Effect Of H-AFEX Pretreatment On The Lignin Structure And Enzymatic Hydrolysis Of Corn Stover

With the depletion of fossil energy and the gradual deterioration of the environment,the search for clean energy has increasingly become the focus of social attention.Biomass fuel ethanol has been widely studied as one of the most important renewable energy sources for industrial applications.Lignin is considered to be a major obstacle in the preparation of biomass fuel ethanol.Because of the presence of lignin,the lignocellulosic material has a natural "resistance",which greatly reduces the conversion efficiency of biomass fuel ethanol.Therefore,in the preparation of biomass fuel ethanol,the raw materials need to undergo a pretreatment process,and an effective pretreatment process can greatly reduce the inhibition effect of lignin in the fuel ethanol process.At the same time,studying the structural changes of lignin in the pretreatment process can promote the research and development of the pretreatment process.In this paper,corn stover were studied,with hydrogen peroxide pretreatment(H2O2 pertreatment),Ammonia Fiber Expansion Pretreatment(AFEX)and Hydrogen peroxide-ammonia Fiber Expansion Pretreatment(H-AFEX)was used as a research method to extract lignin from different pretreatment processes for characterization experiments.The structural changes of lignin in the pretreatment process and the effects of lignin on the enzymatic hydrolysis of corn stover were investigated.This provides a theoretical basis for the optimization of the pretreatment research process and the efficient utilization of lignin.The main research contents and conclusions of the thesis were as follows:(1)After H-AFEX pretreatment,the content of C and H in lignin decreased,and the content of N and O increased.The pretreatment of H-AFEX could break the lignin side chain and reduce the molecular weight of lignin.The ester in lignin Keys,alkyl ethers,and aryl ether bonds undergo significant cleavage.G-type(guaiacyl)lignin is most susceptible to degradation during pretreatment.Ferulic acid and p-coumarate in lignin degradation occurs and the degree of degradation increases with IV the increase of experimental conditions.However,during the pretreatment process,the resin alcohol,the coumarin and the benzene ring structure are relatively stable and are not easily destroyed.(2)The N and O content changes of lignin during pretreatment depend on AFEX pretreatment and H2O2 pretreatment process,respectively;When pretreatment with H-AFEX,the molecular weight of lignin can be significantly reduced,and its structure is more uniform than that of untreated and single hydrogen peroxide and AFEX pretreated lignin;The change of carbonyl and ester bond in lignin mainly depends on AFEX pretreatment;the degree of fragmentation of alkyl ether bond and the degree of degradation of G type lignin structure during H-AFEX pretreatment are weaker than single H2O2 pretreatment and AFEX pretreatment.(3)Lignin has a significant inhibitory effect on the hydrolysis of single microcrystalline cellulase;When unpretreated corn stover is used as the substrate for enzymatic hydrolysis,the type of lignin and the amount of lignin added have little effect on the process of enzymatic hydrolysis.;When pretreated corn stover is used as the substrate for enzymatic hydrolysis,the enzymatic hydrolysis efficiency of corn straw is greatly improved by H-AFEX,and the conversion rate of glucan and xylan is compared with that of untreated straw.The increase of 110.61% and 134.78%,the total sugar yield increased by 2.19 times,The lower molecular weight lignin has a relatively weaker effect on enzymatic hydrolysis;that is,the high temperature pretreatment of lignin has a weak influence on the enzymatic hydrolysis process;at the same time,the high concentration of aliphatic hydroxyl groups from lignin causes the enzymatic hydrolysis efficiency to decrease with the increase of lignin addition;And lignin has a stronger effect on the enzymatic hydrolysis of pretreated corn stover.(4)The enzymatic residue lignin has a relatively high C and N content,but the O content is low,the molecular weight is greatly reduced,the polydispersity coefficient is large,and the molecular weight distribution is wide;The alkyl ether bond in the enzymatic lignin is broken;the enzymatic residue lignin is HGS-type lignin.Due to the degradation of the main G-type lignin during the pretreatment,S/G ratio increases,the S-type(syringyl)structure is relatively increased.The lignin of the enzymatic residue is mainly composed of S-type monomer.The enzymatic residue lignin contains relatively low ferulic acid esters and p-coumarate structure;the enzymatic hydrolysis of lignin pyrolysis requires higher activation energy,higher thermal stability,and post-pyrolysis coke The yield is higher than that of the raw material lignin.