Dear Sai,

If the etching of the tube is the problem during the activation process. Then I would suggest you, to go for post carbonisation activation. Post-carbonisation activation of the carbonised char is also an effective technique and produces AC with appreciable surface properties and also minimises the corrosion to the furnace and reactor.

Regards

Sumit

Hot KOH will always destroy your quartz tube. This is chemistry ;-)

http://www.quartzpage.de/gen_chem.html

You cannnot really decrease the amount of KOH, as the ratio KOH/biomass has a high impcat on the final textural properties of the activated carbon. We always do activation with KOH is a nickel crucible introduced in a stainless steel tube as the reactor, never in a quartz tube for that purpose. Otherwise, as you observed, the tube will always be destroyed. Moreover, activation of carbon with KOH produces carbonates, and hence a caustic foam with comes out of the crucible and touches the reactor. So the materials should resist these conditions. Nickel is acceptable, but zirconium would be even better. Zr crucibles are available for sale, but expensive.

Alain

Dear Alain Celzard

I have the same problem as the post. It would be great if you could suggest me that

Is it possible to use stainless steel crucible instead of nickel

I am afraid of that nickel crucible could not handle at 800 degree celcius

(since I bought nickel crucible from https://www.tedpella.com/beakers_html/crucibles.htm#anchor848-15Z

they said that it can be used up to 600 degrees, but from its melting point, it is around 1400 degrees)

Thank you for your answer

Chemical attack of nickel is moderate up to 800C, but that of stainless steel will be far higher. So you can use the latter, but you should be prepared to recover a material polluted by iron...

Alain 

Dear Alian Celzard

Thank you very much, That would be useful.

One more question, if I use nickel, Will there be nickel contaminate?

Yes, a little contamination. When washing your material with water, you'll see that the solution turns pale green to blue: this is dissolved nickel. If you want a really pure material, better washing it extensively with 1N HCl, then with water until neutral pH.

Alain

Think this is a problem for all thermal treatment of biomass. The mineral content is high enough to make some degree of etching if a quartz tube is used.

@Alian Celzard

Thank you very much. Your answer is very useful.

Does anyoone know what kind of stainless steel can be used as a tube reactor? Will hit resistant steel type 314 ( 1.4841 ) ok for this purpose? What about Impervious aluminous porcelain (IAP) or Recrystallised alumina (RCA, corund)? Thanks a lot!

We use 316 steel (24 mm OD) for the reactors with Swagelock connectors at both ends connected to 6 mm OD. A good advice is to leave the connectors outside the oven. We use some metallic inserts and quartz wool to keep the stuff on place. Change tube often because it will wear out.

We have a plan to change to ceramic tubes because thay can stand higher temperatures.

Thanks everyone for your inputs...this discussion was helpful

Hello everyone,

I have found new problem in relation to this. I mixed my C material with KOH (1:7) the activate at 850 deg C for 1 h under N2 in a tube (S steel) furnace. During activation KOH vapor exits the furnace with N2, then condense into the gas outlet tubing and the outlet of trap reservoir, resulting blockage. That condensed material is very explosive. Very dangerous to wash out. Does anyone know what material could be used to trap the vapor of KOH? K2O? K?

Thanks