Basic catalytic transesterification of oils with homogeneous [(e.g., sodium methoxide, potassium or sodium hydroxide and heterogeneous catalysts (e.g, CaO and sodium silicate) is the most common method for biodiesel production at low temperatures (e.g., 50-60^oC). However, they are easily to form soap with free fatty acids (FFAs) when low qualified oils with high acid value (AV) are used as raw materials, and two-step process composed of esterification and transesterification catalyzed over acidic and basic catalysts was developed. But, the process is too complex and costly. This work aims to directly produce biodiesel from oils with high acid value without any pretreatment using activated nanosized Mg-Al hydrotalcite.

Miss Yitong Wang (Master student), under the guidance of Professor Dr. Zhen Fang from Xishuangbanna Tropical Botanical Garden (CAS), prepared Mg-Al hydrotalcite (HT-Ca) nanoparticles (< 45 nm) by co-precipitation and hydrothermal activation with aqueous Ca(OH)₂solution. HT-Ca presented both acidic and basic due to the formation of Mg₄Al₂(OH)₁₄.3H₂O, Mg₂Al(OH)₇and AlO(OH) nanocrystals to esterify and transesterify oils with high AV. Under conditions of 5 wt% HT-Ca, 160^oC, 30/1 methanol/oil molar ratio and 4 h, 93.4%Jatrophabiodiesel yield was obtained at AV of 6.3 mg KOH/g with 4 cycles (biodiesel yield > 86%). It was further found that it can resist FFAs, and biodiesel yield reached 92.9% from soybean oil with high AV of 12.1. HT-Ca catalyst showed a potential practical application for direct production of biodiesel from oils with high AV without pretreatment.

The results are published in Bioresource Technology:

YT Wang, Zhen Fang*, F Zhang, BJ Xue. One-step production of biodiesel from oils with high acid value by activated Mg–Al hydrotalcite nanoparticles, Bioresource Technology, 193, 84–89 (2015).

活化Mg-Al水滑石纳米颗粒用于一步法催化高酸值油脂制备生物柴油

由于中国的国情限制，用于制备生物柴油的非食用原料油酸值都比较高。这样，碱性催化剂在低温（如50摄氏度）制备生物柴油容易发生严重的皂化反应。而酸性催化剂制备生物柴油时，尽管没皂化反应，但要求较高的反应温度（如220摄氏度），对设备的质量要求也很高，同时易腐蚀设备。所以，本研究目的是制备同时具有酸碱性的催化剂可以一步法直接催化高酸值的油脂变成生物柴油。

中国科学院西双版纳热带植物园生物能源组，硕士生王一同小姐在方真研究员的指导下，成功合成了Mg-Al 水滑石纳米颗粒，将其活化后用于催化高酸值的小桐子油以及高酸值的混合大豆油制备生物柴油。实验结果表明：该纳米颗粒具有较好的抗酸性，在反应温度160^oC, 5%催化剂量，30/1醇油摩尔比和4 h 的反应时间条件下，催化酸值为6.3的小桐子油，生物柴油的产率可以达到93.4%，当催化酸值为12.1的混合大豆油制备生物柴油，产率可以达到92.9%。该纳米颗粒重复使用四次，生物柴油的产率依然可以达到86%以上。活化后的Mg-Al 水滑石纳米颗粒表现出良好的催化性能。

相关研究成果发表在国际著名能源期刊Bioresource Technology上：

YT Wang, Zhen Fang*, F Zhang, BJ Xue. One-step production of biodiesel from oils with high acid value by activated Mg–Al hydrotalcite nanoparticles, Bioresource Technology, 193, 84–89 (2015)