# fume scrubber vacuum pump



## bigpagoda (Jun 4, 2016)

Hello all,
I am beginning to devise plans for a multi-stage fume scrubber similar to the one posted by phildreamer (I think). I am using a 2000ml reaction chamber but may want to go up one day. I will be using 6" PVC approximately 66 inches high with a fogging atomizer in the top above the packing in the first two stages.(but I don"t know what to use) I am thinking I should go with a 3 CFM diaphram style pump so it will hold up better under the corrosive fumes- Or should i just cheap out and buy a used one and let it burn up. I am going to have the vacuum exhaust into the air stream from my fume hood just before it goes outside to help diffuse any residual vapors. I've looked at a lot of posts about fume scrubbers but am still not sure if my plans are on the right track.
To clarify what I am asking:
1. is a diaphram style pump the best way to go.
2. How am I sure 3cfm is the right size
3. What do I use for packing
4. does any of what I said sound right
Any recommendations or observations would be appreciated.
Thanks


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## fishstick (Jun 7, 2016)

I use a diaphragm style high pressure self priming pump and and spray nozzzle (the pump is connected to an on/off switch). I simply suck the gas to a collection vessel and turn on the mist. The rate at which you mist depends on the gas you create. Nitrogen dioxide is incredibly reactive with water. Simple experiment put 200 ml of water in a 1 L flask, pump in NO2 gas and seal the flask - then swirl flask and observe the water absorb the gas. After you observe that, that may determine how to set up your "scrubber"

My point is how you set up your vessel really is up to your imagination/needs but what's important is:

1) vacuum pressure - to keep the gas being "sucked in" to the vessel and not allowing it to escape. I can't say 10 CFM, 100 CFM, etc. because I don't know what the volume of gas is you will create. YOU need to determine the wt of product, whether that is 20 grams, 200 grams or 2,000 grams because the if you design a system to solve for the gas for 100 gm production run and then do more, your vessel even if correct will fail. 
2) correct sealant - to ensure no gas can escape when it's in vessel.

To me, nitrogen dioxide gas gets a bad rep on this board as it is seen as a villian and needs to be neutralized, etc. In a way, it's ironic that the board is about precious metal recovery when the the nitrogen dioxide can be recovered as well. How? (see below)

3NO2 + H2O(l) ---> 2 HNO3 (aq) + NO(g)

Nitric acid is formed by reacting NO2 with water (in scrubber vessel). The NO produced by this disproportionate reaction reacts with air to form more NO2 which, in tern, reacts with water. Most of the nitric acid produced can be reacted with ammonia to form ammonium nitrate for use as a fertilizer. 

***personally, I use a 100 PSI, 4L/min pump and suck the gas into a 5 gallon bucket with 1) hand held vacuum and 2) 100 CFM HVAC in-line fan. I then mist water from the bucket to the gas and recycle that route. Afterwards, I neutralize with NaOH to 8-10 and discard down the drain - since I do small runs and don't create enough to liquid in the bucket to make a decent amount of fertilizer --- BUT I could***

Hope that helps


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