History of molecular sieve
There are two types of molecular sieves: natural zeolite and synthetic zeolite. ① Most natural zeolites are formed by the reaction of volcanic tuff and tuffaceous sedimentary rocks in marine or lacustrine environments. At present, more than 1,000 kinds of zeolite minerals have been discovered, of which 35 are more important. The common ones are clinoptilolite, mordenite, erionite and chabazite. Mainly distributed in the United States, Japan, France and other countries, China has also discovered a large number of mordenite and clinoptilolite deposits, and Japan is a country where natural zeolite is mined. ②Since natural zeolite is restricted by resources, synthetic zeolite has been widely used since the 1950s. As early as more than 200 years ago, B. Kronstedt named aluminosilicate as zeolite. The general formula of chemical composition is: where M and n are metal ions and their valences; x is the number of silicon dioxide molecules. ; Y is the number of water molecules; p is the number of aluminum atoms; q is the number of silicon atoms. Molecular sieves are used as solid adsorbents in the chemical industry. The adsorbed substances can be desorbed, and molecular sieves can be regenerated after use. It is also used for the drying, purification, separation and recovery of gases and liquids. Since the 1960s, it has been used as a cracking catalyst in the petroleum refining industry. Now a variety of molecular sieve catalysts suitable for different catalytic processes have been developed.