Homogeneous Catalysis of Liquid-Phase Hydroperoxide Decomposition in Hydrocarbons

Abstract

The autoxidation of jet fuel takes place via a complex free radical reaction mechanism that involves the decomposition of hydroperoxides.The liquid-phase, unimolecular decomposition of hydroperoxide has been isolated for experimental study. Three hydroperoxides relevant to jet fuel autoxidation, including cumene hydroperoxide (CHP), dodecane hydroperoxide (DHP), and ethylbenzene hydroperoxide (EBHP), were thermally decomposed separately and found to closely fit first-order behavior with respect to hydroperoxide concentration. The activation energy for liquid-phase thermolysis of these hydroperoxides was found to be significantly less than typical gas-phase values. Parameters affecting the rate of hydroperoxide decomposition, such as dissolved metal content, organic acids, and metal deactivator additive (MDA) were explored. Metal type was shown to be a significant factor affecting hydroperoxide decomposition rate, while naphthenic acids (NA) were shown to have little effect on the rate. However, when dissolved metal and NA were added together a strong synergistic effect on hydroperoxide decomposition rate was noted. The increases in decomposition rate due to dissolved metal and/or acid were effectively inhibited by treatment with MDA.

The oxidative stability of synthetic fuels and fuel blends with monoaromatic blending components

“…The oxidation rate of trimethylbenzenes has been observed to follow the order 1,2,3 > 1,2,4 > 1,3,5-trimethylbenzene [19,20]. This supports our observations of lower stability of 1,2,4 vs 1,3,5-trimethylbenzene based on oxygen induction times [21]. This appears to be related to the number of adjacent methyl pairs versus unreactive isolated methyl pairs as discussed by Silva [22].…”

“…Ethylbenzene was found to produce hydroperoxides at lower temperatures than dodecane highlighting that benzylic hydrogens on alkyl aromatics are more reactive than paraffinic hydrogens. Zabarnick's work found that in jet fuels the oxidation pathways are mainly due to alkyl aromatic oxidation and that the normal approximate 80% concentration of paraffins in jet fuel can be considered unreactive with respect to peroxy radical reactions [21,25]. Zabarnick's work highlights the importance of understanding oxidation of potential single component aromatic blending components.…”

Thermolysis and photolysis of 2-ethyl-4-nitro-1(2H)-isoquinolinium hydroperoxide

“…Organic hydroperoxides are formed and decomposed during the oxidation of organic compounds by molecular oxygen, which is the leading source of concern for the air stability of food, gasoline, plastics and other organic materials . For this reason, decomposition of organic hydroperoxides has been addressed in a large number of reports, all of which have clearly indicated the high complexity of the reaction mechanism.…”

Studies of the Role of Heteroatomic Species in Jet Fuel Thermal Stability: Model Fuel Mixtures and Real Fuels

“…Previous work has shown the importance and role of oxygen-containing heteroatoms, such as phenols and hydroperoxides, in fuel autoxidative thermal stability . Phenols have been shown to inhibit oxidation but increase surface and bulk deposit formation. , Hydroperoxides are primary autoxidation products at relatively low temperatures (<120 °C) and rate-controlling reaction intermediates at higher temperatures (≥140 °C). , Some sulfur-containing species (e.g., mercaptans, sulfides, disulfides, thiophenes, and benzothiophenes) have been shown to be detrimental to fuel thermal stability. − Nitrogen species (e.g., indoles, anilines, quinolines, amines, pyridines, carbazoles, and indolines) have been studied less frequently with conflicting results; some nitrogen species greatly increase deposition while others are relatively innocuous. − Most previous model fuel studies considered heteroatomic species in isolation rather than as mixtures of heteroatomic species classes, as occurs in actual fuels. A relatively small number of studies have explored the interaction between heteroatomic species during fuel autoxidation. − …”

“…2,3 Hydroperoxides are primary autoxidation products at relatively low temperatures (<120 °C) and ratecontrolling reaction intermediates at higher temperatures (≥140 °C). 4,5 Some sulfur-containing species (e.g., mercaptans, sulfides, disulfides, thiophenes, and benzothiophenes) have been shown to be detrimental to fuel thermal stability. 6−9 Nitrogen species (e.g., indoles, anilines, quinolines, amines, pyridines, carbazoles, and indolines) have been studied less frequently with conflicting results; some nitrogen species greatly increase deposition while others are relatively innocuous.…”