MFI Hierarchy Zeolite Catalytic Cracking Of Waste Oils For Biofuel Preparation

The energy issue is one of the major challenges facing mankind.Fossil fuels,as one of the major energy sources,have caused serious pollution to the environment and,coupled with their non-renewable nature,have posed a serious threat to the ecological environment as well as the survival and health of human beings.Therefore,it is urgent to find green alternative energy sources.Waste oils are a common plant biomass with abundant resources and potential for recycling.Among them,catalytic cracking of waste oils and fats to prepare biofuels can be a green alternative to fossil energy.However,catalytic cracking of waste fats and oils has many problems,such as poor recyclability of catalysts,low content of light hydrocarbons in the product,coking deactivation due to high coke yield,and other disadvantages that seriously limit the reuse of waste fats and oils.In order to solve this problem,it is important to find a catalyst with the advantages of abundant active centers,good mass transfer performance and excellent anti-coking properties.In order to solve this problem,MFI hierarchy zeolite s catalysts with excellent mass transfer and anti-coking properties were prepared in this paper,the catalyst structure and performance parameters were also tested by various characterization methods,such as X-ray diffraction,N₂ adsorption and desorption,transmission scanning electron microscopy,chemisorption,pyridine infrared,thermogravimetric analysis,Raman spectroscopy and other methods.Raman spectroscopy.Finally,catalytic cracking of waste cooking oil was used to investigate its catalytic performance,and the evaluation criteria included but not limited to conversion,liquid yield,gas yield,coke generation,and gasoline fraction(C₇-C₁₂)and carboxylic acid content.The study is shown as follows:（1）A bottom-up synthesis strategy was adopted to introduce a novel template agent:(C₁₆H₃₃-N⁺（CH₃）₂-C₆H₁₂-N⁺（CH₃）₂-C₆H₁₃·2Br^-),and then MFI hierarchy zeolites were prepared by hydrothermal synthesis,and a series of characterization tools were used to test the zeolites.The cracking performance of MFI hierarchy zeolites and conventional MFI microporous zeolites was investigated by catalytic cracking of waste oils and fats,and the optimal reaction conditions for the catalytic reaction were determined by single-factor experiments.The results showed that MFI hierarchy zeolite had better catalytic cracking performance,mainly in terms of conversion rate,liquid yield and gasoline fraction,and N-Z（50）achieved the best catalytic performance under the reaction conditions of 80 min at 450℃,with 98.08%conversion rate,77.41%liquid yield and 1.92%coke rate,respectively,and the gasoline fraction in the liquid product was as high as 55.14%.The improvement of catalytic activity was closely related to the hierarchy structure.The stacking of lamellar crystals formed a large number of interlayer mesopores,which successfully built a micro-mesoporous hierarchy structure for MFI hierarchy zeolites.Compared with conventional MFI zeolites,MFI hierarchy zeolites possess more surface area,larger pore volume and similar acid properties.The good mass transfer performance and excellent acid properties are the cornerstones of the better catalytic cracking performance of MFI hierarchy zeolites.The former provides the zeolites with larger pores and contact area,which enhances the mass transfer diffusion and active site accessibility of the reactants,and the latter provides the zeolites with a large number of active sites,which together promote the cracking conversion of heavy hydrocarbons and the formation of more short-chain hydrocarbons,which is the main reason for the upgrading of gasoline components.（2）MFI hierarchy zeolites with different silica-alumina ratios were prepared using the same synthesis method as in the previous section,and then its acid properties were adjusted by metal modification.Firstly,the optimal conditions for metal loading were determined by preparing different metal loading amounts and different kinds of loading metals,and finally the N-Z zeolite and C-Z zeolite were metal loaded with the optimal conditions,and then their catalytic properties were investigated by catalytic cracking of waste grease.The results showed that the modified zeolites exhibited better deoxygenation performance as well as more light hydrocarbon yields.The（6）Mg-N-Z（50）zeolite achieved the best catalytic cracking performance under the reaction conditions of 80 min at 450℃,with the gasoline fraction reaching 63.56%and the carboxylic acid fraction decreasing to 11.46%in the liquid product.The loading of metal particles changed the acid distribution and acid species ratio of MFI-hierarchy zeolites,weakened the total acid strength and enhanced the Lewis acid strength.Lewis acid is an important active site for deoxygenation reaction,and its enhancement facilitates the deoxygenation reaction.Among them,the large increase of CO₂/CO ratio in the gas product indicates that the Lewis acid site is more inclined to enhance the decarboxylation reaction in the deoxygenation reaction.Secondly,the incorporation of metal particles weakened the pore system of zeolite,and a small decrease in surface area and pore volume occurred,which slightly weakened the anti-coking property of modified zeolite and led to an increase in coking rate.The effects of pore structure and acid properties of zeolites on catalytic cracking reactions are discussed in this paper.The construction of the hierarchy structure improved the pore structure of zeolite,which not only improved the mass transfer ability of zeolite,but also enhanced the acid site accessibility of zeolite,realizing the diffusion of coke and the enhancement of reaction activity.In addition,the metal modification method provides more Lewis acid active sites,enhances the deoxidation performance in the catalytic cracking process,reduces the content of oxygenated compounds in the liquid product,and improves the quality of the product fuel.In summary,the MFI hierarchy zeolite has good mass transfer ability as well as acid properties,which overcomes the mass transfer limitation of microporous zeolite to a certain extent,the catalytic cracking performance is enhanced,and the yield of light hydrocarbon compounds is improved,which in turn leads to a significant increase in gasoline fraction,and these results indicate that the construction of hierarchy pore system is of guiding significance for the preparation of biofuel.