Oxidative Stability of Middle Distillate Fuels. Part 1: Exploring the Soluble Macromolecular Oxidatively Reactive Species (SMORS) Mechanism with Jet Fuels

The soluble macromolecular oxidatively reactive species (SMORS) mechanism has recently been applied to jet fuel thermal oxidative degradation at high temperatures (250-550 degrees C). The primary purpose of this work is to further test the extant SMORS mechanism with carefully designed experiments at lower temperatures. First, synthetic SMORS precursors, 2-methylindole and 1,4-benzoquinone, were doped into a stable Jet A-1 in both mono- and oligomeric forms. Flask oxidative stress of these solutions at 90 degrees C for 60 min with an oxygen sparge significantly increases jet 41 thermal oxidative degradation. Second, a model compound experiment suggests SMORS precursors, phenol and 1,4-benzoquinone, are generated in situ from flask oxidation of a natural jet fuel component cumene (isopropylbezene) at 160 degrees C with an air sparge for 300 min. This observation is particularly significant for the thermal oxidative degradation of ultra-low sulfur diesel (ULSD) be use it suggests that fuels with low heteroatom content may oxidatively degrade by the SMORS mechanism. Third, doping parts per million (ppm) levels of 2,4-dimethylpyrrole into oxidatively stable jet fuels followed by flask oxidation at 95 degrees C with an air sparge for 30 min results in significant oxidation of the jet fuels. This observation is particularly significant for the storage and thermal oxidative stability of Athabasca-tar-sands-derived middle distillates, which have previously been shown to contain alkylpyrroles; these middle distillates are predominate across the northern tier of the United States.