| In recent years,with the increasing demand for dissolving pulp,the amount of biomass by-products generated from the pre-hydrolysis kraft pulping process also increases significantly,and these biomass by-products mainly include pre-hydrolysis liquor rich in hemicelluloses,lignin,and hemicelluloses remaining in the dissolving pulp.Since the treatment of the above-mentioned by-products is challengeable,this work is mainly focused on the high value-added conversion and utilization of these by-products from the dissolving pulp production process.The hemicelluloses produced from the dissolving pulp were characterized by NMR,which indicated that these hemicelluloses were mainly comprised of the high purity xylan almost without branched-chain.Both acid and enzymatic hydrolyses were applied to prepare xylooligosaccharides(XOS)from the residual hemicelluloses in the dissolving pulp.The results showed that the highest XOS yield(45.18%)obtained from the acid hydrolysis was achieved with 1%sulfuric acid at 120℃ for 60 min,and xylohexaose was the major products,which accounted for 47.00%of the obtained XOS.For enzymatic hydrolysis,under optimal conditions(120 IU/g substrate,8 h),the highest XOS yield of 42.96%was observed,and xylobiose and xylotriose comprised 90.55%of the XOS.The hydrothermal carbon spheres have been prepared by the method of hydrothermal carbonization of the above hemicelluloses.These hydrothermal carbon spheres were activated using different activators(KOH,K2C03,Na2C03,and ZnCl2)at 800℃ under N2 flow to improve their electrochemical performance as supercapacitor electrodes.The structural and properties of the carbon spheres were studied using SEM,N2 adsorption/desorption,XPS,Raman spectroscopy and electrochemical workstation.All carbon spheres maintained spherical morphology,except the carbon spheres activated by KOH.Besides,the specific surface areas and electrochemical performance of carbon spheres after activated were improved significantly,which was in the order of ZnCl2>K2CO3>KOH>Na2CO3.The specific surface area of the carbon spheres treated by ZnC12 was detected to be 2025 m2/g,and a specific capacitance as high as 218 F/g at 0.2 A/g in 6 M KOH was obtained in three-electrode system for the carbon spheres treated by ZnCl2.In addition,the carbon spheres electrodes treated by ZnCl2 showed excellent electrochemical performance in 2 M Li2S04 electrolyte with high specific capacitance(137 F/g at 0.5 A/g),energy densities(15.4 Wh/kg),and good cyclic stability(95%capacitance retention over 2000 cycles).The hydrothermal carbon microspheres have been prepared by the hydrothermal carbonization of hemicelluloses-rich pre-hydrolysis liquor(PHL),and which were used for contaminant removal.The yield of the carbon microspheres directly derived from the hydrothermal carbonization of the hemicelluloses-rich PHL(22.1%)was almost twice than that from xylose(13.1%).Furthermore,sulfuric acid and the lignin in the PHL could significantly improve the yield and change the size of the carbon microspheres obtained from the PHL.Additionally,the activated carbon microspheres functionalized with acrylic acid showed improved adsorption capacities for Pb(Ⅱ)ion(273.4 mg/g)and methylene blue(701.3 mg/g).In order to improve the vanillin yield from lignin,in this work,the relationship between lignin linkages and vanillin yield was explored.Five lignins(kraft lignin,alkali lignin,lignosulfonate,and two enzymatic lignins)and several lignin model compounds(monomers,dimers,and polymers)were characterized by NMR spectroscopy and oxidized to prepare vanillin.Results indicated that the interunit linkages of the lignin had a significant influence on the vanillin yield.The more β-O-4 linkages in lignin,the higher yield of corresponding aldehydes was obtained.It is believed that the vanillin yield can be significantly improved by using lignins with a high content of β-O-4 linkages. |
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