Technical article

Molecular sieve for air separation equipment

2025-08-17

If you are using air separation equipment such as oxygen concentrators and nitrogen generators, then molecular sieve is definitely not unfamiliar. It is one of the most core components in the air separation pre-processing system and is known as the "guardian angel" of air separation equipment. The quality of molecular sieves determines the purity of the final product gases (oxygen, nitrogen, etc.), the operational stability of equipment, and energy consumption directly.
The following article will introduce the commonly used types of molecular sieves in air separation equipment, their application scenarios, and ultimately provide practical customer feedback and guidance.
1、 What is molecular sieve? Why does the air separation equipment need it?
We can imagine it as an extremely small, uniformly sized 'sieve' with holes. Its working principle is to preferentially adsorb: Some molecules in the air (such as water vapor, carbon dioxide) with a diameter smaller than its pores will be "screened" and firmly grasped; If the molecular diameter of nitrogen and oxygen is larger, they can pass through smoothly.
The air contains impurities such as moisture, carbon dioxide, hydrocarbons, etc. If these impurities enter the low-temperature heat exchanger and distillation tower of the air separation unit, they will bring catastrophic consequences:
*Water vapor can freeze, block flow channels, significantly increase energy consumption, and even force production shutdowns.
*Carbon dioxide can dry ice and also cause blockage.
*The accumulation of hydrocarbons at low temperatures poses a risk of explosion.
Therefore, these impurities must be thoroughly removed before the air enters the cold box. This is the core task of the Molecular Sieve Purification System -- molecular sieve.
2、The two commonly used types of molecular sieves in air separation equipment
Although there are various types of molecular sieves, the two most commonly used ones in large and medium-sized air separation equipment are as follows:

1).Molecular sieve 13X APG
Characteristics: This is the most classic and widely used molecular sieve for air separation. Its pore diameter is about 10 angstroms, which can effectively adsorb water, carbon dioxide, and most larger hydrocarbon molecules (such as acetylene and propane).
Core advantages: Strong comprehensive adsorption capacity, especially high adsorption capacity for carbon dioxide, stable and reliable performance, mature technology.

Application location:
*The preprocessing system of the vast majority of conventional air separation equipment.
*In situations where there are strict requirements for removing carbon dioxide content from the air.
*It is the "standard configuration" and "main force" in the field of air separation.

2). Lithium type molecular sieves (such as LiX series)
*Characteristic: This is a modified and upgraded product. By replacing sodium ions (Na⁺) in traditional molecular sieve 13x with lithium ions (Li⁺), its crystal structure has been altered, resulting in extremely strong affinity and high adsorption capacity for water molecules.

*Super water absorption: The water absorption per unit weight of lithium based molecular sieve is 50% or even more higher than molecular sieve 13X APG.
*Energy saving and consumption reducing: A higher adsorption capacity means that when dealing with the same amount of air, the loading amount of molecular sieves can be reduced or the adsorption cycle can be extended, thereby reducing the consumption of regenerated gas (heating gas used for desorption) and directly reducing operating costs.
*Stronger acid resistance: When dealing with occasional acidic gases (such as SO₂, NOx) in the air, it exhibits greater stability and longer lifespan.

*Large and extra large air separation equipment: The energy-saving benefits are very significant.
*High humidity environment: In coastal areas with long rainy seasons, its super absorbent ability is fully demonstrated.
*Projects that are sensitive to energy consumption and operating costs.
*As a layer of protection, it is used in combination with activated alumina to form a composite bed and leverage their respective advantages.

3、Provide customers with selection and maintenance guidance and suggestions
Choosing the right molecular sieve and maintaining it scientifically is the key to ensuring the long-term stable, efficient and economical operation of air separation equipment.
1) How to choose? ——Either the most expensive or the best
*Assess your needs and environment:
*Equipment scale: For small and medium-sized air separation systems (such as<10000NM³/h), 13X-APG is still the good choice due to its high cost-effectiveness. For large and extra large air separators, priority should be given to calculating the energy-saving benefits brought by lithium based molecular sieves, as the saved electricity costs can usually be recovered within 1-2 years to cover additional procurement costs.
*Environmental conditions: If the air humidity is high or the air quality is poor (containing trace amounts of acidic gases) in the location of factory, the stability and long lifespan of lithium based molecular sieves are more advantageous.
*Operation mode: If the equipment needs frequent start stop or variable load operation, the thermal stability and fatigue resistance of the adsorbent are crucial, and high-quality brand adsorbent should be selected.
*Don't just look at the price, look at the "full lifecycle cost":
Molecular sieves are an investment, not a simple consumable. Cheap molecular sieves may have low initial procurement costs, but if they have low water absorption, are prone to pulverization, and have a short lifespan, they can lead to high energy consumption, frequent replacement, and significant production losses, resulting in even higher overall costs.

2) How to maintain? ——30% sorting, 70% usage and maintance
*Strictly follow the procedures: Molecular sieves should be avoid oil stains and liquid water. It is essential to ensure that the pre-filtration system (such as an efficient oil removal filter) is functioning properly, and to strictly prevent oil stains and large amounts of liquid water from entering the adsorption tower, otherwise it may cause permanent poisoning and failure of the molecular sieve.
*Pay attention to the regeneration temperature and gas volume: whether the regeneration is thorough is the key to determining the lifespan of the molecular sieve. Low regeneration temperature and insufficient gas volume can lead to incomplete desorption of moisture and carbon dioxide, gradually accumulating inside the molecular sieve (increasing residual load), ultimately resulting in excessive carbon dioxide content at the outlet, forcing you to replace it in advance.
*Avoid air flow impact: When starting, stopping, and switching equipment, operate smoothly to avoid severe pressure fluctuations that may cause impact on the molecular sieve bed and result in pulverization.
*Regularly monitor the dew point meter and carbon dioxide analyzer values at the outlet of the molecular sieve purification system, and be alert if a trend deterioration is detected.
*During the overhaul period, samples can be taken to test the compressive strength and pulverization rate of the molecular sieve, and its remaining life can be scientifically determined.

For air separation plant, molecular sieve 13X APG is a reliable and affordable "standard model", while lithium based molecular sieve is an efficient and energy-saving "upgraded model". Your choice should be based on a comprehensive consideration of equipment size, operating environment, energy consumption targets, and total cost.
No matter which type of adsorbents you choose, the combination of high-quality products, standardized operation, and careful maintenance is essential to maximize the performance of molecular sieves, safeguard the long-term, stable, and efficient operation of your air separation equipment, and create maximum value for you.

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Molecular sieve for air separation equipment

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