MODELING STUDY OF CARBONATION MECHANISMS OF CO2−CaO AND CO2−NaOH REACTIONS

Abstract

Calcium oxide (CaO) and sodium hydroxide (NaOH) have been used among various solid sorbents for CO2 capture. Therefore, it is necessary to study the major controlling steps between the reactions of CO2 and solid sorbents. The CO2 uptake and the rate constant of the CO2-CaO and CO2-NaOH reactions were investigated using atmosphere thermogravimetric analyzer (ATGA) to understand its reaction mechanisms and speed span. A shrinking core model was utilized to determine the rate controlling steps, mass transfer coefficient, diffusion coefficient, and the time for complete conversion of a particle at ash diffusion controls regime. The results have been shown that the time for complete conversion of CaO and NaOH particles is chemical reaction controls regime for carbonation cycle. The chemical reaction was found to be the major controlling step reaction at initial minutes. After that the product layer diffusion became gradually more dominant controlling step in CO2-CaO and CO2-NaOH reactions. Therefore, the results been shown that diffusion mechanism is the main dominant regime for the remaining reaction cycle. These outcomes contribute to the understanding of how CO2 reacts with CaO and NaOH solid sorbents at various temperature ranges.