Composite body

A flexible composite gas separation membrane body having, on a porous substrate and in the interstices of the substrate that includes fibers,

• a porous layer (1) composed of oxide particles bonded to one another and partly to the substrate that include at least one oxide selected from oxides of the elements Al, Zr, Ti and Si, and having, at least on one side, a further porous layer;
• (2) including oxide particles bonded to one another and partly to layer (1) that include at least one oxide selected from oxides of the elements Al, Zr, Ti and Si, where the oxide particles present in layer (1) have a greater median particle size than the oxide particles present in layer (2), wherein the median particle size (d50) of the oxide particles in layer (1), is from 0.5 to 4 μm and the median particle size (d50) of the oxide particles in layer (2), is from 0.015 to 0.15 μm;
• and wherein the flexible composite gas separation membrane body has a Gurley number of from 250 to 1200 sec, and a gas flow of greater than 50 GPU for carbon dioxide as clean gas;
• and
• further comprises a silicone polymer layer;
• and
• the flexible composite gas separation membrane body has a thickness of from 100 to 400 μm and can be wound around a bar or tube having a diameter of 15 mm or greater.