Application Of Photocatalytic Technology In Component Separation And Resource Utilization Of Pre-Hydrolysis Liquor

In order to improve the profitability and sustainability of biorefinery,scientists have devoted themselves into separating and transforming the whole components of lignocellulosic materials effectively in recent years,so as to realize the comprehensive utilization of the whole components of lignocellulosic resources.Combining the traditional pulping and papermaking industry with the concept of biorefinery,the pre-hydrolysis process of kraft-based dissolving pulp production was proposed to effectively separate hemicellulose,cellulose and lignin.However,some soluble lignin and other impurities in the pre-hydrolysis liquor（PHL）hamper the high-value utilization of hemicellulose.Therefore,the key to the high-value utilization of hemicellulose in the PHL is to remove lignin and other impurities as much as possible on the premise of retaining hemicellulose components.It is a good idea to use economic lignin removal processes and utilize lignin.In addition,new utilization processes of hemicellulose without removing impurities should be explored.In this paper,the application of photocatalytic technology in the component separation and resource utilization of PHL was explored by a series of photocatalysts treating the poplar PHL,and the research contents mainly includes the following four contents:Firstly,the PHL was obtained by hot water pretreatment of poplar chips,the components of poplar chips and PHL were analyzed,and the feasibility of removing lignin from PHL by catalyst electrostatic adsorption was explored.The results showed that there were 24.4%hemicellulose in poplar chips,the concentration of total saccharides in the PHL was 19.4 g/L,and xylosugar is the main component of hemicellulose-derived saccharides（HDS）,accounting for 66.5%.The photocatalysts could remove the lignin in the PHL by electrostatic adsorption,and the removal efficiency of catalysts was Bi OI>Bi OCl>Bi OBr>Ti O₂,while the hemicellulose was basically not lost.The zeta potential of each catalyst suspension was measured to be positive,while the electronegativity of lignin suspension was stronger than that of sugar solution at the same p H,so it was easier for lignin to be electrostatic adsorbed by the positive photocatalyst during the treatment process,while saccharide was preserved due to its lower electronegativity.Secondly,Bi OX（X=Cl,Br,I）was employed to treat the PHL,and the effects of elapsed time and dosage on the contents of lignin and HDS was analyzed.The results showed that the electrostatic adsorptions of Bi OX were very rapid,and the equilibriums could all be achieved within 10 minutes.The removals of lignin in the PHL increased with the increase of Bi OX dosage,accompanying with little loss of hemicellulose.When6.0 wt%Bi OI,Bi OCl and Bi OBr treating the PHL,the removal rates of lignin were 46.7%,36.3%and 33.9%,and the loss rates of HDS were 0.6%,0.1%and 0.1%.Then,lignin was transformed into high value-added product by BIOX photocatalysis,and the characterization and circulation performance of the catalysts were studied.The results showed that the gas products of lignin by photocatalysis were CO and CO₂,and the yield of products increased rapidly at first and then tended to be stable with the progress of photocatalysis.2-6-dimethoxy-1,4-benzoquinone（DMBQ）could also be obtained by Bi OI photocatalysis of lignin,which can be used to produce anticancer agents.The yield of DMBQ increased first and then decreased with the extension of irradiation,and reached the maximum value of 504.5μg in 9 hours.BIOX was recyclable and stable,various characterization of the catalysts at different stages illustrates the authenticity of lignin adsorption and photocatalytic regeneration of the catalysts,meanwhile,showed that the adsorption and photocatalytic reaction will not change the chemical properties of the catalysts.After the degradation of lignin on the surface of BIOX by photocatalysis,BIOX could be reused in the removal and transformation of lignin in the PHL,and maintained good cycle performance.Finally,xylooligosaccharide,the main component of the PHL,was used as the sacrificial agent to study its photocatalytic hydrogen production performance,and compared with methanol.The results showed that no hydrogen was detected in the photocatalytic hydrogen production of Ti O₂ and C₃N₄ without Pt.Pt-Ti O₂ and Pt-C₃N₄could be used as photocatalysts to produce hydrogen after loading 1%mass fraction Pt.After 24 hours of photocatalysis,4298.3μmol/g and 356.5μmol/g hydrogen could be produced with methanol as sacrificial agent,and 3054.5μmol/g and 495.6μmol/g hydrogen could be produced with xylooligosaccharide as sacrificial agent,based on the mass of catalyst.Xylooligosaccharide could be used as a sacrificial agent for photocatalytic hydrogen production,especially for Pt-C₃N₄,its hydrogen production performance was better than that of methanol.Pt-Ti O₂ and Pt-C₃N₄ had excellent cycle performance,the hydrogen production was slightly increased during the cycle photocatalytic experiments.