Preparation of CO₂ permselective Li₄SiO₄ membranes by using mesoporous silica as a silica source

High temperature CO₂ separation is effective for the efficient CO₂ reduction. Li₄SiO₄ is one of the high temperature CO₂ adsorbents. In this study, a Li₄SiO ₄ thin membrane was developed by using a novel solid state conversion method. Li₄SiO₄ membranes were successfully prepared on a porous alumina substrate at 600 °C conversion from mesoporous silica as silica source. Mesoporous silica was better silica source to obtain Li ₄SiO₄ at the low temperature conversion method compared with MFI zeolite, fumed silica and colloidal silica. CO₂/N ₂ permselectivity was 0.85 at 600 °C that is higher than the Knudsen diffusion difference. Thus, Li₄SiO₄ layer showed CO₂ permselectivity at 600 °C. It was important to use the mixtures of Li₂CO₃ and K₂CO₃ to fill the pinholes of the Li₄SiO₄ membrane. N₂ permeance through the Li₄SiO₄ membrane decreased to 1.8 × 10^-9 mol m^-2 s^-1 Pa^-1 from 3.9 × 10^-7 mol m^-2 s^-1 Pa^-1 by the addition of the mixtures of Li₂CO₃ and K ₂CO₃.