Application Of Ionic Liquid In The Catalytic Conversion Of Biomass For High Value-added Chemicals

With the development of social economy,the traditional unrenewable resource has become a major obstacle to the innovation of the industrial technology because of its limited storage and destruction for the environment.Awareness of energy and environment make people pay more and more attention to the development and utilization of renewable resources.Biomass is the unique renewable resource which can provide carbon in nature.It is rich in the world and has a wide range of source with low sulfur content and no carbon dioxide emission.Using the biomass or bio-chemicals as raw materials,instead of fossil resources,is an effective way to solve the energy crisis and environmental pollution of current industrial production.Lignocellulose,which contains cellulose,hemicellulose and lignin as main components,is the most abundant and cheapest biomass resource in nature.Taking lignocellulose and its platform chemicals as material to product industrial chemical product under mild condition through highly selective liquefaction process with catalyst is one of the most important ways of biomass valorization.To date,there are still many problems existing in lignocellulose conversion,such as the severe reaction condition,low selectivity of products and complicate recovery process for catalyst.In this dissertation,we have developed novel and efficient catalytic reaction systems for the transformation of lignocellulose to high value-added chemicals through highly selective liquefaction process.Based on the analysis of the experimental data,possible reaction mechanisms are also proposed.The detailed studies are as follows:(1)Lignin has long been considered as a promising sustainable feedstock for the highly value-added aromatic chemical production.Here,we propose a novel and efficient process for lignin depolymerization in the presence of cooperative ionic liquid pairs([bSmim][HSO4]/[bmim][CF3SO3]),due to its excellent catalytic activity and char inhibition capability.Under the optimized condition,66.7% of the degree of lignin depolymerization is demonstrated without obvious char formation.Furthermore,the volatile products were identified by GC-MS.The structure evolution of the sugarcane lignin was also intensively investigated via the comparative characterization of the original and regenerated lignin using HSQC,1H-NMR,FT-IR,GPC and elemental analysis.It shows that all three structure units of lignin are effectively degraded in this process,whereas,H-lignin is found to be the most active.In additional,the cooperative IL shows good reusability,and a satisfactory lignin depolymerization performance was demonstrated even after the fifth run.(2)Combined with the excellent deplolymerzaition for lignin of sulfonic acid ionic liquid and the multi functions of polyoxometalate acid,a series of polyoxometalate ionic liquid were designed and synthesized,and used as catalyst for selective oxidation of lignin.Under the optimized condition,91.3 % conversion of dealkaline lignin was achieved.Besides,the yield of diethyl maleate,the main product from the reaction,is 376.16 mg/g with 61.4 % selectivity.The study found that the reaction was mainly divided into three parts,depolymerization,oxidation and esterification.The lignin was firstly depolymerized into aromatic monomers with the effect of solvent and the acidity of ionic liquid.Then,these monomers were oxidated to maleic acid/anhydride with oxygen by polyoxometalate ionic liquid as catalyst.Finally,through esterification,the diethyl maleate was produced.Furthermore,the mechanism of the reaction was preliminarily study by using kinds of model lignin compounds as substrate and found the substituents of the aromatic ring had serious effect on the oxidation process.Without significant activity lost after recycling,the ionic liquid can applied in the conversion of raw biomass,which is very significant for industrial production of biomass in the future.(3)Due to its complex components,the selectivity of products from biomass conversion is quiet undesirable.Hence,furfural,an industrial bio-platform chemical,was taken as substrate for catalytic oxidation by polyoxometalate ionic liquids contained excessive metal in methanol as solvent with.The study found that the conversion of furfural achieved 94.5 % with 325.71 mmol/mol yield of binary carboxylic acid ester under the optimized condition(413 K,2 h).Furthermore,according to the analysis of GC-MS spectra,the oxidation mechanism of furfural with polyoxometalate ionic liquid as catalyst had been proposed.