Fatty Acids Methyl Esters (FAME) autoxidation: 1 new insights on insoluble deposits formation process 2 in biofuels

Abstract : 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.