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.
Highlights
Biodiesel is a suitable substitute for petroleum-derived diesel
The authors think that even if biodiesel is not the total solution to any energy crisis, it certainly is an important component of a combined strategic approach to decrease our current dependence on fossil fuels
We have evaluated the catalytic activity of the SnCl2·2H2O in homogeneous phase in the esterification of free fatty acids (FFAs)
Summary
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. The effluent generated in the catalyst neutralization processes and the biodiesel co-products must be discarded in the environment causing great environmental impact For these reasons, the alternative use of Lewis acids as catalysts for that process has been the goal of several discussions and will be addressed on section. The development of alternative catalysts for the esterification of FFAs, based on the Lewis acids, which operate under mild conditions of reaction and are less corrosive, rather than traditional Brønsted acids, is one of the main challenges to be overcome. This technology could allow the production of biodiesel at more competitive costs, in processes of lower environmental impact [16]. The investigation described involves the correlation between key parameters of reaction such as catalyst and fatty acid concentration, as well as the influence of the molar ratio FFA/ethanol and the temperature upon the ethyl oleate production
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