Preparation And Properties Of ZSM-5 Molecular Sieves With Low Si/Al Ratio At Sub-micron Level

ZSM-5 zeolite is a kind of aluminosilicate crystal material with unique pore structure,which has a wide range of SiO2/Al2O3 and hydrophobic properties.Meanwhile,ZSM-5 zeolite has a high thermal stability and catalytic activity,which has an important application in improving the quality of FCC gasoline and the yield of low-carbon olefins such as ethylene and propylene.ZSM-5 zeolite with different physical and chemical properties and crystal morphology also had different effects on catalytic cracking.In this paper,the submicron ZSM-5 zeolite with low SiO2/Al2O3 was synthesized by hydrothermal synthesis with tetrapropylammonium hydroxide as template,The influence of the physical and chemical properties and crystal structure of the zeolite in the hydrothermal system was studied.The thin ZSM-5 zeolite was synthesized by adding urea into the gel to improve its mass transfer performance.The ZSM-5 zeolite with low SiO2/Al2O3 was treated by NaOH solution and explored the effects of different conditions on the structure and properties of ZSM-5 zeolite were studied.XRD,FT-IR,SEM,NH3-TPD and N2 adsorption desorption were used to characterize the ZSM-5 zeolite,and the effects of different reaction conditions on the structural characteristics and physicochemical properties of the zeolite were investigated.ZSM-5 zeolites can be synthesized with silica sol as silicon source in the range of crystallization temperature 175-200?,crystallization time 12-72h,SiO2/TPAOH=0-20,SiO2/Al2O3=25-500,Na2O/SiO2=0.08-0.18;adding urea in the gel can inhibit the growth of zeolites along the b-axis direction,and with the increase of urea content,the b-axis thickness of zeolites decreases gradually;Under certain conditions,ZSM-5 molecular sieve treated with NaOH solution can introduce slit like mesoporous pore structure into the molecular sieve,and with the increasing erosion degree of alkali solution on the pore,the surface of the molecular sieve is gradually rough,and the slit like pore structure increases,so as to improve the mass transfer performance of ZSM-5.