Esterification of Oleic Acid for Biodiesel Production Catalyzed by Sncl2: a Kinetic Investigation

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Energies 2008, 1, 79-92; DOI: 10.3390/en1020079
energies
ISSN 1424-8220
www.mdpi.org/energies
Article
Esterification of Oleic Acid for Biodiesel Production Catalyzed by SnCl2: A Kinetic Investigation
Abiney L. Cardoso, Soraia Cristina Gonzaga Neves and Marcio J. da Silva * Departament of Chemistry, Federal University of Viçosa, Viçosa, Minas Gerais, Brazil, 36570-000. * Author to whom correspondence should be addressed; E-Mail:silvamj2003@ufv.br Received: 5 August 2008; in revised form: 16 September 2008 / Accepted: 17 September 2008 / Published: 24 September 2008

Abstract: The production of biodiesel from low-cost raw materials which generally contain high amounts of free fatty acids (FFAs) is a valuable alternative that would make their production costs more competitive than petroleum-derived fuel. Currently, the production of biodiesel from this kind of raw materials comprises a two-stage process, which requires an initial acid-catalyzed esterification of the FFA, followed by a basecatalyzed transesterification of the triglycerides. Commonly, the acid H2SO4 is the catalyst on the first step of this process. It must be said, however, that major drawbacks such as substantial reactor corrosion and the great generation of wastes, including the salts formed due to neutralization of the mineral acid, are negative and virtually unsurmountable aspects of this protocol. In this paper, tin(II) chloride dihydrate (SnCl2·2H2O), an inexpensive Lewis acid, was evaluated as catalyst on the ethanolysis of oleic acid, which is the major component of several fat and vegetable oils feedstocks. Tin chloride efficiently promoted the conversion of oleic acid into ethyl oleate in ethanol solution and in soybean oil samples, under mild reaction conditions. The SnCl2 catalyst was shown to be as active as the mineral acid H2SO4. Its use has relevant advantages in comparison to mineral acids catalysts, such as less corrosion of the reactors and as well as avoiding the unnecessary neutralization of products. Herein, the effect of the principal parameters of reaction on the yield and rate of ethyl oleate production has been investigated. Kinetic measurements revealed that the esterification of oleic acid catalyzed by SnCl2·2H2O is first-order in relation to both FFAs and catalyst concentration. Experimentally, it was verified that the energy of activation of the esterification reaction of oleic acid catalyzed by SnCl2 was very close those reported for H2SO4.

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Energies 2008, 1
80
Keywords: Tin chloride catalyst, Biodiesel, free fatty acids, ethanolysis. 1. Introduction
Biodiesel is a suitable substitute for petroleum-derived diesel. It is biodegradable, almost sulfurless and a renewable fuel, though still not produced by environmentally friendly routes. This alternative fuel consists of methyl or ethyl esters, a result of either transesterification of triacylglycerides (TG) or esterification of free fatty acids (FFAs) [1]. Biodiesel fuel has become more attractive because of its environmental benefits, due to the fact that plants and vegetable oils and animal fats are renewable biomass sources [2]. Currently, most of the biodiesel comes up from transesterification of edible resources such as animal fats, vegetable oils, and even waste cooking oils, under alkaline catalysis conditions [3-5]. However, the high consumption of catalysts, the formation of soaps, and the low yields, make biodiesel currently more expensive than petroleum-derived fuel [6]. The common processes of biodiesel production from low-cost raw materials use mineral acids as catalysts, owing to the high amounts of FFAs that those resources contain, which make the manufacture of biodiesel from these feedstocks incompatible with alkaline catalysts [7]. Thus, two alternative approaches are normally used. The first is a two-step process, which requires an initial acidcatalyzed esterification of the FFA, followed by a base-catalyzed transesterification of the TG....
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