X-ray Photoelectron Spectroscopy, Photoelectron Energy Loss Spectroscopy, X-ray Excited Auger Electron Spectroscopy, and Time-of-Flight−Secondary Ion Mass Spectroscopy Studies of Asphaltenes from Doba−Chad Heavy Crude Hydrovisbreaking
Bibliographic record
Abstract
The sp 2 -to-sp 3 carbon bonding character in asphaltenes that results from heavy crude visbreaking was evaluated by means of X-ray photoelectron spectroscopy (XPS), photoelectron energy loss spectroscopy (ESCALOSS), X-ray excited Auger spectroscopy (XAES), and time-of-flight secondary ion mass spectrometry (TOF−SIMS). The asphaltenes were precipitated from virgin Doba−Chad heavy crude or from treated crudes after undergoing noncatalytic and (FeS and MoS 2 mediated) catalytic hydrovisbreaking to reduce heavy crude viscosity for meeting pipeline transportation specifications. The sp 2 and sp 3 characters of the asphaltenes were calibrated using, respectively, highly oriented pyrolytic graphite (HOPG) and diamond. Composites of asphaltenes with polyethylene and polystyrene references were used to assess the shift from sp 3 - to sp 2 -dominated structures. It was postulated that the π aromatic character in the asphaltenes condensed polynuclear aromatic rings correlates with sp 2 carbon, whereas the asphaltenes aliphatic character correlates with sp 3 carbon. Percentages of sp 2 sites ranged between 36% and 70% for all the asphaltenes samples with values from XPS being underestimated, with respect to XAES. The splitting between the principal nonloss C 1s line and the largest plasmon loss peak, and the evolution in shape of the π → π* plasmon satellite in the energy loss spectra were in qualitative agreement with XPS and XAES data. In addition to aromatic and aliphatic hydrocarbon ion fragments, the high sensitivity of TOF−SIMS allowed the detection of several hetero-elements (such as nickel, vanadium, sulfur, and nitrogen, in the organometallic-bearing asphaltenes, or iron, chlorine, sodium, potassium, and silicon, as foreign elements). Probing the surface composition through the ΣCH x + /C 2 + ratio indicated that asphaltenes were bearing more aliphatic character than the carbon blacks or graphite, presumably because of the presence of hydrogen during hydrovisbreaking. However, surface probing via the C 2 H - /C 2 - ratio suggested that asphaltenes were less aromatic, as expected, than graphite while exhibiting an aromatic character close to that of some carbon blacks.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.001 | 0.001 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".