| With the global shortage of fossil resources and increasing environmental pollution,strengthening the use of clean and renewable resources and developing green and good performance biomass resources have attracted widespread attention.Lignocellulosic biomass resources have a wide range of application areas and play an important role in pulp and paper,chemical industry,bioenergy,textile and other fields.Cellulose,hemicellulose and lignin as their main components,the complex chemical bonds between components and the multi-scale structure of wood fibers form a natural anti-depolymerization barrier,limiting their comprehensive utilization.In addition,the application of wood fibers suffers from low separation efficiency,cumbersome process and high energy consumption and serious pollution in the traditional method.Therefore,there is an urgent need to develop a green and efficient means of fiber separation.In this project,in view of the structural complexity of biomass components and the drawbacks in the dissociation process,a microwave-assisted organic weak acid treatment method is used to achieve clean and efficient separation of biomass components using kenaf bast as raw material;the mechanism of clean dissociation and changes in structural properties of kenaf components by the new method are explored,while the waste liquid is recycled to improve economic efficiency and environmental protection.The research results are as follows:The first part is a study of organic acid solvent preferences.The effects of different organic weak acid species(formic acid,acetic acid and lactic acid)on the separation effect and structural properties of kenaf single fibers were studied in order to preferably select a suitable organic acid separation reagent.The results showed that after 6 h of externally conducted heating,the acetic acid-treated fibers were incompletely dispersed in flakes and had a lignin content of up to 7.07%.Formic acid and lactic acid could effectively remove non-cellulose components such as hemicellulose and lignin,and the fiber dispersion effect was obvious,with 88.02% and 87.6% removal of lignin and 52% and 64.7% fiber yield for the two reagents,respectively.The action of lactic acid was mild,the fiber polymerization was higher than that of formic acid treated fibers,and the fiber structure was less damaged.In addition,considering that formic acid is highly volatile,flammable and explosive and corrosive to equipment,the greener and milder lactic acid was chosen for the next step of the study.The second part is a technical study of microwave-assisted lactic acid separation of kenaf fibers.To improve efficiency,microwave-assisted lactic acid was selected to treat kenaf,and the effects of heating time,temperature and solid-liquid ratio on fiber chemical composition,yield and fiber scale were investigated by single-factor experiments to determine the optimal process conditions.The results showed that the optimal treatment conditions were 130°C,30 min heating time,and 1:20 bath ratio,under which the fiber yield was 57% with 80.13% cellulose,6.99% hemicellulose,and 1.71% lignin.Compared with the traditional sulfate method,the crystallinity and thermal stability of kenaf fiber were improved due to the removal of pectin,lignin and other non-cellulosic substances,and the degree of polymerization remained unchanged with good fiber properties.Due to the complex structure of lignin,the removal of lignin is the key in the process of fiber separation.In the third part,the effects of different treatment conditions on the chemical structure of biomass lignin were studied,and the changes of its structure and properties were studied by FTIR,GPC,TG,NMR and other characterization methods.The results showed that the lignin obtained by microwave-assisted lactic acid treatment had typical lignin structure,mainly GS lignin,the proportion of s unit was greater than g unit,and the main types of bonding bonds were β-O-4 and β-β mainly;During the process,the lignin underwent depolymerization,fracture,side chain fracture and condensation,which effectively cut off the connecting bond between lignin and polysaccharide.The content of xylose was 0.26% and the purity was high;The ether bond breaks mainly between s units,which reduces the damage degree of lignin structure.The lignin fragment has complete structure,molecular weight of 1950 g/mol,good thermal stability,and degradation temperature of 350.3℃.In order to reduce the cost and pollution caused by waste liquid discharge,the performance of waste liquid recovery and reuse is studied.The economic and environmental benefits of microwave-assisted lactic acid treatment process were explored.The waste liquid from the treatment of Kenaf was recycled.The consumption of chemicals,time and water resources was analyzed and compared with that of sulfate method.The results showed that the purity of the waste liquor from the microwave-assisted lactic acid treatment of Kenaf was 96.54% and the recovery rate was 85%.In addition,compared with the sulfate process,the treatment time is shortened by 82%,the loss of chemicals is reduced by 54.5%,the pollutant discharge is reduced,and it is more efficient and clean. |
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