How to judge molecular sieves saturation

There are several drying towers in a certain factory that often emit an acidic odor. After dismantling and inspection, it was found that the molecular sieve had turned black, and it was then realized that the molecular sieve had failed.

So how to determine if the molecular sieve is out of use? We can simply judge with our eyes:

*Color: First of all, the brand new molecular sieve is usually off white or off yellow. If the molecular sieve turns black, it needs to be stopped and replaced.

*Particle state: Molecular sieves are adsorbents that do not break when exposed to water, and good molecular sieves are hard and do not lose powder. If it shatters at a pinch, it means it has already powdered and needs to be replaced immediately.

*Odor: Molecular sieve is a non-toxic adsorbent with little odor. If there is an acidic or burnt smell, it needs to be shut down for inspection.

*Bed state: The normal state of molecular sieve loading is loose and uniform. If clumping or other phenomena are found, the tower needs to be dismantled and cleaned.

If it cannot be seen with our eyes, then it is necessary to check the operating data:

Testing index	Normal range	Failure critical value	Reason
Adsorption time	Design value±10%	Shorten over 30%	Adsorption capacity decreased
Regeneration temp.	200-300℃	>350℃ regeneration	Pore diameter blockage
Product purity	Over 99.5%	3 times <98%	Selective failure
Pressure variation	Within 10kPa	Increase 50% suddenly	Bed pulverization and clumping

 

If it is still difficult to judge, the following methods can be used for simple testing:

Method 1: Horizontal shaking method - testing water absorption capacity

 

1. Pour 30g of molecular sieve and 100ml of water into a mineral water bottle

2. Shake vigorously for 30 seconds and then let it rest

3. Observation phenomenon: Normally, the bottle wall heats up and the molecular sieve quickly sinks to the bottom; If the bottle wall is not hot and the suspended particles are>50%, it indicates that it has failed.

 

Method 2: Weighing method - detecting water absorption rate

1. Weigh 50g of molecular sieve (record weight W₁)

2. Put it in a bowl and soak it in water for 10 minutes

3. Remove and use a tissue to absorb surface water

4. Weigh W₂

 

If (W2-W1)/W1>20%, the molecular sieve can continue to be used; If it is less than 15%, it indicates that the molecular sieve has failed.

 

Let's list several different scenarios of molecular sieve failure characteristics:

 

Application scenario	Failure performance	Solution
Air dryer	Compressed air dew point > -40℃	Replace 3A molecular sieve
Oxygen generator	Oxygen concentration <90%	Replace 13X molecular sieve or LiLSX type
Refrigerant drying	Compressor abnormal	Replace molecular sieve 5A
Alcohol dehydration	Alcohol content >0.5%	Replace 3A molecular sieve