Abstract
Biodiesel is a renewable plant-based fuel as an alternative for fossil diesel fuel which has many advantages. However, its high content of unsaturated fatty acid causes an oxidation instability during storage. Numerous additives have been used and developed to overcome this problem such as the application of phenolic compound-based antioxidants. Pyrogallol is reported to be one of the best phenolic antioxidants for biodiesel. Unfortunately, pyrogallol has a low solubility in oil solution. In this research, pyrogallol solubility is increased by preparing a pyrogallol derivative through a reaction between pyrogallol and methyl linoleate in the presence of radical 2,2-diphenyl-1-picrylhydrazyl (DPPH). The spectrophotometric method was used for solubility test. Antioxidant potential was examined using acid value determination during a four-week storage period as well as the Rancimat test to see its performance under accelerated oxidation conditions. The reaction produced a molecule which has a molecular weight of 418 g/mol, representing pyrogallol derivative which has a new C–O covalent bond with methyl linoleate. The result was confirmed by using nuclear magnetic resonance (1H-NMR, 13C-NMR, and 2D-HMQC) resulting in a molecular structure of methyl (10E,12E)-9-(2,6-dihydroxyphenoxy)octadeca-10,12-dienoate and its isomer methyl (9E,11E)-13-(2,6-dihydroxyphenoxy)octadeca-9,11-dienoate with a yield of 12.86% and selectivity of 21.05% on the basis of pyrogallol. Compared to pyrogallol, tert-butylhydroquinone (TBHQ), and gallic acid, the pyrogallol derivative has the highest solubility and acid value stability in palm oil biodiesel. The Rancimat induction time (IP) result of the pyrogallol derivative is higher than the biodiesel and is above the accelerated oxidation test American Society for Testing and Materials (ASTM) D 6751 standard.
Highlights
Biodiesel consists of fatty acid methyl ester (FAME)
The Rancimat induction time (IP) result of the pyrogallol derivative is higher than the biodiesel and is above the accelerated oxidation test American Society for Testing and Materials (ASTM) D 6751 standard
The production of pyrogallol derivative is by chemically combining a pyrogallol molecule, which has a relatively high polarity, with one molecule of fatty acid methyl ester representing the nonpolar group
Summary
Biodiesel consists of fatty acid methyl ester (FAME). It is an alternative to conventional diesel which is extensively produced and consumed. It is in compliance with the governmental regulations in many countries. Biodiesel has a major disadvantage: instability against oxidation. The oxidation instability of FAME molecules has been a real challenge and the application of additives to increase its stability is of major interest to many researchers [1]. Oxidative instability takes place during the storage period in the presence of pro-oxidant species [2]. As a result of the oxidation, biodiesel molecules could be deteriorated which might leads to quality degradation
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