The Change Of Lignin Structure And Its Effect On Cellulase During Deep Eutectic Solvent Pretreatment

At present,bioethanol is used as a new type of clean fuel,and it has attracted the attention of various countries.Bioethanol is usually produced from natural and renewable biomass materials through processes such as pretreatment and enzymatic hydrolysis.In the process of cellulase hydrolysis of biomass,lignin often inhibits cellulase hydrolysis.The pretreatment process can effectively remove lignin from biomass and change the structure of lignin.Therefore,this research chooses a green,efficient and clean pretreatment liquid,deep eutectic solvent,to pretreat Broussonetia papyrifera to improve the efficiency of biomass enzymatic hydrolysis.And on this basis,explore the influence mechanism of lignin structure change on cellulase enzymatic hydrolysis.The research content is as follows:(1)Pretreatment of Broussonetia papyrifera with deep eutectic solvent(DES).DES pretreatment shows that increasing the temperature and time can significantly improve the digestibility of cellulose in the pretreated biomass.Extending the treatment time,the digestibility increased from 63.76%to 89.29%.Increasing the temperature,the digestibility increased from 61.43%to 70.48%.When the lignin removal rate is less than 80%,the lignin removal rate has a positive correlation with the enzymatic digestibility.When the lignin removal rate is higher than 80%,further increased delignification will not be an important way to improve the digestibility.DES/E(DES/Ethanol)pretreatment indicated that the presence of ethanol can inhibit the acid degradation of cellulose and hemicellulose by DES.(2)Synthesis of three lignin dimer model objects.Three lignin dimer models(?-O-4 type,?-5/?-O-4 type and 5-5 type)were synthesized using guaiacol and isoeugenol as raw materials.FT-IR,¹H-NMR,¹³C-NMR and 2D-HSQC NMR analysis proved that the synthesized dimer model was the target product.(3)The influence of different structures of lignin and model compounds on the enzymatic hydrolysis of cellulase.DES pretreatment has a strong degradation effect on guaiac-based lignin,and the degradation effect is greater than that of syring-based lignin.Through GPC analysis,it was found that the pretreated lignin contained a small amount of oligomers with a small molecular weight.The Avicel results of cellulase enzymatic hydrolysis of lignin and model objects show that when the lignin structure and S/G ratio are similar,the increase in lignin hydrophobicity is the main effect of inhibiting cellulase enzymatic hydrolysis,and the surface with higher lignin Hydrophobicity enhances the inhibitory effect on cellulase enzymatic hydrolysis.In lignin after pretreatment,the inhibitory effect of small molecule?-O-4 structure dimer on cellulase enzymatic hydrolysis is greater than that of the larger molecular weight?-O-4 structure component.