Study On Synthesis And Surface Coating Process Of Hydrophobic ZSM-5 Molecular Sieve

ZSM-5 zeolite is a kind of high silica zeolite,with three-dimensional cross-pore structure of MFI,high specific surface area and hydrothermal stability.It is widely used in industrial catalysis,biochemistry and environment.Hydrophobic ZSM-5 zeolite is needed in the process of VOCs tail gas adsorption and purification.The hydrophobicity of ZSM-5 is related to the content of Si-OH group on the surface of zeolite.The higher the ratio of silicon to aluminium,the lower the content of hydrophilic Si-OH group on the surface,the hydrophobicity of ZSM-5 is higher.It is suggested that hydrophobicity of the ZSM-5 molecular sieve can be improved by increasing the SiO2/Al2O3 ratio and Si-O-Si groups of the ZSM-5,reducing the content of Si-OH groups on the surface of the ZSM-5 molecular sieve.ZSM-5 is synthesized by in-situ hydrothermal method with beer silica gel as the silicon source,sodium aluminate as the aluminum source,n-butyl amine as the template agent,NaOH used to control system alkalinity.The single factor method was used to investigate the factors such as SiO2/Al2O3 ratio,template/SiO2 ratio,H2O/SiO2 ratio,OH-/SiO2 ratio,crystallization time and crystallization temperature to the effect of the synthesis of hydrophobicity of ZSM-5.The hydrophobic ZSM-5 was coated on different substrates.The relationship between the synthesis conditions and the structure of zeolite was characterized by XRD,BET and SEM and its influence on the coating process was also investigated.On synthesis of SiO2:Al2O3=100,300,500,800and1000,only SiO2:Al2O3=300 and SiO2:Al2O3=500 can reach more than 60%of the feed.The SiO2:Al2O3=300 system,the optimum synthesis condition of hydrophobic ZSM-5:n-butylamine/SiO2=0.3-0.4,H2O/SiO2=40,NaOH/SiO2=0.1-0.2,crystallization temperature of 120? to 150?,the cryst allization time of 48 h.the SiO2:Al2O3=500 system,the optimum sy nthesis condition of hydrophobic ZSM-5:n-butylamine/SiO2=0.4-0.5,H2O/SiO2=40,NaOH/SiO2=0.1-0.2,crystallization temperature of 150?to 160?,the crystallization time of 48 h.In the two systems of Si O2:Al2O3=300 and SiO2:Al2O3=500,the static water absorption of ZSM-5 zeolite prepared under the optimum synthetic conditions is the lowest,and the higher the ratio of silicon to aluminium,the bet ter the hydrophobicity of ZSM-5 zeolite.The surface of the substrate was coated with a self-made aluminum sol and a ZSM-5 mixed ball mill to prepare an active slurry,and the substrate was immersed in the active slurry for surface coating.The loading of ZSM-5 on the surface of flexible ceramic fiber paper increases with the increasing of the apparent viscosity of the mixed slurry.The optimal coating apparent viscosity is 200 mPa·s-400 mPa·s,the loading 20%wt.-60%wt.The coating surface is smooth,dense uniform.The optimal coating amount should be controlled at 50%wt-60%wt,with the feature of the higher loading rate,the higher shedding rate.The optimum apparent viscosity of ZSM-5 coating on the rigidsubstrate(cordierite honeycomb ceramics,FeCrAl substrates,monocrystalline silicon sheets)is 180 mPa·s-2030 mPa·s and the coating amount of cordierite honeycomb ceramics is 5.79%wt.-24.79%wt.The loading rate on FeCrAl substrates is from 0.52%wt to 5.09%wt and the monocrystalline silicon sheet loading rate increased from 0.42%wt to 4.75%wt.The critical loading of monocrystalline silicon sheet&FeCrAl substrates is 8.3%wt.and the critical coating amount of cordierite honeycomb ceramics is 42%wt.