Synthesis Of MOR/MFI Molecular Sieves With Waste Residues From Fluid Catalytic Cracking Catalyst Preparation

During the production of fluidized catalytic cracking（FCC）catalysts,a silica-alumina waste called"waste residues"is discharged.It is harmful to the environment and disposed by landfills,which neglects the utilization value of FCC catalyst waste residues.In this thesis,a series of zeolite molecular sieves were synthesized from FCC catalyst waste residues in the absence of organic templates assisted by crystal seeds and microwave irradiation,and were applied to the dehydration of glucose to prepare 5-hydroxymethylfurfural（5-HMF）.Firstly,physical structure,pore structure,elemental composition and surface morphology of FCC catalyst waste residues were investigated.The FCC catalyst waste residues was activated by alkali fusion and silica and alumina in the slag reacted with sodium hydroxide to form Na₂Si O₃and Na Al O₂.The effects of amount of silica sol and water,heating temperature/duration and aging conditions on the structure of the product phases were investigated using the activated FCC catalyst waste residues as raw material.These results showed that the amount of silica sol and water,alkalinity and heating duration significantly affect the morphology of mordenite.The ageing time and temperature has less influence on the crystallinity of mordenite.Extending the ageing time and improving the ageing temperature were favorable to accelerate the assembly of silica and aluminium tetrahedrons in the crystallization precursors.The heating temperature has less influence on the crystallinity of mordenite.The relative crystallinity of the zeolite increased from 86.6%to 88.3%,93.8%and 100%as the heating duration increased.The synthesized molecular sieve was used in a glucose dehydration reaction in which glucose was isomerized into fructose in the presence of Lewis acid and fructose was dehydrated to produce 5-HMF as the main reaction pathway.Secondly,in order to reduce the energy consumption and the environmental hazards,the effects of heating temperature and duration,alkalinity,amount of silica sol and seed on the product structure were investigated using FCC residues as raw material with MOR seeds.The study found that Amorphous products are converted into crystalline molecular sieves when the heating temperature increased from 170℃to190℃and the heating duration was extended to 5 h.Extending the heating duration,the crystallinity of the product gradually increases and the BET specific surface area increased to 329 m²/g.MOR/MFI intergrowth molecular sieves with different composition were prepared by regulating the alkalinity and silica-sol addition.As the alkalinity of the synthesis system increased,the MFI structure in the zeolite product undergoes a transformation to the MOR structure.In the case of low Si O₂/Al₂O₃,the product tended to be more towards the formation of mordenite phase.Increasing the amount of silica sol,the BET specific surface area of the sample decreased from 212m²/g to 114 m²/g,more silicon atoms entered into the zeolite skeleton,and the content of framework Al species gradually decreased.Increasing the amount of seed was beneficial to induce the formation of mordenite.The product exhibited catalytic performance in the dehydration reaction of glucose to prepare 5-HMF.When the seed was changed to ZSM-5,effects of heating temperature/duration,alkalinity and amount of silica sol and seed on the physical structure of the product were investigated using FCC residues as raw material.As the amount of seeds and heating temperature increased,the transformation from silicon-aluminum precursors to crystal structure was accelerated and the relative crystallinity of ZSM-5 increased.Extending the heating duration,the USY molecular sieves in residues were dissolved,the amorphous silica-alumina material was transformed into ZSM-5 molecular sieves,and the product was changed from irregular particle shape to regular shaped crystal structure.At 24 h of crystallization,the BET specific surface area of the product increased to 289 m²/g,and MFI structure was transformed into MOR structure.A longer heating duration had less effect on the crystallinity and porosity of the product.The proportion of moedenite or ZSM-5 molecular sieves in the composite molecular sieves can be adjusted by changing the alkalinity of the synthesis system and the amount of silica sol.By decreasing the alkalinity of the synthesis system and increasing the amount of silica sol,the precursor gel tended to form ZSM-5 molecular sieves.The MOR/MFI intergrowth molecular sieves exhibited catalytic performance in the dehydration reaction of glucose to prepare 5-HMF.The in-situ FTIR approach proves a dehydration route“glucose→fructose→5-HMF”under the synergistic effect of Br?nsted and Lewis acid sites.The proposed high value-added utilization of FCC catalyst waste residues to synthesize zeolite molecular sieves is important for the treatment of FCC residues and green synthesis of molecular sieves.