Peracetic Acid-Based Strategies For Lignocellulosic Biomass Fractionation And Conversion

Peracetic acid（PAA）as an important oxidant,is widely used in food,wastewater treatment,pharmaceutical,and pulp and paper industries.In recent years,the application of PAA in lignocellulose has been continuously developed,showing good prospects for development.However,high PAA concentration and long reaction time led to the degradation of carbohydrate polymers and resulting products.Therefore,to address the challenges,PAA based oxidative strategies were applied in lignocellulose utilization,avoiding the degradation of carbohydrate polymers and resulting products.The effects of the chemical compositions and structural properties of pretreated biomass on enzymatic hydrolysis were studied.In addition,the structural properties of lignin were studied for further depolymerization.To achieve effective separation of lignin from wood biomass,a synergistic pretreatment（PAO）process of PAA and oxalic acid（OA）was developed and successfully achieved efficient enzymatic hydrolysis conversion of eucalyptus and lignin separation.The PAO pretreatment effectively fractionated lignin（85.4%）and hemicellulose（93.9%）under a mild temperature（140°C and 60 min）and resulted in a high enzymatic digestibility（89.8%）from the pretreated eucalyptus.Also,the PAO pretreatment could fractionate and deconstruct lignin to low molecular weight（1231 g/mol）samples with 5.8%ofβ-O-4 linkages and a relatively uniform molecular weight distribution（PDI 1.3）.The pretreatment using PAA and OA enhanced not only the hydrolysis of cellulose but also the recovery and quality of lignin as a value-added coproduct for a successful biorefinery approach.The synergetic impacts of ferric chloride aided peracetic acid（FPA）pretreatment were investigated to enhance the total biomass utilization through effective cellulose conversion and high-quality lignin production based on the kinds of biomass.The sugarcane bagasse pretreatment with FPA pretreatment effectively removed 57.3%of lignin and 72.2%of xylan from sugarcane bagasse under mild temperature（90°C）.The FPA pretreated sugarcane bagasse was effectively hydrolyzed with a glucose yield（71.1%）,which was 4.5 times higher than the yield of untreated biomass and 1.6 and 3.6 times higher than that of individual PAA and Fe Cl₃pretreated sugarcane bagasse,respectively.The regenerated lignin（FPA lignin）showed great potential for further valorization by preserving the major interunit linkage（up to86%ofβ-O-4）without significant carbohydrate contamination and lignin condensation due to its mild reaction conditions.In this study,the combination of PAA and Fe Cl₃synergistically enhanced the pretreatment efficiency on sugarcane bagasse and resulted in high fermentable sugar and high-quality lignin production.Catalytic oxidative depolymerization of lignin was investigated using Mg Fe₂O₄（MNs）nanoparticles and peracetic acid under mild conditions.Typically,the increase of processing conditions can increase the lignin conversion,while it results in the unwanted further decomposition of aromatic compounds to dicarboxylic acids.However,in this study,the applied MNs nanoparticles not only enhanced the total product yield but also improved the selectivity of aromatic monomers.The oxidative depolymerization system using MNs nanoparticles and PAA resulted in 45.6 wt.%of total bio-oil products with a 61.2%selectivity of aromatic monomers under mild temperature（90°C）.In addition,this catalyst showed relatively good cycling stability based on the total product yield after three times recycling.Overall,MNs nanoparticles play an important role in the oxidative conversion of lignin with a better conversion efficiency and recyclability,and it will facilitate the valorization of lignin in future bio-based fuels and chemicals.The effect of PAA pretreatment on the structural changes of lignin under mild conditions was studied.Based on the strategy of rapid lignin degradation,two different Cu-doped porous metal oxides（Cu PMO）were synthesized to work on the PAA lignin to achieve high value utilization of lignin.Results showed that PAA-E lignin could be depolymerized into aromatic monomers by Cu PMO I and Cu PMO II with a yield of 8.7%and 7.2%,respectively for 60min.The resulting monomeric products showed a uniform molecular weight distribution.In addition,when the Cu PMO I catalyst was carried out on the catalytic depolymerization of milled wood lignin（MWL）,aromatic monomers with a yield of 24.3%were achieved,which further demonstrated its catalytic performance in lignin conversion.