Study On The Performance Of Solid Acid Combined With Alkali Treatment Of Forest Waste Based On Sugar Priority

Since the beginning of the 21st century,with the exploitation and consumption of fossil energy such as coal,oil and natural gas and the environmental problems,people have paid more attention to the development of renewable energy such as wind energy,solar energy,water energy and biomass energy.Biomass energy is one of the earliest energy resources used by human beings,which has the advantages of wide distribution,low cost and renewable.Forestry waste is a typical lignocellulose biomass,but for a long time,most forestry wastes are mainly used by direct combustion,which is not only low calorific value,but also accompanied by a large amount of soot emission,causing environmental pollution.Biomass liquefaction technology is an important technology to improve the utilization efficiency of biomass.However,due to the natural stress resistance of biomass,it is necessary to develop green and efficient pretreatment technology to promote the liquefaction of biomass.Among various pretreatment technologies studied at present,hydrothermal pretreatment of dilute acid is one of the most widely studied methods.However,the current hydrothermal pretreatment of dilute acid has many defects,such as the waste of some biomass components,equipment corrosion and catalyst recycling.Based on this,a polymer solid acid catalyst was prepared in this paper for hydrolysis pretreatment of forest waste poplar and xylose recovery.The residue was treated with mild alkaloid-organic solvent to achieve high cellulose enzymatic hydrolysis rate and lignin retention rate of the residue,the sugar platform was constructed by separating and recovering hemicellulose,cellulose and lignin from poplar wood.The specific research results are as follows:1.Using polystyrene（PS）as a precursor and concentrated sulfuric acid as a direct sulfonated catalyst,the polymer solid acid catalyst was used for the selective preparation of xylose from pretreated poplar.The sulfonation temperature and time of catalyst preparation were optimized with the concentration of xylose as the main index.The optimal pretreatment conditions were determined as follows:reaction of 1 g PS and 40 m L concentrated sulfuric acid at 120℃for 40 min.The catalyst was named SPS120-40 and its acid density reached 5 mmol/g.Scanning electron microscopy（SEM）showed that the sulfonation process would lead to the destruction of PS surface,PS swelling in the sulfonation process,to achieve the high acid density of the catalyst load.The catalyst SPS120-40 was characterized by FTIR,XPS and ¹³CNMR,and it was found that sulfonation introduced a large number of-SO₃H groups and a small amount of-COOH and-OH.The thermal stability of the catalyst was investigated by TG,TG in water vapor atmosphere and TG-FTIR-MS.It was found that catalyst SPS120-40 began to decompose after 220℃both in N₂atmosphere and water vapor atmosphere.The results of TG-FTIR-MS further indicated that the-SO₃H group of the catalyst mainly began to decompose after200℃,which provided a basis for the thermal stability of the catalyst during the hydrolysis pretreatment of poplar wood.2.The reaction conditions of SPS120-40 pretreatment of poplar including pretreatment temperature,time and amount of catalyst were optimized.The optimal pretreatment conditions were defined as pretreatment temperature 150℃,reaction time 20min,amount of catalyst 0.5 g,and the remaining conditions were 1 g poplar and 40 m L deionized water.Under these conditions,the yield of total xylose was 55.96%and the selectivity of monosaccharide was 92.3%.In order to further remove hemicellulose and improve xylose yield,co-catalyst Fe Cl₃was added.The highest total xylose yield and monosaccharide selectivity were 78.92%and 96.6%,respectively,when the addition level was 0.065 g.It was found that Fe Cl₃alone could effectively hydrolyze hemicellulose to xylo-oligosaccharide.The catalyst SPS120-40 had the advantages of better hydrolysis of hemicellulose and further depolymerization of water-soluble xylo-oligosaccharide into xylo-oligosaccharide.The synergistic action of SPS120-40 with Fe Cl₃resulted in 78.92%xylose yield,while 93.4%cellulose was retained in the residue.The reusable performance of catalyst SPS120-40 was investigated.The catalytic performance of the catalyst decreased significantly during the first used and second used.This was mainly due to the loss of high-active acid sites on the surface of the catalyst that were easy to contact with biomass due to mechanical friction and other factors during the pretreatment process,and the physical coverage of the active sites due to humins deposition during the pretreatment process.When the catalyst is used for three times,the catalytic performance becomes stable.3.Enzymolysis experiments were carried out on poplar raw materials and residues under different pretreatment conditions.Under the enzyme load of 20 FPU/g dry matter,the enzymatic hydrolysis rate of poplar residue treated with"SPS-Fe Cl₃+Na OH-1-Butanol"was 74.1%,and the lignin content of the residue was 33.24%.SEM characterization showed that"SPS-Fe Cl₃+Na OH-1-Butanol"treatment could effectively destroy the dense lignocellulose structure of poplar,and the residue showed loose and porous state.Through XPS characterization,it was found that Na OH-Fe Cl₃treatment would lead to the deposition of a large amount of lignin on the biomass surface,and the lignin coverage rate was 91.87%.The post-treatment of Na OH-1-Butanol could effectively remove the deposited lignin,and the lignin coverage rate on the residue surface decreased to 42.32%.This is one of the main reasons for the significant increase of cellulase hydrolysis rate of poplar residue after"SPS-Fe Cl₃+Na OH-1-Butanol"treatment.The enzymolysis conditions were further optimized.When the cellulase supplemental level was20 FPU/g dry matter and 1%Tween 80 was added,the residue enzymolysis rate increased to 89.5%,and 64.4%lignin was retained in the residue after enzymolysis.Based on the above results,poplar treated with self-made solid acid SPS120-40combined with alkaline 1-butanol can efficiently separate and recover its main components,and realize the resource utilization of poplar lignocellulose:hemicellulose is mainly recovered from the pretreatment supernatant in the form of xylose,and the total xylose yield is 78.92%.The residue after two-step treatment can achieve a cellulase hydrolysis rate of 89.5%.64.4%of poplar lignin was retained in the residue after enzymatic hydrolysis.