Experimental study on rapid formation kinetics of CO2 hydrate based on fly ash medium

Hydrate-based marine carbon sequestration is a promising CCUS strategy because of its high gas storage capacity. However, slow hydrate nucleation and growth, together with fluctuations in formation conditions, hinder efficient carbon capture and long-term stable storage. In this study, fly ash was proposed as a medium for hydrate-based marine carbon sequestration, and the kinetics of CO 2 hydrate formation were experimentally investigated in a high-pressure reactor at 3.86 MPa and 274.15 K by varying fly ash type, dosage, and water saturation, as well as temperature, pressure, and additives. Results showed that fly ash promoted hydrate formation through its porous structure and hydration/mineralization-induced interfacial regulation, where the original particle surfaces and in situ generated carbonate products may provide favorable environments for hydrate nucleation, shortening the induction time by about 80% (<20 min), and accelerated hydrate formation. Class C fly ash was more effective than class F fly ash in reducing induction time, but its stronger competition for free water and more intense chemical competition lowered gas storage capacity. In slurry systems, fly ash increased gas storage capacity by 131% to 0.14 v/v compared with static porous-medium conditions, with an optimal slurry concentration of 40 wt%. Addition of 1 wt% L-methionine further reduced the induction time to 19 min and increased gas storage to about 1.9 mol, whereas 3.5 wt% salinity inhibited hydrate formation and intensified particle floating. Under a driving force of 4.5 MPa and a subcooling of 10 K, the induction time was shortened to 11 min. hydrate cementation and gel formation enhanced particle–hydrate interactions, generating a relatively compact fly ash–hydrate composite structure with potential for improving sequestration stability.