Process for recovering oxygen

A process for recovering oxygen from a gas mixture that contains O.sub.2, which comprises:

• (a)--contacting a gas mixture with a metal complex consisting of a metal atom and a polynitrogenated ligand having five coordinating functions and the formula:
• ##STR135## in which X and Z, identical or different, are selected from ##STR136## wherein P.sub.2 is selected from hydrogen, C.sub.1 -C.sub.4 alkyl and C.sub.1 -C.sub.4 alkyl substituted by one or several groups selected from
• --COR in which R is selected from hydroxyl;
• NH.sub.2 ;
• --NH(C.sub.1 -C.sub.4 alkyl);--N(C.sub.1 -C.sub.4 alkyl).sub.2 ;
• --O--(C.sub.1 -C.sub.4 alkyl),
• phenoxy
• phenoxy substituted by one to three groups selected from halogen, C.sub.1 -C.sub.4 alkyl, C.sub.1 -C.sub.4 alkoxy, and nitro;
• phenyl;
• phenyl substituted by one to three substituents selected from halogen, C.sub.1 -C.sub.4 alkyl, C.sub.1 -C.sub.4 alkoxy and nitro;
• C.sub.1 -C.sub.4 alkyl;
• C.sub.1 -C.sub.4 alkoxy;
• halogen and
• nitro;
• and
• an aromatic heterocycle selected from pyridine, imidazole, quinoline, isoquinoline, pyrrole, pyrimidine, pyrazine, pyridazine, indole, carbazole, purine, phenazine, thiazole, isothiazole, oxazole, isoxazole, said aromatic heterocycle substituted with at least one radical selected from C.sub.1 -C.sub.4 alkyl and C.sub.1 -C.sub.4 alkyl substituted by at least one group selected from
• phenyl;
• phenyl substituted by one to three substituents selected from halogen, C.sub.1 -C.sub.4 alkyl, C.sub.1 -C.sub.4 alkoxy and nitro;
• C.sub.1 -C.sub.4 alkyl;
• C.sub.1 -C.sub.4 alkoxy;
• halogen and
• nitro;
• Y and W, identical or different, represent ##STR137## in which P.sub.2 is a defined above, it being understood that one of W, X, Y, and Z is ##STR138## in which P.sub.2 is C.sub.1 -C.sub.4 alkyl substituted by --COR;
• A, E, C and D, identical or different, are selected from C.sub.1 -C.sub.3 alkylene and C.sub.1 -C.sub.3 alkylene substituted with at least one radical selected from C.sub.1 -C.sub.4 alkyl and C.sub.1 -C.sub.4 alkyl substituted at least one group selected from:
• phenyl;
• phenyl substituted by one to three substituents selected from halogen, C.sub.1 -C.sub.4 alkyl, C.sub.1 -C.sub.4 alkoxy and nitro;
• C.sub.1 -C.sub.4 alkyl;
• C.sub.1 -C.sub.4 alkoxy;
• halogen and
• nitro;
• with the proviso that among the five coordinating functions only one is a --COR group, the other being either ##STR139## or an aromatic heterocycle;
• a metal complex prepared starting with a ligand of formula:
• ##STR140## in which Ra represents --(CH.sub.2).sub.n --COOH with n varying from 1 to 3, is excluded;
• in conditions which favor the absorption of O.sub.2 from the gas mixture by the metal complex to yield the dimer C.sub.p O.sub.2 C.sub.p where C.sub.p is a metal complex molecule,
• (b)--desorbing the bound oxygen,
• (c)--recovering the desorbed oxygen, the metal complex being immobilized on a O.sub.2, permeable membrane, said membrane being made of a polymer film which has one side in contact with a gas mixture containing oxygen, while desorption of bound O.sub.2 occurs at the other side.