Esterification of used vegetable oils using the heterogeneous WO 3 /ZrO 2 catalyst for production of biodiesel Young-Moo Park a , Joon Yeob Lee a , Sang-Ho Chung a , In Seon Park a , Seung-Yeon Lee a , Deog-Keun Kim b , Jin-Suk Lee b , Kwan-Young Lee a, * a Department of Chemical and Biological Engineering, Korea University, 5-1, Anam-dong, Sungbuk-ku, Seoul 136-701, Republic of Korea b Biomass Research Center, Korea Institute of Energy Research, Yuseong 305-600, Taejeon, Republic of Korea article info Article history: Received 17 December 2008 Received in revised form 4 April 2009 Accepted 10 April 2009 Available online 9 May 2009 Keywords: Biodiesel Esterification Tungsten oxide zirconia Heterogeneous catalyst Free fatty acid abstract Tungsten oxide zirconia, sulfated zirconia and Amberlyst-15 were examined as a catalyst for a conversion of used vegetable oils (VOs) to fatty acid methyl esters (FAMEs). Among them, tungsten oxide zirconia was a promising heterogeneous catalyst for the production of biodiesel fuels from used VOs because of high activity in the conversion over 93% and no leaching WO 3 in the esterification reaction. The reaction conditions were optimized. A study for optimizing the reaction parameters such as the reaction temper- ature, stirring speed, WO 3 loading over ZrO 2 and reaction time, was carried out. The catalyst was charac- terized by BET, XRD, FT-IR, and NH 3 -TPD. With increasing WO 3 loading over ZrO 2 , the triclinic phase of WO 3 increased and the tetragonal phase of zirconia was clearly generated. The highest acid strength of 20 wt% tungsten oxide zirconia catalyst was confirmed by NH 3 -TPD analysis and the result was correlated to the highest catalytic activity of the esterification reaction. Ó 2009 Elsevier Ltd. All rights reserved. 1. Introduction Recently, many countries have reported rapid progress in renewable fuels, with biodiesel being the most well known. Biodie- sel fuel obtained from vegetable oils (VOs) has attracted consider- able attention over recent decades as a renewable, biodegradable, eco-friendly and non-toxic fuel, and several processes have been developed for its production. Biodiesel is gaining prominence as a substitute for petroleum-based diesel due to environmental con- siderations and the depletion of vital resources, such as petroleum and coal. The possible uses of renewable resources are fuels and major feedstocks for the chemical industry. Petroleum is a rapidly depleting natural resource, making an alternative renewable route to petroleum a necessity. Furthermore, biodiesel is a clean burning fuel with no sulfur emissions and no efficiency loss despite its heat of combustion being slightly lower than that of petro-diesel (Sri- vastava and Prasad, 2000), and no engine adjustments are neces- sary. In addition, it is non-corrosive and can be produced under low pressure and temperature conditions. Biodiesel is commonly derived from triglycerides (VOs) and methanol through transesterification using homogeneous cata- lysts, such as alkali hydroxides (NaOH and KOH), carbonates, and sodium and potassium alkoxides (Canakci and Van Gerpen, 2001, 2003; Dorado et al., 2002; Ghadge and Raheman, 2005). A gener- ally mild process for production of biodiesel from VOs using heter- ogeneous base catalysts was developed in our previous study (Kim et al., 2004). Despite the environmental advantage of the biodiesel, produc- tion cost of biodiesel is pretty high compared to conventional die- sel fuel. In order to reduce the production cost, used VOs has been suggested as feedstock. However, the free fatty acids (FFAs) in used VOs are known to cause severe problems for the transesterification catalyzed by base catalyst. FFA can react with the base catalyst (neutralization reaction), which brings a loss of catalyst and a pro- duction of soap as by-product which accelerates the deactivation of the base catalyst (Park et al., 2008). Consequently, FFA contained in used VOs should be removed or converted to inert material. In this work, we tried to convert FFA to fatty acid methyl esters (FAMEs) using heterogeneous acid catalysts (Eq. (1)), which are the components of biodiesel themselves. The catalytic esterifica- tion activity of SO 2 4 /ZrO 2 , WO 3 /ZrO 2 , and Amberlyst-15 was con- firmed and compared. WO 3 /ZrO 2 was finally chosen on account of its high activity and stability. A series of experiments were per- formed using WO 3 /ZrO 2 with temperature, WO 3 loading, amount of catalyst (g/ml (oil)) and reaction time as parameters to deter- mine the optimal reaction conditions. The WO 3 /ZrO 2 catalyst was characterized by BET, X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, NH 3 -temperature programmed desorption (TPD). Free fatty acids ðFFAsÞþ methanol ! Fatty acid methyl esters ðFAMEsÞþ water ð1Þ 0960-8524/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.biortech.2009.04.025 * Corresponding author. Tel.: +82 2 3290 3299; fax: +82 2 926 6102. E-mail address: kylee@korea.ac.kr (K.-Y. Lee). Bioresource Technology 101 (2010) S59–S61 Contents lists available at ScienceDirect Bioresource Technology journal homepage: www.elsevier.com/locate/biortech