Synthesis Of Phenol And Dihydroxybenzene From Benzene Over TS-1 Catalysts

Phenol is mainly used to produce crucial chemicals such as phenolic resin and caprolactam.Dihydroxybenzene including catechol and hydroquinone are widely used in the industrial area of perfumery,dyes and rubber.At present,more than 92%of phenol is produced by the cumene method in the world,which caused serious corrosion and environment pollution.Dihydroxybenzene is mainly produced by the hydroxylation of phenol with hydrogen peroxide over Inorganic acid salt catalyst,but the process has many problems such as the separation of catalyst from mixture and low conversion.Studying the hydroxylation of benzene under mild conditions has a significant theoretical and application value for developing green production process.In this papar,a nano-sized TS-1 was synthesized by step hydrolysis and hydrothermal method,then it was modified by acid treatment and loading metals with different methods including impregnation and in-situ.The surface morphology and physicochemical properties of TS-1 and modified TS-1 were characterized by Fourier transform infrared?FT-IR?spectra,scanning electron microscope?SEM?,transmission electron microscopy?TEM?,nitrogen adsorption-desorption?BET?,ammonia temperature programmed desorption?NH₃-TPD?,X-ray diffraction?XRD?and Ultraviolet-visible diffuse reflectance?UV-vis?.The results reveal that the TS-1synthesized possesses a typical MFI structure with high crystalline,and the Ti⁴⁺species exist in the TS-1 framework.Meanwhile,the TS-1 with large specific surface area(489m² g^-1)is rich in microporous and small particle diameter?50-100 nm?.After treated by hydrochloric acid,the amount of strong acid on the TS-1 surface increased.The MFI structure of TS-1 has been unchanged after loading metals,and the metal particals are uniformly distributed on its surface.Hydroxylation of benzene to phenol and dihydroxybenzene was performed over TS-1 or modified TS-1.The effects of solvent,v?benzene?/v?30 wt%H₂O₂?,holding time,reaction temperature and number of recycles were studied systematacially on conversion and selectivity of phenol/dihydroxybenzene,then the possible reaction mechanism was proposed and thermodynamic parameters were calculated.The results indicate that increasing the ratio of benzene in reactant results in incomplete reaction and low conversion,while the increase of hydrogen peroxide ratio in reactant results in over oxidation of target products.Water is a suitable solvent for its small molecular size,acetone limit the transfer of hydroxyl radicals,and dihydroxybenzene is easily over oxidized to benzoquinone in acetonitrile.The conversion of benzene increased with the increase of holding time under 6 h,while its keep constant after 6 h.With the increase of temperature from 60 ^oC to 65 ^oC,the conversion of benzene increased,but the conversion decreased above 65 ^oC due to the decomposition of H₂O₂.Under the optimized reaction conditions,i.e.v?benzene?/v?30 wt%H₂O₂?=1,water as solvent,0.2 g HCl-TS-1 as catalyst,reaction temperature 65 ^oC,and holding time 6 h,the conversion of benzene is 36.1%,and the total selectivity of phenol and dihydroxybenzene is 100%.After four cycles,the catalyst still maintain a good catalytic activity,the benzene conversion is 21.1%,and the total selectivity of phenol and dihydroxybenzene is 100%.The paper has 35 figures,10 tables and 95 references.