Experimental Study on Hydrate Structure Transition Using an In Situ High-Pressure Powder X-ray Diffractometer: Application in CO<sub>2</sub> Capture
Bibliographic record
Abstract
Clathrate (gas) hydrates as materials have received great interest due to their high-density gas storage potential and separation applications for their ability to preferentially separate a targeted component such as CO 2 from waste streams. Among the three clathrate hydrate structures, only sH (structure H) hydrates require a large molecule such as neohexane (NH) or tert -butyl methyl ether (TBME) as well as a “help-gas” molecule such as methane (CH 4 ) to form a stable structure. However, attempts to use CO 2 as a help-gas came up with mixed results where it appeared that the sH hydrate formed was stable only at temperatures below the ice point, whereas the compound formed with CH 4 was considerably more stable. sH hydrates have considerable potential for gas separation, for instance, of CH 4 –CO 2 mixtures. Thus, in this work, several compositions were tested for their hydrate forming ability. The large cage guests tested were NH and TBME, the help-gas mixtures were a CO 2 -rich mixture (76% CO 2 and 24% CH 4 ), and a CO 2 lean mixture (24% CO 2 and 76% CH 4 ). The phase behavior of hydrates formed from the various combinations was tested by measuring the endo- and exotherms associated with hydrate formation and decomposition in a high-pressure differential calorimeter. The different phases indicated from the DSC results were identified by employing an in situ high-pressure cell on a powder X-ray diffractometer. Powder patterns were recorded to identify the crystal phase arising from nucleation and possible re-crystallization events after annealing. It was confirmed that the CO 2 lean mixture (24% CO 2 and 76% CH 4 ) forms structure H (sH) hydrate, while the CO 2 -rich mixture (76% CO 2 and 24% CH 4 ) forms structure I (sI) hydrate presenting a structure transition pattern across the gas mixtures investigated. Further, it was observed that the CO 2 lean mixture, which forms sH hydrate, also starts as sI hydrate and gradually converts to the thermodynamically stable sH hydrate. This study, in essence, helps to understand the preference of CH 4 and CO 2 for three different types of cages in sH hydrates and presents a design framework for a suitable gas separation mechanism for this gas mixture of interest.
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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) | 0.001 | 0.001 |
| Meta-epidemiology (broad) | 0.001 | 0.000 |
| Bibliometrics | 0.000 | 0.001 |
| Science and technology studies | 0.001 | 0.001 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.001 | 0.000 |
| Research integrity | 0.001 | 0.001 |
| Insufficient payload (model declined to judge) | 0.002 | 0.001 |
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".