Molecular dynamics simulation and in-situ MRI observation of organic exclusion during CO2 hydrate growth

Zhang, Lunxiang; Sun, Lingjie; Lu, Yi; Kuang, Yangmin; Ling, Zheng; Yang, Lei; Dong, Hongsheng; Yang, Shengxiong; Zhao, Jiafei; Song, Yongchen

doi:10.1016/j.cplett.2020.138287

Cited by 17 publications

(7 citation statements)

References 37 publications

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“…The exclusive effect of hydrate formation controls the dynamic growth of hydrate crystals locally at the bubble interface. Our previously reported works supported the story. − Moreover, in the presence of surfactants, due to the orientation of amphiphilic molecules at the gas–liquid interface, a monolayer hydrophobic film was formed (as shown in Figure c). In such cases, hydrates usually do not nucleate directly on the surface of bubbles but by trapping guest molecules around bubbles to form aggregated hydrate agglomeration.…”

Section: Resultssupporting

confidence: 66%

Morphology Study of Hydrate Shell Crystal Growth on a Microbubble Interface in the Presence of Additives

Kuang

Zheng

Dai

et al. 2023

Crystal Growth & Design

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Bubble dispersions in water can be observed in both wellbore or subsea piping as well as subsea gas seepages. The hydrate risk in subsea pipelines or methane leaks from the cold spring into seawater can be strongly influenced by the hydrate crystal growth on bubbles. In addition, the bubbling method has been proven to be an effective method to enhance the gas–liquid mixing pathway and promote hydrate’s rapid formation in the application of hydrate-based technologies, yet the microscopic mechanism of hydrate film growth on the bubbles still needs to be further clarified. In this study, the hydrate crystal growth morphology evolution at the microbubble interface was investigated by a high-resolution microscope combined with the temperature-controlled stage. The results showed that the hydrate crystals nucleated rapidly at the bubble interface to form a hydrate shell-coated structure in a pure water system. The defect growth mechanism dominated the hydrate crystals growth at the bubble interface in additive solutions. Hydrate did not nucleate directly on the surface of bubbles but by trapping guest molecules around the shrinking bubbles to form aggregated hydrate agglomeration in the presence of surfactants. In addition, the bubbles tend to provide a steady stream of gas source for hydrate formation. The growth of hydrate shells contributed to a normal distribution of bubble shrinking rates, with an average rate of 9 μm/s in 0.5 wt % NaCl solution. The existence of a high concentration of ions or organic molecules at the microbubbles’ interface and the exclusive effect played a dominant role in the process of hydrate formation. In addition, it was found that the repulsive effect of ions at the bubble interface on hydrate formation was weak under a high subcooling degree. However, other organic molecule promoters still accelerated the hydrate’s formation rate because they increased the dissolution and diffusion rate of gas in solution. The results are expected to strengthen further the applications relating to hydrate-based phase transition promotion technology in the industry in energy storage, gas separation, or inhibition techniques in flow assurance of the offshore industry.

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Section: Resultssupporting

confidence: 66%

Morphology Study of Hydrate Shell Crystal Growth on a Microbubble Interface in the Presence of Additives

Kuang

Zheng

Dai

et al. 2023

Crystal Growth & Design

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“…MRI technique has been vastly used to observe the dynamic process of hydrate formation and decomposition in hydrate-bearing sediments due to its immediacy of image acquisition (Figure 8c-f). A standard spin echo multi-slice sequence is applied to detect the 1 H contained in the liquid water phase only [115,116,[126][127][128][129][130]. It should be noted that the 1 H in the gaseous or solid phase is hard to be imaged in the MRI due to much shorter T 2 .…”

Section: Comparison Of Nmr T 2 Methods With Other Technologiesmentioning

confidence: 99%

“…The resolution of MRI is at a scale of several hundred microns or even smaller [126,128]. The acquisition time of the image is about 2 min-1 h [126,130,131]. The signal intensity on the image is related to water saturation.…”

Section: Comparison Of Nmr T 2 Methods With Other Technologiesmentioning

confidence: 99%

Advances in Characterizing Gas Hydrate Formation in Sediments with NMR Transverse Relaxation Time

Liu

Zhan

et al. 2022

Water

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The formation process, structure, and distribution of gas hydrate in sediments have become focal points in exploring and exploiting natural gas hydrate. To better understand the dynamic behavior of gas hydrate formation in sediments, transverse relaxation time (T2) of nuclear magnetic resonance (NMR) is widely used to quantitatively characterize the formation process of gas hydrate and the change in pore characteristics of sediments. NMR T2 has been considered as a rapid and non-destructive method to distinguish the phase states of water, gas, and gas hydrate, estimate the saturations of water and gas hydrate, and analyze the kinetics of gas hydrate formation in sediments. NMR T2 is also widely employed to specify the pore structure in sediments in terms of pore size distribution, porosity, and permeability. For the recognition of the advantages and shortage of NMR T2 method, comparisons with other methods as X-ray CT, cryo-SEM, etc., are made regarding the application characteristics including resolution, phase recognition, and scanning time. As a future perspective, combining NMR T2 with other techniques can more effectively characterize the dynamic behavior of gas hydrate formation and pore structure in sediments.

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“…In addition to the temperature and pressure changes, destabilization of gas hydrates can result from reactions with various organic or inorganic chemical agents that inhibit hydrate formation: salts, acids, and other compounds [21][22][23][24][25][26][27][28]. The effect of dissolved salts on the pressure and temperature limits of hydrate stability has received much attention [21,23,[29][30][31][32][33].…”

Section: Introductionmentioning

confidence: 99%

Migration of Salt Ions in Frozen Hydrate-Saturated Sediments: Temperature and Chemistry Constraints

et al. 2022

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Migration of dissolved salts from natural (cryopeg brines, seawater, etc.), or artificial sources can destabilize intrapermafrost gas hydrates. Salt transport patterns vary as a function of gas pressure, temperature, salinity, etc. The sensitivity of the salt migration and hydrate dissociation processes to ambient temperature and to the concentration and chemistry of saline solutions is investigated experimentally on frozen sand samples at a constant negative temperature (−6 °С). The experiments show that the ambient temperature and the solution chemistry control the critical salt concentration required for complete gas hydrate dissociation. Salt ions migrate faster from more saline solutions at higher temperatures, and the pore moisture can reach the critical salinity in a shorter time. The flux density and contents of different salt ions transported to the samples increase in the series Na2SO4–KCl–CaCl2–NaCl–MgCl2. A model is suggested to account for phase transitions of pore moisture in frozen hydrate-saturated sediments exposed to contact with concentrated saline solutions at pressures above and below the thermodynamic equilibrium, in stable and metastable conditions of gas hydrates, respectively.

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Molecular dynamics simulation and in-situ MRI observation of organic exclusion during CO2 hydrate growth

Cited by 17 publications

References 37 publications

Morphology Study of Hydrate Shell Crystal Growth on a Microbubble Interface in the Presence of Additives

Morphology Study of Hydrate Shell Crystal Growth on a Microbubble Interface in the Presence of Additives

Advances in Characterizing Gas Hydrate Formation in Sediments with NMR Transverse Relaxation Time

Migration of Salt Ions in Frozen Hydrate-Saturated Sediments: Temperature and Chemistry Constraints

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