Effect of CO 2 on the structure and reactivity of char at different isothermal holding times

This study investigates the effects of CO2 atmosphere and isothermal holding times (0, 30, 60 min) on the physicochemical structure and gasification reactivity of chars, with experiments conducted under N2 atmosphere as the control reference. The structural characteristics of the resultant chars were analyzed via nitrogen adsorption, Raman spectroscopy, and scanning electron microscopy. The CO2 gasification reactivity of both raw and demineralized chars was evaluated using a thermogravimetric analyzer (TGA). The results demonstrate that, with increasing isothermal holding time, char yield decreased substantially under CO2 (from 73.8% to 59.5%), whereas under N2, it decreased from 74.0% to 72.9%, confirming the occurrence of concurrent CO2 gasification during pyrolysis. BET surface area increased from 243 to 426 m2/g under CO2, far exceeding the 71 to 126 m2/g under N2. Compared with chars prepared under N2 atmosphere, chars produced under CO2 atmosphere exhibit a lower ratio of small to large aromatic rings, as well as higher gasification reactivity. The gasification reactivity of char-CO2 increases with prolonged holding time; in contrast, demineralized char-CO2 exhibits the opposite trend. This phenomenon can be ascribed to the evolution of pore structure and the enhanced dispersion of minerals induced by pyrolysis under CO2 atmosphere.