Development of a CaO-Based CO₂ Sorbent with Improved Cyclic Stability

Abstract

The carbonation of CaO is an attractive method for removing CO2 from hot gas mixtures. However, regeneration and reuse of a CaO-based sorbent causes a gradual decline in absorption capacity, which ultimately limits the life of the material. Various methods have been proposed for increasing the life cycle performance of a CaO-based sorbent. Two of these methods were selected for further investigation. One method incorporates an "inert" material in the sorbent, while a second method stabilizes the sorbent through controlled sintering. Promising results were achieved with both methods when they were applied separately to a sorbent derived from a natural limestone. In one case MgO was finely dispersed within the sorbent, where it served as an "inert" material in the sense that it did not absorb CO2. A concentration of approximately 20 wt % appeared to be nearly optimal. In a second case the sorbent was stabilized by calcining the material at 1100°Cfor 5 h. Although neither method produced a completely stable material, the stability of the sorbents was improved sufficiently so that by the end of a 1200-cycle test the absorption capacity of either of the treated sorbents was 45% greater than that of an untreated sorbent and the rate of decline was very small. The carbonation of CaO is an attractive method for removing CO 2 from hot gas mixtures. However, regeneration and reuse of a CaO-based sorbent causes a gradual decline in absorption capacity, which ultimately limits the life of the material. Various methods have been proposed for increasing the life cycle performance of a CaO-based sorbent. Two of these methods were selected for further investigation. One method incorporates an "inert" material in the sorbent, while a second method stabilizes the sorbent through controlled sintering. Promising results were achieved with both methods when they were applied separately to a sorbent derived from a natural limestone. In one case MgO was finely dispersed within the sorbent, where it served as an "inert" material in the sense that it did not absorb CO 2 . A concentration of approximately 20 wt % appeared to be nearly optimal. In a second case the sorbent was stabilized by calcining the material at 1100°C for 5 h. Although neither method produced a completely stable material, the stability of the sorbents was improved sufficiently so that by the end of a 1200-cycle test the absorption capacity of either of the treated sorbents was 45% greater than that of an untreated sorbent and the rate of decline was very small.

CO2 multicyclic capture of pretreated/doped CaO in the Ca-looping process. Theory and experiments

“…The effect of thermal pretreatment on multicyclic CaO conversion has been extensively analyzed by Manovic and co-workers in a series of papers [17,19,20] as well as by other authors in the last years [18,[21][22][23]29], being a subject of current debate in the literature [8,24,31]. The influence of preheating temperature, exposition time, type of atmosphere, type of sorbent, presence of additives, pre-hydration, pre-grinding and looping-carbonation conditions is thoroughly analyzed in these works.…”

“…Generally, Eq. 10 may describe the diversity of behaviors observed for pretreated sorbents in the first cycles [17][18][19][20][21][22] depending on the relative values of a, b and β such as the presence of a maximum of conversion at a certain value of N . This maximum will exist in the case b > a and β < 1 and will be placed at a cycle number N 0…”

Enhanced cyclic stability of CO2 adsorption capacity of CaO-based sorbents using La2O3 or Ca12Al14O33 as additives

“…They showed that a weight ratio of CaO to Ca 12 Al 14 O 33 of 75 : 25 that is subjected to calcination at 900 o C for 1.5 h is optimal for preparing this sorbent. A CaO conversion of this sorbent was 65% after 50 cycles, when it was carbonated at 650 o C. Albrecht et al [17] suggested that incorporating finely dispersed MgO or of CaO activity during high temperature reactions. They also found that the sorbents subjected to the more severe initial calcination conditions can have higher adsorption capacity after many cycles.…”

Multicyclic conversion of limestone at Ca-looping conditions: The role of solid-sate diffusion controlled carbonation

“…Current directions of research aimed at this goal are the modification/synthesis of Ca-based sorbents [16,17] and reactivation of natural limestone either by steam [18,19] or heat pretreatment [20][21][22][23][24][25][26][27][28]. Lysikov et al…”