Mixed ion-exchanged zeolites and processes for the use thereof in gas separations
AssigneeUop LLC
InventorsChien C. Chao, John D. Sherman, Joseph T. Mullhaupt, Cornelius M. Bolinger
Life of this patent
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Abstract
Lithium/alkaline earth metal X zeolites in which the lithium:alkaline earth metal equivalent ratio is from about 95:5 to about 50:50 and lithium/alkaline earth metal A zeolites in which the lithium:alkaline earth metal equivalent ratio is from about 10:90 to about 70:30 are useful for separating oxygen and nitrogen from mixtures because they combine high adsorption capacity with high thermal stability.
Claims22
A lithium/alkaline earth metal X zeolite in which the silica:alumina ratio is from about 1.85 to about 3.0 and in which the lithium:alkaline earth metal equivalent ratio is from about 95:5 to about 50:50.
A lithium/alkaline earth metal A zeolite in which the silica:alumina ratio is from about 1.85 to about 4.0 and in which lithium:alkaline earth metal equivalent ratio is from about 10:90 to about 70:30.
A process for preparing a lithium/alkaline earth metal zeolite selected from the group consisting of X zeolites in which the lithium:alkaline earth metal equivalent ratio is from about 95:5 to about 50:50 and A zeolites in which the lithium:alkaline earth metal equivalent ratio is from about 10:90 to about 70:30, which process comprises:
- ion-exchanging an A or X zeolite, in a form having alkali metal cations other than lithium, with a solution of a lithium salt until at least about 90 mole percent of the original alkali metal cations have been replaced by lithium cations;
- and
- thereafter, ion-exchanging the lithium A or X zeolite thus produced with a solution of an alkaline earth metal salt until a sufficient proportion of the lithium cations have been replaced with alkaline earth metal cations to provide a lithium/alkaline earth metal equivalent ratio within the specified range.
In a process for separating nitrogen from oxygen, which process comprises:
- contacting a gaseous feed mixture of nitrogen and oxygen with a molecular sieve under a first pressure, thereby causing nitrogen to be selectively adsorbed into the molecular sieve, and producing a gaseous first product mixture containing a greater proportion of oxygen than the feed mixture;
- separating the first product mixture from the molecular sieve;
- and
- reducing the pressure on the molecular sieve to a second pressure lower than the first pressure, thereby causing desorption from the molecular sieve of a gaseous second product mixture containing a greater proportion of nitrogen than the feed mixture,
- the improvement which comprises using as the molecular sieve a molecular sieve comprising a lithium/alkaline earth metal zeolite selected from the group consisting of X zeolites in which the lithium:alkaline earth metal equivalent ratio is from about 95:5 to about 50:50 and A zeolites in which the lithium:alkaline earth metal equivalent ratio is from about 10:9 to about 70:30.
Dependencies are inferred from the claim text.