Study On The Preparation Of Cyclohexanone Oxime From The Liquid-phase Catalytic Oxidation Of N-methylcyclohexylamine With Molecular Oxygen

Caprolactam is an important raw material for the production of nylon 6,and cyclohexanone oxime is a significant intermediate for the production of caprolactam.The current methods for preparing cyclohexanone oxime in industry mainly include:“cyclohexanone-hydroxylamine”and“cyclohexanone ammoximation”.There are many problems such as low conversion of cyclohexane in per pass,long industrial route,low atomic utilization,high energy consumption and serious environmental pollution.In this work,cyclohexanone oxime was prepared from the liquid-phase aerobic oxidation of N-methylcyclohexylamin in the presence of catalyst employing dioxygen as a green oxygen source and acetonitrile as the solvent.The available reactant N-methylcyclohexylamine can be prepared by the reaction of methanol,ammonia and cyclohexene,and the by-product such as methanol also can be recycled.The advantages of this one-step process include the mild conditions and high atomic utilization.It is a new clean route for the preparation of cyclohexanone oxime.The main research conclusions are as follows:First,the catalytic performance of transition metal oxides and molecular sieves on the reaction were investigated.It was found that anatase Ti O₂played a preferable catalytic role in the process and the reaction conditions were optimized.The results showed that the conversion of raw materials was 40.3%and the selectivity of cyclohexanone oxime was 61.0%under the present reaction conditions:the reaction temperature was 100 ^oC,reaction time was 4 h,reaction pressure was 1.0 MPa,acetonitrile was 10g and catalyst was 0.3g.The stability of anatase Ti O₂in the oxidation reaction was studied,and it still maintained a good catalytic performance after recycling 5 runs.Secondly,the supported Ti O₂catalyst with different loading was prepared and the characterization techniques were tested such as BET,XRD,FT-IR,XPS etc.The results showed that the 30%Ti O₂/MCM-41 supported catalyst prepared by the sol-gel method exhibited a better catalytic performance,and the reaction conditions were optimized.It showed that the reaction temperature was 90 ^oC,reaction time was 4 h,reaction pressure was 1.0 MPa,acetonitrile was 10 g and the catalyst was 0.3g.The N-methylcyclohexylamine conversion was 45.9%and the selectivity of cyclohexanone oxime was 69.1%,the selectivity of the main by-product cyclohexylacetamide was 18.9%under the optimal reaction conditions.Simultaneously,the stability of the supported 30%Ti O₂/MCM-41 catalyst was investigated.It was found that the catalyst still possessed a catalytic performance after five runs,Finally,a supported bifunctional WO₃catalyst was prepared by the impregnation method.The results showed that 10%WO₃/Al₂O₃had the superior catalytic performance and the reaction conditions were optimized.The results showed that the reaction temperature was 90 ^oC,reaction time was 4 h,reaction pressure was 1.0 MPa,acetonitrile was 10 g and the catalyst was 0.3 g.The reactant conversion was 59.7%and the selectivity of cyclohexanone oxime was 70.7%,the selectivity of the main by-product cyclohexylacetamide is 17.5%under the optimal reaction conditions.It was confirmed that WO₃acted as activating molecular oxygen and the surface hydroxyl groups of?-Al₂O₃were responsible for the adsorption activation of N-methylcyclohexylamin.Finally,the stability of the supported 10%WO₃/Al₂O₃catalyst was also investigated,the conversion and the selectivity were basically unchanged after five runs.In this work,one-step catalytic oxidation of N-methylcyclohexylamin to cyclohexanone oxime had been developed employing dioxygen as the green oxygen source,and this method has high atomic utilization,which provides the significant theoretical foundation and the technical basis.