Study On Microwave-assisted Hydrothermal Synthesis And Structural Properties Of Nano-ZSM-5

Nano-ZSM-5 molecular sieves are usually prepared by conventional hydrothermal synthesis.Conventional heating method tends to produce temperature gradients,which the external temperature of the reaction material is higher than the internal temperature.This results in problems such as uneven heating,longer synthesis time,higher crystallization temperature,higher cost,and synthetic products with agglomeration,larger grain size??100 nm?and wider particle size distribution.Therefore,according to the microwave radiation heating with the characteristics of low energy consumption,high speed and uniform heating,nano-ZSM-5 molecular sieves were prepared by microwave-assisted hydrothermal synthesis in this paper.The effects of different synthetic factors on the structural properties of nano-HZSM-5 molecular sieves and nano-NaZSM-5 molecular sieves were investigated.And the catalytic performance and technological conditions of MTO for nano-ZSM-5 molecular sieves were studied.Nano-HZSM-5 molecular sieves were prepared by microwave-assisted hydrothermal synthesis under the mild conditions.The effects of aluminum source,template dosages,water dosages,crystallization time,crystallization temperature and aging temperature on the structural properties of HZSM-5 molecular sieves were investigated by means of XRD,FT-IR,SEM,BET and NH₃-TPD.The results show: High purity nano-HZSM-5 molecular sieve was prepared at the conditions that the raw material molar ratio n?SiO₂?: n?Al₂O₃?: n[?TPA?₂O]: n?H₂O?of 300: 1: 37.5: 1500,aluminum source of isopropyl alcohol aluminum?AIP?,aging temperature of 80 ?,lower crystallization temperature of 160 ?,shorter crystallization time of 1.5 h.And The spherical nano-HZSM-5 molecular sieve crystals performed better dispersibility,more uniform and smaller grain size?about 60 nm?,microporosity and mesoporous structure,larger specific surface area(398.45 m²?g^-1),pore volume(0.63 cm³?g^-1)and the average pore size?6.27 nm?;surface chemical properties of weak acid.Nano-Na ZSM-5 molecular sieves were successfully prepared by microwave-assisted hydrothermal synthesis in the more moderate conditions.The effects of the type and dosages of template and sodium source on the structural properties of NaZSM-5 zeolite were investigated by XRD,SEM,BET and NH₃-TPD.The results show: High purity nano-NaZSM-5 molecular sieve was prepared at the conditions that the raw material molar ratio n?SiO₂?: n?Al₂O₃?: n[?TPA?₂O]: n?H₂O?: n?Na₂O?of 300: 1: 37.5: 1500: 15,template agent of tetrapropylammonium hydroxide?TPAOH?,sodium source of sodium hydroxide?NaOH?.And The spherical nano-Na ZSM-5 molecular sieve crystals performed better dispersibility,more uniform and smaller grain size?about 30 nm?,microporosity and mesoporous structure,larger specific surface area(419.64 m²?g^-1),pore volume(0.68 cm³?g^-1)and minimum average pore size?3.83 nm?,surface chemical properties of weak acid.The MTO catalytic performance and technological conditions were investigated by means of gas chromatography and other analytical methods.The results showed that 30 nm NaZSM-5 molecular sieve?Na-30?was reacted in MTO reaction with the best catalytic performance,the selectivity and yield of methanol were 97.56%,73.18% and 71.39%,respectively.The suitable reaction conditions of MTO were as follows: reaction temperature 360 ?,feed space velocity 1.5 h^-1,N₂ flow rate 15 ml·min^-1.