Unlocking the potential of hydrate-based carbon capture: A review of passive techniques for CO₂ hydrate formation promotion

Active methods for promoting gas hydrate formation, such as agitation, bubbling, and spraying, can lead to increased energy consumption and safety risks. Conversely, studies exploring chemical additives have been extensively reviewed, revealing that these methods often come with certain adverse effects, including reduced gas selectivity, increased mass transfer resistance and shortened lifespan of chemicals involved. However, these adverse effects could be potentially mitigated by using passive methods, which are promising to improve the safety, viability, scalability and lifespan of hydrate-based carbon capture. In this current review paper, passive methods refer to alterations within gas hydrate systems that stimulate hydrate formation without relying on non-mechanical or non-chemical techniques. These passive approaches encompass nano-confinement, surface treatment, suspended nanoparticles, and distributed hydrate systems. The promotion mechanisms, key features, limitations, and challenges associated with these passive methods are summarised in this paper, which provides guidance for the design of CO₂ hydrate reactors for effective carbon capture.