CH₄ Nanobubbles on the Hydrophobic Solid–Water Interface Serving as the Nucleation Sites of Methane Hydrate

Abstract

The surface hydrophobicity of solid particles plays a critical role in the nucleation of gas hydrate formation, and it was found that the hydrophobic surface will promote this nucleation process, but the underlying mechanism is still unveiled. Herein, we proposed for the first time our new theory that the formation of methane nanoscale gas bubbles on the hydrophobic surface provides the nuclei sites for further formation of methane hydrate. First, we studied the effect of hydrophobicity of particles on the nucleation of hydrate. It was found that the hydrophobic graphite and silica particles would promote the nucleation of hydrate, but the hydrophilic silica particles did not promote the methane hydrate nucleation. Then, we designed the atomic force microscopy experiment to explain this mechanism from a nanometer scale. The results showed that the methane nanobubbles were formed on the hydrophobic highly ordered pyrolytic graphite surface, but they were hard to form on the hydrophilic mica surface. These results indicated that the methane nanobubbles on the hydrophobic surface could provide the gas hydrate nucleation sites and may induce a rapid nucleation of methane hydrate.

Anti-gas hydrate surfaces: perspectives, progress and prospects

“…Soon after that, Guo et al reported experimental evidence of methane bubbles on hydrophobic surfaces as nucleation sites for hydrate formation. 136 In their study, methane hydrate formation was found to be promoted on hydrophobic graphite surfaces, but not so on hydrophilic mica surfaces. As characterized by atomic force microscopy (AFM), a large number of methane nanobubbles with an average diameter ∼223.4 nm were observed on the graphite surfaces, which were not observed on the mica surfaces.…”

“…Although experiments showed hydrate deposits formed in water-dominated systems and caused large pressure drop, 132,135 it was not until 2018 that Guo et al successfully observed hydrate deposition initiated by gas bubbles on surfaces with the existence of saturated water. 136 As such, mechanisms I and II both posit that hydrate deposition arises from hydrate formers on pipe walls, despite their occurrence in distinct systems. In contrast, mechanism III subscribes to the view that the hydrate deposits onto surfaces through a cohesion process between hydrate particles.…”

“…144–146 Recently, it was found that gas enrichment and gas bubbles on hydrophobic surfaces were responsible for the hydrate nucleation-promotion effects. 136,146,147 Therefore, strong surface gas wettability is a significant factor affecting hydrate growth, and, thus, deposition, from gas layers and bubbles on the surfaces. Although surface gas nano-bubbles have been widely observed at the interfaces of water and hydrophobic solid surfaces (which are also known as aerophilic surfaces), 148–152 the relationship between interfacial gas bubbles and hydrate formation was not established more clearly until 2017.…”

“…Repelling surface gas concentration should also be considered. 136 For instance, superhydrophobic surfaces can be helpful in repelling surface water, while the gas concentrated in the pores can still assist hydrate formation. 104 Therefore, both water and gas wettability need to be evaluated in anti-hydrate surface design.…”

Interfacial study of clathrates confined in reversed silica pores

“…Indeed, multiple experimental studies have demonstrated the outstanding clathrate promoting effects of hydrophobized silica surfaces. [27][28][29][30] Nevertheless, considering the diversity of types, distribution and concentration of surface ligands available to be introduced into SiO 2 matrices, as well as the different pore sizes of the parent matrix, it is important to establish clear structure-property relationships to guide the choice of high-performance materials without having to rely on serendipity-based experiments.…”