Synergistic Effects Of Hydrothermal And Deep Eutectic Solvent Pretreatment On Enzymatic Hydrolysis Of Poplar Sawdust

In this paper,the goal of high-value utilization of poplar processing residues is to use a clean hydrothermal pretreatment method to preferentially convert poplar hemicellulose to obtain high value-added xylo-oligosaccharides.On this basis,a novel green solvent,a deep eutectic solvent,was used to pretreatment the hydrothermally pretreated poplar to achieve efficient cellulase hydrolysis and green lignin dismantling of poplar.During this process,the strong inhibitory effect of surface lignin on the saccharification of poplar cellulose by combined hydrothermal-deep eutectic solvent pretreatment was revealed,and it is proposed that adding lignin blocking agents to break the inhibitory effect of surface lignin on enzymatic hydrolysis,the enzymatic hydrolysis performance of combined pretreatment poplar can be significantly improved.In addition,the synergistic mechanism of Tween 80 on enzymatic hydrolysis of combined pretreatment of poplar was systematically studied.On this basis,a high substrate concentration semi-simultaneous saccharification and fermentation process of combined pretreatment of poplar was established.Research results were able to provide a basis for the development of the integrated technology for the high value utilization of woody raw materials.The main results of this dissertation were described as follows:The effects of hydrothermal pretreatment,deep eutectic solvent pretreatment,and hydrothermal-deep eutectic solvent combined pretreatment on poplar cellulose saccharification and co-production of xylo-oligosaccharides were systematically compared using poplar processing residues as raw materials.The results indicated that the xylo-oligosaccharide yield was as high as 53.2%after hydrothermal pretreatment(180 ~oC,30 min),while the glucose yield of hydrothermal pretreatment of poplar was only 29.4%.The highest glucose yield was up to76.7%,but the xylo-oligosaccharides yield was only 17.2%by using deep eutectic solvent to pretreat poplar(130 ~oC,choline chloride/lactic acid molar ratio of 1:10).However,using the combined hydrothermal-deep eutectic solvent pretreatment method,the total xylo-oligosaccharide yield was 64.0%,and the glucose yield was only 49.9%,which was much lower than that of the single deep eutectic solvent pretreated poplar(76.7%).This indicated that the combined hydrothermal-deep eutectic solvent pretreatment could achieve high-efficiency conversion of poplar xylo-oligosaccharides,but the promotion of poplar cellulose saccharification was not significant.To investigate the reasons for the lower saccharification efficiency of combined pretreatment of poplar than deep eutectic solvent pretreatment,the substrate characteristics of deep eutectic solvent pretreated and combined pretreatment of poplar were systematically compared.The results showed that the lignin removal efficiency of the combined pretreatment was significantly higher than that of the deep eutectic solvent pretreatment,but the surface lignin content(60.4%-95.6%)was significantly higher than that of the deep eutectic solvent pretreatment poplar(32.6%-79.7%),and the lignin content on the surface of pretreated poplar was negatively correlated with the yield of enzymatic hydrolysis(R~2=0.89).Through the enzymatic hydrolysis experiment with the addition of bovine serum albumin,it was verified that the ineffective adsorption of surface lignin to cellulase protein in the combined pretreatment poplar is the key to inhibiting its enzymatic hydrolysis.The enzymatic hydrolysis performance of combined pretreatment of poplar was significantly improved by adding Tween 80.The addition of 1.5 g/L Tween 80 at the enzyme dosage of 10 FPU/g glucan resulted in a 3.2-fold increase in the combined pretreatment of poplar the glucose yield from 22.6%to 99.6%.Studies have shown that Tween 80 could reduce the surface hydrophobicity of residual lignin of combined pretreatment of poplar.Furthermore,the effect of Tween 80 on the interaction between cellulase and lignin was revealed using Quartz Crystal Microbalance Technology.Tween 80 was able to adsorb to the surface of lignin faster than cellulase,thus occupying the enzyme protein on the lignin.The adsorption site decreased the adsorption amount of cellulase on the lignin film from 270.69 ng/cm~2 to 32.10ng/cm~2.In addition,the addition of Tween 80 was able to increase the residual enzyme activity of cellulase in the enzymatic hydrolysis system and reduce the ineffective adsorption of cellulase and lignin.On this basis,Tween 80 was applied to semi-synchronous saccharification fermentation with high substrate concentration,and the final ethanol concentration was as high as 52.0 g/L at the glucan concentration of 12%(w/v).It provides technical support for the efficient conversion of poplar processing residues to bioethanol.