Knowledge of the structure and characteristics of zeolite molecular sieves collection

Molecular sieve is a silicate or a crystalline aluminosilicate, and formed of silicon oxide or aluminum oxide tetrahedra linked by oxygen bridges tetrahedron. Molecular size (typically 0.3 ~ 2.0 nm) of the pore and cavity system, so as to have characteristics of solid molecules. However, with the synthesis and application of molecular sieve-depth study, researchers found that the aluminophosphate molecular sieves and sieve skeleton elements (silicon or aluminum or phosphorus) may be composed of B, Ga, Fe, Cr, Ge, Ti, V , Mn, Co, Zn, Be and Cu, substituted, its pore size and the cavity may reach 2 nm or more, the zeolite framework elements can be divided according to type aluminosilicate zeolite, aluminophosphate molecular sieves and molecular sieve framework heteroatoms ; divided by pore size, pore size of less than 2 nm, 2 ~ 50 nm and the molecular sieve is larger than 50 nm are referred to as micropores, mesopores and large pore molecular sieves. Because of the larger aperture size becomes larger carrier molecules react well, but the pore walls of mesoporous materials are amorphous, resulting in the hydrothermal stability and thermal stability still can not meet the required conditions for petrochemical applications demanding .
molecular sieve molsiv sieves contain a lower price due to the larger ionic radius and water, the #water #molecules are continuously lost after heating and combined state of the metal ion, but the same crystal framework structure, the formation of many of the same size of the cavity, the cavity there are many the same diameter of pores connected to these tiny hole diameter uniform pores smaller than molecules can adsorb to the internal diameter of the cavity in the past, but larger than the pores of the molecular exclusion, which can diameter molecules of different shapes Different degrees of polar molecules, the boiling point of different molecules, different degrees of saturation molecules separated, that has the effect of "screening" elements, so called molecular sieves. Currently zeolite 5a widely used in the metallurgical, chemical, electronics, petrochemical and natural gas industries.

There are two kinds of synthetic zeolite molecular sieve zeolite and natural. Most ① natural zeolite formed by volcanic tuffs occur and tuffaceous sedimentary rocks in marine or lacustrine environment reaction. Has been found to have more than 1000 kinds of zeolite mineral, the more important ones are 35 kinds, often with clinoptilolite, mordenite, erionite and chabazite, etc. Mainly in the United States, Japan, France and other countries, China also found that a large number of mordenite and clinoptilolite deposits, Japan is the most natural zeolite molecular sieves mined large country. ② due to natural zeolite subject to resource constraints, from the beginning of the 1950s, a large number of synthetic zeolites (see Table).

Goods zeolite crystal structure common prefixes Digital classify the different molecular sieves, such as type 3A, 4A type, 5A zeolite. 4A Class A type that table, aperture 4 & Aring ;. A type containing Na + sieve recorded as Na-A, if one Na + is K + replacement, pore size of about 3 & Aring ;, is the 3A molecular sieve; as Na-A has more than 1/3 of Na + was Ca2 + exchange, aperture is about 5 & ​​Aring ;, is the 5A molecular sieve.