Enhancing carbon dioxide sorption rates using hygroscopic additives

• US 5,480,625 A
• Filed: 09/08/1992
• Issued: 01/02/1996
• Est. Priority Date: 02/24/1992
• Status: Expired due to Term

• Current Assignee: United Technologies Corporation (Rtx Corporation)
• Original Assignee: United Technologies Corporation (Rtx Corporation)
• Inventors: Birbara, Philip J., Nalette, Timothy A.
• Primary Examiner(s): Straub, Gary P.
• Assistant Examiner(s): Vanoy, Timothy C.
• Application Number:
  US07/941,826
• Time in Patent Office: 1,211 Days
• Field of Search: 502/60, 502/64, 502/174, 502/400, 502/407, 502/411, 502/412, 502/415, 55/68, 423/230, 423/232, 423/220, 95/117, 95/139, 266/156, 75/464
• US Class Current: 423/230
• CPC Class Codes: B01D 53/62 Carbon oxides
• CPC Class Codes: B01J 20/041 Oxides or hydroxides
• CPC Class Codes: B01J 20/046 containing halogens, e.g. halides
• CPC Class Codes: B01J 20/06 comprising oxides or hydroxides of metals not provided for in group B01J20/04
• CPC Class Codes: B01J 20/3021 Milling, crushing or grinding
• CPC Class Codes: B01J 20/3078 Thermal treatment, e.g. calcining or pyrolizing
• CPC Class Codes: B01J 20/3204 Inorganic carriers, supports or substrates
• CPC Class Codes: B01J 20/3236 containing metal, other than zeolites, e.g. oxides, hydroxides, sulphides or salts
• CPC Class Codes: Y02C 20/40 of CO2

Abstract

Carbon dioxide sorption using a metal oxide-alkali metal carbonate sorbent typically requires a relative humidity of greater than 25% in order to obtain reaction rate constants of about 2.0 to 3.0 sec.¹ (see Equation 6). The incorporation of alkali halide salt into the metal oxide-alkali metal carbonate sorbent maintains rate constants of about 2.0 to about 4.0 sec.¹ at relative humidities below 25%. Therefore, the hygroscopic alkali halide salt attracts water, thereby providing the necessary hydroxide ions for enhanced absorption at low relative humidities.

Claims

1. A method for removing carbon dioxide from the atmosphere in a closed human habitable environment comprising the steps of:

passing a stream of the atmosphere containing carbon dioxide through a reactor containing a carbon dioxide sorbent;

contacting the sorbent with the stream to absorb carbon dioxide to onto said sorbent thereby removing said carbon dioxide from the stream, wherein the sorbent comprises;

a. a metal oxide;

b. an alkali metal carbonate; and

c. hygroscopic alkali fluoride;

wherein said sorbent removes carbon dioxide from the gaseous stream including removal at relative humidities below about 25%.

2. A method for removing carbon dioxide as in claim 1 wherein said metal oxide is selected from the group consisting of magnesium oxide, silver oxide, zinc oxide, and mixtures thereof.

3. A method for removing carbon dioxide as in claim 1 wherein said alkali metal carbonate is selected from the group consisting of cesium carbonate, potassium carbonate and sodium carbonate.

4. A method for removing carbon dioxide as in claim 1 wherein said alkali fluoride is selected from the group consisting of cesium fluoride, potassium fluoride and sodium fluoride.

5. A method for removing carbon dioxide as in claim 1 wherein said sorbent comprises up to about 10 mole % alkali metal carbonate, between about 10 mole % and about 15 mole % alkali fluoride, balance metal oxide.