Methods for separating oxygen from oxygen-containing gases

A method for separating oxygen from an oxygen-containing gas which is prepared from the steps of:

• (a) providing an oxidation zone and a reduction zone separated from one another by a substantially gas-impermeable membrane having a reduction surface in contact with said reduction zone and an oxidation surface in contact with said oxidation zone said membrane prepared from a mixed conducting metal oxide having the formula:
• A.sub.x A'.sub.x' A".sub.2-(x+x') B.sub.y B'.sub.y' B".sub.2-(y+y') O.sub.5+z
• where:
• x and x' are greater than 0;
• y and y' are greater than 0;
• x+x' is less than or equal to 2;
• y+y' is less than or equal to 2;
• z is a number selected to make the metal oxide charge neutral;
• A is an element selected from the f block lanthanide elements;
• A' is an element selected from the Be, Mg, Ca, Sr, Ba and Ra;
• A" is an element selected from the f block lanthanides or Be, Mg, Ca, Sr, Ba;
• B is an element selected from the group consisting of Al, Ga, In or mixtures thereof;
• and
• B' and B" are different elements and are independently selected from the group of elements Mg or the d-block transition elements;
• (b) passing said oxygen-containing gas in contact with said membrane in said reduction zone to reduce oxygen therein and generate oxygen anions in said membrane material said oxygen anions thereafter transported to said oxidation zone where said oxygen anions are oxidized forming oxygen which is thereby separated from said oxygen-containing gas.