利用固定化菌體 Rhizopus oryzae 生產生質柴油之研究

Abstract

生質柴油為以動植物油或廢食用油脂，經由轉化技術後所產生之酯類，可以直接使用或混合石化柴油作為柴油引擎之燃料。生質柴油具有以下優點：(1)為再生性能源，可被生物分解；(2)燃燒後所產生氣體污染性低；(3)不增加大氣的二氧化碳的淨值；(4)可直接代替石化柴油或混合石化柴油使用；(5)具有能源經濟的正面效應。現今普遍生產生質柴油的方法為轉酯化反應(transesterification)，其中主要以鹼觸媒法來進行轉酯化反應，此轉酯化反應的反應物為三酸甘油脂以及甲醇，產物為甘油以及脂肪酸甲酯，脂肪酸甲酯即為所謂的生質柴油。本研究希望以固定化菌體來進行轉酯化反應，此法可以減少化學法所產生的大量廢水污染，也可節省直接使用脂解酵素(lipase)的成本。 本研究以市面上的過濾生化棉作為固定化用的擔體，先作轉酯化實驗，篩選出適合於轉酯化實驗的擔體。因為轉酯化反應的副產物甘油，會阻礙反應物和酵素作用，因此，將篩選出來的擔體，進行甘油吸附的實驗，希望找到不會有甘油吸附的擔體。接下來測試各項變因對此固定化擔體轉酯化效果的影響，菌重和大豆油重比值需為 15.2% 以上。最適的反應溫度為 35℃，醇油莫耳比為 1:1，水分含量為 10%，pH 值沒有影響。重複使用性方面，不論是固定化擔體或自由菌體，其重複使用性皆不理想，第二次使用時，產生的甲基酯含量都降到 30% 左右。在保存性方面，不論是固定化擔體，或是自由菌體，都至少可保存 15 天以上。 本研究也利用乙酸甲酯來取代甲醇，發現在無水狀態，乙酸甲酯對大豆油莫耳比為 12:1 時，反應五小時可得到 40% 甲基酯含量。

Biodiesel is transformed from vegetable or animal oil. It is biofuel that can be directly used or mixed with petroleum diesel used in diesel engine. Biodiesel has many advantages: (1) It is the renewable energy and biodegradable; (2) It makes less pollution after combustion; (3) It does not increase current net atmospheric levels of carbon dioxide; (4) It can directly displace petroleum diesel or mix with petroleum diesel; (5) It has positive effect on energy economy. Chemical method to produce biodiesel is transesterification which is carried out by alkali catalyst. The reactants are triacylglycerol and methanol, and the products are glycerol and methyl esters. Methyl esters are called biodiesel. In this study, we utilized immobilized cells to produce biodiesel and reduce the pollution from chemical method and save the cost of using lipase directly. Different commercial filtration biochemical sponges was used as immobilization carriers. The suitable carriers for transesterification were selected by transesterification experiments. The glycerol hinders interaction of reactants and immobilized cells. According to the result of glycerol absorption, the carrier which did not absorb glycerol was chosen, and the factors affected transesterification were examined. The weight ratio of cell and soybean oil was at least 15.2%, optimal temperature at 35℃. The molar ratio of methanol and soybean oil was 1:1 with 10% water. The reusability was only 30% both in free cells and immobilized cells, whereas free cells and immobilized cells can maintain their activities at least for 15 days. When methyl acetate was used to displace methanol, the optimal water content was 0% and molar ratio of methyl acetate to soybean oil was 12:1. In this condition, the methyl esters content reached 40% after 5-day reaction.