Production

Activated carbons are produced from different raw materials by one of the following processes: physical or steam activation and chemical activation,

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Physical activation producing High Density Skeleton = HDS

The production method consists of the following main process steps:

    1

    Devolatilization and Carbonization of raw material

    The Carbonization process comprises heating of the raw material to a temperature around 600 °C. This process also removes volatiles from the raw material

    2

    Activation of the carbonized material

    The carbonized material is activated at temperatures around 950 °C with a gasification agent (usually steam) which removes a proportion of the carbon atoms by gasification according to the reactions in table1:

    The steam activation process steps are performed in reactors such as rotary kilns, multiple hearth kilns, shaft kilns, and other high temperature kilns.

    Chemical activation producing Low Density Skeleton = LDS

    The production method mainly consists of the following process steps:

      1

      Mixing of raw material with liquid activation agent

      The activation agent is normally (an aqueous solution of) phosphoric acid. Other Lewis acids/bases may be used.

      2

      Activation of the carbonized material

      The mixture, optionally drained of excess liquor, is heated to temperatures around 500 °C or higher, usually in rotary kilns. Under these conditions the activation agent catalyses the cracking reactions of the raw material forming porous activated carbon without the need for further carbonization or gasification.

      3

      Recovery of the activation agent

      After activation, the pores of the activated carbon remain filled by the activation agent. This is then recovered by washing with water and can be reused. The carbon is then dried.

      Optional steps (both types of activation)

      In addition to the processes above there are a number of physical/mechanical treatments that are often required. Crushing, sieving, milling, extrusion, and/or briquetting can be performed before and/or after the activation, to produce products with the desired properties such as particle size distribution. In addition, the activated carbon may be further purified by washing with aqueous acids and/or alkali and/or water.