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| How
Does Activated Carbon Work? Picture yourself a sponge with ‘holes or entries’ of different diameter and you have a fair idea of what activated carbon looks like if put under a microscope. Depending on the size of the molecules of the compounds to be removed, it is important to select a type of activated carbon offering just the right amount of pores to absorb as much of those molecules as possible. Absorption mainly takes place in the smaller (micro) pores. Here the biggest attraction forces are concentrating. The amount, in which activated carbon is capable to bind the molecules of a certain compound, is called adsorption capacity or affinity. The absorption capacity is mainly determined by the molecular structure of the compound: e.g. benzene (C6H6) is very well absorbed, while carbon monoxide (CO) is not absorbed at all. The larger (meso/macro) pores take care of resp. easy access and further transport of the molecules to their final destination: the micro pores. Highly activated carbon may offer an extremely large total surface area (sometimes over 1.250 m² per gram!) but have a relatively small amount of micro pores. Such carbons are very suitable to treat large volumes of saturated gas streams. The excess amount of molecules will find their way into the meso pores anyway. Gas streams having lower concentrations of impurities are best treated with lesser activated carbon grades offering a more balanced pore size distribution. NOTE:
with activated carbon you do not buy a product, YOU BUY ACTIVITY! |
Humidity
of the Gas Stream
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Water is easily absorbed by activated carbon. This does not necessarily mean that it will influence the adsorptive properties, but it is very important to keep the relative humidity of the gas stream below 75 %. At higher values, the carbon will increasingly absorb water faster than anything else and a small layer of water will form on the surface of the carbon. This water film will hinder the natural attraction forces and will transport the molecules that need to be absorbed through the carbon bed and out of the filter. |
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