Types and Applications of Molecular Sieves

In the global chemical, energy, environmental and other industrial fields, molecular sieves play an important role as a high-performance adsorbent material. Whether used for deep drying of gases, efficient separation of mixtures, or as a key catalyst, the unique properties of molecular sieves make them the "smart core" of modern industry. We will start from the basic principles of molecular sieves, comprehensively analyze their types, application scenarios, and key selection dimensions, and help you make wise purchasing decisions.

One: What is molecular sieve? What is its working principle?

Molecular sieve is a porous material with a uniform microporous structure, and its pore size is comparable to that of ordinary molecules. Its chemical composition is mainly crystalline aluminosilicates (zeolites) or aluminum phosphates.

 

Core working principle: adsorption and screening

1. Selective adsorption: The inner surface of molecular sieves has extremely strong polarity, which can preferentially adsorb polar molecules (such as water, ammonia, hydrogen sulfide, etc.) and unsaturated molecules. In contrast, non-polar molecules have weaker adsorption capacity.

2. Molecular sieving effect: Due to its precise and uniform pore size, only molecules with a diameter smaller than the pore can enter the interior and be adsorbed, while molecules with larger diameters are "sieved" outside, achieving molecular level separation. This is precisely the origin of the name 'molecular sieve'.

 

Two:  Main types and characteristics of molecular sieves

There are many types of molecular sieves, and the most common classification method is based on their pore size and silicon aluminum ratio.

1. Classify by aperture size

* Molecular sieve 3A: pore size of approximately 3Å. Main characteristics: It only adsorbs water molecules and does not adsorb any molecules with a diameter greater than 3 Å (such as ethylene and carbon dioxide). Typical application: Deep drying of chemical products such as petroleum cracking gas and olefins; Dehydration of liquids such as ethanol.

* Molecular sieve 4A : pore size approximately 4Å. Main characteristics: Adsorption of small molecules such as water, carbon dioxide, and sulfur dioxide. Typical applications: deep drying and purification of gases and liquids; Adsorption of moisture and carbon dioxide in the air separation unit; Detergent additives (soften water by adsorbing calcium and magnesium ions).

* Molecular sieve 5A: pore size approximately 5Å. Main characteristics: Able to adsorb molecules with a diameter less than 5 Å, such as n-alkanes (C4-C6). Typical applications: Separation of n-alkanes/isoparaffins in petroleum refining; Pressure swing adsorption (PSA) for oxygen/nitrogen production.

* Molecular sieve 13X: pore size approximately 10Å. Main characteristics: Strong adsorption capacity, capable of adsorbing molecules with a diameter less than 10 Å, including most gas molecules and water. Typical applications: Deep desulfurization of aviation kerosene and liquefied petroleum gas (LPG); Front end purification of air separation unit; Household oxygen concentrator.

2. Classified by chemical composition

*Zeolite molecular sieve: The traditional and most widely used molecular sieve, with aluminosilicate as the skeleton. Including the above-mentioned A type, X type, Y type, etc.

*Aluminum phosphate series molecular sieve: A new type of molecular sieve, whose skeleton is composed of AlO₂ and PO₂, has a richer structure and adjustable acidity, and has broad application prospects in the field of catalysis.

 

Three: The wide application fields of molecular sieves

The application of molecular sieves has almost penetrated into all industrial fields, and the following are several key areas:

1). Petrochemical and Refining

* Hydrorefining: Used to remove impurities such as sulfur and nitrogen from oil products, meeting environmental requirements.

* Olefin separation: 5A molecular sieve can be used to separate high-purity 1-butene and isobutene from mixed C4.

2). Gas separation and purification

*Pressure swing adsorption: using 5A or 13X molecular sieves to separate nitrogen and oxygen from air through pressure changes.

*Natural gas purification: removing water (dehydration), carbon dioxide, and hydrogen sulfide from natural gas, preventing pipeline corrosion, and increasing calorific value.

*Purification before cryogenic air separation: Before the air enters the cryogenic separation tower, 13X molecular sieve is used to adsorb moisture and carbon dioxide to prevent equipment freezing.

3). Refrigeration and air drying

*Refrigerant drying: In air conditioning and refrigeration systems, molecular sieves are used to adsorb trace amounts of moisture in refrigerants (such as R134a) to prevent system icing and corrosion.

*Compressed air drying: Ensure that the compressed air reaches the required dew point to protect pneumatic tools and equipment.

 

Four: Key dimensions for selecting molecular sieves

As a purchaser, it is crucial to choose the appropriate molecular sieve. The following are the core considerations that we have compiled for you:

1). Target isolate: Identify what molecules you need to adsorb or separate (such as water, carbon dioxide, hydrogen sulfide, n-alkanes). Based on the polarity and dynamic diameter of the molecules, select the corresponding pore size and polarity of the molecular sieve type (such as 3A for dehydration and 5A for separating n-alkanes).

2). Working conditions:

* Temperature: Molecular sieves with high thermal stability should be selected in high-temperature environments.

* Pressure: Determine whether it is atmospheric pressure adsorption or pressure swing adsorption (PSA)/temperature swing adsorption (TSA) process.

3). Regeneration performance: Molecular sieves can be regenerated by heating or depressurization. Evaluating the number of regenerations (lifespan), regeneration energy consumption, and adsorption capacity retention after regeneration directly affects long-term usage costs.

4). Competitive adsorption: If there are multiple molecules that can be adsorbed in the system, the competitive relationship between them needs to be considered. Sometimes it is necessary to preprocess or select molecular sieves with higher selectivity for target molecules.

5). Physical specifications: including particle shape (spherical, bar shaped), size, and mechanical strength. This is related to the convenience of loading, bed pressure drop, and resistance to wear and crushing.

6). Professionalism and service of suppliers: Choosing a supplier with strong technical strength and the ability to provide comprehensive technical support and after-sales service is crucial. They should be able to assist you with process analysis, product selection, and fault diagnosis.

 

As your reliable international trade partner, we not only provide a full range of high-quality molecular sieve products (including 3A, 4A, 5A, 13X, etc.), but also have an experienced technical team that can provide personalized product selection suggestions and solutions based on your specific working conditions and needs. We are committed to becoming a trusted partner in your supply chain.