| Lignocellulose is one of the most abundant renewable resources in the world.It is widely used in the production of biofuels instead of fossil fuels.However,the fiber structure of forest biomass has a natural anti degradation barrier,and its dense structure increases the production cost of biofuels.Therefore,in the process of converting forest biomass into biofuel,pretreatment is particularly important.At present,the biggest bottleneck in the development and utilization of forest biomass is how to break its anti degradation barrier more economically and effectively to produce biofuels.In this process,on the one hand,the cellulose should be disassembled and separated to prepare ethanol to solve the energy problem;on the other hand,other components should be prepared into high value-added products to improve the economic feasibility of the production system.In this paper,the pretreatment method of hydrothermal+dilute acetic acid is used to disassemble poplar fiber.On the premise of ensuring that the cellulose is not destroyed,the xylan in poplar hemicellulose is disassembled and separated,and the anti degradation barrier of poplar fiber is opened to improve the enzymatic hydrolysis saccharification rate,and high-value Xylooligosaccharides are obtained at the same time.Dilute NaOH solution and y-Pentanolactone(GVL)solvent system is used to treat hydrothermal residue to remove the components that inhibit enzymatic hydrolysis and saccharification,further improve the enzymatic hydrolysis rate,and prepare lignin with high utilization value to reduce the production cost.The main results are as follows:(1)The effects of acetic acid concentration,solid-liquid ratio,temperature and time on the removal and separation of poplar fibers by hydrothermal and dilute acetic acid pretreatment were studied.The results showed that the optimum conditions were acetic acid concentration 0.5%,solid-liquid ratio 1:20,temperature 170℃ and reaction time 30 min.under these conditions,the yield of hemicellulose and cellulose was 92.88%and 93.99%respectively.SEM and bet were used to analyze the changes of poplar fiber before and after hydrothermal+dilute acetic acid pretreatment.It can be seen that after hydrothermal+dilute acetic acid pretreatment,the complete dense structure of poplar was destroyed,the surface became no longer complete from smooth and complete,and the specific surface area and pore diameter of the fiber increased by 1.54 times and 2.5 times respectively.The results of FTIR and XRD showed that the crystal form of cellulose remained unchanged before and after pretreatment,and the crystallinity increased slightly from 35.38%to 41.45%.The characteristic peak of xylan was significantly weakened,which further proved that hydrothermal+dilute acetic acid pretreatment had little effect on cellulose.By removing Xylan from the fiber,the anti degradation barrier of poplar fiber could be initially opened and the accessibility of cellulase could be improved,The saccharification rate increased from 7.13%to 43.2%.According to the analysis of pretreatment solution by GC-MS,50.13%of hemicellulose converted into xylooligosaccharide exists in the pretreatment solution,indicating that hydrothermal+dilute acetic acid pretreatment can break the anti degradation barrier of biomass and improve the effect of enzymatic hydrolysis and saccharification,and can make more xylans in hemicellulose converted into Xylo-oligosaccharides.(2)NaOH solution was used to delignify the residue of hydrothermal+dilute acetic acid pretreatment,and the effects of various factors were studied.Under the optimum conditions of 3%naoh,temperature 80℃,solid-liquid ratio 1:25 and reaction time 3h,the yield of cellulose disassembly and separation was 93.47%and the lignin removal rate was 71.94%.Through the analysis of the results of enzymatic hydrolysis and saccharification of holocellulose and hydrothermal residue,it can be seen that pseudolignin has a strong inhibitory effect on enzymatic hydrolysis and saccharification.After treatment with dilute NaOH solution,lignin and pseudolignin are largely removed,making the enzymatic hydrolysis and saccharification rate increase from 60.23%to 83.24%.(3)Adopt y-The effects of solvent ratio,temperature,solid-liquid ratio and reaction time on the delignification of hydrothermal+dilute acetic acid pretreatment residue were studied.Under the optimum conditions:solvent ratio 1:3,temperature 120℃,solid-liquid ratio 1:15,time 4h,the yield of cellulose disassembly and separation was 93.11%,the removal rate of lignin was 85.12%,and the purity of extracted lignin was 93.11%.GPC and 2D-NMR analysis showed that GVL/formic acid solvent system could effectively break the β-O-4 aryl ether bond was dissolved and had a high S/G value,indicating that GVL/formic acid solvent treatment was conducive to the further catalytic degradation of lignin for the preparation of bio based chemicals. |
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