Zeolite Molecular Sieve: Size-Selective Gas Adsorption

Pore Aperture (Sieve Type)

Feed Gas Mixture

Conditions

Temperature 300 K

Feed rate 4 /s

Bed State

Capacity filled

Capture efficiency

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Steric exclusions

Breakthrough

How it works

A zeolite is a crystalline aluminosilicate riddled with pores of one precise, uniform aperture — unlike activated carbon's random pore sizes. A molecule is admitted only by steric (size) exclusion:

admit if  d_molecule < d_pore   (kinetic diameter test)
Multi-component Langmuir isotherm on the sites that admit it:
  θ_i = (K_i · P_i) / (1 + Σ_j K_j · P_j)

θ_i is the fraction of adsorption sites occupied by species i, K_i its adsorption equilibrium constant, P_i its partial pressure. Species larger than the aperture never reach a site at all — exclusion happens before any equilibrium is possible.

Aperture buttons — real industrial sieve gradings: 3Å (3A, dries gases — only H₂O fits), 4Å (4A, admits N₂/O₂/CO₂/CH₄ but rejects branched hydrocarbons), 5Å (5A, separates linear from branched paraffins), 8Å (13X-scale, admits everything shown here).
Feed mixture — toggle which real molecules (with their true kinetic diameters) enter the bed.
Temperature — raises thermal velocity (∝ √T) and diffusion rate through the pore throat, so molecules reach and test the membrane faster.
Regenerate bed — models thermal/pressure-swing regeneration: adsorbed molecules desorb and the bed empties, as in a real PSA or TSA cycle.

Real-world use: 3A sieves dry natural gas and solvents; 4A/5A separate O₂/N₂ (medical oxygen concentrators) and straight- from branched-chain hydrocarbons in refining; 13X captures CO₂ from flue gas.

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