Molecular Sieve 5A

Calcium Exchange Opens the Pore to 5 Ångström

SorbiTech 5A is the calcium exchanged form of the 4A sieve. Replacing two sodium ions with one calcium ion widens the effective pore opening from approximately 4 to approximately 5 Ångström. That extra width admits linear normal paraffins from n pentane to n thirty, oxygen, and a range of polar species, while branched and cyclic hydrocarbons are still excluded at the pore mouth.

The empirical formula is 0.7 CaO · 0.30 Na₂O · Al₂O₃ · 2 SiO₂ · 4.5 H₂O. SorbiTech manufactures the 5A grade as 1.6 to 2.5 mm beads with a controlled particle size distribution suited to PSA vessels.

Shape Selective Separation

The 5 Ångström pore is the centre of UOP MOLEX and other n paraffin extraction processes used to produce linear alkylbenzene feedstock for biodegradable detergents. The straight chain paraffins enter the pore and are retained; iso paraffins, naphthenes, and aromatics pass through. A single 5A column therefore replaces a fractionation train that would otherwise be uneconomic.

The same shape selectivity is exploited in oxygen PSA. Oxygen has a smaller kinetic diameter than nitrogen and is adsorbed preferentially in the calcium exchanged crystal under the right cycle, which gives a feed for medical oxygen, aquaculture, and small ozone generators.

Hydrogen Purification

In a hydrogen PSA, 5A is the polishing layer that follows an activated carbon and 13X layered bed. The carbon removes carbon dioxide and heavier hydrocarbons, the 13X holds the residual carbon monoxide and water, and the 5A captures the trace methane and nitrogen that would otherwise reach the product header. The combined SorbiTech bed delivers fuel cell grade hydrogen at ISO 14687 Grade D specifications.

Cycle Performance and Regeneration

• Equilibrium water capacity: ≥ 21 percent by weight
• Oxygen capacity: optimised for VPSA oxygen cycles
• Adsorption pressure: 5 to 30 barg depending on duty
• Regeneration temperature: 200 to 315 °C (TSA) or vacuum (PSA)
• Half cycle time: 1 to 12 hours depending on application

Forms and Supply

Supplied as 1.6 to 2.5 mm beads by SorbiTech with a certificate of analysis per batch. The 5A material is shipped as standard media for n paraffin separation, hydrogen PSA polishing, and oxygen PSA, or loaded by SorbiTech commissioning engineers into the matching SorbiTech engineered vessel. Within the SorbiTech portfolio the 5A grade serves PSA gas separation, n paraffin recovery, and hydrogen polishing; see also the petrochemicals and refining sector and the parent molecular sieves family.