Sealing agent for ion transport membranes

Abstract

A sealing agent for ion transport membranes (ITMs) includes a composition having a glass powder and a ceramic powder. The ceramic powder can include Ba.sub.0.5Sr.sub.0.5Co.sub.0.8Fe.sub.0.2O.sub.3 (BSCF) or La.sub.2NiO.sub.4+ (LNO). The ceramic powder can be identical to the ceramic powder from which the ITM is made. The glass powder can include PYREX glass. The sealing agent can be in the form of a paste. The sealing agent can be used to attach an ion transport membrane to one or more support tubes. The sealing agent includes from about 10 wt. % to about 40 wt. % glass powder and from about 60 wt. % to about 90% wt. % (BSCF) ceramic powder.

Claims

1. A sealing agent for ion transport membranes comprising: a composition including about 10 wt. % to about 40 wt. % glass powder and about 60 wt. % to about 90% wt. % ceramic powder, the ceramic powder including at least one of Ba.sub.0.5Sr.sub.0.5Co.sub.0.8Fe.sub.0.2O.sub.3 (BSCF) and La.sub.2NiO.sub.4+ (LNO).

2. The sealing agent for ion transport membranes according to claim 1, wherein the composition is a paste.

3. The sealing agent for ion transport membranes according to claim 1, wherein the glass powder has a composition including 4.0% boron, 54.0% oxygen, 2.8% sodium, 1.1% aluminum, 37.7% silicon, and 0.3% potassium composition.

4. The sealing agent for ion transport membranes according to claim 1, wherein the composition includes about 20 wt. % glass powder.

5. The sealing agent for ion transport membranes according to claim 1, wherein the composition includes about 80 wt. % ceramic powder.

6. A method of preparing a sealing agent for ion transport membranes comprising the steps of: providing glass pieces; milling the glass pieces to obtain glass powder; mixing the glass powder with ceramic powder to form a mixture, the ceramic powder including at least one of Ba.sub.0.5Sr.sub.0.5Co.sub.0.8Fe.sub.0.2O.sub.3 (BSCF) and La.sub.2NiO.sub.4+ (LNO); and adding water to the mixture to form a paste.

7. The method of preparing a sealing agent for ion transport membranes according to claim 6, wherein the ceramic powder is prepared by first preparing a gel using a sol-gel process, calcining the resulting gel at 250 C. for 30 minutes to obtain a powder, heating the powder at 1000 C. for 10 hours, and milling the powder for 24 hours.

8. The method of preparing a sealing agent for ion transport membranes according to claim 6, wherein the step of milling the glass pieces comprises is ball milling the glass pieces, the ball milling of the glass pieces being conducted in an alumina jar mill with alumina balls.

9. The method of preparing a sealing agent for ion transport membranes according claim 6, wherein the mixture includes about 20 wt. % glass powder and about 80 wt. % ceramic powder.

10. The method of preparing a sealing agent for ion transport membranes according to claim 6, wherein the glass powder and the ceramic powder are less than 1 micron in diameter.

11. A gas separation system comprising: (a) an ion transport membrane, the ion transport membrane including a ceramic material; (b) a sealing agent including about 10 wt. % to about 40 wt. % glass powder and about 60 wt. % to about 90 wt. % ceramic powder, the ceramic powder being identical to the ceramic material of the ion transport membrane, the ceramic powder of the sealing agent including at least one of Ba.sub.0.5Sr.sub.0.5Co.sub.0.8Fe.sub.0.2O.sub.3 (BSCF) and La.sub.2NiO.sub.4+ (LNO); and (c) one or more support tubes secured to the ion transport membrane and the sealing agent.

12. The gas separation system according to claim 11, wherein the sealing agent comprises about 20 wt. % glass powder.

13. The gas separation system according to claim 11, wherein the sealing agent comprises about 80 wt. % ceramic powder.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a diagram showing the parts of an exemplary gas separation system,

(2) FIG. 2 is a diagram showing an exemplary gas separation system connected to a gas permeation measuring system.

(3) FIG. 3 is a graph showing the percentage of oxygen at the permeate side of the membrane during heating of the exemplary gas separation system by the gas permeation measuring system.

(4) FIG. 4 is a graph showing the oxygen permeability of a 0.9 mm thick BSCF membrane at 905 C.

(5) FIG. 5 is a graph showing oxygen permeability of a 1 mm thick La.sub.2NiO.sub.4+ (LNO) membrane at 900 C.

(6) Similar reference characters denote corresponding features consistently throughout the attached drawings.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

(7) A sealing agent for ion transport membranes (ITMs) includes a composition having a glass powder and a ceramic powder. The ceramic powder can include Ba.sub.0.5Sr.sub.0.5Co.sub.0.8Fe.sub.0.2O.sub.3 (BSCF) or La.sub.2NiO.sub.4+ (LNO). The ceramic powder can be identical to the ceramic powder from which the ITM is made. The glass powder can include PYREX glass. The sealing agent can be used to seal gaps that exist between the ITM and one or more adjoined support tubes. The one or more support tubes can include a ceramic or metal material. Preferably, the one or more supports include ceramic. The sealing agent can be in the form of a paste. The sealing agent can include from about 10 wt. % to about 40 wt. % glass powder and from about 60 wt. % to about 90% wt. % ceramic powder. Preferably, the composition includes about 20 wt. % PYREX glass powder and about 80 wt. % ceramic powder.

(8) As used herein, the term PYREX (trademarked as PYREX) refers to a brand introduced by Corning Inc. for a line of clear, low-thermal-expansion borosilicate glass used for laboratory glassware and kitchenware. The composition of both Corning 7740 and Schott 8830 is given as 80.6% SiO.sub.2, 12.6% B.sub.2O.sub.3, 4.2% Na.sub.2O, 2.2% Al.sub.2O.sub.3, 0.04% Fe.sub.2O.sub.3, 0.1% CaO, 0.05% MgO, and 0.1% Cl. According to the National Institute of Standards and Technology, borosilicate Pyrex is composed of (as percentage of weight): 4.0% boron, 54.0% oxygen, 2.8% sodium, 1.1% aluminum, 37.7% silicon, and 0.3% potassium.

(9) The sealing agent can be prepared by providing crushed Pyrex glass pieces; milling the crushed glass pieces in an alumina jar mill using alumina balls to obtain glass powder; and mixing the glass powder with a ceramic powder and water to form a paste. For example, the ceramic powder can be Ba.sub.0.5Sr.sub.0.5Co.sub.0.8Fe.sub.0.2O.sub.3 (BSCF) powder. The BSCF powder can be prepared by first preparing a gel using a sol-gel process and then calcining the resulting gel at 250 C. for 30 minutes to obtain the BSCF powder. The powder can be heated at 1000 C. for 10 hours and then ball milled for 24 hours in the alumina jar mill with alumina balls. The glass and BSCF powder can then be milled to provide a mixture. Water can be added to the mixture to provide the sealing agent in the form of a paste.

(10) A method of attaching an ITM to at least one support tube includes applying a uniform layer of sealing agent to a surface of the at least one support to provide a coated surface and disposing the ITM on the coated surface to provide a gas separation system including the sealing agent described herein. The gas separation system can be heated for at least thirty minutes and then cooled to provide a hermetic or gas-tight seal between the ITM and the at least one solid support. FIG. 1 shows an exemplary gas separation system including support tubes 106a-106d, the ITM 102, and the sealing agent 104.

EXAMPLE 1

Preparation of Sealing Agent

(11) A standard PYREX beaker was crushed and the crushed glass was ball milled for 24 hours in a standard alumina jar mill using alumina balls. The Ba.sub.0.5Sr.sub.0.5Co.sub.0.8Fe.sub.0.2O.sub.3 (BSCF) powder was made from a sol-gel process, where solutions made from nitrates of Ba, Sr, Co and Fe were mixed in stoichiometric ratios and heated while stirring. Ethylene glycol and citric acid were used as polymerization and chelating agents. The resulting gel was calcined at 250 C. for 30 minutes to obtain a powder. This powder was heat treated at 1000 C. for 10 hours and then ball milled for 24 hours in the alumina jar mill with alumina balls. After the Pyrex glass and BSCF powders were milled, mixtures of Pyrex glass powder and BSCF powder with varying concentrations were prepared as illustrated in Table 1. The mixtures were milled for some more time to ensure homogeneity. The typical particle size of the Pyrex and BSCF powders were less than 1 micron in diameter. Finally, some distilled water was added to the mixtures to form a paste.

EXAMPLE 2

Attaching the ITM to Alumina Tubes Using the Sealing Agent

(12) The surfaces of the membrane (ITM) and the alumina support tubes were smoothly polished. A uniform layer about 1 mm thick of the sealing agent was then applied with a spatula on the lower alumina tube surfaces. The membrane (ITM) to be attached to the alumina support tubes was placed over this paste. A layer of the paste was then applied between the top of the membrane and the top alumina tubes as well. After slightly pressing the tubes against the membrane, heat was used to allow the sealing agent to seal the membrane to the tubes. The membrane started to seal at around 830 C. at a rate of 2 C./min. The temperature was maintained at 950 C. for about 30 minutes for optimum sealing. The seal was tested in the temperature range of 800-1100 C., and was found to work well at these temperatures.

EXAMPLE 3

Testing an Exemplary Gas Separation System (BSCF Membrane) Including the Sealing Agent

(13) An exemplary gas separation system 210 including the sealing agent described herein was tested using the gas permeation measuring system 200 shown in FIG. 2. A BSCF membrane was used. The exemplary gas separation system including the sealing agent described herein 210 was heated by the furnace 208 of the system 200. Air was supplied from a tank 218 through a flow meter 216 into the top aluminum tube 106b to heat the tubes. Helium (He) from a helium tank 215 was introduced through a flow meter 202 as the sweep gas for the lower tube 106a, which carried the permeated oxygen 203 to the gas chromatograph 206 in a gas stream 203. The gas chromatograph 206 measured the quantity of O.sub.2 and any other gases present in the stream 203. Any presence of nitrogen in the permeate gas stream 203 would indicate an improper sealing of the membrane. The ITM used was a BSCF membrane that was about 0.9 mm thick.

(14) A total of four mixtures of BSCF and Pyrex powders (referenced in Table 1) were tested. The mixtures varied in amounts of glass and BSCF. The permeation tests were carried out in temperatures ranging from about 700 C. to about 1100 C. The results of these tests are presented in Table 1. As illustrated in Table 1, it was found that the mixtures with 30 and 40 wt. % Pyrex always sealed the membrane between the aluminum support tubes but that this sealing agent was not desirable due to a strong chemical reaction with the membrane material. The bond was also found to be too strong to allow removal of the membrane without breakage. On the other hand, the sealing agent with 10 wt. % Pyrex glass formed a weak bond between the tube and the membrane. As a result it was unable to provide a suitable seal on a regular basis. However, the sealing agent with 80 wt. % BSCF powder and 20 wt. % Pyrex was found to be the best sealing material in all of the experiments. This sealing agent provided desirable bond strength, allowed reuse of the membrane, and resulted in no visible reaction with the membrane material. Thus, this composition is the best sealing material for the ITM based gas separation applications.

(15) TABLE-US-00001 TABLE 1 Summary of Test Results of Seals of Ion Transport Membranes BSCF Pyrex Sr powder glass # (wt. %) (wt. %) Observation 1 60 40 Good wetting, very strong bond, considerable reaction between glass and membrane 2 70 30 Good wetting, very strong bond, slight reaction between glass and membrane 3 80 20 Good wetting, desirable bond strength, no reaction between glass and membrane 4 90 10 Poor wetting, weak bond, no reaction

(16) FIG. 3 is a graph showing the percentage of oxygen at the permeate side of the membrane during heating of the exemplary gas separation system including the sealing agent described herein. As can be seen, by the time the temperature crosses 900 C., the amount of oxygen at the permeate side is above 99%. As such, the sealing agent was working very well at very high temperatures. FIG. 4 is a graph showing the oxygen permeability of the BSCF membrane (0.9 mm thick) at 905 C.

(17) The glass/ceramic mixture prepared from the technique described above has very good wetting properties with both the membrane and the alumina tube. Because the glass content is only 20%, there is not a significant chemical reaction with the membrane material. Also the presence of ceramic particles unexpectedly trap the glass once it melts and stops it from diffusing towards the center of the membrane. As illustrated in FIG. 4, this is shown by the excellent stability in the flux of oxygen through the 0.9 mm thick BSCF membrane for 80 hours.

EXAMPLE 4

Testing an Exemplary Gas Separation System (La2NiO4+ (LNO) Membrane) Including the Sealing Agent

(18) The oxygen permeability of an La.sub.2NiO.sub.4+ (LNO) membrane was also shown to be very stable with the sealing agent at 900 C. as shown in FIG. 5.

(19) It is to be understood that the present invention is not limited to the embodiments described above, but encompasses any and all embodiments within the scope of the following claims.