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
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purely microporous microstructure are outlined.