Knowledge Sharing: Carbon Molecular Sieve in Nitrogen Generators
In a nitrogen generator, carbon molecular sieves use physical adsorption to separate different gases in the air, thereby enriching nitrogen to obtain finished nitrogen gas.
In a nitrogen generator, carbon molecular sieves produce nitrogen gas. The core principle is to utilize their selective adsorption capacity for different gas molecules in the air (mainly nitrogen and oxygen), achieving separation of nitrogen and oxygen through pressure changes. The following details the process from three aspects: structural characteristics of carbon molecular sieves, adsorption mechanism, and nitrogen generation process.
I. Structural Characteristics of Carbon Molecular Sieves
Carbon Molecular Sieve (CMS) is a carbon-based adsorption material with a microporous structure. Its key characteristics are:
Pore Diameter: The micropore diameter is typically 0.3~0.5 nanometers, close to the molecular size of oxygen (O₂, molecular diameter approximately 0.346nm) and nitrogen (N₂, molecular diameter approximately 0.364nm), slightly larger than oxygen and slightly smaller than nitrogen.
Low Surface Polarity: Primarily composed of non-polar carbon elements, adsorption of non-polar gases (such as N₂, O₂) mainly relies on van der Waals forces (intermolecular forces), not chemical adsorption.
High Porosity: The abundant micropores inside provide a large specific surface area (typically 800~1200 m²/g), allowing for efficient adsorption of gas molecules.
II. Mechanism of Selective Adsorption: Kinetic Differences
The separation of nitrogen and oxygen by carbon molecular sieves is not based on "stronger or weaker adsorption capacity", but on the difference in adsorption rates (kinetic separation):
Oxygen molecules are smaller and diffuse faster: Because the oxygen molecule diameter is slightly smaller than the micropores of the carbon molecular sieve, under pressure, oxygen can diffuse into the micropores and be adsorbed faster.
Nitrogen molecules are larger and diffuse slower: The nitrogen molecule diameter is close to the upper limit of the micropores, its diffusion speed is much lower than that of oxygen, and it is difficult to enter the micropores in a short time, remaining mostly in the gas phase.
In short: Under the same time and pressure, the carbon molecular sieve will "prioritize the rapid adsorption of oxygen", while nitrogen is enriched because it "cannot enter" or "is slow".
III. Working Process of the Nitrogen Generator (PSA Pressure Swing Adsorption Method)
Nitrogen generation using carbon molecular sieves usually uses pressure swing adsorption (PSA) technology. The core is the cyclical "pressure adsorption, depressurization desorption", alternately completing oxygen adsorption and molecular sieve regeneration. The specific steps are:
Pressure Adsorption:
Compressed air (containing approximately 78% N₂ and 21% O₂) enters the adsorption tower containing the carbon molecular sieve. Under a pressure of 0.6~0.8MPa, oxygen is rapidly adsorbed by the molecular sieve, and nitrogen, due to its low adsorption capacity, is discharged from the tower as product gas.
Depressurization Desorption (Regeneration):
When the molecular sieve adsorbs oxygen to saturation, the pressure in the adsorption tower is reduced (or vacuum is applied). The adsorbed oxygen is released from the micropores due to the pressure reduction and discharged through the exhaust valve, and the molecular sieve restores its adsorption capacity, preparing for the next cycle.
Alternating Operation of Two Towers:
Actual nitrogen generators usually have two adsorption towers. While one tower is adsorbing, the other tower is undergoing desorption and regeneration. Continuous nitrogen production is achieved through valve switching, and the nitrogen purity can reach 95%~99.999% (adjusted according to requirements).
IV. Summary
The microporous structure of the carbon molecular sieve and the kinetic adsorption difference between oxygen and nitrogen molecules allow for rapid separation of oxygen and nitrogen under pressure. Combined with the cyclical regeneration of PSA technology, efficient nitrogen production is achieved. This process has low energy consumption and simple operation, and is widely used in chemical, food, and electronics industries.
Other areas
Oil storage and pressurized pipeline cleaning and purging of oil and gas wells, nitrogen sealing, nitrogen displacement, solvent recovery.
Used for food preservation and grain storage, pest control, food drying and sterilization, quick freezing of food, etc.
Provide the necessary gas raw materials for the preparation of new energy materials, battery production, and create an inert gas environment.
Ensure the manufacturing of electronic components and the stable operation of equipment, providing gas support for maintenance, combustion assistance, cooling, and other aspects related to thermal power generation equipment.
Nitrogen generator: Prevents oxidation, inhibits bacterial growth, and produces odors in biopharmaceuticals, providing protection throughout the process. Oxygen generator: Provides an oxygen-rich environment.
When signs of fire occur in the goaf or other locations, nitrogen injection is needed for fire prevention. The nitrogen device is lowered into the mine. It is used for annealing protective gas and sintering.
Used in the aerospace composite field, providing the necessary inert atmosphere for the molding and reinforcement processes of large carbon fiber composite wings.
Provide protection for the safety of oil and gas reserves, prevent oxidation, nitrogen sealing, and ensure dust suppression, fire prevention, and nitrogen sealing for coal reserves.