Synthesis And Property Of Norbornyl-Based High-Density Fuels

Compared with traditional jet fuels,high-density hydrocarbon fuels have higher density and volumetric neat heat of combustion,which can improve the payload and range of aircraft.Therefore,high-density hydrocarbon fuels have received extensive attention from researchers all over the world.In this paper,using norbornenes with bridged ring structure as substrates,a series of polycyclic,high-strained four-membered ring and spiro-structure fuels with high energy density were synthesized through acid-catalyzed oligomerization and photocycloaddition reaction,which improve the energy density and combustion performance of fuels.High-density-energy hydrocarbon fuels were synthesized through the oligomeri-zation of norbornene by acidic zeolites with further hydrogenation.The high B/L acid ratio of the zeolite promotes the dimerization reaction and the shape-selective effect of micropores restricts the formation of trimerization products,and the reaction mecha-nism and kinetics of the norbornene oligomerization reaction were discussed.Under the optimal reaction conditions（140℃,8 h,Hβ-25）,the conversion of norbornene is99.5%,and the selectivity of dimers is 72.9%.The synthesized binornborane fuel shows density of 0.978 g/cm³,volumetric neat heat of combustion of 41.49 MJ/L,and viscos-ity of 17.67 mm²/s（20 ℃）.Meanwhile,the hot-plate ignition temperature（272 ℃）and the delay time（0.974 s,430 ℃）of the fuel is much lower than that of JP-10（404 ℃,2.495 s）,which indicates that the synthesized dimer fuel has excellent combustion per-formance.The highly strained four-membered ring fuel was synthesized through the self-sensitized[2+2]photocycloaddition reaction between norbornene and cyclohexanone,with further hydrodeoxygenation.The effects of solvent type,temperature,light inten-sity on the[2+2]reaction was explored,and the reaction mechanism and kinetic analy-sis of[2+2]photocycloaddition process with norbornene and cyclohexenone was fur-ther analyzed by FL spectrum and DFT theoretical calculation.The results show that the exciplex formed by triplet cyclohexenone and ground state norbornene is the key step in the[2+2]photocycloaddition process.The synthesized hydrocarbon fuel shows density of 0.986 g/cm³,volumetric neat heat of combustion of 41.14 MJ/L,viscosity of8.61 mm²/s（20 ℃）,and freezing point of<-65 ℃.The highly strained four-membered-ring fuel with spiro-structure was synthesized through self-sensitized[2+2]photocycloaddition reaction between camphene and cy-clohexanone,with further hydrodeoxygenation.The UV-vis spectrum,FL spectrum and Stern-Volmer quenching kinetics results prove that acetic acid improves the light ab-sorption of cyclohexenone,promotes the formation of triplet cyclohexenone and pro-longs its lifetime.The photocycloaddition reaction mechanism of camphene and cyclo-hexenone was further discussed based on DFT theoretical calculations.It shows that acetic acid reduces the energy gap between the LUMO of cyclohexenone and the HOMO of camphene,and reduce the energy of the exciplex formed by triplet cyclo-hexenone and camphene,which promotes the co-dimerization reaction.The synthe-sized hydrocarbon fuel shows density of 0.992 g/cm³,volumetric neat heat of combus-tion of 41.89 MJ/L,viscosity of 5.69 mm²/s（20 ℃）,and freezing point of<-65 ℃,which is better than that of JP-10.An efficient Z-scheme Zn O-WO₃ photocatalyst was synthesized by two-step sol-vothermal process to promote the synthesis of mixed hydrocarbon fuels through self-sensitized[2+2]photocycloaddition reaction between norbornadiene and cyclohexa-none.The results of TEM,XRD,XPS and DFT theoretical calculations show that the energy band of Zn O bends upward and the energy band of Zn O bends downward due to the Fermi level.The band bending makes the holes of Zn O and the electrons of WO₃form Z-scheme charge migration direction at the interface,which enhances the charge separation and transfer process.The FL spectrum,alkene quenching and PL spectrum results show that Zn O-WO₃ inhibits the formation of triplet cyclohexanone,and makes norbornadiene preferentially undergo intramolecular[2+2]cyclization reaction to gen-erate tetracycloheptane,which effectively inhibited intermolecular[2+2]cycloaddition between cyclohexenone and norbornadiene,thereby realizing the controllable regula-tion of the highly strained four-membered ring fuel components.Furthermore,based on theoretical calculations,the reaction mechanism of[2+2]cycloaddition of norbornadi-ene under the sensitization of Zn O-WO₃ and cyclohexenone was revealed.