Mixed-Matrix Organo-Silica-Hydrotalcite Membrane for CO₂ Separation Part 2: Permeation and Selectivity Study

This study introduces an innovative approach to designing membranes capable of separating CO₂ from industrial gas streams at higher temperatures. The novel membrane design seeks to leverage a well-researched, high-temperature CO₂ adsorbent, hydrotalcite, by transforming it into a membrane. This was achieved by combining it with an amorphous organo-silica-based matrix, extending the polymer-based mixed-matrix membrane concept to inorganic compounds. Following the membrane material preparation and investigation of the individual membrane in Part 1 of this study, we examine its permeation and selectivity here. The pure 200 nm thick hydrotalcite membrane exhibits Knudsen behavior due to large intercrystalline pores. In contrast, the organo-silica membrane demonstrates an ideal selectivity of 13.5 and permeance for CO₂ of 1.3 × 10^-7 mol m^-2 s^-1 Pa^-1 at 25 °C, and at 150 °C, the selectivity is reduced to 4.3. Combining both components results in a hybrid microstructure, featuring selective surface diffusion in the microporous regions and unselective Knudsen diffusion in the mesoporous regions. Further attempts to bridge both components to form a purely microporous microstructure are outlined.