Study On The Synthesis Of O-phenylphenol From Cyclohexanone

O-phenylphenol(OPP)is a fine chemical product which is widely used for the preparation of bactericides,preservatives,surfactants,intermediates of dyes,plastic stabilizers and fire retardants.Using cyclohexanone as a starting material,OPP can be prepared by a two-stage process comprising the condensation of cyclohexanone to its dimer and subsequently dehydrogenation of Dimer to OPP.This process is simple,economic and industrialization.In this thesis our focus is on the new preparation method of the dehydrogenation catalyst and the influence of alkali-metal salts on the catalytic performance.Supported noble metal catalysts were usually prepared by impregnation,ion-exchange process,coprecipitation,Sol-gel method etc.However,these methods often have the same drawbacks:(1)complicated procedure,non-green to environment and many influencing factors;(2)bad catalytic stability.These problems might affect the overall performance of the catalyst.In this thesis,we establish a novel method to prepare dehydrogenation catalyst.The assembled metal catalyst was obtained by capturing metal nanoparticles directly to the supports.First,The metal nanoparticles was produced by decomposing the organometallic Pt2(dba)3 while hydrogen as reductant,propylene carbonate used as solvent.Then,the assembled Pt catalyst was prepared using the support to capture Pt nanoparticles directly.Compared with traditional methods,this process is simple,easy to operate and with high reproducibility.The catalyst prepared by this method showed good catalytic activity and stability for the dehydrogenation of dimer.In this thesis,catalysts applied to the two-step reactions comprising cyclohexanone self-condensation and dimers dehydrogenation had been studied systematically.Our work especially emphasis on the assembled nano-catalysts used for the synthesis of OPP by catalytic dehydrogenation of cyclohexanone dimer.The preparation conditions.of the catalyst,preparation factors and the process conditions of the catalytic dehydrogenation were investigated in detail.Main points of this dissertation are listed as follows.1、Acidic alumina were used for the synthesis of dimer--cyclohexanone by cyclohexanone self-condensation.Effects of reaction temperature,amount of catalyst and reaction time on self-condensation of cyclohexanone were investigated.The one-pass conversion of cyclohexanone reached 80.2%and the selectivity to dimer was 99.9%under the optimal reaction conditions of reaction temperature 150℃,amount of catalyst 10%(wt)and reaction time 5 h.Compared with conventional liquid acid catalyst,acidic solid catalyst featured good catalytic activity and selectivity.As a acidic solid catalyst,alumina catalyst has the perspective for commercial application thanks to the high catalytic efficiency,simple after-treatment of the products and friendly with environment.2.The Assembled Pt dehydrogenation catalyst was prepared by adsorption method using Pt2(dba)3 as precursor and K-salts as promoters to improve the catalytic performance.Factors that influence the performance of the dehydrogenation catalyst were investigated including the properties of the support,the type and amount of the promoters,the amount of platinum supported and the preparation method of the catalyst.The results showed that γ-Al2O3 should be selected as support.Using K2SO4 as promoter,the best amount of the promoter was 5%(based the quality of the support).At 4MPa to decompose the Pt2(dba)3,with the amount of supported Pt of 0.5%,the catalyst showed highly activity and selectivity.The yield of OPP reached 90.5%with the optimization of the reaction conditions at T=380～390 ℃,LHSV=0.48 h-1,H2=10～20 ml/min.3、Assembled Pt-K2SO4/Al2O3 catalyst prepared in this research behave very well in the stability experiment.It kept high activity over 100 hours in the reaction temperature range from 380℃ to 395℃.The selectivity of OPP declined gently and the average yield of OPP reached 85%in this period.The cause of catalyst deactivation was due to Pt metal particles sintering and agglomeration at high reaction temperature.But the decline of catalytic activity was mainly due to surface coating by carbonaceous mass formed in reaction.The deactivated catalyst could be reactivated by surface carbon combustion in oxygen atmosphere.In conclusion,acidic alumina catalyst featured good catalytic activity and selectivity for the synthesis of dimer-cyclohexanone by cyclohexanone self-condensation.As a acidic solid catalyst,alumina catalyst has the perspective for commercial application thanks to the high catalytic efficiency,simple after-treatment of the products and friendly with environment.The obtained facts show that there are many advantages such as simple、green、easy to operate and with high reproducibility for adsorption method.The catalyst prepared by this method show good catalytic activity and selectivity for the dehydrogenation of dimer.Those might be provided new opportunities for the preparation of OPP.