Pretreatment And High-solids Fed-batch Enzymatic Saccharification Of Lignocellulosic Biomass

In recent years, to face the increasingly severe energy problem and theincreasingly serious environmental problems, fuel ethanol has become the mostpopular alternative energy. Lignocellulose, the most abundant renewable biomassresource, has the potential to serve as a sustainable feedstock for bioethanolproduction. The bioconversion of lignocellulose typically involves three steps:pretreatment, hydrolysis, and fermentation.In this study, we chose corn cobs, an abundant and cheap lignocellulosic resource,as the raw material. Two different pretreatment methods were used for the corncobpretreatment. And we also studied how to obtain a high glucose concentrationhydrolysate. The research contents and conclusions are as follows:（1） A treatment process featuring modest conditions was designed to fractionatelignocellulose into cellulose, hemicellulose hydrolysates and lignin by formic acidbased on corn cobs. A central composite design with four independent variables（formic acid concentration, catalyst dosage, reaction temperature and reaction time）was employed to study their simultaneous effects on three responses includinghemicellulose sugars recovery, the ratio of delignification and the cellulose content.The regression analysis performed on the experimental data indicated that theregression coefficients of determination （R²） were good for the second-order models.The experimental results showed that the optimum conditions were：formic acidconcentration85wt%, catalyst dosage （v（FA）/v（HCl））185:1, reaction temperature65oC and time6h. Under these conditions, the recovery ratio of hemicellulose sugarswas87.6%, the ratio of delignification was66.3%and the cellulose content in theresidual solid was76.8wt%.（2） Corn cob was pretreated by H₃PO₄/ethanol under mild conditions. Theeffects of H₃PO₄concentration on the separation of the three components andrecalcitrant characteristics of the corn cob. As the concentration of H₃PO₄increased,more and more hemicellulose and lignin in corn cobs were dissolved and degraded.The CrI of pretreated corn cobs increased slightly and then decreased along with theincrease of H₃PO₄concentrations. Especially when H₃PO₄concentration reached86%,crystalline fraction of corn cobs showed a significant reduction, and particle size of pretreated corn cobs was significantly decreased, especially the fibrillar structure ofcellulose in corn cobs could be completely disrupted.（3） In this study, corn cobs pretreated by phosphoric acid （H₃PO₄）/ethanol wasused as raw material for enzymatic hydrolysis. The optimal pretreatment phosphoricacid concentratiion was86wt%. Under this condition,96.7%of the pretreatedcellulose was hydrolyzed at12h. Mass flow through pretreatment and enzymaticcellulose hydrolysis showed that: the total yields of glucose and xylose were92.0%and83.1%, respectively; the recovery ratio of the phosphoric acid and ethanol were95.6%and92.1%respectively. It makes the subsequent enzymatic hydrolysis possibleto be performed at high solids loading. However, operating hydrolysis at high solidconcentrations still faces many barriers. Enzymatic hydrolysis experiments showedthat fed-batch mode allowed the high solids loading up to30%. For the two enzymesfeeding strategies, enzymes feeding along with fresh substrate was a more applicablestrategy in fed-batch operation,which resulted in a glucose concentration as high as143.5g/L in27h.