What are the advantages of ZSM-5 molecular sieve
The thermal stability of ZSM-5 molecular sieve is very high, which is caused by the five-membered ring with stable structure and high silicon-to-aluminum ratio in the framework. For example, after a sample is calcined at about 850°C for 2 hours, its crystal structure remains unchanged and can even withstand a high temperature of 1100°C. ZSM-5 is one of the zeolites with high thermal stability, therefore, it is particularly suitable for high temperature processes. For example, when it is used as a hydrocarbon cracking catalyst, it can withstand the high temperatures during catalyst regeneration.
ZSM-5 molecular sieve has good acid resistance. In addition to hydrofluoric acid, it can resist various acids.
Water vapor stability
When other zeolites are exposed to water vapor and heat, their structure is usually destroyed, resulting in irreversible deactivation. The use of ZSM-5 as a catalyst for methanol conversion (water is one of the main products), which shows that ZSM-5 Water vapor has good stability. After HZSM-5 and HY zeolite are treated with steam at 540°C with a partial pressure of 22mmHg for 24 hours, the crystallinity is about 70% of that of the fresh catalyst, but the framework of HY zeolite is almost completely destroyed under the same conditions.
ZSM-5 has a high silicon-to-aluminum ratio and low surface charge density, and water is a highly polar molecule, so it is not easy to be adsorbed by ZSM-5. Although the diameter of water molecules is smaller than n-hexane, ZSM-5 adsorbs n-hexane Capacity is generally greater than water.
It is not easy to accumulate carbon.
The effective shape and size of the ZSM-5 orifice plate and the curvature of the channel prevent the formation and accumulation of huge condensate. At the same time, there is no cavity (cage) larger than the channel in the ZSM-5 frame, which limits the The formation of large condensation molecules as side reactions reduces the possibility of carbon deposits on the ZSM-5 catalyst. ZSM-5 prevents alkyl aromatic hydrocarbons from entering the pores, so it cannot continue to react in smaller pores during the reaction process, and finally polycondenses to form coke. Therefore, the carbon deposition rate of ZSM-5 is much slower than that of Y-type and mordenite. Almost two orders of magnitude. The carbon capacity of ZSM-5 molecular sieve is also higher.