Mitigating climate change: investigating the synergistic effects of nanobubbles and gas hydrates for enhanced carbon capture

Given the scale and urgency of the climate crisis, the exploration of innovative approaches for greenhouse-gas CO₂ capture and sequestration is imperative. This hinges on capturing of CO₂ emissions from sources, and storing it into other long-lived, stable carbon “pools” or “sinks”, such as in the form of gas hydrates. Being crystalline solids, gas hydrates have the ability to store gas effectively therein –with gas molecules “imprisoned” in cavities within an otherwise ice-like lattice. To address the limitations of hydrate-based methods for carbon capture, such as stability, scalability, and environmental impacts, gas-nanobubble technology may be integrated into hydrate formation to enhance the efficiency and viability of gas-hydrate formation. Nanobubbles (NBs) have been confirmed to accelerate gas-hydrate crystallisation through the so-called memory effect. However, the mechanism of interactions between NBs and hydrate crystals has not been fully addressed. It is also vital to investigate the optimal conditions for hydrate formation in the presence of NBs for higher stability and scalability.

In this study, a novel method, combining NBs and gas hydrates to enhance the capturing of CO₂, is reported. It aims to demonstrate the effects of NBs on hydrate-formation kinetics, and reveals the mechanism of their interactions during the hydrate-crystallisation process by an integration of laboratory experiments and molecular dynamics simulations. NBs were generated by external electric fields with CO₂ gas in deionized water. By controlling the processing time and applied voltage, different size and concentration of NBs were expected. DLS measurements were applied to characterise the generated NBs. The kinetic properties of CO₂ hydrate formed by NBs solution were analysed experimentally. Numerical dynamics simulations were also applied to simulate the hydrate-formation process in the presence of CO₂ NBs with different concentrations. These modelling efforts help in predicting the behavior of the system under different conditions. The simulation results revealed that throughout the growth process, the size and shape of NBs changed, progressively reducing in size. It appears that the hydrate clusters absorbed gas molecules from the surrounding gas clusters, leading to the disappearance of the NB in some systems. These bubble remains in the vicinity of the hydrate interface and supplies CO₂ for the hydrate growth. When these bubbles reached a critical size where stability was compromised, they collapsed, resulting in a localized increase in CO2 concentration in the aqueous phase, further promoting hydrate growth. The interaction between water and CO₂ molecules increased as the hydrate surface absorbed the gas molecules from the solution and consumed them to form new hydrate cavities. Therefore, CO₂ molecules have less preference to interact with each other and thus the gas clusters were shrinking during the simulation.

The outcome of this study deepens the understanding of nanobubble dynamics and addresses the critical role of nanobubbles in CO₂ hydrate-crystallization processes - directly contributing to the mitigation of climate-change impacts.