Molding Methods of Molecular Sieves
A brief introduction to molecular sieve forming method.
Molding Methods of Molecular Sieves
As an inorganic crystalline material with a regular microporous structure, molecular sieves must be presented in shaped particles for industrial applications. Spherical and strip shapes are currently the two most common molding methods, but they differ fundamentally in process path, physical properties, and applicable scenarios. The following discussion systematically addresses these differences from three dimensions: molding process, performance characteristics, and typical applications.
Differences in Molding Processes
Spherical Molecular Sieves
Spray Drying: Slurry (solid content 40-50%) is atomized and instantaneously dried to form spheres. Used for 20-120μm microspheres, suitable for fluidized bed processes.
Oil Column/Rolling Ball Molding: Paste is dripped into the oil phase to form spheres, or rolled on a rotating disc to form spheres. Used for 0.5-5mm large spheres, suitable for fixed beds.
Strip Molecular Sieves
Extrusion Molding: Raw powder is mixed with binder and additives to form a paste, which is then vacuum-kneaded, extruded, cut, dried, and calcined.
Diameter can be precisely controlled, commonly 1.0, 1.5, 1.8, and 3.0mm, with an aspect ratio of 2:1 to 4:1.
Performance Characteristics Comparison
Performance Dimensions | Spherical Molecular Sieves | Strip Molecular Sieves |
Bulk Density | Low, 0.55-0.65 g/cm³ | High, 0.65-0.75 g/cm³ |
Mechanical Strength | Compressive strength ≥20 N/particle | Axial compressive strength ≥30 N/particle, radial compressive strength ≥15 N/particle |
Abrasion Rate | High, especially in fluidized bed conditions | Extremely low, ≤0.3% |
Specific Surface Area | High retention rate | Binder may clog some channels |
Bed Pressure Drop | Low, porosity approximately 0.38-0.42 | High, porosity approximately 0.32-0.36 |
Mass Transfer Efficiency | Isotropic, short diffusion path | Axial/radial differences exist |
Filling Uniformity | Self-leveling, easy to fill | Requires directional arrangement or vibration compaction |
Anti-clogging Ability | Relatively weak | Relatively strong, especially for large diameter strips |
Typical Applications
Spherical Molecular Sieves – Typical Applications
Fluidization Processes
Catalytic Cracking (FCC): Microspheres with a diameter of 60-100μm, requiring high sphericity, good flowability, and wear resistance. Ensures uniform fluidization and reduces channeling.
Moving Bed Adsorption: 0.5-1.0mm diameter, used for para-xylene separation. Smooth flow, no clogging.
Pressure Swing Adsorption (PSA) for Oxygen/Hydrogen Production
5A, 13X spherical shape, diameter 1.6-2.5mm. Low pressure drop, allowing for higher switching frequency, shorter cycle times, and improved gas production efficiency.
Small Adsorption Units
Household air purification, refrigerator deodorization, medical oxygen generators. Good flowability, easy filling, and neat appearance.
Strip Molecular Sieves – Typical Applications
Fixed Bed Deep Drying and Purification
Natural Gas Dehydration: 4A strip shape, diameter 1.8-3.0mm. High bulk density, large loading capacity, long adsorption cycle, suitable for high-flow-rate continuous operation.
Deep drying of pyrolysis gas: 3A strip shape, diameter 1.5-1.8mm. Requires extremely low dew point, no short-circuiting or channeling in the bed, and stable mass transfer.
Industrial VOCs adsorption and concentration
Hydrophobic molecular sieve rotor: Honeycomb structure, strip extrusion molding. Low pressure drop, large air volume handling capacity.
High mechanical strength requirements
Air separation purification system: 13X strip shape, diameter 1.6-3.0mm. Resistant to airflow impact and pressure fluctuations, with significant strength advantages.
Nuclear waste liquid treatment: Radiation resistant and heat stress resistant.
Selection Principles
Selection by Process Type:
Fluidized bed, moving bed, PSA rapid circulation: Spherical preferred.
Fixed bed, deep purification, high-flow continuous operation: Strip preferred.
Selection by Strength Requirements:
For systems with airflow impact, pressure drop fluctuations, and frequent regeneration: Strip is more advantageous.
Selection by Pressure Drop Requirements:
For energy-sensitive systems requiring low pressure drop: Spherical is superior.
Selection by Packing Space:
For systems aiming for maximum packing volume within a limited volume: Strip has higher packing density.
Selection by Mass Transfer Requirements:
For systems sensitive to diffusion rates: Microspheres or small-diameter strips can be equivalent substitutes.
Summary
Spherical and strip shapes are not a matter of superiority or inferiority, but rather a difference in function. Spherical shapes, with their low pressure drop, good flow, and fast mass transfer, dominate fluidized bed and rapid circulation scenarios; strip shapes, with their high strength, high density, and long lifespan, dominate fixed bed and deep purification scenarios. The essence of selection is a rational matching of process requirements with the physical properties of particle morphology, with the ultimate goal of achieving a balance between adsorption efficiency and operational economy. We are a Chinese industrial ceramics manufacturer. For more information, please contact us via email at annayu@169chem.net or WhatsApp at +8618909016373.