Filters in fume hood

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delboy9891

Well-known member
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Jun 14, 2021
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Hi folks, newbie here from Scotland, I work in a science park so was lucky enough to get a small fume hood for free, it has prefilters and two heavy main filters which slide in to the fume hood, it also has two spare filters which I believe to be hepa filters, the other two are activated carbon filters, my question is what filters are best to extract the acid fumes, safety is my first concern, many thanks in advance for any replies
 
Bad news is the filters will not work for too long , you would be better off adding a scrubber system to the hood, there are full designs here on the forum for home made systems.
 
I would be very careful with a ductless fume hood. It will cause a false sense or security, which is particularly dangerous with poisonous gases.

I do a lot of things inside my house that generate small amounts of fumes and depending on what I’m doing I’ll do my reactions in a flask with a sidearm and bubble the gas through different things depending on what I’m doing.

I do my silver refining in a 2 liter flask with a sidearm and bubble the NOx into hydrogen peroxide, which has the benefit of making some dilute nitric which I either distill or use to dilute concentrated nitric acid.

A more well known scrubber for NOx is the system that is used in Diesel engines and requires DEF (diesel exhaust fluid) which is urea and deionized water. The hot exhaust gasses pass over a membrane that is sprayed with DEF and the urea/water vapor reacts with the NOx and turns them into CO2 and water. Funny enough when I was reading about this, I learned that this was invented by the Engelhard Corporation who must have had to come up with some way to reduce their NOx emissions from refining silver!

I’ve been experimenting with chlorine gas and PGMs (outside!) and I have the same setup, but bubble the gas into sodium hydroxide so that I end up with sodium hypochlorite and sodium chloride which is known as Milton Solution (essentially salty bleach)

A HEPA filter isn’t going to do much aside from filtering particulates out, the carbon is what will do the most work, but as was said earlier, this has a limited lifespan.

Please be careful with the fume hood!
 
You will need to adapt the hood, I’m assuming that you have an exit vent where your supposedly non toxic fumes are pumped out, if so you need to fit plastic piping to the vent , a little diy , which will allow you to put in a scrubber further on, 4metals did a thread about howto build your own , the other option is a sealed reaction set up with the gases pumped from the reaction vessel to a sealed scrubber vessel , again im fairly sure 4metals has done detailed posts on this also.
If you are going to be working near anyone else or their cars pumping out undcrubbed fumes will make you highly unpopular.
 
Ductless fume hoods have no place in the reactions side of refining. There are certain gases that filters will never clean. As others have stated you will need to retrofit your hood to use a scrubbing system. Ideally you'll also want a hood that contains no metallic components. Either that or be prepared to constantly replace them. At best you can perform incineration and melting processes with an unmodified ductless hood.
 
Ok I will look at 4metals designs and add ducting to my fume hood, I will look to see if I can make some sort of scrubber that fits on the ducting, safety is everything
 
Good thing you came here before using that.

You could have killed yourself, literally. :shock: :!:

What you have is not a "fume" hood at all. I suspect it's what is known as a laminar flow hood. It's used to filter dirt, lint, hair, pollen and dust particles out of air so you can work on sensitive parts of things that dust contamination would ruin otherwise. Was never intended to be used with chemicals or gasses of any kind.

There is not a filter on earth that you can use on chemical gasses. Other than some used in respirators as a temporary, emergency escape use. Even then you won't come away without some lung damage.

If I were you, I'd take that back and build one from scratch, made for the purpose. I made mine out of plywood and painted it with regular latex house paint.
 
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