Molecular sieve manufacturer: synthesis of molecular sieves
The synthesis of molecular sieve includes hydrothermal synthesis method, hydrothermal conversion method and ion exchange method. The following molecular sieve manufacturer
will tell you in detail:
① "Hydrothermal synthesis method" is used to prepare higher-purity products, synthesize molecular sieves that do not exist in nature, and combine silicon-containing compounds (water molecular sieve glass, silica sol, etc.), aluminum-containing compounds (hydrated alumina, aluminum salts, etc.), Alkali (sodium hydroxide, potassium hydroxide, etc.) and water are mixed in an appropriate proportion, put into a high-temperature autoclave and heated for a certain period of time to precipitate molecular sieve crystals. The synthesis process can be represented by the following formula:
In the industrial production process, Na molecular sieves are generally synthesized first, such as the synthesis of 13X and 10X molecular sieves. Adding certain additives during the hydrothermal synthesis process can change the structure of the final product. For example, ZSM-5 molecular sieve can be obtained by adding quaternary ammonium salt.
②"Hydrothermal conversion method" In the presence of excess alkali, solid aluminosilicate is hydrothermally converted into sub-sieves. The raw materials used are kaolin, bentonite, diatomite, etc., and silica-alumina gel particles can also be synthesized. The cost of this method is low, but the purity of the product is not as good as that of the hydrothermal synthesis method.
③ The ion exchange method usually converts Na molecular sieves into molecular sieves containing the desired cations in an aqueous solution. The general formula is as follows:
Among them, Z- represents anion skeleton, Me+ represents cations that need to be exchanged, such as NH, Ca2+, Mg2+, Zn2+, etc. The raw materials are usually hollow glass molecular sieve chloride, sulfate, nitrate. Different cations of different properties have different degrees of difficulty in the exchange of cations on molecular sieves, which is called the selection sequence of molecular sieves for cations. For example, the selection order of 13X molecular sieve is Ag+, Cu2+, H+, Ba2+, Au3+, Th4+, Sr2+, Hg2+, Cd2+, Zn2+, Ni2+, Ca2+, Co2+, NH, K+, Au2+, Na+, Mg2+, Li+, and the exchange results are usually as follows The parameters indicate: exchange degree, that is, the percentage of Na+ exchange in the molecular sieve to the original Na+; exchange capacity, that is, the number of milliequivalents of cations exchanged per 100 grams of molecular sieve; mass percentage. In order to prepare a suitable molecular sieve catalyst, the exchange product needs to be mixed with other components, which can be other catalytically active components, co-catalysts, diluents or binders, etc., and the catalyst can be activated.