A comprehensive study of the effects of the Kinetic Hydrate Inhibitor Polyvinylpyrrolidone on Methane Hydrate Forming Systems
Bibliographic record
Abstract
Over the years, methane hydrates have been intensely investigated for their vast potential as a future energy source and hazard to global climate.Polyvinylpyrrolidone (PVP), a water-soluble polymer, was proven to effectively inhibit methane hydrate formation rates in many settings.Although the mechanism is still yet to be fully understood, there are some plausible theories available.It is generally believed that once hydrate nuclei have formed in a system, their growth is slowed by a very rapid adsorption of polymer onto the crystal surface.Other theories have shown that the polymer's ring groups interact with specific cage sites at the hydrate surface.In order to decipher the action played by PVP on the hydrate crystal, the polymer interaction would need to be characterized.The aim of this work is therefore, to provide insight into the effects of PVP on gas hydrates.Due to insufficient data presently available, a range of experiments was conducted on solutions of PVP.The first study, which investigated the dissolution of gas into the bulk liquid, was conducted using a wide range of PVP concentrations.Results showed that at 0.007 wt% PVP, the time constant of the process entrations of 0.00007 wt% and 2 wt% yielded %, respectively.As a result, the overall trend, which includes additional data, was shown to closely follow a normal distribution curve.Hydrate kinetic experiments were also performed using 3 distinctive PVP molecular weights.These molecular weights consisting of 10 000 g/mol, 40 000 g/mol and 360 000 g/mol were used to determine the effects of concentration, pressure, temperature and molecular weight on hydrate growth rates.The outcome of these tests demonstrated that the hydrate growth rate varied considerably with respect to concentration.In general, the trend appears to be sigmoidal, exhibiting an inverted "S" shaped curve for all molecular weights tested.The effect of increasing pressure or driving force, exhibited an overall contraction of the inverted sigmoidal curve while the effect of temperature and molecular weight was determined to be complex and relatively unchanged, respectively.The effect of PVP on the mole fraction of methane in the liquid bulk at the three-phase (H-Lw-V) equilibrium condition and during growth was also investigated to determine its ABSTRACTDany Posteraro -ii-Ph.D. Thesis contribution to the inhibition of gas hydrates.The results of this study indicated that while PVP had a negligible effect on methane solubility, the degree of supersaturation was significantly enhanced with inhibitor loading and followed a sigmoidal trend.The mole fraction data was then correlated to growth rate data using a kinetic model, where the results implied a significant decrease in the surface area available for reaction as a function of inhibitor loading; validating a PVP adsorption model.High-pressure experiments were then performed with PVP to determine if an operational setting exists so that its effect on hydrate growth can be completely eliminated.High operating pressures ranging from 23.78-31.28MPa and a temperature of 277 K was used to determine if the effect of PVP at a concentration of 0.007 wt% could be overcome.Results showed that PVP was ineffective for a relatively short time starting at the point of turbidity while operating at 26.28 MPa.As the operating pressure was increased, the amount of time in which PVP remained ineffective at reducing the hydrate growth rate also increased.At the maximum operating pressure of 31.28MPa, PVP was ineffective for approximately 40% of the time used for hydrate growth.This is the first study where this inhibitor, added to RO water, has proven to be ineffective during hydrate growth, implying that a theoretical pressure may exist in which complete inhibition may be obtained.In order to decipher the above experimental results, experiments were conducted on the PVP methane hydrate system to determine if the concentration of PVP in the bulk liquid increased or decreased with time.Liquid bulk samples were thus extracted at six specific times throughout the hydrate formation process.Results showed that as time progressed in the hydrate forming system, the concentration of PVP in the liquid bulk decreased, suggesting that PVP binds to the surface of the growing hydrates further validating a PVP adsorption model.The results obtained from this work clearly illustrate the effects in which PVP plays on the gas hydrate system.This is the first study in which bulk experimental measurements conclusively validate a surface adsorption inhibition mechanism.Although the precise mode of action is still yet to be fully understood, it may one day be revealed with the aid of this dissertation.
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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 | 0.001 |
| Meta-epidemiology (narrow) | 0.001 | 0.001 |
| Meta-epidemiology (broad) | 0.001 | 0.000 |
| Bibliometrics | 0.000 | 0.001 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.001 | 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".