Study On Preparation And Application Of ZSM-5/SiC Composites In The Oxidation Of Benzene To Phenol By Hydrogen Peroxide

ZSM-5/SiC composites material have attracted considerable interest due to its easy loading active constituent properties, good characteristic of heattransfer and mass transfer, and other advantages. The prepared Fe-ZSM-5/SiC composites were used as catalysts to study direct hydroxylation of benzene to phenol in this paper.ZSM-5zeolite and ZSM-5/SiC composites material were synthesized by hydrothermal synthesis method. The Fe-ZSM-5/SiC composites were prepared by incipient wetness impregnation of ferric nitrate ninehydrate in solution. The factors affecting the synthesis of ZSM-5 zeolite and ZSM-5/SiC composite material were studied, including crystallization time and temperature, the value of pH in mother solution of zeolite, Si/Al ratio, carrier pretreatment methods such as pickling and calcining. The experiment results indicateds:(1) The better molecular sieve was prepared under the conditions which was crystallize at 175℃ for 48 h, pH≥9 in mother solution of zeolite.(2) The SiO2 generated on Surface of SiC powder by high temperature calcinationed,which involved in the molecular sieves synthesisas silicon source, was conducive to the growing of ZSM-5 zeolite the SiC powder surface, which improved the bonding strengthbetween ZSM-5 zeolite anc SiC.The Fe-ZSM-5/SiC composites were prepared by incipient wetness impregnation of ferric nitrate ninehydrate in solution. Using H2O2 as the oxidant, as-prepared Fe-ZSM-5/SiC composites were used as catalysts to study direct hydroxylation of benzene to phenol. The influence of reaction time, reaction temperature, the value of Fe3+ in composite, H2O2 dosage and stability of the catalyst on the catalytic behavior was studied. The experimental resultes showed:(1) The conversion of benzene reached 27%. The conditions were follows:reaction time was 3 h, reaction temperature was 60 ℃ and the dosage of H2O2 was 1.8 mL. (2) Fe-ZSM-5/SiC composites exhibited higher catalytic performance than Fe-ZSM-5.The intrinsic kinetics of benzene hydroxylation to phenol with hydrogen peroxide over Fe-ZSM-5/SiC were studied by the initial rate method. Through the research on effects of agitation rate, benzene concentration, hydrogen peroxide concentration and temperature on the initial reaction rate of benzene,we can establish an intrinsic kinetic model:r= 8×106 exp (-59.3×103/RT)×CC6H6/0.6×CH2O2/1.32.The formula shows that the reactionorders hydrogen peroxide were 0.6 and 1.32 and the activation energy was 57.3 kJ/mol.