5A molecular sieve is a calcium-exchanged synthetic zeolite with uniform 5-angstrom (Å) pores, widely used for gas separation and purification due to its selective adsorption properties. 

1. Chemical Composition & Structure** 

- Formula: 0.7CaO·0.3Na₂O·Al₂O₃·2SiO₂·4.5H₂O 

- Key Features: 

  - 5Å pore size (0.5nm), formed by Ca²⁺ ion exchange from 4A sieve 

  - Adsorbs molecules <5Å (e.g., n-alkanes, H₂O, CO₂) while excluding branched hydrocarbons 

2. Key Properties 

- Selectivity: Preferentially adsorbs linear over branched/cyclic molecules 

- Capacity: 21-23% water adsorption by weight 

- Thermal Stability: Regenerable at 250-350°C 

- Kinetics: Faster adsorption than 3A/4A for larger molecules 

3. Primary Applications 

- Petrochemical: 

  - n-Paraffin separation from iso-paraffins and aromatics 

  - Natural gas purification (H₂O/CO₂ removal) 

- Industrial Gases: 

  - Oxygen/nitrogen separation (O₂ preferential adsorption) 

  - PSA (pressure swing adsorption) systems 

- Other Uses: 

  - Refrigerant drying 

  - Volatile organic compound (VOC) removal