Activated Carbon Chemical Activation Method

The chemical activation method involves uniformly mixing various carbon-containing raw materials with chemicals, such as phosphoric acid, zinc chloride, potassium hydroxide, and undergoing processes like carbonization, activation, chemical recovery, rinsing, and drying at a specific temperature to prepare activated carbon. These activation reagents promote the activation of raw materials through erosive, hydrolysis or dehydration effects on the raw materials and oxidation effects. Phosphoric acid, zinc chloride and potassium hydroxide are the most commonly used activators. The principle of chemical activation is not yet fully understood but it is believed that chemical activators erode and dissolve cellulose in the raw material while decomposing hydrogen and oxygen contained in hydrocarbons to form small molecules such as H2O and CH4 which results in the formation of numerous pores. Additionally, they inhibit tar by-products formation during pyrolysis process thereby improving activated carbon yield.China has achieved large-scale automated production of powdered activated carbon using wooden phosphoric acid method.
(1) Phosphoric acid activation method
In the process of preparing activated carbon using phosphoric acid method, the mechanism of action between phosphoric acid and wood fiber raw materials can be divided into the following aspects: swelling effect, accelerated activation effect, dehydration effect, oxidation effect, and aromatic condensation effect. [2]
The basic processes of phosphoric acid activation method include wood chip screening, drying, preparation of phosphoric acid solution, mixing (or impregnation), carbonization, activation, recovery, rinsing (including acid treatment and water washing), centrifugal dehydration, drying and grinding, etc. If producing granular activated carbon, kneading process needs to be added. In addition, a dedicated exhaust gas purification system is installed to recover phosphoric acid and carbon powder from the flue gas, reducing environmental pollution. In the production process of phosphoric acid activation method, attention should be paid to controlling the degree of carbonization, allowing phosphoric acid to fully penetrate into wood chips, and then cooperating with the activation section for control, which can significantly improve the adsorption capacity of activated carbon and stabilize product quality. At the same time, appropriately reducing the activation temperature is beneficial for reducing product ash content. The use of multi-stage liquid-phase recovery for carbon activation tail gas can increase the recovery of phosphoric acid and fine carbon powder, and the use of high-voltage electrostatic method is also beneficial for the removal of tar in the tail gas.