| As one of the most promising renewable energy sources,cellulosic ethanol has been widely studied by numerious researchers.However,there is still a large gap in the current industrial productionof cellulosic ethanol.It seems to be of big promiseto improve the enzymatic hydrolysis of the lignocellulosic substrate with a reasonable pretreatment and to achieve high-solid enzymatic saccharification and fermentation by fed-batch.Based on this,this thesis focused on new pretreatment and enzymatic hydrolysis at low enzyme loading,in order to obtain high concentration of ethanol.The detailed contents are as follows:First of all,acid-/alkaline-catalyzed atmospheric pressure glycerol organsolv pretreatment?ac-AGOP,al-AGOP?was tried to build.With single-factor and response surface design experiments on several key conditions affecting pretreatment,the pretreatment conditions of ac-AGOP were optimized as below:pretreatment temperature 245°C,acid addition 0.1%?w/w?and pretreatment time 38 min.Pretreatment conditions of al-AGOP were optimized as follows:pretreatment temperature 257°C,alkali addition 0.27%?w/w?and pretreatment time 18 min.After that,several analytic tools?TGA,SEM,FTIR,XRD,CLSM,etc.?were used to characterize the structural features of the sugarcane bagasse before and after pretreatments.The characterization is helpful at least partly to explain why the two pretreatment methods?ac-AGOP and al-AGOP?established herein can significantly improve the enzymability of the lignocellulosic substrate.Then,an efficient enzymatic hydrolysis and fermentation process was built.Thebatch enzymatic hydrolysis process was optimized with additives and accessory enzymes by single-factor and orthogonal experiments.The hydrolysis condition was optimized as below:10 mg·g-1 dry mass BSA,25 mg·g-1 dry mass Tween 20,10 mg·g-1 dry mass tea saponin and 0.6 mg·g-1dry mass endoxylanase.Yeast extract of 0.1 mol·L-1 was added at the beginning of the fermentation.Under these selected conditions,the glucose concentration was 95.0 g·L-1 at 60 h pre-enzymatic hydrolysis with 82%of the enzymatic hydrolysis.And the ethanol concentration after fermentation 48 h was 43.0 g·L-1 with 74.1%of the cellulose-ethanol conversion rate and0.9 g·L-1·h-1 of the fermentation productivity.Finally,the high-solid saccharification and fermentation was made by means of fed-batch mode,mechanical agitation,wet substrate feeding,and extention of pre-enzymatic time.The operation conditions were selected as follows:50%of moisture in the substrate,19%of the initial solid concentration,6%,5%and 5%of the substrate feeding at 7 h,10 h and 13 h,respectively.Under selected condition,the glucose concentration was as high as 160.7 g·L-1 at48 hwith 76.5%of glucose yield,and xylose concentration reached 58.7 g·L-1 with 57.8%of the xylose yield.After 48 h of ethanol fermentation,ethanol concentration was as high as 78.2g·L-1 with 73.2%of cellulose-ethanol conversion rate and 1.6 g·L-1·h-1 of fermentation productivity. |
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