Abstract
•The effects of porous surfaces on hydrate nucleation and growth were evaluated.•Surface defects and inner pore convection give rise to numerous nucleation sites.•Hydrate nucleating in inner pore grows into hydrate fibers.•Porous surfaces enhance hydrate dissolution and Ostwald ripening.•Hydrate dissolution/re-growth cycles on porous surfaces were observed.
Porous media were reported to significantly enhance hydrate nucleation and growth kinetics due to abundant specific surface area and pore texture, but the mechanisms behind the promotion remain an open topic, and little is known with respect to hydrate morphologies on porous surface. In this work, we investigated hydrate formation loaded by activated carbon (AC), and the influence of porous surfaces on hydrate nucleation and growth was evaluated. Three hydrate morphologies of rime-like hydrates, hydrate fibers and hydrate chunks appear in turn, which form at surface bulges, inner pores and interstitial pores, respectively. Surface micro bulges and two-way convection in inner pores increase gas–liquid contact area at micro scale and provide numerous potential nucleation sites, so fast hydrate nucleation is anticipated. The induction time is less than 30 min for 52.17% of the experiments, while no induction period was observed for 28.26% of the experiments. Since hydrate fibers grow out form inner pores, their diameter depends on pore size, the average diameter and median diameter of them are 178.25 μm and 147.89 μm separately, and more hydrate fibers were observed under milder conditions, which is completely different from that in bulk water systems. Hydrate dissolution and Ostwald ripening at stable hydrate regimes occur, which is significantly enhanced by porous surfaces, giving rise to hydrate dissolution/re-growth cycles. These findings would shed light on the understanding of hydrate nucleation and growth on porous surfaces.