Hydrophobically Modified Cr-MIL-101 Cooperated With NHPI For Selective Catalytic Oxidation Of Cyclohexane

Cyclohexanone is an important organic chemical raw material.It is a key intermediate for the production of caprolactam and adipic acid.The market demand at home and abroad is very large.At present,most cyclohexanone is obtained mainly by cyclohexane non-catalytic oxidation process,but this route has some disadvantages,such as the harsh reaction conditions,the conversion of cyclohexane is controlled at 3.5%-4%,selectivity is only about 83%towards cyclohexanol and cyclohexanone,environmental pollution problems still exist.In this thesis,the non-metallic catalyst materials,N-hydroxyphthalimide(NHPI)was selected as the main catalyst,the metal organic framework material Cr-MIL-101 was used as a co-catalyst.In order to modulate the hydrophobic environment of the reaction site,Cr-MIL-101 was modified by post-synthetic silylation modification and in situ methyl modified modification,respectively.Through the synergistic effect of NHPI with hydrophobic modified Cr-MIL-101,realizing the selective oxidation of cyclohexane under mild conditions which was aimed to provide effective technical accumulation for the development of cyclohexane catalytic oxidation.Firstly,NHPI was applied to the cyclohexane oxidation reaction under solvent-free and without assisted catalyst condition.The results of the investigation of the process conditions showed that NHPI could effectively catalyze the selective oxidation of cyclohexane under mild conditions.Under the optimized reaction conditions,the reaction temperature was 120 ?,the oxygen pressure was 0.6 MPa,the amount of catalyst was 6 mol%of the substrate,and reaction time was 2 h,The cyclohexane conversion reached 7.0%and the total selectivity of cyclohexyl hydroperoxide,cyclohexanol and cyclohexanone was 95.0%.Compared to the non-catalytic oxidation technology of DSM company,the conversion rate of cyclohexane is doubled while maintaining the total selectivity unchanged.Secondly,the Cr-MIL-101 metal-organic framework material was prepared by hydrothermal method,then silylation modification of Cr-MIL-101 with chlorotrimethylsilane,and the hydrophobic material TMCS-Cr-MIL-101 was prepared by post-synthesis method.The structure of catalysts was characterized by FT-IR,N2 physical adsorption,etc.,the catalytic performance of each material composited with NHPI in cyclohexane oxidation was evaluated.The results showed that the successfully prepared Cr-MIL-101 as a co-catalyst had a synergistic effect on NHPI in this reaction,especially in the condition of acetonitrile as a solvent,the mole ratio of NHPI to substrate was 8mol%and Cr-MIL-101 to substrate was lwt%,the cyclohexane conversion was reached 16.5%and the total selectivity of cyclohexyl hydroperoxide,cyclohexanol and cyclohexanone was 75.9%at 120 ? for 40 min,under 0.6 MPa oxygen pressure.TMCS-Cr-MIL-101 obtained from silylation modification had certain improvement in stability and hydrophobicity.However,the efficiency of silanation is relatively low,so the catalytic performance has not been significantly improved.Finally,three kinds of methyl hydrophobic modified materials of Cr-MIL-101-CH3 were synthesized in situ by using 2-methylterephthalic acid as ligand,different chromium sources and mineralizers.The structure and hydrophobic properties of samples were characterized by FT-IR,XRD,thermogravimetry.The catalytic performance was evaluated composited with NHPI in cyclohexane oxidation reaction and the effects of the reaction conditions on the catalytic performance were also investigated.The results showed that the thermal stability of Cr-MIL-101-CH3 was significantly higher than Cr-MIL-101.The decomposition temperature was increased from 255 ? to about 360 ?,and the adsorption value of cyclohexane was significantly increased.Catalyst system NHPI/Cr-MIL-101-CH3,under the optimized reaction conditions,acetonitrile as solvent,the mole ratio of main catalyst NHPI to substrate was 6 mol%,Cr-MIL-101-CH3 to substrate was lwt%,the temperature was 110 ?,the oxygen pressure was 1.4 MPa,and reaction time was 30 min,the conversion of cyclohexane was up to 22.3%,the total selectivity of cyclohexyl hydroperoxide,cyclohexanol and cyclohexanone was 85.1%.