| Benzaldehyde, as an important organic intermediate, wildly employed in dyestuff, medicines, food additives, perfumery, etc. Traditionally, benzaldehyde is achieved by chlorization-hydrolysis of toluene or direct oxidation of toluene. These technologies require high temperature, high pressure and gives low yield selectivity. The selective oxidation of benzyl alcohol to benzaldehyde, with hydrogen peroxide as oxidant, was received widespread attention, because of its simple technology and environment-friendly process. The Fenton system, which uses hydrogen peroxide as oxidant, has been wildly used in environmental chemistry.In the thesis, Fenton system was studied, and the system was applied and promoted to the oxidation of alcohols and olefins.A new reasonable method to raise the selectivity of oxidizing alcohol catalyzed by Fenton system was built, which can be easily achieved by adding proper additives. Instructed by this method, both the selectivity and conversion can be improved by adding NHPI to the Fenton system. And a possible mechanism for the benzyl alcohol oxidation was proposed. Based on this, subsequent optimizations of Fenton/NHPI system were performed to seek an improved process. The Fenton/NHPI system is cheaper, safer, more green and effective, compared with the traditional catalyst. Then, recycling experiment was performed, which not only fully confirmed the reliability of those results from laboratory experiment, but also established the base for the related research on industrialization. The purposes of this thesis are not limited in efficiently preparing benzaldehyde from benzyl alcohol. The oxidation of different alcohols and styrene were performed, to investigate its generalizability.The first part of the thesis concerns the effect of the additives to the Fenton system, such as inorganic salt, ionic liquid, phase transfer agent and active radical scavengers. And before studying the effect, the reaction temperature, time, oxidant amount were investigated. The obtained results indicated that the conversion were reduced by adding inorganic salt, ionic liquid or phase transfer agent to the reaction system. However, adding NHPI to the Fenton system, the selectivity can be obviously improved without the cost of catalytic activity. Hydroxybenzyl alcohol was found during the studying of reaction products and a possible mechanism was presented including the water-phase and oil-phase oxidation. This mechanism can be successfully used to explain why high selectivity and conversion were achieved at the same time. Based on20mmol benzyl alcohol, using the condition of catalyst2.5mol%, NHPI2.5mol%,4.5ml H2O2and adding by the speed of0.2ml/min, the conversion of benzyl alcohol reached36.66%, the selectivity of benzaldehyde and benzoic acid over99%, and the selectivity for benzaldehyde was93.36%. Considering industrial applications, the reaction was magnified3.4times,6.7times,13.4times and53.4times. The results indicated that the conversion and selectivity were all good, and the utilization rate of antioxidants was improved. The NHPI can be simply recycled by extraction separation and reduced pressure distillation.The main content of this research is improving the selectivity by green chemistry principle. The approach focused on suitable co-catalyst. On experiment, the aims of this research are design and application of powerful, cheap, green and easy to recycle catalysts. The new catalytic system not only shows good catalytic activity and high selectivity in oxidation of benzyl alcohol, but also it provides more choice for the research in oxidation of other alcohols. |
PDF Full Text Request