LDHs Instability in Esterification Reactions and Their Conversion to Catalytically Active Layered Carboxylates
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LDHs Instability in Esterification Reactions and Their Conversion to Catalytically Active Layered Carboxylates Claudiney Soares Cordeiro • Fabiano Rosa da Silva Rafael Marangoni • Fernando Wypych • Luiz Pereira Ramos
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Received: 19 March 2012 / Accepted: 25 March 2012 / Published online: 11 April 2012 Ó Springer Science+Business Media, LLC 2012
Abstract Layered double hydroxides (LDH) containing Zn/Al and Mg/Al with different counter-ions and M2?/M3? ratios were synthesized and used as catalysts in the esterification of fatty acids with methanol. High conversion rates were obtained depending on the reaction conditions. However, LDHs were also converted in situ into layered carboxylates and this new material was responsible for the observed catalytic activity, which was preserved even after several consecutive reuse cycles. Keywords Layered double hydroxides Layered carboxylates Catalysis Esterification Methyl esters
1 Introduction Biodiesel is defined as a renewable substitute of mineral diesel, which can be produced by alcoholysis of vegetable oils and/or animals fats or by esterification of fatty acids in the presence of short monohydroxylated alcohols and a catalyst either homogeneous or heterogeneous [1–3]. Biodiesel production technologies evolved a lot in the last few years but the majority of the currently available industrial facilities are still based on the alcoholysis of low acid number feedstocks in alkaline media. For biodiesel production using homogeneous basic catalysts, low acid number fatty materials are crucial to avoid soap formation,
C. S. Cordeiro F. R. da Silva R. Marangoni F. Wypych L. P. Ramos (&) Research Center in Applied Chemistry (CEPESQ), Department of Chemistry, Federal University of Parana´, P.O. Box 19081, Centro Polite´cnico, Jardim das Ame´ricas, Curitiba, PR 81531-980, Brazil e-mail: [email protected]
which decreases the catalyst availability and promotes emulsification. For this reason, low cost feedstocks such as acid oils, rendered materials, soapstocks and used cooking oils must be pretreated before use in such processes [1, 2, 4]. In general, alkyl esters produced by homogeneous base catalysts must be purified in order to meet the current biodiesel standards through a series of washings stages, starting with a dilute acid solution that is usually needed to breakdown the soap [2]. On the other hand, glycerin is obtained as a co-product with glycerol contents typically in the range of 80–85 %. Besides a low acid number, ideal feedstocks must present a suitable chemical composition for biodiesel production and these are independent of the method used for synthesis. For instance, feedstock chemical composition has a direct influence on the viscosity, oxidative stability, and cold flow properties of the resulting biofuel, among others. Several studies have discussed these aspects in detail [5–7]. With the aim of minimizing the generation of effluents, reducing the production costs and facilitating the use of low cost fatty materials, heterogeneous catalysts ha
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