Liquid-phase Catalytic Oxidation Of Cyclohexanone To Adipic Acid

Adipic acid (AA) is one of most important aliphatic dicarboxylic acids with wide application, which is mainly used in the manufacture of nylon-66with increasing demand worldwide year by year. Currently,"two-step cyclohexane oxidation" is the primary process for adipic acid industrial production. Cyclohexane is firstly oxidized into cyclohexanol and cyclohexanone mixture (KA oil) by air, and then KA oil is oxidized into adipic acid by nitric acid. High conversion and selectivity are achieved by KA oil oxidation. However, equipment are seriously corroded by nitric acid and a large amount of NOx are emitted which occupies10%of world NOx emission. Up to now, green synthesis of AA is still a technology challenge worldwide. Therefore, it is highly desirable to study and develop environmentally friendly methods for the manufacture of AA.Based on this, without any additive and initiator, liquid-phase catalytic oxidation of cyclohexanone to AA has been investigated in600ml stainless autoclave without mass transfer effect, using molecular oxygen, cyclohexane as oxidant and solvent respectively.Through screening series of cobalt catalysts, the results indicate cobalt complex (II) has high catalytic activity and selectivity. Oxidation of cyclohexanone to AA by cobalt complex is firstly carried out in the paper. The effects of solvent and NHPI on cyclohexanone oxidation have been briefly discussed. Reaction conditions (reaction time, reaction temperature, initial concentration of cyclohexanone, catalyst concentration and oxygen pressure) on cyclohexanone oxidation have been also systematically investigated. The results indicate that the optimum conditions are as follows:reaction temperature110℃. oxygen pressure0.6MPa, initial concentrati-on of cyclohexanone4.84mol/L, catalyst/cyclohexanone100ppm (mole ratio). Under optimum conditions, conversion of cyclohexanone and yield of adipic acid are up to18%and53.2%respectively for60min.Co-substituted aluminophosphate molecular sieve (CoAPO-5) is synthesized by hydrothermal method using triethylamine as organic template agent, diaspore as aluminium source, phosphoric acid as phosphorus source and cobalt acetate as cobalt source. The physicochemical properties of CoAPO-5are investigated by AAS, XRD, FT-IR, SEM and particle size distribution. Oxidation of cyclohexanone to AA by CoAPO-5is then carried out. The result shows CoAPO-5has an excellent catalytic performance on the oxidation of cyclohexanone to AA:conversion of cyclohexanone and yield of adipic acid are up to36.6%and54.08%respectively under the conditions of reaction temperature110℃, CoAPO-5/cyclohexanone=1/50(mass ratio),air pressure0.72MPa, after reaction7h.