Study On Extraction Of Lignin And Hydrogenation By Deep Eutectic Solvents

With the shortage of fossil resources and the serious environmental pollution,people pay more and more attention to the development and utilization of biomass resources.Biomass is composed of three major components of cellulose,hemicellulose and lignin,which are widely used in the production of chemicals.However,the complex chemical bonds existing between the three major components in biomass make it difficult to convert directly and the utilization effect is not good.Therefore,it is necessary to select appropriate separation means to separate the three major components.The lignin in the three major components which is the only natural macromolecule containing an aromatic ring structure,can be used by producing many aromatic chemicals and fuels.However,the structure of lignin is complex,and it is easy to cause repolymerization during depolymerization,and it is easy to coke or deposit carbon.In addition,additional solvent needs to be added in the process of extracting lignin and depolymerization of lignin,increasing its utilization cost.Therefore,this paper first uses hydrothermal-deep eutectic solvent method?Deep Eutectic Solvents,DES for short?to extract lignin,and then directly catalytically hydrogenates the lignin dissolved in the deep eutectic solvent under mild reaction conditions.The selective depolymerization of lignin was realized under mild conditions.This paper combined the extraction of lignin with DES and the hydrogenation of lignin,which saved a larger mount of solvent required for extraction lignin and the solvent needed for lignin hydrogenation,which helps to reduce the cost of industrialization of this process in the future.The main contents of this paper are as follows:?1?The hydrothermal-DES two-step method was used to separate the components of eucalyptus wood powder,and the effect of reaction conditions on the separation effect was investigated.The results showed that the removal rate of hemicellulose is 80.2%at the condition of 170?,1 h;the hydrothermal residue was used as the feed for DES treatment.After treatment hydrothermal residues by Choline Chloride?Ch Cl in short?-formic acid,Ch Cl-acetic acid,and Ch Cl-lactic acid at 120?,4 h,the solid solubility was 35.9%,34.7%,and 3.5%,respectively.The recovery rate of cellulose was 91.0%,91.4%,and 92.0%,respectively.The removal rate of lignin was 87.8%,88.2%and 87.1%,respectively.The obtained cellulose materials were characterized by FT-IR,XRD and SEM.It was found the cellulose materials were basically free of lignin,indicating that the chemical bond between the three major components could be destroyed by hydrothermal-DES method.Hemicellulose and lignin could be removed to obtain high purity cellulose materials.?2?The DES filtrate dissolved in lignin was directly hydrogenated.The results showed Ru/?-Al₂O₃ had the best effect on the hydrolysis lignin under the Ch Cl-acetic acid system due to Ru/?-Al₂O₃with the appropriate BET surface area,the largerest pore volume and pore size distribution in the prepared Ru-based catalyst.Under the optimal reaction conditions?220?,4 h,the catalyst dosage was 100 mg?,in Ch Cl-acetic acid with Ru/?-Al₂O₃ as catalyst,conversion rate of lignin,the solid residue rate,the yield of liquid product and phenolic products were 81.4%,4.5%,20.5%,and 18.2%,respectively;and Ch Cl-acetic acid and Ru/?-Al₂O₃ had a universal adaptability to the substrate.It was found that the Ru/?-Al₂O₃catalyst could be reused,which effectively reduces the cost of commercialization with the proof of catalyst circulation experiments.