CO₂ hydrate formation in superabsorbent hydrogels for carbon capture—A comparison of water-confined framework vs non-water framework

Abstract

This study investigates the kinetics of CO2 hydrate formation in saturated hydrogel particles—water-confined frameworks—through both experimental and numerical methods, and compares the results with those obtained in silica gels, silicon-based frameworks. Three hydrogel materials with varying swelling ratios were synthesized via radical polymerization. An advanced shrinking core model was developed, incorporating factors of CO2 solubility, gas diffusion, gas–water reaction, capillary effects, and hydrogel functional groups. Results showed rapid CO2 hydrate growth within the first 100 min, with CO2 uptake reaching 78%–82% of the final amount by 600 min. The highest percent water conversion achieved was 96.6%. Simulations indicated a significant decrease in CO2 diffusion coefficient through the hydrate shell over time, especially in hydrogels with higher methacrylic acid content. Capillary effects diminished as the reaction proceeded, with final water consumption via capillaries accounting for 14.4%–26.7% of the total. Hydrogels with higher swelling ratios and higher agglomeration degree formed more porous hydrate shells, enhancing CO2 diffusion but resulting in lower overall CO2 uptake due to their lower water content. Comparisons with hydrophilic porous silica gel revealed that, although hydrogels initially posed greater mass transfer resistance, they ultimately exhibited superior CO2 absorption capacity and rate.