Pretreatment Process Of Biomass And Simultaneous Saccharification And Fermentation For Bioethanol Production

Biomass utilization has attracted great attention in the world. In this paper, the objective feedstocks were corn stover and medicinal plants. According to the characteristics of feedstocks and the desired productions, the specific pretreatment process was established with steam explosion and low-temperature plasma technology. The effects of pretreatment process on the recalcitrance disruption, extraction of the active ingredient and efficiency of enzymatic hydrolysis were evaluated, also its mechanism was discussed. The utilization pattern of starch-rich medicinal plants to produce ethanol was achieved by steam explosion, expanding the feedstock for bio-ethanol production. The feasibility of the large-scale pre-hydrolysis and simultaneous saccharification and fermentation ethanol was approved, which may provide the guidance for the commercial bioethanol production.The main results were obtained as follows:(1) The biomass of steam explosion pretreatment were expanded from corn stover to medicinal plants. Firstly, through controlling the parameters, the hemicellulose degradation rate was selectively improved, and the inhibitor concentration within the hydrolysate was reduced. Therefore, the selective-fractionation technology of corn stover using steam explosion pretreatment has been established. Secondly, the gelatinization process of the rich-starch feedstock with 30-120 min was replaced by unpolluted steam explosion pretreatment (0.4-1.0 MPa,2-4 min), thereby the gelatinization process of starch-feedstock with steam explosion was established. Lastly, a novel air-steam explosion with low temperature was developed to treat Eucommia ulmoides leaves, in order to achieve the desirable extraction yield of thermosensitive chlorogenic acid. After pretreatment for 120 s, the yield and extraction rate of chlorogenic acid from air-steam exploded sample were 2.83% and 0.246 min-1, respectively, which were 62.49% and 423.0% higher than those of raw sample. Additionally, the equilibrium time of chlorogenic acid extraction decreased from 120 min to 15 min. The fibrous networks and the cell walls of the leaves were destroyed by air-steam explosion pretreatment, which improved the solute-solvent accessibility and the internal mass transfer during extraction process.(2) The atmospheric-pressure dielectric barrier discharges plasma pretreatment (ADBDPP) was introduced. The effects of pretreatment process on the recalcitrance disruption, extraction of the active ingredient and the process of enzymatic hydrolysis were evaluated, and compared with steam explosion pretreatment. After ADBDPP, the yield of chlorogenic acid and the permeability of corn stover rind were increased by 14.27% and 30.12% compared with that of the untreated material, respectively, but the yield and permeability from steam exploded feedstock were increased by 62.49% and 431.60%. However, owing to the special high-energy particle, ADBDPP was able to react, which would not be done by steam explosion treatment. Plasma was employed in the enzymatic hydrolysis and the correlation of plasma, cellulase activity and enzymatic hydrolysis of corn stover was evaluated. Results showed that the cellulase activity was increased, and then decreased with the increase of plasma intensity. The highest cellulase activity was achieved when the cellulase was treated with plasma at 75 W for 30 s, under which the cellulase activity was increased by 14.35% than that of untreated sample. The enzymatic hydrolysis yield and velocity constant with the plasmas duty cycle of 1 h were increased by 52.26% and 45.71%, respectively, whereas the enzyme loading was decreased by 31.52% to achieve the same hydrolysis yield.(3)The efficiency of ADBDPP was closely related to the plasma parameters and the characteristics of feedstock. The effects of ADBDPP parameters (plasma power, plasma time and gas flow rate) on xylose and glucose conversion rate were analyzed, then the optimized plasma parameters were attained, which was plasma power of 100 W, N2 of 0.5 L/min and H2O of 0.1 L/min. Under the optimized condition, the xylose and glucose conversion rate from hemicellulose oligosaccharides and microcrystalline cellulose were increased by 44.52% and 45.89%, respectively. The particle size of corn stover was reduced using ball milling treatment, which resulting in improved the efficiency of ADBDPP. After the ball milling treatment of 2 h and ADBDPP of 20 min, the glucan and xylan conversion rate were increased by 41.04% and 65.94% than that of untreated corn stover. The reactive particle was gained in the process of ADBDPP, which resulted in the acid reaction with biomass. Furthermore, the crystal structure and the hydrogen bonds were disrupted to break glycoside.(4) The effects of solid loading, enzyme loading, pre-hydrolysis time and steam explosion parameters on the efficiency of enzymatic hydrolysis and simultaneous saccharification and ethanol fermentation were studied, and the optimized parameters were attained. Based on these paramaters, the pre-hydrolysis and simultaneous saccharification and ethanol fermentation (PHSSEF) for steam exploded corn stover was established. The yield of ethanol reached 4.15%, which corresponded to72.3% theoretical yield of ethanol in the large-scale project. Therefore, the feasibility of PHSSEF in industrialization was approved.(5) The production of ethanol and isoflavones from steam-exploded Kudzu by solid state fermentation was established. The yield of ethanol and isoflavones was 9.20 g/100g fresh Kudzu and 1.87 g/100g Kudzu, respectively, and the utilization rate of starch was 95.0%. Therefore, the process was clean and energy-saving, which provided a new way of starch-rich medical plants utilization, and expanded the feedstock for production ethanol.