Enhancement of Ca‐Based Sorbent Multicyclic Behavior in Ca Looping Process for CO₂ Separation

Abstract

The Ca-based sorbent looping cycle represents an innovative way of CO 2 capture for power plants. However, the CO 2 capture capacity of the Ca-based sorbent decays sharply with calcination/carbonation cycle number increasing. In order to improve the CO 2 capture capacity of the sorbent in the Ca looping cycle, limestone was modified with acetic acid solution. The cyclic carbonation behaviors of the modified and original limestones were investigated in a twin fixed-bed reactor system. The modified limestone possesses better cyclic carbonation kinetics than the original limestone at each cycle. The modified limestone carbonated at 640-660°C achieves the optimum carbonation conversion. The acetic acid modification improves the long-term performance of limestone, resulting in directly measured conversion as high as 0.4 after 100 cycles, while the original limestone remains at a conversion of less than 0.1 at the same reaction conditions. Both the pore volume and pore area distributions of the calcines derived from the modified limestone are better than those derived from the original limestone. The CO 2 partial pressure for carbonation has greater effect on conversion of the original limestone than on that of the modified sorbent because of the difference in their pore structure characteristics. The carbonation conversion of the original limestone decreases with the increase in particle size, while the change in particle size of the modified sorbent has no clear effect on cyclic carbonation behavior.

Ca-based synthetic materials with enhanced CO2capture efficiency

“…38,39 Acetication of limestone minimizes the loss of surface area and pore volume as the modied sorbent is cycled over, which gives rise to a considerable increase of the capture capacity for a wide range of particle sizes as seen in Fig. 7.…”

Ca‐Rich Ca–Al‐Oxide, High‐Temperature‐Stable Sorbents Prepared from Hydrotalcite Precursors: Synthesis, Characterization, and CO2 Capture Capacity

“…This loss in capacity is caused by sintering of CaO and CaCO 3 during the adsorption-desorption process, which is particularly detrimental to CaCO 3 because it leads to the aggregation of crystals and a reduction of the surface area and pore volume. To overcome this problem, several methods have been proposed to produce CaO-based sorbents, which include: i) developing a tailored CO 2 sorbent such as CaO from precipitated CaCO 3 , [14,15] ii) improving the porosity of CaO by hydration treatment, [16,17] iii) modifying CaO-based sorbents, [18,19] and iv) synthesizing new CaO-based sorbents. [20,21] Layered double hydroxides (LDHs) are a type of anionic clay of inorganic layered materials and their structural stability is dependent on the temperature and the molar ratio (…”

Enhanced CO2 adsorption capacity and stability using CaO‐based adsorbents treated by hydration

“…23,25 On the other hand, to further improve adsorption performance of sorbents, a variety of methods to modify the freshly prepared sorbents have been reported. [26][27][28][29] Li et al 30 used an ethanol solution to modify CaO sorbents derived from limestone, and obtained an $85% carbonation conversion in the first cycle and an $51% carbonation conversion in the 15th cycle for carbonation at 700 C and calcination at 920 C. It is worth mentioning that sorbents using calcium acetate as a precursor or ethanol treatment have a comparatively high capacity. Nevertheless, the further improvement of capacity and stability is still desirable comparing the maximum theoretical adsorption value (78.6%) and considering commercial capacity.…”