Improving Chemical Pretreatment Of Corn Stover For Enhancing Its Enzymatic Hydrolysis Accessibility

Resources, energy and environment are currently three critical issues the worldfacing with, therefore, there is an increasing interest among researchers in utilizingrenewable lignocelulloses for developing biofuel and bio-based materials. Currently,the bioconversion of agricultural residues, such as crop straw and bagasse, has receivedattention in many countries, for acquiring the biofuels （ethanol, butanol, etc., derivedfrom saccharides） and lignin products （water reducer, phenolic resin, etc., obtained fromchemical and biological conversion of biomass）. Efforts are focused on searching foreconomic and applicable approaches for pre-treating lignocellulosic materials so thatenzymatic digestibility can be extensively improved. It is hoped that effective andpractical methods can be established, to improve the enzymatic digestibility of biomassand benefit to the subsequent process of biochemical conversion.In this study, corn stover was pretreated underwent chemical processes of NaOH,NaOH+AQ, NaOH+Na₂SO₃, H2SO4+Na₂SO₃, NaOH+Na₂S and H2SO4, respectively.The influences of pretreatments on solid yield, carbohydrate recovery, delignification,enzymatic efficiency and the final sugar yield under different pretreatment conditionswere investigated. Alkaline sulfite pretreatment was optimized by varying dosage ofNaOH and Na₂SO₃, and improved sugar conversion was achieved. The influence oftemperature, treatment time and alkali dosage on biomass digestion and sugarconversion was analyzed by orthogonal design method.Results showed that sodium hydroxide pretreatment combined with otherchemicals could improve efficiency of enzymatic hydrolysis and sugars production.Particularly, the alkaline sulfite pretreatment can delignify90%lignins with10%totalalkali charge at140°C. Subsequent hydrolysis with cellulase and β-glucosidaseindicated that84.7%and81.1%of glucan and xylan were hydrolyzed respectively, andthe total yield of monosaccharides （glucose and xylose） can reach to44.1%.Compared with the pretreatment by sodium hydroxide, it was raised by about13.5%.Under optimized pretreatment by alkaline sulfite, i.e.10%total alkali dosage at140°C, when Na₂SO₃concentration was0.8%（w/v）, treated material with0.48g/gfermentable saccharides （glucose and xylose） was achieved, in combiation with20FPU/g of cellulase. Compared with the sodium hydroxide pretreatment, it wasincreased by about24%. That means the fermentable glucose and xylose in theoriginal biomass could be theoretically as high as78.2%, i.e. glucose and xylose were 0.34g/g and0.14g/g, respectively. Application of orthogonal design optimized theparameters in the sodium sulfite pretreatment. It showed that the alkali charge was themost important factor. The order in effects of total sugar yield was: alkali charge>temperature> duration time. Therefore, alkaline pretreatment combined with sodiumsulfite could improve enzymatic hydrolysis of carbohydrate, and it could be anappropriate approach for of industrial bioconversion in utilizing corn stover.