Fatty Acids Methyl Esters (FAME) autoxidation: New insights on insoluble deposit formation process in biofuels

• Published in: Fuel (Guildford) Vol. 268; p. 117074
• Main Authors: Alves-Fortunato, M., Ayoub, E., Bacha, K., Mouret, A., Dalmazzone, C.
• Format: Journal Article
• Language: English
• Published: Kidlington Elsevier Ltd 15-05-2020; Elsevier BV
• Subjects: Autoclaving; Autoxidation; Biodiesel; Biodiesel fuels; Biofuels; Demixing; Deposit; Diesel; Emulsions; Esters; Fatty acids; FTIR; Insoluble; Light microscopy; Light scattering; Liquid phases; Methyl oleate; Nuclear fuels; Oil; Optical microscopy; Oxidation; Oxidation process; Phase separation; Phase separation rate; Polarity; Rapeseed; Rapeseed methyl ester (RME); Sedimentation; Soy methyl ester (SME); Stability; Transportation industry; Turbines; Turbiscan; Viscosity measurement; TAN; B10; Deposit; Soy methyl ester (SME); Turbiscan; SME; RME; Methyl oleate; Biodiesel; B0; EIS; Autoxidation; FIS; FAME; IDID; Phase separation rate; Rapeseed methyl ester (RME); Insoluble; FTIR; B30
• ISSN: 0016-2361; 1873-7153
• DOI: 10.1016/j.fuel.2020.117074

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•Oxidized fuel form an oil-oil complex emulsion.•Oxidized fossil diesel presents the most dense and viscous oxidation products, but it is the slowest fuel to demix and to form deposits, i.e. products mass weight has a second order impact on deposits formation.•The polarity of the oxidized fuel seems to play a major role in the liquid film deposits formation.
The thermal and oxidation stability of fatty acids methyl esters (FAME) is arousing attention in the transport industry, since they are the main components present in biodiesel products used in the market. Low FAME stability can induce easy fuel degradation and produce oxidation products that can form sticky deposit causing serious malfunctioning and failures of engine and turbines components. We have focused the present work on the study of fuel oxidation process and the characterization of oxidation products in order to identify the main levers to avoid deposit formation. Soy and Rapeseed biodiesels were oxidized using an autoclave Parr reactor and characterized by FTIR, density and viscosity measurements. After oxidation, two different liquid phases were clearly observed. These two phases tend to form complex oil-oil emulsions after remixing as evidenced by optical microscopy. The separation behavior of the different liquid phases remixed after oxidation were studied using Multiple Light Scattering (TurbiscanTM). A comparison was made between the chemical functions of deposit obtained in the liquid phase after demixing (sedimented phase) and the solid deposit obtained on hot metallic surfaces. Results showed a that a complex oil-oil dispersion seems to form during the oxidation process. The phase separation rate of the oil-oil emulsified systems formed from oxidized fuels seems strongly related to the differences of polarity (e.g. oxygenates content) of both sedimented and supernatant phases. The understanding of this sedimentation or “demixing” process leading to deposit can be a key feature to develop strategies to prevent deposit formation in real systems.