Research article Study of kinetics and thermodynamic parameters of the degradation process of biodiesel produced from fish viscera oil Jailson Silva Rodrigues a, ⁎, Camila Peixoto do Valle a , Priscilla de Araújo Gois Pinheiro Guerra b , Maria Alexandra de Sousa Rios c , Jackson de Queiroz Malveira d , Nágila M.P.S. Ricardo a, ⁎ a Department of Organic and Inorganic Chemistry, Federal University of Ceará, P.O. Box 6021, 60.440-900 Fortaleza, Brazil b Department of Food Engineering, Federal University of Ceará, 60.356-001 Fortaleza, Brazil c Department of Mechanical Engineering, Federal University of Ceará, 60.445-760 Fortaleza, Brazil d Technology Center Foundation of Ceará, Prof. Rômulo Proença St., Campo do Pici, 60.455-700 Fortaleza, Brazil abstract article info Article history: Received 22 January 2017 Received in revised form 10 March 2017 Accepted 10 March 2017 Available online xxxx The present study determines the kinetic and thermodynamic parameters of the degradation process of the bio- diesel produced from fish viscera oil. The analyses were performed through the accelerated trials of oxidation of biodiesel (EN 14112) at different temperatures (100, 105, 110, 115, 120 e 125 °C). Through the analyses of the results of the induction period, the reaction was considered to be of the first order. It was determined by the rate constants (K) varying from 0.0868 to 0.42271 h -1 , activation energy (E a ) of 81.99 kJ·mol -1 , the pre-expo- nential factor (A) of 2.61 × 10 10 h -1 , enthalpy of activation (ΔH ≠ ) of 78.79 kJ·mol -1 , entropy of activation (ΔS ≠ ) – 55.94 J·k -1 ·mol -1 and Gibb's free energy of activation (ΔG ≠ ) average of 100.25 kJ·mol -1 . The results showed that biodiesel oxidation reaction is non-spontaneous (ΔG ≠ N 0), endothermic (ΔH ≠ N 0), and that the temperature and the oxidation concentration influences significantly the degradation process of methyl esters. © 2017 Elsevier B.V. All rights reserved. Keywords: Biodiesel Fish viscera oil Antioxidant Oxidation stability 1. Introduction Biodiesel is a renewable and biodegradable fuel produced from veg- etable oil or animal fat [1,2]. This fuel is presented as an alternative to replace diesel oil derived from petroleum. Once it causes less environ- mental problems when compared to diesel oil such as sulfur com- pounds reduction during combustion, more lubricity and higher flash point, what attaches more safety in both handling and storage [3,4]. However, this fuel presents some disadvantages because unlike fos- sil fuels, which are relatively inert and maintain their essential charac- teristics little altered in storage period, biodiesel degrades more easily when exposed to the action of light, atmospheric air, temperature and humidity [5]. Biodiesel degradation process may occur in three different ways: En- zymatic oxidation, photo-oxidation and autoxidation [6,7]. Being the last one the main responsible for methyl esters degradation process. Its mechanism is divided into three stages, at the first stage, named ini- tiation, the formation of free radical occurs due to the scavenging of the hydrogen from the allylic carbon in the molecule in favorable conditions of heat and temperature [5]. At the second stage, it occurs the propagation of the radicals that react with the atmospheric oxygen forming the peroxides and hydroperoxides, which are the primary products of oxidation, and the formation of other radical, resulting in a high catalytic process. At the third stage, it occurs the end of the reac- tion, with the appearance of the secondary products of oxidation, ob- tained from split and rearrangement of peroxides (epoxides, volatile and nonvolatile compounds) [8,9]. With the purpose of inhibiting or delaying biodiesel lipid oxidation are used antioxidants [10]. The use of antioxidants and their mecha- nisms have been widely studied and are classified into primary, syner- gistic, oxygen scavenging, biological and chelating agents [9,4]. The primary antioxidants are composed of phenolic chemical substances that promote the scavenging or the inactivation of free radicals formed during the initiation or propagation of the reaction, interrupting the chain reaction [9]. Vegetable oils present natural antioxidants that provides a good ox- idative stability and the most commons are the tocopherols. The antiox- idant activity of tocopherols is mainly due to the ability of donating their phenolic hydrogens to lipid free radicals [8,4,11]. However, the oils pro- duced from fish viscera do not present natural antioxidant, and added to the large amount of unsaturation present in their carbon chains, they present a low oxidative stability [1,12]. For this it is used synthetic anti- oxidants as butylhydroxyanisole (BHA), butylhydroxytoluene (BHT), tert-butylhydroquinone (TBHQ) and propyl gallate (PG) [6,10,9]. The Fuel Processing Technology 161 (2017) 95–100 ⁎ Corresponding authors. E-mail addresses: jailson.sr@alu.ufc.br (J.S. Rodrigues), naricard@ufc.br (N.M.P.S. Ricardo). http://dx.doi.org/10.1016/j.fuproc.2017.03.013 0378-3820/© 2017 Elsevier B.V. All rights reserved. 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