1. Selective Adsorption

Pore Size Characteristics:

• 3A molecular sieve has a pore size of approximately 3 angstroms (0.3 nanometers).
• It adsorbs molecules smaller than 3 angstroms, such as water molecules (≈2.6 Å).
• It excludes larger molecules, such as ethanol (≈4.4 Å), preventing their adsorption.

Adsorption Process:

• When ethanol containing water passes through a bed of 3A molecular sieve, water molecules are trapped in the sieve’s pores.
• Ethanol molecules, which are too large to enter the pores, pass through unchanged, effectively separating ethanol from water.

2. Dehydration Process

Initial State – Ethanol-Water Azeotrope:

• Ethanol and water form a constant-boiling azeotropic mixture at ~95.6% ethanol and 4.4% water, making distillation alone insufficient for dehydration.

Adsorption Stage:

• Ethanol containing water is passed through an adsorption column filled with 3A molecular sieve.
• Water molecules are adsorbed, while ethanol continues to flow through, resulting in dehydration.

Regeneration Stage:

• Once the molecular sieve becomes saturated with water, it must be regenerated to restore its adsorption capacity.
• Regeneration is achieved by heating the sieve to 200–300°C, causing water to desorb and allowing the molecular sieve to be reused.

3. Purification Effect

✅ High-Purity Ethanol – The adsorption process can increase ethanol purity to 99.9% or higher.
✅ Industrial Applications – High-purity ethanol is required in pharmaceuticals, cosmetics, and electronics, where ultra-low water content is critical.

4. Optimal Operating Conditions

• Temperature: Adsorption is typically performed at room temperature or slightly above to enhance efficiency.
• Pressure: Operates at ambient or slightly elevated pressure for effective dehydration.
• Flow Rate: Controlled ethanol flow ensures maximum contact time with the molecular sieve for optimal adsorption.

Summary

3A molecular sieve efficiently removes water from ethanol through selective adsorption, allowing for the production of high-purity ethanol. The process involves adsorption, dehydration, and regeneration, making it a cost-effective and reusable solution. By optimizing temperature, pressure, and flow rate, the efficiency of ethanol purification can be significantly improved.