Selective Hydrogenation Of Phenol To Cyclohexanone

Now cyclohexanone is widely used in fiber, pesticides, pharmaceuticals, organic solvents and industrial coatings field as chemical material. Expecially, it is used to produce the caprolactam and adipic acid which are the important intermediates to synthesize nylon-6 and nylon-66. In this paper, the composite catalyst of Pd/C-Lewis, the composite catalyst of Pd/C-Heteropolyacid and the ionic liquid stabilized Pd nanoparticles were applied in the hydrogenation of phenol in order to solve the low conversion and selectivity, and the problem of recycling hardly and short catalyst life.The preparation of cyclohexanone from phenol selective hydrogenation was studied in the composite catalyst of Pd/C-Lewis. The results showed that the composite catalyst had high catalytic activities. Under the optimum conditions of phenol 0.1 g, Pd/C 0.06 g, ZnCl2 0.02 g, solvent CH2Cl2 10 mL, hydrogen pressure 1.0 MPa, reaction time 5 h, and reaction temperature 100 ℃, the conversion of phenol was closed to 100%, and the selectivity of cyclohexanone reached 97.8%. The catalyst was reused for 6 times without obvious decreasing the selectivity, and the conversion of phenol decreased to 65.6%. The reason for this result may be that the catalyst coked easily under long term high temperature and pressure, so the catalyst active components lost.The composite catalyst of Pd/C-heteropoly acid was applied in the preparation of cyclohexanone from phenol selective hydrogenation. The results exhibited that the composite catalyst of Pd/C-heteropolyacid had good catalytic performance. Under the optimum conditions of phenol 0.1 g, Pd/C 0.005 g, heteropoly acid 0.05 g, solvent CH2Cl2 10 mL, hydrogen pressure 1.0 MPa, reaction time 3 h, and reaction temperature 80 ℃, the conversion of phenol was near 100%, and the selectivity of cyclohexanone reached 93.6%. Compared to the composite catalyst of Pd/C-Lewis, the composite catalyst of Pd/C-heteropoly acid could catalyze the same quality phenol using fewer Pd/C, and heteropolyacid showed higher catalytic activity than Lewis acid. The conversion of phenol decreased to 71.1% and the selectivity did not obviously decrease when it was reused for 6 times. That may be due to the catalyst coked and the loss of the catalystic center under long term high temperature and pressure.Ionic liquid with polyethylene glycol chain and the ionic liquid stabilized Pd nanoparticles were synthesized and characterized. The results showed that the target ionic liquid was synthesized and the molar ratio of ionic liquid to Pd affected the nanoparticles size. When the the molar ratio of IL to Pd was 100:1, the nanoparticle size of Pd was evenly distributed in the ionic liquid and its size was at least 2.86 nm. The results showed that the synsthesized IL had a good stable performance for the nanoparticle. The preparation of cyclohexanone from phenol selective hydrogenation was studied in the ionic liquid stabilized Pd nanoparticles catalyst with ZnCl2. Under the optimum conditions of phenol 0.1 g, ILMPEG-750/Pd(100:1) 0.5 g, n(ILMPEG-750/Pd): n(ZnCl2)=12, toluene 1.0 g, n-heptane 0.25 g, reaction temperature 100 ℃, reaction time 5 h, hydrogen pressure 2 MPa, the catalyst system exhibited good catalytic performance, the conversion of phenol was nearly 90.4%, and the selectivity of cyclohexanone was 94.5%. It was also found that the catalytic system had a good thermoregulated performance with solvents in the process of reaction, which was convenient for the separation and recycling the catalyst. The reusability of the catalyst was examined, and its conversion was 87.2% and selectivity reached 95.4% when it was reused for 6 times. The results showed that ILMPEG-750/Pd-ZnCl2 had good reusability.In summary, the composite catalyst of Pd/C-Lewis and the composite catalyst of Pd/C-heteropoly acid exhibited good conversion and selectivity during the hydrogena-tion of phenol to cyclohexanone, and nano-metal catalytic system stabilized by the ionic liquid not only showed the good catalytic performance, but also overcame effectively the shortcomings of the conventional catalyst separation, which provided effective support for the integration of reaction-separartion of phenol hydrogenation to prepare cyclohexanone.