Kinetic Study of Alcoholysis of the Fatty Acids Catalyzed by Tin Chloride(II): An Alternative Catalyst for Biodiesel Production

Abstract

A valuable alternative for making the biodiesel price more competitive than petroleum-derived fuel is the use of raw materials of low cost. However, these feedstocks contain a high amount of free fatty acids (FFAs). Currently, the biodiesel production from this kind of resource is comprised in a two-step process, where an initial acid-catalyzed esterification of the FFA followed by a base-catalyzed transesterification of the triglycerides occurs. Commonly, the sulfuric acid is the catalyst on the acid step. However, some serious drawbacks, such as substantial reactor corrosion and the great generation of wastes, even of the salts formed by mineral acid neutralization, are negative aspects of these processes. In this work, the SnCl2-catalyzed esterification of saturated and unsaturated FFA was evaluated. High yields and selectivities were achieved on the ethanolysis of FFA, under mild conditions of reaction. The SnCl2 catalyst has shown to be as active as the mineral acid H2SO4. Their use has relevant advantages in comparison to mineral acid catalysts, such as lower corrosiveness and as well as the unnecessary neutralization after the reaction finishes. Herein, the effects of the principal parameters of the reaction have been investigated. Kinetic investigations revealed a first-order dependence upon both the oleic acid and the catalyst concentration. The energy of activation achieved for this process was approximately similar to those reported for H2SO4-catalyzed FFA esterification.