Reactivating activated carbon

[Holy_makerel]

I work with borosilicate glass and looked into this hoping i could just put it in my kiln and reactivate but my kiln will only get to about 750c. Thats much hotter than the normal operating temp of about 650c and would most likely shorten the life of my elements, so i just buy it haha

 

[Randy Holmes-Farley Verified Community Expert]

It says 1900ish celcius

Sounds like you'd burn it up. lol

 

[GoVols]

@Cory
You got a sick mind but (lol) this is a great thread.

Have you filled out your Last Will and Testament, yet?
https://www.lawdepot.com/contracts/...gclid=COK_t5u3idQCFQMHaQodmZECcg#.WSX1ZZLyvb0

 

[Cory]

Sounds like you'd burn it up. lol

But are you implying that a high temperature, provided it doesnt burn the activated carbon to co2, should effectively reactivate the carbon?

Is it mostly organics that make carbon spent?

 

[T Carey]

But are you implying that a high temperature, provided it doesnt burn the activated carbon to co2, should effectively reactivate the carbon?

Is it mostly organics that make carbon spent?

The trick to making activated carbon is to get it up to those high temps in an oxygen free atmosphere. As I understand it the commercial process is to use steam to purge the oxygen out of the retort.

 

[Cory]

The trick to making activated carbon is to get it up to those high temps in an oxygen free atmosphere. As I understand it the commercial process is to use steam to purge the oxygen out of the retort.

So if i put some water im the bottom of a metal can or pipe, and torch the bottom, seems like it would be reactivated. No?

Steam lifts o2?

 

[T Carey]

I suspect it will be a bit more challenging than that. The water will boil off and the steam will exit the container carrying all of the oxygen out with it. You need to get the temperature up to 700 to 800° C. That means some method of measuring the temperature and for distributing the heat evenly so all of the carbon gets heated up. The next problem is cooling it off without letting much oxygen back into the can till it gets below ignition temperature.

After doing a bit of research on this process I strongly advise against trying it. There are too many things that could go wrong and most of them have nasty consequences.

 

[Riqaq]

I think that the microwave technique looks promising, I might try this at home, in the cellar with a cheap microwave oven. The tricky bit will be safely getting the inlet and outlet pipes into the microwave oven without affecting the integrity of the shielding of the microwave oven.
http://www.ipcbee.com/vol54/007-ICEES2013-ES1012.pdf describes the basic method and efficiencies. Interestingly, the microwave reactivation seems to preserve the integrity of the pores of the activated carbon better than the hot oven approach.

 

[Dkeller_nc]

A couple of notes about this discussion. The process for producing activated charcoal does indeed use steam and very high temperatures (about 1800 deg F) to produce activated carbon from bone or wood char. However, this process is designed to remove a substantial amount of the carbon from the surface of the char by reacting it with steam to produce carbon monoxide and hydrogen:

C(s) + H2O(g) = CO(g) + H2(g)

Industrial processes typically lose about 2/3rds of the weight of the initial carbon in the activation process. And for 99% of the global production, the activated charcoal is used once and then disposed of.

There are, however, industrial applications for activated charcoal that continuously regenerate an existing activated charcoal bed with fairly low-temperature steam (at about 400 deg F). These applications are typically for solvent vapor recovery systems. The regeneration temperature is selected primarily on the basis of the steam pressure at that temperature (i.e., the max temp to avoid rupture of the sealed activated charcoal bed) and the minimum temperature needed to vaporize whatever solvent is being recovered.

For aquarists, the situation is different. We are using the activated carbon to adsorb all sorts of things from tank water. Some of these will be proteinaceous compounds, some will be humic acids (that turn the water yellow), and many will be of unknown chemical structure. That makes regeneration problematic. The only sure way would be to repeat the industrial process, which removes all adsorbed compounds except for any heavy metals. But not only are the temperatures and pressures dangerous, you'd also lose 2/3rds of the activated carbon mass with each regeneration.

To further dissuade amateurs from trying this, at least with high temperature and steam, when carbon is heated to 1800 deg F in the absence of oxygen, it will spontaneously catch fire if the container is opened (or there's an air leak). That combustion has the potential to be explosive, depending on the size of the carbon particles and the size of the air leak.

 

[Riqaq]

To add to @DKeller's warning above, from the microwave perspective, the same would be true with a build-up of carbon dust using the microwave method, dust in the microwave (if not sealed and protected by an inert gas) may mix with air and cause a flammable vapour. Given the nature of carbon, oxygen fuel-air mixes, such a flammable atmosphere would burn with explosive speed.

Additionally, causing modifications or damage to the protective shielding of a microwave oven is dangerous and should not be carried out except by trained experts.