pretty good at absorbing ammonia. Not sure what your constraints are or how permanent a setup you want. But here are some ideas using water:
  • attach an air pump to your feed line to keep positive pressure and then bubble through a flask of water
  • spray a mist of water through your exhaust gases
  • pass you gas over or through some gamp cloths or paper towels. You could add an indicator too if you wish.

    If you want to go gaseous, then an open container of concentrated hydrochloric acid will quickly tell you if you have ammonia present and react pretty well. A small fan directed at the surface will increase effectiveness.


    • Using water is a great idea, I forgot how well it absorbs ammonia when there is no or very low concentrations of ammonia in the water. It would be a very easy setup if I used water b/c there is a water supply & drain right were the air filter would be. I'd probably just recirculate the water down the filter & discharge it at set intervals or as needed (from evaporation).

    RogueRose - 4-5-2024 at 19:54

    Quote: Originally posted by Twospoons  
    I built a gas scrubber using oxalic acid solution to remove the stink from rotting meat* - which I believe is largely due to amines from protein breakdown. It works extremely well for that, and would no doubt work even better with ammonia, given its solubility.

    * my daughter breeds flies to feed her frogs.


    Interesting. How often do you have to replace the solution & do you run into any "contamination" like molds or bacteria growing?

    Twospoons - 5-5-2024 at 15:31

    I fill the scrubber with ~100g of oxalic acid in about 5l of water. That seems to be good for a year or more - I doubt the amine concentration coming off the rotting meat is very high (its quite capable of stinking up the whole back yard though). Air flow is provided by an aquarium air pump, so its not that high - just enough to create a negative pressure in the fly breeding box.
    I haven't noticed any mold or anything. I would imagine the oxalic acid would be pretty unfriendly to bacteria and fungi, given the low pKa.

    I should probably add a suitable pH indicator - would be easy to see if the acid is getting used up.