| The industrial fiber residues (furfural residues and sugarcane bagasse) are potential materials for bio-ethanol production due to their large production and low transportation cost. A potential commercial pretreatment for furfural residues (FRs) and sugarcane bagasse were investigated by using a combination of green liquor and hydrogen peroxide (GL-H2O2) or ethanol (GL-ethanol). The results showed that:56.2% of lignin removal was achieved when the sample was treated with 0.6 g H2O2/g-DS (dry substrate) and 6 mL GL/g-DS at 80℃ for 3h. After 96h hydrolysis with 18 FPU/g-cellulose for cellulase,27 CBU/g-cellulose for (3-glucosidase, the glucose yield increased from 71.2% to 83.6%. Ethylenediaminetetraacetic acid was used to reduce the degradation of H2O2, the glucose yield increased to 90.4% after the addition of 1%(w/w). The untreated FRs could bind more easily to cellulase than pretreated FRs could. The structural changes on the surface of sample were characterized by X-ray photoelectron spectroscopy. The results indicated that the surface lignin could be effectively removed during pretreatment, thereby decreasing the enzyme-lignin binding activity. Moreover, the carbonyl from lignin plays an important role in cellulase binding.Furfural residues (FRs) were pretreated with ethanol and a green liquor (GL) catalyst to produce fermentable sugar. Anthraquinone (AQ) was used as an auxiliary reagent to improve delignification and reduce cellulose decomposition. The results showed that 42.7% of lignin was removed and 96.5% of cellulose was recovered from substrates pretreated with 1.0 mL GL/g of dry substrate and 0.4% (w/w) AQ at 140℃ for 1 h. Compared with raw material, ethanol-GL pretreatment of FRs increased the glucose yield from 69.0% to 85.9% after 96 h hydrolysis with 18 FPU/g-cellulose for cellulase,27 CBU/g-cellulose for β-glucosidase. The Brauner-Emmett-Teller surface area was reduced during pretreatment, which did not inhibit the enzymatic hydrolysis. Owing to the reduced surface area, the unproductive binding of cellulase to lignin was decreased, thus improving the enzymatic hydrolysis.During GL-H2O2 and GL-ethanol pretreatments, the wettability and electrostatic contributions of untreated and pretreated FRs was investigated as well as that of isolated lignin (cellulolytic enzyme lignin (CEL) and cellulose. Lignin is the key factor that affects the hydrophily of substrate. The cellulase binding for lignin was reduced due to the increase of hydrophily of lignin, resulting in the improvement of enzymatic hydrolysis. The electrostatic contributions was also an important factor that influenced the cellulase binding of lignin. After pretreatments, the negative charge of lignin was decreased. Accordingly, the cellulase binding capacity was reduced. This effect was more significant after the GL-ethanol pretreatment. Thus, the glucose yield of the substrate obtained from the GL-ethanol pretreatment (86.1%) was larger than that from the GL-H2O2 pretreatment (82.2%).Lignin samples (cellulolytic enzyme lignin (CEL) and black liquor lignin (BLL)) isolated from furfural residues(FRs) pretreated using green liquor combined with hydrogen peroxide (GL-H2O2) and ethanol (GL-ethanol) pretreatments were used for cellulase and cellobiase adsorption. The results showed that the BLL had the highest celluase and cellobiase adsorption capacities compared with CEL lignin, owing to its low molecular weight. In addition, CEL and BLL isolated from GL-ethanol pretreated FRs had the lowest cellulae and cellobiase adsorption capacities due to their highest hydrophilic. The liquid after adsorption was used for SDS-PAGE analysis. The results indicated that the CBHII and EGII from cellulase and the compositions of 245KD and 30KDa from cellobiase were easily adopted on CEL and BLL.The effect of lignin samples (CEL and BLL) on the activities of cellulase and cellobiase were investigated. The results showed that the BLL had a strong inhibition on cellulase activity, which was in line with the adsorption results. But, the glucose yield variation after enzymatic hydrolysis was according with the change of cellulase activity. The solid state NMR analysis indicated that the BLL included more aliphatic side chain and alcoholic hydroxyl group, the CEL had more phenolic hydroxyl group. These differences in structure caused the different of effect of lignin on cellulase and cellobiase activities. In addition, the CEL from GL-ethanol pretreated FRs had the lowest inhibition on cellulase, which had the highest glucose yield during enzymatic hydrolysis after mixing with cellulose.Green liquor (GL) combined with H2O2 (GL-H2O2) and green liquor (GL) combined with ethanol (GL-ethanol) were chosen for treating sugarcane bagasse. Results showed that the glucose yield of sugarcane bagasse from GL-ethanol pretreatment (97.7%) was higher than that from GL-H2O2 pretreatment (41.7%) after 72h hydrolysis with 18 filter paper unit (FPU)/g-cellulose for cellulase,27 175 cellobiase units (CBU)/g-cellulose for β-glucosidase. Furthermore, about 94.1% of xylan was converted to xylose after GL-ethanol pretreatment without additional xylanase, while the xylose yield was only 29.2% after GL-H2O2 pretreatment. Scanning electron microscopy showed that GL-ethanol pretreatment could break up the fiber severely. Moreover, GL-ethanol pretreated substrate was more accessible to cellulase and more hydrophilic than that of GL-H2O2 pretreated. Therefore, GL-ethanol pretreatment is a promising method for improving the overall sugar (glucose and xylan) yield of sugarcane bagasse. |
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