The difference between zeolite and molecular sieve

Molecular sieve is powder crystal with metallic luster, hardness of 3 ~ 5 and relative density of 2 ~ 2.8. Natural zeolite has color, synthetic zeolite is white and insoluble in water. Thermal stability and acid resistance increase with the increase of SiO2 / Al2O3 composition ratio. Molecular sieve has a large specific surface area, up to 300 ~ 1000m2 / g, and the inner crystal surface is highly polarized. It is not only a kind of efficient adsorbent, but also a kind of solid acid. The surface has high acid concentration and acid strength, which can cause positive carbon ion type catalytic reaction. When the metal ions in the composition are exchanged with other ions in the solution, the pore size can be adjusted to change its adsorption and catalytic properties, so as to prepare molecular sieve catalysts with different properties.
Zeolite is the general name of zeolite group minerals. It is an aluminosilicate mineral containing aqueous alkali metal or alkaline earth metal. According to the characteristics of zeolite minerals, it can be divided into four types: frame, sheet, fibrous and unclassified. According to the characteristics of pore system, it can be divided into one-dimensional, two-dimensional and three-dimensional systems. Any zeolite is composed of silica tetrahedron and alumina tetrahedron. Tetrahedrons can only be connected by vertices, that is, they share one oxygen atom, not "edges" or "faces". The aluminum oxygen tetrahedron itself cannot be connected, and there is at least one silicon oxygen tetrahedron between them. The silicon oxygen tetrahedron can be directly connected. Silicon in silicon oxygen tetrahedron can be replaced by aluminum atoms to form aluminum oxygen tetrahedron. However, the aluminum atom is trivalent, so in the aluminum oxygen tetrahedron, the electricity price of one oxygen atom is not neutralized, resulting in charge imbalance, which makes the whole aluminum oxygen tetrahedron have negative points. In order to keep neutral, there must be positively charged ions to offset, which are generally compensated by alkali metal and alkaline earth metal ions, such as Na, CA, Sr, Ba, K, Mg and other metal ions. Because of its unique internal structure and crystalline chemical properties, zeolite has a variety of characteristics that can be used in industry and agriculture. The natural zeolite is light gray, and sometimes it has been found in the world. Holding it in your hand is obviously lighter than ordinary stones. This is because the zeolite is filled with subtle holes and channels, which is much more complex than the hive. If zeolite is compared to a hotel, there are 1 million "rooms" in this "Super Hotel" of 1 cubic micron! These rooms can automatically open or block the door according to the gender, height, weight and hobbies of "passengers" (molecules and ions), and will never let "fat" go to "thin" rooms, nor will tall people live in the same room with short people. According to this characteristic of zeolite, people use it to screen molecules and obtain good results. This is of great significance for the recovery of copper, lead, cadmium, nickel, molybdenum and other metal particles from industrial waste liquid. Zeolite has the properties of adsorption, ion exchange, catalysis, acid resistance and heat resistance, so it is widely used as adsorbent, ion exchanger and catalyst, as well as gas drying, purification and sewage treatment. Zeolite also has "nutritional" value. Adding 5% zeolite powder to the feed can accelerate the growth of livestock, make them strong, fresh meat and high egg laying rate. Due to the porous silicate nature of zeolite, there is a certain amount of air in the pores, which is often used to prevent explosion and boiling. During heating, the air in the small hole escapes, playing the role of gasification core, and small bubbles are easy to form on its corners.
The main difference is that in their use, zeolites are generally natural with different pore sizes. As long as there are bubbles, they can prevent boiling. The function of molecular sieve is much higher, such as screening molecules, making catalysts, slow-release catalysts, etc. Therefore, it has certain requirements for pore size, which is often synthetic.