Evaluation of the formation and carbon dioxide capture by LiSiO using in situ synchrotron powder X-ray diffraction studies.

Carbon capture and storage using regenerable sorbents are an effective approach to reduce CO emissions from stationary sources. In this work, lithium orthosilicate (LiSiO) was studied as a carbon dioxide sorbent. For a deeper understanding of the synthesis and carbonation mechanism of LiSiO, an in situ synchrotron radiation powder X-ray diffraction technique was used. The LiSiO powders were synthesized by a combination of ball milling of a LiCO and SiO mixture followed by a thermal treatment process at low temperature. In situ studies showed that formation of LiSiO from the as-milled 2LiCO-SiO mixture involves decomposition of LiCO by reaction with SiOvia LiSiO as an intermediate compound. No evidence of LiSiO formation was obtained, in spite of thermodynamic predictions. The CO capture by LiSiO was evaluated dynamically over a wide temperature range, reaching a maximum weight increase of 34 wt% and good cyclability after about 10 cycles. By thermogravimetric and microstructural analyses in combination with ex situ and in situ measurements, a two step carbonation mechanism and its influence on the final CO capture was clearly elucidated. Under dynamical conditions up to 700 °C, the lower number of LiCO nuclei initially formed retards the double shell formation and the nucleation and growth of the LiCO particles remains the controlling step up to higher CO capture capacity. Isothermal carbonation at 700 °C favours the formation of a higher number of LiCO nuclei that creates a thin carbonate shell. The CO diffusion through this shell is the limiting step from the beginning and further carbonation is hindered as the reaction progresses.