Glycerol Organosolv Pretreatment And High-titer Ethanol Fermentation Of Crop-based Biomass

The expensive production of bioethanol is due to that it has not yet reached the‘THREE-HIGH’(High-titer, high-conversion and high-productivity) technical level as the starchy ethanol production. To cope with it, it is necessary to manage a high-gravity mash bioethanol production(HMBP), in which the sugar hydrolysate is thick, the purity of cellulose is high and fermentation-inhibitive compounds are negligible. In this thesis, a new pretreatment and bioethanol fermentation of lignocellulosic materials was studied.The hydrolyzability of sugarcane bagasse was improved by an atmospheric aqueous glycerol autocatalytic organosolv pretreatment(AAGAOP). With a preliminary optimization on some key factors such as cooking temperature and cooking time, the pretreatment of sugarcane bagasse was processed as below: 70% glycerol solution at 220 ℃ for 2 h. At the optimized condition, the pretreatment had a good cellulose recovery(95%), and high hemicellulose(70%) and lignin(65%) removals. Interestingly, the cellulose conversion of the pretreated substrate was up to 90% with an enzyme loading of 16 FPU·g-1 dry substrate.Several modern analytic techniques(TGA, SEM, AFM, CLSM, FT-IR, XRD and CP/MAS 13C-NMR) were used to characterize changes of wheat straw and sugarcane bagasse before and after the AAGAOP. The good hydrolyzability of substrates subjected to AAGAOP is mainly due to that the AAGOAP can effectively disrupt the complex, recalcitrant architecture of lignocellulosic substrates, which divides into three hierarchies:compositionally to selectively remove some component barriers(i.e., lignin, hemicellulose and acetyl group), structurally to dissect the native physical structure into some features helpful for hydrolyzability, and structure-chemically to dissociate key chemical bonds and functional groups(i.e., β-ether bond, β-ester band and hydrogen bond) of inter- and intramolecules, resulting in allomorphous transformations(from crystalline to amorphous or para-crystalline).Finally, HMBP from wheat straw after the AAGAOP was carried out with different fermentation strategies. Under an optimized condition(15% substrate concentration,(NH4)2SO4 10 g·L-1, 30 FPU·g-1 dry matter, inital p H4.8, fermentation temperature 37 ℃,10%(v/v) inoculum ratio), the HMBP was at 31.2 g·L-1with a shaking simultaneous saccharification and fermentation(SSF) for 72 h, which reached a conversion of 73% and a productivity of 0.43 g·(L·h)-1. Further by a semi-SFF with a pre-hydrolysis time of 24 h, the HMBP reached 33.7 g·L-1, with 79% of the conversion and 0.47 g·(L·h)-1 of the productivity.During the SSF and semi-SSF, more than 90% of the cellulose in both substrates was found to hydrolyze into fermentable sugars. Again, a fed-batch semi-SFF was developed with an initial substrate concentration of 15%. The HMBP achieved 52.8 g·L-1for 96 h with a productivityof 0.55 g·(L·h)-1 and a cellulose conversion of 62%. Finally, such several strategies as purifying the substrate cellulose, increasing substrate concentration, extending the fed-batch time, adding the surfactant and using the new cellulase preparation Cellic CTec2, were used.With an equivalent substrate concentration of 35%, the HMBP reached 73.1 g·L-1for 72 h with a high productivity of 1.02 g·(L·h)-1 and a cellulose conversion of 67%. Notably, the fermentation inhibitive compound was mainly the acetic acid at less than 4.0 g·L-1, and there were no other inhibitors detected, commonly as such furfural and hydroxymethylfurfural existing in the slurry, during the three types of fermentation. The data indicate that the lignocellulosic substrate subjected to the AAGAOP is very applicable for the HMBP.