The formation of sediments is a serious instability problem in the storage of fossil fuels. Reactions that lead to sediment formation can be linked to the oxidation of certain fuel components that contain oxygen, nitrogen, or sulfur. To study the oxidation reactions that occur during aging of fuels, we doped a model fuel with several representatives of such compound types. The compounds used were 2,6-dimethylphenol, 2-naphthol, 2,5-dimethylpyrrole, 2-methylindole, dibenzothiophene, and pentamethylene sulfide. After an artificial aging of the samples according to the DGMK-714 protocol, the formed sediments were analyzed by electrospray ionization mass spectrometry (Orbitrap, ESI-MS), elemental analysis, infrared measurements, and mass analysis. Mass spectrometry indicated monomeric and dimeric oxidation products with two to nine oxygen atoms as well as products with different hydrocarbon structures (different C/H ratios) from 2,6-dimethylphenol. 2-Naphthol led to oligomers consisting of up to six monomer units and showing different degrees of oxidation. The first ever recorded cross-coupling between 2,6-dimethylphenol and 2-methylindole and between 2-naphthol and 2,5-dimethylpyrrole is also shown. In general, the tested nitrogen compounds and especially the phenols tended to form oxidized oligomers, whereas the sulfur compounds led to sulfoxides and sulfones.

The formation of sediments in biogenic and fossil heating oils as well as in their blends is a well-known problem. These deposits can plug filters and nozzles in heating systems and, consequently, cause economic losses. Polymerization and the formation of corrosive acids are possible explanations for these incidents. To study the influence of long-term storage on different heating oils (biogenic, fossil, and a 10% blend) and to investigate the changes in their composition, the oils were stored for a period of 12−24 months at nearly ambient (40 °C) and analyzed with different techniques every 6 weeks. The formation of several kinds of oxidation products was demonstrated, including ketones, epoxides, aldehydes, carboxylic acids, and furans. Sizeexclusion chromatography was used to demonstrate the formation of oligomeric products of the fatty acid methyl esters (FAMEs) (up to pentamers). Short-chain (C 1 −C 6 ) carboxylic acids were quantified with ion chromatography, and larger carboxylic acids were indicated by mass spectrometry. The first recorded experimental evidence for a coupling reaction between a FAME and components of the fossil oil, namely, such containing the nitrogen heterocycle indols, is described. Cross-coupling products between biogenic and fossil compounds were detected using Orbitrap ultrahigh-resolution electrospray ionization mass spectrometry.

The formation of deposits in fossil and biogenic home heating oils as well as in their blends is well-known. As a result, sediments can plug filters and nozzles in heating systems and thus cause operability problems. Different kinds of compounds are presumed to be involved in these processes. It is well-known that phenols play an important part but, on the other hand, phenols are also known to act as antioxidants that delay the oxidation of fuel compounds, and thus the formation of reactive products. To study the antioxidant effect of different phenols, model fuels (biogenic, fossil and a 10% v/v blend) were doped with several representatives of this class of compounds. The samples were artificially aged using the PetroOXY (DIN EN 16091) method. The induction time was recorded and gave information on the impact of the tested substance on the model fuel. Infrared spectrometry was used to investigate the oxidation products. Furthermore, the phenols of a commercial heating oil were extracted and then the oil was aged to test the influence of phenols in real samples. All the tested phenols, both synthetic and naturally occurring (biogenic and fossil), increased the induction time of artificial model fuels and commercial heating oil. In each model fuel, a different phenol showed the largest influence on the stability whereas phenols alkylated in both the ortho and the para positions generally showed the largest beneficial effects.