Influence Mechanism Of Lignin On Cellulase Hydrolysis And Application Of Lignin

Using lignocellulose as a raw material to produce clean energy is currently the most effective way to replace fossil energy.Enzymatic hydrolysis of lignocellulose is very essential in the process of lignocellulosic biorefinery.While the adsorption of substrate and enzyme is a prerequisite for enzymatic hydrolysis,so it is very important to understand the mechanism of adsorption.Lignocellulose is mainly composed of cellulose,hemicellulose and lignin.However,only when cellulase is adsorbed on cellulose,reducing sugars can be produced.If the cellulase is adsorbed on lignin,sugars cannot be obtained.The adsorption between lignin and cellulase is called inefficient adsorption(or non-productive adsorption).Therefore,in this study,in order to enhance the utilization of cellulase as well as decrease the amount of adsorption between cellulase and lignin,the effect of a type of lignin on the enzymatic hydrolysis of different substrates and the effect of different lignins on the enzymatic hydrolysis of a substrate were studied through exploring the physicochemical properties of substrates and lignins as well as the adsorption profiles between lignin and cellulase.In addition,in order to make an effective use of lignin which plays a negative role in enzymatic hydrolysis,the lignin-CMC composite films were prepared and the functions of the composite films were also explored.The main contents and results of this research are as follows:(1)First,the p-toluenesulfonic acid(p-TsOH)lignin(PL)was prepared by pretreating bagasse with p-TsOH.Taking PL as the research object,the effects of PL on the enzymatic hydrolysis of bagasse pretreated by p-TsOH(PB)and pure cellulose(Avicel)were explored.The results showed that PL decreased the enzymatic hydrolysis efficiency of Avicel significantly(from 56.63% to 39.28%)while increased the adsorption of cellulase(from 60.57% to 68.26%);however,PL had no significant effect on the enzymatic hydrolysis efficiency of PB(from 39.65% to 37.16%)while reduced the adsorption of cellulase significantly(from 90.76% to 61.62%).Through the analysis of the particle size and crystallinity of the substrates,it was found that not only more cellulase was absorbed but also the adsorption of cellulase and Avicel was hindered,which caused the decrease of hydrolysis efficiency of Avicel.As for PB,the nonproductive adsorption decreased which caused the decrease of amount of adsorbed cellulase,but the hydrolysis efficiency did not change significantly.By analyzing the interaction(electrostatic repulsion,hydrogen bond and hydrophobicity)between lignin and cellulase before and after adding PL,it was found that after adding PL in Avicel,the hydrogen bond and hydrophobic interaction force dominated.As for PB,the electrostatic repulsion was dominant.(2)In order to explore the effect of different lignins on the enzymatic hydrolysis of a type of substrate,enzymatically hydrolyzed wood lignin(WL),enzymatically hydrolyzed corn stover lignin(CL),and p-TsOH bagasse lignin(PL)were respectively added in Avicel's enzymatic hydrolysis system.It was found that WL reduced the enzymatic hydrolysis efficiency of Avicel(72 h)by 33%,CL reduced it by 46%,and PL reduced it by 87%.In order to explore the reasons that the difference in the inhibition of Avicel hydrolysis by lignin,the non-productive adsorption of three kinds of lignin and cellulase and the relative enzyme activity in the adsorption solution were measured.The results showed that the greater the adsorption capacity of lignin and cellulase was,the lower the enzyme activity in the adsorption solution was,and the greater the inhibition of substrate enzymatic hydrolysis was.In order to further explore the reasons for the difference in non-productive adsorption,the physicochemical properties of lignin were studied.The results showed that the smaller the molecular weight of lignin was,the more condensed structures and the more H groups were,the easier it was to adsorb cellulase.The interactive forces that caused the adsorption of lignins and cellulase were also analyzed.The results showed that different interactive forces played a different role in the adsorption process of different lignin and cellulase.For WL,the hydrogen bonding force was dominant;for CL,the hydrophobic interaction force was dominant;and for PL,electrostatic interaction was dominant.(3)Based on the characteristics of lignin(for example,it inhibits the enzymatic hydrolysis of substrate,but owns many functional properties such as antibacterial and antioxidant properties).In this study,three lignins(WL,CL and PL)were respectively mixed with CMC to form composite film.According to the performance characterization of the three composite membranes of WL-CMC,CL-CMC and PLCMC,it was found that because of the difference in the structural characteristics of lignin,the membrane had different advantages.The results showed that the addition of WL improved the UV barrier performance and antioxidant activity of the CMC film;the addition of CL improved the water vapor barrier and mechanical properties of the CMC film;the addition of PL improved the mechanical and antibacterial properties of the CMC film.This study would not only help understand the effect of lignin on enzymatic hydrolysis of lignocellulosic substrates systematically and deeply from the perspective of adsorption between lignin and cellulase,but also provide a theoretical reference for the high-value utilization of lignin.