Green Materials & Process Group, Korea Institute of Industrial Technology, 89 Yangdaegiro-gil, Ipjang-myeon, Seobuk-gu, Cheonan-si, Chungcheongnam-do, 31056, South Korea.
SKKU Advanced Institute of Nanotechnology, Sungkyunkwan University, 2066 Seobu-ro, Jangan-gu, Suwon-si, Gyeonggi-do, 16419, South Korea.
BMC Biotechnol. 2017 Sep 9;17(1):70. doi: 10.1186/s12896-017-0390-1.
Waste animal fat is a promising feedstock to replace vegetable oil that widely used in commercial biodiesel process, however the high content of free fatty acid in waste fat makes it unfeasible to be processed with commercial base-catalytic process. Enzymatic process is preferable to convert waste fat into biodiesel since enzyme can catalyze both esterification of free fatty acid and transesterification of triglyceride. However, enzymatic reaction still has some drawbacks such as lower reaction rates than base-catalyzed transesterification and the limitation of reactant concentration due to the enzyme inhibition of methanol. Supercritical CO is a promising reaction media for enzyme-catalyzed transesterification to overcome those drawbacks.
The transesterification of waste animal fat was carried out in supercritical CO with varied concentration of feedstock and methanol in CO. The CO to feedstock mass ratio of 10:1 showed the highest yield compared to other ratios, and the highest FAME yield obtained from waste animal fat was 78%. The methanol concentration effect was also observed with variation 12%, 14%, and 16% of methanol to feedstock ratio. The best yield was 87% obtained at the CO to feedstock ratio of 10: 1 and at the methanol to feedstock ratio of 14% after 6 h of reaction.
Enzymatic transesterification to produce biodiesel from waste animal fat in supercritical fluid media is a potential method for commercialization since it could enhance enzyme activity due to supercritical fluid properties to remove mass transfer limitation. The high yield of FAME when using high mass ratio of CO to oil showed that supercritical CO could increase the reaction and mass transfer rate while reducing methanol toxicity to enzyme activity. The increase of methanol concentration also increased the FAME yield because it might shift the reaction equilibrium to FAME production. This finding describes that the application of supercritical CO in the enzymatic reaction enables the application of simple process such as a packed-bed reactor.
废动物脂肪是一种很有前途的替代植物油的原料，被广泛应用于商业生物柴油工艺中，但废脂肪中游离脂肪酸含量高，使其无法用商业碱性催化工艺进行加工。由于酶可以同时催化游离脂肪酸的酯化和甘油三酯的酯交换，因此酶法转化废脂肪为生物柴油更为可取。然而，酶反应仍然存在一些缺点，例如反应速率比碱性催化酯交换低，以及由于甲醇对酶的抑制作用，反应物浓度受到限制。超临界 CO 是一种很有前途的酶催化酯交换反应的反应介质，可以克服这些缺点。
在超临界 CO 中，用不同浓度的原料和甲醇在 CO 中进行了废动物脂肪的酯交换。与其他比例相比，CO 与原料的质量比为 10:1 时显示出最高的产率，从废动物脂肪中获得的最高 FAME 产率为 78%。还观察到甲醇浓度的影响，甲醇与原料的比例分别为 12%、14%和 16%。在 CO 与原料的质量比为 10:1，甲醇与原料的比例为 14%，反应 6 小时后，获得了最佳的产率 87%。
在超临界流体介质中用酶法从废动物脂肪生产生物柴油是一种有潜力的商业化方法，因为超临界流体的特性可以增强酶的活性，从而消除传质限制。使用高 CO 与油的质量比可以获得高 FAME 产率，这表明超临界 CO 可以提高反应和传质速率，同时降低甲醇对酶活性的毒性。甲醇浓度的增加也提高了 FAME 的产率，因为它可能使反应平衡向 FAME 生产方向移动。这一发现表明，超临界 CO 在酶反应中的应用可以实现简单的工艺，如填充床反应器。
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