(455d) Low Temperature Carbonation of Solid Sorbents By Reactive Milling

CO₂ capture and storage will play a significant role in climate change mitigation. In addition to the industrialized amine-based media, CaO and Ca(OH)₂ have been extensively studied as promising CO₂ capture media due to their ability to form calcium carbonate. In this work the carbonation behavior of calcium-containing sorbents, CaO and Ca(OH)₂, was investigated under pressurized CO₂ at nominal room temperature. The carbonation reaction was mechanically driven via reactive ball milling. The carbonation rate was determined by monitoring the CO₂ pressure inside the sealed milling jar. Two different versions of CaO were fabricated as starting materials. The addition of citric acid in CaO synthesis resulted in a significant increase in sorbent surface area, bringing up the conversion of CO₂ from 18% to 41% after 3 h of reactive milling. The hydroxide formation from these two oxides closed the surface area gap. Nevertheless, we found that hydroxides had a higher initial carbonation rate and greater final CO₂ uptake than their oxide counterparts. However, the formation of byproduct water limited further carbonation of Ca(OH)₂. When we added a controlled amount of water to the CaO-containing milling jar, a high carbonation rate and an extensive CO₂ uptake were attained due to the in situ formation of reactive Ca(OH)₂ nanoparticles. We saw CaCO₃ X-ray diffraction peaks only when Ca(OH)₂ was involved in this low-temperature carbonation, indicating that the grain growth of the CaCO₃ is easier on the Ca(OH)₂ surface than on the CaO surface. Finally, CaO was in situ functionalized with 3-aminopropyl-triethoxysilane (APTES) aqueous solution during milling. This amine-based modification led to a higher CO₂ conversion. We used the Friedman isoconversional method to calculate the effective activation energy of decarbonation for the tested sorbents. The trend in the observed effective activation energies was correlated to our sorbent preparation conditions.