Sciencemadness Discussion Board - Activated Carbon as a fume filter: What DOESN'T it absorb?

Activated Carbon as a fume filter: What DOESN'T it absorb?

RareEarth - 29-7-2015 at 13:28

I am somewhat petrified that years of knowing about this material and having done so many searches about it, I have been unable to find how it truly works, or better yet, a list of what it can or can't absorb as a filter medium. The only thing I know about it is that it is highly porous, but I have never really understood what is "activated" about it.

Simply put, if I have a fume hood leading to a activated carbon filter, whether redirecting back in the lab or outside, what kinds of compounds are at risk for not getting absorbed by the filter? For mundane things like solvent's, this isn't a big deal. For things that absolutely require a fume-hood, that are toxic am terrified that of the thought of a significant amount going through the filter unscathed, whether into the outside air for people to breath, or into my lab.

How are volatile hazardous things actually trapped by activated carbon? Where can I find some confidence for what is safe to rely on such a filter for?

[Edited on 29-7-2015 by RareEarth]

Sulaiman - 29-7-2015 at 15:20

I am a complete noob when it comes to carbon filters,
done some reading but no experience, so take with a few mg of NaCl

first, good information and links here https://en.wikipedia.org/wiki/Activated_carbon
e.g. link to one manufacturers adsorption ratings http://www.sentryair.com/activated-carbon-filter.htm

since different carbon sources and different activation processes giving different pores sizes and grain sizes are available
and the amount and type of contaminants already adsorbed is unknown
I suspect that there is no 'correct' answer,
so one approach would be to test your exhaust for expected contaminants,
probably a more complex experiment than the one that is being filtered though !?

aga - 29-7-2015 at 15:28

If you can hold on for a few days, i am about to do a bit of a study of Activated Carbon, as i too was totally unaware of what the stuff actually is.

Generically it is Carbon with a vastly increased surface area.

In that form it seems to adsorb (not absorb) halogens very well, and has an affinity for other elements, such as Sulphur.

The things it adsorbs is determined by how it was 'Activated', and for what purpose.

RareEarth - 30-7-2015 at 09:38

Yes definitely do post again once you have done your study.

Very good to hear about the halogens/sulfur. I would hope phosphorous as well. These fall under the things of hazard, which are oh so useful in the lab, that I am concerned about. I've always wanted to be able to safely work with various acid gases and the powerful phosphorous and sulfurous halogenating agents, but I've been somewhat fairly concerned about them slipping through the filter. Included would be a number of highly reactive lachrymal alkyl halides as well. Things you definitely don't want your filter failing on you for.

unionised - 30-7-2015 at 11:17

Most things are absorbed by charcoal to some extent.
However it's important to realise that the absorption isn't permanent. More important too is the fact that something poorly absorbed can be displaced by things that stick more strongly. It's possible that some toxic material would stick to the charcoal but be displaced again later by a less toxic, but more "sticky" material.
That's one reason I'd never trust a recirculating fume cupboard.

aga - 30-7-2015 at 14:40

Not to put too fine a point in it, a fume hood should blast the nasty stuff you just made out into the first bit of Nature that is at least 30m away from you.

Reason being is that Nature can deal with it a whole lot better than you ever will.

As unionised rightly implies, an AC filter is a delaying tactic, not a solution to the problem.

RareEarth - 30-7-2015 at 18:19

Blasting it into nature can't be the typical practice in an industrial setting, is it?

Blasting it outside, "just in case", would be the ideal, scenario, but I would be concerned about passerbyers smelling something strange.

With a home-made filter, activated charcoal can be purchased very cheaply, and could even be replaced on a very frequent basis as to minimize any risk of any sort of odor-leakage.

DJF90 - 30-7-2015 at 22:29

Quote: Originally posted by aga

Not to put too fine a point in it, a fume hood should blast the nasty stuff you just made out into the first bit of Nature that is at least 30m away from you.

Unionised was talking about a recirculating fume hood, where the exhaust is passed through an activated carbon filter before being returned to the room.

Quote: Originally posted by RareEarth

Blasting it into nature can't be the typical practice in an industrial setting, is it?

For lab scale research/manufacture, yes it is. But you have to have a scrubber in place if theres potential for release of anything nasty. For pilot plant, even solvent vapors are monitored, and the place I used to work at had drums of activated carbon on the exhaust of the ventilation system. The drums were monitored by mass and were changed as required by the SOP.

Quote: Originally posted by RareEarth

With a home-made filter, activated charcoal can be purchased very cheaply, and could even be replaced on a very frequent basis as to minimize any risk of any sort of odor-leakage.

Would you really trust your life to home-made PPE? Schott and 3M both sell affordable "half masks" (as do others) and the filters aren't too expensive if you shop around. A pair of ABEK1 filters can be had for less than a tenner, and depending on usage could last a fairly long time. If you're not planning on using ammonia, then ABE1 cartidges are even cheaper.

These respirators absorb most nasties, although they're not suitable for use in an oxygen deficient atmosphere (as they only filter nasty stuff out) and IIRC they're no good for carbon monoxide.

[Edited on 31-7-2015 by DJF90]

lullu - 31-7-2015 at 01:19

A2B2E2K1HGP3 would be a good choice for most amateur chemists, not too expensive and its a good allrounder. I would recommend to go with a fullmasks they are often very cheap on eBay.

Tabun - 31-7-2015 at 03:36

Quote: Originally posted by lullu

A2B2E2K1HGP3 would be a good choice for most amateur chemists, not too expensive and its a good allrounder. I would recommend to go with a fullmasks they are often very cheap on eBay.

You may buy many cheap things and if they fail that's it but don't you simply don't play it like this with gas masks and filters.You will also need to see if it fits your face.

lullu - 31-7-2015 at 04:40

If you would check that filter you will see that it is perfectly suited you smart a**.

Also I am talking about full masks like Dräger which often come unused from inventorys (at least where I am from) that are not allowed to be used anymore but were well groomed and are perfectly okay to use. If you have a normal head Dräger Panoramas etc will fit you perfectly.

You are right that one should not save on these issues, still the mentioned filter and a used Dräger fullmask can be aquired for a reasonable budget.

RareEarth - 31-7-2015 at 10:22

Quote: Originally posted by DJF90

I would trust a home-built filter, but I wasn't talking about recirculating it back into the lab. Even if I was blasting it filtered outside, if I was working with highly toxic compounds I would still want a mask of some kind. I was debating on getting a supplied-air mask, that doesn't even filter the air you breath, but compresses air before hand, though, it could be bulky. This way prevents the failure of a mask-filter.