Morphology study of methane–propane clathrate hydrates on the bubble surface in the presence of SDS or PVCap

The characteristics of methane–propane hydrate crystal growth on the surface of gas bubble in pure water were investigated using optical microscope and compared with those in aqueous solutions of sodium dodecyl sulfate (SDS) or poly-N-vinylcaprolactam (PVCap). Most of morphology works in literature mainly focused on the hydrate crystal growth at the gas/water interface or surface of water droplets. However, this study monitors crystal growth at the bubble surface. In the case of pure water, smooth hydrate film was formed initially and the film surface on the bubble became rough as experiment proceeded. It was also observed that the hydrate crystals developed as the dendritic shape from the surface of hydrate film. In the presence of SDS, drastic changes in morphology were observed in that smoke-like crystals appeared from the top of the bubble. Besides, the gas bubble was not fully covered by hydrate film when the SDS concentration increased. In the PVCap solution, seed-like or small spot of hydrate crystals occurred sparsely on the bubble surface and spread out the whole surface as experiment progressed. The experimental results showed that the presence of SDS or PVCap affect morphological characteristics of methane–propane hydrate crystal on the surface of gas bubble. •We monitored hydrate crystal growth at the bubble surfaces.•In pure water hydrate crystal was initiated by the formation of a hydrate film.•With SDS solution hydrate formation occurred mainly at the bubble top in smoke shape.•In the case of addition of PVCap, hydrates like scattered seeds occurred on the film.