标题: 微藻养殖生产油脂并利用微藻油脂产制生质柴油之研究
Study on the lipid production from microalgal cultures and producing biodiesel from the microalgal lipid
作者: 蔡明达
林志生
生物科技学系
关键字: 微藻、小球藻、拟球藻、微藻油脂、生质柴油、转酯化反应;Microalgae, Chlorella sp., N. oculata, Microalgal lipid, Biodiesel, Transesterification
公开日期: 2008
摘要: 近年来,全球面临地球暖化危机与石化能源耗竭两大危机。由于人类大量开采石化能源及发展工业化社会导致温室气体CO2大量累积与石化燃料枯竭之严重问题。因故低污染的再生能源与CO2减量之策略发展为世界各国所积极研究的议题。然而以海洋微藻培养之利用正是一项高效益的绿色能源开发方法。微藻为能行使光合作用之单细胞植物,能快速且大量生产植物生物质与累积大量油脂于微藻细胞中。有鉴于此,本研究之目的为以高脂海洋微藻利用废气CO2培养以进行大量油脂生产并藉由转酯化反应生成生质柴油之研究。在最佳培养状况下所筛选海洋微藻生长效率可达一天微藻增生2至3倍。微藻培养时Chlorella sp.与N. oculata之微藻内油脂从生长对数期至生长稳定期,培养状态进行至氮源缺乏时,可由12%与21%分别提升至21%与50%。然而以半连续式微藻培养于光生物反应器,通入2% CO2之半连续式微藻光生物反应器中,其生长能力与产脂率表现最佳,氮在不同浓度CO2培养下(2至15%),高浓度CO2对于微藻的生长与产脂量能保持稳定并不受高浓度CO2的抑制。然而微藻也能利用不同的有机碳源在混营或异营脂培养状态下进行生长与油脂堆积。本研究指出,以蔗糖行异营培养之N. oculata其油脂累积虽可达54%,但其生物质产量有降低的情形,而在以蔗糖进行混营之培养下油脂产量可提升至每公升0.284公克。因此微藻培养时可分为两个阶段:增值阶段及肥育阶段,先利用最适生长环境来快速培养增加微藻的细胞浓度,再将其转入低硝酸盐或以蔗糖混营培养环境中肥育,即可有效率的大量产脂。
本研究中,微藻油脂转酯化生成生质柴油因其转化方式可分为化学制程以及生物制程两种,以最佳油醇莫耳比下,酸化学催化反应与微生物脂解酶催化反应可分别达到88%与82%。酵素催化之转化率虽佳,但其成本高且反应时间过长,在工业上多以快速简便之化学催化转酯化反应达到快速、低成本且高产率的目的。本研究成果证明由藻类油脂制成生质柴油作为再生燃料具可行性与未来性,且在藻类培养过程中能有效的降低环境中的温室气体之危害并能提供快速且大量生物油脂之生产以提供生成生质柴油。
In recent years, people over the world face some acute problem with regard to global warming and energy crisis. Humans exploited the fossil energy and developed the industry and civilization well in past hundred years to result in the environmental problems, green-house gas emission rising, and petrochemical fuel exhausting. Photosynthetic organism, microalgae, can use solar energy efficiently to combine water with CO2 to produce biomass. Microalgae can not only produce biomass but accumulate lipid in microalgal cells. Lipids from microalgae can be extracted and converted to biodiesel fuel by transesterification.
In the study, the biomass and lipid productivity of Chlorella sp. and Nannochloropsis oculata were evaluated in the different conditions of culture in the closed photobioreactors. Results showed that the lipid accumulation of Chlorella sp. and N. oculata from logarithmic phase to stationary phase were significantly increased from 12% to 24% and 21% to 50%, respectively. In the semiconscious culture of Chlorella sp. and N. oculata, the total lipid productivity was 0.143 and 0.142 (g/L/d), respectively although the cultures were daily replaced half of broth. The results showed that Chlorella sp. and N. oculata were potential candidates for biomass and lipid production by semicontinuous cultures. The comparison of lipid productivities in the semicontinuous systems in which the culture broth were replaced at an interval of 24 h (one-day replacement) or 72 h (three-day replacement) was performed. The result indicated the total lipid yield in the semicontinuous culture operated by one-day replacement was more efficient.
Moreover, different carbon sources supplied in the culture could make distinct growing ability and lipid accumulation. The results showed the cultivation of N. oculata using sucrose as carbon source in mixotrophic growth gave the highest maximum biomass (0.80 g/L) and the lipid productivity was up to 0.284 (g/L). Although the lipid contents from the heterotrophic cultivations with sucrose could increase to 54%, the biomass productivity decreased in the heterotrophic cultures. Therefore, the recovery of microalgal cells from semicontinuous cultures can transfer to mixotrophic cultivation for higher lipid production. The fast analysis of lipid contents of live microalgal cells by Nile red staining under fluorescence was established. The linear regression of fluoresce intensity of lipid content was established to measure the lipid contents of microalgae.
The typical transesterification method used in this study was chemical and enzymatic processes. The results indicated the efficiency of transesterification by acid catalyst could approach 88% and the efficiency by lipase-catalyzed transesterification could reach 82% by the optimal oil/methanol molar ratio. The high cost and long reaction time of enzymatic processes may be not convenient for usage. In industrial and commercial application, the chemical catalyst is common for transesterification to reach the purposes of low-cost and fast reaction rate. Therefore, the fast and suitable transesterification method in this study is acid-catalytic process.
URI: http://140.113.39.130/cdrfb3/record/nctu/#GT079628523
http://hdl.handle.net/11536/42726
显示于类别:Thesis


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