CO2-induced pore blocking in dolomite during the carbonation stage of the calcium looping process.

The continuing development of carbon capture technologies, particularly calcium looping (CaL), relies on optimizing sorbent performance and understanding degradation mechanisms. CaL long-term efficiency is compromised by sorbent deactivation, primarily due to pore blockage during carbonation and sintering over repeated calcination/carbonation cycles. This study focuses on elucidating the pore blockage phenomena in a Brazilian dolomite-based sorbent during the carbonation stage. Dolomite samples were subjected to partial carbonation in a vertical tubular reactor for residence times ranging from 0 to 60 min. Thermogravimetric analysis (TGA) was employed to validate the carbonation states achieved during sample preparation, whereas N2 porosimetry was used to monitor the temporal evolution of pore blockage. A novel approach utilizing the Kullback-Leibler divergence was employed to quantify deviations in pore volume distribution caused by carbonation relative to a freshly calcined reference, and the pore size distributions were parameterized using a Beta Probability Density Function (PDF). Porosimetry analysis showed carbonation predominantly affected mesopores in the 30-100 Å range. While pore blockage was initially distributed relatively uniformly across pore sizes, after about 10 min it became increasingly localized within this specific pore size interval, resulting in a progressive shift of the overall distribution toward smaller pores. Notably, even after 60 min of carbonation, a residual pore volume remains available. The proposed methodology successfully quantified the transition from the kinetically controlled to the diffusion-controlled carbonation stage within approximately 5-7.5 min. The Beta PDF provided an excellent fit to the experimental pore size distributions (R2≥0.90), and the proposed correlation for pore blockage dynamics reproduced the experimental behavior with satisfactory accuracy (mean R2=0.76). Overall, this framework demonstrates the potential of combining Beta-PDF modeling and Kullback-Leibler divergence as quantitative tools for investigating pore blockage phenomena in CaL sorbents.