Carbon dioxide adsorbents

1. A carbon dioxide adsorbent comprising:

a hierarchical zeolite defining:

micropores having a pore width between about 0.4 nm and about 2 nm; and

at least one of:

mesopores having a pore width between about 2 nm and about 50 nm; and

macropores having a pore width greater than about 50 nm,

wherein the hierarchical zeolite comprises:

anatase; and

aggregates of crystallites having a faujasite structure, wherein the crystallites are intergrown and have an average size up to about 100 nm, wherein the hierarchical zeolite has a crystallinity of at least about 80% based on the micropore volume of the hierarchical zeolite estimated from gas sorption measurements, and wherein the carbon dioxide adsorbent is formed in the absence of a binder.

2. The carbon dioxide adsorbent of claim 1 , wherein the hierarchical zeolite defines mesopores.

3. The carbon dioxide adsorbent of claim 2 , wherein the mesopores are textural.

4. The carbon dioxide adsorbent of claim 1 , wherein the hierarchical zeolite has a ratio of silicon atoms to aluminum atoms up to about 3.

5. The carbon dioxide adsorbent of claim 1 , wherein the hierarchical zeolite is at least partially ion-exchanged with an alkali metal ion, an alkaline earth metal ion, a rare earth metal ion, a transition metal ion, or a combination thereof.

6. The carbon dioxide adsorbent of claim 5 , wherein the hierarchical zeolite is at least partially ion-exchanged with lithium, potassium, rubidium, cesium, magnesium, calcium, strontium, barium, or a combination thereof.

7. The carbon dioxide adsorbent of claim 1 , wherein the carbon dioxide adsorbent is in the form of a powder, a film, a fiber, granules, beads, pellets, or a coating.

8. The carbon dioxide adsorbent of claim 7 , wherein the carbon dioxide adsorbent is in the form of a fiber, and the fiber is hollow.

9. The carbon dioxide adsorbent of claim 7 , wherein the carbon dioxide adsorbent is in the form of granules, beads, pellets, or a coating, and the granules, beads, pellets, or coating are formed with or without a binder.

10. A method of forming a carbon dioxide adsorbent, the method comprising:

heating a composition comprising a geopolymer resin up to about 100° C. to yield a heated composition; and

separating a solid from the heated composition to yield the carbon dioxide adsorbent,

wherein the mole fraction of water in the geopolymer resin before heating is up to about 0.85, and

wherein the carbon dioxide absorbent comprises a hierarchical zeolite defining:

micropores having a pore width between about 0.4 nm and about 2 nm; and

at least one of:

mesopores having a pore width between about 2 nm and about 50 nm; and

macropores having a pore width greater than about 50 nm,

wherein the hierarchical zeolite comprises:

anatase; and

aggregates of crystallites having a faujasite structure, wherein the crystallites are intergrown and have an average size up to about 100 nm, wherein the hierarchical zeolite has a crystallinity of at least about 80% based on the micropore volume of the hierarchical zeolite estimated from gas sorption measurements, and wherein the carbon dioxide adsorbent is formed in the absence of a binder or with a clay binder.

11. A method of removing carbon dioxide from a gas stream comprising carbon dioxide, the method comprising:

contacting a first gas stream comprising carbon dioxide with a carbon dioxide adsorbent comprising a hierarchical zeolite; and

adsorbing carbon dioxide from the first gas stream onto the carbon dioxide adsorbent, thereby removing some of the carbon dioxide from the first gas stream to yield a second gas stream, wherein the second gas stream has a lower concentration of carbon dioxide than the first gas stream,

wherein the hierarchical zeolite defines:

micropores having a pore width between about 0.4 nm and about 2 nm; and

at least one of:

mesopores having a pore width between about 2 nm and about 50 nm; and

macropores having a pore width greater than about 50 nm,

wherein the hierarchical zeolite comprises:

anatase; and

aggregates of crystallites having a faujasite structure, wherein the crystallites are intergrown and have an average size up to about 100 nm, and wherein the hierarchical zeolite has a crystallinity of at least about 80% based on the micropore volume of the hierarchical zeolite estimated from gas sorption measurements, and wherein the carbon dioxide adsorbent is formed in the absence of a binder or with a clay binder.

12. A carbon dioxide adsorbent comprising:

a hierarchical zeolite defining:

micropores having a pore width between about 0.4 nm and about 2 nm; and

at least one of:

mesopores having a pore width between about 2 nm and about 50 nm; and

macropores having a pore width greater than about 50 nm,

wherein the hierarchical zeolite comprises:

anatase; and

aggregates of crystallites having a faujasite structure, wherein the crystallites are intergrown and have an average size up to about 100 nm, wherein the hierarchical zeolite has a crystallinity of at least about 80% based on the micropore volume of the hierarchical zeolite estimated from gas sorption measurements, and wherein the hierarchical zeolite is shaped with a clay binder.

13. The carbon dioxide adsorbent of claim 1 , wherein the hierarchical zeolite has an ideal adsorbed solution theory (IAST) carbon dioxide-over-nitrogen adsorption selectivity of at least about 46 when contacted with a gas mixture comprising about 15 mol % carbon dioxide and about 85 mol % nitrogen at about 20° C. under a total pressure of about 100 kPa.

14. The carbon dioxide adsorbent of claim 13 , wherein the hierarchical zeolite has an ideal adsorbed solution theory (IAST) carbon dioxide-over-nitrogen adsorption selectivity of at least about 100 when contacted with a gas mixture comprising about 15 mol % carbon dioxide and about 85 mol % nitrogen at about 20° C. under a total pressure of about 100 kPa.

15. The carbon dioxide adsorbent of claim 14 , wherein the hierarchical zeolite has an ideal adsorbed solution theory (IAST) carbon dioxide-over-nitrogen adsorption selectivity of at least about 200 when contacted with a gas mixture comprising about 15 mol % carbon dioxide and about 85 mol % nitrogen at about 20° C. under a total pressure of about 100 kPa.

16. The carbon dioxide adsorbent of claim 15 , wherein the hierarchical zeolite has an ideal adsorbed solution theory (IAST) carbon dioxide-over-nitrogen adsorption selectivity of at least about 400 when contacted with a gas mixture comprising about 15 mol % carbon dioxide and about 85 mol % nitrogen at about 20° C. under a total pressure of about 100 kPa.

17. The carbon dioxide adsorbent of claim 12 , wherein the hierarchical zeolite has an ideal adsorbed solution theory (IAST) carbon dioxide-over-nitrogen adsorption selectivity of at least about 46 when contacted with a gas mixture comprising about 15 mol % carbon dioxide and about 85 mol % nitrogen at about 20° C. under a total pressure of about 100 kPa.

18. The carbon dioxide adsorbent of claim 17 , wherein the hierarchical zeolite has an ideal adsorbed solution theory (IAST) carbon dioxide-over-nitrogen adsorption selectivity of at least about 100 when contacted with a gas mixture comprising about 15 mol % carbon dioxide and about 85 mol % nitrogen at about 20° C. under a total pressure of about 100 kPa.

19. The carbon dioxide adsorbent of claim 18 , wherein the hierarchical zeolite has an ideal adsorbed solution theory (IAST) carbon dioxide-over-nitrogen adsorption selectivity of at least about 200 when contacted with a gas mixture comprising about 15 mol % carbon dioxide and about 85 mol % nitrogen at about 20° C. under a total pressure of about 100 kPa.

20. The carbon dioxide adsorbent of claim 19 , wherein the hierarchical zeolite has an ideal adsorbed solution theory (IAST) carbon dioxide-over-nitrogen adsorption selectivity of at least about 400 when contacted with a gas mixture comprising about 15 mol % carbon dioxide and about 85 mol % nitrogen at about 20° C. under a total pressure of about 100 kPa.