PERMEATION MEMBRANE AND METHOD FOR PRODUCING A PERMEATION MEMBRANE

Abstract

Disclosed is a permeation membrane and a method for producing a permeation membrane. The permeation membrane can be used in particular in the field of membrane-based material separations. The permeation membrane is composed of an inorganic semi-permeable substance in which an additional substance is incorporated in some locations such that existing intermediate spaces in the semi-permeable substance are at least partly filled by the additional substance and thus only the intermediate spaces are blocked for a permeating species.

Claims

1.-9. (canceled)

10. A permeation membrane, wherein the permeation membrane is composed of an inorganic, semipermeable substance into which a further substance is incorporated at certain points such that existing intermediate spaces in the semipermeable substance are at least partially filled by the further substance and thus only intermediate spaces are blocked for a permeating species such that small gas molecules can be separated from one another in a mixture according to their size.

11. The permeation membrane of claim 10, wherein the permeation membrane is capable of separating water from hydrogen.

12. The permeation membrane of claim 10, wherein the permeation membrane is capable of separating water from nitrogen.

13. The permeation membrane of claim 10, wherein the permeation membrane is capable of separating water from methane.

14. The permeation membrane of claim 10, wherein the permeation membrane is capable of separating water from carbon dioxide.

15. The permeation membrane of claim 10, wherein the further substance comprises an x-ray amorphous carbon.

16. The permeation membrane of claim 10, wherein the semipermeable substance is a crystalline substance with a zeolite structure.

17. The permeation membrane of claim 15, wherein the semipermeable substance is a crystalline substance with a zeolite structure.

18. The permeation membrane of claim 10, wherein the semipermeable substance is selected from aluminosilicates and aluminophosphates.

19. The permeation membrane of claim 10, wherein the semipermeable substance is selected from silicon aluminophosphates.

20. The permeation membrane of claim 10, wherein the semipermeable substance is selected from metal-organic frameworks.

21. The permeation membrane of claim 16, wherein the crystalline substance with a zeolite structure is a representative of the structures SOD, LTA, ERI, CHA, MFI, FAU.

22. The permeation membrane of claim 15, wherein the carbon has no measurable porosity.

23. The permeation membrane of claim 15, wherein the carbon has pores smaller than those of the semipermeable substance.

24. A method for producing a permeation membrane, wherein the method comprises: a) production of a zeolite membrane having intergranular pores and defects, b) incorporation of an x-ray amorphous carbon into the intergranular pores and defects of the zeolite membrane.

25. The method of claim 24, wherein the incorporation of the carbon into the intergranular pores and defects of the zeolite membrane is carried out by infiltration of an organic precursor and subsequent pyrolysis under inert conditions.

26. The method of claim 24, wherein the incorporation of the carbon into the intergranular pores and defects of the zeolite membrane is carried out by condensation of a vaporous, organic precursor and subsequent pyrolysis under inert conditions.

27. The method of claim 24, wherein the incorporation of the carbon into the intergranular pores and defects of the zeolite membrane is carried out by reactive deposition of a vaporized organic species from a gas phase (chemical vapor deposition).

28. The method of claim 24, wherein the incorporation of the carbon into the intergranular pores and defects of the zeolite membrane is carried out by pyrolysis of excess template.

29. A method for separating water from mixtures of water with one or more of hydrogen, nitrogen, methane or carbon dioxide, wherein the method comprises contacting the mixture with the permeation membrane of claim 10.

Description

[0024] The invention will be described in the following in greater detail by means of examples. The drawings are as follows:

[0025] FIG. 1. Permporosimetry tests (He/n-hexane) of the ?-Al.sub.2O.sub.3 membranes in the starting state and in comparison after treatment with acetylene.

[0026] FIG. 2. Individual gas permeances of selected gases on MFI membranes after production (as-prepared) and after treatment with acetylene at 750? C. with a duration of deposition of 45 min (post-treated). The measurement temperature was 150? C.

[0027] FIG. 3. Ideal permselectivities of H.sub.2/SF.sub.5 and He/SF.sub.5 for MFI membranes calculated from the individual gas permeance measurements.

[0028] FIG. 4. Permporosimetry measurement of a ceramic membrane with an 0.9 nm pore diameter before and after carbon infiltration by infiltration and pyrolysis of a liquid precursor.

[0029] FIG. 5. Individual gas permeance measurement of a carbon-infiltrated zeolite membrane produced by infiltration and pyrolysis of a liquid precursor into a nanozeolite layer.

[0030] FIG. 6. Permeances in binary 50:50 mixtures of H.sub.2O and N.sub.2, H.sub.2O and CH.sub.4, H.sub.2O and CO.sub.2 as well as H.sub.2O and H.sub.2, and respective H.sub.2O/N.sub.2, H.sub.2O/CH.sub.4, H.sub.2O/CO.sub.2 and H.sub.2O/H.sub.2 permselectivities measured at 200? C., a feed pressure of 11 bar absolute, and a permeation pressure of 1 bar to 4 bar absolute on a carbon-infiltrated zeolite membrane produced by infiltration and pyrolysis of a liquid precursor into a nanozeolite layer (MFI).

[0031] FIG. 7. Permeances of individual gases (He, CO.sub.2 and N.sub.2) and mixed gases (CO.sub.2:N.sub.2 1:1 and 1:5) and the resulting ideal and real selectivity for separation of the gases CO.sub.2 and N.sub.2 at 25? C. of an SAPO-34 membrane (SAPO-34/M), a carbon-integrated SAPO-34 zeolite membrane (SAPO-34/CiZM, infiltration by immersion) and a carbon-integrated ?-Al.sub.2O.sub.3 carrier (CiAl.sub.2O.sub.3); and

[0032] FIG. 8. Raman spectrum of a carbon-integrated ?-Al.sub.2O.sub.3 carrier (CiAl.sub.2O.sub.3) and a carbon-integrated SAPO-34 zeolite membrane (SAPO-34/CiZM).

[0033] FIG. 9. XRD diffractogram of a SAPO-34 zeolite membrane and a carbon-integrated SAPO-34 zeolite membrane (SAPO-34/CiZM).

[0034] As described in the introduction of the description, a zeolite membrane requires a carrier that imparts mechanical stability to the system, but without affecting separation or substance transport. For this reason, the production of various carriers will first be presented, and these will be referred to in the following examples: [0035] 1a) A porous ceramic tablet of ?-Al.sub.2O.sub.3 with an average pore diameter of 3 ?m, a tablet diameter of 18 mm, and a thickness of 2 mm produced by ceramic calendering was progressively coated one side with ceramic slurries of ?-Al.sub.2O.sub.3 powders of decreasing particle size by spin coating and subsequent sintering until a final covering layer with an average pore diameter of 200 nm had been applied. [0036] 1b) A porous ceramic tube of ?-Al.sub.2O.sub.3 with an average pore diameter of 3 ?m, an external diameter of 10 mm, an internal diameter of 7 mm, and a length of 100 mm produced by extrusion was progressively coated on the inner side with ceramic slurries of ?-Al.sub.2O.sub.3 powders of decreasing particle size by slip casting and subsequent sintering until a final covering layer with an average pore diameter of 100 nm had been applied. A colloidal gel layer was deposited on this covering layer from a colloidal boehmite sol by one-side immersion coating, which after sintering resulted in a final ?-Al.sub.2O.sub.3layer with an average pore diameter of between 2 nm and 5 nm. [0037] 1c) A tube according to example 1b), after coating with the 100 nm ?-Al.sub.2O.sub.3 layer, was progressively coated with a colloidal TiO.sub.2 sol, a colloidal ZrO.sub.2 sol, and a polymeric TiO.sub.2sol with interspersed thermal treatment of the respective coatings. The final covering layer was composed of amorphous TiO.sub.2 and had an average pore diameter of 0.9 nm.

WORKING EXAMPLE 1

[0038] A membrane from example 1b) was subjected to a deposition process from the gas phase (chemical vapor deposition, CVD) as follows: the membrane was placed in the constant heating zone of a vertical oven. Before the deposition process began, an inert atmosphere was produced by purging with nitrogen. After sufficient purging, the oven containing the membrane and an inert atmosphere was heated to a deposition temperature of 650? C. After this temperature was reached, the gas composition was changed from 100% nitrogen to 96.4% nitrogen (99.8%, Linde) and 3.6% acetylene (99.6%, Air Liquide). The duration of this treatment was 30 min. Following the carbon deposition, the atmosphere was changed to 100% nitrogen and the oven was cooled to room temperature before the sample was removed. Analytical detection was carried out by permporosimetry with He as the permeable phase and n-hexane as the condensed phase (FIG. 1).

[0039] It was found that as expected, the starting membrane had a pore diameter of <3 nm. The He dry gas permeance was approx. 180 m.sup.3/(m.sup.2.Math.h.Math.bar). After blocking of all pores <3 nm, the He permeance decreased to approx. 0.42 m.sup.3/(m.sup.2.Math.h.Math.bar), which was equivalent to approx. 0.2% of the starting permeance. The remaining permeation corresponded to the gas flow through defects >3 nm. After carbon deposition, the He dry gas permeation decreased by a factor of 30 to approx. 6 m.sup.3/(m.sup.2.Math.h.Math.bar). With the first 4 n-hexane wetting, the He permeance decreased to approx. 0.4 m.sup.3/(m.sup.2.Math.h.Math.bar) and then remained largely constant with further wetting. Accordingly, it was already possible by carbon infiltration using the CVD method to reduce pores with a diameter of <3 nm to a diameter of <1 nm. Larger pores, however, were not blocked. The method used for CVD deposition of carbon is therefore suitable for reducing the diameter of pores in the magnitude range of defects and intergranular pores of zeolite membranes.

WORKING EXAMPLE 2

[0040] A porous ceramic tube with a final covering layer of ?-Al.sub.2O.sub.3 with an average pore diameter of 100 nm was coated on the inner side of the tube by slip casting with a mixture of silicalite particles, a colloidal silica sol, and water in the mass ratio of 1:4:15. The layer was baked in air at 450? C. After this, hydrothermal treatment was carried out for 24 h at 180? C. in a sealed, Teflon-coated autoclave container in a solution composed of colloidal silica sol, aluminum (Merck), tetrapropylammonium hydroxide (TPAOH 25%, Acros Organics), tetrapropylammonium bromide (>98% TPABr, Alfa Aesar), sodium hydroxide pellets (>99%, VWR) and water (deionized) in the stoichiometric ratio of 90 SiO.sub.2/0.225 Al.sub.2O.sub.3/1 Na.sub.2O/4.15 TPAOH/1.85 TPABr/1990 H.sub.2O. The resulting MFI membrane was detemplated in air at 450? C.

[0041] The MFI membrane was subjected according to Working Example 2 to CVD treatment with a 2.4% acetylene nitrogen mixture for a deposition duration of 45 min and a deposition temperature of 750? C. Both the produced and the treated membranes were tested by means of individual gas permeance measurement with selected gases.

[0042] It is clear at the individual gas permeances shown in FIG. 2 that by the CVD treatment, the permeances of all of the gases decrease, and the ideal He/SF.sub.6 permselectivity increases from 4.5 to 6.0. This improvement is attributable to controlled blocking of the defect pores or defects.

WORKING EXAMPLE 3

[0043] An MFI membrane according to Working Example 2 was treated with n-hexane (>99%, Merck) as a vapor phase. For this purpose, a nitrogen flow was loaded with n-hexane and guided for 45 min over the membrane, wherein an applied temperature of 550-800? C. was to produce immediate pyrolysis of the condensing n-hexane. For all of the pyrolysis temperatures, it was possible to detect significant increases in the ideal H.sub.2/SF.sub.6and He/SF.sub.6 permselectivities, which is attributable to blocking of the intergranular pores (FIG. 3).

WORKING EXAMPLE 4

[0044] A membrane according to 1c) was infiltrated with a mixture of phenol resin powder (0235DP, Momentive) dissolved in methanol (Merck) and 1-methyl-2-pyrrolidone (Merck) in the mass ratio 3.25:22.5:20 by pouring the mixture into the ceramic tube. After this, thermal treatment was carried out at 150? C. for crosslinking of the phenol resin, followed by pyrolysis under Ar at 740? C. The starting membrane and the carbon-infiltrated membrane were examined by permporosimetry using He as a gas phase and n-hexane as a condensed phase. It was found that as expected, the starting membrane had a pore diameter of <2 nm. The He dry gas permeance was approx. 350 m.sup.3/(m.sup.2.Math.h.Math.bar). After blocking of all of the pores <2 nm, the He permeance decreased to approx. 12 m.sup.3/(m.sup.2.Math.h.Math.bar), equivalent to approx. 3% of the starting permeance. The remaining permeation corresponded to the gas flow through defects >2 nm. The permeance through defects >4 nm was approx. 10 m.sup.3/(m.sup.2.Math.h.Math.bar), and thus 2% of the He dry gas permeance. After carbon deposition, the He dry gas permeance dropped by a factor of 30 to approx. 12 m.sup.3/(m.sup.2.Math.h.Math.bar). With increasing n-hexane wetting, only a slight decrease in He permeance was observed. For pores >4 nm, the He permeance was identical to that of the membrane without carbon infiltration at 10 m.sup.3/(m.sup.2.Math.h.Math.bar). Accordingly, it was possible by means of the carbon infiltration to largely block pores with a diameter of <4 nm. Larger pores, on the other hand, were not blocked. The method used of infiltration of a membrane with a liquid precursor and subsequent pyrolysis is therefore suitable for blocking smaller pores that are in the magnitude range of defects and intergranular pores of zeolite membranes.

WORKING EXAMPLE 5

[0045] A tube-shaped ceramic membrane with a final layer of ?-Al.sub.2O.sub.3 with an average pore diameter of between 2 nm and 5 nm according to 1b) was coated with a layer of zeolite nanocrystals produced by hydrothermal synthesis at 60? C. for 14 days in a mixture of TPAOH, TPABr and TEOS (>99%, ABCR) at a molar ratio of 25 SiO.sub.2:9 TPAOH 360 H.sub.2O:100 ethanol according to Person et al., Zeolites, 1994, Vol. 14, September/October, 557-567. Coating was carried out by adhesion of the MFI crystals measuring 50 nm to 60 nm to the porous ceramic substrate using dimethylammonium chloride (65% in water, Fluka) according to Hedlund et al.; J. Membr. Sc. 159 (1999) 263. The zeolite nanolayer obtained in this manner was calcined in air at 450? C. The sample was then infiltrated on one side with phenol resin powder (0235DP, Momentive) dissolved in methanol (Merck) and 1-methyl-2-pyrrolidone (Merck) in the mass ratio of 3.25:22.5:20, followed by polymerization at 150? C. and pyrolysis under Ar at 740? C. The carbon-infiltrated zeolite membrane obtained was tested by individual gas permeation at 150? C. An He permeance of 3 m.sup.3/(m.sup.2.Math.h.Math.bar), an H.sub.2 permeance of 6 m.sup.3/(m.sup.2.Math.h.Math.bar), and an SF.sub.6 permeance of approx. 0.002 m.sup.3/(m.sup.2.Math.h.Math.bar) were observed. With an ideal He/SF.sub.6 permselectivity of approx. 1,650 and an ideal H.sub.2/SF.sub.6 permselectivity of approx. 3,600, a carbon-infiltrated zeolite membrane with molecular sieve properties was obtained (FIG. 5).

[0046] Gas mixtures composed to 50% of H.sub.2O and N.sub.2, H.sub.2O and CH.sub.4, H.sub.2O and CO.sub.2 as well as H.sub.2O and H.sub.2 respectively were then directed at 11 bar absolute onto a membrane produced in this manner at 200? C. The pressure on the back side of the membrane was atmospheric pressure (1 bar absolute) or slightly elevated pressure (4 bar absolute). The gas flow passing through the membrane was guided through a cold trap (?10? C.) in which the water produced was condensed. The residual gas flow was measured using a multiscale bubble counting tube. It was found that after switching from one gas mixture to the next, after a brief period, permeation of the gas CO.sub.2 decreased by a factor of about 10 and permeation of the gases N.sub.2, CH.sub.4 and H.sub.2 fell below the detection limit, while water permeation constantly remained in the considerably higher permeation range or even increased. Accordingly, infinitely high H.sub.2O/N.sub.2, H.sub.2O/CH.sub.4, and H.sub.2O/H.sub.2permselectivities, as well as an H.sub.2O/CO.sub.2 permselectivity of 400, were measured. The membrane is therefore permeable to water in any event, but for other gases, it is considerably less permeable to totally impermeable (FIG. 6).

WORKING EXAMPLE 6

[0047] In order to produce a zeolite membrane composed of the active components SAPO-34 and a porous carrier structure, a-aluminum oxide, in situ crystallization is carried out by means of hydrothermal synthesis. For this purpose, a synthesis solution is first produced as follows: The structure-directing agent (SDA), tetraethylammonium hydroxide (TEA-OH, 35 wt %, Sigma Aldrich) is prepared and mixed with the silicon source, tetraethyl orthosilicate (TEOS, 99%, Alfa Aesar) and the additionally required distilled water. This obtained solution A is stirred for 10 min at 600 rpm. Under further stirring at 600 rpm, the aluminum source, aluminum isopropoxide (Al isopropoxide for synthesis, 98%, Merck) is slowly added, and the resulting solution B is stirred for a further 2 h. The phosphorus source, orthophosphoric acid (85 wt %, VWR), is added dropwise to this solution B. The obtained solution C, with a resulting molar composition of 1.0 Al.sub.2O.sub.3:4.0 P.sub.2O.sub.5 0.6 SiO.sub.2:2.0 TEA-OH 139 H.sub.2O, is aged under stirring at 600 rpm for 30 min. After this, 30 ml of this aged solution C is transferred to a stainless steel autoclave (45 ml, 4744, Parr Instruments) with a Teflon insert, which already contains the ?-aluminum oxide carrier to be seeded according to 1a). The subsequent hydrothermal synthesisin situ crystallizationis carried out statically at 180? C. for 48 h. After the required synthesis time has elapsed, the obtained SAPO-34 membrane (carrier coated during in situ crystallization with SAPO-34) is separated from the resulting excess SAPO-34 powder by centrifugation.

[0048] The SAPO-34 membrane synthesized in this manner is first dried at 75? C. and then calcined to remove the template. During the calcination process, the SAPO-34 membrane is heated in air at a heating rate of 0.2 K min.sup.?1 to 400? C., exposed to this temperature for 16 h, and then slowly cooled. The SAPO-34 membrane produced is stored in an oven heated to 100? C.

WORKING EXAMPLE 7

[0049] Starting from a zeolite membrane, a carbon-integrated membrane is produced by two method steps: [0050] 1. liquid infiltration of the zeolite membrane [0051] 2. carbonization of the infiltrated zeolite membrane

[0052] For infiltration of the produced SAPO-34 membrane, a solution of the monomer furfuryl alcohol (?98.0%, Merck) and nitric acid (HNO.sub.3, 65 wt %, Fluka) is first produced. For this purpose, the furfuryl alcohol is prepared, and the required amount of nitric acid is then added dropwise under stirring. Under further stirring, prepolymerization of this solution takes place for 40 min. After this, the produced SAPO-34 membrane is immersed for 5 min in this solution. The infiltrated SAPO-34 membranes are first dried for crosslinking of the polymers for 16 h at 75? C. and then carbonized. The carbonization takes place in a nitrogen atmosphere at 500? C. for 16 h. The heating rate in this case is also 0.2 K min.sup.?1.

WORKING EXAMPLE 8

[0053] As a system for comparison with the produced carbon-integrated zeolite membranes, starting from an ?-Al.sub.2O.sub.3 carrier with a pore size of 200 nm according to 1a), a carbon-integrated ?-Al.sub.2O.sub.3 carrier (CiAl.sub.2O.sub.3) was produced. As in the case of Working Example 7, the ?-Al.sub.2O.sub.3 carrier is immersed in a prepolymerized solution of furfuryl alcohol and nitric acid, dried, and then carbonized. The produced SAPO-34 membrane (SAPO-34/M, Working Example 6), the carbon-integrated SAPO-34 membranes (SAPO-34/CiZM, Working Example 7), and the carbon-integrated ?-Al.sub.2O.sub.3 carrier (CiAl.sub.2O.sub.3, Working Example 8) are characterized at different temperatures (25? C.) by means of permeance measurements of individual gases and mixed gases (FIG. 7), and selectivities for the separation of CO.sub.2 and N.sub.2 are determined from this.

[0054] The pure SAPO-34 membrane showed extremely high permeances in the magnitude range around 2?10.sup.?5 mol/(m.sup.2.Math.s.Math.Pa) (individual gas permeation) or around 7?10.sup.?7 mol/(m.sup.2.Math.s.Math.Pa) (mixed gas permeation). With permselectivities of about 1, there was virtually no selective substance separation. The integration of carbon caused the permeances to decrease to values of 0.5?10.sup.?8 mol/(m.sup.2.Math.s.Math.Pa) (N.sub.2) to 5?10.sup.?8 mol/(m.sup.2.Math.s.Math.Pa) (CO.sub.2), and the permselectivities increased to 9 (ideal permselectivity of the individual gas measurement) or to 14 or 15 (mixed gas measurements), which corresponds to a membrane with highly selective separation. An ?-Al.sub.2O.sub.3 membrane integrated with carbon having a pore diameter of 200 nm, on the other hand, showed selectivities of only 1 to 2. Accordingly, the separation properties of the carbon-integrated zeolite membrane are the separation properties of the zeolite crystals, the intergranular pores of which were blocked by carbon.

[0055] The carbon species produced were further tested by Raman spectroscopy. The Raman spectra of the two samples (in the infiltrated ?-Al.sub.2O.sub.3 carrier with 200 nm pores and in intergranular pores of the infiltrated zeolite membrane) show the bands typical for carbon at approx. 1350 cm.sup.?1 and approx. 1590 cm.sup.?1. The band at 1590 cm.sup.?1 represents the stretching vibration sp.sup.2 of hybridized carbon bonds in the plane. In amorphous structures, in addition to these bands, one can see a further band at 1350 cm.sup.?1 that shows a different symmetry. The Raman spectra indicate an amorphous structure of carbon (FIG. 8).

[0056] A pure zeolite membrane on an ?-Al.sub.2O.sub.3 carrier with 200 nm pores (SAPO-34/M) and a zeolite membrane subsequently treated with carbon (SAPO-34(CiZM) were examined by x-ray diffractometry (FIG. 9). In both diffractograms, only the characteristic x-ray reflexes of the zeolite and the ?-Al.sub.2O.sub.3 carrier ceramic could be found. The carbon could not be detected as a crystalline species. Accordingly, the infiltrated carbon is x-ray amorphous carbon.