Synthesis of biodiesel from vegetable oil with methanol catalyzed by Li-doped magnesium oxide catalysts Zhenzhong Wen a , Xinhai Yu a, * , Shan-Tung Tu a , Jinyue Yan b,c , Erik Dahlquist b a School of Mechanical and Power Engineering, East China University of Science and Technology, Meilong Rd. 130, Shanghai 200237, China b School of Sustainable Development of Society and Technology, Mälardalen University, SE-721 23 Västerås, Sweden c School of Chemical Science and Engineering, Royal Institute of Technology, Stockholm, SE-100 44 Stockholm, Sweden article info Article history: Received 20 July 2009 Received in revised form 17 September 2009 Accepted 17 September 2009 Keywords: Biodiesel Transesterification Li-doped MgO Solid base abstract The preparation of a Li-doped MgO for biodiesel synthesis has been investigated by optimizing the cat- alyst composition and calcination temperatures. The results show that the formation of strong base sites is particularly promoted by the addition of Li, thus resulting in an increase of the biodiesel synthesis. The catalyst with the Li/Mg molar ratio of 0.08 and calcination temperature of 823 K exhibits the best perfor- mance. The biodiesel conversion decreases with further increasing Li/Mg molar ratio above 0.08, which is most likely attributed to the separated lithium hydroxide formed by excess Li ions and a concomitant decrease of BET values. In addition, the effects of methanol/oil molar ratio, reaction time, catalyst amount, and catalyst stability were also investigated for the optimized Li-doped MgO. The metal leaching from the Li-doped MgO catalysts was detected, indicating more studies are needed to stabilize the catalysts for its application in the large-scale biodiesel production facilities. Ó 2009 Elsevier Ltd. All rights reserved. 1. Introduction Due to the depletion of fossil based fuels and increasing envi- ronmental concern, alternative renewable energy sources have been developed [1,2]. Biodiesel, defined as fatty acid methyl ester, made from biological sources such as vegetable oils, animal fats and waste cooking oils, is becoming a favorable biofuel in many re- gions of the world [3,4]. Compared with the diesel fuel, biodiesel is biodegradable and non-toxic [3,5]. Besides, the exhaust gas from this fuel contains little SO x and a relatively small amount of CO, un-burnt hydro-carbons and particulate matter, which can make it as a green fuel substitute [6,7]. Biodiesel can be produced through transesterification of vegeta- ble oils and fats with methanol in the presence of a suitable cata- lyst [3]. Generally, this reaction can be catalyzed by both acid- and alkali-catalysts. Alkalis used for the transesterification include NaOH, KOH, and alkoxides. The main alkoxides are sodium meth- oxide and potassium methoxide. The alkali-catalyzed transesterifi- cation proceeds approximately 4000 times faster than that catalyzed by acid, and thereby is more competitive commercially [8]. Acid-catalyzed transesterification uses the homogeneous non-green catalysts (sulfuric, phosphoric, hydrochloric, and organ- ic sulfonic acids) and the reaction is much slower than that by al- kali catalysis [3,8]. However, this procedure seems to be more suitable for the oil containing high level of free acid or water be- cause the alkaline catalyst can react with free fatty acid, therefore leading to the loss of catalyst and lowering the biodiesel yield. The homogeneous catalysts of both alkalis and acids have been exploited successfully in industrial biodiesel production. However, the subsequent neutralization, separation, and purification steps will cause time consuming and require several washing stages with a large amount of water [3,8]. These drawbacks significantly contribute additional cost to the final biodiesel products. Studies involving enzymes have been reported as well but these proce- dures require large volumes and a long reaction time [9]. Compared with homogeneous catalysts, heterogeneous cata- lysts can provide green and recyclable catalytic systems [10,11]. There are many solid heterogeneous acid- and alkali-catalysts for biodiesel synthesis. Zeolite beta modified with La 3+ prepared by an ion exchange method was reported as an alternative to the homogeneous acid catalysts [12]. Heteropolyacid impregnated on different supports (silica, zirconia, alumina, and activated carbon) as solid acid catalysts were also indicated as catalysts for the transesterification of canola oil with methanol to produce biodiesel [13]. Unfortunately, the performances of these acid catalysts are still inferior compared with the base catalysts. For this reason, a wide variety of solid bases have been examined for transesterifica- tion reactions for biodiesel synthesis. Examples include basic 0306-2619/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.apenergy.2009.09.013 * Corresponding author. Tel./fax: +86 21 64253513. E-mail address: yxhh@ecust.edu.cn (X. Yu). Applied Energy 87 (2010) 743–748 Contents lists available at ScienceDirect Applied Energy journal homepage: www.elsevier.com/locate/apenergy