Molecular sieves are a type of insoluble aluminosilicate with uniform pore size. Traditional molecular sieves are zeolite-type aluminosilicates with a microporous structure (pore size <2nm), but with the development of molecular sieve science, new types of molecular sieves and porous compounds such as phosphoaluminate and phosphoaluminosilicate have been developed. By 2003, there were 145 kinds of molecular sieves with unique framework structures, and more than 30 kinds of framework elements composed of micropores.
Molecular sieves have uniform micropores equivalent to the molecular size of general substances, an open framework structure, the pore volume accounts for 30%-50% of the total volume, a large specific surface area (300~1000m2/g) and a small outer surface (about 1% of the total surface area) and high thermal stability.
The synthetic molecular sieve is white crystalline powder. When natural minerals are used as raw materials or impurities are mixed in the synthesis process, the product sometimes has a slight color. Its particle size ranges from 1 to 10 μm and the average particle size is 1 to 5 μm. It is insoluble in water and organic Solvent, generally soluble in strong acid. In order to meet the needs of industrial applications, the raw molecular sieve powder is usually bonded with a binder such as clay and made into a certain shape. The common ones are: granular, strip, block, honeycomb, etc. The basic properties of molecular sieves are mainly reflected in: ion exchange, adsorption performance and catalytic performance.