Guanidine compounds for removal of oxyanions from aqueous solutions and for carbon dioxide capture
Methods for removing oxyanions from water according to the following steps: (i) dissolving an oxyanion precipitating compound into the aqueous source to result in precipitation of an oxyanion salt of the oxyanion precipitating compound; and (ii) removing the oxyanion salt from the water containing the oxyanion to result in water substantially reduced in concentration of the oxyanion; wherein the oxyanion precipitating compound has the following composition: wherein A is a ring-containing moiety and X m− is an anionic species with a magnitude of charge m. The invention employs bis-iminoguanidinium compounds according to Formula (1 a ) as well as neutral precursor compounds according to Formula (1), which can be used for removing undesirable species from aqueous solutions or air, such as removal of sulfate from water and carbon dioxide from air.
1. A method for removing an inorganic oxyanion from an aqueous source containing an inorganic oxyanion salt, the method comprising:
(i) dissolving an oxyanion precipitating compound into said aqueous source containing said inorganic oxyanion salt to result in precipitation of an inorganic oxyanion compound salt of said oxyanion precipitating compound; and
(ii) removing said inorganic oxyanion compound salt from said water containing the inorganic oxyanion salt to result in water reduced in concentration of said inorganic oxyanion salt;
wherein said oxyanion precipitating compound has the following formula:
wherein:
A is a ring-containing moiety;
one or more of the hydrogen atoms in Formula (1a) may be replaced with one or more methyl groups;
X m− is an anionic species with a magnitude of charge m, where m is an integer of at least 1, provided that X m− is an anionic species exchangeable with the inorganic oxyanion in said inorganic oxyanion salt in said aqueous source before said oxyanion precipitating compound contacts said inorganic oxyanion salt in step (i), and X m− is said inorganic oxyanion in the inorganic oxyanion compound salt of said oxyanion precipitating compound; and
n is an integer of at least 1;
provided that n×m=2.
2. The method of claim 1 , wherein said inorganic oxyanion is selected from the group consisting of sulfate, nitrate, chromate, selenate, phosphate, arsenate, carbonate, bicarbonate, and perchlorate.
3. The method of claim 1 , wherein said inorganic oxyanion is sulfate.
4. The method of claim 1 , wherein A is a monocyclic ring.
5. The method of claim 4 , wherein said monocyclic ring is a five-membered, six-membered, or seven-membered ring.
6. The method of claim 1 , wherein A is a carbocyclic ring or ring system.
7. The method of claim 6 , wherein said carbocyclic ring or ring system is unsaturated.
8. The method of claim 7 , wherein A comprises a benzene ring.
9. The method of claim 1 , wherein A is a heterocyclic ring or ring system.
10. The method of claim 9 , wherein said heterocyclic ring or ring system is unsaturated.
11. The method of claim 9 , wherein said heterocyclic ring or ring system contains at least one nitrogen ring atom.
12. The method of claim 11 , wherein A comprises a pyridine ring.
13. A method for removing carbon dioxide from a gaseous source, the method comprising:
(i) contacting said gaseous source with an aqueous solution containing a carbon dioxide complexing compound to result in precipitation of a carbonate or bicarbonate salt of said carbon dioxide complexing compound; and
(ii) removing said carbonate or bicarbonate salt from said aqueous solution;
wherein said carbon dioxide complexing compound has the following formula:
wherein:
A is a ring-containing moiety;
one or more of the hydrogen atoms in Formula (1a) may be replaced with one or more methyl groups;
X m− is an anionic species with a magnitude of charge m, where m is an integer of at least 1, provided that X m− is hydroxide in said carbon dioxide complexing compound before said carbon dioxide complexing compound is contacted with carbon dioxide in step (i), and X m− is carbonate or bicarbonate in said carbonate or bicarbonate salt; and
n is an integer of at least 1;
provided that n×m=2.
14. The method of claim 13 , wherein A is a monocyclic ring.
15. The method of claim 14 , wherein said monocyclic ring is a five-membered, six-membered, or seven-membered ring.
16. The method of claim 13 , wherein A is a carbocyclic ring or ring system.
17. The method of claim 16 , wherein said carbocyclic ring or ring system is unsaturated.
18. The method of claim 17 , wherein A comprises a benzene ring.
19. The method of claim 13 , wherein A is a heterocyclic ring or ring system.
20. The method of claim 19 , wherein said heterocyclic ring or ring system is unsaturated.
21. The method of claim 19 , wherein said heterocyclic ring or ring system contains at least one nitrogen ring atom.
22. The method of claim 19 , wherein A comprises a pyridine ring.