Experimental and modeling insights into the kinetics of calcium looping CO2 capture process: Assessment of limestone treatment

This investigation aimed to offer a precise and detailed understanding of the intricate mechanisms governing the rapid and diffusion stages of carbonation within the calcium looping process, while also exploring the effects of treatment on mineral limestone (Raw limestone) as the primary sorbent for CO2 capture. Two modified samples treated with acetic acid (Acidified limestone) and hydrophobic silica nanoparticles (Silica-mixed limestone), were analyzed to provide deeper insights into the kinetics of the slow and fast stages of the carbonation reaction. The Acidified limestone had a significant influence on the carbonation conversion rates of both the rapid and slow stages, resulting in a notable enhancement in conversion efficiency. Notably, the carbonation conversion rates in the 20th cycle were measured as 0.201, 0.348, and 0.231 for the Raw, Acidified, and Silica-mixed limestones, respectively. An increase in the number of reaction cycles led to an increased percentage contribution of the diffusion stage, a decrease in transition time and consequently, a reduction in the overall carbonation conversion rate. Specifically, the share percentage of carbonation conversion for the diffusion stage in the 20th cycle was determined as 31.55%, 34.88%, and 30.36% for the Raw, Acidified, and Silica-mixed limestones, respectively. The results obtained from the modeling application demonstrated a reduction in the maximum absolute error with an increase in the reaction cycles. Additionally, the prediction results indicated that the carbonation conversion rates for the Raw and Acidified limestones in the 100th cycle were determined to be 0.07 and 0.12, respectively.