Synthesis and characterisation of nanocomposite Ge-MFI-alumina membranes for CO2/N2 separation from wet flue gases

In this study, Al-MFI and Ge-MFI (Si/Ge = 12–400) membranes with nanocomposite architecture have been prepared on α-alumina tubes by pore-plugging hydrothermal synthesis at 443 K for 89 h using a precursor clear solution with molar composition 1 SiO2:0.45 TPAOH:27.8 H2O:x GeO2 (x = 0–0.02). The membrane materials and powders have been characterised by XRD, SEM, FTIR, N2 adsorption at 77.4 K, water adsorption at 303 K and CO2 adsorption in the temperature range 303–474 K. The crystallization kinetics is promoted upon Ge incorporation to the synthesis solution, the MFI particles becoming rounded. The incorporation of Ge to the MFI framework increases the hydrophobic behaviour of the MFI framework and the activation energy for CO2 diffusion. The synthesised membranes present optimal permeation properties and partial CO2/air separation even in the presence of huge amounts of water in the feed stream. The best material consists of a Ge-MFI-alumina membrane with a Si/Ge ratio of 12, offering a steady-state CO2 permeance as high as 0.4 μmol m−2 s−1 Pa−1 at 373 K in the presence of 10% water concentration in the feed.

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► We have prepared Ge-MFI-alumina membranes with nanocomposite architecture.
► The MFI crystallization kinetics is promoted in the presence of Ge.
► Ge incorporation increases the activation energy for CO2 diffusion.
► The membranes present high CO2 permeances even in the presence of moisture.