The working principle of carbon molecular sieve is mainly based on physical adsorption, that is, using its microporous structure to selectively adsorb gas molecules of different sizes. According to the diffusion rate and adsorption characteristics of different gas molecules on the surface and in the pores of carbon molecular sieve, effective separation of gases can be achieved by changing pressure or temperature.

Composition and structure

Carbon molecular sieves are generally made from coal, coconut shells or other organic materials through complex processes such as carbonization and activation. Its micropore size is very uniform, usually between 0.3 and 1 nanometers, which allows it to selectively adsorb gases of different molecular sizes.

 Main characteristics

High selectivity: Due to the small and uniform pore size, carbon molecular sieves can accurately separate molecules of different sizes. For example, in the separation of nitrogen and oxygen, oxygen molecules are slightly larger than nitrogen molecules, so they can pass through carbon molecular sieves more quickly, while nitrogen is more adsorbed.

High adsorption capacity: With a large specific surface area, a unit mass of carbon molecular sieve can adsorb a large amount of target gas.

Chemical stability: It has high chemical stability and is not easily corroded by most chemicals, so it can be used under a variety of working conditions.

Thermal stability: It can maintain its adsorption capacity and structural integrity at higher temperatures.

Main applications

Gas separation (mainly nitrogen production): The most widely used application of carbon molecular sieves is industrial nitrogen production. In the nitrogen production process, the carbon molecular sieve is used to selectively adsorb oxygen and a small amount of impurity gases in the air through the pressure swing adsorption (PSA) technology, so that the nitrogen can be separated. The purity of the nitrogen produced is usually between 95% and 99.999%.

Hydrogen purification: Carbon molecular sieves are also used to separate high-purity hydrogen from mixed gases such as ammonia decomposition gas or water gas.

Methane/nitrogen separation: In the process of natural gas recovery and processing, methane and nitrogen can be effectively separated by carbon molecular sieves.

Other gas separation: In some special applications, carbon molecular sieves can be used to purify target gases from gases such as carbon dioxide and nitrous oxide.

Pressure swing adsorption (PSA) technology

This is the most commonly used operating mode of carbon molecular sieves. The specific steps are as follows:

Adsorption stage: Under high pressure, the mixed gas passes through the carbon molecular sieve, smaller molecules (such as oxygen) are adsorbed, and larger molecules (such as nitrogen) pass through to obtain nitrogen-rich gas output.

Desorption stage: Reduce the pressure, the adsorbed gas such as oxygen is released, and the carbon molecular sieve is regenerated to prepare for the next cycle of adsorption operation.