Metal oxide-stabilized calcium oxide CO2 sorbent for multicycle operation

• Limestone stabilization by incorporation of inert metal oxides (Al, Zr, Y, Mg).
• Application of novel two-step calcination along with limestone acidification.
• Enhanced stability of stabilized sorbent in cyclic operation compared to CaO.
• Zr-stabilized CaO shows the best results in severe operating condition.

This work proposes a number of metal oxide (M: Al, Zr, Mg and Y)-stabilized calcium oxide (CaO) CO2 sorbents directly produced from two-step calcination (argon and air atmospheres) of acidified natural limestone sources. The incorporation of a metal support into the CaO structure during limestone acidification step mainly aims to enhance sorbent stability. This study is focused on (i) the determination of the optimum mixing ratios, (ii) the analysis of the effect of precursor (soluble or insoluble) on sorbent activity, as well as (iii) the investigation of the influence of calcination atmosphere on sorbent durability and activity. A M/Ca molar ratio of 0.1 was found to offer the optimum composition to obtain the best activity for Zr- and Al-stabilized CaO samples under mild operating condition, while a M/Ca ratio of 0.4 was the optimum ratio for Mg-stabilized sorbent. The activity of metal (Zr, Al and Mg)-stabilized CaO sorbents with optimum composition was also investigated during severe operation condition (presence of CO2 in the calcination atmosphere), where an intensification of structural sintering is usually expected. The results indicated a considerable sorbent stability improvement for the metal oxide-stabilized CaO in comparison to pure CaO which showed significant cyclic capacity decay under similar conditions. Among the studied materials, Zr-stabilized CaO showed the most adequate behavior in severe operating condition. However, the cost impact of Zr-stabilized sorbent might be a matter of concern. On the contrary, Al-stabilized CaO sorbent could be an interesting choice due to low cost of Al-precursors used in the material preparation. The choice of Al-precursors, which was found to affect the sorbent activity, is discussed in detail.