The near-surface structure of the room-temperature ionic liquid 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)amide has been investigated as a function of temperature between 100 and 620 K. We used a combination of photoelectron spectroscopies (XPS and UPS), metastable induced electron spectroscopy (MIES), and high-resolution electron energy loss spectroscopy (HREELS). The valence band and HREELS spectra are interpreted on the basis of density functional theory (DFT) calculations. At room temperature, the most pronounced structures in the HREELS, UPS, and MIES spectra are related to the CF3 group in the anion. Spectral changes observed at 100 K are interpreted as a change of the molecular orientation at the outermost surface, when the temperature is lowered. At elevated temperatures, early volatilization, starting at 350 K, is observed under reduced pressure.

Thermal desorption and pyrolysis of various heavy oils and asphaltenes (precipitated with different paraffinic solvents) were studied. For this purpose evolved gas analysis was realized by hyphenation of a thermobalance to ultrahigh-resolution mass spectrometry (FT-ICR MS). The chemical pattern was preserved by applying soft atmospheric pressure chemical ionization (APCI). Collision induced dissociation (CID) was performed for deeper structural insights. Viscous or solid petroleum samples and fractions can be easily measured by the setup. The SARA fractions (maltenes, C7-asphaltenes, aromatics, saturated, and resins), deployed for evaluation purposes, revealed a very complex molecular pattern, and fractionation drastically increased the number of assigned elemental compositions. Species from m/z 150 to m/z 700 and two main phases (desorption and pyrolysis), which transits at roughly 300–350 °C, are observed. Both phases overlap partially but can be separated by applying matrix factorization. The heavy oil and asphaltene mass spectra are dominated by CH-, CHS-, and CHN-class compounds, whereas for the CID spectra a lower abundance of oxygenated species was found. Furthermore, physicochemical properties and the molecular response were correlated for the heavy oils and asphaltene samples, finding a strong correlation between sulfur content and abundance of CHS x -class compounds as well as between double bond equivalent (DBE) and API gravity. As the CID leads mainly to dealkylation, the length of alkylated side chains of components evolved thermally or by pyrolytic processes can be traced during the temperature ramp. In general, an increase of dealkylation in the desorption phase, followed by a decrease during the transition to pyrolysis and an increase reaching a stable plateau for stable pyrolysis, was detected. This behavior was found to be similar for all asphaltenes and for the mean DBE progression. Deploying a lighter paraffinic solvent for asphaltene precipitation causes a higher abundance of species emitted in the desorption phase. They belong mainly to CHO x -class compounds from the maltene fraction occluded and coprecipitated with the asphaltenes. Besides this, no significant effect of the precipitation solvent on the asphaltenic core structures and molecular pattern in the pyrolysis phase was observed. The DBE distribution suggests the presence of the archipelago asphaltene molecular architecture.

In this study, the asphaltene and corresponding crude oil, distributed within the Asphaltene Characterization Interlaboratory Study for PetroPhase 2017, were characterized on the molecular level. For this purpose, three different thermal analysis mass spectrometry hyphenations with five diverse ionization techniques varying in selectivity were deployed: (1) thermal desorption/pyrolysis gas chromatography electron ionization (TD/Pyr–GC–EI–QMS), (2/3) thermogravimetry single-photon/resonance-enhanced multiphoton ionization time-of-flight (TG SPI/REMPI TOF–MS), and (4/5) thermogravimetry atmospheric pressure photo-/chemical ionization ultrahigh-resolution mass spectrometry (TG APPI/APCI FT-ICR MS). For the investigated C7 asphaltene, no mass loss was detected at <300 °C and the pyrolysis phase was dominant, whereas the parent crude oil exhibits a high abundant desorption phase. At roughly 330 °C, pyrolysis begins and mass loss as well as complex mass spectrometric patterns were recorded. The resulting information on the effluent gained by the different soft ionization mass spectrometric approaches was combined with the GC–EI–MS data for structural cross-evaluation. We showed that the combination of the applied techniques leads to a more comprehensive chemical characterization. For the asphaltene, TG SPI TOF–MS shows high abundances of alkanes, alkenes, and hydrogen sulfide during pyrolysis. TG REMPI TOF–MS is selective toward aromatics and reveals clear patterns of polyaromatic hydrocarbons (PAHs) and minor amounts of nitrogen-containing aromatics tentatively identified as acridine- or carbazol-like structures. GC–EI–MS provides information on the average chain length of alkanes, alkenes, and PA­(S)­H. Both atmospheric pressure ionization techniques (APPI and APCI) hyphenated to FT–MS showed CHS (in particular, benzothiophenes) and CH as dominant compound classes, with an average number of condensed aromatic rings of 2–4. Combining the information of all techniques, including the average asphaltene mass obtained by field desorption experiments and aromatic core size received by collision-induced dissociation, the archipelago-type molecular structure seems to be dominant for the investigated asphaltene.

Despite extensive research, the molecular-level chemical characterization of asphaltenes, a highly aromatic solubility fraction of petroleum, remains an analytical challenge. This fraction is related to diverse problems in crude oil exploration, transportation, and refining. Two asphaltene architecture motifs are commonly discussed in the literature, "island" (single-core)-and "archipelago" (multicore)-type structures. The thermal desorption and pyrolysis behavior of island-and archipelago-enriched asphaltenes and their extrography fractions was investigated. For this purpose, the evolved chemical pattern was investigated by thermal analysis coupled with ultrahigh-resolution mass spectrometry (Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS)). Soft atmospheric pressure chemical ionization preserved the molecular information of the thermal emission profile. Time-/temperature-resolved analysis allowed the chemical characterization of the occluded material as well as of asphaltene building blocks during pyrolysis. Regarding the thermogravimetric information, the island-type enriched sample (Wyoming asphaltenes) revealed a significantly higher coke residue after the pyrolysis process compared to the archipelago-type enriched sample (Athabasca asphaltenes). In contrast to whole asphaltenes, extrographic fractions revealed that occluded material evolved during the desorption phase. For the acetone fraction, this effect was the most abundant and suggests cooperative aggregation, which persists at high temperatures. Pyrolysis revealed a bimodal behavior for most of the compound classes, suggesting the presence of both architecture motifs in each asphaltene. double-bond equivalent (DBE) vs #C diagrams of the pyrolysis molecular profile revealed specific compositional trends: compounds with high DBE values and short alkylation are likely to be originated from island-type asphaltenes, whereas species with low DBE values and high carbon numbers likely derive from archipelago-type asphaltenes. In the asphaltene structural debate, thermal analysis ultrahigh-resolution mass spectrometry serves as an additional technique and supplements results obtained by other techniques, such as direct infusion approaches. Consistent results on the structural motifs are indicated by the molecular fingerprint visualized by DBE vs #C diagrams and serve as a measure for the dominance of a structural motif.