Studies On The Oxidation Process Of Diethylamine To Diethylhydroxylamine Over Hollow Titanium Silicalite Sieves And On The Machanism Of Side Reactions

The oxidation of DEA to DEHA catalyzed by titanium silicalite seives is an easy operation, green and friendly process. However, the excessive oxidation of DEHA is the vital problem for such process. In this study, the catalytic oxidation of DEA to DEHA in HTS/H2O2 system has been investigated systematically. The research contents mainly consisted of three parts. Firstly, the effects of various conditions such as temperature, reaction time, solvents and catalyst on the reactions were investigated. Secondly, based on the accumulated experimental data and with the help of characterization techniques of electron paramagnetic resonance(EPR), etc., the mechanisms of the main and side reactions in oxidation process of DEA over HTS were analyzed. Thirdly, the deactivation and regeneration of HTS catalyst in the oxidation reaction of DEA were explored, and the mechanism of catalyst deactivation was dissected by means of common charaterization methods. In summary, the key conclusions are deduced as follows:(1) The proper reaction conditions for catalytic oxidation of DEA to DEHA in HTS/H2O2 system were found as:temperature 60 ℃, hydrogen peroxide to be added into the reaction system continuously and slowly, and CH3OH suitable to be solvent. The preferable molar ratio of n(DEA):n(H2O2) could be controlled bewteen 1.0 to 1.1. Under the conditions of 0.50g HTS catalyst,0.10 mol DEA,20 mL solvent and 1.5 h reaction time, the gas yield of DEHA reached 80.7%.(2) In this catalytic reaction system, the deep oxidation of DEHA might mainly go through three pathways:the first was the direct oxidation of DEHA by free H2O2 to form nitrones, which was the primary reason for the excessive oxidation of DEHA; the second was the formation of peroxide-titanium active centers over HTS/H2O2, which could catalyze not only the oxidation of DEA to DEHA, but also the oxidation of DEHA to nitrones to cause side reactions; for the third, the results of EPR characterization and Fenton-like experiments indicated that OH radicals played a important role in side reactions, giving a subsidiary effect on the excessive oxidation of DEHA.(3) The study of catalyst deactivation and regeneration showed that the activity of HTS catalyst would decrease significantly after recycling 8-10 times in the batch process. After reusing 13 times, the catalyst activity descended to 81.3% of the fresh HTS catalyst. The deactivated catalyst could be regenerated by high-temperature calcination and solvent washing. The activity of the regenerated HTS could almost return to the same level of fresh HTS catalyst. With the characterizing by TG, NH3-TPD, BET and XRD, the mechanisms of catalyst deactivation in the oxidation process of DEA to DEHA were described to suggest that the reversible deactivation of HTS was mainly caused by pore blocking and active sites covering.