Patent ID: 7578938

Claim:
Filtering medium based on activated carbon comprising three superposed layers which include top and bottom outer layers and an inner layer between said outer layers, wherein the inner layer consists of 80 to 90% by dry weight of activated carbon, the balance to 100% consisting of organic and/or inorganic chemical fibres; and wherein the bottom layer comprising from 45 to 100% by dry weight of organic chemical fibres having OH functional groups and optionally inorganic fibres, the possible balance to 100% consisting of activated carbon and/or of a material having a density below 0.9, wherein all or some of the OH functional groups have reacted with a grafting reagent RX, where R is a suitable hydrophobic group in order to be able to be in the liquid state at a temperature of at least 200° C. at atmospheric pressure and in order to be able to react on the OH functional groups at least under certain reaction conditions, while producing covalent grafting of hydrophobic groups R onto the OH functional groups with formation of a volatile compound HX under the reaction conditions, and wherein the top layer comprises from 5 to 25% by dry weight of activated carbon, the balance to 100% consisting of organic and/or inorganic chemical fibres.