Separation And Characterization Of Lignin From Agroforestry Biomass By Alkali-Catalyzed Organic Solvent

The over-dependence of human on petrochemical resources leads to the shortage of resources and causes many environmental problems.Biomass is the most abundant renewable organic carbon resource in nature,which can be converted into energy,materials and chemicals instead of petrochemical resources.As one of the main components of biomass,lignin is abundant and the only aromatic polymer in plants,which has great application potential.Therefore,the development of biomass refining technology will be restricted if lignin can be separated efficiently from agricultural and forestry biomass components and be utilized with high-added value.In this thesis,corncob hydrolyzed residue and willow from agricultural and forestry biomass as raw materials.Firstly,the milled wood lignin structure of the prepared corncob and its acid hydrolysis residue were characterized and the antioxidant properties of the lignin were studied.Then,high yield extraction of lignin from corncob hydrolyzed residue was carried out by alkali catalyzed methanol/water solvent system,and the lignin obtained under mild conditions was comprehensively characterized.Finally,the lignin in willow was separated and extracted by alkali catalyzed sulfoxide/aqueous solvent system,which was characterized comprehensively.In the process of biomass refining,agricultural and forestry biomass corncob can be acidified to produce xylose,and the acid hydrolysis residue can be further utilized.Here,we prepared and characterized MWL in corncob and its acid hydrolysis residue in detail.The results showed that the content of carbohydrate in MWL was less(1.1%)and the separation rate was higher(8.9%).The molecular weight of hydrolysis residue MWL(Mw: 6121 g/mol,Mn: 4104 g/mol,PDI: 1.5)was higher than that of corncob MWL(Mw: 2847 g/mol,Mn: 2283 g/mol,PDI: 1.3),indicating that condensation reaction occurred in xylose production process.Compared with corncob MWL,the hydrolyzed residue MWL contains more phenolic hydroxyl groups and carboxyl groups,indicating that the fracture of β-O-4 and the formation of carboxyl groups are the main structural changes.The hydrolysis residue MWL(RSI=0.5)had good antioxidant activity and was higher than the commercial antioxidant BHT(RSI=0.4),indicating that lignin in the hydrolysis residue of corncob has the potential as a natural antioxidant.Lignin in the hydrolyzed residue of agricultural and forestry biomass corncob has a relatively complete structure and retains the characteristics of high activity,which has high application value.Therefore,it is of great significance to extract lignin from hydrolysis residue by a mild method.The addition of alkali catalyst in methanol/water system promoted the dissolution of lignin from the hydrolysis residue,and the extraction rate of lignin increased from 4.5% to 61.8%.The optimal conditions for high extraction rate of lignin were 1%Na OH,1 h and 80 °C.At this time,the yield of solid residue was 63.2%,the removal rate of raw lignin was 81.9%,the extraction rate of lignin was 61.8%,the retention rate of glucan in solid residue was 71.9%,and the retention rate of xylan was 37.3%.Regarding the molecular weight of lignin,the molecular weight of lignin hydrolyzed residue(Mw: 3265 g/mol,Mn: 1866 g/mol,PDI: 1.8)is lower than that of MWL by hydrolyzed residue,which is due to the higher polydispersability caused by lignin condensation in xylose production.High purity and antioxidant lignin from biomass willow was isolated by alkali catalyzed sulfoxide/aqueous solvent system.In the experiment,the effects of temperature,water/sulfoxide ratio,Na OH dosage on the extraction of lignin were investigated.In a 50/50(w/w)sulfoxide/water system at 170 °C,44.4% of the lignin was recovered after 54% delignification.With the increase of the amount of alkaline catalyst,the removal rate of lignin was increased to about 94%,and the yield of lignin was increased to about 70%.Among them,50/50(w/w)sulfoxide/water solvent system containing 4%Na OH extracted lignin with high yield and purity,with typical structural characteristics of lignin.A comparative study was carried out between the recovered lignin and the control lignin(MWL).In addition,extracted lignin has richer in phenolic hydroxyl groups and has a good free radical scavenging ability,and its antioxidant activity is better than that of commercial antioxidants.Therefore,lignin can play a role as an antioxidant in the field of food and promote the application of lignin in the process of biological distillation.