The Study On Hexanol To Hexanal Under Catalytic Oxidation On Modified ZSM-5 Zeolite

Hexanal is an important synthesis intermediate in food and medicine industry.In traditional method,hexanal is obtained by using the strong oxidizer such as potassium permanganate and hypochlorite.However,this method is gradually replaced by other green methods due to high cost and environmental pollution.At present,heterogeneous catalytic oxidation is widely concerned by everyone due to its good oxidation effect,mild reaction conditions and easy recovery of catalysts.Heterogeneous catalyst ZSM-5 molecular sieve and its modified catalyst were prepared in this paper,and molecular oxygen was used as oxidant to synthesize hexanal.The following results are obtained through the characterization of catalyst structure and catalytic performance:(1)ZSM-5 molecular sieves with different silicon-alumina ratio(n(Si)/n(Al))for 20,30,40,and 50,was prepared by hydrothermal method with sodium silicate as the source of silicon and aluminum sulfate as the source of aluminum,ethylamine as template.At catalysis of ZSM-5 molecular sieves,hexanol was catalyzed to hexanal under normal pressure.Results showed that under the reaction conditions(15.00 m L hexanol,0.50 g catalyst,molecular oxygen 25 m L/min,and 120 ℃,8 h),at the catalysis of ZSM-5(40),conversion rate of hexanol,selectivity and yield of hexanal were 12.3%,15.1% and 1.8% respectively.(2)Doping metal Cr and Co to modifiy ZSM-5(40),and catalyst Cr(300)-ZSM-5(40)and Co(300)-ZSM-5(40)were obtained.The catalytic performance of the modified catalyst was tested.The results showed that the catalyst Cr(300)-ZSM-5(40)had better catalytic performance,the conversion rate of hexanol,the selectivity and yield of hexanal were 20.7%,20.1% and 4.2% respectively.It can be seen that ZSM-5(40)after doping Cr improved the selectivity of hexanal significantly.(3)Using metal Cr as metal modifier,it studied the effects of Cr-ZSM-5(D),Cr-ZSM-5(E)and Cr-ZSM-5(S)on catalytic oxidation of hexanol.It was found that different modification methods have great influence on the activity of catalyst at the condition of the same metal modifier.The catalyst Cr-ZSM-5(D)prepared by doping method had better effect on the catalytic oxidation of hexanol.The conversion rate of hexanol,the selectivity and yield of hexanal were 20.7%,20.1% and 4.2% respectively.(4)On the basis of Cr-ZSM-5(D),it researched catalytic performance of different ZnO amounts(1wt%ZnO、3wt%ZnO、5wt%ZnO、7wt%ZnO)of Cr-ZSM-5(D),the experimental results suggested that the conversion rate of hexanol,the selectivity and yield of hexanal were 28.1%,29.4% and 8.3% respectively when ZnO amounts was 3wt%.(5)In the optimization of reaction process conditions,the reaction conditions were as follows: hexanol is 15 ml,catalyst dosing quantity is 0.5 g,the reaction temperature is 120 ℃,the reaction time is 8 h,conversion rate of hexanol,selectivity and yield of hexanal reached 36.3%,33.1% and 12.0% respectively.