Directional Fractionation Mechanism And Fertilizer Utilization Study Of Biomass Remnant Lignin

Directional fractionation of three major components of biomass(cellulose,hemicellulose and lignin)is the basis of green and efficient utilization of biomass.Gradient acid method and bionic catalysis method were developed around cellulose first strategy and lignin first strategy.The composition,structure and fractionation strategy of biomass residual lignin were systematically studied,the mechanism of lignin fractionation were revealed.Meanwhile,two kinds of lignin modified slow-release fertilizers were prepared successfully.A good foundation for the green full recycling mode of biomass conversion was established.The main conclusions are as follows:(1)Research on directional fractionation of residual lignin from cellulose first process.Heterogeneous characteristics of lignin,especially molecular weight and functional groups,possess challenges to the effective conversion of lignin to valuable products.The residual lignin from fermentation process of cellulose first was directional fractionated,and its structure was systematically qualitative and quantitative analyzed.Different pH lignins were obtained from lignocellulosic ethanol fermentation residue of bagasse by alkaline solution and gradient acid precipitation.The lignin structures from different fractionized pH were identified using advanced techniques such as gel permeation chromatograph(GPC),quantitative 13C,31P,and HSQC nuclear magnetic resonance(NMR)in combination with chem/thermal property measurements.GPC results indicated the gradually decreased molecular weight of lignin with the fractionized pH.The results also demonstrated that the lignin precipitated at pH 9 had the highest β-O-4 ether bond and those at pH 5.0 owned the highest yield and relatively high aliphatic and phenolic hydroxyl groups.The lignin precipitated at pH 3 and below were mainly monomers or dimers.The study indicates that the gradient acid method is an convenient and effective method to fractionalize lignin into different types,that provides a possible path to customize the different lignin structures to enhance its processability(e.g.modification,polymerization,depolymerization and etc.)towards value-added bioproducts.(2)Research on directional separation and biomimetic catalytic degradation of lignin by lignin first strategy.Paper type Municipal Solid Wastes(MSW)as raw material,lignin first strategy was adopted for treatment.For the harsh treatment conditions of Fenton reagent catalytic process in previous studies(>220℃,supercritical),in this paper,H2O2 was replaced by sodium persulfate,combining with ferrous ions as biomimetic catalysts to catalytic oxidation degrade lignin.The results showed that the lignin was directional depolymerization into low molecular weight aromatics,the carbohydrate content in the solid residues increased significantly from 75.63%to 87.86%,and the saccharification rate of cellulose enzymatic hydrolysis reached 85.44%.The process avoided the use of complex and harsh pretreatment process,and the treatment temperature was reduced to 140℃.As follows,the reactor volume of carbohydrate saccharification and fermentation process was reduced,the amount of hydrophobic enzyme used for saccharification was reduced,and value from the lignin was added.(3)Research on the mechanism of oxidative degradation of lignin by bionic catalyst based on lignin model compounds.Lignin model compounds,such as 1-β,4-dimethoxy phenyl)-2-(2-methoxy phenoxy)-1 and 3-propanediol,1-(4-hydroxy-3-methoxy phenyl)-2-(2-methoxy phenoxy)-1 were successfully prepared.Lignin model compounds were directional depolymerized into aromatic compounds by persulfate catalyst under mild reaction conditions.The results showed that,compared with hydrogen peroxide-based bionic catalyst,the higher oxidizing power of persulfate catalyst can significantly reduce the need for harsh reaction conditions.Under mild reaction conditions(less than 100℃,1atm),up to 99%of lignin dimer can be effectively directional depolymerized as monomers.Gibbs free energy calculations show that the activation energy barrier of β-O-4 and Cα-Cβ bonds on persulfate radicals is lower than that of hydrogen peroxide,and a five-membered ring reaction mechanism is proposed,namely,the formation of 5-membered ring transition state between the sulfate radical anion(SO4-·)and lignin,which leads to the breakage of β-O-4 bond.It provides a theoretical basis for bionic persulfate catalyst to treat biomass and lignin valorization.(4)Research on fertilizer functional utilization of biomass residual lignin.According to the above research results,the residual lignin from fermentation process of cellulose first can be used as an excellent slow-release fertilizer raw material.Through simple modification/compound of the residual lignin,the coated type and carrier type slow-release fertilizers were successfully prepared.Residues with Polyvinyl Alcohol(PVA)were crosslinked by formaldehyde(FA),through etherification reaction.The LER-PVA-FA crosslinking film were prepared by flow casting method.Through single factor experiment,the crosslinking reaction conditions on the film optical properties and water absorption effects were analysed.Using SEM,FTIR,hot glue tensile test apparatus,the chemical structure,surface morphology and tensile strength of the of crosslinked membrane were characterized and analyzed.Slow-release fertilizer was prepared by coating method with cross-linked membrane and its slow-release effect in still water was measured.After CTAB and OTAC intercalating,organic montmorillonite was prepared successfully from sodium montmorillonite,which has a uniform layer spacing and a high inter-layer space(4.12 nm).With LER,alginate sodium,organic montmorillonite and chitosan as raw materials,developed the LER based vector SRF.The optimized preparation condition was got by uniform experimential design,and total nitrogen content can reach more than 40%.Through pot culture experiment,the fertilization effects of plant height,chlorophyll,POD activity,root activity of soil,urease activity and microbial diversity of the coated type SRF and normal fertilizers were tested.It verify that the SRF is more beneficial to plant growth than ordinary fertilizer,the nutrient period is longer than ordinary fertilizer,and the fertilizer effect of SRF can strengthen plant metabolism ability.It has markedly improved on nutrient utilization effect.The research of LER based SRF established a full amount of lignocellulosic utilization model.