Clathrate Adhesion Induced by Quasi-Liquid Layer

Abstract

The adhesive force of clathrates to surfaces is a century-old problem of pipeline blockage for the energy industry. Here, we provide new physical insight into the origin of this force by accounting for the existence of a quasi-liquid layer (QLL) on clathrate surfaces. To gain this insight, we measure the adhesive force between a tetrahydrofuran clathrate and a solid sphere. We detect a strong adhesion, which originates from a capillary bridge that is formed from a nanometer-thick QLL on the clathrate surface. The curvature of this capillary bridge is nanoscaled, causes a large negative Laplace pressure, and leads to a strong capillary attraction. The microscopic capillary bridge expands and consolidates over time. This dynamic behavior explains the time-dependent increase of measured capillary forces. The adhesive force decreases greatly upon increasing the roughness and the hydrophobicity of the sphere, which founds the fundamental basics for reducing clathrate adhesion by using surface coating.

Critical Shear Stress of Clathrate and Semiclathrate Hydrates on Solid Substrates

“…Among these four findings, the most important one is that the critical shear stress diminished with heating and became negligibly small just below the dissociation temperature. This finding may at first appear contrary to expectations because of the normal adhesive force that has been known to be enhanced by the quasi-liquid layer due to the capillary action. , However, our finding actually makes sense. To explain why, we start from the fundamental difference between adhesion forces and adhesion hysteresis …”

“…No significant change in the critical shear stress was observed with the hydrophobicity of the substrate other than this single jump around the contact angle of 60°. Our prior expectation that was in line with the literature ,,,,, has been that the critical shear stress would decrease with the hydrophobicity of the substrate because a clathrate hydrate would have a higher affinity to a hydrophilic substrate than to a hydrophobic one.…”

“…An important factor that likely plays a major role in the adhesive strength of gas hydrates is the presence of a so-called quasi-liquid layer (QLL). ,− Akin to the premelting of ice, , a QLL on a surface of gas hydrates is expected to grow in thickness with increasing temperature and diverges at the thermodynamic equilibrium dissociation temperature of the gas hydrates. The presence of a QLL gives rise to a capillary force between solid contacts, which in turn increases the normal force between gas hydrate particles . Since the past studies on the adhesive strength of gas hydrates mentioned above were carried out at different supercoolings and QLL thicknesses, some variations in the reported values of adhesive strengths are to be expected.…”

Molecular Dynamics Study on the Spontaneous Adsorption of Aromatic Carboxylic Acids to Methane Hydrate Surfaces: Implications for Hydrate Antiagglomeration

“…Nevertheless, some of these free H 2 O molecules can occasionally replace H 2 O molecules in the hydrate at the interface and thus show a slightly higher F 4 value than that of the water molecules in the L2 and R2 layers contacting with the aqueous phase (Figure A,E). Such thin quasiliquid water films have also been observed at the hydrate/gas interface and are supposed to promote the coalescence of hydrate particles by forming capillary liquid bridges among neighboring hydrate particles. ,, It is worth mentioning that in the practical oil and gas transportation pipelines, the water molecules in the capillary liquid bridges may also come from the original liquid water existing in the pipelines, not just from the liquid-like water decomposed from the interfacial hydrate. With the presence of aromatic carboxylic acids in the systems, similar changes in the F 4 values (Figure B–D,F–H) and in the interfacial hydrate structures are also observed, further confirming the impacts of liquid-phase environments.…”

Surface Science in the Research and Development of Hydrate-Based Sustainable Technologies

“…132−135 Nguyen et al quantified the QLLinduced capillary adhesion involved in these systems. 131 The measured adhesion force between a silica sphere and a THF hydrate surface exhibits three distinct temperature-dependent regimes (Figure 11). First, low adhesion forces were observed at temperatures below −5 °C, possibly due to the vanishing or discontinuity of the QLL at low temperatures that make the hydrate surfaces behave like typical solids with only vdW forces acting.…”