隨著人類社會的高度發展，對於能源的需求與日俱增，然而化石燃料終有枯竭之日，因此尋找替代能源成為目前人類必須要面對的重要課題。在眾多再生能源當中，生質能源因其原物料容易取得以及技術成熟等，一直被視為極具潛力的再生能源之一。而目前生質柴油原物料選擇上，由於微藻具有高生長速率、易栽培以及高含油量等特性，成為目前最被重視的研究主題之一。
　　本研究使用之原物料為國立成功大學培養之Chlorella vulgaris的濕藻體，採用CO2膨脹甲醇(CO2-expanded methanol, CXM)的方法進行就地萃取轉酯化反應(In-situ extraction and transesterification)製備生質柴油，此方法能改善有機溶劑萃取與超臨界流體萃取的缺點並提高油脂在甲醇中的互溶性，同時藉由二氧化碳溶於微藻水分降低pH值有利於水解細胞壁。由於微藻是固體原料，在進行就地轉酯化反應時會使用較大量的甲醇以促進其攪拌與萃取進行，為了利用多餘的甲醇，本研究額外添加由國立清華大學曾晴賢教授提供的蓖麻油作為額外油源，期許能藉由添加額外油源增加每次反應的產量並有效利用多餘的甲醇。
　　經由實驗，我們觀察到添加蓖麻油之後的總產率與微藻油的轉化率較只使用微藻有顯著的提升，顯示蓖麻油可作為微藻在進行萃取時的共溶劑使微藻萃取效果提升並提高轉化率。接著討論蓖麻油添加量、微藻含水量、反應溫度、壓力與反應時間等變因對脂肪酸甲酯(FAMEs)產率的影響。實驗結果顯示蓖麻油添加量較低會導致共溶劑能力降低，轉化率下降，添加過多導致醇油莫耳比下降也會降低轉化率，存在一最佳添加量；含水量提高兩種油的轉化率均下降，微藻油轉化率下降較明顯，但以乾藻進行反應蓖麻油的轉化率會降低，此時部分蓖麻油與微藻細胞膜表面形成氫鍵鍵結；反應溫度提高兩種油的轉化率皆提高，蓖麻油在230℃後發生裂解導致轉化率下降；在到達某一個壓力後，壓力對轉化率的影響會較小，本研究中1400psi以上產率便無明顯提升；反應時間延長雖會提高產率，大部分的反應在前30分鐘便已完成。
　　本研究發現在微藻中混合蓖麻油進行就地轉酯化可以提高總產率，並比較不同變因對兩種油源轉化率的影響。此方法或可應用在其他植物油上，在進行生質柴油生產時提高產量並提高甲醇使用率，減少回收成本，具發展潛力。

As the human society highly develops, the requirement of energy increases. However, the total amount of fossil fuel is limited, so finding alternative energy is important for human. Among the several kinds of alternative energy, bioenergy seems to be one of the promising alternative energy because of the accessible raw material and mature technology. For the choice of raw material of biodiesel, microalgae is one of the valued research topics since its high growing speed, easy to cultivate and high lipid content.
In this research, we use the wet microalgae called Chlorella vulgaris cultivated by National Cheng Kung University as the raw material. We use the method of CO2-expanded methanol (CXM) to conduct in-situ extraction and transesterification to produce biodiesel. It can improve the organic solvent extraction and supercritical fluid extraction and increase the mutual solubility between oil and methanol. Carbon dioxide solutes in water can decrease the pH value and assist the hydrolysis of the cell wall of microalgae. Since microalgae is solid material, in the process of transesterification we need to use much methanol to assist the stir and extraction. To utilize extra methanol, we add the castor oil provided by Professor Tzeng Chyng-Shyan in National Tsing Hua University as another oil source. We hope we can increase the amount of product and utilize extra methanol by adding another oil source.
By experiment, we observe the total yield and conversion yield of microalgae increase significantly after adding castor oil. It demonstrates that castor oil can serve as co-solvent of extraction of microalgae, improve the effect of extraction and increase the conversion yield. We discuss the factor that affected the yield of fatty acid methyl ester (FAMEs) includes the amount of castor oil added, moisture of microalgae, temperature, pressure and reaction time. The result shows that the yield decreases when the amount of castor oil decreases since the ability of co-solvent decreases, and the yield decreases when the amount of castor oil increases since the methanol-to-oil ratio decreases, so there is a best amount of castor oil added. Both yields of oil will decrease when the moisture increases, and microalgae oil is more obvious. However, the yield of castor oil is low if the microalgae is dry. It is because some of the castor oil forms hydrogen bond with cell membrane of microalgae. Yields of two kinds of oil increase as the temperature increases, and castor oil cracks at 230℃. When the pressure increases to a specific point, the effect of pressure for yield will decrease. In this research, the specific pressure is about 1400psi. Although increasing reaction time will increase the yield, most of the reaction is finished in 30 minutes.
In this research, we find that blending castor oil with microalgae to conduct in-situ extraction and transesterification can increase total yield. We discuss different factors that affected the yield of two kinds of oil. This method may apply to other vegetable oil to increase yield and usage rate of methanol to reduce the cost of recycling, can be seen as a promising process.

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