Preparation Of Aviation Kerosene Intermediate From Biomass Derivatives Using Modified Zeolite

The synthesis of biomass-based aviation kerosene based on lignocellulosic biomass has great economic,environmental and strategic significance under the background of the continuous development of the global aviation industry and the continuous consumption of fossil energy.The aldol condensation reaction using biomass platform compounds as reactants is a key step in the preparation of biomass-based aviation kerosene.Although alkali-catalyzed aldol condensation reaction has high efficiency and low cost,the traditional alkali catalyst is not suitable for preparing biomass-based aviation kerosene because the biomass conversion process is mostly in an acidic environment.Zeolite is an ideal acid catalyst because of its adjustable acid-base catalytic site and strong acid resistance.However,the application of zeolite for aldol condensation reaction,the key step in the preparation of biomass-based aviation kerosene,still has some problems that need to be solved,such as low efficiency,easy coking,and poor hydrothermal stability.This dissertation focuses on the zeolite catalyst and the key carbon-carbon bond formation reaction in the synthesis of biomass aviation kerosene.The synthesis of biomass-based aviation kerosene intermediates via aldol condensation is studied using biomass platform compounds such as furfural,5-hydroxymethylfurfural and levulinic acid as raw materials and modified zeolite as a catalyst.Firstly,the catalytic properties of two different topological tin-modified microporous zeolite(Sn-MFI and Sn-Beta)on the aldol condensation reaction of furfural with acetone were studied.The results showed that due to the influence of pore diffusion,the catalytic activity of Sn-Beta was significantly higher than that of Sn-MFI.However,due to the ten-membered ring structure of Sn-MFI,Sn-MFI exhibited product shape-selectivity and could generate the monocondensation product with high selectivity.Since water could enter the pores of zeolite and occupy catalytic sites,resulting in fewer accessible catalytic sites to the reactants,so the catalytic activity of both Sn-MFI and Sn-Beta in the aqueous system significantly reduced.At the same time,Sn-Beta's product selectivity changed in the reaction system with high water content,which can only selectively produce monocondensation product.Secondly,in order to solve the problems of diffusion,hydrothermal stability and coking carbonization of microporous MFI zeolite in the reaction,the improvement effect of the hierarchical structure on the above problems of MFI zeolite was studied.The hierarchical MFI zeolite had a larger specific surface area,outer surface area and mesopore volume,and faster internal diffusion,so the catalytic effect was better compared with microporous MFI zeolite;at the same time,hierarchical MFI zeolite would also generate the dimercondensation product due to the larger outer surface area and the presence of mesopores.Compared with the microporous MFI zeolite,the hydrothermal stability of hierarchical MFI zeolite was improved,and the catalytic activity in the aqueous system remained unchanged.Unlike the product selectivity in the pure organic phase system,hierarchical MFI zeolite tended to produce dimercondensation product in the aqueous system.In addition,the diffusion limitation of hierarchical MFI zeolite was improved,so the carbon deposition of hierarchical MFI zeolite was lower than that of microporous MFI zeolite.Thirdly,since the improvement effect of hierarchical structure on the catalytic activity and hydrothermal stability of microporous MFI zeolite was not significant,and alkali metal was widely used in zeolite modification,the improvement effect of potassium modification on the catalytic properties of Sn-MFI was studied.CO2-TPD and infrared test after pyridine adsorped showed that the potassium-modified Sn-MFI had a new basic catalytic site,and the original Lewis acidity had also been enhanced.The element map showed that part of the potassium phase distributed on the outer surface of the zeolite.Under the synergy of acid-base catalysis,the catalytic activity of potassium-modified Sn-MFI was greatly enhanced.The total product yield was up to 85.0%,and the total product selectivity was up to 95.0%.Because of the alkaline sites brought by the potassium phase and the distribution of potassium phase on the outer surface,the hydrothermal stability of the potassium-modified Sn-MFI was improved.In the aqueous system,the catalytic activity of potassium-modified Sn-MFI was unchanged,and dimercondensation product was a preferred product.Subsequently,based on the advantages of hierarchical structure and potassium modification,the catalytic performance of potassium-modified hierarchical MFI zeolite for the aldol condensation reaction of furfural with levulinic acid was studied.CO2-TPD and infrared test after pyridine adsorped showed that potassium-modified hierarchical MFI zeolite had both acidic and basic catalytic sites.Compared with potassium-modified microporous MFI zeolite,the specific surface area,outer surface area and mesopore volume of the potassium-modified hierarchical MFI zeolite were increased,and the outer diffusion limitation was improved.The catalytic results showed that the potassium-modified hierarchical MFI zeolite exhibited excellent catalytic activity in the aqueous phase,and the total product yield could reach 70.0%.At the same time,delta-FDLA was the main product due to the majority of basic catalytic sites.Finally,due to the light diffusion limitation of mesoporous zeolite,large specific surface area,easy surface modification,the high cost of tin,gallium and other metals,the low price of iron,and the wide range of iron precursors,the catalytic performance of iron-modified mesoporous MCM-41 zeolite for aldol condensation reaction of furfural,5-hydroxymethylfurfural with acetone was studied.Infrared test after pyridine adsorped showed that the addition of iron phase increased the Lewis acidity of MCM-41 zeolite.The catalytic results showed that using iron-modified mesoporous MCM-41 zeolite as the catalyst,the yield of the total condensation product of furfural with acetone reached 67.0%,and the yield of the total condensation product of 5-hydroxymethylfurfural with acetone reached 44.0%.