CO2 Capture and Sequestration by Gas Hydrates: An Overview of the Influence and Chemical Characterization of Natural Compounds and Sediments in Marine Environments

Due to the rising atmospheric carbon dioxide levels driven by human activity, extensive scientific efforts have been dedicated to developing methods aimed at reducing its concentration in the atmosphere. A novel approach involves using hydrates as a long-lasting reservoir of CO2 sequestration. This review provides an initial overview of hydrate characteristics, their formation mechanisms, and the experimental techniques commonly employed for their characterization, including X-ray, Raman spectroscopy, cryoSEM, DSC, and molecular dynamic simulation. One of the main challenges in CO2 sequestration via hydrates is the requirement of high pressures and low temperatures to stabilize CO2 molecules within the hydrate crystalline cavities. However, deviations from classical temperature-pressure phase diagrams observed in natural and engineered environments can be explained by considering that hydrate stability and formation are primarily governed by chemical potentials, not just temperature and pressure. Activity, which reflects concentration and non-ideal interactions, greatly influences chemical potentials, emphasizing the importance of solution composition, salinity, and additives. In this context the role of promoters and inhibitors in facilitating or hindering hydrate formation is discussed. Furthermore, the review presents an overview of the impact of marine sediments and naturally occurring compounds on CO2 hydrate formation, along with the sampling methodologies used in sediments to determine the composition of these natural compounds. Special attention is given to the effect and chemical characterization of dissolved organic matter (DOM) in marine aquatic environments. The focus is placed on the key roles of various natural occurring molecules, such as amino acids, protein derivatives, and humic substances, along with the analytical techniques employed for their chemical characterization, highlighting their central importance in the CO2 gas hydrates formation.