Interfacial Gas Enrichment at Hydrophobic Surfaces and the Origin of Promotion of Gas Hydrate Formation by Hydrophobic Solid Particles

Abstract

Hydrophobic solid surfaces have been found to promote the formation of gas hydrates effectively and thus help to realize the immense potential applications of hydrates in many sectors such as energy supply, gas storage and transportation, gas separation, and CO2 sequestration. Despite the well-known effectiveness, the molecular mechanism behind the promotion effect has not been thoroughly understood. In this work, we used both simulation and experimental means to gain insights into the microscopic level of the influence of hydrophobic solid surfaces on gas hydrate formation. On one hand, our simulation results show the presence of an interfacial gas enrichment (IGE) at hydrophobic surface and a gas depletion layer at hydrophilic surface. In the meantime, the analysis of water structure near the hydrophobic solid interface based on the molecular trajectories also shows that water molecules tend to get locally structured near a hydrophobic surface while becoming depressed near a hydrophilic surface. On the other hand, the experimental results demonstrate the preferential formation of gas hydrate on a hydrophobic surface. The synergic combination of simulation and experimental results points out that the existence of an IGE at hydrophobic solid surface plays a key role in promoting gas hydrate formation. This work advances the molecular level understanding of the role of hydrophobicity in governing the gas hydrate as well as interfacial phenomena in general.

Effect of hydrophilic silica nanoparticles on hydrate formation: Insight from the experimental study

“…Therefore, the adsorbed water molecules aligned on the surface of the nanoparticles become difficult to re-arrange themselves to form a clathrate hydrate structure surrounding the CH 4 molecules. At the same time, the hydrophobic and nonpolar methane molecules near the hydrophilic nano-SiO 2 surface may be inadequate for hydrate formation according to the accumulation behaviors of methane molecules near hydrophobic nanoparticles through molecular simulations [47,48] . Consequently, the presence of hydrophilic surface can reduce the amount of hydrate formation under the condition of low drive force of hydrate formation (see Fig.…”

“…8 and Supplementary material). In contrast, hydrophobic nanoparticles will facilitate rearrangement of water molecules that form a clathrate hydrogen bond network structure near the hydrophobic solid interface because of the existence of interfacial gas enrichment [26,[48][49][50][51][52] . Correspondingly, the zeta potential values show significant difference before and after exposing to different gases (see Fig.…”

The inhibition of methane hydrate formation by water alignment underneath surface adsorption of surfactants

“…The instantaneous temperature and pressure inside the reactor were simultaneously monitored and recorded by a data acquisition system. A fuller description of the experimental procedure has been reported in our previous publication [42][43] . The gas uptake was calculated using state equation of real gas in which the compressibility factor of methane was calculated by using Brill-Beggs correlation 44 .…”

Effects of additives on the formation of methane and carbon dioxide gas hydrates

“…These effects respectively share the same physicochemical principle with the effects of a hydrophobe and a hydrophile on local water structure as discussed previously. Moreover, simulation data also showed that gas concentration was increased near a hydrophobic surface while decreased near a hydrophilic surface (Figure 9.10) [132]. Both of the effects (on water structure and gas density)…”

“…The analyses of the solution-solid interface by using molecular dynamics simulation and Raman spectroscopy have shown two important findings [111,132]. First, water structure was enhanced near a hydrophobic surface but disrupted near a hydrophilic surface [111,132].…”