How to Choose Carbon Molecular Sieve by Pore Size: 0.3nm / 0.4nm / 0.5nm?

May 29, 2026

When selecting carbon molecular sieves (CMS), pore size is the core factor determining nitrogen purity and application suitability.

1.What Pore Size Actually Does: "Sieving" Gas Molecules by Size

Carbon molecular sieves work by selectively adsorbing impurities. Under pressure, smaller molecules like oxygen (kinetic diameter: 0.346nm) diffuse faster into the micropores and are adsorbed, while nitrogen (0.364nm) diffuses more slowly and remains in the gas phase, ultimately collected as product gas. An unsuitable pore size will either fail to reach the required purity or reduce the gas production rate.

2.Applications of 3 Common Pore Sizes

Pore Size	Core Function	Suitable Nitrogen Purity	Common Scenarios
0.3nm	Separates very small molecules like hydrogen and helium	-	Separate tiny molecules such as hydrogen and helium
0.4nm	Efficiently adsorbs oxygen and CO₂	99.5%-99.9%	Laser cutting, metal heat treatment, general industrial nitrogen generation
0.5nm	Low-purity nitrogen generation	95%-98%	High-flow, lower-purity applications where production rate is prioritized over purity

3. Two Common Selection Mistakes to Avoid

（1）Larger pore size is not always better: 0.5nm sieves also adsorb nitrogen, which reduces production rate and increases overall costs.

（2）Do not arbitrarily change pore size in standard nitrogen generators: Different pore sizes require matching pressure and cycle parameters; random changes will cause system performance imbalance.