Evaluation of MgO- and CaZrO3-promoted CaO-based pellets produced via solution combustion synthesis

Abstract

Synthetic CaO-based sorbents stabilized with CaZrO3 and MgO were produced using a facile one-step fabrication procedure. Powdered sorbents were pelletized using two types of binders (calcium aluminate cement and boehmite) to shape the solids into forms suitable for reactor testing and evaluation under industrially relevant conditions. The CO2 uptake capacity and stability of pelletized sorbents were initially screened in a thermogravimetric analyzer, and subsequently assessed in a fixed and fluidized bed reactor. Sorbents showed a residual uptake capacity of 0.24 g/g after 100 cycles of carbonation and calcination in TGA, indicating a near threefold improvement over the residual CO2 uptake of natural Cadomin limestone (0.08 g/g). Similar improvements were observed when the sorbents were tested in a lab-scale reactor system, where the synthetic sorbents showed 0.4–0.45 g/g uptake after 5 cycles, whereas the uptake of Cadomin dropped to 0.15 g/g. Characterization of fresh and spent sorbents indicated an increase in the BET surface area of sorbents after cycling. Pore size distribution profiles exhibit increase of pore volume in the 20–100 nm region, whereas the pore volume in the < 6 nm region reduced. SEM images indicated formation of cracks after cycling, resulting from the expansion and contraction of sorbent over carbonation and calcination cycles.