Research On The Direct Hydroxylation Of Benzene To Phenol

Phenol is an important intermediate for many industrial products. Currently, the industrial route to prepare phenol has mainly been produced from benzene via the cumene process, which is characterized by a multistep process and the production of acetone as a byproduct. It is inconsistent with the environment-friendly development strategy. Many researchers have attempted one-step hydroxylation of benzene to phenol without byproducts. Direct hydroxylation of benzene to phenol is an attractive and challenging field from an economical and environmental point of view. The bond energy of C-H bond on benzene ring is very high, benzene is difficult to activate, directly introduce hydroxyl into benzene ring, and selectively oxide benzene to synthesis phenol is an important also with great challenge classical organic reaction, there is a multitude of studies in this field. The aim of this dissertation is to optimize the reaction condition, choose the effective catalysts and reducing agent in order to improve the conversion of benzene and selectivity of phenol.The effect of different reducing agents on direct hydroxylation of benzene to phenol by O2 over the V/SiO2, prepared by a sol-gel process was investigated. This work shows that the reduction power of the different reducing agents on the V/SiO₂ can be tuned by increasing the reaction temperature and affect, in turn, benzene conversion, product selectivity, and the amount of leaching of V species into solution. Among the reducing agents investigated, Under the optimized reaction conditions, we obtained 13.92% benzene conversion and 100% selectivity of phenol with hydroquinone as reducing agent at 120℃. Hydroquinone the percentage of leaching of V species from the V/SiO₂ was effectively suppressed from 88.73% at 40℃to 32.56% at 120℃. Catalyst characterized by means of BET, XRD, and TPR has been investigated, it can be seen that catalyst with vanadium oxide species were highly dispersed on the silica surface.The catalytic property of modified Fe/SiO2 catalyst over the reaction of oxidation of benzene to phenol in acetonitrile solvent using hydrogen peroxide as the oxidant was studied. Ferric species was the catalytically active and phenol was the complexing agent .The influence of calcined atmosphere and temperature of catalyst on the hydroxylation were studied. Fe(P)₉/SiO₂ (the ratio of ferric species/ phenol is 1:9) calcined under N₂ atmosphere at 550℃shows good catalytic activity. The possible path of the catalytic reaction is Fenton-like mechanism. Best results were obtained benzene conversion of 40.62% and phenol selectivity of 100% , Under the optimized reaction conditions: catalyst 0.08 g; reaction temperature 90℃; reaction time 8 h; solvent CH3CN 5 ml.