@misc{13671,
  abstract     = {{The aging of biodiesel proceeds via multiple pathways, with oligomerization playing a central role. In this study, we investigated an epoxide-dependent oligomerization pathway, which had previously only been postulated. Using methyl oleate (C18:1) as a model monounsaturated fatty acid and acetic acid as a representative, reactive nucleophile and known biodiesel aging product with a suitable boiling point, oligomeric products were identified by size-exclusion chromatography (SEC) coupled with electrospray ionization quadrupole time-of-flight mass spectrometry (ESI-QTOF-MS). The concentration of 20 wt% was chosen to ensure a measurable kinetic effect while maintaining stable reaction conditions. Furthermore, the role of methyl oleate during biodiesel aging was addressed. Time-resolved analysis confirmed the proposed sequential order of reactions. It was pointed out that elimination reactions may occur. The data support the formation of epoxides, despite the isobaric overlap with ketones, and show that hydroxyl intermediates undergo esterification and etherification. Moreover, experiments with pure C18:1 demonstrated that acetic acid–derived oligomers are generated. Under Rancimat conditions, addition of 20 wt% acetic acid resulted in an approximately 1.1 – 2.6 increase in product yield. Kinetic analysis revealed structure-dependent formation and decay behavior of the aging products, with slightly faster epoxidation and shifted product distributions toward higher oligomeric species in the presence of acetic acid. Reactive intermediates were consumed more rapidly than oligomeric species and all decay processes followed apparent second-order kinetics. These findings provide direct experimental evidence for the involvement of epoxide-dependent pathways in biodiesel aging.}},
  author       = {{Türck, Julian and Funke, Carsten and Schmitt, Fabian and Schneider, Jan and Danneel, Hans-Jürgen and Türck, Ralf and Ruck, Wolfgang and Krahl, Jürgen}},
  booktitle    = {{Fuel : the science and technology of fuel and energy }},
  issn         = {{1873-7153}},
  keywords     = {{Biodiesel aging, Epoxide-dependent oligomerization, Acetic acid, Identification of aging products, Kinetics of aging products}},
  publisher    = {{Elsevier}},
  title        = {{{Kinetic study and confirmation of epoxide-dependent oligomerization of methyl oleate}}},
  doi          = {{10.1016/j.fuel.2026.139339}},
  volume       = {{424}},
  year         = {{2026}},
}

@misc{12846,
  abstract     = {{The decarbonization of the energy supply is one of the biggest and most important challenges of the 21st century. This paper contributes to the solution of the energy crisis by investigating the stability of alcohols as e-fuels. The focus is on the investigation of the aging mechanism of the linear alcohols 1-hexanol and 1-octanol compared to the iso-alcohol 2-hexanol. It is analysed in detail how the time-dependent aging varies depending on the chain length and the position of the hydroxy-group, both in the liquid and in the gas phase. It is shown that a variety of aging products such as aldehydes, acids, short-chain alcohols and esters are formed during the aging of the n-alcohols by oxidation, decarboxylation, oxidative C-C bond cleavage and esterification. In contrast, the decomposition of the iso-alcohol is significantly lower. The results show that the total acid number is significantly higher for aged n-alcohols than for the aged iso-alcohos, while the kinematic viscosity decreases for all alcohols during aging. Carbon mass balancing shows that after accelerated aging for 120 hours, around 80% of the iso-alcohol is still present, compared to only around 57-63% for the n-alcohols. In addition, significantly fewer acids are formed with the iso-alcohol. In this study, iso-alcohols have a higher stability against thermo-oxidative aging compared to n-alcohols, showing their potential as e-fuels. Furthermore, the chain length of the alcohols has also an influence on aging, as more different aging products can be formed with increasing chain length.

This paper contributes to the solution of the energy crisis by investigating the stability of alcohols as e-fuels. The focus is on the investigation of the aging mechanism of 1-hexanol and 1-octanol compared to the 2-hexanol.}},
  author       = {{Lichtinger, Anne and Poller, Maximilian J. and Schröder, Olaf and Türck, Julian and Garbe, Thomas and Krahl, Jürgen and Jakob, Markus and Albert, Jakob}},
  booktitle    = {{  Sustainable energy & fuels : interdisciplinary research for the development of sustainable energy technologies }},
  issn         = {{2398-4902}},
  keywords     = {{OXIDATION, 1-OCTANOL, PERFORMANCE, CATALYSTS, KINETICS, ACID}},
  number       = {{15}},
  pages        = {{3329--3340}},
  publisher    = {{Royal Society of Chemistry (RSC)}},
  title        = {{{Thermo-oxidative aging of linear and branched alcohols as stability criterion for their use as e-fuels}}},
  doi          = {{10.1039/d4se00400k}},
  volume       = {{8}},
  year         = {{2024}},
}

@misc{12836,
  abstract     = {{The complexity of biodiesel aging has shown that the mechanism needs further research. The rate of aging product formation and associated interactions can help improve fuel quality. Since biodiesel is a multicomponent system and constant changes occur in the chemical environment, which interactions yield which products must be shown in more detail. Particularly under observation was the correlation between peroxides and epoxides. In addition, it is critical that the influence and interactions of new drop-in fuel candidates be investigated. In this work, the kinetics of the formation of aging products of methyl oleate (C18:1) are studied. The aim was to reduce the complexity in order to be able to make more precise and detailed statements about the mechanism. Ketones, acids, peroxide, and epoxide values were recorded. A distinction is made between pure methyl oleate and mixtures with 3 wt% isopropylidene glycerine (solketal). After solketal decomposed in the blends, the aging process showed changes. The influence of solketal resulted in a higher number of acids and epoxides over time. It implied that peroxides are not necessarily the precursor of epoxides. In summary, correlation and solketal’s influence showed that a sequence of aging products could be detected.}},
  author       = {{Türck, Julian and Schmitt, Fabian and Anthofer, Lukas and Lichtinger, Anne and Türck, Ralf and Ruck, Wolfgang and Krahl, Jürgen}},
  booktitle    = {{Energies : open-access journal of related scientific research, technology development and studies in policy and management}},
  issn         = {{1996-1073}},
  keywords     = {{oxidation kinetics, biodiesel aging, methyl oleate, solketal, alcohol influence, sequence of aging products}},
  number       = {{7}},
  publisher    = {{MDPI AG}},
  title        = {{{Oxidation Kinetics of Neat Methyl Oleate and as a Blend with Solketal}}},
  doi          = {{10.3390/en16073253}},
  volume       = {{16}},
  year         = {{2023}},
}