| Abstract: | ABE(acetone-butanol-ethanol)發酵製程是一個歷史悠久的生物發酵製程，但是近年來生物發酵丁醇的製程卻逐漸沒落，主要原因在於丁醇的毒化抑制現象導致其低生產效率和碳源的低利用率，以及後續高純化成本，進而降低了生物發酵丁醇的商業生產競爭性。傳統上採用同步分離方法(in-situ removing)可以有效的降低丁醇的回饋抑制，但是卻會增加製程中的能源消耗。 本研究採用liquid-liquid extraction的分離技術，利用生質柴油當作萃取劑來同步移除發酵液內丁醇與其他代謝產物，減少丁醇抑制情形，而生質柴油所萃取得到的丁醇可以增進整體生質柴油的性質。在搖瓶批次培養的實驗中發現，添加生質柴油並不會干擾菌體的生長，在比例測試方面以添加體積比1:1的生質柴油對菌體生產丁醇有最好的效果。在批次饋料中，總丁醇濃度(水相+油相)可達到29.51 g/L，轉化率(yield)從原本(控制組)的0.34 g/g上升至0.45 g/g，其葡萄糖利用率有明顯提升之趨勢。而5L反應器添加生質柴油結合固定化的部分，在批次饋料實驗中，最大總丁醇生產濃度為28.44 g/L，其ABE的轉化率與生產速率(productivity)分別是0.29 g/g和0.38 g/L/hr。而連續式發酵實驗中，在稀釋速率(dilution rate)為0.024 1/hr，與生質柴油替換速率為0.012 1/hr時，其最大總丁醇生產濃度為175.92 g/L，ABE轉化率與生產速率為0.27 g/g和0.55 g/L/hr，與本實驗室之前的固定化連續式培養相比分別是0.29 g/g和0.46 g/L/hr，其生產速率有明顯提升之趨勢。因此，可發現以生質柴油同步移除丁醇，不但可以減少丁醇對細胞產生的抑制現象，對於提高整體溶劑的生產速率也有明顯的助益。關鍵字:ABE發酵、丁醇、liquid-liquid extraction、生質柴油、連續式發酵
The acetone–butanol–ethanol (ABE) fermentation process continues to receive attention as a source of fuel and chemical feedstock based on renewable resources. The traditional batch fermentation process, however, suffers from various problems which impede its commercial development. End-product inhibition, low product concentration, large volumes of fermentation broth, requirement of large bioreactors, and high costs associated with generating the required steam to distill the fermentation products from broth has largely contributed to the decline in fermentative ABE production.In-situ solvent extraction during fermentation has been shown to be one technique that enhances solvent production in ABE fermentation by reducing end- product inhibition by butanol. In this study, biodiesel was used as the in-situ extractant to reduce end product inhibition and to enhance solvent productivity for ABE fermentation, to bypass the energy intensive butanol recovery process, and to result in an ABE enriched biodiesel with improved fuel properties. During batch operation, no significant toxicity of biodiesel on the growth of cell is observed, and its effect results the best in producing butanol when biodiesel is added at the ratios of 1:1(vol%). In the fed-batch operation, the maximum of butanol in total obtained is 29.51 g/L, the glucose utilization enhanced significantly from 0.34 to 0.45 g/g. During fed-batch operation, scale up with adding biodiesel and immobilization, the maximum of butanol in total obtained is 28.44 g/L, the solvent productivity and yield was 0.38 g/L/hr and 0.29 g/g respectively. On the other hand, during continuous operation, the maximum of butanol in total obtained is 175.92 g/L when the dilution rate was at 0.024 and 0.012 1/hr of broth and biodiesel; the solvent productivity and yield was 0.55 g/L/hr and 0.27 g/g respectively. As compared to the previous experiment (without the addition of biodiesel) the productivity enhanced significantly from 0.46 to 0.55 g/L/hr. Therefore, the in situ removal of butanol by additions of biodiesel contains great potential for commercial usages in ABE fermentation.Keywords: ABE fermentation, butanol, liquid-liquid extraction, biodiesel, continuous process. |
