CO2 captures and sequestration by gas hydrates in marine environments: chemical characterization of natural organic compounds, sediments and their influences

Climate change is known to be predominantly caused by the increasing amount of greenhouse gases in the atmosphere, in particular as CO2. To prevent excessive accumulation of CO2 in the atmosphere, it is therefore necessary to implement countermeasures through capture and sequestration, that can slow down the increasing of carbon dioxide. The sequestration of carbon dioxide (CO2) in the form of gas hydrates presents a promising strategy for mitigating climate change by securely storing CO2 in marine environments. Gas hydrates are crystalline structures consisting of water molecules organized in cages which encapsulate different guest molecules, like CO2; they are formed at low temperature and high-pressure conditions, commonly found in deep-sea; thus, the marine environment offers ideal conditions for hydrate formation, with natural sediments acting as reservoirs [1]. This study focused on the characterization of natural occurring compounds, and sediments, and aims to analyse and uncover their effects on the CO2-gas hydrates formation; this characterization is important since most of scientific studies are focused on the addition of chemicals, that would nullify the properties of gas hydrates in the storage of carbon dioxide without further emission of compounds in the environment. To find their effects, different tools were needed, starting from the sampling of sediments and seawater, with their subsequent sample preparation for analytical analysis, exploiting pore water extraction from sediments and solid phase extraction for the pre concentration of natural occurring compounds. The analytes were then identified with chromatographic techniques like HPLC-DAD-FLD, HPLC-MS and Q-TOF. Conductivity and pH of seawater and pore water were evaluated, and the ionic composition were determined through IC and ICP-MS analysis. Characterization tools were then applied, both for the direct study of CO2-gas hydrates structure and for sediments role evaluation, exploiting FE-SEM and RAMAN studies [2]. In particular, the RAMAN results suggested that, examining the ice structure and the behaviour of the -OH vibrational bands, valuable information can be obtained and favourable used for predicting the structure of gas hydrates and understanding the interactions between water molecules and sediments during gas-hydrate formation. The aim of this study falls within the PRIN 2022 PNRR project entitled “Reliable long-term CO2 storage as clathrate hydrates in seawater and marine sediments (CO2-RESTO)”, funded by the European Union – Next Generation EU and led by the University of Perugia, the University of Camerino, and the OGS Institute as a research unit.