Novel Separation Method Construction And Structure Analysis Of Lignin Based On Biorefinery

With the overuse of petrochemical products,the production and use of bio-based products to replace petroleum-based products has grabbed the global attention.The abundant and renewable lignocellulose,as a potential precursor material,has received unprecedented attention.Lignin,the main component of lignocellulosic biomass,has a great application prospect in the production of bio-based phenol chemical products instead of petroleum resources because of its natural aromatic ring structure.However,the cell wall is highly resistant to the biorefinery process due to the "natural complexity" of the structure,and lignin plays a crucial role in the resistance due to the complexity of structure and the uncertainty of bonding mechanisms.Thus,the efficient separation of lignin macromolecules and the comprehensive understanding of lignin in the biorefining process is an important means to solve this obstacle.Therefore,this study systematically constructed a new separation method of lignin from biomass and analyzed the lignin macromolecular structure obtained from the separation.(1)Swelling with DMSO/[Emim]OAc solvent system and separating with low concentration dioxane were used to separate lignin components with high yield and complete structure under mild conditions to study the changes of lignin structure before and after swelling.During swelling,the components in the plant cell wall were rearranged and the compact structure was broken,which made the enzymatic hydrolysis efficiency of matrix reach 88.7%,and promoted the subsequent lignin separation.The yield of lignin obtained under 80% dioxane aqueous solution was up to 85.3%,and the lignin structure were less affected by the dissolution and regeneration process,and the structure is representative.(2)A double ball mill and enzymatic hydrolysis method for separating lignin was developed.The method is simple and can obtain lignin with high yield(up to 95%),which can be used to analyze the structural properties of lignin in poplars of different growth ages.After two ball milling treatments,the accessibility of cellulase can be increased,so that most of the carbohydrates can be removed,which can represent the lignin macromolecules in different morphological regions in the plant cell wall.Compared with the traditional enzymatic hydrolyzed lignin,there is no significant difference in the structural characteristics except for p-hydroxybenzoate(PB)and S/G.Except for the high PB content in 1-year-old poplar,there was no significant change in the structure of lignin in 1-5-year-old poplar.(3)Low-cost and environmentally friendly hydrothermal treatment combined with various chemical pretreatment processes was used to achieve efficient separation of lignin from bamboo and Triarrhena lutarioriparia.The effect on lignin structure under different hydrothermal conditions and delignification solvent was also clarified.The results showed that most of the hemicelluloses can be separated by hydrothermal treatment,and the effect was different to some extent depending on the raw materials.The synergy of hydrothermal and subsequent chemical treatment can achieve high yield of lignin separation,The separation of lignin in acidic conditions caused severe cleavage of lignin linkages,while the organic base(n-propylamine)assisted with AQ can effectively protect the lignin structure.(4)A solvent system complexed with zinc chloride(Zn Cl2)and lactic acid(Lac)was used to achieve the efficient separation of lignin under mild conditions,while lactic acid converted from the residue and the solvent system recycled can realize closed-loop biorefinery.The results showed that this solvent system had a good swelling effect on the cell wall,and the removal ratio of lignin can reach 79.7% at 90 ° C,which is much higher than that of Ch Cl/Lac and single Zn Cl2 or lactic aqueous solutions under higher conditions.The residue went through Zn Cl2/Lac treatment could be converted into 84.6% lactic acid.Besides,the lignin structure was greatly affected by temperature,and could be tailored for specific applications by changing the reaction conditions.The Zn Cl2/Lac solvent system exhibited excellent recyclability providing a great potential to achieve a closed-loop biorefinery.(5)An aldehyde-assisted lignin component separation method was established.The lignin components with high yield and high content of ?-O-4 were separated by adding formaldehyde/acetaldehyde solvent in the process of biomass component separation and its degradation was also studied.The results showed that lignin with high ?-O-4 content can be obtained with the assist of formaldehyde,but the enzymatic hydrolysis efficiency of the residue after the acid hydrolysis to eliminate the modification effect was only 30.38%.The yield of acetaldehyde-assisted separation of lignin could reached to 85.1%,and the glucose yield of residue without acid hydrolysis was up to 75.12%.The total yield of monomers was 33.00%,and the selectivity of lignin monomer(2,6-dimethoxy-4-propylphenol)was 46.61%.