Preparation of thermostable amorphous SiCO membrane and its application to gas separation at elevated temperature

Abstract An amorphous SiCO membrane was formed on the outer surface of an α-alumina support (2.4 mm o.d., 1.8 mm i.d., average pore size ca. 150 nm). The precursor film was formed by dip-coating with p-xylene solutions of polycarbosilane. It was dried, cured and pyrolyzed under various conditions. Polystyrene was also added to develop the porous structure of membrane and decrease its effective thickness by gas evolution during pyrolysis. Pore volume and BET surface area showed maxima at a pyrolysis temperature of 823 K. Hydrogen and nitrogen permeances were also highest at this pyrolysis temperature. Membranes were also pyrolyzed at temperature up to 1223 K to promote applicability at higher permeation temperature. For an SiCO membrane coated three times with the single-component PC solutions and pyrolyzed at 1223 K, H2 permeance was about 10−8 mol m−2 s−1 Pa−1, and H 2 N 2 selectivity was 18–63 at a permeation temperature of 773 K. The addition of polystyrene effectively increased H2 permeance by one order of magnitude, while H 2 N 2 was 13 at 773 K.

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