Study On The Direct Hydrogenation Of Phenol To Cyclohexanone

Cyclohexanone is widely used in the fields of fibers,pesticides,medicines and organic solvents,and it is also a kind of important intermediate for the preparation of nylon-6 and nylon-66.At present,hydrogenation and dehydrogenation of phenol is the main process route on the production of cyclohexanone.This process includes two aspects:1)complete hydrogenation of phenol to prepare cyclohexanol;2)dehydrogenation of cyclohexanol to prepare cyclohexanone.However,this method has the disadvantages of long route,high energy consumption and low yield,all the shortcomings above restrict the development of China's cyclohexanone industry.Therefore,a new directional hydrogenation catalytic technology has extremely important theoretical and realistic significance,which not only can realize direct hydrogenation of phenol with high conversion rate to directly generate cyclohexanone,but also can realize self-separation,recovery and reuse of the catalyst after the reaction.?1?Through the impregnation method,the metal hydrogenation active center?Pd,Pt,Ni or Ru?is supported on the M-MCM-41 carrier modified with L-acid metal?Sn,Zr,Al,Mo or Zr-Mo?to prepare acidic hydrogenation catalyst.XRD,XPS,TEM,NH₃-TPD,N₂-adsorption desorption and other characterization results showed that metal with lewis acidic and hydrogenation active center had good stability and dispersion on the carrier MCM-41,and their introduction had not break the good channel structure and long-range order of MCM-41.The synthetic catalytic system was used to the directional hydrogenation of phenol to prepare cyclohexanone.The results show that the catalyst Pd/Zr-MCM-41 has good catalytic performance.When the optimal reaction conditions of 0.1 g of phenol,Pd/Zr-MCM-41?the loading amount of Pd and Zr doping amount are 20%and the molar ratio Si/Zr=30?0.08 g of catalyst,10 mL of dichloromethane solvent,100 ^oC of reaction temperature,1.0 MPa of hydrogen pressure,and 5 h of reaction time,the conversion rate of phenol and the selectivity of cyclohexanone are 100%and 94.5%,respectively,and there's no by-product cyclohexane;The introduction of metal with lewis acidic active promoted the non-coplanar adsorption of phenol on the carrier,and the enol reaction intermediate forms a complex,and it was also improves the residence time of the enol intermediate,which is beneficial to the formation of cyclohexanone;The catalyst reuse performance research results show that:after the catalyst recycled 5 times,the selectivity of cyclohexanone fell to 80.7%.?2?The metal with hydrogenation active center?Pd,Pt,Ni or Ru?was supported on a pure silicon MCM-41 carrier synthesized by ultraviolet light assisted,and then hydrogenation catalyst with hydroxyl radicals was prepared by the impregnation method based on the carrier above.XRD,XPS,TEM,NH₃-TPD,N₂-adsorption desorption,hydroxyl radical detection and other characterization results show that the introduction of hydroxyl radical did not destroy the good pore structure and long-range order of MCM-41,and increased specific surface area and pore volume.The synthetic catalytic system was used to the directional hydrogenation of phenol to prepare cyclohexanone.The results showed that the catalyst Pd/MCM-41 had good catalytic performance.Under the optimal reaction conditions:0.1 g of phenol,Pd/MCM-41?Pd loading was 20%?catalyst 0.08 g,10m L of solvent dichloromethane,100 ^oC of reaction temperature,1.0 MPa of hydrogen pressure,5 h of reaction time,phenol conversion rate and cyclohexanone selectivity were100%and 94.1%,respectively.The introduction of hydroxyl radicals improves the selectivity of the carrier,improves the non-coplanar adsorption of phenolic hydroxyl groups which was conducive to the formation of enol intermediates,and it was also beneficial to the adsorption of phenol,the desorption of cyclohexanone and improvement of the selectivity of cyclohexanone;The results of the reuse performance of the catalyst showed that there was no significant change in the conversion rate of phenol after the catalyst was used for 5 times,and the selectivity of cyclohexanone was reduced to 71.0%.?3?The metal hydrogenation active center?Pd,Pt,Ni or Ru?was loaded on the Zr-MCM-41 carrier,which was synthesized by ultraviolet light.XRD,XPS,TEM,NH₃-TPD,N₂ adsorption desorption and other characterization results showed that active metal with lewis acidity and catalytic hydrogenation activity have good stability and dispersion on MCM-41,and the introduction of active metal did not destroy the good pore structure and long-range order of Zr-MCM-41;The introduction of hydroxyl radicals did not destroy the good pore structure and long-range order of MCM-41,and increased the specific surface area and pore volume of MCM-41.The synthesized catalytic system was used to catalyze the directional hydrogenation of phenol to produce cyclohexanone,and it was found that the catalyst Pd/Zr-MCM-41 had good catalytic selectivity.When the ultraviolet light exposure time was 3 h,the phenol was 0.1 g,the Pd/Zr-MCM-41?Pd loading and Zr doping amount were 20%and molar ratio Si/Zr=30?catalyst was 0.08 g,the solvent methylene chloride was 10 mL,reaction temperature was 100 ^oC,hydrogen pressure was 1.0 MPa,reaction time was 5 h,phenol conversion rate and cyclohexanone selectivity could reach as high as 99.6%and 91.5%respectively.L-acid metal active center and hydroxyl group introduced can promote the non-coplanar adsorption of phenol on the carrier,and form a complex with the enol reaction intermediate,improve the residence time of the enol intermediate,which is beneficial to the formation of cyclohexanone.In conclusion,Lewis acid modified and hydroxyl radical modified hydrogenation catalysts to catalyze the hydrogenation of phenol to produce cyclohexanone were synthesized.Both L-acid modified and hydroxy-modified catalysts has good and stable mesoporous structure and exhibited good catalytic performance.At the same time,the catalytic performance of the hydrogenation catalyst prepared by the simultaneous modification of Lewis acid and hydroxyl radicals for phenol hydrogenation were studied.It has been found that the simultaneous modification of L acid and hydroxyl did not achieve a better catalytic results.This article provides a new idea for the cooperative catalysis of L-acid modification and hydroxy modification,and plays a key role in the development of friendly catalysts and reasonable reduction of energy consumption.