Dear all,
I was just wondering whether there was any difference between granular and powdered activated carbon, apart form the grain size. Some suppliers have mentioned that PAC is simply ground GAC using a mill.
I am interested in linking GAC physicochemical properties (PSD, pore volume, charge, etc) to NOM adsorption whilst differentiating between DBP precursors and membrane fouling. I am soon to start tests on GAC adsorption tests, but wanted to use the PAC version. However, it seems really difficult to source the PAC version of the GACs of interest. I can grind the GAC myself, but I wanted to avoid cross-contamination between samples and altering its physicochemical properties.
More details available on my research page on the STREAM-IDC website:
http://www.stream-idc.net/dangolea
Thank you very much for your help in this matter.
Best wishes,
Dan
It is important for the the adsorption from solution. Because, if particle smaller, the auther surface area is larger.
It has different adsorption properties since GAC has a larger particle size. Also, GAC can provide better molecular adsorption with a variety of contaminants.
Several answers are possible. If powder is the direct result of activation, it is probably more homogeneous than grains, for which activation started from the surface and was not so efficient in the inner part of the grain. If powder is the product of grain grinding, part of the macroporosity, and sometimes part of the widest mesopores, may have disappeared. Grinding indeed induces locally high pressures, and therefore pore collapse (see fig. 7 of attached file). As for applications, diffusion within the powder will be much easier than in grains, and therefore the adsorption kinetics will be higher. But powders are much more difficult to handle than grains, the latter being easy to collect after use. Powders are difficult to separate and produce fouling.
Alain
Thank you very much everyone for your kind replies!
Alain, that is exactly the dilemma I'm facing right now. I need to complete initial NOM adsorption tests by various GACs. For that I need to grind the GACs otherwise the solution will not achieve equilibrium. I'm testing 0.2, 2, 20, 200, 500 mg GAC in 100ml water samples. If I won't grind the GAC, 0.2 mg are likely to be 1 grain... Moreover, I wanted to avoid grinding and sieving due to potential cross-contamination (in the sieves even if I discard the first batch).
However, as you have mentioned, if I grind the GAC, it is likely that the meso-macro pores will be lost. As I understand, for NOM adsorption is is exactly the meso-pores that are essential.
I am also aware that the RSSCT (rapid small scale column tests) are a better way of evaluating GAC adsorption capacity, and that is my next step.
I need to find a compromise somehow..Potentially I could grind the GACs to a higher particle size (>106 um) and perform equilibrium tests?
Your comments are greatly appreciated.
Best wishes,
Dan
We always do the adorption in liquid phase by using activated carbons ground and sieved to get the fraction 100 - 200 µm. This fraction is the one we investigate by adsorption techniques (BET, etc.) and by adsorption in the liquid phase. As far as we always compare the same fraction, things are reproducible and easy to understand. It is indeed not obvious that you'll get the same results for different fractions, ground or not. This is why I recommend using small grains in a given range of sizes, and doing all the textural characterisations on this single fraction, not on the initial big grains.
Alain
Thank you very much Alain! Your advice is greatly appreciated.
Best wishes,
Dan
Powdered Activated Carbon (PAC) can be used at any point prior to filtration while Granular Activated Carbon (GAC) is used as a filter medium during filtration.
PAC may give greater accesss to the pores availabel on the AC. However, brerakthrough of fines must be handled when using PAC. High pressure drop probloems may also affect those using PAC instead of GAC
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