Activated carbon is carbon which is oxidised by a carefully controlled procedure which creates an extremely porous carbon structure. This highly porous structure creates an extremely large surface area for a given quantity of carbon. The more surface area you have to pass your airflow over the more carbon is available for the adsorption of a wide range of compounds.
Activated carbon has the highest volume of adsorbing porosity of any known material. A piece of activated charcoal weighing only 5 grams would have roughly the same surface area as a football field!!
Activated carbon can be made from any material with high carbon content, including wood, coal, peat and even coconut shells. The raw material has a large influence on the characteristics and performance of the activated carbon. Coal based activated carbon has mainly meso-pores (2 – 25 nm diameter) and macro-pores (25 nm diameter and above), and due to its unique distribution of pores, coal based activated carbon is very effective in gas phase purification. This is why Prima Klima have chosen to used activated carbon made from pit coal for their filters
CTC Activity is a measure of the adsorptive characteristics of activated carbon. A test is performed using Carbon Tetrachloride to see how much can be adsorbed per unit weight of activated carbon. This gives the CTC Activity percentage. Prima Klima use very high grade CTC 70% activated carbon for their industry line filters and a standard grade CTC 55% activated carbon for their eco line filters.
Some filter manufacturers specify an alternative Butane Number test. To obtain the butane number from the CTC you simply divide by 2.55. So our industry line filters have a Butane Number 27.5 and the eco line filters have a butane number 21.5.
For a more in depth description of activated carbon see the entry in Wikipedia – Activated carbon