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

Abstract

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.

Comprehensive chemical description of pyrolysis chars from low-density polyethylene (LDPE) by thermal analysis hyphenated to different mass spectrometric approaches

“…In contrast, archipelago-enriched asphaltenes revealed another distribution at intermediate DBE (5)(6)(7)(8)(9)(10)(11)(12) values and broad carbon number spread resulting from the pyrolysis of the bridged building blocks. 54 This compositional space is not dominantly found for the investigated plastic pyrolysis char. Thus, we hypothesize only a small fraction of archipelago-type aromatics and a strong influence of more condensed island-type structures as a pyrolytic precursor to even fully graphitized char.…”

“…Utilizing the DBE, a measure for the unsaturation of a molecule, aromatic structures can be discussed. 54 Two molecular distributions can be observed, with the first distribution (Figure 5c, yellow) exhibiting rather low DBE values (1)(2)(3)(4)(5)(6) and a broad carbon number spread (#C 12-41) and the second pattern (Figure 5c, green) closely located to the planar aromatic limit with high DBE values (12)(13)(14)(15)(16)(17)(18)(19)(20)(21)(22) and a narrower carbon number spread (3-7 #C width). The first pattern accounts for the alkenes (DBE 1), dienes (DBE 2), benzene-(DBE 4), and naphthenic-derivatives (DBE 2-5) in detail discussed above and additionally validated here using the exact mass measurement.…”

Comprehensive Chemical Description of Pyrolysis Chars from Low-Density Polyethylene by Thermal Analysis Hyphenated to Different Mass Spectrometric Approaches

“…Consequently, the plastic pyrolysis coke still revealed a significant contribution of pyrolyzable material belonging to the archipelago motif as a pyrolytic precursor to more condensed island motifs or even fully graphitized char. [54] Two distinct chemical distributions, one at higher DBE values with comparable low #C spread and second at low DBE 0-5 with a high #C spread, attributed to polycyclic aromatic hydrocarbons and alkenes, dienes, benzene-derivatives, and naphthenic species, can be found, respectively.…”

“…Utilizing the DBE, a measure for the unsaturation of a molecule, aromatic structures can be discussed. [54] Two molecular distributions can be observed, with the first distribution (Figure 5c, yellow) exhibiting rather low DBE values (1-6) and a broad carbon number spread (#C 12-41) and the second pattern (Figure 5c, green) closely located to the planar aromatic limit with high DBE values (12)(13)(14)(15)(16)(17)(18)(19)(20)(21)(22) and a narrower carbon number spread (3-7 #C width). The first pattern accounts for the alkenes (DBE 1), dienes (DBE 2), benzene-(DBE 4), and naphthenic-derivatives (DBE 2-5) in detail discussed above and additionally validated here using the exact mass measurement.…”

Comprehensive chemical description of pyrolysis chars from low-density polyethylene (LDPE) by thermal analysis hyphenated to different mass spectrometric approaches

“…Utilizing the DBE, a measure for the unsaturation of a molecule, aromatic structures can be discussed. [54] Two molecular distributions can be observed, with the first distribution (Figure 5c, yellow) exhibiting rather low DBE values (1)(2)(3)(4)(5)(6) and a broad carbon number spread (#C 12-41) and the second pattern (Figure 5c, green) closely located to the planar aromatic limit with high DBE values (12)(13)(14)(15)(16)(17)(18)(19)(20)(21)(22) and a narrower carbon number spread (3-7 #C width). The first pattern accounts for the alkenes (DBE 1), dienes (DBE 2), benzene-(DBE 4), and naphthenic-derivatives (DBE 2-5) in detail discussed above and additionally validated here using the exact mass measurement.…”