Chemical activation is generally used for the production of activated carbon from sawdust, wood or peat. The process involves mixing an organic chemical compound with the carbonaceous raw material, usually wood, and carbonizing the resultant mixture. The raw material and reagent are mixed into a paste, dried and carbonized in a rotary furnace at 600 degrees C. When phosphoric acid is the activating agent the carbonized product is further heated at 800- 1000 degrees C during which stage the carbon is oxidized by the acid. The acid is largely recovered after the activation stage and converted back to the correct strength for reuse.
The raw material is mixed with an activating agent, usually phosphoric acid, to swell the wood and open up the cellulose structure. The paste of raw material and phosphoric acid is dried and then carbonized, usually in a rotary kiln, at a relatively low temperature of 400 to 500 degree Celsius. On carbonization, the chemical acts as a support and does not allow the charcoal produced to shrink. It dehydrates the raw material, resulting in the charring and amortization of the carbon, thereby creating a porous structure and an extended surface area.
Chemical Activation is generally used for the production of activate carbon from sawdust, wood or peat. Chemical activation involves mixing the raw material with an activating agent, usually phosphoric acid, to swell the wood and open up the cellulose structure. The paste of raw material and phosphoric acid is dried and then carbonized, usually in a rotary kiln, at a relatively low temperature of 400C to 500C. On carbonization, the chemical acts as a support and does not allow the char produced to shrink. It dehydrates the raw material resulting in the charring and amortization of the carbon, creating a porous structure and an extended surface area.
Activated carbons produced by this method have a suitable pore distribution to be used as an adsorbent without further treatment. The process used means that the activated carbons are acid washed carbons although they have a lower purity than specifically acid washed steam activated carbons. This chemical activation process normally yields a powdered activated carbon. If granular material is required, granular raw materials are impregnated with the activating agent and the same method is used. Granular activated carbons (GACs) produced have a low mechanical strength, and are not suitable for many gas phase uses. In some cases, chemically activated carbons are given a second activation with steam to impart additional physical properties.
Activity can be controlled by altering the proportion of raw material to activating agent, between the limits of 1:05 to 1:4. By increasing the concentration of the activating agent, the activity increases although control of furnace temperature and residence time can achieve the same objective.
Activity is controlled by altering the proportions of raw material to reagent used. For phosphoric acid the ratio is usually between 1:0.5 and 1:4; activity increases with higher reagent concentration and is also affected by the temperature and residence time in the kiln.
Activated carbons produced by this method have a suitable pore distribution to be used as an adsorbent without further treatment. This is because the process used involves an “acid wash” which is used a purifying step in steam activated carbons, post activation. Chemically activated carbons, however, have a lower purity than specifically acid-washed steam activated carbons as they contain small amount of residual phosphate.
This chemical activation process mostly yields a powdered activated carbon. If granular material is required, granular raw materials are impregnated with the activating agent and the same method is used. The granular activated carbons produced have a low mechanical strength, however, and are not suitable for many gas phase uses. In some cases, chemically activated carbon is given a second activation with steam to impart additional physical properties.
