Structural And Distributive Characterization Of The Main Components Of Eucalyptus During The Hydrothermal And Alkaline Pretreatments

At present,the utilization of lignocellulosic raw materials is only 2%,which is due to the natural recalcitrance of the plant cell wall,making the efficient use of different components difficult to achieve.Therefore,an effective pretreatment technology can be used to reduce the natural recalcitrance of biomass and realize the efficient utilization of lignocellulosic raw materials.The raw material used in this experiment was Eucalyptus due to its rapid growth rate and adaptability.A synergistic pretreatment process based on hydrothermal pretreatment followed by alkaline pretreatment has been applied to treat Eucalyptus.The structure changes of the lignin and hemicellulose components were comprehensively characterized.At the same time,the topochemical changes of lignin and polysaccharide and the surface morphology of the cell walls were detected by confocal Raman and scanning electron microscopies.(1)A synergistic pretreatment process based on hydrothermal pretreatment followed by alkaline pretreatment has been applied to treat Eucalyptus,the structure changes of the lignin fractions were comprehensively characterized.It was found that the chemical bonds between lignin and hemicelluloses were cleaved to some extent,and thus can reduce the lignin content in biomass.The results also indicated that the contents of ?-0-4',?-?',and ?-5' linkages were decreased with the increase of hydrothermal pretreatment temperature and the cleavage of ?-O-4' linkages in lignin was accompanied with repolymerization reactions.31P NMR analysis showed that the content of aliphatic OH was reduced as the temperature increased and the total phenolic OH was elevated and then declined with the increase of temperature.(2)A synergistic pretreatment process based on hydrothermal pretreatment followed by alkaline pretreatment has been applied to treat Eucalyptus,the hydrolysis products in the hydrothermal hydrolysate,the structure changes of the hemicellulose fractions were comprehensively characterized.It was found that the linkages between hemicelluloses and lignin were significantly cleaved and more hemicelluloses were dissolved.The hydrolysis products in the hydrothermal hydrolysates were mainly monosaccharides,XOS and inhibitory compounds.Sugar and spectral analyses indicated that when the pretreatment temperature is low,the hemicelluloses(H0 and H170)were assumed to be mainly composed of a(1?4)-?-D-Xylp backbone with 4-O-methyl-D-glucuronic acids at 0-2 of the xylose residues and attached with various monosaccharides of rhamnose,arabinose,galactose,glucose,and mannose.(3)The topochemical changes of lignin and polysaccharide and the surface morphology of the cell walls were detected by confocal Raman and scanning electron microscopies.It was found that the cell wall was destroyed during the hydrothermal pretreatment with the formation of cracks on the biomass surface,and the disruption degree of cell walls was anabatic with the increased temperature.The lignin Raman spectra analysis revealed that the dissolution rate of lignin in the secondary wall regions was faster than that in cell corner middle lamella regions during the pretreatments.The polysaccharide Raman spectra revealed that the dissolution of hemicelluloses in different morphological regions was not uniform,and the hemicelluloses were dissolved mostly from the secondary cell wall regions during the pretreatments.