Organic amine substitution method of molecular sieve

Some zeolite molecular sieves are directly synthesized in inorganic cationic systems, such as A, P, mordenite, X, Y and L zeolites, while others often need to be synthesized in organic amine (ammonium) systems, such as ZSM-5, ZSM-11, Beta zeolite, MCM-2, SAPO-34 and TS-1, etc. In comparison, the zeolite products synthesized with organic cations as templates are easier to control in terms of crystallinity, grain size and Si/Al ratio. But the cost of raw materials is relatively high. In addition, many new types of molecular sieves are often synthesized from relatively expensive organic amines (ammonium) at the beginning of their discovery, and the cost is very high. 

Organic amine substitution method

According to the previous experience in the synthesis of molecular sieves, it is recognized that in many systems for the synthesis of molecular sieves from organic amines (ammonium), the amount of organic amines is often excessive, which greatly exceeds the amount of organic amines contained in the product molecular sieve structure, which means that there is only a small amount of organic amines. Amines really play a structure-oriented role and participate in the nucleation and growth of molecular sieves, while most organic amines only play a role in regulating alkalinity and pore filling. It is precisely based on this point that organic amine substitution methods have been studied and developed, that is, in the synthesis of organic amines. In addition to adding a small amount of organic amines as structure-directing agents, other inexpensive organic amines were added as alkali modifiers and pore fillers. For example, they synthesized SSZ-25 by partially replacing quaternized amantadine with cheap isobutylamine. (MWW) molecular sieve, thereby greatly reducing the synthesis cost, organic amine handling cost and crystallization time. Similarly, they used N,N,N-trimethylanilinium to replace part of the special amantadine to synthesize SSZ-13 ( CHA), SSZ-33 (CON), SSZ-35(STF) and SSZ-42 (IFR); SSZ-13 was also synthesized by the combination of tetramethylammonium hydroxide and amantadine. It is worth mentioning that the double organic amine method can also change the structural composition of molecular sieves, silicon-alumina For example, for SSZ-47 molecular sieve, it is a symbiosis of three structures of EUO, NES and NON, and the existence of NON structure can greatly reduce the adsorption capacity and molecular diffusion rate of molecular sieve. SSZ-47B was synthesized by the amine method. Compared with SSZ-47 synthesized by the single organic amine method, the NON structure content of SSZ-47B was greatly reduced, so its adsorption capacity and molecular diffusion rate were also greatly improved. Synthesized by the double organic amine method SSZ-32X (MTT) has a lower silicon-to-alumina ratio and smaller crystallites than the SSZ-32 molecular sieve synthesized only with imidazolamine, and its catalytic dewaxing performance is also better. In addition, the industrially applied MCM-22 (MWW) zeolite is generally produced by using hexamethyleneimine as the structure directing agent. The UZM series of zeolite molecular sieves were synthesized with a combination of organic amines commonly used in the industry. Among them, diethyldimethylammonium hydroxide was used as the structure directing agent. When synthesizing UZM-8 (MWW) zeolite, compared with amantadine or hexamethyleneimine as structure directing agent, it has certain advantages in terms of synthesis cost or environmental friendliness. Phosphoaluminum and its heteroatom molecular sieves with AFI structure were synthesized by methylguanidine instead of organic amines.