Mechanism Of Carbohydrate Dissolution During Hydrothermal Pretreatmrnt Of Bamboo

In recent years,the reserves and reproducibility of fossil energy is limited despite the increasing global energy demand.Therefore,the use of biomass energy has arose extensive attention.As an environmentally friendly method,hydrothermal pretreatment has mainly used to pre-extract hemicellulose in woody biomass and obtain solid residue containing cellulose after pretreatment.Hydrothermal pretreatment to extract hemicellulose has gradually become the premise and core segment in utilization of biomass.In this thesis,the southern fast-growing wood powdery bamboo was selected as the raw material,and the effect of p H on the dissolution and degradation of carbohydrates and lignin was investigated by p H pre-adjustment hydrothermal pretreatment.In addition,the dissolution rule of xylan was also studied during hydrothermal pretreatment.The results provide reference for the further research on separation and purification of hemicellulose in hydrolysate and the high-value utilization.The main results are as follows:The effect of pH value and temperature of hydrolysate on the content of residual solid components and soluble components were studied.The influence of p H value on the recovery of cellulose,hemicellulose and lignin in the residual solid components was discussed.In addition,the dissolution and degradation mechanism of carbohydrate and lignin during p H pre-adjustment hydrothermal pretreatment was studied.The hydrolysis of cellulose and hemicellulose was investigated by measuring the content of carbohydrates in the hydrolysate.And the content of phenolic compounds was determined by ultraviolet spectrophotometer?UV?to explore the effect of p H on lignin degradation and dissolution.It indicates that the extraction rate of hemicellulose was 46.00%at p H 4.0.Meanwhile,the hydrolysis of cellulose and the degradation of lignin were inhibited maximally.The effcet of pH value on the residual solid components was studied by scanning electron microscopy?SEM?,fourier infrared spectroscopy?FTIR?,X-ray diffractometer?XRD?,and thermogravimetric analyzer?TGA?.In addition,two-dimensional nuclear magnetic technology?2D-NMR?was used to compare the changes of lignin structure with or without hydrothermal pretreatment.Through the analysis of the physical and chemical properties of the remaining solids components,the smoother surface and the increasing fiber crystallinity index of bamboo after p H adjustment hydrothermal pretreatment was founded.And the fiber bundles become clearly distributed,independent and complete.It also indicates that the thermal stability of the remaining solids components was improved,as well as the degradation of lignin was effectively inhibited during the pretreatment.The reaction kinetic model of the oligosaccharides and monosaccharides in the hydrolysate was constructed.And the effect of p H value and temperature on the reaction rate constant was discussed.The results show that the hydrolysis reaction rate of xylose was higher with the lower the p H value and the higher the temperature.And under the conditions of hydrolysate p H 4.0 and reaction temperature of 170?,the rate constant k₁ of the xylan hydrolysis reaction was1.99×10^-2,and the oligosaccharide hydrolysis rate k₂ was 5.10×10^-3.It indicates that the content of xylo-oligomers in the reaction liquid was high.The relationship between reaction rate K and hydrolysis temperature T was obtained from was found that the activation energy of the reaction was approximately equal at p H 4.0 and 170?.And under this condition,the rate of xylan hydrolyzing to oligosaccharides was faster,and consequently xylo-oligomers in the hydrolysate become increasing.