Separation Of Poplar Lignin With DESs And Its Preparation And Application Of Nanoparticles

In order to alleviate the energy crisis and environmental pollution caused by the excessive use of non-renewable resources,and to promote the green and scientific development model of circular economy to achieve carbon neutrality and emission peak,it is imperative to develop new renewable resources to deal with the potential energy crisis and replace fossil resources.Lignocellulosic biomass resources,as a kind of biomass,have attracted extensive attention of researchers,due to a series of advantages such as wide distribution,abundant reserves,and recyclability.In the process of rational utilization of biomass resources,whether it is processed into composite materials or converted into energy,the first job is to separate its various components efficiently and economically to achieve high-value utilization.Through physical or chemical means to efficiently separate and extract the three components in the form of complete components,and then carry out various chemical reactions through the chemical groups in the components to prepare functional materials for utilization,so as to achieve the purpose of high-value biomass resources.In this study,poplar wood was used as raw material to extract lignin by deep eutectic solvent（DESs）,and the obtained lignin was synthesized with UV shielding composite membrane and p H corresponding gel to achieve high value utilization of biomass energy.The extraction regular pattern of lignin components in poplar and the morphological structure and physicochemical properties of lignin were systematically discussed.The lignin was extracted and separated by pure DESs system and solid acid catalyst.The dissolution regular pattern and physicochemical properties of the extracted lignin in different solvent systems were analyzed by FT-IR,2D-NMR and GC-MS.The DESs of lignin in different molar systems,the lignin dissolution regular pattern of different pretreatment time and the retention rate of solid residue were discussed,and the quantitative relationship between lignin yield and solid residue yield was discussed;The promoting effect of three different solid acids(H₃O₄₀PW₁₂,Fe Br₃ and Al Cl₃)were added to DESs system on lignin separation was discussed to achieve the rapid separation of lignin.The preparation of lignin from DESs and the preparation of nano shield lignin from dripping precipitation method and dialysis method were used to prepare UV shielding composite film,and p H corresponding gel to realize the high value utilization of biomass resources.This work may provide a new idea for developing high efficiency,green and low energy lignin conversion process.The main research contents and innovative achievements of this paper are as follows:（1）Based on the DES system synthesized by choline chloride and lactic acid,glycerin,ethylene glycol and isopropanol,the rules of lignin separation and extraction from poplar materials were explored.The solvent was a green solvent and has the advantage of low price.It can separate lignin components from lignocellulosic materials under relatively mild conditions.This experiment mainly explored the separation effect of DESs system synthesized by choline chloride,lactic acid and ethylene glycol on poplar lignin.In particular,choline chloride and lactic acid system were very obvious for the extraction of biomass raw materials.It was found that the most suitable condition was 120℃,the molar ratio was 1:10,and the reaction time was 12 h.Under this condition,80.4%of the lignin was separated.Lignin was characterized by FT-IR,GPC,2D-NMR and a series of analytical methods.The obtained lignin has a complete structure,the basic skeleton of lignin was intact,and unsaturated groups exist in lignin.The purity of lignin isolated from lactic acid and glycerol was 94.18%and 91.31%respectively.Lignin has a lower molecular weight（<3000）and a lower polydispersity index（PDI<2.0）.（2）The lignin extracted by DESs with high purity and lower molecular weight,but the process was inefficient,which required 12 h or more.In order to further improve the efficiency of pretreatment of lignin separation with DESs system synthesized by choline chloride and lactic acid,three solid catalysts(H₃O₄₀PW₁₂,Fe Br₃ and Al Cl₃)were added to DESs to promote component separation.The catalytic effect of phosphotungstic acid catalytic system was the most obvious.H₃O₄₀PW₁₂ and Fe Br₃ enhanced separation of DESs system was an effective method to extract lignin with high-purity and antioxidant.The recoveries yield of DES-W（4h）and DES-Fe（8h）systems were 82.2%and 80.9%respectively.FT-IR and 2D-NMR results showed that the poplar lignin isolated by DESs was mainly composed of syringyl and guaiacyl unit.（3）Lignin nanoparticles（LNPs）were prepared from the residual solution pretreated by DESs by dialysis and drop precipitation method.The prepared nanoparticles were characterized by dynamic light scattering（DLS）,transmission electron microscopy（TEM）,scanning electron microscopy（SEM）,GPC,2D-HSQC,etc.The effect of p H value on the morphology,size and chemical structure of LNPs was discussed.The results showed that the size of LNPs prepared by dialysis method and drop precipitation method was 100-200nm,and the particles still possessed the aromatic structure of original lignin by FT-IR,2D-NMR and other instruments.At the same time,the prepared LNPs were stored at room temperature for 60 days,and DLS analysis showed that the particle size distribution of LNPs was stable and uniform,and there was a Tyndall effect in the colloid.（4）The LNPs composite film with UV shielding function was prepared by mixing LNPs with heated PVA.LNPs and PVA were successfully cross-linked and had good hydrophobicity.The measured contact angle of the composite film was as high as 115.1°.With the increase of LNPs content in the composite membrane,the UV shielding ability of the composite film was gradually enhanced,and the barrier ratio was 84.2%when the content was 6%.Through the mechanical property test of the composite film,it was found that the addition of LNPs improves the tensile strength of the composite membrane.When the content of LNPs is 10%,the tensile stress of the composite membrane reaches 74.6 Mpa.Because LNPs and PVA are degradable materials,composite film materials have ideal biodegradability and environmental protection.（5）p H-responsive gels were synthesized using LNPs and PEGDGE under alkaline conditions.Through analytical characterization,the gel has good mechanical properties,rapid p H stimulation response and reversibility.The gel can achieve"straight-bend"deformation by alternating immersion in KOH at p H=12 and HCl at p H=2.At the same time,the fully responsive gel was used to prepare activated carbon under high temperature environment to realize the reuse.The obtained activated carbon had a very high specific surface area(2069 m² g^-1),and had a very good adsorption effect on methylene blue.The adsorption amount was 667 mg/g,realizing the high value utilization of wood biomass resources.