Ultrasound-assisted synthesis of ethyl esters from soybean oil via homogeneous catalysis Jeane Q.A. Brito a , Creuza S. Silva a , Jorge S. Almeida a , Maria G.A. Korn a, c , Mauro Korn b, c , Leonardo S.G. Teixeira a, c, ⁎ a Instituto de Química - Universidade Federal da Bahia, Campus Universitário de Ondina, Salvador, Bahia, 40.170-115, Brazil b Departamento de Ciências Exatas e da Terra - Universidade do Estado da Bahia - Rua Silveira Martins 2555, Cabula, Salvador, Bahia, 41150-000, Brazil c INCT de Energia e Ambiente, Universidade Federal da Bahia, Salvador, Bahia, 40170-115, Brazil abstract article info Article history: Received 30 December 2010 Received in revised form 17 October 2011 Accepted 6 November 2011 Available online 3 December 2011 Keywords: Ethyl esters Soybean oil Biodiesel Transesterification Ethanolysis Ultrasound-assisted reaction A transesterification reaction of esters from soybean oil with ethanol assisted by low-frequency ultrasound (20 kHz) was performed in the presence of a potassium hydroxide catalyst. The effects of the following vari- ables on the reaction performance were studied simultaneously through a full two-level factorial design 2 3 : the concentration of the catalyst, the oil:ethanol molar ratio and the sonication time. The three investigated factors significantly affected the yield. Further experimentation was performed using a three-step reaction. An ethyl ester yield of approximately 98% was attained in the third step. The physicochemical properties of the products were compared with the technical limits of biodiesel, and the results suggest that the ultrasound-assisted ethanol transesterification reaction could be a viable and efficient method for the pro- duction of quality biodiesel from soybean oil. © 2011 Elsevier B.V. All rights reserved. 1. Introduction Environmental awareness and an increasing demand for energy have prompted a considerable amount of research on the production of fuels from renewable resources that are environmentally benign. In this context, biodiesel can be considered an alternative fuel to fossil- based diesel. Biodiesel is produced from a large variety of renewable lipid–vegetable sources. Traditionally, biodiesel has been obtained by alcoholysis of the oil in the presence of an alkaline catalyst, meth- anol and heat. The two immiscible phases of triglycerides and meth- anol, after one or two hours in a batch reactor, react to produce esters and glycerol that can be separated by gravitational settling [1]. The handling risks and the poor sustainability associated with methanol production are disadvantages related to the use of metha- nol for biodiesel production. Methanol is a nonrenewable fossil source of energy produced from natural gas; thus, the production of biodiesel by a reaction with methanol is not an eco-friendly process [2]. Ethanol is less toxic, less volatile and less corrosive than metha- nol, and therefore provides a safer work environment during the transesterification process. In addition, ethanol is readily available by fermentative processes from biomass feedstocks (e.g., corn and sugar cane) [3,4], which makes the use of ethanol appealing for bio- diesel production [5]. With respect to economic considerations, abso- lute ethanol is expensive; for this reason, methanol is customarily used because it is the cheapest alcohol available in most countries. However, in Brazil, the use of ethanol is advantageous because it is al- ready produced in large quantities [6]. The yield efficiency of biodiesel depends on the alcohol used in the reaction. During transesterification under the same reaction condi- tions, ethanol, because of its longer carbon chain, exhibits a lower re- activity than methanol [5,7]. The time required for the ethanolysis reaction of ethanol is longer than that for methanol, and more energy is consumed. In addition, higher alcohol:oil molar ratios are necessary to increase ester conversion in shorter reaction times [8,9]. One method of decreasing the transesterification reaction time when using ethanol is through the use of ultrasonic irradiation. The reaction of the triglycerides with ethanol occurs in the interfacial re- gion between the two immiscible liquids. The conventional base- catalyzed transesterification is characterized by slow reaction rates at both the initial and final reaction stages, and is limited by the mass transfer between the polar alcohol/glycerol phase and the non-polar oil phase [10]. The use of ultrasound can increase the inter- action between the phases through the collapse of cavitation bubbles and the ultrasonic jet that disrupts the phase boundary and causes emulsification [11,12]. This process enhances the mass transfer and allows for shorter reaction times, cheaper reagents and less extreme physical conditions. Fuel Processing Technology 95 (2012) 33–36 ⁎ Corresponding author at: Instituto de Química - Universidade Federal da Bahia, Campus Universitário de Ondina, Salvador, Bahia, 40.170-280, Brazil. Tel.: + 55 71 32836800; fax: + 55 71 32355166. E-mail address: lsgt@ufba.br (L.S.G. Teixeira). 0378-3820/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.fuproc.2011.11.007 Contents lists available at SciVerse ScienceDirect Fuel Processing Technology journal homepage: www.elsevier.com/locate/fuproc