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Author
Alcántara Galindo, Antonio
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Nowadays, changes are constant in our daily life. In this regard, transport and energy use are one of the main areas where we are experiencing a big transformation, and that is why there is a need to look for alternatives to traditional fuels. Biodiesel is an interesting alternative to substitute diesel fuel partially or totally. While obtained through a transesterification process from animal fats and especially vegetable oils, this product is under strict requirements, regulated by the UNE-EN 14214, to be used safely and correctly. Among many properties, density and viscosity are two key properties that must be controlled for proper final use. However, they are strongly dependent on biodiesel composition and origin.
In this project, characterization of different biodiesels obtained from a variety of oil types has been carried out combining an experimental study with the development of an accurate thermodynamic model to describe the physicochemical data obtained. In particular, the soft-SAFT equation of state, based on the sum of contributions to Helmholtz's total energy, has been used in combination with the Free-Volume Theory to determine the density and viscosity of different biodiesel based on vegetable oils, obtaining a model with a predictive capacity.
To perform this study, the project has been divided into two differentiated blocks, first based on an experimental analysis of the reactants and products obtained by reacting transesterification at different temperatures and atmospheric pressure. The second block is based on the characterization of the compounds involved and a study of how they interact at the molecular level. The processes carried out for density and viscosity have been different.
In terms of density, a series of vegetable oils have been studied as a function of temperature and have been theoretically modeled, building a characterization that departs from the fatty acids that form the oils and its compositions and capacity to form triglycerides with glycerol. Following a similar pattern, the density of several biodiesels has been experimentally measured and theoretically characterized using the composition of fatty acids methyl esters. The model has then been completed by connecting the results of the interactions between each vegetable oil and methanol, simulating the transesterification reaction, to obtain a pseudo-compound that is later compared to the experimental measurements of the biodiesel in the laboratory.
In terms of viscosity, a fully predictive model has been developed to determine the viscosity of the final product from its composition. This model is strongly dependent on the density previously calculated.
In summary, the characterization study provides insight into the differences in the biodiesel properties as a function of the origin and type of vegetable oil used. More interestingly, it is possible to reproduce the data measured using a soft-SAFT model. The advantage of this method is the fact it can be extended to any type of vegetable or frying oil once the fatty acids’ composition analysis of the product in question is known.
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