The Origin Of The Names Of Zeolites And Molecular Sieves
In 1756, the Swedish mineralogist Cronstedt discovered that when a type of natural aluminosilicate ore is burned, the water inside the crystal is driven out, resulting in a phenomenon similar to bubbling and boiling, which is vividly called “boiling stone”. , referred to as “zeolite” (zeolite).
In 1932, McBain proposed the concept of “molecular sieves”, which refers to porous materials that can sieve substances in terms of molecular size. Molecular sieves have uniform internal micropores, and their pore sizes are comparable to the size of ordinary molecules. Substances whose molecular diameter is smaller than the pore diameter of the molecular sieve crystal can enter the molecular sieve crystal and be adsorbed, otherwise they will be rejected, achieving the purpose of sieving molecules. Molecular sieves can determine the order of preferential adsorption based on the polarity of molecules of different substances. According to its effective pore size, it can be used to sieve fluid molecules of different sizes. This effect is called molecular sieve effect. Although zeolite is only a type of molecular sieve, zeolite is the most representative of molecular sieves, so the terms “zeolite” and “molecular sieve” are often used interchangeably. In order to accurately express the molecular sieve category, the name of the substance should be added in front of the molecular sieve, such as zeolite molecular sieve, carbon molecular sieve, etc.
Structure And Properties Of Type A Zeolite Molecular Sieve
Type A zeolite has a tetragonal structure similar to sodium chloride, its chemical formula is Na2O·Al2O3·2SiO2·4.5H2O, and its internal pore diameter is 4.2 Angstroms, so it is referred to as 4A zeolite. When more than 60% of the sodium ions in 4A zeolite molecular sieve are replaced by potassium ions, it is called 3A zeolite molecular sieve; when more than 70% of the sodium ions in 4A zeolite molecular sieve are replaced by calcium ions, it is called 5A zeolite molecular sieve. Therefore, 4A molecular sieve is the basic raw material for preparing 3A and 5A molecular sieve.
Since Type A zeolite has a tetragonal structure similar to sodium chloride, it has many special properties such as ion exchange properties. Each oxygen atom in the 4A zeolite skeleton is shared by two adjacent tetrahedrons. This structure can Internal pores that accommodate substances such as cations and water molecules, and these cations and water molecules have greater mobility, allowing for cation exchange and reversible dehydration. The ion exchange of 4A zeolite is carried out on the framework with aluminum ions. Each aluminum ion carries a negative charge, which can not only combine with sodium ions, but also with other cations. For example, calcium and magnesium ions can enter the large crystal holes originally occupied by sodium ions and replace the sodium ions in 4A zeolite. That is, the sodium ions in 4A zeolite can perform ion exchange and exchange with Ca2+ and Mg2+ ions in hard water. Thereby achieving the purpose of softening water quality.
Although 4A zeolite binds calcium and magnesium ions slower than sodium tripolyphosphate (STPP), and its binding ability to magnesium ions is weaker, 4A zeolite can easily remove a small amount of harmful heavy metal ions such as Pb2+, Cd2+, Hg2+, etc. in the aqueous solution. The rapid removal is of great significance to purifying water quality.
Through experiments, the same formula containing different additives was changed to compare its decontamination ability. It was found that 20% STPP, 20% 4A zeolite, and 4% polymer had the same decontamination effect as 40% STPP. In the formula, 10% sodium carbonate and 4.5% polymer are added to 20% 4A zeolite to obtain a product with ideal decontamination ability.
The liquid carrier function of 4A zeolite, due to the hole structure of 4A zeolite crystals and the large specific surface area of the particles, 4A zeolite has strong adsorption performance. In terms of adsorption performance for nonionic surfactants, 4A zeolite is three times that of nitrilotriacetate (NTA) and sodium carbonate, and five times that of sodium tripolyphosphate (STPP) and sodium sulfate. This property is generally used in To produce highly concentrated laundry detergent, more surfactants can be added to greatly improve the washing performance and fluidity of detergents. Experiments have shown that when the liquid carrying capacity of 4A zeolite is ≥30%, adding 4A zeolite during the production process of laundry detergent can produce a detergent product with good appearance, fluidity and anti-caking properties.
4A zeolite also has good resistance to redeposition. 4A zeolite has good oil adhesion. After adding 4A zeolite to additives such as sodium carbonate, sodium carboxymethyl cellulose (CMC), sodium silicate and sodium sulfate, It can significantly reduce the adsorption of oil stains by nylon cloth. When the particle size of zeolite is 0.4-1.0 μm, its dispersion is relatively good and can effectively prevent adhesion on fabrics. Although the dispersing ability of 4A zeolite is not as good as that of STPP, its dispersion problem of dirt can be solved by compounding with sodium polyacrylate.
Applications Of 4A Zeolite
4A zeolite is one of the most widely used zeolite varieties in industry and has a wide range of applications. Different industries have different quality requirements for 4A zeolite.
Its main uses are:
(1) Used as a washing aid. The function of 4A zeolite as a detergent additive is mainly to exchange calcium and magnesium ions in the water to soften the water and prevent the redeposition of dirt. At present, 4A zeolite is the most widely used and mature product in replacing phosphorus-containing additives. 4A
Zeolite replaces sodium tripolyphosphate as a washing aid, which is of great significance to solving environmental pollution.
(2) 4A zeolite can also be used as a forming agent for soap.
(3) 4A zeolite can also be used as a friction agent in toothpaste.
Currently, the largest amount of 4A zeolite is used in laundry detergents. As 4A zeolite for washing, it is mainly required to have high calcium exchange capacity and fast exchange rate.
Environmental protection industry
(1) Used for sewage treatment. 4A zeolite can remove NH3-N, Pb2+, Cu2+, Zn2+ and Cd2+ in sewage. The sewage discharged from industry, agriculture, civil use and aquatic animal husbandry contains ammonia nitrogen, which not only harms the survival of fish and pollutes the breeding environment, but also promotes the growth of algae and causes the blockage of rivers and lakes. Because 4A zeolite has high selectivity for NH4+, it has been successfully used in this field. Wastewater discharged from metal mines, smelters, metal surface treatment and chemical industries contains heavy metal ions that are extremely harmful to the human body. Using 4A zeolite to treat this sewage not only ensures that the water quality is up to standard, but also heavy metals can be recovered.
As 4A zeolite for sewage treatment, it is necessary to remove harmful ions in sewage as much as possible, so a product with a relatively high crystallinity is required.
(2) Improve drinking water quality. Utilizing the ion exchange performance and adsorption performance of zeolite, the circulation system is used to liquefy seawater, soften hard water, and selectively remove or reduce elements, bacteria, viruses, etc. that are harmful to the human body in certain drinking water sources.
(3) Harmful gas treatment. Applications in this area include industrial gas purification, industrial and domestic waste gas environmental treatment.
The plastic processing industry, especially polyvinyl chloride (PVC for short), uses calcium/zinc heat stabilizers to absorb free hydrogen chloride during PVC processing and prevent PVC degradation (i.e. aging). 4A zeolite is not only alkaline, but also has a porous internal structure, so it can neutralize and adsorb free hydrogen chloride in PVC, and can prevent PVC from aging. When 4A zeolite is used with a calcium/zinc heat stabilizer, 4A zeolite not only acts as a heat stabilizer, but also reduces the cost of the calcium/zinc heat stabilizer.
4A zeolite is used as a heat stabilizing additive for PVC, which is environmentally friendly and economical. At present, the application of 4A zeolite in PVC is in its infancy, and it is expected that there will be huge demand in the near future. my country is a major country in the production and processing of PVC. The output of PVC ranks first in the world, and it will still grow at an annual rate of 5-8% in the future. Therefore, the application prospects of 4A zeolite in PVC are broad.
When using 4A zeolite as a heat stabilizing additive for PVC, there are strict restrictions on foreign matter such as black spots, generally no more than 10 pieces/25g. Because black spots are generally hydrophilic and incompatible with high-molecular organic compounds (hydrophobic) such as PVC, they will cause defects in processed products and affect the strength and appearance of the products.
4A molecular sieve is mainly used as adsorbent, desiccant and catalyst in the petrochemical industry.
(1) As an adsorbent. 4A molecular sieve is mainly used for the adsorption of substances with a molecular diameter smaller than 4A, such as water, methanol, ethanol, hydrogen sulfide, sulfur dioxide, carbon dioxide, ethylene, and propylene. Its selective adsorption performance for water is higher than that of any other molecules.
(2) As a desiccant. 4A molecular sieve is mainly used for drying natural gas and various chemical gases and liquids, refrigerants, pharmaceuticals, electronic materials and volatile substances.
(3) As a catalyst. 4A molecular sieve is rarely used as a catalyst. In the field of catalysis, X-type zeolite, Y-type zeolite and ZK-5 zeolite molecular sieves are mainly used.
The petrochemical industry basically requires zeolites of the 4A molecular sieve type, and therefore requires a higher degree of crystallinity.
(1) Used as soil conditioner. The cation exchange performance and adsorption performance of zeolite are directly used as a soil conditioner to improve the supply of beneficial trace elements required by crops, reduce soil acidity, and increase the salt exchange capacity of the soil.
(2) Used as long-acting fertilizer and fertilizer slow-release agent. For example, combining zeolite with dihydroamine, hydrogen phenol, rare earth elements and other trace elements can be used to formulate a long-term fertilizer synergist, which can not only greatly extend the effectiveness of nitrogen fertilizers, improve nitrogen utilization efficiency, but also significantly improve the efficiency of nitrogen fertilizers. Improve the nutritional status of crops, promote crop growth and development, improve anti-virus capabilities, and increase crop yields.
(3) Used as feed additive. Utilizing the adsorption performance and cation exchange performance of zeolite and using zeolite as a carrier to manufacture feed additives can enhance the antiviral ability of farmed animals, promote protein synthesis, accelerate weight gain, and improve feed utilization.
(4) Used as a preservative for freshness. The adsorption and exchange properties of zeolite can be used to prevent and control crop diseases and insect pests, and improve the freshness and antisepsis capabilities of vegetables, fruits and other agricultural products as well as aquatic products.
In the metallurgical industry, it is mainly used as a separating agent to separate and extract potassium, rubidium, cesium, etc. in brine and is used in processes such as enrichment, separation and extraction of metals; it can also be used for the refining and purification of certain gases or liquids, such as argon. Preparation, separation of methane, ethane and propane.
(1)Pharmaceutical industry. The adsorption and easy dispersibility of zeolite are used to adsorb the active ingredients of the drug on the zeolite. Made into medicine for internal or external use. Because of the sustained-release effect of zeolite on the active ingredients of drugs, it can effectively improve the efficacy and extend its action time, and at the same time, kill or inhibit bacteria and viruses by loading them. It can effectively kill pathogenic bacteria and viruses without any other toxic side effects.
(2) Inorganic fungicide products. The reproduction and spread of microorganisms, bacteria, and viruses in air conditioners, refrigerators, and home environments have seriously affected people’s health. Utilize the ion exchange performance of zeolite to load suitable heavy metal ions. Can become a highly active and durable inorganic fungicide. Bactericidal and antibacterial materials or other bactericidal (deodorizing) material products such as coatings, plastics, rubber, chemical fiber textiles, etc. can be developed as fillers. These sterilization materials and their products are safe and reliable to use and have no toxic or side effects.
Using zeolite as filler in the paper industry can improve the performance and quality of paper, increase its porosity, enhance water absorption, make it easier to cut, improve writing performance, and have certain fire resistance.
Zeolite, as a filler and prime pigment in paints, can give paints properties such as antibacterial, abrasion resistance, corrosion resistance, heat resistance and climate change resistance
Pengfeng’s products include 4A zeolite for detergents, 4A molecular sieve (original powder) and PVC heat stabilizing additives. The production of Pengfeng Company’s 4A zeolite is grafted on the sintering process, so its products have the advantages of high whiteness, few black spots and low heavy metals.