The Study Of Fractionation And Separation Of Lignin And Preparation Of Nanosphere Based On GVL/H₂O System

In nature,lignin is the second largest plant source polymer after cellulose.Lignin is produced in large quantities as a by-product of pulping and bioethanol production processes.In order to improve the conversion efficiency of biomass and the utilization value of lignin,the fractionation and separation of lignin and preparation of nanosphere using GVL/H2O system were studied in this paper.(1)Corn straw was using a pretreatment ofsteam explosion(different severity factor,SF,3.29-4.37)coulping GVL(γ-valerolactone)/water extraction(30-60%,v/v,for 0.5-2 h)at room temperature.After compound pretreatment,the corn straw showed significantly different cell wall compositions with respect to cellulose,hemicelluloses and lignin fractions.In this paper,the lignin content was reduced by significant 74.0×0.20%,and reported maximum cellulose content(68.60%)with almost all of hemicelluloses solubiluzation when corn straw pretreated with 60%GVL/H2O system.Enzymatic saccharification of SECS(1.5 MPa for 10 min)and GSECS(60%GVL for 0.5 h)at various solid loadings,an increase in the solid loadings significantly improved the concentration of sugar.And a maximum glucose concentration of 55.51±0.57 g/L and 81.25±0.06 g/L were obtained from SECS and GSECS at 20%solid loading,respectively.Moreover,a hydrolysis saccharification rate was produced from GSECS substrate(20%solid loading)of 63%(489 mg/g reducing yield).The results indicated that the CS implementation of a combined pretreatment step to removed lignin before enzymatic saccharification is promising for bioethanol production with great potential.(2)Based on the polydispersion of lignin molecular weight,y-valerolactone(GVL)was used as a green solvent for fractionation to improving the homogeneity of lignin molecular weight when mixed with H2O.The enzymatic hydrolysis lignin(EHL)was subdivided into three different fractions(F1,F2,and F3)by dissolving it completely in 60%aqueous GVL and then following gradient precipitation in 40%,30%,and 5%aqueous GVL solutions,sequentially.Detailed characterization techniques(GPC、2D-HSQC NMR、31PNMR、Py-GCMS)were conducted to provide a comprehensive evaluation of the three obtained lignin fractions.The gel permeation chromatography(GPC)analyses showed that the three fractions presented lower polydispersity than the parent EHL and,furthermore,a gradual decreasing molecular weight due to the different solubility of various molecular weight lignins in aqueous GVL solvents.The structural analyses revealed that with the decrease of molecular weight,the guaiacyl unit content in lignin fractions decreased,with significant increases of functional groups(i.e.,aromatic/aliphatic hydroxyl and carboxyl groups).Moreover,the proposed fractionation mechanism was further investigated on the basis of Kamlet-Taft parameters.The solvent recycling study showed that the aqueous GVL has a high recovery,and the recycled GVL had the same lignin fractionation performance as fresh GVL.(3)To investigate the effect of lignin heterogeneity on the preparation properties of nanospheres,the lignin fractions were dissolved in 60%GVL/water system,and the lignin nanosphere carrier was prepared by adding water drop by drop.The results show that the GVL/H2O system can successfully produce the uniform shape of lignin spheres at room temperature,and the particle size decreases with the increase of lignin molecular weight.Pd@lignin complex was formation under acidic conditions by sedimentation reduction method.Pd@lignin was characterized by the various structure characterization technology including FTIR,SEM,HR-TEM,TEM-EDS,TEM-Mapping,XPS,XRD,ICP-OES,particle size distribution and Zeta.When compared to the lignin fraction with small molecular weight(Pd@Fl),the lignin that with large molecular weight(Pd@F3)can prepare the nanosphere more efficiently,and the content of palladium(0)nanoparticles supported on lignin is higher.which greatly improved the catalytic efficiency of reduction of Cr(Ⅵ)to Cr(Ⅲ).