Phosphotungstic Acid（Salt）-catalyzed Synthesis Of Polycyclic Alkanes Precursors From C₅-C₆ Alcohols/Ketones

Bio high-density fuel is a special aviation oil with polycyclic hydrocarbons as the main component and biomass as the raw material.Replacing conventional fuels with synthetic high-density fuels from biomass could contribute to achieve the goal of carbon peaking and carbon neutrality.Typically,the synthesis of high-density polycyclic alkanes requires two steps.The polycyclic alkane precursors are synthesized firstly,and then the polycyclic alkane precursors are hydrogenated.The carbon skeleton structure of polycyclic alkane precursors plays a decisive role in the properties of synthetic fuel molecules.The synthesis of precursors relies on efficient C-C coupling reactions,which requires efficient solid acid catalysts with good water resistance and anti-coke properties.Therefore,this thesis focuses on the designing and constructing of efficient solid acid catalysts by combining simple impregnation and co-deposition methods.And we used this catalyst to synthesize fuel precursors with polycyclic alkanes as the main components by an aldol/alkylation reaction of lignocellulosic ketones/alcohols.Finally,we explored the relationship between the catalyst and the reactions by characterization.Water and coke resistant HfTPA/SBA-15 is synthesized and synthesize 2～3 ring-linked fuel precursors by aldol condensation of lignocellulosic ketones.Lignocellulosic ketones are converted to bicyclic alkanes precursors under strong acids through aldol condensation reactions.The process produces water that easily causes catalyst poisoning,and over condensation reactions produce polymers,and strong acid coking causes catalyst deactivation.Herein,we prepared 2～3 ring-linked cyclic alkane precursor mixtures by aldol condensation reactions catalyzed by HfTPA/MCM-41 using lignocellulosic mono-or mixed ketones as feedstock.The catalysts are synthesized using phosphotungstic acid to provide strong acid sites and MCM-41 to limit macromolecular formation and Hf metal cation to deposit phosphotungstic acid to create water-resistant property.Among the catalysts,80%Hf_1.5TPA/MCM-41 has higher activity than80%TPA/MCM-41 and commercial zeolites.The yield of the cyclic-linked cycloalkane precursors mixture generated from ketone mixtures is 66.8%.The good performance of the catalyst is attributed to the large acid amount,the new strong Lewis acid,the large surface area,and the coke-and water-resistance properties.The catalyst enhances the aldol condensation reaction activity by changing the surface electronic structure through doping phosphotungstic acid with Hf to activate the C=O bond of ketones to form a metal enolate intermediate.Water and coke resistant SnTPA/SBA-15 was synthesized and used to synthesis of decalin and alkane precursors by alkylation of lignocellulosic alcohols.Synthesis of decalin from cyclic alcohols is a continuous reaction process including alcohol dehydration,alkylation,rearrangement and hydrogen transfer.Solid acid is used to complete the C-C coupling reactions and strong acids are introduced to complete the hydrogen transfer reaction.However,strong acid is unavoidable to cause coking and alcohol dehydration produce water,both of which go against the reaction.Therefore,we prepared strong acid,water-resistant and confinement SnTPA/SBA-15 by introducing phosphotungstic acid to provide strong acid sites and depositing phosphotungstic acid with Sn to create water-resistant sites,and using SBA-15 as a carrier to limit macromolecular formation and provide sufficient space for hydrogen transfer reactions.By this catalyst,the yield of decalin and its precursors reach to 65.1%,of which the yield of decalin is 36.7%.The high activity of SnTPA/SBA-15 is attributed to the big acid amount,high acid density and suitable pore size.In addition,this catalyst has a longer lifetime than 80%TPA/SBA-15,attributing to its improved coke and water resistance.Finally,the catalyst is applied to the alkylation of mixed cyclitols and the yield of the products is up to 65.4%.