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

Abstract

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.