Synthesis of Fatty Acid Methyl Esters from Pomace Oil Catalyzed by Zinc Stearate: A Kinetic Study of the Transesterification and Esterification Reactions

Mariana Soledad Alvarez Serafini,Gabriela Marta Tonetto

doi:10.3390/catal9120978

Abstract

In this work, the simultaneous transesterification and esterification reactions of olive pomace oil with methanol catalyzed by zinc stearate were studied. This catalyst is a crystalline solid at room temperature, but it is soluble in the reaction medium at reaction temperature. Zinc stearate has surfactant properties that cause the formation of an emulsion in the reaction system. The stability of the emulsion formed in the oil–methanol–catalyst system was compared to that in the FAME (fatty acid methyl esters)–methanol–catalyst system. It was observed that the emulsion formed in the presence of high amounts of FAME is much more unstable, which makes the catalyst easy to separate from the reaction products. The kinetics of esterification and transesterification were also studied. All the kinetic and equilibrium constants were determined with a complete model, considering the three stepwise reactions corresponding to the transesterification of triglycerides and the esterification of free fatty acids. The parameters obtained were used to model the operating conditions that would allow obtaining biodiesel that meets the quality standards.

Highlights

Biodiesel (FAME) is an alternative fuel that can be used to replace diesel fuel completely or partially in auto-ignition engines without requiring any modification [1]
Before proposing a mathematical model that describes the methanolysis of pomace oil catalyzed by zinc stearate, all the reactions that take place in the reactor must be identified
The water could react with the the TG or with FAME, hydrolyzing them according to the following equations: TG or with FAME, hydrolyzing them according to the following equations: (1)

Summary

Introduction

Biodiesel (FAME) is an alternative fuel that can be used to replace diesel fuel completely or partially in auto-ignition engines without requiring any modification [1]. The industrial process most commonly used for biodiesel production is the transesterification of triglycerides (TG) with a low-molecular-weight alcohol in the presence of acid or base catalysts, depending on the quality of the raw material. Vegetable oils have been the preferred raw material, especially due to their high energy content and easy processing for large-scale production. Biofuels obtained from edible oils are the so-called first-generation fuels. The loss of biodiversity associated with deforestation is another problem associated with these first-generation biofuels. These oils continue to be used for biodiesel production, the development of second-generation biodiesel is being encouraged, using alternative raw materials such as waste from the food industry, animal fats, and low-quality or used oils

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