Study On Preparation Of Sn-Beta Molecular Sieve And Its Catalytic Performance In The Oxidation Of Cyclohexanone

?-Caprolactone is widely used in the production of polycaprolactone?PCL?,which can be used to synthesize biodegradable plastics.?-Caprolactone can also be used to produce polycaprolactone polyol and caprolactam,and be used as a solvent for less soluble resins such as polyurethane resins.China's?-caprolactone market demand is huge,but it mainly depends on import.The oxidation of cyclohexanone by hydrogen peroxide is a green chemistry route to the production of?-caprolactone.Sn-Beta molecular sieve is the most potential catalyst for this reaction.Therefore,this thesis has carried out a series of studies related to the preparation of Sn-Beta molecular sieve with dealuminized Beta molecular sieve and the oxidation of cyclohexanone with dilute hydrogen peroxide.The main research contents are as follows.First,H-Beta molecular sieve with SiO₂/Al₂O₃ ratio of 25 was used as parent zeolite,and a dealuminated Beta molecular sieve with SiO₂/Al₂O₃ ratio of 690 was obtained by using 13mol/L nitric acid solution.Then a series of Sn-Beta molecular sieve with Si/Sn ratio of 80,60and 30 were prepared by solid-state ion-exchange method.It was found that the content of tetrahedral coordination tin species and the amount of Lewis acid sites increased with the increase of tin content according to catalyst characterizations.In the cyclohexanone oxidation reaction,the conversion rate of cyclohexanone was also observed increasing with the increase of tin content.Based on the above work,effects of reaction temperature,reaction time,hydrogen peroxide dosage,catalyst loading,the type and amount of solvent on the cyclohexanone oxidation reaction were preliminarily investigated.Results show that 1,4-dioxane is the best solvent for this reaction.The reaction time is an important factor which affects the selectivity of?-caprolactone.It was observed that,as the reaction time increased,the selectivity of?-caprolactone decreased due to the side reaction of hydrolysis.Under the suitable conditions of temperature 90?,catalyst dosage 0.5 g,n?cyclohexanone/H₂O₂?=2,the mass ratio of 1,4-dioxane solvent to cyclohexanone 40,reaction time 2 h and Si/Sn ratio 30,the conversion of cyclohexanone reached 32.43%,selectivity of?-caprolactone reached 88.15%,and effective utilization rate of hydrogen peroxide reached 72.15%when Sn-Beta catalyst with Si/Sn rastio of 30 was used as catalyst.Finally,the effect of alkaline solution treatment with different concentrations of NaOH,NH₃·H₂O and TEAOH solutions on the performance of Sn-Beta molecular sieve catalyst was prilinarily investigated.It was found that none of the alkaline solution treatments achieved the purpose of improving the catalyst's reactivity.The main cause for this result might be owing to the loss of tetrahedral coordination tin species during the post-alkaline solution modification process.Therefore,it is necessary to investigate the feasibility of performing alkali treatment on the dealuminated Beta molecular sieve before the final synthesis of Sn-Beta molecular sieve by solid-state ion-exchange.