Adsorption of Bitumen Model Compounds on Kaolinite in Liquid and Supercritical Carbon Dioxide Solvents: A Study by Periodic Density Functional Theory and Molecular Theory of Solvation
Bibliographic record
Abstract
The geometry of phenanthridine, benzothiophene, tetralin, and naphthalene representative of the heterocyclic, naphthenic, and aromatic components of bitumen adsorbed on kaolinite is optimized using density functional theory and periodic boundary conditions in gas phase. These bitumen model compounds preferentially adsorb on the aluminum hydroxide surface of kaolinite with energy decreasing in the order phenanthridine > naphthalene > tetralin ∼ benzothiophene. The adsorption of phenanthridine is strengthened by hydrogen bonding between the pyridinic N atom and an axial hydroxyl group of kaolinite, while the rest of the molecules adsorb through van der Waals interactions. The mechanism of solvation in CO 2 and the effect of liquid and supercritical CO 2 on the adsorption thermodynamics are studied using the three-dimensional reference interaction site model theory with the closure approximation of Kovalenko and Hirata (3D-RISM-KH) molecular theory of solvation at 293–333 K and 10–30 MPa. The CO 2 solvent interacts with the aluminum hydroxide surface of kaolinite by hydrogen bonding, with the pyridinic N atom of phenanthridine by electrostatic interactions, and with the rest of the bitumen model compounds by hydrophobic interactions, as inferred from the 3D site density distribution functions of CO 2 . The molecule–kaolinite potentials of mean force in CO 2 show that the adsorption of naphthalene and tetralin on kaolinite is substantially weakened as the pressure is increased and the temperature is decreased. Benzothiophene adsorption is the least sensitive to CO 2 temperature and pressure changes. In liquid CO 2 at 30 MPa and 293 K, the hydrocarbon molecules are weakly adsorbed and can be desorbed by CO 2, while the heterocycles would remain adsorbed, suggesting an approach for extraction of deasphalted bitumen from oil sands. While the most favorable thermodynamic conditions for desorption are in liquid CO 2, the kinetic barrier for desorption is the most sensitive to small changes in the temperature and pressure in supercritical CO 2, indicating that supercritical conditions are important for desorption rate control. These results suggest that the investigated bitumen components can be selectively desorbed from kaolinite by controlling the temperature and pressure of the CO 2 solvent and agree with experimental reports on heavy oil recovery. These insights are valuable for the development of improved techniques for extraction of bitumen from oil sands and deasphalting of bitumen using liquid and supercritical CO 2 .
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How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| 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) | 0.000 | 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 teacher head, 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".