Preparation And Characterization Of Hydrophobically Modified MCM-41Immobilized Cosalen And Its Selective Oxidation Of Cyclohexane

Cyclohexane selective oxidation to prepare cyclohexanol and cyclohexanone is always achallenge in the field of petrochemical technology. How to develop a highly efficient, mildcatalytic oxidation reaction system is still the research focus. In our previous work,N,N-Bis(salicylidene)ethylenediiminocobalt (Cosalen) with carrying oxygen function asactive components, immobilized on NaY, MCM-41molecular sieve carrier, respectively.Which used as catalyst for the cyclohexane oxidation with molecular oxygen, and the resultsshow that hydrophobic molecular sieve MCM-41is more suitable as the carrier thanNaY,which is favor of forming the product cyclohexanol and cyclohexanone. Thefollowing work try to enhance the hydrophobic performance for MCM-41by methylmodification, aims to make the polar product adsorb from the catalyst timely, avoiding thedeep oxidation of cyclohexanol and cyclohexanone. The results show that the increaing theconversion of cyclohexane can maintain a higher selectivity of cyclohexanol andcyclohexanone at the same time. This thesis based on the aforementioned work process afurther study on the preparation and characterization of MCM-41carrier’s hydrophobicmodification, after immobilized with Cosalen for cyclohexane selective oxidation, discussthe relationship between the structure and the properties of the catalyst.Firstly, the “two-step” method was used for amino-functionalized and methylhydrophobic modification of MCM-41with silanizing agent γ-aminopropyltriethoxysilaneand methyltriethoxysilane, then Cosalen was immobilized on the modified carrier. Thepreparation conditions of catalyst were investigated in detail. the N2physical adsorption,Elemental analysis, XRD means were used to evaluate the modified effect. The results showthat: the Soxhlet extraction can washing clean the remained agent on the carrier aftermodification; Only use the MCM-41molecular sieve with pore diameter3.46nm as carriercan matain the mesoporous structure of the carrier after modification and immobilization;The small polar solvent hexane had no significant effect on improving the value of porestructure during the modification for carrier. The higher Co content can be obtained fromimmobilization under the reflux temperature than the room temperature.The results ofcatalytic oxidation of cyclohexane showed that the larger the value of surface areas and porevolume, the higher the activity of the catalyst. Under the similar pore structure of thecatalyst, the higher Co content made the better catalytic performance. The catalyst withlarger surface areas and pore volume was used under the reaction conditions: initial oxygenpressure0.8Mpa, under temperature130℃for2h, the amount of catalyst0.10g,tert-butyl hydroperoxide0.02g, the conversion of cyclohexane reached12.08%and the selectivity ofcyclohexanol and cyclohexanone was up to71.81%.As for the effect on the carrier resulted from the long reaction time and much stepprocess for the “two-step” method, double function silane reagent3-aminopropylmethyldiethoxy silane was chosen for the amino-functionalized and methyl hydrophobicmodification of MCM-41by “one-step” method. Cosalen was immobilized after themodification. The influence of the concentration of the silane agent was investigated. Thecontent of N,C were analysized by the means of element analysis. The number of the Si-OHof the carrier reacted with silane agent was3.0/nm2by calculation. The proper modificationconditions were as follow: the concentration of silane agent4.0mmol/g, under thetemperature100℃for4h, toluene as solvent. The N2physical adsorption and X-raydiffraction were used to characterize the structure of the catalyst and the static adsorption,TG analysis were adopted to evaluate the degree of carrier’s hydrophobicity. The resultsshowed that the extent of damage for carrier brought from "one-step" modification was lessthan "two-step" method; The carrier’s hydrophobic performance was improved after beingmodificated by amino and methyl groups, which was favor of increaing the selectivity ofcyclohexanol and cyclohexone in the catalytic cyclohexane oxidation.