First, the principle of molecular sieve:
Adsorption function: The adsorption of molecular sieves to substances comes from physical adsorption (van der Waals force), and its crystal pores have strong polarity and Coulomb field, showing strong adsorption capacity for polar molecules (such as water) and unsaturated molecules.
Screening function: The pore size distribution of molecular sieves is very uniform, and only substances with a molecular diameter smaller than the hole diameter can enter the crystal cavity of the molecular sieve.
Second, the use of molecular sieve:
3A molecular sieve application: drying of various liquids (such as ethanol); drying of air; drying of refrigerants; drying of natural gas and methane gas; drying of unsaturated hydrocarbons and cracked gases, ethylene, acetylene, propylene, butadiene.
4A molecular sieve application: deep drying of air, natural gas, alkane, refrigerant and other gases and liquids; preparation and purification of argon; static drying of pharmaceutical packaging, electronic components and perishable substances; as a dehydrating agent in paints, fuels and coatings .
According to catalytic properties, molecular sieve catalysts:
(1) Acid catalyst, which utilizes the surface acidity of molecular sieve to catalyze the reaction.
(2) Bifunctional catalyst, the molecular sieve can support platinum and palladium metals to obtain a bifunctional molecular sieve catalyst with both metal catalytic function and acid catalytic function.
(3) For shape-selective catalysts, since the catalytic effect of molecular sieves generally occurs in the inner space of the crystal, the pore size and pore structure of molecular sieves have a great influence on the catalytic activity and selectivity. Molecular sieves have regular and uniform intracrystalline pores, and the pore size is close to the molecular size, so that the catalytic performance of molecular sieves changes significantly with the geometric size of reactant molecules, product molecules or reaction intermediates.
