Decomposition Of Cyclohexyl Hydroperoxide Catalyzed By Cobalt Supported On MCF Mesoporous Molecular Sieves

Cyclohexanone is an important organic chemical raw material for the production of chemical products such as hexamethylenediamine and caprolactam.In the industry,cyclohexanone is mainly produced by non-catalytic oxidation of cyclohexane.First,cyclohexane is oxidized to obtain an important intermediate,cyclohexyl hydroperoxide?CHHP?,and then catalyzed the decomposition of CHHP to give a mixture of cyclohexanol and cyclohexanone.The traditional CHHP alkali-catalyzed decomposition process can only obtain a total selectivity of 87%of cyclohexanol and cyclohexanone,and produces a large amount of waste alkali liquor,causing environmental pollution.Therefore,the development of a highly efficient green decomposition process plays an important role in improving the production efficiency of cyclohexanone.Molecular sieve supported transition metal catalysts have high catalytic activity and alcohol ketone selectivity in CHHP decomposition reaction,however,the loss of metal components is widespread.Therefore,how to suppress the loss of active metal components becomes the key that needs to be solved to improve the stability of the decomposition catalysts.This article will address the problem of loss of active metal components from the following three parts.Firstly,using mesoporous silica foam?MCF?as a carrier,XCo-MCF?X=4%,8%,10%,20%?with different cobalt content were prepared by in-situ synthesis method.The structureof the catalysts were characterized by means of N₂ physical adsorption,FT-IR,UV-Vis and so on.The catalytic performance and stability of the obtained catalysts in the decomposition reaction of CHHP were investigated.The results showed that the active component was mainly in the form of tricobalt tetraoxide.Co-MCF catalysts with different cobalt contents had good initial catalytic performance in decomposition reaction of CHHP,the CHHP conversion is higher than 90%,and selectivity of cyclohexanol and cyclohexanone is higher than 100%.Among them,8%Co-MCF has the best catalytic activity,CHHP conversion rate reached 96%,selectivity of cyclohexanol and cyclohexanone was 77.5%and 53.5%,respectively.The total selectivity of cyclohexanol and cyclohexanone was over 100%may be due to oxidation of small amount of cyclohexane or the esters in the reaction system hydrolyzed to cyclohexanol.After four times recovery,the CHHP conversion was 95%catalyzed by the 8%Co-MCF,and the catalytic activity was basically maintained stable,but the catalytic activities of other catalysts reduced to some extent.The results of ICP showed that the active components of cobalt catalysts were lost to different extents.When the loading amount of cobalt reached 20%,the loss rate of the active component was effectively inhibited.Secondly,the Schiff base cobalt metal complex Cosalen was highly dispersed and supported on the MCF carrier by in-situ calcination method and chemical grafting method,respectively.The catalysts were characterized and evaluated in decomposition reaction of CHHP.The results showed that the cobalt catalysts had good initial catalytic performance in the decomposition reaction of CHHP.The G-Cosalen@MCF catalyst prepared by grafting method catalyzed the decomposition of CHHP with the conversion rate of 97%,and the selectivity of cyclohexanol and cyclohexanone were 80.5%and 40.8%,respectively.After four recyclings,the conversion rate remained at 95%.The active components of G-Cosalen@MCF-c and S-Cosalen@MCF-c after roasting mainly existed in the forms of CoO,and the CHHP conversion rates were 95.5%and 97%in the decomposition reaction,respectively.After four recyclings,the CHHP conversion rate decreased to 89%.Finally,silica-coated core-shell type catalyst Co-MCF@Silicalite-1 was prepared by hydrothermal synthesis using Co-MCF as the core,and the catalyst was applied to the decomposition reaction of CHHP.The catalytic activity of the core-shell catalyst was lower than that of Co-MCF,Co-MCF@Silicalite-1-I prepared by dynamic crestallization and Co-MCF@Silicalite-1-II prepared by static crestallization had CHHP conversion rates of 62.3%and 70.9%,respectively.When the amount of Co-MCF@Silicalite-1-I catalyst increased to0.2g/10mL cyclohexane oxidizing solution,the conversion rate of CHHP reached 82.9%.After four times recovery,the catalytic activity decreased seriously.The reason for this phenomenon may be due to the small pore size of the silica shell,which affects the diffusion of the reactants and the contact of the active components.The reaction product easily blocks the pores,resulting in a drop in catalytic performance.