What is activated carbon and how to make it.

1. Chemical activation method

The general process steps adopted in this method are as follows: firstly, carbon-containing raw materials are impregnated with chemical reagents, and then activated under the protection of inert gas at a certain temperature to directly obtain activated carbon. The process flow is shown in the following figure:

Liu Haiyan and others use shell, anthracite and petroleum coke as raw materials, and activated with KOH to obtain activated carbon with a specific surface area of about 3,3m2/g. Some people take coal as raw material, remove inorganic minerals from it by chemical method and acid treatment, then impregnate it with chemical reagents such as phosphoric acid (such as zinc chloride, potassium hydroxide, sodium hydroxide, potassium carbonate, etc.), and then activate it under the protection of nitrogen to produce activated carbon with good quality, less ash, less tendency of volume shrinkage and carbon volatilization loss. As for the mechanism of chemical activation, the author thinks that chemical reagents and carbon can realize dehydrogenation and crosslinking of tar, catalytic gasification of carbon and dissolution of silicon and aluminum at high temperature.

at present, potassium hydroxide alkaline melting method is the most effective method to improve the specific surface area of activated carbon. Especially for raw materials such as petroleum coke, petroleum pitch and coal pitch which are difficult to activate, activated carbon with higher specific surface area-super activated carbon can be prepared by using potassium hydroxide as activator. The advantage of this method is that activated carbon with different pore size distribution and surface chemical properties can be prepared with different activators and their dosage, and it is easier to control the pore size distribution of activated carbon.

second, physical activation method

physical activation method is to react carbonized materials with carbon materials with oxidizing gases such as water vapor, carbon dioxide or air at high temperature, and form a developed microporous structure inside the carbon materials. The carbonization temperature is generally 6℃, and the activation temperature is generally between 8~9℃. The process of preparing microporous activated carbon by physical activation is mature, especially for preparing low-cost coal-based activated carbon, and the effect is very remarkable. However, in this process, the activity of raw materials is low, the activation time is long, the pore size distribution of micropores is difficult to control, the quality of the prepared activated carbon is unstable, the specific surface area is low, and the mesopores are not developed enough, which limits the application of activated carbon.