Study On Preparation And Catalytic Reactivity For MTH Process Of ZSM-5/SAPO-11 Composite Molecular Sieve

ZSM-5 molecular sieve as catalyst for methanol to hydrocarbons process?MTH?has the disadvantages of high aromatics content for gasoline product in MTG process and low light olefins selectivity in MTO process.Combined with the advantages of SAPO-11 molecular sieve?AEL topology structure of ten-membered ring and one-dimensional channels,smaller micro hole properties and weak surface acidity?and the adjustable surface acidity properties of ZSM-5 molecular sieve,SAPO-11?AEL?and ZSM-5?MFI?were taken into account to prepare the ZSM-5/SAPO-11 composite molecular sieve via a novel catalyst design and molecular sieve composite technology.Thus,the preparation and catalytic reactivity for MTG process of ZSM-5/SAPO-11 composite molecular sieve from ZSM-5 with low silica to alumina ratio was investigated,also the preparation and catalytic reactivity for MTO process of ZSM-5/SAPO-11 composite molecular sieve from ZSM-5 with high silica to alumina ratio was researched in this paper.The effect of different preparation conditions on structure properties of SAPO-11 molecular sieve synthesized from diethylamine template via microwave-assisted hydrothermal route was firstly investigated.By means of XRD,SEM,BET and NH₃-TPD characterization methods,the microstructure and physicochemical properties of the synthesized products were discussed.The results showed that silicon source type,silicon source concentration,template concentration,system pH,crystallization temperature,crystallization time and other factors had great impacts on phase composition,morphology,pore structure and surface acidity.Crystallinity and high purity spherical,uniform grain crystal size,high specific surface area and pore volume(199.4 m²·g^-1 and 0.15 cm³·g^-1),weak surface acidity SAPO-11 molecular sieve could be prepared under the condition of alkaline silica sol as silicon source,the raw material molar ratio of Al₂O₃:P₂O₅:SiO₂:DEA:H₂O=0.85:1:0.5:1:60,pH=4,crystallization temperature of 200 ? and crystallization time of 1 h.The effect of various silica to alumina ratios of ZSM-5 molecular sieves on structure properties synthesized via microwave-assisted hydrothermal route was investigated.Moreover,the impact of silica to alumina ratio of ZSM-5,different preparation methods,mass ratio on structure properties and catalytic performance of composite molecular sieve was further studied.With the help of XRD,SEM,BET,NH₃-TPD and TG/DSC characterization methods,the morphology and physicochemical properties of the composite molecular sieve were discussed and the catalytic performance was studied by microreactor.The results showed that ZSM-5 silica to alumina ratio,different preparation methods and mass ratio had great effects on composite molecular sieve properties and catalytic performance;When the mass ratio was 1,the ZSM-5?80?/SAPO-11 composite molecular sieve was spherical particles with short hexagonal prism and weak acidity on the surface when the specific surface area as 127.2 m²·g^-1,and it showed higher selectivity of C₅₊ hydrocarbon?45.89%?and lower aromatics content in oil phase?25.79%?when used in MTG process;When the mass ratio was 1,the ZSM-5?360?/SAPO-11 composite molecular sieve was made up of a large number of spherical particles with long hexagonal prism and a lot weak acid on the surface when the specific surface area as 120.1 m²·g^-1,and it showed higher selectivity of light olefins?91.29%?and conversion of methanol?99.54%?when used in MTO process.In order to further improve the catalytic performance of composite molecular sieve,the MTH process conditions were optimized over ZSM-5/SAPO-11 composite molecular sieve.The effects of water-alcohol mass ratio,reaction temperature,airspeed and reaction time on selectivity for light olefins and conversion of methanol were investigated using the optimized ZSM-5?360?/SAPO-11 composite molecular sieve as the catalyst;The effects of reaction temperature,airspeed and reaction time on selectivity for C₅₊ hydrocarbon and the aromatics content in oil phase were investigated using the optimized ZSM-5?80?/SAPO-11 composite molecular sieve as the catalyst.The results showed that the ZSM-5?360?/SAPO-11 composite molecular sieve exhibited excellent catalytic performance with the selectivity of 91.29% for gas phase light olefins and catalyst life of 128 h for MTO process under the condition of water-alcoho mass ratio of l,reaction temperature of 380 ?,reaction time of 10 h and airspeed of 2 h^-1;the ZSM-5?80?/SAPO-11 composite molecular sieve exhibited excellent catalytic performance with the selectivity of 45.89% for C₅₊ hydrocarbon,the aromatics content of 25.79% in oil phase and catalyst life of 72 h for MTG process under the condition of reaction temperature of 380 ?,reaction time of 10 h and airspeed of 2 h^-1.