Molecular Understanding of CO<sub>2</sub> and H<sub>2</sub>O in a Montmorillonite Clay Interlayer under CO<sub>2</sub> Geological Sequestration Conditions
Bibliographic record
Abstract
Grand canonical Monte Carlo (GCMC) simulations are carried out to investigate a supercritical carbon dioxide (scCO 2 )-water mixture in the Na-montmorillonite clay interlayer under typical CO 2 geological sequestration conditions ( T = 323 K, P = 90 bar and T = 348 K, P = 130 bar). The stable clay interlayer distances at different relative humidity (RH) are determined based on the normal pressure and free energy curves of the CO 2 –H 2 O–Na + complex in the montmorillonite clay interlayer. Simulation results show that stable monolayer hydrates (1W) with a basal spacing around 12 Å are formed at RH = 30–60%. As RH is increased to 70% and above, bilayer CO 2 –H 2 O mixtures with a basal spacing around 15–16 Å (2W) are more stable. In general, the CO 2 intercalation process is strongly influenced by RH. While a high relative humidity facilitates water molecules entering the clay interlayer, it nonetheless decreases CO 2 intercalations. The sorbed H 2 O concentrations from our simulations compare remarkably well with the in situ infrared (IR) spectroscopy experimental data by Loring et al. [ Langmuir, 2014, 30, 6120–6128], if the continuous experimental curve is considered as the “smear-out” of the stepwise curve from our simulations. However, the overall sorbed CO 2 concentrations from our simulations are higher than the IR experimental results. We attribute these discrepancies in both sorbed H 2 O and CO 2 concentrations (measured from experiments and simulations) to the complexity of hydrated clay particles in the IR spectroscopy experiment, to which the hydration-heterogeneity model could provide a reasonable interpretation. Molecular dynamics (MD) simulations show that the hydration state of CO 2 molecules is changed from the partial hydration in 1W to the full hydration in 2W with the increase in RH, and CO 2 dimers are frequently seen in both 1W and 2W hydration states. CO 2 dimers largely take the slipped parallel configurations, while the remaining dimers take the perpendicular T-shaped geometry. Further, sodium ions in the interlayer tend to be fully hydrated by water molecules due to their relatively large hydration energy. Moreover, we find that CO 2 molecules hardly migrate into the first hydration shell of sodium ions. The overall diffusion coefficients of CO 2 molecules are larger than those of water molecules and sodium ions. This comparably high mobility of CO 2 molecules in the clay interlayer, together with the low probability of CO 2 participation in the first hydration shell of Na + ions, essentially prevents CO 2 and Na + from direct interactions in clay interlayers.
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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 | 0.001 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.001 |
| 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".