The Research Of Microwave-assisted Depolymerization Of Ethanol Solvent Lignin From Bamboo With The Organic Solvent

With the further development of human society,the problems of higj-polluting and non-renewable fossil resources has become more and more serious.In order to solve the energy crisis,reduce environmental pollution,people began to pay more attention on the development and utilization of biomass resources.Lignin is a renewable,biodegradable,abundant.Also because of its unique aromatic and aliphatic characteristics it can be used to produce fuel and low molecular weight phenolic chemicals as a substitute for petroleum.Due to its complex chemical structure,high-value utilization of lignin polymer has not gained any great breakthrough.In this paper the organic solvent was adopted to grad the lignin according to their different molecular weights.The methods of HPLC,FT-IR,NMR and TGA are also used to embody its stucture and property.The paper is aimed at theoretical basis and pertinence for the futher degradation of lignin research.Solvent pulping can effectively realize full utilization of biomass resources,an d reduce pollution of this process.In the process of bamboo solvent pulping,the remo val of lignin is the most crucial step.Therefore,the delignification mechanism researc h become particularly important.This study is aimed to investigate microwave depoly merization of lignin using glycerin as solvent and study the effect of it on lignin depol ymerization,which can provide theoretical basis for the removal of lignin in the pulpi ng process,And to realize the value added utilization of lignin byproduct in pulping process.Using bamboo as raw materials source for bamboo lignin,we extracted lignin with the help of ethanol.Using ether,ethyl acetate,methanol,acetone and dioxane/water?9/1,v/v?for continuous grading extraction of alcohol soluble lignin so as to get five kinds of lignin fractions F0,F1,F2,F3 and F4.The highest yield of F1was 50.27%.Through the structure and characterization of these components It was found that the molecular weight of ethyl acetate group is the lightest?M_w is2940g/mol and M_n is 1665g/mol?and it has the least dispersion with 1.77;In the elemental analysis results,there is a higher level of nitrogen and oxygen content in F4,which indicates that the higher content of nitrogen and oxygen compounds.Thermogravimetric results show that all groups at temperatures in excess of 200?,began a large number of decomposition,so in the process of producing thermoplastic products by alcohol soluble lignin or polymer product based on lignin,the temperature should be controled under 200 degrees centigrade.Using alcohol soluble lignin as test material for depolymerization,high-boiling-point glycerin as solvent,we explores the differences between conventional thermal cracking and microwave pyrolysis of lignin macromolecules depolymerization,and further explores the effects of six kinds acidic catalyst?sulfuric acid,hydrochloric acid,phosphoric acid,acetic acid,oxalic acid and citric acid?on microwave-assisted depolymerization of lignin.It was founded that the lignin depolymerized by microwave heat are more likely to make lignin?-O-4 bond cleavage than conventional pyrolysis,and performance on lignin liquefaction rate significantly increased by 18.8%to 22.6%).The effect of sulfuric acid during the depolymerization is the most obvious.Inorganic acid catalytic effect significantly better than that of organic acids such as acetic acid.The liquefaction rate was 36.3%,35.6%,30.4%,27.4%,28.5%,and38.9%,respectively,from sulfuric acid to citric acid.After depolymerization,the average molecular weight of lignin residue decreased greatly,from 6009g/mol to3124g/mol between 4650g/mol and the dispersion decreased from 2.42 to 1.91between 2.31.Liquid products made by lignin depolymerization are mainly monomer and dimer,their total content are as high as 75%.Among that,the highest monomer content amount of liquid products catalyzed by sulfuric acid are 64.62%,and the minimum polymer content was only 3.35%.Sulfuric acid oxidation of lignin made lignin?-O-4 bond and other ether bonds cleavage more easily,lead to reduce the content of methoxyl group and fewer side chain groups on the benzene ring.The results of thermal stability analysis shows that the lignin residue after microwave depolymerization has stronger thermal stability.With sulfuric acid as a catalyst,we further explored the different effect of the sulfuric acid addation,microwave reaction temperature and reaction time on lignin depolymerization.It was found that the amount of liquid product catalyzed by 0.2%H₂SO₄ was the largest.The monomer and the polymer content of the liquid product were the highest in the liquid product.With the increase of sulfuric acid,the reunion reaction is more and more obvious.The resulting monomer and other small molecular product content is higher.With the increase of reaction time,the yield of lignin increased first and then decreased.Small molecular reunion reaction degradated from lignin will increase.The results of molecular weight analysis showed that the higher the temperature,the lower the molecular weight,and the weight average molecular weight of the residue was only 2804g/mol at 210?.The optimum conditions for lignin depolymerization in glycerol by microwave assisted is0.2%H₂SO₄ as the catalyst,170?as reaction temperature and 30 minutes as the reaction time.