Study On The Efficient Catalytic Conversion Of Lignocellulosic Biomass To Furan-based Energy Chemicals

Natural abundant and cheap biomass is a renewable,environment friendly,partial alternative to non-renewable fossil fuels,has been applied to the field of heat energy,chemicals,liquid and gas fuel.Lignocellulosic biomass is an important zero-carbon energy,which is carbon neutral by plant photosynthesis.5-Hydroxymethylfurfural（HMF）,a kind of furan compounds derived from lignocellulosic,is a key bio-based platform chemical,which can be used for the preparation of pesticides,pharmaceutical intermediates and fine chemicals.The etherification product of HMF,5-ethoxymethylfurfural（EMF）,has become a very promising biomass based fuel or fuel additive due to its high energy density（8.7 k W h/L）.The oxidation product of HMF,2,5-furandicarboxylic acid（FDCA）,has been listed as"twelve bio-based platform chemicals"by the U.S.Department of Energy,which is recognized as an ideal bio-based polyester monomer and could be expected to replace the traditional fossil energy product terephthalic acid（TPA）.In order to achieve efficient catalytic conversion of biomass to furan energy chemicals,a series of multifunctional solid catalysts were designed and constructed in this thesis.Firstly,in view of the complex reaction process,low yield and selectivity of HMF product when employing cellulose as raw material,the types of active sites and pore structure of the catalyst were controllable and adjusted to achieve efficient preparation of HMF biomass energy platform compounds.Secondly,in order to achieve the“one-pot”conversion of biomass based carbohydrates containing different sugar units to prepare biofuel EMF in ethanol-co-solvent system,the porous catalysts with multi-active sites,adjustable pore structure and acid-base strengths were synthesized.Finally,an efficient nanoreactor catalyst was developed to achieve the catalytic oxidation of furfuralcohols and furfurals to biomass-derivrd high value chemical furancarboxylic acids.And the further upgrade and transformation of biomass platform chemicals was realized.The main research work and results of this paper are as follows:1.Preparation of 5-hydroxymethylfurfural by catalytic conversion of cellulose（1）The Br?nsted solid acid catalyzed conversion of relatively cheap cellulose to prepare biomass-based platform compound HMF,instead of fructose and glucose as raw materials,has obvious cost advantage.First,two halloysite nanotubes（HNTs）based porous carriers（HNTs-PSt-PDVB）were prepared by precipitation polymerization and Pickering emulsion polymerization,respectively.Secondly,two heterogeneous catalysts with Br?nsted acid site（HNTs-PSt-PDVB-SO₃H）were obtained by sulfonating the support with concentrated sulfuric acid.The yields of HMF for the two catalysts used in the conversion of cellulose into HMF in ionic liquid reached 28.5%and 32.9%,which realized the“one-pot”catalytic conversion of cellulose to prepare HMF biomass energy platform compounds.（2）The natural clay particles attapulgite（ATP）and alloxite nanotubes（HNTs）with large specific surface area,environmental friendliness and high economic benefits were used to prepare functional catalysts.The further introduction of Lewis acid can promote the isomerization of glucose into fructose.After the sulfhydryl group（-SH）was grafted onto the surface of HNTs and ATP,the sulfonic acid catalysts HNTS-SO₃H and ATP-SO₃H containing sulfonic acid were oxidized by hydrogen peroxide.After grafting chromium chloride（Cr Cl₃）,the bifunctional catalyst of ATP-SO₃H-Cr（Ⅲ）and HNTs-SO₃H-Cr（Ⅲ）has been prepared for conversion of cellulose to 5-hydroxymethylfurfural in ionic liquid by a“one-pot”manner.Under the optimal reaction conditions,the yields of 31.2%and 41.2%were obtained for ATP-SO₃H-Cr（Ⅲ）and HNTs-SO₃H-Cr（Ⅲ）,respectively.（3）Pore structure is one of the important characteristics of heterogeneous catalysts.The preparation of catalysts containing hierarchical porous structure can effectively improve the utilization rate of active components and enhance the permeability of cellulose macromolecules in the catalyst.Firstly,poly（HIPE）（PH）was constructed by water in Oil（W/O）type High Internal Phase Emulsions（HIPEs）template method.Then MSNs-SO₃H-NH₂was loaded on PH and then the composite was sulfonated to obtain multifunctional solid catalysts with Br?nsted acid-base and macroporous mesoporous multipore structures.The prepared multifunctional solid catalyst can catalyze the conversion of cellulose into HMF in ionic liquid solvent in a“one-pot”manner.And the highest yield of HMF from cellulose is further increased to 44.5%.2.Preparation of 5-ethoxylmethylfurfural from the catalytic conversion of biomass-based carbohydrateThe further etherification reaction of biomass-based platform HMF can obtain high energy density biomass-based fuel or fuel additive EMF.Compared with HMF,the direct preparation of EMF using biomass-based carbohydrates as raw materials can further reduce the cost of raw materials.Firstly,HNTs modified by divinylbenzene and acrylamide were used as stabilizing particles to construct stable Pickering HIPEs templates.Then,Poly（HIPEs）was obtained after thermal initiation polymerization.Secondly,the obtained polymer further reacted with sulfuric acid by introducing sulfonic acid group（-SO₃H）to obtain Br?nsted acid catalyst（S-Poly）.Finally,the bifunctional functional catalysts（BFC）with Br?nsted-Lewis acid sites were successfully synthesized by introducing chromium ions onto the pore surface of S-Poly composites using the pore filling strategy.Employing the carbohydrates with different sugar units containing starch,maltose,cellobiose,sucrose,inulin,fructose,glucose as raw materials,this developed catalytic system can achieve the efficient preparation of EMF.And the highest EMF yield of 68.8%can be obtained when adopting fructose as a raw material.3.Preparation of 2,5-furandicarboxylic acid from the catalytic conversion of5-hydroxymethylfurfural（1）The high value-added polyester monomer FDCA prepared by the selective catalytic oxidation of the biomass platform compound HMF can replace the petroleum-based bulk chemical TPA for the production of biodegradable polyester materials.A hierarchical porous bowl nitrogen-doped carbon-supported metal-palladium bimetallic catalyst nanoreactor（Au Pd/p BNx C）was synthesized by precipitation polymerization,carbonization,removal of silicon spheres and Au Pd bimetallic particles loading process.The loaded Au Pd nanoparticles can achieve the simultaneous catalytic oxidation of both hydroxyl and aldehyde groups in the conversion of HMF to FDCA,avoiding the low selectivity of FDCA product.In addition,the alkaline active site formed by the doping of nitrogen in the carbon material can promote the hydroxyl group to form alkols in the oxidation reaction and prevent the metal leaching.The nanoreactor can effectively catalyze the highly selective oxidation of HMF to FDCA in aqueous solution,and the yield is as high as97.6%under the optimal reaction conditions.（2）The development of noble metal catalyst with higher activity and stability to realize the selective oxidation of HMF in the absence of alkali is the key to realize the green preparation process of bio-based polyester monomer FDCA.By changing the surface wettability of nitrogen-doped carbon carrier,and then regulating the adsorption and desorption process of substrates and products on the catalyst surface,the catalytic oxidation process can be greatly promoted and the yield of target products can be increased.By means of precipitation polymerization,carbonization,removal of silicon spheres,nitrification and other methods,a kind of hydrophilic porous material p BNC-x%HNO₃with a bowl-shaped hierarchical pore structure was designed.And the nitrate modified nitrogen doped carbon loaded Au Pd nanoreactor was successfully prepared by further loading Au Pd double precious metals.FDCA can be prepared by catalytic oxidation of HMF without alkali,and the yield of FDCA is up to 95.4%under the optimal reaction conditions.Meanwhile,employing the other furfuralcohols and furfurals as the substrates,furancarboxylic acids with acceptable yields can also be obtained.