Investigation of Aging Processes in Bitumen at the Molecular Level with High-Resolution Fourier-Transform Ion Cyclotron Mass Spectrometry and Two-Dimensional Gas Chromatography Mass Spectrometry

Abstract

Bitumen is a highly viscous and chemically complex petroleum-derived material, which is applied as a binder in road construction. However, the asphalt undergoes hardening, cracking, and embrittlement not only due to oxidative short-term aging during the mixing and paving process but also due to long-term aging during the service time of the pavement. In this study, chemical changes occurring during short-term aging, mimicked by a prolonged rotating flask procedure, are investigated for an artificial bitumen model at the molecular level. The model bitumen enables the application of two complementary analytical techniques for obtaining a comprehensive insight into the aging effects: high-resolution Fourier-transform ion cyclotron mass spectrometry (FT-ICR MS) coupled to thermogravimetry was applied to investigate the aging effects on polar to semipolar high-molecular-weight compounds ionized by atmospheric pressure chemical ionization. Aromatic core structures were analyzed by alternating collision-induced dissociation. In order to support structural assignments from FT-ICR MS data in the semivolatile region, comprehensive two-dimensional gas chromatography mass spectrometry (GC × GC–HRTOFMS) with electron ionization at 70 eV was applied for the group-type analysis and the investigation of particular chemical functionalities. Oxidation processes were revealed to be the prevalent reactions caused by short-term aging of the hydrocarbons (CH-class) and sulfur-containing classes. Aromatic species with low steric hindrance or activated carbon positions as well as high aromatic core structures are favorably oxidized, forming carbonyl functionalities. For molecules with one sulfur atom (S1-class), nonaromatic species such as tetrahydrothiophenes decrease, whereas aromatic S1-compounds remain constant. Nonaromatic S1O1-species tend to further oxidize, while higher aromatic species are formed with ongoing aging time. Moreover, this study highlights the aging behavior of nitrogen-containing compounds, such as carbazoles. A significant reduction of the N-classes was observed during aging, indicating thermal-induced condensation reactions as well as favored oxidation of highly aromatic core structures.

Investigation of Island/Single-Core- and Archipelago/Multicore-Enriched Asphaltenes and Their Solubility Fractions by Thermal Analysis Coupled with High-Resolution Fourier Transform Ion Cyclotron Resonance Mass Spectrometry

“…As ionization technique, atmospheric pressure chemical ionization (APCI) was applied, which covers semi-polar to polar compounds expected to be present in the solubility fractions. It's value for analyzing complex mixtures in combination with TG-FT-ICR MS has been demonstrated in previous studies [33,44,51]. Here, we showed that TG-FT-ICR MS can address the controversial issue of the predominant structural motif of asphaltenes exhibiting corresponding results to previous studies on the same asphaltenes with DI-IRMPD-FT-ICR MS [48,50].…”

Study of Thermal Aging of Model Compounds Present in Asphalt Cement by GC/MS, ESI-MS, NMR, and FTIR

“…45 However, Neumann et al (2020) observed a decrease in the presence of carbazol groups after aging bitumen. 46 This result shows that carbazol is a thermally stable compound; however, it can act as a reagent in certain compounds present in asphalt. This may be an indication for future studies showing the influence of nitrogen groups, even thermally stable compounds, on asphalt aging.…”

“…Carbazole is used in the synthesis of thermally stable polymers as an electron donor . However, Neumann et al (2020) observed a decrease in the presence of carbazol groups after aging bitumen . This result shows that carbazol is a thermally stable compound; however, it can act as a reagent in certain compounds present in asphalt.…”

Exploring Complex Mixtures by Cyclic Ion Mobility High-Resolution Mass Spectrometry: Application Toward Petroleum

“…The isomeric diversity of heavily alkylated constituents hinders a more targeted approach. Collision-induced dissociation (CID) is known for dealkylation of petroleum constituents. , Without the selection of a precursor, so-called all-ion fragmentation can be used as a valuable approach for the structural description of the dominant aromatic core structures. , Structural description of the aromatic core is crucial for a variety of applications, such as the design of refining processes or in understanding flow/deposition and aggregation properties of asphaltenes, a high aromatic fraction of petroleum. , …”

“…11,57 Without the selection of a precursor, so-called all-ion fragmentation can be used as a valuable approach for the structural description of the dominant aromatic core structures. 57,58 Structural description of the aromatic core is crucial for a variety of applications, such as the design of refining processes or in understanding flow/deposition and aggregation properties of asphaltenes, a high aromatic fraction of petroleum. 47,52 Here, the concept of all-ion fragmentation is deployed as follows: The whole ion mixture is fragmented by collisioninduced dissociation (CID) applying a voltage of 75 V to the trap gas cell.…”