| The acid pretreatment applied on lignocellulose to facilitate the conversion of carbohydrate into the fermentable monosaccharides is an important step in the production of bioethanol.In this study,the impact of the acid pretreatment on the enzymatic hydrolysis of sugarcane bagasse,the structure of pseudo-lignin and its formation mechanism,and the interaction between LCC and cellulase were studied in detail.The main contents were as follows:(1)The bagasse was pretreated by the acid pretreatment with various severities.IC and HPLC were used to quantify mono-sugars and inhibitors of hydrolyzate.The chemical composition of the pretreated samples was quantified.In addition,SEM and XRD were used to analyze the surface morphology and crystallinity of the solids.The effects of acid pretreatment on surface morphology,crystal structure and enzymatic hydrolysis of bagasse were studied.(2)The model compounds(cellulose,hemicellulose,furfural,5-HMF,MWL)were pretreated by the acid to obtain pseudo-lignin.The structure of pseudo-lignin was analyzed by FT-IR,SSNMR and Py-GC-MS.The formation mechanism of pseudo-lignin was proposed.In addition,the pseudo-lignin cellulose complex was prepared by the regeneration of pseudo-lignin and cellulose dissolved in ionic liquid.(3)RM-LCC and LHW-LCC were extracted from raw material and pretreated samples by Bjorkman method.LCC structure was characterized by 13C NMR and 1H-13C HSQC NMR.LCC biosensor was prepared by electrical spinning coating.(4)The pseudo-lignin cellulose complex was enzymatically hydrolyzed to investigate the inhibitory effect of pseudo-lignin on the enzymatic hydrolysis.The adsorption and desorption behavior of cellulase on LCC was monitored using QCM-D at 4? and 50? to investigate the interaction between LCC and cellulase.The main results were sumaried as follows:(1)The acid pretreatment mainly removed hemicellulose from bagasse.The removal of hemicellulose was 83.08%when the severity was 0.46.When the severity was increased to 3.25,the removal of cellulose was 76.55%.Simultaneously,acid pretreatment produced inhibitors such as furfural and 5-HMF which was further converted into pseudo-lignin.For example,the acid insoluble matter of pretreated bagasse content increased to 28.58%when the pretreatment severity is 3.25.The specific gravity of increased,and the enzymatic hydrolysis rate of pretreated bagasse decreased due to the increase of the acid-insoluble matter including pseudo-lignin.When the pretreatment severity was 3.25,the enzymatic hydrolysis effciency was only 46.24%.(2)When the pretreatment severity was 3.25,76.4%of furfural and 40.81%of 5-HMF were consumed to produce pseudo-lignin.5-HMF and furfural underwent polycondensation or molecular rearrangement to form intermediates such as BTO,DMC,Humins,FPHG and FPCD.The intermediate reacted with 5-HMF and furfural form pseudo-lignin by phenolic condensation reaction,aldol addition reaction and acetal reaction.(3)RM-LCC and LHW-LCC mainly composed by phenyl glycosidic bonds and ester bonds between carbohydrate and lignin,the polysaccharides are mainly O-acetyl-?-D-xylopyranoside and P-D-glucopyranoside.The interaction between LCC and cellulasewas divided into two stages,namely enzyme adsorption stage and desorption stage.In the enzyme adsorption stage,higher temperature and enzyme concentration were beneficial to the binding of cellulase to substrate.Lignin and hemicellulose hinder cellulase binding to cellulose and reduce cellulase and cellulose accessibility.(4)The physical adsorption and steric hindrance of pseudo-lignin inhibited the enzymatic hydrolysis.For example,the enzymatic efficiency of the substrate decreased from 97.11%to 58.42%,when the pseudo-lignin content increased from 0 to 50%.In the enzymatic hydrolysis stage,a higher enzyme concentration favors cellulase hydrolysis of cellulose in LCC,but the hydrolysis effect is poor.The inefficient adsorption of lignin and the influence of LCC linkages may be the main factors hindering enzymatic hydrolysis. |
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