Study On Fast Hydrothermal Pretreatment Of Poplar Wood And Its Enzymatic Hydrolysis

Poplar is one of the world’s three major fast-growing trees(poplar,pine and eucalyptus).In China,it is mainly distributed mainly in Central China,North China,Northwest China,and Northeast China.The distribution of fast grow poplar trees is relatively concentrated.Therefore,poplar wood is an important raw material for biomass refining.Under the current shortage of fossil resources,developing the full use value of poplar wood and converting it into high-quality bioenergy is of great significance for reducing excessive dependence on petroleum resources and protecting the environment.It can also increase the value of wood fiber resources.Utilization to create huge economic value,environmental value and social value.Artificial antioxidants are synthesized from fossil sources and now widely used in polymer,food,and cosmetics industries.The gradual depletion of fossil sources makes it practically significant and necessary to produce green antioxidants using renewable lignocellulosic resource.Herein,short-time hydrothermal(STH)treatment was developed for production of lignin-derived polyphenol antioxidants(LPA)from poplar wood under conditions of high temperature and high pressure.LPA yield from 21.5%to 37.6%on basis of lignin in untreated wood was obtained from STH treatments as result of lignin depolymerization at conditions of 190-200°C,10 MPa,5-8 min.Depolymerization reactions was confirmed by the much lower molecular weight of1076 g/mol of LPA than 4094 g/mol of native lignin.NMR analysis revealed the structural features of lignin in the isolated LPA,namely syringyl and guaiacyl units with well-preserved inter-unit linkages.Folin-Ciocalteu assay indicated that each LPA molecule contains 5.4 phenolic hydroxyl groups on average,much higher than other technical lignins.The remarkable antioxidant ability of LPA was verified by the radical scavenging index of 53.5-67.3,much higher than 0.2-11.1 of commercial antioxidants BHT and BHA.STH treatment only requires water and heat for production of high-value antioxidant,and therefore provides a green and sustainable way for lignocelluloses utilization.The STH treatment of poplar wood was conducted and attained 81%of hemicelluloses yield and 38%of lignin yield,respectively,within 5 min at 200°C.The combined process of microfiltration,ultrafiltration and activated carbon adsorption was developed to fractionate lignin and sugars in hydrolysate.Removal of about 56.75%of the lignin in the poplar rapid hydrothermal treatment solution through a 5μm microporous membrane.Afterwards,ultrafiltration using 3000 daltons molecular weight cut-off membrane recovered 68.69%of the residual lignin.The filtrate from ultrafiltration was further processed by adsorption using activated carbon,and 87.97%of the residual lignin was recovered.The fractionated lignins from the combined processes showed diversity in molecular weight and functional groups,which is valuable for product diversification.The obtained sugar syrup showed a good sugar recovery of 42.8%and remarkable purity of 88.2%.To elevate the glucose yield from the enzymatic hydrolysis of poplar wood for bio-ethanol production,STH treatment of poplar wood was conducted at 200°C for a short period of time from 5 min to 25 min.It was found that the STH treatment could remove more than 85%of the hemicelluloses and more than 30%of the lignin in the poplar wood.The cellulose conversion of enzymatic hydrolysis achieved 82%at a low cellulase dosage of 10 FPU/g substrate.The enhancement digestibility of poplar wood was ascribed to the higher accessibility of cellulose,as the specific surface area of the substrate increased from 3.0 m~2/g to 7.1 m~2/g from the of untreated wood to the STH-treated wood.