Study On Integrated Process Of Enzymatic Hydrolysis And Fermentation Of Green Liquor Pretreated Corn Stover

In this thesis, three different fermentation strategies for bioethanol production from cornstover were studied, including fermentation of the whole slurry of enzymatic hydrolystae(strategy1), liquid-fermentation of the recovered sugar (strategy2) and an integratedfermentation strategy (strategy3). The main results were illustrated as follows:Fed-batch was applied in strategy1, in order to increase the substrate loading insimultaneous saccharification and fermentation (SSF), subsequently enhancing the ethanolconcentration after fermentation to match the economic feasibility of the distillation process.With the combination of fed-batch to achieve a substrate loading of20%(w/v) and SSFsupplemented with cellulase of25FPIU/g-cellulose for72h,48.57g/L of ethanol was detected,which was equal to an ethanol productivity of0.432g/g-cellulose.In strategy2, enzymatic hydrolysis at a low substrate loading was carried out to ensurehigh hydrolysis efficiency, followed by s separation of the supernatant and solid residue of theenzymatic hydrolysate. Sugar in the solid residue was washed out and subsequently mixed withthe supernatant of the enzymatic hydrolysate, followed by a condesation of the sugar solutionand fermentation. Following enzymatic hydrolysis performed at substrate loading of10%(w/v),50℃for48h, supplemented with cellulase of25FPIU/g, β-glucosidase of20IU/g andxylanase of120IU/g,49.69g/L of glucose and20.07g/L of xylose were detected in thehydrolysate, which was equal to glucan hydrolysis yield of79.57%and xylan hydrolysis yieldof72.75%. As a result of washing, the glucose and xylose recovery yield from the solid residuereached78.61%and79.42%. After mixing the washig water with the supernatant of enzymatichydrolysate, a condesation was carried out by vacuum evaporation at160mbar,70℃, so as toenhance glucose to a concentration of99.80g/L. A sequential fermentation strategy was applied:prior to xylose fermentation,99.80g/L of glucose was converted to48.41g/L ethanol at48hfermentation by Saccharomyces cerevisiae, which was equal to95.11%of the theoreticalethanol yield and a ethanol productivity of0.387g/g-cellulose, and the ethanol was removed soas to avoid the inhibition on xylose fermentation. Pichia Stipitis converted54.28g/L xylose to19.43g/L ethanol, equal to79.88%of the theoretical ethanol yield and a ethanol productivityof0.267g/g-xulose.The combination of enzymatic hydrolysis, liquid fermentation and solid state fermentationof enzymatic hydrolysis residue in strategy3aims to maximize the ethanol production. Theenzymatic hydrolysis performed at substrate loading of10.0%(w/v) with cellulase of25FPU/g, β-glucosidase of20U/g and xylanase of120U/g for48h, obtained glucan hydrolysisyield and xylan hydrolysis yield of79.57%and72.75%, respectively. The concentrated liquorcontaining92.66g/L glucose was fermented by S. cerevisiae, obtaining45.43g/L ethanol, representing ethanol yield of96.14%and ethanol productivity of0.391g/g-cellulose. Afterdistillation of ethanol,60.96g/L xylose was converted to19.47g ethanol by P. stipitis,representing ethanol yield of80.26%and ethanol productivity of0.232g/g-xylose.200g Solidstate fermentation was performed with enzymatic hydrolysis residue, obtaining5.61g ethaol,which was1.50g higher than the theoretical value.Regardless of the cost of raw material strategy1was considered as the best one amongthese three strategies, for the simple operation makes the whole process economicallycompetitive.