Some aspects of hydrate formation and wetting

Fotland, Per; Askvik, Kjell Magne

doi:10.1016/j.jcis.2008.01.031

Cited by 29 publications

(30 citation statements)

References 17 publications

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“…The clathrate is always sI filled with methane, and the simulations are performed at 277 K and 100 bar with a 5.22 nm –2 surface coverage for the pure dodecanol monolayer and 4.43 nm –2 for the mixed aligned monolayer that consist of dodecanol and dodecane. We find that water wets the clathrate–dodecane interface with a contact angle θ = 34 ± 2° (Figure 6a) in agreement with previous assumptions 35,43,99,100 and experiments that report θ = 29° for water at the clathrate–freon interface. 43 We use the Young equation, 101 cos θ = (γ c-o – γ w-c )/γ w-o , and the surface tensions of the clathrate–water interface, γ w-c = 33 ± 4 mJ m –2 , 2,44,45 and the dodecane–water interface, γ w-o = 53 mJ m –2 , 46,47 to determine that the surface free energy of the clathrate–dodecane interface is γ c-o = 76.9 ± 2 mJ m –2 .…”

Section: Results and Discussionsupporting

confidence: 91%

How Do Surfactants Control the Agglomeration of Clathrate Hydrates?

2019

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Clathrate hydrates can spontaneously form under typical conditions found in oil and gas pipelines. The agglomeration of clathrates into large solid masses plugs the pipelines, posing adverse safety, economic, and environmental threats. Surfactants are customarily used to prevent the aggregation of clathrate particles and their coalescence with water droplets. It is generally assumed that a large contact angle between the surfactant-covered clathrate and water is a key predictor of the antiagglomerant performance of the surfactant. Here we use molecular dynamic simulations to investigate the structure and dynamics of surfactant films at the clathrate–oil interface, and their impact on the contact angle and coalescence between water droplets and hydrate particles. In agreement with the experiments, the simulations predict that surfactant-covered clathrate–oil interfaces are oil wet but super-hydrophobic to water. Although the water contact angle determines the driving force for coalescence, we find that a large contact angle is not sufficient to predict good antiagglomerant performance of a surfactant. We conclude that the length of the surfactant molecules, the density of the interfacial film, and the strength of binding of its molecules to the clathrate surface are the main factors in preventing the coalescence and agglomeration of clathrate particles with water droplets in oil. Our analysis provides a molecular foundation to guide the molecular design of effective clathrate antiagglomerants.

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Section: Results and Discussionsupporting

confidence: 91%

How Do Surfactants Control the Agglomeration of Clathrate Hydrates?

2019

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“…7, and the immersion depth was observed close to zero in these experiments. The radius of the hydrate particles used in these experiments was 0.003 ± 0.001 m. It was previously suggested by Fotland and Askvik [35] that for hydrate particles nucleating and growing at oil/brine interfaces, their positioning at the interface is largely dominated by the wetting state of the system, as long as the particles have radius smaller than 0.01 m. Capillary force was suggested to dominate for particles with a radius smaller than 0.001 m [35]. In this present work, the hydrate particles are mechanically removed from the oil/water interface, overriding the natural force balance of the system, but the observed differences in immersion depth could be argued to be related to differences in wetting state and capillary forces in the systems.…”

Section: Influence Of Watersupporting

confidence: 56%

Adhesion force between cyclopentane hydrates and solid surface materials

Aspenes

Dieker

Aman

et al. 2010

Journal of Colloid and Interface Science

153

143

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The mechanisms by which hydrates deposit in a petroleum production line are related to pipeline surface properties, fluid composition and properties, and water cut. In this work, adhesion forces between cyclopentane hydrates and solid surfaces were investigated as a function of the solid material, the presence of water and the presence of petroleum acids in the oil phase. The influence of dissolved water on hydrate adhesion forces was also investigated. The results show that the adhesion force between hydrates and solid surfaces was dependent on the surface material; solids with low surface free energy lead to the lowest adhesion forces. The adhesion force was strongly dependent on the presence of water in the system. When a water drop was deposited on the solid surface, the adhesion force between the hydrate and the solid surface was more than 10 times larger than hydrate-hydrate adhesion forces. The presence of a water-saturated oil phase also led to an increase in adhesion force between hydrate particles. Adhesion forces were highest when the solid surfaces are water-wet. Addition of petroleum acids to the oil phase drastically reduced adhesion forces.

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“…When no surfactant molecules are adsorbed, the hydrate surface is wetted by water. 22 When the hydrate particles are preferentially wetted by the oil phase, this means that the surfactant molecules are adsorbed head-down, with the headgroup attached to the hydrate surface and the tail of the alkyl chain oriented away from it. If they are wetted by the surfactant solution, the headgroup of the adsorbed surfactant molecules is oriented away from the hydrate surface.…”

Section: Resultsmentioning

confidence: 99%

Using Microscopic Observations of Cyclopentane Hydrate Crystal Morphology and Growth Patterns To Estimate the Antiagglomeration Capacity of Surfactants

et al. 2019

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The crystal growth and morphology of cyclopentane (CP) hydrates at a quiescent water/oil interface in the presence of 10 different surfactants were observed under a microscope. In most cases, the oil was CP, but for some of the observations a 50/50 vol % mixture of CP and n-octane (n-C8) (or n-dodecane (n-C12)) was used instead. For some of the surfactants, gas hydrates formed from a methane (CH 4)/propane (C 3 H 8) gas mixture at a quiescent water/n-C8 interface were also observed. The capacity of the surfactants to prevent the hydrate particles from agglomerating was assessed by measuring torque on oil-dominated systems (70 vol %) in a stirred autoclave at subcoolings of 6 and 10°C for the CP hydrates and CH 4 / C 3 H 8 hydrates, respectively. The oil phases were the same as those used in the morphology study. In the case of CP hydrates, the agglomeration state of the system was directly observed by opening the autoclave at the end of the hydrate formation. The size of the CP hydrate particles was measured, and their wettability was determined. The effect of the presence of salt (NaCl) on the crystal morphology and AA performance was also studied for some systems. All the surfactants that induced the formation of hydrate crystals that rapidly agglomerated at the water/CP interface showed poor AA performance. Whenever the surfactants induced the formation of individual oil-wettable crystals, their AA performance was good. If the individual crystals formed were water-wettable, two main behaviors were observed: (1) when the surfactant induced a very low water/CP interfacial tension (<1 mN/m), its AA performance was good, (2) but when it induced a higher interfacial tension (>1 mN/m), it exhibited poor AA performance. These trends in the AA performance of the surfactants were observed on both hydrate systems (CP hydrates and CH 4 /C 3 H 8 hydrates). From the experimental results obtained in this work, we can infer that the microscopic observation of the morphology and growth pattern of CP hydrate crystals formed at a quiescent water/CP interface might be a simple way to rapidly assess if a surface-active molecule has an antiagglomeration effect on sII gas hydrates.

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Some aspects of hydrate formation and wetting

Cited by 29 publications

References 17 publications

How Do Surfactants Control the Agglomeration of Clathrate Hydrates?

How Do Surfactants Control the Agglomeration of Clathrate Hydrates?

Adhesion force between cyclopentane hydrates and solid surface materials

Using Microscopic Observations of Cyclopentane Hydrate Crystal Morphology and Growth Patterns To Estimate the Antiagglomeration Capacity of Surfactants

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