Study On The Catalytic Selective Nitration Of Biphenyl And Its Derivates Over Modified Zeolites

The reaction yield and selectivity could be highly improved by adding suitable zoelites as catalyst in reaction systems. The industrial nitration involving the concentrated mineral acids as the catalyst is one of the most environmentally harmful processes. The process produces huge amounts of wastes along with a large amount of undesired product due to the nonselective nitration of aromatics. Catalysis affect of zoelites on nitration of biphenyl and its derivatives were discussed in this paper. The main works and results were as follows:(1) The ZSM-5, BEA, MCM-41, Y, and USY zeolites modified by metal ions Cd2+, Fe3+, Ce3+, Gd3+, Nd3+, La3+, Sm3+, Pr3+,, Y3+, Co2+ were characterized by FT-IR, XRD, EDS, SEM, DTA-TG, N2 adsorption-desorption and laser particle size. The results show that the metal ions enter the surface and interior of the zeolite, the crystal structure of modified zeolite remains intact. The recovered zeolite was consistent with the original structure after calcination, therefore, zeolite can be regenerated.(2) The regioselective nitration of biphenyl catalyzed by ZSM-5% MCM-41、Y and USY zeolites modified by metal cation was studied. Modified zeolites can promote formation of nitroxyl cation by providing acid site to accelerate the reaction speed, and the content of the products increased by the shape-selective ability of modified zeolites. Experimental results show that para selectivity of nitration of biphenyl catalyzed by modified zeolites in nitric acid/dichloromethane system is superior to nitric acid/acetic anhydride system. Because the ring structure of biphenyl in nitric acid/acetic anhydride heterogeneous system is more conducive to the formation of ortho product. The ratio of ortho-para is between 0.69-0.73 and yield up to 78.1-83.4% in the nitric acid/dichloromethane system catalyzed by modified ZSM-5 and USY, MCM-41 catalysts.(3) The regioselective mono-nitration and di-nitration of biphenyl catalyzed by BEA zeolite modified by metal ions was investigated. Experimental results show that the para selectivity of biphenyl nitration in nitric acid/acetic anhydride system superior to nitric acid/dichloromethane system over modified BEA zeolite catalyst. The reason may be formation of a complex by BEA zeolite and acetic anhydride and conducive to the formation of the para products. The ratio of ortho-para of biphenyl mononitration product is 0.40 and yield up to 65.51% in nitric acid/acetic anhydride system catalyzed by modified BEA zeolite. The isomer ratio of biphenyl di-nitration product (2,2’:2,4’, 4,4’-dinitrobiphenyl) is 2:37:61 and yield could reach 92% above in the nitric acid/acetic anhydride system catalyzed by modified BEA zeolite. Selectivity nitration of biphenyl in NO2/O2/acetic anhydride system over modified BEA zeolite was investigated. The system experienced a free radical substitution process, the presence of oxygen can accelerate the reaction rate. The optimum ratio of ortho-para of biphenyl mononitration product is 0.34, the yield can reach about 85% in NO2/O2/acetic anhydride system catalyzed by modified BEA zeolite.(4) The regioselective nitration of biphenyl derivatives (4-acetylbiphenyl, 4-bromobiphenyl,4,4’-dibromobiphenyl,4,4’-dichloromethylbiphenyl, 4,4’-dimethylbiphenyl)overZSM-5、BEA、MCM-41、Y and USY zeolites modified by metal cations was studied. The results show that the excellent selectivity and high yield were obtained in the nitric acid/acetic anhydride system over modified BEA zeolite.