Molecular sieve has clear pore cavity distribution, extremely high internal surface area (600m2/s), good thermal stability (1000 ℃), and adjustable acid site center. The acidity of molecular sieve mainly comes from three coordinated aluminum atoms and aluminum ions (AlO)+on the framework and in the pores. OH based acid sensitive site center on molecular sieve HY obtained by ion exchange, Activated carbon filter screen Beijing The aluminum ions outside the framework will strengthen the acid site and form the L acid site center. Polyvalent cations such as Ca2+, Mg2+and La3+can show the acid site center after exchange. The reduction of transition metal ions such as Cu2+and Ag+can also form acid site centers. In general, the higher the Al/Si ratio, the higher the specific activity of OH group. The modification of zeolite acidity can introduce protons through direct exchange of dilute hydrochloric acid. This method often leads to dealumination of molecular sieve framework. So NaY will become NH4Y and then HY. Because there are uniform small internal pores in the structure of molecular sieves, when the molecular linearity of reactants and products is close to the pore size in the crystal, the selectivity of catalytic reaction often depends on the corresponding size of molecules and pore size. Activated carbon filter screen purchase This selectivity is called shape selective catalysis. There are two mechanisms leading to shape selectivity. One is caused by the difference of diffusion coefficient of molecules participating in the reaction in the pore cavity, which is called mass transfer selectivity; The other is caused by the space limitation of the transition state of the catalytic reaction, which is called transition state selectivity.

Activated carbon filter screen purchase The highly effective selective adsorption is due to the fact that the alumina tetrahedron of zeolite has a negative charge, while the skeleton hole contains cations, which forms a strong electric field around the cations. Therefore, the adsorption force of zeolite not only has a strong dispersion force, but also has a large electrostatic force. It is precisely because of this electrostatic relationship that zeolites have preferential selective adsorption on polar, unsaturated and polarizable molecules. It can strongly adsorb molecules containing polar groups such as hydroxyl ion, ammonium ion and other polarizable groups, especially water, which can form hydrogen bonds with aluminum silicon skeleton, so zeolite has strong water absorption. It can still adsorb even under low relative humidity and concentration, and its water absorption is higher than that of silica gel and activated alumina. The adsorption capacity of zeolite for organic pollutants mainly depends on the polar size and molecular diameter of organic molecules. Small molecules are easier to be adsorbed than large molecules, while polar molecules are easier to be adsorbed than non-polar ones. Different substances (such as organic molecules, metal ions and water molecules) exist in water, Activated carbon filter screen manufactor Their polarity and molecular size are different, and competition will occur during adsorption.

Molecular sieve is a crystalline silicate or aluminosilicate, which is a pore and cavity system with molecular size (usually 0.3nm to 2.0nm) formed by connecting silicon oxygen tetrahedron or aluminum oxide tetrahedron through oxygen bridge bond, Activated carbon filter screen Beijing Therefore, it has the characteristics of screening molecules. However, with the deepening of molecular sieve synthesis and application research, researchers have found phosphoaluminate molecular sieves, and the skeleton elements (silicon or aluminum or phosphorus) of molecular sieves can also be replaced by B, Ga, Fe, Cr, Ge, Ti, V, Mn, Co, Zn, Be and Cu, and the size of its pores and cavities can also reach more than 2 nm, Activated carbon filter screen purchase Therefore, molecular sieves can be divided into silicon aluminum molecular sieves, phosphorus aluminum molecular sieves and skeleton heteroatom molecular sieves according to the composition of skeleton elements;

High silica zeolite type molecular sieves, this kind of zeolite has a series, and ZSM-5 is widely used, with ZSM-8 and ZSM-11 having the same structure; The other group is ZSM-21, ZSM-35 and ZSM-38. ZSM-5 is often called high silica zeolite, with the Si/Al ratio up to 50 and ZSM-8 up to 100. This group of molecular sieves also shows hydrophobic characteristics. Activated carbon filter screen manufactor Their structural units are similar to those of mordenite, consisting of pairs of five membered rings, with no cage like cavities and only channels. ZSM-5 has two sets of cross channels, one is straight through, the other is zigzag perpendicular to each other, both formed by ten yuan rings. The channel is oval and its window diameter is (0.55-0.60) nm. Activated carbon filter screen purchase Zeolites belonging to the high silicon group also have silicalite-1 of all silicon type, which has the same structure as ZSM-5, and silicalite-2 is the same as ZSM-11.