Journal of Molecular Catalysis A: Chemical 379 (2013) 234–242 Contents lists available at ScienceDirect Journal of Molecular Catalysis A: Chemical j ourna l ho me pa g e: www.elsevier.com/locate/molcata Catalytic properties of spinel-type mixed oxides in transesterification of vegetable oils T.M. Sankaranarayanan a,b,∗ , R. Vijaya Shanthi a , K. Thirunavukkarasu a , A. Pandurangan b , S. Sivasanker a a National Centre for Catalysis Research, Indian Institute of Technology, Chennai 600 036, India b Department of Chemistry, Anna University, Chennai 600 025, India a r t i c l e i n f o Article history: Received 10 July 2013 Received in revised form 23 August 2013 Accepted 24 August 2013 Available online 4 September 2013 Keywords: Spinels ZnFe2O4 Biodiesel Transesterification Vegetable oils a b s t r a c t Crystalline mixed oxides of AB 2 O 4 composition, where A = Co, Ni, Cu and Zn and B = Al, Fe and Co, were prepared by co-precipitation of hydroxides and calcination at 873 K. The catalytic activity of these mate- rials in the transesterification of sunflower oil with methanol to produce fatty acid mono esters (FAME; biodiesel) was investigated. The transesterification activity was found to depend on element A, the order of activity being: Zn > Cu > Ni > Co. The Zn containing spinels were more active than the others and their activity was found to go through a maximum with Sanderson’s intermediate electronegativity. Detailed investigations carried out on ZnFe 2 O 4 revealed it to be a suitable solid catalyst for the transesterification of used cooking oil and Jatropha oil. The catalyst was reusable many times. The performance of this spinel was also investigated in a bench-scale (30 g catalyst loading) fixed-bed reactor. Crown Copyright © 2013 Published by Elsevier B.V. All rights reserved. 1. Introduction The use of renewable transportation fuels made from biomass, such as ethanol and fatty acid methyl esters (FAME), is slowly increasing over the years due to concerns regarding atmospheric CO 2 build up and depletion of fossil fuels. The transesterification of vegetable oils is at present mostly carried out using soluble alkali catalysts. The disadvantages of using alkali catalysts are soap for- mation, poor quality of byproduct glycerol, waste water generation and non-suitability for oils containing free fatty acids (FFA). There- fore, search for solid acid catalysts that can transform non-edible oils and those with FFA have been on for many years. Many solid catalysts have been reported to be suitable for the reaction [1–5]. A few representative, recently reported solid catalysts are double metal cyanides [6], heteropoly acid/zirconia [7], Amberlyst, Nafion [8,9], basic zeolites [10], supported metal hydroxides and salts [11–13] and mixed metal oxides [14–18]. A fixed-bed process based on zinc-aluminate (ZnAl 2 O 4 ) was devel- oped for transesterification by the Institut Francais du Petrole (IFP) and was commercialized by Axens [19]. Pugnet et al. and Alves ∗ Corresponding author at: National Centre for Catalysis Research, Indian Institute of Technology, Chennai 600 036, India. Tel.: +91 44 2257 4238; fax: +91 44 2257 5245. E-mail addresses: tmsankaranarayanan@gmail.com, tms2003@rediffmail.com (T.M. Sankaranarayanan). et al. have also reported the transesterification of vegetable oil over ZnAl 2 O 4 [20,21]. Spinel-type oxides possess many advantages, such as good thermal stability, good chemical stability preventing their dissolution during reaction, and ease of preparation with reason- ably large external areas. We now present our studies on the performance of a number of other spinels as catalysts for the transesterification of vegetable oils with and without free fatty acids (FFA) carried out as part of our continuing research on the transesterification of vegetable oils with solid oxide catalysts [22]. The spinel-type oxides investigated are CuAl 2 O 4 , NiAl 2 O 4 , CoAl 2 O 4 , ZnFe 2 O 4 , NiFe 2 O 4 and ZnCo 2 O 4 . Addi- tionally, a comparison of the catalytic activities of the above spinels is also made with that of the already reported ZnAl 2 O 4 . All the com- pounds were prepared by a co-precipitation method and not by blending of the component oxides [20]. These were characterized by physicochemical methods and their activity in the transesteri- fication of sunflower oil with methanol was evaluated in a batch reactor. The transesterification of used cooking oil and Jatropha oil was also evaluated over ZnFe 2 O 4 . Additionally, the activity of ZnFe 2 O 4 was examined using a fixed-bed bench scale reactor. 2. Experimental 2.1. Materials used and preparation of catalysts Cooking grade sunflower oil, waste (used) sunflower oil and Jat- ropha oil were procured locally. Their fatty acid compositions are 1381-1169/$ – see front matter. Crown Copyright © 2013 Published by Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.molcata.2013.08.027