Publication: Advances on kinetics and thermodynamics of non-catalytic supercritical methanol transesterification of some vegetable oils to biodiesel
Authors
Andreo Martínez, Pedro ; García Martínez, Nuria ; Durán del Amor, María del Mar ; Quesada Medina, Joaquín
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Publisher
Elsevier
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Description
© <2018>. This manuscript version is made available under the CC-BY-NC-ND 4.0 license http://creativecommons.org/licenses/by-nc-nd/4.0/
This document is the Accepted Manuscript version of a Published Work that appeared in final form in Energy Conversion and Management. To access the final edited and published work see https://doi.org/10.1016/j.enconman.2018.07.069.
Abstract
Kinetic and thermodynamic parameters of the non-catalytic supercritical methanol transesterification reaction of
castor, jatropha, pongamia, tobacco, soybean and jojoba oils to biodiesel production were evaluated in the
present study. The experiments were conducted in an 83 ml closed batch reactor at different temperatures
(250–350 °C) and reaction times (15–90 min), and at optimal methanol-to-oil molar ratios (15:1 in the case of
jojoba wax-oil and 43:1 for the rest of the oils). The pressure reached in the reactor ranged from 10 to 43 MPa.
Integral method was used to determine appropriated reaction orders by an adjustment of experimental data to
pseudo-zero, pseudo-first and pseudo-second order kinetic equations using Levenberg-Marquardt algorithm.
Pseudo-first-order kinetic equation was found to be the most appropriate to describe the supercritical transesterification
reaction of the vegetable oils studied. Rate constants and Arrhenius parameters were calculated, the
activation energy followed the sequence: castor oil < jatropha oil < tobacco oil < pongamia oil < soybean
oil < jojoba wax-oil. It is difficult to explain the behavior of jojoba and castor oils in relation to that of the rest
of vegetable oils because they have a very different structure and fatty acid composition, respectively. However,
the aforementioned sequence observed for the rest of vegetable oils (jatropha, tobacco, pongamia and soybean
oils), which have a similar structure and fatty acid composition, can be attributed to the content of linolenic acid
in the oil: the higher the content of linolenic acid, the higher the activation energy and the lower the reaction
rate. Finally, thermodynamic study showed that the non-catalytic supercritical methanol transesterification
reaction is non-spontaneous (endergonic) and endothermic in nature.
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