Separation Mechanism Of Fast-growing Poplar Pre-hydrolysate Components And Xylo-oligosaccharide Preparation

The development and application of biomass refining technology is the transformation and innovation of traditional pulp and paper industry.With the progress of biomass refining technology,the high-valued utilization of hemicellulose dissolved in pre-hydrolysate（PHL）has aroused extensive attention.However,the presence of lignin in PHL would hinder the conversion of hemicellulose-based high value-added products,so it is urgent to develop efficient separation technology.To realize the purification and further high-valued utilization of hemicellulose,firstly,the PHL was prepared from fast-growing poplar by hydrothermal pretreatment;Then the effects of rotary evaporation,horseradish peroxidase and manganese peroxidase on PHL compnents were studied,and the mechanisms were elucidated by optimizing technological conditions;Finally,xylo-oligosaccharide was prepared from purified xylan by xylanase,and its structure and properties were analyzed.The results will provide theoretical and technical support for the hemicellulose purification and high-valued utilization from PHL.Evaporation could change the PHL properties and separate acetic acid and furfural without sugar loss.The PHL was concentrated by evaporation,the properties and compotents of PHL were characterized during the concentration process,and the effect of evaporation on xylan purification was investigated.The results indicate that evaporation could improve the ionic strength of hydrolyzate,compress the double electric layer of colloidal lignin and destroy its stability,lead to the lignin aggregation and self-sedimentation,and finally improve the removal rate of lignin in the purification process.When the volume ratio was 1.74,71.91%of lignin was removed by the synergistic treatment of 1.0 wt%Ca（OH）₂ and 0.8wt%activated carbon（AC）,the total xylose loss rate was 7.90%.Meanwhile,90.84%of furfural and 23.63%of acetic acid could be recovered.Horseradish peroxidase could polymerize small molecules of lignin to promote its separation efficiency.Horseradish peroxidase and AC were used to purified PHL,the properties and composition of PHL in the purification process were analyzed,and the changes of AC properties were characterized.The results showed that under the optimal conditions:HRP dosage 900 U·L^-1,H₂O₂ dosage29.40 m M·L^-1,p H=7,temperature 25°C and time 5 h,the molecular weight of lignin was significantly increased,the lignin removal was 80.78%,the total xylose recovery was 95.35%,and 62.02%of furfural was removed.AC shows high adsorption selectivity for lignin,and the total HHV of AC after first and second steps adsorption was 55.81 and 53.74 MJ·kg^-1,respectively.The efficient polymerization of manganese peroxidase on lignin showed great significance for the PHL components separation.Manganese peroxidase was used to treat the pre-hydrolysate and lignin was separated by AC,the effect was evaluated by lignin removal rate and the reaction mechanism of Mn P on PHL was further discussed.The results showed that Mn P could convert phenolic hydroxyl groups of lignin into phenoxy radicals,then achieve the polymerization of lignin by coupling withβ-O-4,β-β,β-5 bond types,and further improving the AC adsorption of lignin in PHL.Under the optimal conditions:H₂O₂ dosage 6.88m M·L^-1,Mn P dosage 375 U·L^-1,Mn²⁺dosage 0.25 m M·L^-1,p H=4.5,temperature30°C,and time 6 h,65.71%of lignin was removed and the total xylose recovery was 97.78%treated by 0.2wt%AC.The total HHV of AC after adsorption was71.12 MJ·kg^-1.The enzymatic hydrolysis method has the advantages of mild conditions,environmental friendliness and few by-products.Xylo-oligosaccharides were prepared by xylan in purified-PHL with endoxylanase,the enzymatic hydrolysis parameters were optimized,and the structure and properties of xylo-oligosaccharide were analyzed.The XOS 2-4 content reached 69.31%,56.44%and 56.95%when the enzyme dosage were 35.49,119.05 and 55.56 U/g xylan,p H was 5.5 at 50°C for 8 h.FT-IR,2D-HSQC and TG analysis demonstrated thatβxylose was the main unit of XOS and posess good stability lower than 150°C.The DPPH assay showed that the XOS exhibited concentration-dependent antioxidant activity.