CO₂ Absorption Studies on Mixed Alkali Orthosilicates Containing Rare-Earth Second-Phase Additives

Abstract

Lithium silicate containing eutectic orthosilicate mixtures developed by a solid-state route displayed excellent characteristics as carbon dioxide absorbents at elevated temperature, showing absorption capacity of 256 mg g −1 . Incorporation of second-phase materials was investigated as a strategy to enhance the stability of the absorbent materials against agglomeration and sintering during powder processing and high-temperature cyclic absorption/desorption loading. Yttrium oxide, gadolinium oxide, and lanthanum phosphate were added as second phases to the absorbent. It was found that when the composites were rich in absorbents (10:1 and 20:1 absorbent/second phase), the absorption performance was hardly influenced by the type of the secondphase material present. Yttrium oxide or gadolinium oxide additions in large quantities were found to enhance the absorption capacity of the orthosilicate phase. The 2:1 sample containing yttrium oxide gave absorption capacity of 315 mg g −1 of orthosilicate absorbent present in the composite sample. On the basis of the structural and morphological studies, we believe that the nonreactive second-phase components formed a virtual shell against the segregation of absorbent phase, thereby helping to improve their absorption performance. Cyclic studies have supported the superior stability and performance of such composite absorbent materials.

Surface modification induced enhanced CO2 sorption in cucurbit[6]uril, an organic porous material

“…[1][2][3] The selective adsorption of CO 2 from industrial gaseous wastes and flue gases, followed by its recycling/removal, is therefore a research topic of prime importance. [4][5][6][7][8][9][10] The inherent ability of amine solutions to capture CO 2 selectively from flue gas through the absorption between amine and CO 2 molecules is well established in the literature. [11][12][13][14] However, the handling and corrosion issues associated with the use of liquid amines and the loss of liquid amine at working temperatures remain the main drawbacks of these kinds of materials.…”

Germanium-incorporated lithium silicate composites as highly efficient low-temperature sorbents for CO2 capture

“…However the use of high temperature can induce compositional changes due to the sublimation of lithium during irradiation leading to poor absorption and kinetics during the sorption process. We have earlier reported the synthesis of Li 4 SiO 4 through microwave assisted sol-gel process resulting in the formation of Li 4 SiO 4 nano-rods that displayed near theoretical absorption capacity with enhanced sorption rates [31][32] . However, the CO 2 absorption properties of the pure Li 4 SiO 4 powder were found insignificant below 450 °C.…”

Understanding the flue gas components on the mechanism governing CO2 adsorption on the Li4SiO4 surface

“…Kato and Nakagawa first synthesized Li 4 SiO 4 from Li 2 CO 3 and SiO 2 precursors via a solid‐state reaction route. In later studies, identifying potential silicon sources and Li precursors , emerging synthesis routes (impregnated suspension , precipitation , carbon templating , and sol‐gel methods ), and the incorporation of hetero elements into the Li 4 SiO 4 crystal structure have been substantially used to prepare effective Li 4 SiO 4 sorbents. Despite these improvements in capture capacity, most sorbents still suffer from slow kinetics at low CO 2 partial pressures .…”

“…The particle size/pore structure of the sorbent, doped elements, adsorption temperature, and flue gas components all play essential roles in the adsorption reaction, thereby making the specific mechanisms significantly complex. For CO 2 adsorption on pure Li 4 SiO 4 , it has been widely reported that rapid and chemically controlled chemisorption is followed by slow Li + and O 2‐ diffusion, which was based on shrinking core, double‐exponential, and Avrami–Erofeev models . According to this mechanism, small‐sized sorbents reduced the diffusive limitations, allowing Li 4 SiO 4 to achieve fast diffusion; meanwhile, higher surface areas improved the chemisorption process.…”