A new flow UV–Vis kinetics spectrophotometric method based on a photodegradative reaction for determining the oxidative stability of biodiesel

Abstract

The biodiesel (BD) is an alternative fuel with some remarkable advantages compared to conventional diesel. However, the fatty acid methyl esters (FAMEs) which commonly compose BD are potentially oxidizable. This inherent characteristic of BD constitutes a problem for its storage and commercialization. In this sense, the evaluation of the oxidative stability (OS) of BD is still an important issue for being studied. According to EN 14112:2017, the minimum induction time limit is 6 h at 110 °C determined by Rancimat® reference method. The method developed in this work, proposes an alternative for determining the OS by means of a new flow UV Vis kinetics spectrophotometric method based on a photodegradative reaction and new term defined as Oximax at 4 min. This allowed the assessment of the OS of different BD samples at 4 min of photodegradation instead of the hours required by the reference method which uses thermal degradation. The studied BD samples were produced from different feedstock (i.e. sunflower, grapeseed, corn and soybean oils) at laboratory scale through a base-catalyst transesterification using methanol. Also, some BD samples were purchased from regional companies in order to apply the proposed method to commercial samples. Moreover, some parameters of quality of BD such as acid index, density and kinematic viscosity were determined in BD samples in accordance with the methods described in the Argentinian standard IRAM 6515-1:2006, and the obtained results were found satisfactory.