Gas separations using mixed matrix membranes
First Claim
1. A process for separating two gases having different molecular sizes in the range of about 2.5 Angstroms to about 5.0 Angstroms in a feedstream including these two gas components, the process comprising:
- (a) providing a polymer membrane having feed and permeate sides that incorporates carbon-based molecular sieve particles and that is selectively permeable to a first gas component over a second gas component, and (b) directing a feedstream including the first and second gas components to the feed side of the membrane and withdrawing a retentate stream depleted in the first gas component and withdrawing a permeate stream enriched in the first gas component from the permeate side of the membrane;
wherein the selectivity of the first gas component through the particles is greater than the selectivity of the first gas component through the polymer.
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Abstract
Mixed matrix membranes capable of separating carbon dioxide from mixtures including carbon dioxide and methane, and processes for purifying methane using the membranes, are disclosed. The membranes are polymer membranes with a selective layer thickness of between about 1000 Angstroms to about 0.005 inch, that include discrete carbon-based molecular sieve particles with sizes of between about 0.5 microns to about 5.0 microns. The preferred ratio of particles to polymer is about 20% to about 50% by volume. A preferred method for preparing the mixed matrix membrane is by dispersing the particles in a solvent, adding a small quantity of the desired polymer or “sizing agent” to “size” or “prime” the particles, adding a polymer, casting a film of the polymer solution, and evaporating the solvent to form a mixed matrix membrane film. The mixed matrix membrane film permits passage of carbon dioxide and methane, but at different permeation rates, such that the ratio of the relative permeation rates of carbon dioxide to methane is larger through the mixed matrix membrane film than through the original polymer. The polymer is preferably a rigid, glassy polymer, more preferably, with a glass transition temperature above about 150° C. The mixed matrix membrane is preferably in the form of a dense film or a hollow fiber. A mixture containing carbon dioxide and methane can be enriched in methane by selective passage of carbon dioxide over methane in a gas-phase process through the membrane.
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Citations
21 Claims
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1. A process for separating two gases having different molecular sizes in the range of about 2.5 Angstroms to about 5.0 Angstroms in a feedstream including these two gas components, the process comprising:
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(a) providing a polymer membrane having feed and permeate sides that incorporates carbon-based molecular sieve particles and that is selectively permeable to a first gas component over a second gas component, and (b) directing a feedstream including the first and second gas components to the feed side of the membrane and withdrawing a retentate stream depleted in the first gas component and withdrawing a permeate stream enriched in the first gas component from the permeate side of the membrane;
wherein the selectivity of the first gas component through the particles is greater than the selectivity of the first gas component through the polymer. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16)
wherein typical substituents providing substituted polymers include halogens comprising fluorine, chlorine and bromine;
hydroxyl groups;
lower alkyl groups;
lower alkoxy groups;
monocyclic aryl; and
lower acyl groups.
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7. The process of claim 1, wherein the carbon-based molecular sieve is formed by pyrolysis of a polymer selected from the group consisting of those listed in claim 5.
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8. The process of claim 1, wherein the polymer is selected from the group having a permeation rate for one gas component through the polymer that is at least 2 times faster than the permeation rate for the other gas component through the polymer.
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9. The process of claim 1, wherein the volume ratio of particles to polymer is between about 10% and about 50%.
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10. The process of claim 1, wherein the feedstream comprises the product stream from a Fischer-Tropsch reaction.
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11. The process of claim 1, wherein the membrane is in the form of a film.
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12. The process of claim 1, wherein the membrane is in the form of a hollow fiber.
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13. The process of claim 1, wherein at least one of the gases to be separated is selected from the group consisting of carbon dioxide, helium, hydrogen, hydrogen sulfide, oxygen and nitrogen.
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14. The process of claim 1, wherein the separation is performed down-hole.
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15. The method of claim 1, wherein the membrane is subjected to an annealing treatment by heating it above the glass transition temperature of the polymer.
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16. The method of claim 15, wherein the annealing is carried out at a temperature between 10 and 30°
- C. above the glass transition temperature.
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17. A mixed matrix membrane comprising:
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(a) a rigid, glassy polymer and (b) discrete carbon-based particles dispersed in the polymer;
wherein the membrane is in the form of a film or a hollow fiber, the thickness of the selective layer of the membrane is between about 1000 Angstroms and about 0.005 in., and the volume ratio of particles to polymer is between about 10% and about 50%.
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18. A method of “
- priming”
carbon molecular sieve particles with a polymer, comprising;(a) dispersing carbon molecular sieve particles in a suitable solvent, (b) adding a small amount of a polymer to the dispersion, where the polymer is soluble in the solvent, and (c) adding a non-solvent for the polymer to the dispersion to initiate precipitation of the polymer onto the carbon particles. - View Dependent Claims (19, 20, 21)
- priming”
Specification