The difference between molecular sieve and activated alumina

I.Differences in Essential Structure and Adsorption Principles

1. Active Aluminum Oxide (γ-Al₂O₃)

Material: Alumina is heated and then transformed into porous amorphous aluminum oxide with uneven pore size distribution (ranging from 2 to 10 nm), without regular crystalline pore channels;

Adsorption Mechanism: Physical adsorption + surface hydroxyl polar adsorption, absorbing water through the large specific surface area;

Pore Channel Characteristics: Many large and mesopores, few micropores, strong affinity for high-concentration water vapor and liquid water droplets.

2. Molecular Sieves (3A/4A/5A/13X, silicate crystals)

Material: Crystalline silicate, with uniform and precisely controllable micropores (0.3/0.4/0.5/1.0 nm), single and regular pore size;

Adsorption Mechanism: Sieving effect + polar adsorption, only adsorbing molecules smaller than the pore size;

Example: 3A molecular sieve has a pore size of 0.3 nm, can only absorb water (0.28 nm), and does not adsorb hydrocarbons such as methane and ethane;

Pore Channel Characteristics: Predominantly micropores, with very few large pores, highly selective for extremely low concentration trace water.

II.Key Performance Comparisons (Most Core for Deep Dehydration)

1. Water Absorption Capacity (Saturated Wet Air at Room Temperature)

Active Aluminum Oxide: 15% - 22% mass water absorption rate, capacity is much higher than molecular sieves under high water vapor content;

Molecular Sieves: 10% - 16%, the capacity saturates quickly when the raw gas contains a lot of water, and is relatively low.

2. Low Dew Point Trace Water Adsorption Capacity (Core Difference)

Active Aluminum Oxide: The adsorption capacity drops sharply when the water vapor pressure is extremely low, the limit dew point can only reach -40 to -60°C, unable to remove ppm-level trace water;

Molecular Sieves: Still maintain strong adsorption even at extremely low water vapor pressure, stable dew point can reach -70 to -100°C, water content < 1 ppm, it is the only adsorbent that can achieve ultra-deep dehydration.

3. Resistance to Liquid Impact and Pollution Resistance

Active Aluminum Oxide: High mechanical strength, resistant to impact, can withstand a small amount of liquid water and trace oil mist, not prone to powdering; suitable for placement as a pre-buffer to intercept liquid droplets and oil stains;

Molecular Sieves: Easily shattered by a large amount of liquid water, oil and heavy hydrocarbons are prone to blocking the regular micropores, causing permanent failure, cannot directly contact saturated wet gas flow / liquid droplets.

4. Regeneration Conditions (Temperature, Energy Consumption)

Active Aluminum Oxide: Regeneration temperature 180 - 240°C, cold blowing recovery is fast, heating energy consumption is low;

Molecular Sieves: Must be regenerated at a high temperature of 240 - 290°C, insufficient temperature will not completely dehydrate the trace water in the micropores, regeneration energy consumption is higher.

5. Applicable Water Vapor Range

Active Aluminum Oxide: Coarse / moderate dehydration in the medium-high water content range (high inlet humidity, with a small amount of liquid droplets);

Molecular Sieves: Terminal fine polishing in the low water content range (pre-filter has removed most of the water, only trace water vapor remains).

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