Conversion Of Biomass-derived Levulinic Acid(Esters) To Liquid Fuel And Chemicals

As a potential renewable substitute for fossil resources,biomass has been converted to food,heat,electricity,liquid fuel and platform chemi cals,which are the bases of human society.As the most abundant bio-based raw material,lignocellulose can be fractionated to three main components:cellulose,hemicellulose and lignin through various pretreatment methods.Cellulose and hemicellulose are degraded to sugars by acid catalyzed hydrolysis/alcoholysis and further converted to levulinic acid(LA)and levulinate esters(LE)including methyl levulinate(ML)and ethyl levulinate(EL),which are very important platform molecules for the production of liquid fuel,fuel additives,essences,building blocks and other downstream value-added chemicals.In this dissertation,LA and LE are adopted as off the shelf starting materials for the preparation of heterocyclic,alicyclic compounds and their derivatives.Besides the atom-economic preparation of gamma-valerolactone(GVL),the synthesis of a series of LA/LE derivatives,including methyl 4-methoxypentanoate(MMP),ethyl levulinate dimer(ELD),saturated ethyl levulinate dimer(SELD),5-methylthiophene-2-thiol(MTT)and the condensation products of LA derived a-angelicalactone(AL)with 5-chloromethylfurfural,(5-CMF)or 2,5-diformylfuran(2,5-DFF).Firstly,GVL was synthesized from EL under a solvent-free condition with the catalysis of a Cu-Cr oxide,which was in-situ activated by molecule H2.The yield of GVL was up to 95%with a catalyst loading of 1 wt%,H2 pressure of 4 MPa at 250 ℃ after 4 h.The catalyst was reused without any reactivation processes and provided excellent recyclability.Considering that methanol could be decomposed on the Cu-Cr catalyst,an atom-economic method for GVL synthesis was developed.ML was used as starting material and an extremely low amount of methanol was introduced as in-situ hydrogen donor.A 90%yield of GVL was obtained with the addition of 0.23 equivalent of methanol at 250℃ after 4 h.As the in-situ generated methanol during ML cyclization was also effectively utilized for H2 supply,this system was proved to be more atom-economical than previous research.Secondly,the ring-opening reaction of GVL in methanol in the presence of HUS Y and CaCO3 was studied,in which GVL was converted to a novel molecule MMP with a conversion of 58%and a selectivity up to 87%at 250 ℃ in 4 h under 4 MPa of N2.MMP was reported as a by-product for GVL ring-opening reaction with a selectivity lower than 10%,which could be applied as building block,fuel additive and essence.By studying the ring-opening chemistry of gamma-butyrolactone as a model compound under same conditions,insoluble carbonates such as CaCO3 was proved to promote the generation of methoxyl anions,thus inhibited the generation of pentenoates and improved the selectivity to MMP.Subsequently,we studied the aldol condensation of EL in the presence of sodium ethoxide(EtONa).EL was converted to a mixture of dimer(ELD)and various trimers with 100%carbon yield in EtONa/ethanol at 70 ℃ in 5 h.The addition of water absorbent such as Na2SO4 promoted the condensation while replacing the reaction atmosphere to argon effectively suppressed side reactions,leading to a highest ELD yield of 40%.ELD and its saturated deravitave SELD with a five-membered alicyclic diester structure are regarded as potential renewable monomers for preparing polyesters with diols.Moreover,ELD was converted to branched C8-10 cycloalkanes as ideal biogasolines by hydrogenation-decaboxylation.The dimer/trimers mixture could also be hydrogenated/decarboxulated to give a cycloalkane mixture with a carbon range of 8-13.Afterwards,the cascade thionation of LA to a family of thiophene products in the presence of Lawesson reagent(LR)was studied for the first time.LA was converted to 5-methylthiophehe-2-thiol(MTT)with a yield up to 78%in toluene under reflux after 40 min.MTT was regarded as a condiment additive,pharmaceutical intermediate and monomer for conductive polymer.Further study showed that LA was initially thionated to thienones and then formed MTT by the elimination of H2S.An intergrated synthesis pathway of MTT from cellulose was also developed using toluene as both extractant and reaction agent.The dissertation also included two side projects.First,Cu catalyzed hydrogenation-liquefaction of miscanthus to bio-oil was studied in a glycerol-methanol system.The hydrogen consumed was in-situ supplied by the decomposition of methanol on Cu catalyst,providing a miscanthus conversion of over 90%.This system was also applicable to other herbal and woody biomass.Second,we studied the aldol condensation of LA derived AL and furan aldehydes such as 5-CMF and 2,5-DFF.The products possessed large conjunctive structure,special colors and fluorescence properties,which ensure their applications as dyes and fluorescent paints.