| 摘要: | 在纖維酒精的製程當中，由於可放大的特性，稀酸前處理被認為是眾多前處理程序中最有效率且最具商業可行性的的前處理技術，稀酸前處理可將大部分的半纖維素分解為木醣並溶於半纖維水解液中，在這同時也有有許多分解於葡萄糖、木糖和木質素的發酵抑制物(inhibitor)，如：呋喃甲醛(furfural)、羥甲基糠醛(Hydroxymethylfurfural) 和酚類化合物(phenolic compound) 也會被釋放至半纖維水解液中，這一些發酵的抑制物導致菌株在半纖維水解液的發酵表現不佳，同時也影響了纖維酒精的商業化可行性。有鑑於此，提升半纖維水解液中木醣的發酵效率被視為生質酒精商業化相當重要的工作。在本篇論文的第一部分主要是測試馴化的菌株Pichia stipitis 在100L 發酵槽進行木糖發酵生產酒精的可行性，實驗發現當通氣量設定為0.05 vvm 且使用過鹼化去毒化水解液時可得到最佳發酵效率為 0.44±0.02 gp/gs ，使用氨水中和以及氫氧化鈉中和的實驗組分別也可得到0.39±0.01 gp/gs and 0.34±0.01 gp/gs 的酒精生產效率，然而如果考量到過鹼化時所造成的木醣濃度的損失時，可發現使用氨水中和水解液的實驗所得到的酒精總量是和使用過鹼化法的酒精總量是接近相同的，因此氨水中和法可以取代傳統的去除化程序達到簡化木糖發酵的程序，此結果驗證了使用稻稈的木糖發酵成纖維酒精的商業化潛力。本論文的第二部分，發現了水解後的稻稈 (Hydrolyzed rice straw, HRS) 添加於木糖發酵反應中可以提高其酒精的產量，實驗發現發酵時在使用氫氧化鈉中和的水解液中加入HRS後可提升酒精生產效率至0.45 gp/gs ，HRS 同時也應用在合板、蔗渣和竹子的半纖維水解液中，發現菌株的酒精轉化效率也可被提高20%~51% ，證實HRS 這項技術可以被應用在不同的纖維原料的纖維酒精製程中，研究中也針對了HRS 對於菌株可能產生的影響進行推論和研究。綜合以上所述，本研究中利用兩種不同的策略改進了長久以來被認為是一個纖維酒精製程中低效率的木糖發酵程序，利用水解液的調理和改善發酵條件明了木糖發酵在放大規模操作的可行性，水解後的稻稈成功的應用實例驗證了改善木糖發酵效率的科技技術，添加HRS 的實驗也被拿來做測試及改善不只是稻稈還包括蔗渣、合板以及竹子的半纖維水解液都拿來與水解後的稻稈做測試及改善發酵效率的測試實驗。根據本篇論文研究成果，木糖發酵將不會被再被視為一個低效率且被放棄的製程，反而會被視為一個可以提高纖維酒精產量以及商業化潛力的程序。;Among the procedure of cellulosic ethanol, diluted acid pretreatment is considered as most effective and scalable pretreatment among various conditions of pretreatment, duo to its low cost of construction and scalability. When applying diluted acid pretreatment, most part of hemicellulose is dissolved into hemicellulosic hydrolysate as xylose. At the same time, various inhibitors, such as furfural, hydroxymethylfurfural and phenolic compound degraded from xylose, glucose and lignin are also be generated. These fermentative inhibitors hinder the performance of microorganism in hemicellulosic hydrolysate and further the commercialization of lignocelulosic ethanol. Improving efficiency of xylose fermentation is regarded as a critical for commercialization of lignocellulosic ethanol. In first part of thesis, adapted Pichia stiptis was used to demonstrate the feasibility of bioethanol production in 100-L fermentation using rice straw hydrolysate. The results indicated the highest ethanol yield of 0.44±0.02 gp/gs, when the aeration rate was at 0.05 vvm for overliming-detoxified hydrolysate. Hydrolysate conditioning with ammonia and NaOH also gave 0.39±0.01 gp/gs and 0.34±0.01 gp/gs of ethanol yield under the same aeration rate, respectively. However, actual ethanol yield from the fermentation of hydrolysate with ammonia neutralization was similar to that with overliming detoxification after considering the xylose loss resulted from conditioning processes. The results demonstrate the potential in the industrialization of xylose fermentation for bioethanol production from rice straw. In the second part of this research, hydrolyzed rice straw (HRS) was found to increase ethanol yield of xylose fermentation. In NaOH-neutralized hydrolyzate, HRS could induce ethanol yield up to 0.45 gp/gs. With the addition of HRS in hemicellulosic hydrolysate from plywood, bagasse and bamboo, the ethanol yields were increased for 20~51%. Xylose fermentation, usually regarded as low efficient process within the production procedure of lignocellulosic ethanol, was improved by two different strategies proposed in the present studies. The conditioning method of hydrolysate and optimized condition of fermentation proved the feasibility of xylose fermentation in pilot-scale operation. HRS was applied successfully to demonstrate technology improving efficiency of xylose fermentation. Fermentation of hemicellulosic hydrolysate from not only rice straw, but also bagasse, plywood and bamboo were also tested and improved with addition of HRS. According to the results mentioned in this dissertation, the xylose fermentation would not be seen as less efficient and abandoned process, but be taken into account for elevating the production and potential of commercialization of lignocellulosic ethanol. |
