Eggshell as a Carbon Dioxide Sorbent: Kinetics of the Calcination and Carbonation Reactions

This study investigates the calcination and carbonation reaction kinetics of eggshell. Nonisothermal (dynamic) thermogravimetry using multiple heating rates was conducted to study the calcination process. On the other hand, isothermal conditions were applied to report on the carbonation process in a carbon dioxide (CO2) atmosphere. Several model-based and isoconversional kinetic methods were used to evaluate the calcination kinetic parameters. The methods include the Friedman, Coats and Redfern, modified Coats and Redfern, Kissinger, Flynn-Wall-Ozawa, and Kissinger-Akahira-Sunose methods. Furthermore, an analytical solution method was developed to evaluate the kinetic parameters and to predict the experimental conversion. The carbonation reaction was modeled with a modified form of the shrinking core model. Both the rapid surface reaction-controlled and the slow diffusion-limited stages of carbonation were analyzed. The results showed that the kinetic parameters obtained with the various methods are in good agreement with each other, and the computed average activation energies for calcination are in the range of 209-221 kJ mol(-1). It is also observed that the activation energy of the calcination reaction varies with the extent of conversion, suggesting that the mechanism is not a single-step type. In addition, the results showed that the carbonation reaction mechanism of the eggshell is controlled by the combination of surface reaction and product layer diffusion. An activation energy of 49.6 kJ mol(-1) was obtained for the chemical reaction stage and 72.5 kJ mol(-1) for the diffusion-limited stage for carbonation temperatures from 500 to 700 degrees C.