| The development of economically viable and environmentally sustainable liquid fuel is essential to meet rising energy demands and address environmental concerns.Renewable biodiesel with a chemical structure of long-chain alkanes,mostly derived from non-edible oil,is a good candidate as an alternative or additive of regular petroleum-derived fuel.After isomerization,long-chain alkanes can be further updated to jet fuel range hydrocarbons(typically C8 to C16 linear and branched alkanes).Jet fuel produced from biorenewable resources can significantly lower the greenhouse gas emissions and reduce the carbon footprint when compared with petroleum derived jet fuel,which contributes to the safety of supply and benefits the local economy.Six biomass to jet fuel conversion processes have been reported,namely,gasificationFT(FT),fast pyrolysis(PY),hydrothermal liquefaction(HTL),direct sugars to hydrocarbons(DSCH),alcohol to jet(ATJ),and hydrotreated esters and fatty acids(HEFA).Among these,the HEFA conversion process shows high potential to obtain highenergy density products due to its mature technology while others show expensive technology cost,involve complicated reaction pathways and give low yields of products,which is free from the "blend wall" limitations imposed on bioethanol and biodiesel.However,the production cost for obtaining jet fuel by the HEFA conversion process is relatively high,mainly due to the high cost of raw materials.In order to improve the process economy,it is advisable to build up an efficient catalytic system which can selectively convert natural oil to jet fuel and some other valuable products,e.g.fatty alcohols,under mild reaction conditions.As the important intermediate products in the conversion of oil to jet fuel,fatty alcohols have attracted growing attention in the past few years due to their wide and essential applications in the synthesis of plasticizers,surfactants,food additives,cosmetics and pharmaceuticals.The market price of fatty alcohols is almost twice that of alkanes.Therefore,selective conversion of natural oil to fatty alcohols has great potential to increase the economy of the process for jet biofuel production.The main challenge in producing jet fuel from a bio-based feedstock is the removal of oxygen.By deoxygenation,natural oil components can be converted into jet fuel and valuable chemicals.Fatty acids and their esters as well as triglycerides,usually vegetable oils,have been employed extensively as feedstocks in catalytic deoxygenation.The reaction pathways for the deoxygenation of natural oil components include decarboxylation,decarbonylation and hydrodeoxygenation(HDO).Sulfur-free metal catalysts including Ru,Pt,and Ni are mainly employed for the generation of green hydrocarbons from oil components.However,the processes are accompanied inevitably by decarboxylation or decarbonylation,resulting in one carbon loss from oil components and producing CO2 and CO,which impairs both the atom economy and the environment.Meanwhile,due to their high deoxygenation activity,fatty alcohols cannot be obtained with high selectivity.Low cost Cu catalysts have been reported to produce fatty alcohols via hydrodeoxygenation,especially as part of synergistic compositions of two or three metals,including Cr,Zn,Fe and/or Al.However,Cu leaching and relatively harsh reaction conditions are the major issues in this process.Moreover,we know that almost no Cu catalyst has been reported for long-chain alkane production under mild conditions.Therefore,seeking a low cost and stable catalyst for selective hydrodeoxygenation of natural oil to various targeted products under controllable and mild conditions is highly desirable.In this work,we report a novel catalytic system based on a Pd stabilized commercial Cu/ZnO/Al2O3(CuZnAl)catalyst to convert oil components to alcohols or long-chain alkanes with high selectivity and tunability.It has great potential to increase the sustainability and economy of conversion of natural oil components to valuable chemicals and liquid fuel. |
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