以「直接皂化-酯化程序」轉化含油脂濕藻製備生質柴油

Abstract

微藻由於能夠快速生長且不與農耕作物競爭，並能有效率消耗二氧化碳，因此近幾年逐漸成為一受矚目的生質柴油原料，然而如何有效率地將微藻轉化為生質柴油仍有許多困難。本論文提出一新穎的轉化濕藻油脂程序，並建立動力學模型描述反應情形，再以初步放大反應驗證所提出的動力學模型。 本研究使用小球藻(Chlorella sp. ESP -6)為原料，結合傳統油脂萃取與油脂轉化反應，將油脂萃取、反應及純化合併為兩步驟反應。第一步驟加入氫氧化鈉甲醇溶液，使微藻細胞破碎釋放油脂，進行轉酯化及皂化反應，第二步驟加入鹽酸甲醇溶液，將皂化產物中和為游離脂肪酸，再酯化為脂肪酸甲酯(生質柴油)。 實驗結果顯示，以直接皂化-酯化轉化濕藻油脂具有許多優點；除了能夠節省傳統萃取必須去除水分以及油脂萃取的能量成本，與鹼催化轉酯化製程相比，能夠克服含水量及游離脂肪酸的限制，另一方面，只需要酸催化轉酯化製程完成反應約五分之一的時間。當含有0.05g乾重的濕藻0.5ml，加入2M的氫氧化鈉甲醇溶液1ml後反應20分鐘，再接著加入1M的鹽酸甲醇溶液2ml並反應15分鐘，兩步驟反應的水浴溫度皆為100℃，所達到的生質柴油產率為0.18 g-biodiesel/g-dried cell。 在本研究中，同時以假設的反應機制所建立的動力學模型，對於實驗結果進行模擬具有不錯的描述結果；由初步放大反應的實驗，更進一步地驗證了所提出的動力學模型。

Microalgae has become a potential resource of biodiesel in recent years for its fast growth, non-food source, and CO2 capture ability. However, efficient and economic production of biodiesel from microalgae is still a challenge. In this study, we presented a novel strategy of direct saponification-esterification conversion (DSEC) from wet microalgae (Chlorella vulgaris) to biodiesel. The process was accomplished with two consecutive additions into wet algae. With the first addition of NaOH/methanol solution, lipids of triglycerides and free fatty acids were released from disrupted algae and primarily converted into soaps by means of saponification. Then with further HCl/methanol addition, soaps were acidified into free fatty acid and esterified into fatty acid methyl ester (biodiesel). The experimental results supported several advantages of DSEC process. First, DSEC eliminates lipid extraction/purification step in conventail process, which usually accounts for more than half of production cost. Secondly, compared with the alkali catalyzed transesterification process, DSEC completely alleviated the restriction of incapable of dealing with the case of high content of water and free fatty acid. While compared with acid catalyzed transesterification process, the production time of DSEC was only about one-fifth. For example, at 100oC water bath, with 0.5 ml wet microalgae containing 0.05 g-dried-cell, yielded 0.18 g-biodiesel/g-dried-cell when 1 ml of 2 M NaOH/methanol was added for 20 mins and 2 ml of 1 M HCl/methanol was consequently added for another 15 mins. Moreover, the proposed kinetic model indicated a good fit, and the results in preliminary scale-up reactions further verified the kinetic model.