CO2 capture performance of tubular MgO and stability analysis

https://doi.org/10.1039/D2NA00213B

“The CO₂ capture performance of MgO-based sorbents during 30 cycles of carbonation–calcination was measured by TG-DSC, and the results are shown in Fig. 3. Weight profiles of MgO-based sorbents during carbonation (indicated as increments) and calcination (indicated as decrements) are shown in Fig. 3(a). MgO conversion (X_N) as a function of cycle number is given in Fig. 3(b). In Fig. 3(a), MgO-based sorbents exhibit different reaction patterns according to their weight profiles. The MgO/CNT_N₂ sample exhibited a continuous decrement of calcined weight, particularly in the early stages, and then the carbonation–calcination reactions were almost inactivated. On the other hand, the MgO/CNT_Air sample exhibited more stable patterns in each cycle, although slightly fluctuating patterns occurred in the early cycles. The MgO sample exhibited quite different patterns from those of the other samples. The weights of the MgO sample after calcination continuously increased for the first 10 cycles and stabilized for further cycles. The incomplete calcination indicates that MgCO₃ was not fully regenerated to MgO, reducing the available MgO for the next CO₂ capture cycle. The reason for incomplete calcination can be found in the work of Maya et al.,²⁸ in the CaCO₃–CaO reaction system. They claimed the “die-off” phenomenon that the CO₂ catalyzed sintering of the product CaO layer on the particle surface causes covering of the inner CaCO₃ by surface CaO. The reaction pattern of the MgO sample follows the die-off phenomenon. In this situation, higher regeneration energy is required because the inner MgCO₃ layer requires energy for thermal decomposition and CO₂ escape through the surface MgO layer. The agglomerate-based morphology of the MgO sample might induce surface layer sintering for die-off. Interestingly, the multiple carbonation–calcination reactions of MgO/CNT_Air were relatively stable, particularly compared to the case of the MgO sample. This indicates that the modified morphology of MgO/CNT_Air possibly requires less regeneration energy. Note that the reaction conditions of the multiple carbonation–calcination were set identically for MgO, MgO/CNT_Air, and MgO/CNT_N₂.”

“Fig. 3 CO₂ capture performance of MgO-based sorbents for 30 cycles of carbonation–dissociation measured by TG-DSC. (a) Normalized weight (wt%) profiles and (b) MgO conversion (X_N). Weight profiles are normalized according to each weight of pristine MgO-based sorbents.” “For MgO/CNT_N₂, the MgCO₃ in the MgCO₃/CNT powder was thermally decomposed to MgO at 450 °C for 2 h in a tube furnace purged with N₂ gas. For MgO/CNT_Air, the MgCO₃ and CNT in the MgCO₃/CNT powder were thermally decomposed to MgO at 450 °C for 2 h in a tube furnace purged with air. For the MgO control sample, the prepared MgCO₃ was thermally decomposed at 450 °C for 2 h in a tube furnace purged with N₂ gas. “