Study On Synthesis And Commercial Sacle-up Of ZSM-5 And Mordenite Zeolites At Low Cost

Mordenite and ZSM-5 are two kinds of commonly used industrial molecular sieves.As the mordenite have good acidity,adsorption and thermal stability,it is widely used in xylene isomerization,C5/C6 isomerization,wastewater treatment and other fields.At present,the synthesis of low SiO₂/Al₂O₃ ratio mordenite molecular sieve with amine free method is often accompanied with mixed crystal.Although the template method can solve this problem,It will cause pollution to the environment,either,the process of wastewater's treatment is difficult and the industrial cost is relatively high.The small particle size ZSM-5 zeolite has a larger specific surface area and a short diffusion channel,and exhibits excellent activity and stability than the conventional ZSM-5 zeolite in catalyzing many reactions.However,the synthesis of outstanding catalytic performance ZSM-5 zeolite with small particle size requires the use of expensive TEAOH as a template,which will increase the cost and applying to commercial production will greatly increase the economic input of the product.Therefore,the main purpose of this subject is to get relatively regular morphology and higher crystallinity mordenite and smaller particle size ZSM-5 zeolite under a simpler process and lower cost..By adjusting the synthesis parameters of the reaction system,mordenite and ZSM-5 molecular sieves with different morphologies,sizes and properties were obtained and the industrial amplification studies were also conducted.The conclusions are as follows:1.Using the method of amine-free synthesis and hydrothermal synthesis of mordenite,the pure mordenite phase of SiO₂/Al₂O₃=10.3 to 16.8 is successfully synthesized,and we also found that the products will appear in analcime crystal phase when the ratio of products' SiO₂/Al₂O₃ is below 10.3,when the ratio of products' SiO₂/Al₂O₃ is more than 16.8,it turned out to be mixed crystal of mordenite and MFI structure.The results show that the morphology and size of the products are different as to different SiO₂/Al₂O₃ ratios,and with the increase of feeding SiO₂/Al₂O₃,the morphology of mordenite has changed from uniform needle like to uniform rod then to flat plate.2.In the amine-free hydrothermal synthesis of mordenite with SiO₂/Al₂O₃=12,the effects of alkalinity,crystallization time,crystallization temperature and water content on the synthesis were investigated.The results are as follows: the conditions during the ranges of NaCl/SiO₂=0 to 0.07,H2O/SiO₂=15 to 21,OH^-/SiO₂=0.04 to 0.08,the temperature is from 170? to 180? and crystal time is from 24 h to 48 h can all be used to synthesize pure phase mordenite.Beyond the ranges,it is easy to cause amorphous structure,ANA or MFI structure.In the reaction system,an excess Na+ and excess alkali as well as a too long crystallization time and too high temperature will lead to the emergence of hybrid zeolite.3.Template has a significant effect on the morphology of mordenite.Appropriate increase of the content of template agent can accelerate the reaction rate and promote the growth of crystal.However,too much template can cause the alkalinity of the system to be too high,which leads to the appearance of zeolite.4.The effects of OH^-/SiO₂ and crystallization time on the synthesis of ZSM-5 zeolite were investigated by hydrothermal synthesis of ZSM-5 zeolite.The results are as follows:a.The effect of OH^-/SiO₂ on the morphology and particle size of ZSM-5 zeolite was significant.As the alkalinity increases,product 's size becomes larger.Crystal morphology was spherical or ellipsoidal particles.If OH^-/SiO₂ is too high,the agglomeration occurs between the grains.For ZSM-5 zeolite with high SiO₂/Al₂O₃,the product's size increases first and then decreases,and finally increases.The morphology of product is rectangular particles.If OH^-/ SiO₂ is too low,there is amorphous in the product.If OH^-/SiO₂ is too high,the product crystallinity decreases,accompanied by spherical small particles appear.b.Appropriate extension of the system's low temperature crystallization time is advantageous to synthesize the small grain ZSM-5 zeolite molecular sieve.With the crystallization time prolonged,the crystallinity of the two kinds of SiO₂/Al₂O₃ ZSM-5 products increased first and then decreased,and the product size increased.5.Mordenite and ZSM-5 molecular sieve amplification effect is obvious.The size of the reactor before and after the amplification,heating and mixing methods lead to different mass transfer and heat transfer during the crystallization process,thus affecting the product's morphology and grain size.