Promoting gas hydrate formation with ice-nucleating additives for hydrate-based applications

Gas hydrates are crystalline icy compounds capturing small gas molecules in the cavities made of hydrogen-bonded water molecules. Hydrates can store a large amount of gas and selectively capture certain gas species depending on thermodynamic conditions and formation pathways. In addition, any impurities that are not stabilized in hydrates are excluded upon hydrate formation. Such interesting properties have allowed the proposal of a variety of hydrate-based applications, including energy storage, CO2 capture, gas separation, and desalination. However, they are not yet utilized as viable technologies, mainly because of the low process efficiency. The major challenges here are to improve the formation kinetics and to enable hydrates to be properly managed in industrial processes. Here, inspired by the similarities in crystallization processes of ice and gas hydrates, we identified the capabilities of two ice-nucleating additives, Icemax® (protein) and Drift® (surfactant), as kinetic promoters for hydrate-based applications. Our experimental results demonstrate that both additives increase the formation kinetics of CH4 (structure I) and CH4/C2H6 (structure II) hydrates under high and low shear. Drift® enlarges the interfacial area at the gas-liquid interface, enhancing the mass transfer, and thus increases the hydrate conversion 18 times under non-stirred cases. Icemax® can better accelerate the initiation of hydrate formation by providing additional nuclei for heterogeneous nucleation. According to visual observations, both additives form porous and soft hydrates, which can be easily handled in industrial scale processes. Major findings confirm the potential of ice-nucleating additives to facilitate hydrate-based applications by improving the production rate and process efficiency.