Influence of CO2 concentration for Li4SiO4 based carbon capture

Pacciani et al. [71] reported that the CO₂ absorption rate of Li₄SiO₄ material rose apparently when CO₂ concentration in absorption atmosphere increased from 2.5 to 24.5 vol.%. Essaki et al. [77] prepared the pelletized Li₄SiO₄ materials with an average particle size of 5 mm and K₂CO₃ and Li₂ZrO₃ were doped into the materials to promote the absorption reaction and prevent reduction of absorption capacity, respectively. The absorption property of Li₄SiO₄ pellets was investigated in 5 vol.% CO₂ at first, and they found that 500 °C was the most appropriate temperature in the range of 400–600 °C for the CO₂ absorption by Li₄SiO₄. However, when the absorption tests were carried out in 10 or 15 vol.% CO₂, it was found that the CO₂ absorption capacity rose as the temperature increased from 400 to 600 °C. Essaki et al. [77] ascribed this phenomenon to the influence of reaction equilibrium, as shown in Figure 12. The equilibrium temperature of CO₂ absorption and regeneration showed an increasing trend with increasing CO₂ concentration, and the weight increase was used to evaluate the CO₂ absorption performance of Li₄SiO₄ material, which can be calculated according to Equation (11):

where I_N is the weight increase of Li₄SiO₄ material during the Nth cycle, wt.%; W_N is the weight gain, wt.%; N is the number of cycles. It was also noteworthy that the CO₂ absorption process of Li₄SiO₄ was limited in low CO₂ concentration (5 vol.%), while it was controlled by the diffusion of Li⁺ and O²⁻ in high CO₂ concentration (15 vol.%).”