Short Communication Biodiesel and FAME synthesis assisted by microwaves: Homogeneous batch and flow processes J. Hernando, P. Leton, M.P. Matia, J.L. Novella, J. Alvarez-Builla * Planta Piloto de Quı ´mica Fina, Universidad de Alcala, 28871 Alcala de Henares, Madrid, Spain Received 8 September 2006; received in revised form 31 October 2006; accepted 2 November 2006 Available online 30 November 2006 Abstract Fatty acids methyl esters (FAME) have been prepared under microwave irradiation, using homogeneous catalysis, either in batch or in a flow system. The quality of the biodiesel obtained has been confirmed by GC analysis of the isolated product. While the initial exper- iments have been performed in a small scale laboratory batch reactor, the best experiment has been straightforward converted into a stop-flow process, by the use of a microwave flow system. Compared with conventional heating methods, the process using microwaves irradiation proved to be a faster method for alcoholysis of triglycerides with methanol, leading to high yields of FAME. Ó 2006 Elsevier Ltd. All rights reserved. Keywords: Biodiesel; FAME; Microwaves 1. Introduction The transesterification of natural triglycerides (e.g. oils and fats) is employed to obtain fatty acid methyl esters (FAME) which are key reagents in the chemical industry [1–4]. The FAME are the raw materials for the production of long chain carboxylic acids, detergents, alternative fuels for diesel engines (biodiesel) and mono and diglycerides, employed as additives for foods, cosmetics and pharmaceu- ticals [5]. Biodiesels are biodegradable and non-toxic and have lower CO and hydrocarbon emissions than petro- leum-based diesel when burned [6,7]. They present, how- ever, other technical challenges such as low cloud points and elevated NO x emissions [8]. The most commonly used technology for triglycerides transesterification is based on the use of batch processes, in which a basic homogeneous catalyst is used (NaOH or NaOMe) and, at the end of the reaction, the catalyst is neu- tralised [9,10, as recent examples]. A continuous transeste- rification process would be a good opportunity to reduce production costs [11]. Several processes are currently employed for homoge- neous catalytic transesterification, although these processes suffer from the presence of by-products that reduce selec- tivity and increase the separation time between products, while recently heterogeneous catalysts have been claimed to produce cleaner processes. In any of those situations, when the reaction is carried out under microwaves, transe- sterification is efficiently activated, with short reaction times, and as a result, a drastic reduction in the quantity of by-products and a short separation time is obtained, and all with a reduced energy consumption. Several examples of microwave irradiated transesterifi- cation methods have been published in the literature, by Loupy [1] and Mazzocchia [12], but they have made use of batch laboratory ovens, which do not allow to study the process at a higher scale. Similar results have been described by adapting domestic ovens to use them as flow systems [13,14]. A recent paper from Leadbeater describes the use of two batch laboratory microwave apparatus, one monomode to perform micro experiments, the other multimode able to irradiate flasks up to 5 L [15]. Some 0016-2361/$ - see front matter Ó 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.fuel.2006.11.003 * Corresponding author. E-mail address: julio.alvarez@uah.es (J. Alvarez-Builla). www.fuelfirst.com Fuel 86 (2007) 1641–1644