The properties of zeolite(1)

Zeolite is the general name of zeolite family minerals, a kind of shelf-like aqueous aluminosilicate minerals, the common ones are plagioclase, filamentous zeolite, rhodochrosite, grossular zeolite and sheet zeolite, etc. They have unique ion exchange, ion exchange, catalytic, thermal stability and acid resistance, etc. They are widely used in the fields of building materials, environmental protection, ion exchange, catalytic cracking, daily light industry, petrochemical industry, agriculture and animal husbandry, paper making and plastics, etc.

1、Physical and chemical properties of zeolite

(1) Selective adsorption

The pore structure of zeolite gives it a large internal surface area, and after dehydration, it has a larger internal surface area due to the connectivity and openness of the pore structure, and the huge internal surface area forms the efficient adsorption performance of zeolite.

Selective adsorption and molecular sieve effect is an important feature of zeolite adsorption performance. The pore channels and pores in zeolites are generally larger than 50% of the total volume of the crystals and are uniform in size, with fixed dimensions and regular shapes, generally 0.66-1.5 nm in pore diameter and 0.3-1.0 nm in pore channel. obviously, molecules with diameters smaller than the pores of zeolites can enter the pores, while molecules larger than the pores are rejected, thus zeolites have a screening effect on molecules called molecular sieve effect Therefore, zeolite has a screening effect called molecular sieve effect.

In addition, the nature of the adsorbed molecules also has an important influence on the adsorption behavior of zeolite. Zeolite has a strong affinity for polar molecules such as H2O, NH3, H2S, CO2, etc. The adsorption effect is very strong, and conditions such as humidity, temperature and concentration have little effect on it.

The silica-alumina ratio of zeolite directly affects the electrostatic field inside the zeolite crystal, which affects the strength of the adsorption force. The larger the silica-alumina ratio is, the weaker the adsorption force will be.

(2) Ion-exchange property

The ion exchangeability of zeolite originates from the exchangeable cations, such as K+, Na+ and Ca2+, present in the pore channels of zeolite due to the valence imbalance caused by the replacement of Si4+ by Al3+ in the equilibrium zeolite structure.

The ion exchange of zeolite shows obvious selectivity, for example, Na+ in square zeolite is easily exchanged by Ag+, Ti, Pb, etc., while the amount exchanged by NH4+ is low.

(3) Catalytic performance

Zeolite has high catalytic activity, and is resistant to high temperature and acid, and has anti-poisoning properties, making it an excellent catalyst and its carrier. The mechanism by which zeolites present catalytic properties is mainly determined by the acidic position in their crystal structure, the size of their pores and their cation exchange properties.