Study On The Preparation Of Mn-SAPO-34 And Its Catalytic Reaction Of α-pinene Epoxidation

Turpentine was a kind of natural renewable resources,and most of its products were high value-added green products,such as camphor,borneol,terpineol,aromatic alcohol,sandalwood,terpene resin etc..It is mainly composed byα-pinene andβ-pinene,which were a pair of isomers with the similar properties.Owing to its unique molecular structure,α-pinene had an extremely active chemical property which can participate in many chemical reactions,such as hydrogenation,epoxidation,pyrolysis and polymerization reaction.There was a rich resource of turpentine in our country and its production ranks first in the world,however,the deep processing utilization,was low.Therefore,research and development of high-performance and environmentally-friendlyα-pinene epoxidation catalysts are of great significance to the field of deep processing of turpentine in China.SAPO-34 was a kind of chabazite zeolite with of eight members ring ellipsoidal cage molecular framework structure.Its molecular skeleton was negatively charged with ability to cation exchange.A large number of B acid centers were existed on the surface of SAPO-34 molecular sieve,and its acidity and pore size can be adjusted.In addition,SAPO-34 molecular sieve had higher thermal and mechanical stability.Therefore,this kind of molecular sieve was always used as excellent catalyst carrier and attracting more attention.In this study,Mn-SAPO-34 supported catalyst was prepared by ion-exchange method,with SAPO-34 molecular sieve as a carrier and manganous acetate as active constituent.And then the carrier and catalyst were characterized.The specific research aspects are as follows:（1）SAPO-34 molecular sieve was prepared by hydrothermal method.And the surface area of the material was used as probes to determine the optimal conditions:the molar ratio of TEA/Al₂O₃/P₂O₅/Si O₂/H₂O was 3:1:1:0.6:50,the crystallization temperature was 200℃,and the crystallization time was 48h.Under this preparation condition,SAPO-34 molecular sieve was characterized by XRD,TG,BET,SEM,TEM and NH₃-TPD.the results showed that the material that silicoaluminophosphate molecular sieve SAPO-34 with CHA was successfully synthesized.It had high crystallinity,smooth surface,no amorphous structure,higher thermal stability,surface area at 562.60m²·g^-1,and the crystal size was almost identical.（2）Mn-SAPO-34 catalyst was prepared by ion exchange method and investigated optimal catalyst preparation conditions by single factor test and BBD response surface method,and the optimal preparation conditions are as follows:m(Mn²⁺)/m（SAPO-34）at 0.2,system p H at 5,preparation temperature at 61.5℃,preparation time at 6h.After that,the process conditions ofα-pinene epoxidation reaction were investigated to determine the optimal conditions for the reaction temperature at 17℃,the acetonitrile dosage at 25g,the catalyst dosage at 100mg,the cocatalyst dosage at 1g.Under this conditions,the conversion ofα-pinene was99.92%,2,3-epoxypinane selectivity was 94.62%,2,3-epoxypinane yield was 94.54%,and the reproducibility was well.（3）The age of the catalyst was studied,and the characteristics of catalyst subsequently were characterized by XRD,ICP,SEM,TEM and SEM-EDS.The experimental results showed that Mn-SAPO-34 catalyst can be the most efficiently used 5 times and more effectively used 6 times.when the catalyst used at 7th times,it began to be inactive,and the reason are as follow:1)The loss of active components;2)Some active components are oxidized;3)Because of the skeleton structure of the carrier partially collapsed and its specific surface area decreased,the agglomerate phenomenon of active components were aggravated until the catalyst was inactivated;4)Loss of Si elements.In that the content of silicon can directly affect the catalytic activity of the catalyst when SAPO-34 molecular sieves were treated as carriers.