Stabilization of Porous Morphologies for High Performance Carbon Molecular Sieve Hollow Fiber Membranes

• US 20130152793A1
• Filed: 11/01/2012
• Published: 06/20/2013
• Est. Priority Date: 12/20/2011
• Status: Active Grant

• Current Assignee: Air Liquide Advanced Technologies U.S. LLC (L'Air Liquide SA), Georgia Tech Research Corporation (University System of Georgia)
• Original Assignee: Georgia Tech Research Corporation (University System of Georgia)
• Inventors: Koros, William John, Williams, Paul Jason, Bhuwania, Nitesh
• Granted Patent: US 9,211,504 B2
• Time in Patent Office: Days
• US Class Current: 96/4
• CPC Class Codes: B01D 2325/022 Asymmetric membranes
• CPC Class Codes: B01D 2325/20 Specific permeability or cut-off range
• CPC Class Codes: B01D 53/228 characterised by specific membranes
• CPC Class Codes: B01D 67/0067 by carbonisation or pyrolysis
• CPC Class Codes: B01D 67/0076 Pretreatment of inorganic membrane material prior to membrane formation, e.g. coating of metal powder
• CPC Class Codes: B01D 69/08 Hollow fibre membranes manufacture of hollow fibres D01D5/24, D01F1/08
• CPC Class Codes: B01D 71/021 Carbon
• CPC Class Codes: Y02C 20/40 of CO2

Abstract

Carbon molecular sieves (CMS) membranes having improved thermal and/or mechanical properties are disclosed herein. In one embodiment, a carbon molecular sieve membrane for separating a first and one or more second gases from a feed mixture of the first gas and one or more second gases comprises a hollow filamentary carbon core and a thermally stabilized polymer precursor disposed on at least an outer portion of the core. In some embodiments, the thermally stabilized polymer precursor is created by the process of placing in a reaction vessel the carbon molecular sieve membrane comprising an unmodified aromatic imide polymer, filling the reaction vessel with a modifying agent, and changing the temperature of the reaction vessel at a temperature ramp up rate and ramp down rate for a period of time so that the modifying agent alters the unmodified aromatic imide polymer to form a thermally stabilized polymer precursor.

Claims

1. A process for forming a carbon membrane using precursor pre-treatment comprising:

providing a polymer precursor;

pre-treating at least a portion of the polymer precursor; and

subjecting the pre-treated polymer precursor to pyrolysis;

wherein the step of pre-treating at least a portion of the polymer precursor provides at least a 300% increase in the gas permeance of the carbon membrane in contrast to the carbon membrane without precursor pre-treatment.

2. The process of claim 1, wherein the step of pre-treating at least a portion of the polymer precursor provides at least a 400% increase in the gas permeance of the carbon membrane in contrast to the carbon membrane without precursor pre-treatment.

3. The process of claim 1, wherein the gas permeance comprises CO₂ permeance.

4. The process of claim 1, wherein the step of pre-treating at least a portion of the polymer precursor provides an increase in the gas separation selectivity of the carbon membrane in contrast to the carbon membrane without precursor pre-treatment.

5. The process of claim 4, wherein the gas separation selectivity comprises CO₂/CH₄ separation selectivity.

6. The process of claim 1, wherein the polymer precursor comprises a soluble thermoplastic polyimide.

7. The process of claim 1, wherein pre-treating at least a portion of the polymer precursor comprises chemically modifying the polymer precursor.

8. The process of claim 1, wherein the polymer precursor comprises an asymmetric hollow polymer fiber.

9. The process of claim 1, wherein the polymer precursor comprises an aromatic imide polymer precursor.

10. In a process of forming a carbon membrane from a polymer precursor including the steps of providing a polymer precursor and subjecting the polymer precursor to pyrolysis, wherein the carbon membrane has a first gas permeance and a first gas separation selectivity, the improvement comprising the step of pre-treating at least a portion of the polymer precursor prior to pyrolysis such that after pre-treatment and pyrolysis, the improved carbon membrane has a second gas permeance and a second gas separation selectivity, wherein at least one of the second gas permeance or second gas separation selectivity is greater than the respective first gas permeance or first gas separation selectivity.

11. The process of claim 10, wherein the gas permeance comprises CO₂ permeance.

12. The process of claim 10, wherein the gas separation selectivity comprises CO₂/CH₄ separation selectivity.

13. The process of claim 10, wherein the polymer precursor comprises a soluble thermoplastic polyimide.

14. The process of claim 10, wherein pre-treating at least a portion of the polymer precursor comprises chemically modifying the polymer precursor.

15. The process of claim 10, wherein the polymer precursor comprises an asymmetric hollow polymer fiber.

16. The process of claim 10, wherein the polymer precursor comprises an aromatic imide polymer precursor.

17. A process for modifying a polymer precursor for use as a carbon membrane comprising:

providing a polymer precursor in a vessel;

providing a modifying agent in the vessel;

contacting at least a portion of the modifying agent with the polymer precursor in the vessel to provide for the modification of at least a portion of the polymer precursor; and

subjecting the modified polymer precursor to pyrolysis forming the carbon membrane.

18. The process of claim 17, wherein the carbon membrane comprises a hollow fiber membrane.

19. The process of claim 18, wherein the hollow fiber membrane comprises an asymmetric membrane.

20. The process of claim 17, wherein the carbon membrane comprises a substantially non-collapsed, asymmetric hollow fiber membrane.

21. The process of claim 17, wherein the modifying agent is a silane having the formula R¹R²R³R⁴Si, where each of R¹, R², R³, and R⁴ are independently vinyl, C₁-C₆ alkyl, —

O-alkyl, or halide, with the proviso that the silane contain at least one vinyl group and at least one —

O-alkyl or halide.

22. The process of claim 17, wherein the modifying agent is vinyl trimethoxy silane or vinyl triethoxy silane.

23. The process of claim 17 further comprising providing an initiator in the vessel.

24. The process of claim 17, wherein the polymer precursor is an aromatic imide polymer precursor.

25. The process of claim 17 further comprising flowing an inert gas during pyrolysis.

26. The process of claim 17, wherein the polymer precursor is a composite structure comprising a first polymer supported on a porous second polymer.

27. The process of claim 20, wherein asymmetric hollow fiber membrane comprises a group of membrane fibers that are in contact with one another during the pyrolysis process and do not adhere to one another after pyrolysis.

28. A process for making a carbon membrane comprising:

providing a polymer precursor comprising a soluble thermoplastic polyimide;

chemically modifying the polymer precursor with a modifying agent; and

heating the chemically modified precursor in a chamber to at least a temperature at which pyrolysis byproducts are evolved;

wherein the carbon membrane has a CO₂ permeance (GPU) of greater than 35 and a CO₂/CH₄ selectivity greater than 88 in 100 psia in pure CO₂ and CH₄ gas streams at 35°

C. in at 100 psia and at 35°

C.

29. The process of claim 28, wherein the modifying agent comprises vinyl trimethoxy silane or vinyl triethoxy silane.

30. A process for making a carbon membrane comprising:

providing a polymer precursor comprising a soluble thermoplastic polyimide;

chemically modifying the polymer precursor with a cross-linked polyethylene; and

heating the chemically modified precursor in a chamber to at least a temperature at which pyrolysis byproducts are evolved;

wherein the carbon membrane has a CO₂ permeance (GPU) of greater than 53 and a CO₂/CH₄ selectivity greater than 48 in 100 psia in pure CO₂ and CH₄ gas streams at 35°

C. in at 100 psia and at 35°

C.

31. The process of claim 30, wherein the modifying agent comprises vinyl trimethoxy silane.

32. A carbon molecular sieve membrane formed by the process comprising:

providing a polymer precursor;

pre-treating at least a portion of the polymer precursor; and

subjecting the pre-treated polymer precursor to pyrolysis;

wherein the step of pre-treating at least a portion of the polymer precursor provides at least a 300% increase in the gas permeance of the carbon membrane in contrast to the carbon membrane without precursor pre-treatment.

33. A carbon molecular sieve membrane formed from a polymer precursor by a process including the steps of providing a polymer precursor and subjecting the polymer precursor to pyrolysis, wherein the carbon membrane has a first gas permeance and a first gas separation selectivity, the improvement comprising the step of pre-treating at least a portion of the polymer precursor prior to pyrolysis such that after pre-treatment and pyrolysis, the improved carbon membrane has a second gas permeance and a second gas separation selectivity, wherein at least one of the second gas permeance or second gas separation selectivity is greater than the respective first gas permeance or first gas separation selectivity.

34. A carbon molecular sieve membrane formed by the process comprising:

providing a polymer precursor in a vessel;

providing a modifying agent in the vessel;

contacting at least a portion of the modifying agent with the polymer precursor in the vessel to provide for the modification of at least a portion of the polymer precursor; and

subjecting the modified polymer precursor to pyrolysis forming the carbon membrane.

35. A carbon molecular sieve membrane formed by the process comprising:

providing a polymer precursor comprising a soluble thermoplastic polyimide;

chemically modifying the polymer precursor with a chemical modifying agent; and

heating the chemically modified precursor in a chamber to at least a temperature at which pyrolysis byproducts are evolved;

wherein the carbon membrane has a CO₂ permeance (GPU) of greater than 35 and a CO₂/CH₄ selectivity greater than 88 in 100 psia at 35°

C. in pure CO₂ and CH₄ gas streams C.