Molecular Sieve 4A

The Reference Sodium Form A Sieve

SorbiTech 4A is the unmodified parent of the A family, with the empirical formula Na₂O · Al₂O₃ · 2 SiO₂ · 4.5 H₂O. The sodium cation in the lattice leaves the pore window at approximately 4 Ångström, wide enough to admit water, carbon dioxide, hydrogen sulphide, methanol, ethanol, and methyl mercaptan, but tight enough to exclude propane and every larger hydrocarbon.

SorbiTech manufactures the active crystal and binds it with a clay matrix into 1.6 to 2.5 mm and 2.5 to 5.0 mm beads. The bead form delivers a low pressure drop in deep beds and a controlled particle size distribution that resists fluidisation during pressurisation cycles.

Why 4A and Not 3A or 5A

The 4A pore is the highest capacity sieve in the A family for water adsorption. Where the gas stream contains no propylene, ethylene, methanol, or other species that would coadsorb, 4A delivers more water per kilogram of media than the 3A grade and at a lower cost per cubic metre of treated gas.

For sweet methane, refrigerant drying, insulating glass units, and clean compressed gases, 4A is therefore the engineering default. SorbiTech specifies the 3A grade only where the feed contains C₂ and heavier hydrocarbons that would compete for the wider pore, and 5A where shape selective separation of n paraffins or hydrogen purification is required.

Cycle Performance and Regeneration

Equilibrium water capacity is 22 percent by weight or more at 25 °C and 17.5 mbar water partial pressure. A correctly sized 4A bed in a temperature swing unit delivers outlet water dew points below minus 70 °C with an adsorption half cycle of 8 to 16 hours.

Regeneration uses a dry hot purge at 200 to 315 °C. SorbiTech sizes the heater for the highest expected water load with a 10 to 15 percent margin, then the cooling step returns the bed to within 10 °C of adsorption temperature before switchover.

• Adsorption pressure: up to 150 barg
• Adsorption temperature: minus 20 to plus 60 °C
• Regeneration temperature: 200 to 315 °C, ramped
• Purge ratio: typically 8 to 12 percent of dry product
• Half cycle time: 8 to 24 hours, set by inlet water load

Common Applications

Sweet natural gas dehydration, recycle gas drying in refinery hydrotreaters, insulating glass unit desiccation, refrigerant filter driers in HVAC and refrigeration, alcohol recovery dehydration, and ammonia and amine drying. The grade is also widely used in air separation pre purification where the feed is clean and the carbon dioxide load is moderate.

Forms and Supply

Supplied as 4×8 mesh beads (1.6 to 2.5 mm) and 8×12 mesh beads (2.5 to 5.0 mm), manufactured to ISO 9001:2015 and released against a certificate of analysis per batch. Halal and Kosher eligibility is held on the standard grades. Available as standard media for an existing dryer or as the charge in a SorbiTech twin tower TSA dehydration unit, with SorbiTech delivering turnkey where the project scope requires it. SorbiTech specifies the 4A grade for sweet methane and air pre purification duties; see the dehydration application, the matched TSA package, the industrial gas sector, and the broader molecular sieves family.