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Hydrate surface wettability is a fundamental aspect to better understand agglomeration present in oil bearing petroleum pipelines. Coupling these measurements with hydrate film growth gives further information on kinetic effects that may also be present from natural surfactants in different oils. In situ measurements of wettability (quantified by the contact angle) and film growth rates were performed on cyclopentane hydrate surfaces at atmospheric pressure and subcooling of 4 ◦C. Contact angle and film growth results were obtained for the baseline system (pure cyclopentane), one model oil, and seventeen natural oils (diluted to 0.02 vol% in cyclopentane). Results showed a wide variety of contact angles and film growth values where higher asphaltene contents in the oils corresponded to higher contact angles and lower film growth rates, thought to be from better alignment of natural surfactant molecules at the hydrate/hydrocarbon interface. It was also shown for select oils that increasing the oil concentration in the cyclopentane increases the contact angle and decreases the film growth rate compared to the baseline system. For select oils that had higher contact angles, increasing the water content of the system decreases their contact angle and film growth compared to the baseline system. Isolating different oil fractions for select oils also shows which fractions tend to play a larger role in wettability behavior. Typically, the fractions with more surface active components (asphaltene and resins) are shown to contribute to the higher contact angle and slower film growth rates for select oils. Evidence of the competition between film growth and capillary suction of water into the hydrate has been shown, and a mechanistic breakdown of three different transient scenarios has been proposed. Each of these observed interfacial behaviors gives information on what can be expected from larger scale phenomena, including hydrate agglomeration, with very small oil samples.
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This content will become publicly available on May 14, 2025
Experiments and Molecular Simulations to Study the Effect of Surface-Active Compounds in Mixtures of Model Oils on CO2 Corrosion during Intermittent Oil–Water Wetting
Intermittent oil–water wetting can have a significant effect on the internal corrosion of steel pipelines. This paper presents a combined experimental and molecular modeling study of several influential factors on the surface properties and corrosion behavior of mild steel in CO2 environments. The influence of different model oils (LVT-200 and Aromatic-200) and select surface-active compounds (myristic acid, cyclohexane butyric acid, and oleic acid) on the corrosion behavior of carbon steel during intermittent oil–water wetting was determined by measuring the corrosion rate after intermittent wetting cycles. The interfacial tension measurements were performed to study the incorporation of the oil phase along with surface-active molecules in the protective layer formed on the specimen surface. Results showed that the interfacial tension for an aromatic oil–water interface is lower than that for an aliphatic oil–water interface. To understand this result, molecular dynamics simulations of oil–water interfaces were performed in the presence of surface-active molecules and different oils to analyze the structure of the layer formed at the interface. The simulations supported the hypothesis that aromatic molecules are less structured at the interface, which results in the incorporation of more water molecules into the protective layer formed at the steel surface, causing a higher corrosion rate. On the other hand, the simulations revealed that myristic acid in an aliphatic oil forms a well-aligned structure at the interface, devoid of any water molecules. This is in agreement with the hypothesis that the linear molecular structure of myristic acid favors the alignment of molecules at an aliphatic oil–water interface, resulting in a lower interfacial tension and more effective corrosion mitigation as compared to the other two nonlinear compounds tested. It is concluded that an important factor controlling the corrosion behavior is the molecular structure of the oil–water interface, which is adopted by the steel surface layer through the Langmuir–Blodgett process.
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- Award ID(s):
- 2046095
- PAR ID:
- 10510885
- Publisher / Repository:
- American Chemical Society
- Date Published:
- Journal Name:
- Langmuir
- Volume:
- 40
- Issue:
- 19
- ISSN:
- 0743-7463
- Page Range / eLocation ID:
- 9945 to 9956
- Subject(s) / Keyword(s):
- Surfactants self-assembly, co-adsorption, oil-water interface, molecular dynamics
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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