Sciencemadness Discussion Board

HEPA Filters for fume absorption?

Electra - 22-2-2014 at 05:05

After building curiosity to construct a fumehood, I began to look into various types of filters. Carbon Filters from what I have read are ineffective for absorbing solvent, acid, and other sorts of fumes that would be found in an organic chemistry lab. Further investigation lead me to discovering HEPA filters. Only one site(that sells them) on the web, claims that their HEPA filters can absorb nearly everything from most strong acids, Solvents like Toluene, DCM, Xylene, Acetone, Methanol, and practically every other solvent you can think of - Link to site

I did some searching on here and there was speculation that HEPA filters are no good for absorbing these various gaseous fumes. I can't find many/any other sites that talk about the sort of things HEPA filters can absorb. It's not so much dust particulates I am concerned with absorbing, but I would not want to be pumping out noxious fumes into my work space nor outside to my neighborhood. Somewhat defeats the purpose of having a fume hood I think.

Can anyone comment on the effectiveness of HEPA filters? I contacted the company above with some questions so hopefully they can clear some things up, but I am at a loss to why there are not many other sites with technical information on these filters. Are their better filters suited for chemical-solvent/acid fume absorption?

Maya - 22-2-2014 at 05:25

You are completely Wrong.

#1 the site you linked has a variety of filters on it

#2 HEPA filters offer ZERO absorption of solvents, acids, organics or fumes etc etc. HEPA filters only filter out particulate materials.

#3 Carbon filters are the only filters that will absorb Organics etc. They will quickly get overloaded if you have high conc's and airflow
and become saturated with Organics at which point will not absorb any more. Your best bet is to have a deep activated carbon layer
which will also decrease flow rate

Electra - 22-2-2014 at 05:39

I have read that activated carbon does absolutely nothing to absorb acids and many of the solvents listed above like Toluene, DCM, Xylene, Acetone, Methanol, etc.

How does a deep activated carbon layer differ from a normal activated carbon layer?

A better question is, can you suggest a specific proper filter that I should look into? Flow rate of the air is not really an issue as that can be compensated by fan strength, of course, but after having lung-based run ins with unwanted materials, I would like to avoid all future incidences of such.

Yet now I find this site.... confirming what you said

Why is there so much contradictory information on the types of material carbon filters can absorb? Activated Carbon is activated carbon. Either it chemically interacts with the compounds flowing through it, or it does not, while partially clogging/stopping certain materials, right? Or wrong?

[Edited on 22-2-2014 by Electra]

confused - 22-2-2014 at 09:31

all activated charcoal does is absorb the gases, it does not generally react with most gases, and while i recommend scrubbing the gases of the experiment through some kind of bubbler, to prevent quick clog up of the filter, carbon filter should take care of the rest if most of the gases are neutralized straight out of the reaction

testimento - 22-2-2014 at 10:48

Activated carbon filters are excellent for most organics, but they are not universal.

ACF can be reactivated by heating it up to 500-900C. This is challenging to do for most hobbyists, but wether someone happens to have any good ovens in which they can use inert gas(nitrogen, argon, CO2), heating it up to 300-500C for several hours will probably allow reactivation in excess of 60-80% of original capacity. The absorbed gases and impurities are then released as gas, and since AC can absorb up to 1/3 of its weight of several compounds, the evolved fumes need to be safely exhausted.

For most, it's just simplest to buy new filter. They are used in ventilation systems of controlled substances cultivation and sold in several shops for reasonable price. A 1000m3 ACF can be obtained for little more than 100 bucks and attached into a line fan of 500m3 it can very easily last more than year for most hobbyists. ACF don't clog if only pure air is blown through them, so they can be safely let run for long periods of time. Particle filter(HEPA or normal filtering sheets, very economic) are preferred to remove solid particles which may eventually clog the filter.

For odor and fumes removal, it's important to have the line fan suck through the ACF, or simply, place the filter before the fan. This is because there is minor risk of vapor explosion caused by the electric motor of the sucking fan.

Electra - 22-2-2014 at 13:32

I have no problem replacing it when it needs to be replaced, I just want to make sure I get a good one so I don't waste my money. I'm not entirely sure the activated carbon filters people use for indoor-smelly-botanical gardens would be effective for my purposes. Should I seek a more professional source?