How to improve the service life of molecular sieves and the drying effect of activated alumina adsorbents?

In industrial gas treatment and petrochemical industries, the combined adsorption application of molecular sieves and activated alumina has become a core technology for improving drying efficiency and extending service life. These two adsorbents, leveraging their respective product advantages and chemical properties, form a multi-level purification system, particularly suitable for industrial applications with strict humidity and pollutant control standards.

Molecular Sieves Adsorbents: Molecular sieves are microporous aluminosilicate crystals with uniform pore size and extremely high specific surface area. They possess high adsorption capacity, rapid adsorption, and strong adsorption strength. They selectively adsorb molecules smaller than the pore size of molecular sieves and exhibit strong selective adsorption of polar substances such as water and carbon dioxide. Zeolite molecular sieves are classified according to application into 3A, 4A, 5A, 13X, 13X APG, 13X HP, lithium molecular sieves, and carbon molecular sieves.

Activated Alumina Desiccant: Activated alumina is a porous and highly dispersed adsorbent material with high strength, low abrasion, and resistance to softening, cracking, and powdering. Its surface is rich in hydroxyl groups, thus exhibiting polar adsorption capacity for polar molecules such as water. This results in high adsorption capacity and low regeneration costs. However, its wide pore size distribution and relatively weak screening selectivity make it suitable for use as a coarse adsorbent material in the early stages.

Principle of Use: The combination of molecular sieves and activated alumina follows the synergistic principle of "pretreatment and deep precision treatment," fully utilizing their performance advantages.

Pre-adsorption Pretreatment: Activated alumina has a large adsorption capacity, preferentially removing large amounts of moisture, some heavy hydrocarbons, and other easily adsorbed impurities from the system, reducing the load on the molecular sieve and preventing frequent regeneration due to rapid saturation.

Deep Screening and Purification: After pretreatment, the material enters the molecular sieve unit, where its uniform pore size and strong selectivity precisely remove residual moisture, carbon dioxide, or specific molecules, achieving deep purification.

Application Scenarios: Oxygen Production Industry: In pressure swing adsorption (PSA) oxygen production systems, compressed air first passes through an activated alumina bed, rapidly removing over 80% of moisture and some oil contaminants, preventing moisture from entering the molecular sieve bed and causing its failure.

Pretreated air then enters an oxygen-producing molecular sieve bed, where the sieve selectively adsorbs impurities such as nitrogen and carbon dioxide, ultimately producing oxygen with a purity exceeding 90%. This combination extends the lifespan of the molecular sieve and improves the stability of the oxygen production system.

Natural Gas Purification: Natural gas extraction typically contains significant amounts of moisture, hydrogen sulfide, and heavy hydrocarbons. Activated alumina first acts as a pre-adsorbent, efficiently removing most of the moisture and heavy hydrocarbons. Subsequently, the natural gas enters a molecular sieve bed for further removal of residual moisture and hydrogen sulfide. This prevents subsequent pipeline damage caused by hydrate blockage or corrosion, ensuring the safe transport of natural gas.