Molecular sieve is a kind of siovenate compound with cubic lattice. The molecular sieve has a uniform microporous structure, and its hole diameter is even. These holes can adsorb molecules smaller than their diameter into the inner pore cavity, and it has the priority adsorption capacity for polar molecules and unsaturated molecules, so it can separate molecules with different polarity degree, saturation degree, molecular size and boiling point, it has the function of "screening" molecules, so it is called molecular sieve. Molecular sieve is widely used because it has advantages such as high adsorption capacity, strong thermal stability and so on which other adsorbents do not have.
American scientists have found that by adjusting the temperature, the hole size of a kind of titanium Portland material can be precisely controlled to produce a precise new molecular sieve. There are a large number of uniform micropores inside some crystal materials. Molecules smaller than the holes can pass through, while macromolecules cannot pass through, so they can separate different molecules. This kind of material is called molecular sieve.
In fact, in 2001, scientists reported in the British magazine nature that they found that a substance called Ti-Portland ETS-4 could be used as a good molecular sieve. When the temperature rises, the ETS-4 will be dehydrated gradually, and the size of micropores will decrease accordingly. By using this method, the microporous size can be finely adjusted within the range of 3 to 4 Egyptian (1 Egyptian equals one billion meters. Scientists said that the sizes of some common molecules such as nitrogen, methane, oxygen, argon and water molecules were about 3 to 4 Egyptian, and the sizes of them were almost the same, molecular sieves made of ETS-4 can effectively separate them. Researchers have tried to use ETS-4 to reduce the nitrogen content from 18% to below 5% from the mixture of nitrogen and methane, and have also achieved success in the experiment of separating argon and oxygen, nitrogen and oxygen. It is believed that this technology will have an important commercial application prospect. Adsorption function: the adsorption of molecular sieve on substance is derived from physical adsorption (Van der Huali), and there are strong polarity and coulometric field inside the crystal hole, for polar molecules (such as water) and unsaturated molecules show strong adsorption capacity.
Screening function: the aperture distribution of the molecular sieve is very uniform, and only the substance whose molecular diameter is smaller than that of the hole can enter into the hole of the molecular sieve. It is called "molecular sieve" vividly by distinguishing molecules of different substances through the priority and size of adsorption ".
There are two kinds of molecular sieve: Natural zeolite and synthetic zeolite. ① Most of the natural zeolites are formed by the reaction of volcanic tuff and cinerite sedimentary rocks in the sea or lake environment. At present, more than 1000 kinds of causite ores have been found, among which 35 kinds are more important, among which the common kinds are inclined zeolite, mercerized zeolite, mottite and leek zeolite, etc. It is mainly distributed in America, Japan, France and other countries. China has also found a large number of mercerized zeolites and oblique-hair felites. Japan is the country with the largest exploitation amount of natural zeolites. ② Due to the resource restriction of natural zeolites, a large number of synthetic zeolites have been adopted since 1950s.
Commercial molecular sieves usually use prefix digital to classify molecular sieves with different crystal structures, such as 3A type, 4A type and 5A type molecular sieves. Type 4A, that is, type A in the table, aperture 4 & Aring ;. The type A molecular sieve containing Na + is recorded as Na-A. If Na + is replaced by K +, its aperture is about 3 & Aring; that is 3A type molecular sieve; for example, more than 1/3 of Na + in Na-A is replaced by cod +, and the aperture is about 5 & Aring;, namely 5A type molecular sieve.
Molecular Sieve Performance: The molecular sieve is powder crystal, with metallic luster and hardness of 3 ~ 5, the relative density is 2 ~ 2.8. Natural zeolites have colors, and synthetic zeolites are white, soluble in water. The thermal stability and acid resistance increase with the increase of the ratio of SIO/al-003. Molecular sieve has a large specific surface area, up to 300 ~ 1000 m 2/g, the surface of the inner crystal is highly polarization, it is a kind of high-efficiency absorbents, also a kind of solid acid, the surface has very high acid concentration and acid strength, can cause positive carbon ion type catalytic reaction. When the metal ions in the composition exchange with other ions in the solution, the aperture can be adjusted to change its adsorption property and catalytic property, so as to produce molecular sieve catalyst with different properties.
Other functions: the protein polysaccharide polymer formed from this is winding and forming a microporous sieve structure, which is called molecular sieve. Molecular sieve is only allowed to be smaller than its Micro. The passage of materials in the molecular sieve pores has a barrier effect on the macromolecule materials and bacteria which are larger than their micropores. Make the matrix become the defense barrier to restrict the diffusion of harmful substances such as bacteria. Hemonali and cancer cells can produce hyaluronic acid enzyme, decompose protein polysaccharide, destroy matrix structure and spread. Protein polysaccharide polymer also binds many hydrophilic groups, which can combine a large number of water molecules to form the extracellular "reservoir ".
The application of 13xAPG molecular sieve ended the era of deep cold separation of switching plates. There are also molecular sieve adsorbents for absorbing oxygen and nitrogen, which are directly used for pressure-changing adsorption on oxygen production and nitrogen production. Now 13xAPG molecular sieve has developed the third generation of products, and the adsorption capacity of water and carbon dioxide has doubled, and the energy needed for deadsorption has also been reduced, which is gradually recognized by everyone. It will be popularized soon.
