Fig. 1: Schematic diagram showing methane hydrate nucleation. | Communications Chemistry

Fig. 1: Schematic diagram showing methane hydrate nucleation.

From: Open questions on methane hydrate nucleation

Fig. 1

In the induction stage, increasing methane concentration will slow down molecular mobility, reduce system entropy, and increase free energy. When the critical concentration is reached in a local region near the gas–water interface, a blob forms with methane separated by water. At such high concentrations, water cages occur with a very large probability. Then, water cages adsorb surrounding methane molecules so as to concentrate the methane again. This process is spontaneous, and the adsorption interaction helps the blob to overcome energy barriers with forming a critical hydrate nucleus (i.e., cage clusters). Because the types of the first cage and the linking pattern of the subsequent cage clusters are uncertain, the critical nucleus’ structure is stochastic, leading to multiple pathways: directly forming the crystalline hydrate and indirectly forming the amorphous hydrate followed by an annealing/ripening process to ultimately reach the crystalline hydrate.

Back to article page