79 CHEMICAL ENGINEERING TRANSACTIONS VOL. 42, 2014 A publication of The Italian Association of Chemical Engineering www.aidic.it/cet Guest Editors: Petar Sabev Varbanov, Neven Duić Copyright © 2014, AIDIC Servizi S.r.l., ISBN 978-88-95608-33-4; ISSN 2283-9216 DOI:10.3303/CET1442014 Please cite this article as: Hajek M., Kocik J., Smolakova L., Kutalek P., Čapek L., 2014, Preparation of methyl ester by heterogeneous catalysed esterification and transesterification, Chemical Engineering Transactions, 42, 79-84 DOI:10.3303/CET1442014 Preparation of Methyl Ester by Heterogeneous Catalysed Esterification and Transesterification Martin Hájek, Jaroslav Kocík, Lucie Smoláková, Pert Kutálek, Libor Čapek Faculty of Chemical Technology, University of Pardubice, Studentská 573, 532 10 Pardubice, Czech Republic martin.hajek2@upce.cz The aim of this work is to study and test two types of catalyst – acid and basic for the preparation of methyl esters. The first goal is to describe the transesterification catalysed by Mg-Al mixed oxides in a broad range of Mg/Al ratio (from 1.0 to 8.4) including the relation between the variables by statistical analysis and catalyst stability. The mixed oxides with a different Mg/Al molar ratio were synthesized by thermal pre- treatment of hydrotalcite at 450 °C. The influence of the Mg/Al molar ratio on the yield of ester, leaching of magnesium and catalyst properties such as the concentration of basic sites, crystallite size of MgO and specific surface area were studied. It was found that the crystallite size and the yield of ester increases and the concentration of basic sites decreases with an increasing Mg/Al molar ratio; the specific surface area does not depend on the Mg/Al molar ratio. The relation between the variables was described by statistical analysis (the correlation matrix and principal component analysis). There was observed only negligible magnesium leaching from solid Mg/Al mixed oxides to the liquid phases. Five types of zeolites (MOR-C and D, ZSM-5, Y and mesoporous BEA) were tested in the esterification of oleic acid and the results were compared with pure alumina. The highest yield exhibited mesoporous BEA. The comparison of catalytic and non-catalytic esterification was carried out at the same reaction conditions. 1. Introduction Methyl esters (biodiesel) are an ecological fuel and are produced by transesterification of triglycerides contained in vegetable oils by low molecular alcohols. Reaction is usually catalysed by a basic homogeneous catalyst (KOH or NaOH). This way has several disadvantages (e.g. saponification of oil, reuse of catalyst is impossible), therefore nowadays research has turned to heterogeneous catalysts, one of them is mixed oxides as a basic catalyst or zeolites as an acid catalyst. Other sources such as animal fats, waste and frying oils can also be used. The disadvantage of these sources is that they contain a higher amount of free fatty acids and water, which supports the saponification reaction (reaction between hydroxide and oil) and therefore reduction in the product yield. For this reason, use of a basic catalyst is not possible. The first step of ester production is the decreasing of fatty acids by acid-catalysed esterification and the second step is basic-catalysed transesterification. Therefore two different catalysts are necessary and in this paper both types were studied. The Mg/Al mixed oxides are advantageously prepared by thermal pre-treatment of Mg/Al hydrotalcites. Hydrotalcites are layered materials known also as anionic clays or layered double hydroxides with a general formula. The symbol M represents bivalent or trivalent metallic cations, A represents an anion and x is the molar ratio of M3+. The combination and ratio of metallic ions influence the structure and chemical properties of hydrotalcites. A controlled thermal decomposition of hydrotalcite-like precursors leads to the formation of finely dispersed mixed oxides with a large surface area. This oxide possesses strong surface basicity, high surface area and a high quantity of defects resulting from the incorporation of Al 3+ in the MgO lattice. Mg-Al mixed oxides are attractive catalysts for reactions such as transesterification (Castro et al., 2013) – focusing on basicity and (Shumaker et al., 2008) focusing on the structure, as well as aldol or Knoevenagel condensation (Abello et al., 2008). Many authors study the system (catalyst characterization and transesterification) separately for narrow range of molar ratio Mg/Al (usually 2-4) (Carvalho et al., 2012). However, we study the system together.