Claims
- 1. A membrane assembly for removing metabolic carbon dioxide (CO2) from a habitable environment, said membrane assembly comprising a porous hydrophilic membrane, pores of which contain a low vapor pressure hygroscopic solvent having an alkali metal carbonate compound dissolved therein.
- 2. The membrane assembly of claim 1 wherein said membrane has a CO2 permeation rate of 8.5×10−4 cm3/cm2·s·Hg, wherein cm3is the volume of the gas transferred through the membrane; cm2is the area of the membrane surface; s is time in seconds; and cmHg is pressure in mercury column centimeters.
- 3. The membrane assembly of claim 1 wherein the relative rate of transfer of CO2 versus O2 through the membrane assembly, which is also known as the “separation factor” is at least 333.
- 4. The membrane assembly of claim 3 wherein the separation factor is about 895.
- 5. The membrane assembly of claim 3 wherein the amount of O2 transferred through the membrane assembly is about 0.014 lb/hr.
- 6. The membrane assembly of claim 1 wherein the membrane is formed from a polymer which is selected from the group consisting of a polysulfone and a polyvinylidene.
- 7. The membrane assembly of claim 1 wherein said solvent is a hygroscopic solvent which is selected from the group consisting of glycerol, diethanolamine and polyethylene glycol.
- 8. The membrane assembly of claim 1 wherein said alkali metal carbonate compound is a compound which is selected from the group consisting of sodium carbonate, cesium carbonate, potassium carbonate and calcium carbonate.
- 9. A method for removing metabolic carbon dioxide (CO2) from an air stream derived from a closed habitable environment so as to produce a lower CO2 concentration in said air stream, said method comprising:
a) the step of providing a porous hydrophilic membrane, pores of which contain a solution of a low vapor pressure hygroscopic solvent having an alkali metal carbonate compound dissolved therein; and b) the step of passing the air stream over an entry side of the membrane so as to convert CO2 in the air stream to a bicarbonate in said solution in the membrane thereby reducing the amount of CO2 in the air stream.
- 10. The method of claim 9 further comprising the further step of returning the air stream to the habitable environment.
- 11. The method of claim 9 wherein partial pressure of CO2 on the entry side of the membrane is greater than partial pressure of CO2 in an ambient environment on an exit side of the membrane, in which said ambient environment the habitable environment is located.
- 12. The method of claim 11 wherein atmospheric pressure on the entry side of the membrane is greater than atmospheric pressure in the ambient environment on the exit side of the membrane so as to draw the air stream to entry side of the membrane.
- 13. The method of claim 11 wherein the bicarbonate is converted back to CO2 in the ambient environment.
- 14. The method of claim 9 wherein passage of oxygen (O2) through said membrane is restricted.
- 15. A method for removing metabolic carbon dioxide (CO2) from an air stream which contains oxygen (O2) and metabolic CO2, which air stream is derived from a closed habitable environment, said method comprising:
a) the step of providing a porous hydrophilic membrane, pores of which contain a solution of a low vapor pressure hygroscopic solvent having an alkali metal carbonate compound dissolved therein, said solution being permeable by CO2 and being substantially impermeable by O2; and b) the step of drawing the air stream toward an entry side of the membrane so as to selectively draw CO2 into said solution while restricting O2 entry into said solution thereby reducing the amount of CO2 in the air stream.
- 16. A system for removing metabolic carbon dioxide (CO2) from an air stream which is derived from a closed habitable environment, said system comprising:
a) a first line for drawing the air stream from the habitable environment; b) said line communicating with an entry side of a porous hydrophilic membrane, pores of which membrane contain a solution comprising a low vapor pressure hygroscopic solvent and an alkali metal carbonate compound dissolved therein, said solution being operable to convert CO2 in said air stream to a bicarbonate compound in said solution; and c) a second line for removing reconverted CO2 from an exit side of said membrane.
- 17. A solution for removing metabolic carbon dioxide (CO2) from an air stream which air stream is derived from a closed habitable environment, said solution comprising a low vapor pressure hygroscopic solvent having an alkali metal carbonate compound dissolved therein.
- 18. A method for preparing a membrane assembly which is useful for removing metabolic carbon dioxide (CO2) from an air stream which is derived from a habitable environment, said method comprising:
a) the step of providing a porous hydrophilic membrane; b) the step of preparing a solution of an alkali metal carbonate solute which is dissolved in a low vapor pressure hygroscopic solvent; c) the step of contacting the membrane with the solution in a manner wherein the membrane will wick up the solution into the membrane's pores; and d) the step of removing excess solution from the membrane.
Government Interests
[0001] The invention described herein was made in the performance of work under NASA Contract No. NAS9-18587 and is subject to the provisions of Section 305 of the National Aeronautics and Space Act of 1958 (42 U.S.C. 2457).