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.
Prof. FANG Zhen and his team of Xishuangbanna Tropical Botanical Garden (XTBG) conducted a study aiming to directly produce biodiesel from oils with high acid value without any pretreatment using activated nanosized Mg-Al hydrotalcite.
The researchers prepared Mg-Al hydrotalcite (HT-Ca) nanoparticles (< 45 nm) by co-precipitation and hydrothermal activation with aqueous Ca(OH)2 solution. Reaction conditions were optimized by single-factor experiments. Catalysts were characterized by various techniques before and after biodiesel production. The activated Mg–Al hydrotalcite-calcium nanoparticles showed high activity to produce biodiesel from crude oils with high acid value without pretreatment. The catalyst presented both acidic and basic to catalyze esterification and transesterification due to the formation of Mg4Al2(OH)14·3H2O, Mg2Al(OH)7 and AlO(OH) nanoparticles. Under conditions of 5 wt% HT-Ca, 160 oC, 30/1 methanol/oil molar ratio and 4 h, 93.4% Jatropha biodiesel 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 free fatty acids to achieve 93.4% Jatropha biodiesel yield at AV of 6.3 mg KOH/g and recycle 4 times with biodiesel yield >86%. Soybean biodiesel yield reached 92.9% even from oil with high AV of 12.1 mg KOH/g. Thus, HT-Ca catalyst showed a potential practical application for direct production of biodiesel from oils with high AV without pretreatment.
The study entitled “One-step production of biodiesel from oils with high acid value by activated Mg–Al hydrotalcite nanoparticles” has been published online in Bioresource Technology.
Activated nanosized Mg-Al hydrotalcite used to produce biodoesel.
(Image by WANG Yitong)
Key words
Activation; Nanoparticles; High acid value; Jatropha biodiesel
Contact
FANG Zhen Ph.D Principal Investigator
Key Laboratory of Tropical Plant Resources and Sustainable Use, Xishuangbanna Tropical Botanical Garden, Chinese Academy of Sciences, mneglun 666303, Yunnnan, China
Tel: 86 872 65137468
E-mail: zhenfang@xtbg.ac.cn
