FORMATION AND DISSOCIATION OF CO2 HYDRATES WITHIN A NATURAL BASALTIC-BASED POROUS MEDIUM FROM ICELANDIC MARGINS

Carbon dioxide hydrates were formed and dissociated in a lab-scale apparatus, filled with demineralized water and porous sediments. Two different porous media were tested; the first consists of glass beads, commonly used to reproduce marine environments during lab-scale hydrate formation experiments. Natural basaltic sand, typical of the Icelandic margins, was chosen as second sediment. The role played by the two sediments was analyzed during both the hydrate formation and dissociation processes and the results were compared with each other. In particular, the pressure-temperature values measured during the dissociation phase were compared with the phase boundary equilibrium conditions for pure carbon dioxide hydrates, carried out in the absence of any porous sediment, collected from the scientific literature. The presence of porous sand favored the preservation of hydrates during the dissociation phase; in detail, hydrates melted at pressures 1.1 bar higher (on average) in the presence of glass beads, and 1.0 bar higher with the basaltic sand. The formation was more abundant in the presence of glass beads: 0.227-0.232 mol of hydrates were produced, against 0.141-0.21 mol achieved when the basaltic sediment was used