Evaluation of 1,3-dioxolane in promoting CO2 hydrate kinetics and its significance in hydrate-based CO2 sequestration

To reduce anthropogenic CO2 emissions for the mitigation of climate change require novel CCUS solutions. Hydrate-based CO2 sequestration (HCS) is a novel carbon-neutrality technology that aims to store CO2 in solid hydrate form with long-term stability. However, imminent issues exist for the application of HCS in terms of demanding thermodynamic conditions, slow formation kinetics, and low CO2 gas uptake. These challenges necessitate the quest for an efficient and eco-friendly CO2 hydrate promoter. In this study, 1,3-dioxolane (DIOX) as a low-toxicity CO2 hydrate promoter was systematically examined. The phase equilibria, cage occupancy, and the kinetics of binary CO2 + DIOX hydrate were measured for DIOX concentrations (C-DIOX) varying from 0.05 mol% to 5.56 mol%. It was confirmed that DIOX is a dual-function promoter for CO2 hydrate, but its promotion effect is weakened for C-DIOX between 0.60 mol% and 1.00 mol% and for all C-DIOX at relatively high pressure. The CO2 uptake in the hydrate phase increases with C-DIOX above 2.00 mol% and is the highest for C-DIOX = 5.56 mol% (57.08 +/- 6.39 mmol/mol). Based on the morphology observation, hydrate transits from ice-like to slurry to mushy-like and finally to snow-like with increasing C-DIOX. Interestingly, we observed that the aqueous phase separates into two phases (i.e., DIOX-rich and H2O-rich) at pressure above 3.09 MPa, which explains the gradual loss of the promotion effect. The results of our study provide a comprehensive evaluation on DIOX as a possible promoter for CO2 hydrate in HCS application.