KR100622988B1 - Method for producing palladium alloy composite membrane for hydrogen gas separation - Google Patents

Abstract

The present invention relates to a method for producing a hydrogen gas separation palladium alloy composite membrane, comprising the steps of: (a) surface treatment of the upper portion of the porous support using a plasma; (b) forming a primary metal coating layer on the porous support by an electroplating method; (c) forming a palladium coating layer by sputter deposition on top of the primary metal coating layer; And (d) heat-treating the palladium coating layer to form an alloy layer of palladium and a primary metal.

Description

Preparation Method of Palladium Alloy Composite Membrane for Hydrogen Separation Membrane for Hydrogen Separation             

Figure 1 is a photograph showing the scanning electron microscope cross section observation results of the palladium-nickel alloy layer coated on the porous metal support surface according to the present invention.

2 is a scanning electron micrograph showing that erosion of stainless steel occurred in the hydrochloric acid solution used in the plating activation pretreatment process.

FIG. 3 is a scanning electron micrograph observing that impurities remaining in the porous stainless support / nickel plating layer migrated by a subsequent heat treatment process to form large pore shapes or cracks.

4 is a scanning electron micrograph of the nickel layer plated on the surface of the porous nickel support.

5 shows a scanning electron microscope surface microstructure photograph of a nickel plated layer prepared using a hydrogen plasma surface modification process.

6a shows a scanning electron microscope surface microstructure photograph of a specimen subjected to a nickel plating process and palladium electroplating on a porous nickel support followed by heat treatment at 600 ° C. for 5 hours in a nitrogen atmosphere.

Figure 6b shows a scanning electron microscope microstructure photograph of the palladium-nickel alloy composite film after the nickel plating process and palladium electroplating on the porous nickel support, followed by continuous heat treatment at 600 ℃ for 20 days.

7A shows a scanning electron microscope surface microstructure photograph of a specimen coated on a porous nickel support using a nickel plating process and a palladium sputtering process and then heat treated at 600 ° C. for 5 hours in a nitrogen atmosphere.

Figure 7b shows the crystallinity of the palladium-nickel alloy composite film after heat treatment at 600 ℃ 5 hours using a nickel plating process and a palladium sputtering process on a porous nickel support.

FIG. 8 shows a scanning electron microscope microstructure photograph of the palladium-nickel alloy composite film shown by continuously heat-treating the palladium-nickel alloy composite film formed in FIG. 7 at 600 ° C. for 20 days.

FIG. 9 is a cut-away view of the palladium-nickel alloy composite film (FIG. 9a) and the EDS line scan (FIG. 9b) of the palladium-nickel alloy composite film that is continuously heat-treated at 600 ° C. for 20 days using a palladium sputtering process.

Figure 10 shows the results of measuring the H ₂ / N ₂ transmittance and the gas separation degree of the palladium-nickel alloy composite membrane.

The present invention relates to a method for producing a hydrogen gas separation palladium alloy composite membrane, and more particularly, even with a small amount of palladium, it is possible to produce a separation membrane having excellent selectivity to hydrogen gas and at the same time excellent durability. It relates to a method for producing a hydrogen gas separation palladium alloy composite membrane that can improve the characteristics of the hydrogen gas separation membrane irrespective of the type.

Since the separation membrane used for the production of ultra-high purity hydrogen has a low permeability, studies are mainly underway to improve the selective permeability of the membrane by coating a non-porous palladium membrane on the porous support. As a porous support, ceramic substrates are usually used, but attention is focused on researches on using a metal substrate as a support because of high production cost, inadequate modularity, poor adhesion between ceramic as a support and metal as a separator, low thermal shock resistance, and difficulty in processing. Lee, et al., "Preparation and characterization of SiO ₂ composite membrane for purification of hydrogen from methanol steam reforming as an energy carrier system for PEMFC", Separation and purification technology, 32, 45-50 (2003)].

Recently, a palladium alloy composite separator was developed by using an electroplating process on a metal support of porous stainless steel, but a complicated pretreatment process is required to coat the palladium separator due to the large pore size and surface roughness of the porous stainless steel support. When using the electroplating process of the palladium alloy coating on the surface of the porous stainless steel support, erosion of the support by hydrochloric acid, the main component of the plating activation, deterioration of hydrogen separation characteristics by impurities in the plating solution, and at a commercialization temperature of 500 ° C. Not only does palladium metal diffuse into the internal support causing a decrease in durability, but also has problems that the base metal is destroyed by hydrogen embrittlement of the stainless steel base material by hydrogen absorption during the reforming of hydrogen gas. [R.Checchetto, et. al., "Palladium membranes prepared by RF magnetron sputtering for hydrogen purification ", Surface and Coating Technology, 73, 177-178 (2004)]

The present invention has been made to solve the problems of the prior art, the first object is to provide a separation membrane having excellent selectivity for hydrogen gas and at the same time excellent durability even with a small amount of palladium, as well as a support It is to provide a method for producing a hydrogen gas separation palladium alloy composite membrane that can improve the characteristics of the hydrogen gas separation membrane irrespective of the type.

In order to achieve the above object, the present invention comprises the steps of (a) surface treatment of the upper surface of the porous support using a plasma; (b) forming a primary metal coating layer on the porous support by an electroplating method; (c) forming a palladium coating layer by sputter deposition on top of the primary metal coating layer; And (d) heat-treating the palladium coating layer to form an alloy layer of palladium and a primary metal.

The present invention preferably provides a method for producing the porous support, characterized in that the metal support or ceramic support.

The present invention preferably provides a manufacturing method characterized in that the porous support is a porous nickel support.

The present invention preferably provides a manufacturing method characterized in that the porous support is flat or tubular.

The present invention preferably provides a manufacturing method characterized in that the step of removing the foreign matter by forming the primary metal coating layer by the electroplating method and heat treatment in step b.

The present invention preferably provides a manufacturing method characterized in that the palladium coating layer is formed to a thickness of 2㎛ or less.

The present invention preferably provides a manufacturing method characterized in that the heat treatment in step d is carried out by an in-situ heat treatment method.

The present invention preferably provides a production method characterized in that the primary metal comprises at least one metal selected from silver, nickel, copper, ruthenium, molybdenum.

Hereinafter, the content of the present invention in more detail as follows.

As the support for the composite membrane according to the present invention, a porous metal support or a ceramic support may be used. In addition, the porous support may be flat or tubular. The porous metal support has advantages of low production cost, excellent thermal shock resistance and mechanical strength, processability and modularity, and easy application to a high purity hydrogen separation purification system or a catalytic reactor, compared to a porous ceramic support.

In particular, the porous nickel support has an excellent chemical affinity with palladium and nickel, which are main components of the palladium alloy composite membrane. In addition, the porous nickel support does not generate hydrogen embrittlement due to its inherent properties compared to the porous stainless steel metal support, and has the advantage that the erosion by hydrochloric acid is superior to other metals. The porous nickel support calcined using nickel powder has an average pore size of submicron or less, and the pore density is uniform, so that complicated pretreatment is not required when coating the palladium alloy composite membrane. In addition, the porous nickel support itself has a hydrogen selectivity of about 8 to 10 and a permeability of 150 ml / cm 2 · atm · min or more, and thus has very suitable characteristics as a metal support of the palladium alloy composite membrane.

In order to coat the palladium alloy layer having excellent hydrogen separation characteristics on the surface of the porous support, a double coating layer is required as shown in FIG. 1.

The primary metal coating layer is a coating layer containing an alloying element for the formation of a palladium alloy film in the future. The primary metal coating layer should have a microstructure for complete embedding and surface planarization of the surface pores of the porous support, and at the same time can be accompanied by the diffusion barrier of the palladium metal. The metal which may be such a primary metal layer does not require any particular limitation, but may preferably be selected from at least one metal selected from silver, nickel, copper, ruthenium, molybdenum, and the like, more preferably porous When a metal support is used, it is preferable to select the same metal as the component of the metal support, and more preferably nickel metal.

Formation of the primary metal coating layer is preferably carried out through the electroplating method for the complete filling of the porous support surface pores and planarization of the surface. The deposition method using dry sputtering is not preferable because it is difficult to completely embed the surface pores of the porous support. The electroplating method is considered as a coating method suitable for mass production that is not limited to the shape of the base material by a simple process, but when coating with a porous support as a base material, the activation process of hydrochloric acid solution, a plating pretreatment process, and foreign substances present in the porous support or plating layer And surface roughness due to the formation of a thick plating layer is a major problem. These problems can be identified through FIGS. 2 to 4. FIG. 2 shows an example in which stainless steel is eroded by the hydrochloric acid solution and destroyed as a result of using the hydrochloric acid solution in the porous stainless steel metal support as a plating activation pretreatment process. Figure 3 shows an example in which the foreign matter contained in the plating solution in the porous stainless steel support or nickel plating layer is moved by a subsequent heat treatment process to form a large pore shape or cracks in the coating layer.

In order to improve the problems of the above-described plating process, first, the pretreatment process of the hydrochloric acid solution, which is a plating activation process, may be improved by replacing the dry plasma surface modification process (for example, disclosed in US Pat. No. 6,406,601 B1). Way). Specific plasma conditions for surface modification may vary depending on process characteristics, and are not particularly limited. For example, when a porous nickel support is used, a hydrogen plasma atmosphere of RF 100W and 50 mTorr may be used. As described above, the surface of the porous support may be modified by using plasma to improve adhesion to the nickel plating layer.

Second, the problem that foreign matters contained in the plating solution remain in the porous support or the plating layer is to use an insulating mask to prevent the coating of the primary metal on the back of the coating layer or the primary on the back when electroplating the primary metal coating layer When the metal coating layer is formed, it can be eliminated by removing the plating layer coated on the rear surface and heat-treating under vacuum atmosphere. In this case, specific heat treatment conditions may vary depending on the process, and are not particularly limited. For example, when a porous nickel support is used, a vacuum atmosphere of 10 ^-3 to 10 ^-5 Torr is used at a temperature of 200 to 400 ° C. After heat treatment for 1 to 2 hours, the solution containing the foreign matter is vacuum-dried and discharged through the back of the open support, and when cooling, it can be solved by drying with a reducing atmosphere of hydrogen.

In addition, the plating layer manufactured by the electroplating method is difficult to control the plating thickness due to the fast plating speed, and the surface of the plating layer is rough to reduce the hydrogen permeability, and defects, pores, etc. are also present in the palladium coating layer, which is a subsequent process. Difficult to control, adversely affects the hydrogen separation characteristics. 4 is an example in which a thick plating layer having a rough surface is formed of a nickel layer plated on a porous stainless steel support surface.

This problem can likewise be easily overcome by surface modification of the surface of the porous support using plasma as set forth in US Pat. No. 6,406,601B1. This surface modification not only improves the adhesion between the porous support and the nickel plated layer, which is the primary metal coating layer, but also flattens the surface of the electroplated nickel plated layer.

In addition, the electroplating process conditions (for example, nickel chloride solution, current density of 1A / dm 2, room temperature, plating time 1 minute conditions can be adopted) by adjusting the nickel plated layer in the horizontal direction rather than perpendicular to the support It is possible to further flatten the nickel coating layer produced by having a fine structure of the needle-like growth grown.

The secondary coating layer is a palladium coating layer, preferably coated with a very thin film free of impurities or defects, and the palladium alloy composite film finally produced by heat treatment should be very dense and thermally stabilized. Although not particularly limited, the secondary coating layer may be formed to a thickness of 2 μm or less.

Preferably, the surface of the primary metal coating layer is plasma-modified before forming the secondary coating layer. Plasma treatment conditions may be the same as in the above porous support.

Formation of the palladium coating layer is carried out according to the dry sputter deposition method. Conventional sputter deposition equipment may be used for dry sputter deposition, for example, at a sputter process condition of a pressure of 1.0 × 10 ⁻³ torr, a DC voltage of 40 W, and a substrate temperature of 400 ° C.

After the deposition is completed, the deposited film is subjected to an in situ heat treatment to form an alloy composite film. Examples of specific conditions of the heat treatment may be performed under N ₂ atmosphere at 600 ° C. for 5 hours.

Hereinafter, the metal palladium-nickel alloy composite film having the nickel metal layer as the primary metal coating layer on the surface of the porous nickel support will be described in more detail.

First, the porous nickel support is uniformly ball milled with 80% by weight of 2-5 micron nickel powder and 20% by weight of 0.2-0.5 μm submicron nickel powder, and is produced in a disk form by applying a load of 7 ton / cm 2 using a press. . In this case, the heat treatment of the produced specimen may be carried out for hydrogen reduction atmosphere, 500 ℃, 1 hour. Subsequent processes are carried out using the porous nickel support prepared as a base material. For the pretreatment of the base material, the wet acid treatment, which is a problem for the subsequent process, is excluded, and the pretreatment is performed with a dry method of hydrogen plasma. At this time, the plasma pretreatment may be performed under conditions of an AC power source of 100 W, a process pressure of 50 mTorr, a process gas hydrogen, and a process time of 5 minutes. Then, nickel electroplating is performed as a process for filling the surface pores of the base material itself. In this case, the electroplating process may be carried out using a nickel chloride solution at a current density of 1 A / dm 2, a plating time of 1 minute, and room temperature. Then, in order to remove foreign substances and water present in the support, heat treatment at 200 ℃, 10 ^-3 torr, 1 hour in a vacuum drying furnace and cooled in a reducing atmosphere of hydrogen.

FIG. 5 is a surface photograph of a nickel plating layer manufactured using the nickel electroplating process described above, in which the nickel plating layer completely fills the surface pores of the porous support and shows a dense structure having a needle-like structure having excellent surface flatness. can confirm.

Palladium coating layer as shown in Figure 1 plays a very important role of high purity hydrogen purification when using electrolytic plating, as described above, in order to improve the problems of the electrolytic plating itself, plasma surface modification and heat treatment process for removing foreign matters, etc. Should be used. In this case, however, some foreign matter remaining in the palladium plating layer is diffused by subsequent heat treatment to form defects and pores of vacancy and interstitial atoms in the palladium film, thereby incompletely modifying the microstructure of the palladium film and at a commercialization temperature of 500 ° C. For a long time, the palladium metal elements diffuse to the nickel support or the nickel plating layer through the medium of the point defect, thereby reducing the durability of the composite film.

6 is a scanning electron microscope surface microstructure photograph of a palladium-nickel alloy composite film formed by using a nickel electroplating process and a palladium electroplating process according to a conventional method on a porous nickel support surface, followed by alloying heat treatment.

Figure 6a is a photograph of the surface microstructure of the palladium-nickel alloy composite film, Figure 6b is a scanning electron microscope microstructure of the palladium-nickel alloy composite film after a continuous heat treatment for 20 days at 600 ℃ temperature.

As can be seen in FIG. 6, the composite membrane prepared by palladium electroplating may be deteriorated in the microstructure of the palladium-nickel alloy composite membrane by prolonged heat treatment at 600 ° C. for 20 days, thereby significantly reducing the durability of the hydrogen separation membrane. .

When the nickel coating layer as the primary coating layer maintains a flat surface layer without surface pores, the palladium film may be manufactured by a sputter deposition method which is a dry process. In this case, a dense palladium film free of impurities and defects is formed and the thickness can be adjusted to produce a thermally stabilized palladium film having a thickness of 1 to 2 탆.

In order to form a palladium film, it is preferable to perform plasma pretreatment on the surface of the nickel plating layer. Plasma pretreatment conditions may be the same conditions as in the previous support. After surface modification of the nickel plated layer using hydrogen plasma, a palladium film was deposited at a sputtering process condition of 1.0 × 10 ⁻³ torr, a DC voltage of 40 W, and a substrate temperature of 400 ° C., and for 5 hours at 600 ° C. The deposited film is heat treated in situ in N ₂ atmosphere to form a palladium-nickel alloy composite film. The microstructure and crystallinity of the composite film formed at this time is as shown in FIG.

As can be seen in Figures 7a and 7b, it can be seen that the palladium-nickel alloy composite film forms a very dense film without pores or defects, and the weight ratio of palladium and nickel metal is 80 to 20. You can check it.

FIG. 8 is a microstructure photograph of the palladium-nickel alloy composite film shown by continuously heat-treating the palladium-nickel alloy composite film shown in FIG. 7 at 600 ° C. for 20 days. A heat treatment for 20 days at 600 ° C. shows a diffusion effect equivalent to more than one year at 500 ° C. actually used when all the conditions of palladium diffusion remain the same. According to this, the composite membrane according to the present invention maintains a dense surface shape similar to the surface microstructure of the initial coating coating observed in FIG. These results demonstrate that the durability is superior to the palladium sputtering process compared to the palladium wet plating process observed in FIG. 6b.

Factors affecting the durability of the porous support may include thermal diffusion of palladium metal in addition to the thermally stable microstructure of the composite membrane, in particular diffusion of palladium metal must be considered in order to ensure durability in the porous support.

FIG. 9 is an EDS section line scan photograph of a palladium-nickel alloy composite film obtained by continuously heat treating the palladium-nickel alloy composite film at 600 ° C. for 20 days using a sputter process.

In order to scan the cut surface of the composite membrane, a nickel coating layer was formed on the surface of the porous nickel support with a thickness of 4 μm. The palladium coating layer was generally thickly coated with a thickness of 4 μm by sputtering, and the palladium and nickel components were analyzed.

As observed in FIG. 9b, when heat treated at 600 ° C. for 20 days, the palladium metal tends to diffuse about 8 μm into the porous nickel support, but the heat treatment effect at 600 ° C. for 20 days is about at the actual commercialization temperature. Considering the situation equivalent to the heat treatment effect of 1 year or more, the composite film according to the present invention still has a large amount of palladium in the coating layer, and as shown in FIG. 9a, the chemical affinity of the palladium and nickel metal components as the heat treatment proceeds. This good and thermally diffused bond is generated strongly, it can be confirmed that the bonding strength is very excellent.

In addition, as shown in FIG. 8, the composite membrane according to the present invention also has a fine structure of the surface layer, so that no micropores or defects exist. Therefore, the composite film according to the present invention is excellent in thermal stability without the need for a diffusion barrier film of palladium, thereby ensuring considerable durability in commercialization.

Hereinafter, the content of the present invention will be described in more detail with reference to Examples. However, these examples are only presented to understand the content of the present invention, and the scope of the present invention should not be construed as being limited to these embodiments.

<Example>

Surface treatment was carried out using hydrogen plasma on the porous nickel support. Surface treatment using hydrogen plasma was performed with RF power of 100 W, amount of hydrogen of 40 sccm, process pressure of 50 mTorr, and time of 5 minutes. Then, using the nickel chloride plating solution on the surface-treated support, a nickel electroplating process was performed at room temperature for a current density of 1 A / dm 2 and a plating time of 2 minutes. After the nickel plating was carried out again, the support was dried at 60 ° C. in a vacuum drying furnace, and then maintained at 200 ° C. in a vacuum atmosphere of 10 ⁻³ torr for 1 hour to remove impurities and foreign substances present in the support.

After the drying, hydrogen plasma surface treatment was carried out again to carry out the subsequent palladium sputter drying process, followed by a sputter process condition of 1.0 × 10 ⁻³ torr, 25 sccm of argon gas, 40 W of DC power, and a substrate temperature of 400 ° C. Palladium film was prepared in. Then, the palladium-nickel alloy composite film was subjected to in-situ heat treatment for 5 hours under a nitrogen atmosphere of 1 mTorr without exposing to the atmosphere.

The results of observing the microstructure and crystallinity of the alloy composite film using the scanning electron microscope and XRD are shown in FIGS. 7A and 7B, respectively. From these results, it can be seen that the palladium and nickel layers are alloyed to form a very dense structure.

8 and 9 are scanning electron micrographs and EDS line scan pictures of the composite membrane cut surface when the above specimens were heat-treated at 600 ° C. for 20 days, respectively, and the composite membranes according to the present invention were thermally stable. .

Experimental Example

The hydrogen and nitrogen permeability of the palladium-nickel alloy composite membrane prepared according to Example 1 and the gas separation degree of the mixed gas of hydrogen and nitrogen were measured at a pressure difference of 15 psi between the ends of the membrane. According to the results of FIG. 10, it can be seen that the hydrogen-nitrogen separation performance of the palladium-nickel alloy composite film according to the present invention is superior to the composite films prepared by other conventional methods.

According to the present invention, it is possible to produce a composite membrane having excellent selectivity with respect to hydrogen gas and at the same time with a low amount of palladium, and at the same time, it is possible to improve the characteristics of the composite membrane for separation of hydrogen gas regardless of the type of support. It has an effect.

As described above, although described with reference to a preferred embodiment of the present invention, those skilled in the art will be variously modified and modified within the scope of the present invention without departing from the spirit and scope of the present invention described in the claims below. It will be appreciated that it can be changed.

Claims (8)

(a) surface treating the top of the porous support using plasma; (b) forming a primary metal coating layer on the porous support by an electroplating method; (c) forming a palladium coating layer by sputter deposition on top of the primary metal coating layer; And (d) heat treating the palladium coating layer to form an alloy layer of palladium and a primary metal. The method of claim 1, wherein the porous support is a metal support or a ceramic support. The method of claim 2, wherein the porous support is a porous nickel support. The method of claim 1, wherein the porous support is flat or tubular. The method of claim 1, wherein the step of forming a first metal coating layer by an electroplating method in step b and heat treatment to remove the foreign matter is added. The method of claim 1, wherein the palladium coating layer is formed to a thickness of less than 2㎛ The method according to claim 1, wherein the heat treatment in step d is performed by an in-situ heat treatment method. The method of claim 1, wherein the primary metal comprises at least one metal selected from silver, nickel, copper, ruthenium, and molybdenum.

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