蔗渣產製生質乙醇

Abstract

生質乙醇，泛指以生質物為原料所產製之乙醇，具有高純度、方便儲存與低危險性等優點，可與汽油混合用於車輛引擎，是一項具有潛力之替代燃料。 本研究以台灣特用作物甘蔗於製糖後剩餘之蔗渣作為原料，先以0.25 M之稀硫酸，於1大氣壓與95℃條件下前處理60分鐘，並透過前處理液與前處理物之葡萄糖、木糖含量與組成分析，了解酸前處理之效果。再單獨或合併利用劑量不等之纖維水解酶與葡萄糖苷酶，對前處理物酵素水解，探討酵素種類、劑量、基質濃度與水解時間對酵素水解效果之影響，找出最佳之酵素水解條件。接著使用啤酒酵母 Saccharomyces cerevisiae BCRC 21685，於30℃、pH 4.6等條件下，對酵素水解後之水解液進行醱酵，先探討水解液之可醱酵性，其次於加入葡萄糖下探討有無排毒、滅菌對於醱酵反應之影響，最後探討加入葡萄糖或蒸發水分方式提高葡萄糖濃度對醱酵反應之影響。 研究結果顯示：在酸前處理階段，有1.46%之纖維素、91.85%之半纖維素、0.49%之木質素與77.31%之其他成分在過程中被溶解，並於前處理液中測得濃度分別為0.52 mg/mL與4.29 mg/mL之葡萄糖與木糖濃度。在水解酵素階段，最佳之酵素組合為5 mL 之Cellulclast 1.5L搭配 1 mL之Novozyme 188，可於基質濃度1%、溫度50℃、80 rpm、pH值 4.6與水解時間24小時等條件下，獲得339.21 mg/g之葡萄糖產率、49.25%之纖維素轉換率，過程中並有57.17%之纖維素、20.0%之半纖維素、3.81%之木質素、12.48%之其他物質被溶解。若提高水解基質濃度至5%，並無助於纖維素轉換率之提高。在醱酵階段，若未經排毒與滅菌程序，則在歷經48小時之醱酵後，仍有26.7 g/L之葡萄糖未轉換成乙醇，乙醇產率為0.367g ethanol/g glucose，約為理論值之72%。若先經排毒與滅菌程序，則所有葡萄糖可在24小時內醱酵完畢，乙醇產率提高至理論值之84%。若以蒸發水分之方式提高葡萄糖濃度且經排毒與滅菌程序，則葡萄糖可在30 小時內醱酵完畢，乙醇產率為79%。

Bioethanol is a kind of clean and renewable energy which can be used directly or mixed with gasoline as fuel on vehicles. In this study, sugarcane bagasse which contained 33.34% cellulose, 22.11% semicellulose, and 6.49% lignin was pretreated by 0.25 M sulfuric acid under 95℃ and 1 atm pressure for 60 mins. After pretreatment, dried solid material was hydrolyzed by mixing enzymes of cellulase from Trichoderma reesei C2730 (Celluclast 1.5L) and cellobiase from Aspergillus niger (Novozyme 188) under conditions of pH 4.6, 50℃ in 80 rpm shaking water bath for 24 hours. Different enzyme loadings and substrate ratios were tested to find out the optimum parameters. Hydrolysate was then fermented with Saccharomyces cerevisiae BCRC 21685 under conditions of pH 4.6, 30℃ for 24-48 hours. The effect of additional glucose, sterilization, and detoxification were investigated in this step. As result, 0.52 mg/mL of glucose and 4.29 mg/mL of xylose concentrations were observed in liquid fraction and the content of solid material showed that 91.85% semicellulose and 1.46% cellulose was removed in pretreatment. In hydrolysis step, the enzyme loading of 5 mL Celluclast 1.5L plus 1 mL Novozyme 188 represented the best balance between economy and efficiency. 339.21 mg/mL of yield and 49.25% of conversion ratio were obtained under this enzyme loading with 1% substrate ratio and rising the substrate ratio did not help improving both of them. In fermentation step, without sterilization and detoxification, 26.7 g/L of glucose remains after 48 hours fermentation and ethanol yield was 0.367 g ethanol / g glucose, corresponding to 72% of theoretical ethanol yield. With sterilization and detoxification, glucose was fermented within 24 hours. The ethanol yield was 0.43 g ethanol/g glucose, , corresponding to 84% of theoretical ethanol yield. With evaporation to enhance the glucose concentration, the glucose concentration did not decrease to zero until after 30h. The ethanol concentration was 40.7 g/L, corresponding to 79% of theoretical ethanol yield.