Insight Into The Mechanism Of Fenton Pretreatment To Promote The High-value Conversion Of Lignocellulose

As a common lignocellulosic material,corn stalk is a good renewable lignocellulosic material with abundant yield,wide source and low price.It can be used in the production of biomass ethanol,which not only solves the agricultural environmental pollution caused by crop stalks burning,but also turns waste into treasure to alleviate the energy crisis.However,due to the long-term evolution of plants,a self-protective barrier has evolved.Its complex and compact structure protects itself from the external environment and brings many difficulties to the transformation and utilization of biomass resources.In this experiment,corn stalks were used as raw materials.In order to fully understand the molecular structure and mutual bond relationship of various components of lignocellulose,the key chemical structures affecting the separation performance and ultrastructure of the components in the molecular structure,we studied the mechanism of Fenton pretreated corn stover to promote its component separation and enzymatic hydrolysis and the mechanism of thioglycolic acid-assisted Fenton treatment of corn stover to increase its enzymatic properties.Finally,we also researched a preliminary study on ethanol fermentation of pretreated materials.This project aims to provide an important theoretical reference and practical basis for the construction of a highly efficient and clean pretreatment system for lignocellulose.After the Fenton pretreatment,the enzymatic hydrolysis efficiency of corn stalks was significantly improved,and the separation of lignin was more clean and efficient.The extraction efficiency of lignin was increased by 254%after Fenton treatment for 72 hours,and was extracted from corn stalks and their samples before and after treatment.Structural characterization and analysis of lignin extracted from its samples yielded the following conclusions;The molecular weight of the lignin extracted from the sample after Fenton treatment was slightly lower than that of the untreated sample and the main chemical bonds of lignin such as methoxy group and β-O-4 bond did not change much,but some of the CC bond was destroyed after treatment,such as the absorption intensity of B β bond was disappearedCombined with the structure of solid-state nuclear magnetic carbon spectrum,it was found that the change of these chemical bonds caused the destruction of the original connection structure between hemicellulose and lignin,and the lignin main body benzene ring structure did not change greatly.The side chain and the hemicellulose-linked group are destroyed,causing them to separate from the hemicellulose,which leads to the partial hemicellulose release,thereby forming a large number of pores and open structures on the surface of the substrate,destroying the original "lignin".-Hemicellulose" protective barrier that exposes cellulose inside the substrate to improve enzymatic performance and efficient clean separation of lignin.In terms of composition,the Fenton process retained most of the cellulose while removing some hemicellulose and a small amount of lignin.After the corn stover was treated with Fenton for 72 hours,the cellulose retention rate was 91.26%,hemicellulose.The retention rate was 87.14%and the lignin retention rate was 90.4%.Then the chemical composition and physical structure of corn stover before and after pretreatment were analyzed.The solid-state nuclear magnetic carbon spectra of corn stover before and after Fenton treatment showed that the hemicellulose content of the substrate after Fenton treatment was significantly reduced.The XRD results showed that the crystallinity of the sample after Fenton treatment increased,and the FT-IR results showed that after Fenton treatment,the content of amorphous cellulose is obviously increased which indicating that the Fenton treatment process destroys the crystalline region of cellulose,and at the same time removes part of hemicellulose and lignin,and removes the amorphous component(hemicellulose and lignin).The cellulose crystallinity rises higher than the cellulose crystallinity caused by the destruction of the cellulose crystal region,so that the cellulose crystallinity is generally increased.The Fenton process breaks the original structural order of the substrate,forming a large number of pores and lamellar structures on the surface,forming an open structure with greater roughness and specific surface area and porosity;due to the Fenton reaction has a strong oxidizing effect,the oxygen-carbon ratio of the surface of the substrate is obviously increased after Fenton treatment.And the contact angle test of the substrate after Fenton treatment shows stronger hydrophilicity,which is beneficial to the adsorption of cellulase and enhance enzymatic hydrolysis effect.The mechanism of the effect of thioglycolic acid on accelerating Fenton treatment and shortening the reaction time was preliminarily demonstrated:the surface morphology of the substrate increased significantly after the addition of thioglycolic acid,and a large open structure was formed,and the pore volume increased significantly.The larger pore volume increases the inner surface of the substrate,which can accommodate more cellulose.It is beneficial to the adsorption of cellulase,and is more conducive to the enzymatic hydrolysis of cellulose inside the substrate,thereby improving the conversion efficiency of cellulose.