Addressing Thermal Behavior and Molecular Architecture of Asphaltenes by a Thermal-Optical Carbon Analyzer Coupled to High-Resolution Mass Spectrometry

Abstract

In the past decade, extensive molecular-level research on asphaltenes, primarily based on mass spectrometric approaches, acknowledged the coexistence of two primary architecture motifs, “island” single-core- and “archipelago” (multi-core)-type structures. Nonetheless, analytical methods for a classification are still limited. In this study, the thermal desorption and pyrolysis behavior of a diverse set of asphaltenes covering island- and archipelago-enriched samples and their extrographic fractions has been investigated by a thermal-optical carbon analyzer (TOCA) hyphenated to high-resolution mass spectrometric evolved gas analysis. The capability of the TOCA for a temperature-resolved quantification of the released carbon is used together with the option of applying an inert or oxidative atmosphere. We found that the relative proportion of organic carbon emitted under an inert atmosphere and below 580 °C (OCdes/pyr) and the organic carbon released at elevated temperatures (>580 °C) and oxidative atmosphere (OCpyrogen) can be used as a classification approach for the prevalent architecture motif. This finding is likely caused by differences in the coking and charring behavior dependent on molecular structure. Hypothetically, single-core constituents will form more resistive shot-like coke due to their larger aromatic cores, whereas multi-core constituents seem to produce easier combustible sponge-like coke. Simultaneously, resonance-enhanced multiphoton ionization (REMPI), a soft ionization scheme particularly selective and sensitive for aromatic constituents, together with Orbitrap Fourier-transform mass spectrometry, allowed for time/temperature-resolved in-depth insights into the evolved chemistry. The alkylation pattern/length of the mass spectra received in OCdes/pyr (480/580 °C) fractions has been identified as a classification measure with lower and more narrow patterns for the asphaltenes dominated by single-core species. However, grouping based on the quantified TOCA results has been significantly more striking. Conclusively, TOCA of asphaltenes and their extrographic fractions can be used for structural classification as well as insights into coprecipitated maltenes, presumably also successfully applicable in future studies on residues from renewable oil sources.

Chemistry and Properties of Carbon Fiber Feedstocks from Bitumen Asphaltenes

“…Coke formation during thermal analysis has also been linked to the predominant structural motif. Island-type asphaltenes revealed potentially higher amounts of residue due to their high content in highly aromatic compounds, which serve already as coke precursors. ,,, …”

“…Island-type asphaltenes revealed potentially higher amounts of residue due to their high content in highly aromatic compounds, which serve already as coke precursors. 35,37,40,41 Figure 9 shows the mass loss curves from thermogravimetric measurements (black line) as well as the temperature-resolved total summed intensity detected by APPI-FT-ICR MS (red line). The yellow and the gray lines represent the temperatureresolved summed intensity for all compounds of the S x -class and HC-class.…”

“…During pyrolysis, asphaltenes of different structural motifs released pyrolysis products with contrasting composition: archipelago-type asphaltenes featured products with smaller aromatic cores and preserved alkylation, whereas island-type asphaltenes released products with high aromaticity, close to the polycyclic aromatic hydrocarbon (PAH) limit, and low to non-aromatic compounds originated from cleaved side chains. Highly aromatic compounds and highly aggregated asphaltenes were shown to form coke rather than produce evaporable material. , …”

“…Highly aromatic compounds and highly aggregated asphaltenes were shown to form coke rather than produce evaporable material. 40,41 The work herein deals with the molecular and rheological characterization of asphaltene-enriched feedstocks and their use as precursors for carbon fibers. An asphaltene-rich material was obtained by solvent deasphalting of Athabasca bitumen with n-pentane.…”

Brown Coal and Logwood Combustion in a Modern Heating Appliance: The Impact of Combustion Quality and Fuel on Organic Aerosol Composition

“…Analytical pyrolysis is a common tool used to give insights into chemical structures of samples that are hardly accessible by conventional gas and liquid chromatography because of a low vapor pressure or poor solubility, e.g., chars from biomass and plastic pyrolysis 78,79 or asphaltenes in crude oil. 80,81 Organic species that have not evaporated up until the end of OC2 are characterized by a low vapor pressure, and they rather degrade thermally than evaporate in OC3 and OC4 (480 and 580 °C). This analytical pyrolysis induces a shift in mass evolving organic compounds from higher m/z ranges to low ones below m/z 100, and evolving species can be analyzed with a SPI-TOF-MS. 76 For BCB emissions, it was found that the evolving patterns of low molecular species resulting from analytical pyrolysis in OC3 and OC4 changed substantially with varying CO emissions.…”