The difference between zeolite and molecular sieve in concept and characteristics

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In 1932, McBain put forward the concept of "molecular sieve". Represents a porous material that can sieve substances at the molecular level. Zeolite is only one kind of molecular sieve. Because zeolite is representative in molecular sieve, the words "zeolite" and "molecular sieve" are easily confused by beginners.

The artificial zeolite is: sulfonated polystyrene;

Natural zeolite: sodium aluminosilicate.

Zeolite group minerals are commonly found in the pores of extrusive rocks, especially basalt, sedimentary rocks, metamorphic rocks, hydrothermal deposits and some modern hot spring deposits. SDIC Shengshi has two high-grade zeolite mining rights, with an annual approved mining volume of 1.1 million tons and an expandable reserves of 1.5 billion tons. The reserves of high-grade zeolite account for more than 70% of the country.

Molecular sieve is a crystalline silicate or aluminosilicate, which is a pore and cavity system with molecular size (usually 0.3nm to 2.0nm) formed by connecting silicon oxygen tetrahedron or aluminum oxide tetrahedron through oxygen bridge bond, so it has the characteristics of screening molecules.

However, with the deepening of molecular sieve synthesis and application research, researchers have found phosphoaluminate molecular sieves, and the skeleton elements of molecular sieves (silicon or aluminum or phosphorus) can also be replaced by B, Ga, Fe, Cr, Ge, Ti, V, Mn, Co, Zn, Be and Cu, and the size of their pores and cavities can also reach more than 2 nm. Therefore, molecular sieves can be divided into silicon aluminum molecular sieves Phosphorus aluminum molecular sieves and framework heteroatom molecular sieves;

According to the pore size, molecular sieves with pore size less than 2 nm, 2-50 nm and more than 50 nm are called microporous, mesoporous and macroporous molecular sieves respectively.

Due to its large pore size, mesoporous materials have become a good carrier for molecular reaction with large size. However, the pore wall of mesoporous materials is amorphous, so their hydrothermal stability and thermal stability cannot meet the harsh conditions required for petrochemical applications.

Because there are metal ions with low electricity price and large ion radius and water in the combined state, water molecules are continuously lost after heating, but the crystal skeleton structure remains unchanged, forming many cavities with the same size. The cavities are connected by many micropores with the same diameter. These tiny holes have uniform diameters, which can adsorb molecules smaller than the diameter of the hole into the interior of the hole, Molecules larger than pores are excluded, so they can separate molecules with different shapes and diameters, different polar degrees, different boiling points, and different saturation degrees, that is, they have the function of "screening" molecules, so they are called molecular sieves.

At present, molecular sieves are widely used in metallurgy, chemical industry, electronics, petrochemical industry, natural gas and other industries.

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