Study On The Effect Of Pretreatment On The Microstructure And Physicochemical Properties Of Plant Cell Wall

Lignocellulose is the most abundant carbon source in the world.After enzymatic hydrolysis,it can produce a large number of monosaccharides such as glucose and xylose.Monosaccharide can produce ethanol,butanol and other fuels and chemicals after fermentation by microorganisms.Therefore,it is considered as an ideal alternative material for fossil energy.The complex components and dense structure of lignocellulose are the key factors that hinder the biotransformation of lignocellulose.Pretreatment can break the natural resistance of lignocellulose and significantly improve the enzymatic conversion.The main research object of this paper was the effects of the three typical pretreatment methods,such as alkaline hydrogen peroxide pretreatment(AHP),hydrothermal pretreatment and deep eutectic solvents(DES),on the microstructure and physicochemical properties of plant cell wall,and the relationship between these changes and the increase of enzymatic conversion.The main research contents and results of this paper are as follows:1.Effect of pretreatment on chemical composition and enzymatic conversion of corn stover was explored.The main chemical composition and enzymatic conversion of corn stover before and after pretreatment were analyzed.It was found that the chemical composition of corn stover after pretreatment changed significantly,and the enzymatic conversion also increased significantly.After alkaline hydrogen peroxide pretreatment,the lignin content of corn stover decreased by about 63.0%,the hemicellulose content decreased less,the cellulose basically did not lose,and the glucan conversion increased by 139.8%.After hydrothermal pretreatment,the hemicellulose content of corn stover was reduced by 65.0%,the lignin content was not significantly reduced,the cellulose was slightly lost,and the glucan conversion was increased by 71.8%.The hemicellulose content and lignin content of corn stover pretreated with low eutectic solvent decreased by 50.0%and 43.5%,respectively,and the conversion of glucan increased by 74.5%.2.Effects of pretreatment on microstructure and physicochemical properties of corn stover was explored.The microstructure and physicochemical properties of corn stover before and after pretreatment were characterized by infrared spectroscopy,X-ray diffraction,thermogravimetric analyzer,X-ray photoelectron spectroscopy,scanning electron microscope,zeta potential and particle size analyzer.The specific surface area,crystallinity,zeta potential absolute value,water holding capacity and swelling capacity of pretreated corn stover increased significantly.Cellulose was enriched on the surface of lignocellulose,which increased the contact area with cellulase.The results showed that the specific surface area,crystallinity,zeta potential absolute value,water holding capacity and swelling capacity of corn stover were positively correlated with the enzymatic hydrolysis effect.The reason was that the removal of lignin and the destruction of hydrogen bond between lignin and cellulose and hemicellulose was increased the accessibility of cellulase,reduced the non productive adsorption of cellulase,and significantly improved the conversion rate of enzymatic hydrolysis.3.The particle size distribution of enzymatic hydrolysis residue and the molecular weight and dispersion coefficient of enzymatic hydrolysis product before and after pretreatment were analyzed.SEC-MALLS-RI and particle size analyzer were used to analyze the molecular weight of the hydrolysate and the particle size distribution of the hydrolysate residue.The results showed that the median particle size of enzymatic hydrolysis residue decreased from 425 ?m to 325 ?m,290 ?m and 250 ?m after hydrothermal pretreatment,DES pretreatment and AHP pretreatment.The molecular weight of enzymatic hydrolysis products were larger,and the proportion of incomplete enzymatic hydrolysis material was less,which indicated that the enzymatic hydrolysis of pretreated samples were more thorough,which verified the conclusion that pretreatment could effectively improve the glucan conversion.