High-temperature CO₂ sorption over Li₄SiO₄ synthesized from diatomite: study of sorption heat and isotherm modeling

The Li₄SiO₄ seems to be an excellent sorbent for CO₂ capture at post-combustion. Our work contributes to understanding the effect of the natural Algerian diatomite as a source of SiO₂ in the synthesis of Li₄SiO₄ for CO₂ capture at high temperature. For this purpose, we use various molar % (stoichiometric and excess) of calcined natural diatomite and pure SiO₂. To select the best composition, CO₂ sorption isotherms at 500 °C on the prepared Li₄SiO₄ are obtained using TGA measurements under various flows of CO₂ in N₂. The sorbent having 10% molar SiO₂ in diatomite (10%ND-LS) exhibits the best CO₂ uptake, probably due to various factors such as the content of the different secondary phases. A comparative study was performed at 400 to 500 °C on this selected 10%ND-LS and those with stoichiometric composition obtained with diatomite and pure SiO₂. The obtained isotherms show the endothermic character of CO₂ sorption. In addition, the evolution of isosteric heat highlights the nature of the involved CO₂/Li₄SiO₄ interactions, by considering the double-shell mechanism. Finally, the experimental sorption isotherms are confronted with some well-known adsorption models to explain the phenomenon occurring over our prepared sorbents. Freundlich and Jensen-Seaton models present a better correlation with the experimental results.