Composite material type oxygen transport membrane

Abstract

A composite material type oxygen transport membrane and its preparation method are disclosed. The composite material that is an ionic-electronic mixed conducting material having high ionic conductivity is stirred into slurry and formed into a thin strip-shaped green tape substrate through tape casting to obtain a predetermined half-finished substrate, and then sintered to form the half-finished substrate into a conductive function type oxygen ion conducting substrate, followed by choosing small particle shaped highly catalyzed ionic-electronic mixed conducting material to be evenly adhered to at least one side surface of the conductive function type oxygen ion conducting substrate to form a reductive function type oxygen ion conducting layer. The reductive function type oxygen ion conducting layer and the conductive function type oxygen ion conducting substrate are then bonded to produce a composite material type oxygen transport membrane element.

Claims

1. A method for preparation of a composite material type oxygen transport membrane, comprising following steps: preparing a substrate green tape by tape casting and forming the substrate green tape into a preformed half-finished product, sintering the substrate green tape of the half-finished product at a temperature range from 1000 to 1200? C. for about 4 hours to form into a conductive function type oxygen ion conducting substrate, measuring the gas permeability of the conduction function type oxygen ion conducting substrate to confirm the predetermined gas separation efficiency by checking the dense property and microstructure of the conduction function type oxygen ion conducting substrate, if the gas permeability is maintained below 1.0?10.sup.?5 Darcy, the process proceeds to the next step, attaching an ionic-electronic mixed conductor material having small particles with high catalytic capacity to at least one surface of conductive function type oxygen ion conducting substrate to form a reductive function type oxygen ion conducting layer, in which the small particles of high catalytic capacity are adhered evenly through a predetermined attaching procedure by bonding the reductive function type oxygen ion conducting layer and the conductive function type oxygen ion conducting substrate, forming a composite material type oxygen transport membrane element.

2. The method for preparation of a composite material type oxygen transport membrane of claim 1, wherein the step of preparing the substrate green tape includes thermally laminating and water pressure equalizing the thin strip-shaped substrate green tape to form a half-finished substrate with bulk thickness between 300 and 800 ?m.

3. The method for preparation of a composite material type oxygen transport membrane of claim 1, wherein the sintering temperature is preferably about 1100? C., and the sintering temperature rate is preferably increased and/or decreased at 3? C./min.

4. The method for preparation of a composite material type oxygen transport membrane of claim 1, wherein the sintered dense property is determined by the gas permeability meter, and the microstructure is checked by a scan type electron microscope.

5. The method for preparation of a composite material type oxygen transport membrane of claim 1, wherein the attachment procedure is selected from one of a laser melting sintering, a physical vapor deposition, a chemical vapor deposition, a sol gel method, a screen printing, and a high temperature sintering.

6. The method for preparation of a composite material type oxygen transport membrane of claim 5, wherein the laser melting sintering method is a low power CO.sub.2 laser with a wavelength of 10.6 ?m and a maximum power of 50 W, which is focused by a focusing lens to 120 ?m spot size on the surface of the conductive function type oxygen ion conducting substrate, and 8% power for the whole scan.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a plan view of a composite material type oxygen transport membrane according to the present invention.

(2) FIG. 2 is a flow chart of the main preparation method of the composite material type oxygen transport membrane of the present invention.

(3) FIG. 3 is a view showing the surface microstructure of a composite type oxygen transport membrane prepared by a laser melting sintering method according to the present invention;

(4) FIG. 4 is a graph comparing the oxygen transporting amount of the composite type oxygen transport membrane of the present invention with the conventional oxygen transport membrane.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

(5) Referring to FIG. 1, the main structure of the composite material type oxygen transport membrane 1 of the present invention comprises a conductive function type oxygen ion conducting substrate 11 and a reductive function type oxygen ion conducting layer 12, wherein the composite material type oxygen transport membrane 1 is made of ionic-electronic mixed conductors of sheet structure having a relatively high ionic conductivity characteristic. In a preferred embodiment, the mixed conductor material of the conductive function type oxygen ion conducting substrate 11 is barium strontium cobalt iron oxide (Ba.sub.0.5Sr.sub.0.5Co.sub.0.8Fe.sub.0.2O.sub.3-?, BSCF).

(6) The reductive function type oxygen ion conducting layer 12 is composed of an ionic-electronic mixed conductor material having a relatively high catalytic capacity, and the reductive function type oxygen ion conducting layer 12 is formed in a small particle uniformly dispersed and adhered to at least one surface of the conductive function type oxygen ion conducting substrate 11.

(7) In a preferred embodiment, the mixed conductor material of the reductive function type oxygen ion conducting layer 12 is lanthanum strontium cobalt iron oxide (La.sub.06Sr.sub.0.4Co.sub.0.2Fe.sub.0.8O.sub.3-?, LSCF) or selected from the group consisting of barium iron zirconium oxide (BaFe.sub.0.975Zr.sub.0.025O.sub.3-?, BFZ), Barium lanthanum iron oxide (BaLa.sub.0.95Fe.sub.0.05O.sub.3-?, BLF), barium zirconium cobalt oxide (BaZr.sub.0.2Co.sub.0.8FeO.sub.3-?, BZCF), lanthanum strontium manganese oxide (La.sub.0.8Sr.sub.0.2MnO.sub.3-?, LSM), lanthanum strontium cobalt oxide (La.sub.0.8Sr.sub.0.2CoO.sub.3-?, LSC), samarium strontium cobalt oxide (Sm.sub.0.5Sr.sub.0.5CoO.sub.3-?, SSC), sodium bismuth titanium oxide (Na.sub.0.54Bi.sub.0.46TiO.sub.2.96, NBT).

(8) Referring to FIG. 2, the main preparation method of the composite material type oxygen transport membrane of the present invention comprises main steps, S11: forming the substrate green tape, S12 laminating a plurality of substrate green sheets forming a half-finished substrate; S13: sintering the substrate green tape of the half-finished product to form into a conductive function type oxygen ion conducting substrate: S14: measuring the gas permeability of the conduction function type oxygen ion conducting substrate to confirm the preset gas separation efficiency; S15: attaching an ionic-electronic mixed conductor material having small particles with high catalytic capacity to at least one surface of the oxygen ion conducting substrate to form a reductive function type oxygen ion conducting layer. Hereinafter, each step of the preparation method of the composite material type oxygen transport membrane of the present invention will be described in reference to the configuration of FIG. 1.

(9) First, the step S11 is a step of selecting an ionic-electronic mixed conducting powder material having a high ionic conductivity property, and the powder is stirred and formed into a slurry-like thin strip-shaped substrate green tape by tape casting.

(10) The step S12 is a step of thermally laminating and water pressure equalizing the thin strip-shaped substrate green tape to form a half-finished substrate with bulk thickness between 300 and 800 ?m.

(11) The step S13 is a step of sintering the substrate green tape of the half-finished product at a temperature range from 1000 to 1200? C., preferably 1100? C. with increased and/or decreased rate at 3? C./min, for about 4 hours to form into a conductive function type oxygen ion conducting substrate 11,

(12) The step S14 is a step of measuring the gas permeability of the conduction function type oxygen ion conducting substrate to confirm the preset gas separation efficiency, checking the dense property and microstructure of the conduction function type oxygen ion conducting substrate, in which the sintered dense property is determined by a gas permeability meter and the microstructure is checked by a scan type electron microscope.

(13) The step S15 is a step of attaching an ionic-electronic mixed conductor material having small particles with high catalytic capacity to at least one surface of the oxygen ion conducting substrate 11 to form a reductive function type oxygen ion conducting layer 12, in which the small particles of high catalytic capacity are adhered uniformly through a predetermined attaching procedure and bonding the reductive function type oxygen ion conducting layer 12 and the conductive function type oxygen ion conducting substrate 11, forming a composite material type oxygen transport membrane 1.

(14) In a preferable embodiment, the attachment procedure is selected from at least one of a laser melting sintering, physical vapor deposition, chemical vapor deposition, sol gel method, screen printing, high temperature sintering and the like.

(15) The laser melting sintering method uses a low power CO.sub.2 laser with a wavelength of 10.6 ?m with a maximum power of 50 W, which is focused by a focusing lens to 120 ?m spot size on the surface of the conductive function type oxygen ion conducting substrate 11, and the whole scan is carried out with 8% of the maximum power.

(16) In a preferred embodiment, the attachment procedure can be performed using a laser melting sintering process with low power carbon dioxide lasers having a wavelength of 10.6 ?m with a maximum power of 50 W to focus through a focusing lens 120 ?m spot on the surface of the conductive function type oxygen ion conducting substrate 11 and using 8% power to scan over the small particle ionic-electronic mixed conducting biphasic material having high catalytic ability dispersed on the surface of the conductive function type oxygen ion conducting substrate 11, causing the change of the local temperature field on the surface of the small particle ionic-electronic mixed conductor material, leading to the biphasic material to be melted and sintered between the interfaces, and the ionic-electronic mixed conductor material is uniformly adhered to the surface of the conductive function type oxygen ion conducting substrate 11 and forms a reductive function type oxygen ion conducting layer 12.

(17) Referring to FIG. 3, the surface microstructure of the composite material type oxygen transport membrane 1 prepared by the laser melting sintering method was checked by an electron microscope, and it was found in the non-laser scanning region that the original conductive function type oxygen ion conducting substrate 11 (BSCF material) has no matter attached. On the contrary, the laser-scanned region of the conductive function type oxygen ion conducting substrate 11 exhibits ablating and gelled coating over the reductive function type oxygen ion conducting layer 12 (LSCF material), which was previously dispersed on the surface of the conductive function type oxygen ion conducting substrate 11, and a part of powder particles of the reductive function type oxygen ion conducting layer 12 with diameter 0.6-1.5 ?m will be ablated by laser to form smaller particles, less than 0.5 ?m, adhering to the surface of the oxygen ion conducting substrate 11 to further enhance the reaction area.

(18) In addition, the laser melting and sintering method can avoid the thermal stress rupture caused by the difference of coefficient of thermal expansion between materials that arose in the conventional sintering process. Also the costly equipment or complicated procedures that are adopted in other kinds of attaching method are not required in the present invention, thus it can effectively reduce the equipment investment and production cost.

(19) Referring to FIG. 4, after the composite material type oxygen transport membrane 1 of the present invention is tightly packed, it is tested by feeding the air and argon of 100 sccm (standard cubic centimeters per minute), It was found that the oxygen transport flow rate of the composite material type oxygen transport membrane 1 had increased by more than 10% as compared with that of the conventional oxygen transport membrane at an operating temperature of 900? C., and more than 60% at an operating temperature of 700? C.

(20) It can be seen, therefore, that the conductive function type oxygen ion conducting substrate 11 itself can provide a good catalytic ability at a relatively high temperature environment, so that the overall oxygen transport flow rate is less noticeable; however, at a relatively low temperature the surface of the conventional oxygen transport membrane dissociates and the oxygen ion velocity is greatly reduced, and due to the overall transport rate is limited by the number of oxygen ions, the overall transport is transferred to surface reaction control, and the reductive function type oxygen ion conducting layer 12 will help increase the dissociation of oxygen into oxygen ions and the number of surface oxygen ions arises more and increases the ion concentration difference at both ends, which can enhance the overall diffusion rate and oxygen transport flow.

(21) In summary, the composite material type oxygen transport membrane of the present invention and the method for preparing the composite material type oxygen transport membrane can effectively reduce the catalytic capacity of the conventional high ionic conductivity material at a relatively low temperature and improve the overall oxygen transport flow rate and reduce the production cost.

(22) It is to be understood that even though numerous characteristics and advantages of the present invention have been set forth in the foregoing description, together with details of the structure and function of the invention, the disclosure is illustrative only, and changes may be made in detail, especially in matters of shape, size, and arrangement of parts within the principles of the invention to the full extent indicated by the broad general meaning of the terms in which the appended claims are expressed.