Study On Enzymatic Hydrolysis Of Corn Straw Based On Photocatalysis And Alkaline H₂O₂ Co-pretreatment

The hydrolyzed carbomer in lignocellulosic material is simple fermentable sugar,which can be used as raw material for biomass resource utilization such as biological hydrogen production and bioethanol.An effective biomass pretreatment strategy is essential to improve product yield and the overall efficiency of the biorefining system.In this paper,a method of alkali photocatalytic pretreatment is proposed by combining photocatalysis with alkaline H₂O₂.This paper mainly studies the effect of alkaline photocatalytic pretreatment method（U-AHP）based on H₂O₂ photocatalysis on the enzymatic hydrolysis of corn straw and the changes in the composition and mass loss of solid residue after pretreatment.Through the characterization of the structure of corn residue before and after pretreatment,the cooperative mechanism of U-AHP pretreatment of corn straw is speculated.In order to solve the problem of H₂O₂ participating in photocatalysis,a variety of semiconductor photocatalysts were screened for photocatalytic pretreatment.Then,TiO₂ based photocatalyst was used in UAHP photocatalytic pretreatment to form a new pretreatment method,that is,TiO₂ based photocatalyst base photocatalytic pretreatment method（UT-AHP for short）,to study the influence on the enzymatic hydrolysis of corn straw and the composition of the solid residue after pretreatment,and to characterize the structure of the corn straw residue before and after pretreatment.The main results are as follows:（1）The effect of alkali photocatalytic pretreatment method（U-AHP）based on H₂O₂ photocatalysis on the change of main components of corn straw and the subsequent enzymatic hydrolysis saccharification effect was studied.The results showed that the optimal process parameters of U-AHP pretreatment were 1%Na OH,2%H₂O₂ and 8 h irradiation time,and the reducing sugar conversion rate was 88.3%,the saccharification rate was 94.7%,and the lignin removal rate was 88.2%.Compared with AHP pretreatment,U-AHP pretreatment of corn straw had better lignin removal effect,seriously damaged spatial structure,and higher content of reducing sugar by enzymolysis.Response surface method was used to optimize the enzymatic hydrolysis process at p H=5,46 h,50℃,2.6 FPU/g enzyme load,and the conversion rate of reducing sugar was 83.1%.There may be three synergistic mechanisms in the reaction process of U-AHP,namely,the synergistic mechanism between lignin dissolution and microfibril morphology change in alkali pretreatment,the synergistic mechanism between alkali pretreatment and H₂O₂,and the synergistic mechanism between ultraviolet light and AHP.U-AHP pretreatment is a complex pretreatment through multiple synergistic effects,which reduces Na OH compared with AHP pretreatment.The use of H₂O₂ can shorten the reaction time,which is an effective means to pretreat corn straw.（2）A variety of solid photocatalysts were screened for the problem that H₂O₂ participating in photocatalysis could not be recovered.The results showed that TiO₂ photocatalyst selected from Zn O,TiO₂,ZrO₂,Cd S,Si C and g-C₃N₄ was more suitable for the photocatalytic pretreatment of corn straw.TiO₂-based modified photocatalysts such as FTiO₂,Cu-TiO₂,Zn O-TiO₂,g-C₃N₄-TiO₂ and self-doped R-TiO₂ were prepared.After photocatalytic pretreatment of corn straw,the content of enzymatic reducing sugar was used as the evaluation index of catalyst activity.The results showed that the content of reducing sugar after enzymolysis was higher when g-C₃N₄-TiO₂ and R-TiO₂ were used as photocatalysts.The photocatalyst was characterized by XRD,UV-Vis DRS,XPS and SEM.The crystal form of the prepared photocatalyst was anatase and a small amount of rutile,and the crystal form was good.The visible light absorption performance of the doped photocatalyst was greatly changed.The selected g-C₃N₄-TiO₂ and R-TiO₂ were characterized by XPS.In the presence of all the main elements of photocatalyst,Ti3+ species were formed in R-TiO₂,O/Ti=0.59,significantly lower than 2,and there was oxygen vacancy（Ov）.（3）The effect of alkali photocatalytic pretreatment method based on TiO₂-based photocatalyst on the change of main components of corn straw and the subsequent enzymatic hydrolysis and saccharification effect.The results showed that the pretreatment of UT-AHP system could effectively remove lignin and some cellulose,destroy the spatial structure of corn straw,and improve the efficiency of enzymatic hydrolysis.Compared with R-TiO₂,H₂O₂ concentration has a greater effect on g-C₃N₄-TiO₂ reaction.Under the same conditions,the amount of R-TiO₂ photocatalyst is less.After pretreatment of g-C₃N₄-TiO₂ and R-TiO₂,there is a small difference in the content of reducing sugar by enzymatic hydrolysis,so it is possible for R-TiO₂ to achieve photocatalytic pretreatment of straw under visible light.Adding solid catalyst in U-AHP system can effectively reduce the use of H₂O₂.UT-AHP system is a promising pretreatment method.