Study On Liauid-phase Catalytic Oxidation Of Cyclohexylbenzene

Phenol and cyclohexanone are important chemical raw materials,and widely used in the production of bisphenol A,phenolic resin,caprolactam,adipic acid and other fine chemical products.The new process of producing phenol and cyclohexanone through the oxidation of cyclohexylbenzene will have a good application prospect.However,liquid-phase catalytic oxidation of cyclohexylbenzene has met the problem of low oxidation efficiency,and it is urgent to develop an efficient catalyst for the reaction.In this paper,liquid phase catalytic oxidation of cyclohexylbenzene into 1-phenylcyclohexyl hydroperoxide(CHBHP)was studied using NHPI and B as the catalyst system in the glass bubble reactor with solvent and solvent-free system,respectively.Then,the decomposition reaction of CHBHP was conducted using sulfuric acid as a catalyst.Main results were summarized as follows:Firstly,NHPI and B were used to catalyze liquid-phase oxidation of cyclohexylbenzene in different kinds of solvents such as ethanol,n-propanol,isopropanol,acetic acid,acetonitrile,ethyl acetate and benzene so on.It was found that solvents had great effects on the reaction.The influence of solvents embodied in the following aspects:(i)Protic solvent and NHPI easily formed intermolecular hydrogen bonds,resulting in the increase of NHPI O-H bond dissociation energy,which was not conducive to initiation of radical reactions.(ii)Different polar aprotic solvents had different solvency to NHPI,which led to diverse catalytic oxidation of cyclohexylbenzene.The more polar,the more favorable the free radical reaction.Secondly,effects of different catalysts on the liquid-phase oxidation of cyclohexylbenzene were studied with acetonitrile as the solvent.We could make the conclusion that the catalytic system composed of NHPI and B could obviously accelerate the rate of cyclohexylbenzene oxidation and had a good synergistic catalytic effect.Then,cyclohexylbenzene initial concentration,NHPI dosage,B concentration,and reaction temperature on the oxidation of cyclohexylbenzene were discussed using NHPI and B as the catalyst system in acetonitrile.Through the single-factor experiments,suitable reaction conditions were found as:1:5 mass ratio of cyclohexylbenzene and acetonitrile,NHPI dosage of 15 mol%,B concentration of 100 ppm,reaction temperature of 75?.Kinetics model of cyclohexylbenzene oxidation was carried out under the condition of liquid-gas mass transfer resistance above oxygen flow rate of 60 mL/min.It was found that oxidation of cyclohexylbenzene was the second order reaction,the apparent activation energy was 42.24 kJ/mol,and the frequency factor was k0=2.71×106 L·mol-1·h-1.Thirdly,effects of NHPI dosage,B concentration,reaction temperature and oxygen flow rate on the oxidation of cyclohexylbenzene were studied using NHPI and B without any solvent.It was found that 46.89%CHB conversion and 35.65%CHBHP yield were obtained under the following affable reaction conditions:NHPI dosage of 2 mol%,B concentration of 35 ppm,reaction temperature of 100 ?,oxygen flow rate of 100 mL/min.Then we made the conclusions that NHPI and B existed an optimal ratio and B could react with CHBHP to reduce CHBHP selectivity.Finally,decomposition reaction of CHBHP was a reversible reaction and had a characteristic of high heat release with,sulfuric acid as the catalyst.Effects of sulfuric acid dosage,CHBHP initial concentration and initial experimental temperature on the decomposition reaction of CHBHP were discussed under the single-factor experiments.It was found that 95.47%CHBHP conversion,78.68%cyclohexanone yield,87.14%phenol yield and 3.95%1-phenylcyclohexene yield were achieved under the following proper reaction conditions:3 mol%sulfuric acid(0.3 mol/L H2SO4),CHBHP initial concentration of 0.08 g · mL-1,and initial experimental temperature of 25 ?.