What is the working principle of carbon molecular sieve?

Carbon molecular sieve uses the characteristics of sieving to achieve the purpose of separating oxygen and nitrogen. When the molecular sieve adsorbs impurity gas, the macropores and mesopores only serve as channels, and the adsorbed molecules are transported to the micropores and submicropores, and the micropores and submicropores are the actual volume of adsorption. Carbon molecular sieve contains a large number of micropores. These micropores can allow molecules of small dynamic size to rapidly diffuse into the pores while restricting the entry of molecules with large diameters. Due to the different relative diffusion rates of gas molecules of different sizes, the components of the gas mixture can be better separated. Therefore, in the manufacture of carbon molecular sieves, according to the molecular size, the distribution of micropores in the carbon molecular sieve should be 0.28nm and 0.38nm. Within this micropore size range, oxygen can quickly diffuse into the pores through the micropores, but it is difficult for nitrogen to pass through the micropores, thereby achieving the separation of oxygen and nitrogen. The pore size of the micropores is the basis for separating oxygen and nitrogen through carbon molecular sieve. If the pore size is too large, oxygen and nitrogen molecular sieves can easily enter the pores, and thus cannot perform the separation effect; when the pore size is too small, neither oxygen nor nitrogen can enter the pores and have no separation effect.



Due to conditions, domestic molecular sieves cannot be well controlled by the pore size. The carbon pore size distribution of carbon molecular sieve on the market is 0.31nm, and only Iwatani molecular sieve has reached 0.28nm and 0.36nm. The raw materials of carbon molecular sieve are coconut shell, coal, resin, etc., which are kneaded with basic materials after processing and crushing. The main purpose of the substrate is to increase strength and prevent crushing and powdering. Activate pores. The activator is introduced at a temperature of 600 to 1000°C. Commonly used activators include water vapor, carbon dioxide, oxygen and their mixtures. They undergo thermochemical reactions with relatively active amorphous carbon atoms to gradually expand the specific surface area to form pores. The pore formation time varies from 10 to 60 minutes. The third step is to use chemical vapor to adjust the pore structure: for example, benzene in carbon deposits the pore walls of the molecular sieve to adjust the pore size to meet the requirements.