Du Wei, Xu Yuan-yuan, Zeng Jing, Liu De-hua
Department of Chemical Engineering, Tsinghua University, Beijing 100084, People's Republic of China.
Biotechnol Appl Biochem. 2004 Oct;40(Pt 2):187-90. doi: 10.1042/BA20030142.
When crude soya-bean oil was used as the source for biodiesel production, the yield of methyl ester was significantly lower than that from refined soya-bean oil. The major difference between refined and crude soya-bean oils was found to be due to the contents of phospholipids, free acid and water, which have varied influences on biodiesel production. Phospholipid content was the most influential factor; the higher the phospholipid content in the oil, the lower is the methyl ester yield. The optimal water activity was found to be in the range 0.12-0.44, and free acid included in crude soya-bean oils showed no negative effect on enzymic transesterification. During our study of three-step methanolysis of crude soya-bean oils for biodiesel production, we noted that the second-step methanolysis was much faster than the first-step reaction. On the basis of this finding, the proposal that immersing pretreatment of lipase in oils contributes to improvement in enzyme activity has been put forward. In addition, it has been demonstrated that immersing pretreatment of lipase in oils could improve both the reaction rate and methyl ester yield significantly. A methyl ester yield of 94% could be achieved by immersing lipase in crude oils for 120 h and this was just as high as the yield for refined oils.
当使用粗制大豆油作为生物柴油生产的原料时，甲酯的产量显著低于精制大豆油。精制大豆油和粗制大豆油之间的主要差异被发现是由于磷脂、游离酸和水的含量，它们对生物柴油生产有不同的影响。磷脂含量是最具影响力的因素；油中磷脂含量越高，甲酯产量越低。发现最佳水分活度范围为0.12 - 0.44，粗制大豆油中的游离酸对酶促酯交换没有负面影响。在我们对粗制大豆油进行三步甲醇解以生产生物柴油的研究中，我们注意到第二步甲醇解比第一步反应快得多。基于这一发现，提出了将脂肪酶在油中进行浸泡预处理有助于提高酶活性的建议。此外，已经证明将脂肪酶在油中进行浸泡预处理可以显著提高反应速率和甲酯产量。通过将脂肪酶在原油中浸泡120小时可实现94%的甲酯产量，这与精制油的产量一样高。
