Calcium oxide is a known adsorbent for the capture of carbon dioxide. In this study, CaO-based sorbents were prepared using the precipitation of solutions containing different anion precursors, including nitrate NO3 – and chloride Cl–, by different alkaline precipitants. The sorbents prepared from the precipitation of salt solutions by alkaline solutions under specific precipitation conditions resulted in the excellent uptake capacity for CO2. These sorbents formed as a fine powder with a BET surface area (16.5 m2/g) and pore volume (0.35 cm3/g) showed almost 100% carbonation, at temperatures between 650 and 750 °C. Moreover, the carbonation proceeded predominantly during an initial short period. Under numerous carbonation/calcination cycles, these sorbents demonstrated a good reversibility. During a 17-cycle operation, the sorbents maintained a fairly high conversion of 70% at 700 °C. As the carbonation/calcination cycles progress, sorbent particles conglomerate to a loosely integrated lump resulting in a greater mass transfer resistance for CO2 molecules to reach the unreacted core of calcium oxide. It is observed that grinding of the formed chunk to fine particles could recover the activity of sorbent completely.

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In this study, a novel approach for the synthesis of zeolite Y is described. The effect of varying the starting silica source on the purity of zeolite Y was investigated, while all other reaction parameters were kept constant. The purity of zeolite was expressed in terms of percent crystallinity obtained from the powder XRD. The silica sources were all powders of varying types (except for silica sol). To study the influence of the varying silica sources on the purity of the resulting zeolite Y, the best gel composition and synthesis condition for one batch were chosen. The gel composition was 4Na 2 O:1Al 2 O 3 :6SiO 2 :200H 2 O. The aging temperature and duration of aging were chosen as room temperature and 120 h, respectively. The synthesis temperature and synthesis time were 100 °C and 48 h. The experiments were all conducted in sealed 30 mL Teflon bottles. The extent to which the pure zeolite Y was formed depended on the BET specific surface area of the silica sources (ranging from 150 to 300 m 2 /g) but not on the synthesis conditions. This novel method for zeolite Y preparation allows one to eliminate the vigorous agitation step required for the preparation of a homogeneous silica solution, thereby simplifying the synthesis of zeolite Y in one single vessel.

Immobilizing amino acid ionic liquids (AAILs) into a porous support is a promising way to fabricate robust solid sorbents with high capacities for CO2 capture. One of important factors to be evaluated toward the practical use is the impact of water vapor in inlet gases on the CO2 capture performance as real flue gases contain some fraction of water vapor. In this study, CO2 sorption–desorption experiments of supported 1-ethyl-3-methylimidazolium amino acid ([EMIM]­[AA]) IL sorbents on porous microspheres were conducted under dry and humidified CO2 inlet conditions using a TGA-MS analysis system, and their outcomes were compared with those of supported amino acids (AA) sorbents. The presence of water vapor changed the CO2 sorption behaviors depending on the sorbent types. In humidified CO2 inlet, the CO2 capture capacities of supported [EMIM]­[glycine] and [EMIM]­[lysine] decreased as the adsorbed water hindered their reaction with CO2, whereas the CO2 capture of those with supported lysine and arginine increased, since water content exerted a positive impact on the CO2 capture behavior.

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Synthetic CaO sorbents were prepared using alumina as a sintering inhibitor via a simple precipitation method. The effects of three mixing procedures on the physical properties and CO2 capture performance of the sorbents were examined. The cyclic CO2 capture performance of the sorbent derived from the precipitation of calcium salts over colloidal alumina (highly dispersed alumina gel) showed the best performance of the three mixing methods. It was found that variation of alumina‐to‐CaO ratios did not significantly change the sintering influence on the sorbent capacity in cyclic operations. CaO particles homogeneously mingled with alumina at higher ratios. Sintering prevention, however, was not observed. This important observation indicates that alumina appeared to merely act as a binder for the fabrication of mechanically enhanced strength particles that are suitable for large‐scale operations. It was determined that CO2 uptake was not dependent on either the mixing technique or the type of synthetic materials incorporated into a sorbent in cyclic operation. The sorbent derived from the precipitation of calcium salts over colloidal alumina with an alumina‐to‐CaO ratio of 20:80 achieved the highest CO2 uptake of 13.1 moles/kg sorbent for half an hour of carbonation in the first cycle and retained a sorption capacity of 6.5 moles/kg sorbent after 17 successive cycles (50 % activity loss), which is in agreement with the reported results. It was demonstrated that the quantity of CO2 uptake increased moderately with decreasing sorbent particle sizes. The effect of pressure on sorbent CO2 uptake was insignificant.