Carbon Chain Adjustment And Catalytic Hydrodeoxygenation Of Bio-based Intermediates For Bio-aviation Fuel Preparation

Amidst the growing concern over global greenhouse effects,renewable biomass-based synthetic liquid fuel presents a viable solution for reducing CO₂emissions while simultaneously contributing to China’s carbon peak and carbon neutrality goals,meeting the significant demands of national development.Current biomass resource utilization technologies yield an abundance of bio-based platform molecules.Recent research has focused on converting these molecules into high-value products,particularly clean liquid fuels.Aviation fuel is composed of straight-chain alkanes,branched-chain alkanes,cycloalkanes,and aromatic hydrocarbons with carbon numbers typically ranging from 8 to 16.The challenge lies in selectively converting bio-based platform molecules,deoxygenating them and adjusting their carbon chain to fit within this range for bio-aviation fuel synthesis.In this study,ethanol,ABE fermentation liquid（a mixture of acetone-ethanol-butanol）,caryophyllene（a bio-based sesquiterpene）,and 2-methylfuran（2-MF）were used as starting materials.The research established novel pathways for bio-aviation fuel synthesis and emphasized the mechanisms research for directional conversion（controllable carbon chain growth,carbon chain structure adjustment,and catalytic hydrodeoxygenation）of bio-based platform molecules.Through collaborative innovations in catalyst design,reaction technology,and reactor engineering,targeted chemical bond adjustments and high-efficiency hydrodeoxygenation saturation under engineering conditions were achieved,thereby facilitating bio-aviation fuel production.The dissertation has accomplished the following four primary sections,addressing different aspects of the chemical transformation process1.The chain growth reaction of bio-based platform molecules and their mechanisms research:The balance of acid and basic of catalysts exerts significant influence on performance in targeted carbon chain growth process.A series of mixed metal oxide catalysts,such as Mg O-Si O₂,Zn O-Zr O₂ and Ca O-Si O₂,with an adjustable acid or basic property were synthesized and used for converting ethanol to C4 olefins and converting ABE fermentation into higher ketones.Advanced analysis technologies were employed for investigating the reaction mechanism synchronously.In situ Synchrotron-based vacuum ultraviolet photoionization mass spectrometry（SVUV-PIMS）was employed to observe unstable intermediates during the ethanol conversion process.The presence of acetaldehyde condensation into acetaldol was confirmed in converting ethanol to butadiene over Mg O-Si O₂ catalyst process.The formation of isobutene involves the self-condensation of acetone,accompanied by the production of pentene.It was also proved that ketene existed in the two processes.Zn O-Zr O₂ has the best isobutene selectivity（58%）among the investigated catalysts.Its ability for catalyzing acetone condensation was reduced when deactivated.A series of supported Ni-based catalysts was prepared for the conversion of ABE fermentation to ketones with suitable carbon chain length of aviation fuel.The Ni-Ca O-Si O₂ catalyst showed the best selectivity of ketones and C8+products.3-Hepten-2-one in the liquid product was detected by GC×GC/MS,which suggested that the ketones were formed through aldol condensation.Ni-Ca O-Si O₂ catalyst underwent phase transition after reaction and resulted in deactivation.It can be regenerated by calcination in air and hydrogen atmosphere successively.2.Adjustment of the carbon chain structure in bio-aviation fuel precursors:The adjustment of the carbon chain is crucial for producing bio-aviation fuel.It can be achieved either as a separate step during or after the growth of carbon chain.A homemade solid acid catalyst was developed for environmental and separation benefits,and its catalytic performance was found to be comparable to that of the commercial Nafion catalyst.The experimental results showed that both cyclododecatriene（CDT）and caryophyllene were converted into polycyclic aviation fuel precursors using this catalyst.The trimerization of2-MF can also be catalyzed efficiently with a 98%selectivity of the trimer.It is highlighted to modify the product’s branch chain by altering the reagent.3.The hydrogenation saturation process for biofuel precursors and its optimization:The use of multifunctional hydrodeoxygenation catalysts is necessary due to the differences in unsaturated bonds in bio-aviation fuel intermediates.A range of catalyst supporters with various acid properties was used for synthesizing precious metal/acid bifunctional catalysts.This section emphasizes the importance of catalyst stability and the efficient hydrodeoxygenation while maintaining the original carbon chain structure.The Pt/Al₂O₃ catalyst was found to effectively saturate the C=C bonds in bio-aviation fuel precursors（isomers of CDT or caryophyllene）with good stability.The hydrogenation product of the caryophyllene isomer remained unchanged for 200 hours.The physical mixture of Pt/C and Pt/Ti O₂ catalysts showed excellent hydrodeoxygenation performance of the 2-MF trimer.It can effectively remove O atoms while preserving the original carbon chain structure.The catalyst also had good stability,and the proportion of C10 and C15 was always higher than 93%within 100 hours time of stream.During research,a significant exotherm was found during the hydrodeoxygenation of the 2-MF trimer.Using a traditional fixed bed reactor with a 100 m L capacity led to a rapid increase in the catalyst bed temperature,resulting in lower product selectivity and catalyst deactivation.However,using a double-pipe fixed bed reactor could inhibit the temperature increase of the catalyst bed to a certain extent.4.The pilot-scale production bio-aviation fuel and production properties:Several bio-aviation fuel preparation routes were tested on a pilot-scale through a step-by-step scaling-up process.The hydrogenation of CDT/caryophyllene isomers using Pt/Al₂O₃ catalyst was successfully conducted in a pilot-scale fixed bed reactor with a 100 t/y capacity.A microchannel reactor was designed and manufactured by using 3D printing technology in this thesis for pilot hydrodeoxygenation of the 2-MF trimer.The study assesses the properties of bio-aviation fuels prepared from different raw materials.The bio-aviation fuel produced from ethanol has a high density（0.95 g/m L,20°C）and good low-temperature fluidity.The bio-aviation fuel synthesized from caryophyllene has a higher energy density than 3#jet fuel.C15 bio-aviation fuel（2-MF as raw material）,has an excellent fluidity in low temperature.These three products can be used as drop-in aviation fuel.