Types and Properties of Molecular Sieves

    هناك نوعان من المناخل الجزيئية: natural zeolite and synthetic zeolite. Most natural zeolites are formed by the reaction of volcanic tuff and tuffaceous sedimentary rocks in marine or lacustrine environment. At present, more than 1000 kinds of zeolite mines have been found, of which 35 are more important. The common ones are clinoptilolite, mordenite, mordenite and siderite. It is mainly distributed in the United States, Japan, France and other countries. A large number of mordenite and clinoptilolite deposits have also been found in China. Japan is the country with the largest exploitation of natural zeolite. Due to the limitation of natural zeolite resources, synthetic zeolite has been widely used since the 1950s. Commercial molecular sieves are commonly used to classify molecular sieves with different crystal structures, such as 3A, 4A and 5A molecular sieves. 

    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 / AI2O3 composition ratio. Molecular sieve has a large specific surface area of 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 no performance.