Abstract
Methanolysis of vegetable oils in the presence of homogeneous catalysts remains the most important process for producing biodiesel. However, there is still a lack of accurate description of the reaction kinetics. This is in part due to the complexity of the reacting system in which a large number of interconnected reactions take place simultaneously. In this work, attention is focused on the biphasic character of the reaction medium, formed by two immiscible liquid phases. The behavior of the phases is investigated regarding their physicochemical properties, mainly density and mutual solubility of the components, as well as composition. In addition, two kinetic models with different level of complexity regarding the biphasic character of the reaction medium have been developed. It has been found that a heterogeneous model considering the presence of the two phases and the distribution of the several compounds between them is indispensable to get a good description of the process in terms of oil conversion and products yields. The model captures the effects of the main variables of an isothermal batch methanolysis process: methanol/oil molar ratio, reaction time and catalyst concentration. Nevertheless, some adjustment is still required as concerns modelling of the saponification reactions and catalyst deactivation.
Highlights
Triglyceride transesterification is the basis of biodiesel synthesis from vegetable oils.Methanol is the most commonly used transesterification reagent; in this case, the reaction is known as methanolysis; the fatty acid methyl esters (FAMEs or MEs) formed constitute biodiesel
The alcoholic and the lipidic phases do not contain a single reactant because methanol and sunflower oil are not fully immiscible
Two levels of detail have been ered in the description of the reaction medium nature as concerns its biphasic character
Summary
Methanol is the most commonly used transesterification reagent; in this case, the reaction is known as methanolysis; the fatty acid methyl esters (FAMEs or MEs) formed constitute biodiesel. Pseudo-homogeneous models are characterized by disregarding the biphasic nature of the reacting system which, consists in an emulsion formed by droplets containing methanol and glycerol dispersed in a continuous phase constituted by the partially converted triglycerides and fatty acid methyl esters. This model has been adopted in several previous woks [5,6]
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