Quantification and Identification of Hydroperoxides in Oxidized Surrogate Fuels by HPLC-PcR

Hydroperoxides are major products of the autoxidation of hydrocarbon fuels and play a central role in the oxidation kinetics of organic compounds. The quantification of hydroperoxides is a key factor for the qualification of jet fuels and is determined through a standardized method. A recent comparison of different iodometric methods of quantification showed that an HPLC chain coupled with a post-reaction column (HPLC-PcR) is highly accurate, with a high reproducibility, low detection limits, and a large dynamic range. In this work, HPLC-PcR is used to detect and quantify the total hydroperoxide content of different oxidized surrogate fuels and separate the different hydroperoxides. Surrogate fuels were oxidized in PetroOxy and in a microreactor and then analyzed by HPLC-PcR. n-decane and cumene were used as surrogate jet fuels, and n-butanol as a surrogate biofuel. The separated fractions of aged cumene in HPLC-PcR were analyzed by GC-MS/FID, demonstrating that the typical hydrocarbon oxidation pathways take place for cumene autoxidation, yielding mainly cumene hydroperoxide, 2-phenyl-2-propanol, and acetophenone. On the contrary, n-butanol behaves very differently from hydrocarbons: we demonstrate that the typical mechanism leading to ROOH does not prevail and that its autoxidation mainly yields H₂O₂ as peroxide content. The oxidation of n-decane yields several decane hydroperoxides and other oxygenated compounds that were quantified and separated by HPLC-PcR and the GC-MS/FID allowed a thorough identification of hydroperoxides and quantification of secondary oxidation products depicting a global view on the oxidation mechanism of n-decane.