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Synthesis of metallosilicates MFI zeolite containing boron from industrial hexafluorosilicic acid and catalytic performance evaluation

Wang Xianqiao;Jin Fang;Yuan Ming;Wu Yuanxin;Liu Tieliang;Fan Yangchun;Key Laboratory for Green Chemical Process of Ministry of Education,Hubei Novel Reactor & Green Chemical Technology Key Laboratory,School of Chemical Engineering and Pharmacy,Wuhan Institute of Technology;  
Two-step ammoniation method was applied to recover high-quality silica from by-product hexafluorosilicic acid,and the recovered silica can be used to synthesize B contained metallosilicates MFI zeolite(B-ZSM-5).The hydrothermal synthesized B-ZSM-5 zeolite crystalline samples were characterized by XRD,SEM,TG,and BET etc..The catalytic performances of B-ZSM-5 and ZSM-5 to toluene and 1,2,4-trimethylbenzene disproportionation reaction were compared on a continuous fixed bed reactor.Results showed the silicon gel recovered from hexafluorosilicic acid could be used as the raw material for synthesizing MFI zeolites in the range of 1~70 of the amount-of-substance ratio of silicon and boron.The crstallinity was the highest when the amount-of-substance ratio of silicon and boron was 12.For the B-ZSM-5 synthesis,with the increase of Si/B ratio the crystal type of synthesized B-ZSM-5 transformed from the orthorhombic to the monoclinic phase.During the hydrothermal process,the existence of F-as the mining agent had great influence on the crystal size of synthesized B-ZSM-5.The topography of the synthesized B-ZSM-5 exhibited perfect crystal with smooth surface and crystal size at 10~50 μm.The catalytic performance showed that the boron has been incorporated to the zeolite crystal lattice and can be used to modify the acidity of zeolite.
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