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Analysis of Knowledge Related to 4A Molecular Sieves

Release Date:

2023-04-10

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Molecular sieves are synthetically produced aluminosilicates with a microporous cubic crystal lattice. Depending on the size of the pores within their crystals, they adsorb or repel molecules of different substances, which is why they are called “molecular sieves.” Substances whose molecular diameters are smaller than the pore sizes of the molecular sieve can enter the crystal and be adsorbed; otherwise, they are excluded. The properties of molecular sieves are as follows:

1. Ion-exchange properties—water softening capability: In the framework of 4A molecular sieves, each oxygen atom is shared by two adjacent tetrahedra, creating large cavities that can accommodate cations and water molecules. These cations and water molecules exhibit high mobility, enabling ion exchange and reversible dehydration. The ion exchange in 4A molecular sieves occurs on a framework bearing aluminum ions; the negative charge associated with each aluminum ion can bind not only sodium ions but also other cations. Calcium and magnesium ions can enter the large cavities previously occupied by sodium ions, displacing the sodium ions within the 4A molecular sieve—thus, the sodium ions in the sieve are capable of undergoing ion exchange, interacting with Ca²⁺ and Mg²⁺ ions in hard water to achieve the purpose of water softening.

4A molecular sieve binds calcium and magnesium ions more slowly than sodium tripolyphosphate and exhibits weaker binding affinity for magnesium ions. However, 4A molecular sieve can readily and rapidly remove trace amounts of harmful heavy metal ions (such as Pb²⁺, Cd²⁺, and Hg²⁺) from aqueous solutions, making it highly significant for water purification.

2. Adsorption of surfactants—carrier‑liquid functionality: Due to the pore structure of 4A molecular sieve crystals and the large specific surface area of its particles, 4A molecular sieve exhibits strong adsorption performance.

Regarding the adsorption of nonionic surfactants, 4A molecular sieve exhibits an adsorption capacity three times that of NTA (nitrilotriacetate) and sodium carbonate, and five times that of sodium tripolyphosphate (STPP) and sodium sulfate. This property is highly advantageous for incorporating greater amounts of surfactant in agglomeration‑based production of high‑concentration laundry detergents, enabling the formulation of products with excellent washing performance and flowability. Experimental results show that 4A molecular sieve can hold at least 30% liquid; when added during detergent powder manufacturing, it enhances material flowability, adjusts viscosity, and yields products with superior appearance, improved flow characteristics, and enhanced resistance to caking.

3. Detergency: Experiments comparing the detergency of formulations containing the same base ingredients but varying amounts of auxiliary agents revealed that a blend of 20% STPP, 20% molecular sieve, and 4% polymer delivers detergent performance comparable to that of a formulation with 40% STPP. In phosphate‑free formulations, incorporating 10% sodium carbonate and 4–5% polymer into a 20% molecular sieve system yields a product with exceptionally strong detergency.

4. Anti‑re‑deposition performance: 4A molecular sieve exhibits strong affinity for oil stains; when zeolite is added to auxiliaries such as sodium carbonate, CMC, sodium silicate, and sodium sulfate, the adsorption of oil stains onto nylon fabrics is significantly reduced. When the particle size of the zeolite ranges from 0.4 to 1.0 μm, its dispersibility is excellent, effectively preventing it from adhering to the fabric.

Although the dispersing ability of 4A molecular sieve is inferior to that of STPP, its poor dirt‑dispersing performance can be overcome by compounding it with sodium polyacrylate.

5. Compatibility with Other Additives: When appropriately combined with other additives, 4A molecular sieve can achieve complementary performance. Although its dispersing ability for soil and its chelating capacity for hardness ions are inferior to those of STPP, blending 4A molecular sieve with STPP can yield a detergency comparable to that achieved by using STPP alone. This is because STPP rapidly complexes calcium and magnesium ions from solid surfaces and transfers them to the 4A molecular sieve via the aqueous medium. Since 4A molecular sieve has limited affinity for magnesium ions, this deficiency can be offset by formulating it with silicates and carbonates.

6. pH‑buffering effect: 4A molecular sieves are alkaline, with a pH of approximately 11.0 in a 1% aqueous solution, thereby exhibiting a certain buffering capacity.

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Analysis of Knowledge Related to 4A Molecular Sieves

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