Study On High-concentration Enzymatic Hydrolysis Characteristics And Improvement Measures Of Eucalyptus Pretreated With Chloride Salts

With the shortage of fossil energy,the continuous increase in global oil prices and the growing global climate and environmental crisis,the research on the production of environmentally friendly bioethanol from woody fiber biomass is of great importance in various aspects such as energy utilization and environmental protection.In the conversion of woody fiber biomass to bioethanol,enzymatic hydrolysis is a key component.Previous studies have mostly considered the removal of lignin as much as possible as an effective measure to improve the efficiency of enzymatic hydrolysis,but recently it has been found that some lignin also has a positive effect on enzymatic hydrolysis.In addition,high-concentration enzymatic hydrolysis is a key way to achieve economically viable bioethanol production.However,changes in the rheology of the system with increasing substrate concentration affect the final enzymatic yield.In this paper,we investigated the physical and chemical properties of lignin,the adsorption relationship with cellulase and the effect on enzymatic hydrolysis after chlorine salt pretreatment.The results of the study are as follows:1.Chlorine salt pretreatment leads to the breakage of chemical bonds of large lignin molecules and the polymerization of small lignin molecules.For the effect of groups on lignin model substances,magnesium chloride pretreatment mainly acted on carboxyl groups and ammonium chloride pretreatment mainly acted on phenolic hydroxyl groups.2.Hydrophobic interactions and electrostatic interactions jointly affect the kinetics of lignin-cellulase adsorption,with hydrophobic interactions playing a dominant role.In addition,the spatial repulsive forces influenced by the molecular weight size of lignin also had an effect on the adsorption of cellulase.3.The non-productive adsorption of lignin itself to cellulase leads to a decrease in cellulase activity,but the addition of lignin to the enzymatic hydrolysis system with eucalyptus lysis pulp as substrate has various degrees of enzymatic hydrolysis yield promotion.This was related to the increase in total hydroxyl content,hydrophilicity and electronegativity of the whole system with the addition of lignin.The adsorption of lignin to cellulase was related to the methoxy（-OCH₃）,hydroxyl（-OH）and carbon-carbon double bonds（C=C）of lignin,and there was non-inhibitory adsorption.4.As the substrate concentration of the enzymatic hydrolysis system increases,the free water content decreases and the viscosity of the whole system increases continuously.The enzymatic hydrolysis system with different substrate concentrations is a non-Newtonian fluid with shear thinning or pseudoplasticity in a certain range.In a certain range,the shear thinning of the enzymatic hydrolysis system deepens with the increase of substrate concentration.5.The viscosity of the enzymatic hydrolysis system is one of the factors that affect the efficiency of enzymatic hydrolysis.With the increase of enzymatic hydrolysis time,the viscosity of the enzymatic hydrolysis system did not show a single decreasing trend.With the increase of temperature,the viscosity of the system decreases with the increase of temperature because of the increase of thermal movement of molecules in the low-concentration system;the viscosity of the high-concentration system increases with the increase of temperature because of the decrease of free water and the filling of gas between particles.6.Although sodium lignosulfonate can improve the efficiency of enzyme hydrolysis,the addition of sodium lignosulfonate increases the viscosity of the enzymatic system from the rheological analysis.The use of cetyltrimethylammonium bromide and Tween 80 in combination with sodium lignosulfonate could release free water and further improve the effect of sodium lignosulfonate on the viscosity of the enzymatic system.