Zr-Doped CaO for CO2 capture

https://doi.org/10.3390/en13164110

“The Zr-doped CaO sorbents were prepared by the mechanical mixing of CaCO₃ powder (99.5%, Sigma-Aldrich, Saint Louis, MO, USA) and baddeleyite concentrate powder (99.3%, Kovdorsky GOK, Kovdor, Russia), taken in amounts required to obtain the Zr/Ca molar ratios of 1:10, 2:10 and 3:10 in the sorbent, followed by wet high-energy co-milling in a planetary mill Pulverisette 7 Premium Line (Fritsch, Idar-Oberstein, Germany) for 5 h using 1.5 mm beads of stabilized zirconia. The mass ratio of the mixed powder, distilled water and milling media was 1:3:10. The grinding product we dried in air atmosphere at 80 °C for 24 h in an oven OV-11 (Jeio Tech Co., Ltd., Seoul, Korea). The reference undoped CaO sorbent (0:10) was fabricated in the same way. Wet high-energy milling in the planetary mill with the similar parameters was used previously for baddeleyite treatment to prepare nanostructured ZrO₂ powder [16].”

“For all the sorbents, an evaluation of their CO₂ uptake capacity in multiple carbonation–calcination cycles was performed (Figure 1). The pure CaO sorbent showed a rather high initial capacity of 16.1 mmol/g since the stoichiometric capacity of CaO was 17.9 mmol/g. However, after the 3rd cycle, its capacity started to decrease rapidly reaching 1.2 mmol/g in the 24th cycle and then continued to decrease slowly to a steady-state value of about 1.0 mmol/g. Adding ZrO₂ resulted in a sorbent initial capacity reduction. The dopant was inactive for CO₂ capture which reduced the initial CO₂ uptake capacity of the material on a weight basis. The rise in the Zr/Ca molar ratio from 0:10 to 3:10 led to a sorbent initial capacity decrease from 16.1 to 8.1 mmol/g. Although the capacity of the Zr-doped CaO sorbents was initially lower than that of the undoped one, it showed better stability in time with the Zr/Ca molar ratio increase. A decrease in capacity of 15.1, 8.2, 1.9 and 1.8 mmol/g in relation to the initial value was registered in the 50th cycle for sorbents with the Zr/Ca molar ratio of 0:10, 1:10, 2:10 and 3:10, respectively. Among the fabricated sorbents, the one with the Zr/Ca molar ratio of 2:10 (hereinafter referred to as the Zr-doped CaO sorbent) showed the best performance in terms of capacity value and its cyclic stability.”

“During the multi-cycle carbonation–calcination process, the Zr-doped CaO sorbent prepared by wet high-energy milling showed the CO₂ uptake capacity steady-state value of 8.6 mmol/g exceeding those of the Zr-doped CaO sorbents with the same Zr/Ca molar ratio previously synthesized using a more laborious sol–gel technique [14] and a surfactant-template/ultrasound-assisted method [19].”

“Figure 1. The dependencies of the CO₂ uptake capacity of the sorbents with different Zr/Ca molar ratios on the number of carbonation–calcination cycles.”