Sciencemadness Discussion Board

Adsorption capacity of activated carbon?

Twospoons - 28-8-2007 at 18:10

I just recently became interested in solar powered adsorption refrigeration, (I'm that kind of guy). Of the adsorption systems out there ( CaCl2 /ammonia, carbon/ammonia, carbon/methanol, zeolite/water ...) the most accessible for the home experimenter would seem to be activated carbon/ methanol, as both are easy to get and easy to handle.
What I'm trying to work out is the methanol adsorption capacity of the carbon. The datasheets for the carbon usually specify an Iodine number for adsorption capacity - can anyone tell me how that would relate to methanol adsorption? I'm only after a rough estimate so I will know if a kg of C will handle a kg , or 100g , or 1g of MeOH.

Reference Information

solo - 28-8-2007 at 18:31

Study of the performance of activated carbon–methanol adsorption systems concerning heat and mass transfer
L. W. Wang, J. Y. Wu, R. Z. Wang, Y. X. Xu, S. G. Wang and X. R. Li
Applied Thermal Engineering,Volume 23, Issue 13, September 2003, Pages 1605-1617

Three types of adsorbers and two types of activated carbon–methanol adsorption systems are studied, and the structure of adsorbers, performance of adsorbents, performance of different adsorbers and different systems are compared. Results show that the heat transfer coefficient of solidified bed are much higher than that of granular bed, the design of gas flow channels in adsorbers is very important to the performance of mass transfer and the performance of the whole system. Performance of the adsorber with good design of gas flow channels is much better than that of other two types of adsorbers.

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Twospoons - 28-8-2007 at 19:42

Thanks Solo. Looks like the ballpark figure is around 0.22kg/kg.

Tacho - 29-8-2007 at 03:49

I have been very interested in this same topic over the last two weeks. I even built a device to make some basic tests. It consist of two metal tubes connected by a PVC tube on the top. One is filled with activated carbon as a fine powder and the other with 50ml of methanol. I heated the carbon tube for about half an hour at 110ºC and connected it to the PVC "bridge". Nothing happened. There has to be some extra trick. I think it may be the use of some vaccum or of granulated cabon.

I'll read solo's paper to see if I find any new info.

Some papers on the subject: (very good) (is that a link or what!)

not_important - 29-8-2007 at 05:15

Either pumping it down or heating the methanol so as to fill most of the space with MeOH vapour before sealing it up will help. Otherwise you are going to have to wait for vapour to diffuse the length of the air-filled tube before it can be absorbed.

You'll want a lot of surface area for the methanol, and similarly you don't want to have the vapour to fight its way through saturated carbon to reach carbon that can absorb it. And it's not quick, if you don't insulate the methanol evaporator you may not see much of a cooling effect on the small scale of your test.

Something similar has been made to work using metallic 'sponge' instead of activated carbon, working as a "heat diode" that takes advantage of the low temperature of the night sky to condense the working fluid, which runs back into the evaporator.When the sun is up, the vapours don't condense and there is no flow from the evaporator/cold side to the radiator.

roamingnome - 29-8-2007 at 06:53

you may have seen this article, but this guy is on it.....

Tacho - 29-8-2007 at 09:06

By the way,

my activated carbon is too fine. So fine that it forms a black cloud that lingers in the air every time I use it. This is very annoying.

I would appreciate any suggestion of a binder that does not interfere with its adsorbing properties.

I was thinking of a small ammount of gypsum or maybe sodium silicate.

[Edited on 29-8-2007 by Tacho]

Twospoons - 29-8-2007 at 14:04

Everything I've seen so far concentrates on getting good heat transfer through the carbon, and short vapor pathways. I think you are going to need granulated or pelletised carbon.