[DanielS]

We are running into some issues with charcoal treating our raw materials.  Before my company moved to the US they used to get a 5% loss with each charcoal treatment and now we are getting a little over 10.  Our filters are clogging up.  My thought was that the charcoal we are using now is too fine to the stuff they used in Australia but my boss tells me that they used similar charcoal there.  He thinks it could be slightly finer than the stuff in Australia but not much.  We pressure filter under nitrogen through a 50 micron filter to a 0.45 micron filter.  Way too much charcoal is going through the 50 micro filter; the 50 micron filter doesn't seem to catch much of the charcoal before it goes to the 0.45 filter.  Any suggestions?  My two thought were to increase the size of the charcoal granules or use a smaller micron filter first.  The 0.45 filters are approximately $300 a piece so for them to "gunk" up so fast is costing us a pretty penny.

[Dan]

I had a similar problem once before. Following normal charcoal treatment, mix in Celite and filter the resultant celite/charcoal slurry through a (well packed) pad of Celite. Because the celite particles are larger, they disrupt the tight packing of the charcoal and reduce blockage. In my case, the celite retained most of the charcoal, and a 0.45 micron treatment removed the last traces.

I don't know what grade of charcoal I was using at the time, so there's no telling if it's going to help in your case, but probably worth a shot on test scale.

[K4carbon]

Powdered activated carbon (PAC) and granular (GAC) have a myriad of particle size distributions and the level of dust and fines varies.  I have been in the activated carbon industry for over 30 years and would be happy to try to help with your carbon questions. 

[DanielS]

Thanks for the replies guys.  I'm checking into some solutions now.  We are using PAC and my boss says they cannot use the granular type.  The weird thing is that they did the same set-up and used same charcoal and never ran into this problem over there.  I find this hard to believe but I have to listen to the boss lol.  I am looking into the celite idea.  We are treating 6 kilo batches of BHTD [1,3-Bis(4-Hydroxybutyl)Tetramethyldisiloxane (CAS 5931-17-9)] at a time with 2% PAC and then filtering it like I said above.  I feel the filter and set-up is more for small scale but again they said they had no problem using it in Australia.  Does powdered activated carbon come in different particle sizes?

[K4carbon]

PAC can be have size charaterizations such as 90% -325 mesh (44 micron) 60% -325 mesh, etc.  -200 and -100 mesh typically given also.  ASTM defines PAC as any activated carbon smaller than 80 mesh (U.S. Sieve Series).  I see grape juice applications that use DE as filter aid and have heard of new PAC that is magnetic and easy to remove using magnets in small systems.  In Australia, the common PAC is 90% -325 mesh for drinking water applications and 90% -200 mesh for some commercial applications.

Two PAC products may both say 90% -325 mesh but differ in how much is < 400 mesh for example.

[DanielS]

I discussed the Celite plan and turns out they tried it before and it cause the BHTD to gel up in the Celite bed.