Biofuel Surrogate Oxidation: Insoluble Deposits Formation Studied by Small-Angle X-ray Scattering and Small Angle Neutron Scattering
Résumé
The stability of biofuels toward oxidation is currently one of the major challenges for its widespread use. In fact, insoluble deposits issued from biofuels degradation can cause several types of damages with the blockage of injectors, filters, and lines in contact with the fuel, seriously compromising the operation of the engines and aircraft turbines. The aim of this work was to characterize a surrogate biofuel (90% n-dodecane and 10% methyl oleate) under different oxidation conditions (110, 130, and 150 °C, and ranging from 0 to 5 h) under constant oxygen pressure, in order to follow nucleation and growth mechanisms of primary insoluble deposits precursors. Therefore, advanced scattering techniques were implemented, such as small-angle X-ray scattering (SAXS) and small angle neutron scattering (SANS), in addition to more conventional molecular characterization approaches based on gas chromatography. Epoxides and ketones were produced through oxidation at different rates depending on temperature, thus highlighting different kinetic phases. Scattering techniques allowed us to observe aggregates in fatty acid mono-alkyl esters oxidized products for the first time, with a number of aggregations ranging from 1 in mild conditions up to ∼25 in severe conditions.