Methods for separating
carbon dioxide from a fluid
stream at a temperature higher than about 200° C. with selectivity higher than Knudsen
diffusion selectivity include contacting a
porous membrane with the fluid
stream to preferentially transport
carbon dioxide. The
porous membrane includes a porous support and a continuous porous separation layer disposed on a surface of the porous support and extending between the fluid
stream and the porous support layer. The porous support comprises
alumina, silica, zirconia, stabilized zirconia, stainless steel,
titanium,
nickel-based alloys, aluminum-based alloys,
zirconium-based alloys or a combination thereof. Median pore size of the porous separation layer is less than about 10 nm, and the porous separation layer comprises titania, MgO, CaO, SrO, BaO, La2O3, CeO2, HfO2, Y2O3, VOz, NbOz, TaOz, ATiO3, AZrO3, AAl2O4, A1FeO3, A1MnO3, A1CoO3, A1NiO3, A2HfO3, A3 CeO3, Li2ZrO3, Li2SiO3, Li2TiO3, Li2HfO3, A4N1yOz, YxN1yOz, LaxN1yOz, HfN2yOz, or a combination thereof;whereinA is La, Mg, Ca, Sr or Ba;A1 is La, Ca, Sr or Ba;A2 is Ca, Sr or Ba;A3 is Sr or Ba;A4 is Mg, Ca, Sr, Ba, Ti or Zr;N1 is V, Nb, Ta, Cr, Mo, W, Mn, Si or Ge;N2 is V, Mo, W or Si;x is 1 or 2;y ranges from 1 to 3; andz ranges from 2 to 7.