KR20010045207A - A palladium alloy composite membrane for permeances of hydrogen, and preparation thereof - Google Patents

Abstract

The present invention relates to a palladium alloy composite membrane for hydrogen gas separation and a method for manufacturing the same, and more particularly, to reduce the pore size and roughness of the support by performing a pretreatment process of dispersing and heat-treating the porous metal support surface with nickel fine powder. Also, between the support and the palladium alloy layer, a silica thin film layer by sol-gel is introduced to promote thermal and chemical stability between the metal support and the palladium alloy layer, and a vacuum plating method is used as the palladium alloy layer introduction method. The present invention relates to a palladium alloy composite membrane for hydrogen gas separation and a method of manufacturing the same, which not only deeply prevent pores present on the surface, but also form a thin film layer having a thickness of 2 μm or less, thereby improving selective permeability to hydrogen gas.

Description

A palladium alloy composite membrane for permeances of hydrogen, and preparation etc.

The present invention relates to a palladium alloy composite membrane for hydrogen gas separation and a method for manufacturing the same, and more particularly, to reduce the pore size and roughness of the support by performing a pretreatment process of dispersing and heat-treating the porous metal support surface with nickel fine powder. Also, between the support and the palladium alloy layer, a silica thin film layer by sol-gel is introduced to promote thermal and chemical stability between the metal support and the palladium alloy layer, and a vacuum plating method is used as the palladium alloy layer introduction method. The present invention relates to a palladium alloy composite membrane for hydrogen gas separation and a method of manufacturing the same, which not only deeply prevent pores present on the surface, but also form a thin film layer having a thickness of 2 μm or less, thereby improving selective permeability to hydrogen gas.

In general, it is widely known that a palladium-based metal film is excellent in selective permeability to hydrogen gas. However, when the palladium self-membrane is used, a large amount of hydrogen is absorbed according to the pressure and temperature of the hydrogen gas, and the palladium lattice is considerably widened, causing twisting and deformation in the palladium. In order to solve this problem, alloy films of palladium and other metals are manufactured and used.

In addition, in order to further improve the performance of the membrane, a method of coating a porous support and palladium and thinning it is considered, and a study on such a membrane of a composite membrane type is mainly underway. When using a palladium self film or a palladium alloy self film without using a composite film type (US Patent No. 2,773,561), a relatively thick film having a thickness of about 25 to 150 µm must be formed to withstand the use temperature or pressure, and expensive palladium may be formed. In addition to excessive use, as the thickness of the membrane becomes thick, there is a problem that the permeation rate of the hydrogen gas becomes small.

On the other hand, as a recent research and development, to form a palladium alloy film on the surface of the porous support by electroplating, to modify the surface of the support in order to enable the formation of a uniform palladium alloy thin film without pinholes, in particular during plating [0004] There has been a patent application for a method for producing a composite membrane for hydrogen gas separation that improves the selective permeability to hydrogen gas in a mixed gas containing hydrogen by applying a vacuum on the opposite side of the surface to reduce the thickness of the plating layer. Republic of Korea Patent Publication No. 99-53804].

The present invention is an improvement of the above-described Korean Patent Publication No. 99-53804, wherein the silica thin film layer by the sol-gel method prior to introducing the palladium alloy film by the vacuum-electroplating method on the porous metal support modified with nickel fine powder It is introduced between the support and the palladium alloy membrane to provide thermal and chemical stability between the metal of the palladium alloy layer and the metal on the support, and also has a hydrogen gas separation composite membrane having excellent permeability and separation performance of the hydrogen gas and a method of manufacturing the same. Its purpose is to.

FIG. 1A illustrates a Electron Probe Microanalyzer (EPMA) measurement result of a composite membrane including a porous metal support layer and a palladium alloy layer, in which a silica thin film layer is not formed between the two layers.

Figure 1b shows the results of the Electron probe microanalyzer (EPMA) measurement for the composite film on which the silica thin film layer is formed.

FIG. 2A illustrates a gas permeation test result for a composite membrane in which a silica thin film layer is not formed between the two layers in the composite membrane composed of a porous metal support layer and a palladium alloy layer.

Figure 2b shows the results of gas permeation experiment for the composite membrane formed silica thin film layer.

The present invention relates to a hydrogen gas separation composite membrane in which a plating layer of a palladium alloy is introduced on a porous metal support, wherein a silica thin film layer is formed between the porous metal support and the plating layer of a palladium alloy. It is characterized by the palladium alloy composite film.

In addition, the present invention is a method for producing a hydrogen gas separation composite membrane in which a plating layer of a palladium alloy is introduced on the porous metal support, a) the surface of the support surface to be subjected to heat treatment after dispersion coating nickel fine powder on the porous metal support surface A process of reforming, b) coating a silica sol precursor prepared by hydrolyzing tetraethyl orthosilicate (TEOS) on the modified porous metal support to form a silica thin film layer, and c) forming the silica thin film layer Another method is to provide a method for preparing a hydrogen gas separation palladium alloy composite membrane including forming a plating layer of palladium alloy on the other side of the support while applying a reduced pressure of 700 Torr or less on one side of the support.

Referring to the present invention in more detail as follows.

As the support of the composite membrane according to the present invention, a porous metal is used, and a conductive metal material or a ceramic or glass material coated with a conductive material is used. Here, the conductive metal material has the property of energizing when direct current is applied to the electroplating, for example, copper, nickel, chromium, cadmium, gold, silver, platinum, cobalt, iron, antimony, indium, manganese, Rhenium, rhodium, palladium, osmium, iridium, tungsten and the like, and alloys such as stainless steel. Particularly preferred as a porous metal support, porous stainless steel (Mott Metallurgical Corporation, SUS 316L) can be used, which is economical compared to other materials, has no fear of cracking or corrosion, and is easy to process, and has high mechanical properties. Because of its strength and easy modularity, it is easy to apply to actual high purity hydrogen separation purification system or catalytic reactor. The porous metal support may have a pore size of 0.2 to 0.5 µm, and may be used in various forms such as flat membrane, hollow fiber membrane, and tubular.

When the plating layer is directly formed on the surface of the porous metal support, the plating layer may be thick and somewhat have pinholes, and thus may have an unsuitable structure for gas separation. Therefore, modification of the support surface is essential before forming the plating layer. That is, the pore size, structure, and smoothness of the surface of the porous metal support have a significant effect on the state of the plating layer, and thus, there is a need to adjust them. Therefore, in the present invention, the surface of the support is coated with nickel fine powder of 1 μm or less and heat-treated at 700 to 800 ° C. for about 4 to 6 hours to reduce the roughness of the support surface and to maintain proper porosity and pore size. .

Meanwhile, when hydrogen gas permeates the manufactured composite membrane at high temperature for a long time, the intermetallic diffusion phenomenon between the palladium alloy layer and the metal support occurs, thereby significantly reducing the separation performance of the hydrogen gas. Accordingly, in the present invention, in consideration of thermal and chemical stability, the silica thin film layer formed by the sol-gel method between the palladium alloy layer and the support serves as a barrier to suppress the intermetallic diffusion phenomenon. In other words, by controlling the hydrolysis reaction of tetraethyl orthosilicate (TEOS) by applying a predetermined size of silica sol precursors between the palladium alloy layer and the support to prevent such intermetallic diffusion phenomenon.

The process of forming the silica thin film according to the present invention will be described in more detail as follows: First, in the sol manufacturing process, a hydrolysis reaction and a condensation reaction occur. . There are two kinds of silica sol, polymer sol and colloidal sol, both of which are inorganic salts or organometallic compounds. In the case of polymer sol, the precursor is reacted with a small amount of water to slow down the hydrolysis rate and the resulting gel has an interconnect structure. In contrast, in the case of a colloidal sol, a fast hydrolysis precursor is reacted with a large amount of water to rapidly hydrolyze and redisperse the resulting hydroxide or hydroxide oxide to form a stabilized colloidal solution. The initial particle size is about 3 to 15 nm depending on the starting material and the reaction conditions, and the aggregate is about 5 to 1000 nm. The monodisperse silica spheres used in the present invention are prepared by the Stober method, and experimentally estimated by preparing a monodisperse silica sol having a uniform particle size in order to obtain pores in a uniform and dense mesopore region. A sol of about 95% size at 500 nm could be prepared. The hydrolysis and condensation reaction mechanism of silica described above is shown in Scheme 1 below.

Si (OC ₂ H ₅ ) ₄ + 4H ₂ O → Si (OH) ₄ + 4C ₂ H ₅ OH

Si (OH) ₄ → SiO ₂ + 2H ₂ O

As shown in Scheme 1, 1 mol or 2 mol of tetraethylorthosilicate (TEOS) reacts with 4 mol of water to undergo hydrolysis. Usually the water-TEOS ratio is greater than 20/1, and condensation is accelerated at very high pH. Usually, the particle size ranges from -5 to 8% in the mean value, and the surface tension is greater than the repulsive force between the particles, so that agglomeration of silica particles occurs on the surface. The pores of the support treated with nickel fine powder by the silica spheres grown to a suitable size had a uniform size in the mesopore (mesopore) range was adjustable to have a suitable structure as the support of the gas separation membrane.

In producing a composite membrane comprising a palladium membrane or a palladium-containing thin film on a porous support, up to now, mainly electroless plating method [J. of Memb. Sci., 77 (1993) 181, Ind. Eng. Chem. Res., 32 (1993) 3006], electroplating method [H.P. Hsieh, Inorganic Membranes for Separation and Reaction, Elservier, 1996], chemical vapor deposition method [Ind. Eng. Chem. Res., 33 (1994) 616, J. of Memb. Sci., 120 (1996) 261, sputtering [J. of Memb. Sci., 94 (1994) 299, J. of Memb. Sci., 104 (1995) 251, and the like. When manufacturing a composite membrane by electroplating on a metallic porous support, not only can the composite membrane be prepared by a simple process but also easy to control the thickness of the membrane and takes less time than the electroless plating method or the chemical vapor deposition method. It's a very economical way. However, in order to produce a uniform film without pinholes by a conventional electroplating method or an electroless plating method, a relatively thick plated film of 5 μm or more may be formed, thereby causing a decrease in the permeation performance of the film.

Thus, in the present invention, the electroplating method is applied to form a palladium alloy film on the porous metal support, but when the electroplating, the support by performing the electroplating while applying 700 torr or less, preferably 500 to 650 Torr vacuum on the opposite side of the plating surface In addition to deeply preventing pores present on the surface, the thickness of the plating layer was reduced to 2 μm or less. As a result, the permeation characteristics of the hydrogen gas are significantly improved as compared with the case of the membrane prepared by the conventional electroplating method, and it solves the problems of the prior art and shows much better permeability and selectivity.

Meanwhile, in the manufacture of palladium alloy films, palladium is used in the form of palladium complexes (Hydmen Gijutsu, M. Matsunaga, M. Hara, A. Ablimit, Y. Tsura and K. Hosokawa, 43 (10) (1992) 987). It is more preferable to do. In addition, a transition metal is used as the alloy metal of the palladium metal, and Group VIII elements such as Pt, Rh, Ir, Fe, Co, and Ni; Group Ib elements, such as Cu, Ag, and Au; VIA group elements such as Cr, Mo, and W; Group IVA elements such as Ti and Zr; Group V elements such as Ta, Nb, and V. In order to facilitate the alloy between the palladium and the transition metal, the transition metal is more preferably used in the form of an ionic compound. In addition, the palladium alloy layer has a content of palladium of 50% by weight or more, and preferably a content ratio of palladium / transition metal of 50-90 / 10-50% by weight.

In order to test the performance of the composite membrane prepared by the above manufacturing method, the permeability was measured by using a steady state gas permeability device. The sealing between the hydrogen separation membrane and the permeation cell was made of graphite ring, and the furnace was installed at the outside of the cell. Was adjusted.

In general, the gas permeation flow of the support used in the gas separation membrane is controlled by Knudsen diffusion inversely proportional to the square root of the molecular weight of the permeate gas molecules. At this time, the separation coefficient of hydrogen and nitrogen is about 3.7. In fact, the separation coefficient of hydrogen and nitrogen of the support prepared by coating the nickel fine powder on the support was about 2.7, and the separation coefficient of hydrogen and nitrogen was about 3.5 to 3.7 when the nickel fine powder was coated and the silica layer was formed. It can be seen that it has a suitable structure as a support for the gas separation membrane. By performing palladium alloy plating on the thus prepared support, it was possible not only to maintain a stable structure even in a long time hydrogen gas permeation experiment at high temperature, but to obtain a plated layer having a thin film form without pinholes.

As described above, the composite membrane in which the thin film of palladium alloy was formed was increased as the temperature of the hydrogen gas increased and the pressure difference between the gases of the hydrogen separation membrane increased, and it could be used as a practical hydrogen gas separation membrane that selectively permeates only hydrogen gas. .

Such a present invention will be described in more detail based on the following examples, but the present invention is not limited thereto.

Example 1

In order to alleviate the roughness of the surface of the porous stainless steel support having a 0.5 μm pore size, fine nickel powder of 1 μm or less is uniformly coated on one side by using an aspirator, and then subjected to a high vacuum atmosphere at 800 ° C. for 5 hours. Sintered. A colloidal sol was used to deposit a 500 nm size silica sol, followed by drying and sintering to form a silica layer. With tetraethyl orthosilicate (Aldrich Co., TEOS, 98% ) as a starting material for the synthesis of colloidal sol TEOS: H ₂ O: EtOH: an NH ₃ 0.28: 10.0: 9.0: 0.35 were mixed in a mol% ratio It was prepared as follows. 1) Prepare ammonia solution prepared by adding basic NH ₃ to H ₂ O, and then 2) mix EtOH with TEOS. 3) Add 1) little by little to 2) and keep it at 50 ℃ in oil bath. It was refluxed for time. In order to deposit the silica sol on only one side of the nickel-treated porous metal support, an adhesive sheet was attached to the back side, and the support was placed at right angles in a well-dispersed solution. It was dried to some extent. Sintering was carried out in the electric furnace under a constant air (static air) at a heating rate of 0.55 ℃ / min, the temperature was raised to 650 ℃ and maintained for 2 hours, the cooling rate was the same as the heating rate.

The support prepared by the above method was washed with distilled water and sodium hydroxide to remove foreign substances, and then surface-activated by 5% acid treatment, followed by palladium / nickel alloy plating. During electroplating, a vacuum of 600 Torr was applied on the opposite side of the plating surface, followed by 10 minutes at 40 kPa, and then lowered to 550 Torr for 10 minutes. The plated membrane was washed with distilled water, dried at room temperature for 24 hours, and then heat-treated at 450 ° C. for 2 hours under a nitrogen atmosphere. The plating state of the prepared composite film was uniform and the composition of palladium and nickel was about 80/20. The permeability to hydrogen and nitrogen gas was measured and the hydrogen gas was selectively permeated and the results are shown in Table 1 below. At this time, the gas permeability of the prepared composite membrane was observed almost constant for about 40 days.

Example 2

A composite film was prepared in the same manner as in Example 1, except that the palladium alloy plating was performed at 40 kPa for 15 minutes.

Example 3

A composite film was prepared in the same manner as in Example 1 except that a colloidal sol was formed to form a silica layer, and then a silica layer was secondly formed by a polymer sol. The HNO ₃ 1:: tetraethyl orthosilicate (Aldrich Co., TEOS, 98% ) by the TEOS as a starting material for synthesizing the polymer _{sol: H 2 O: EtOH 6.4:} 3.8: 0.085 mol% were mixed at a ratio It was prepared as follows. 1) Prepare a solution by adding acidic HNO ₃ to H ₂ O, and then 2) mix EtOH with TEOS, 3) add 1) to 2) little by little, keep at 50 ℃ in oil bath and reflux for 3 hours. 4) was diluted 30-fold in EtOH to prepare a polymer sol solution. When the silica layer was formed by the colloidal sol and then the silica layer was formed by the polymer sol, the size of the pores on the surface of the support was greatly reduced due to the coating by the polymer sol solution.

Example 4

A support was prepared in the same manner as in Example 1, except that a palladium / copper alloy layer was formed as a plating layer to prepare a composite film. Heat treatment was carried out at 450 ℃ for 2 hours. The plating state of the prepared composite film was uniform and the composition of palladium and copper was about 60/40. Permeability for hydrogen and nitrogen gas was measured, and the results are shown in Table 1 below. At this time, the gas permeability of the prepared composite membrane was observed almost constant for about 40 days or more, and hydrogen gas was selectively permeated, and the result is shown in FIG. 2B.

Comparative Example 1

In order to alleviate the roughness of the surface of the porous stainless steel support having a 0.5 μm pore size, nickel powder having a size of 1 μm or less is uniformly coated on one side by using an aspirator and then subjected to high vacuum atmosphere at 800 ° C. for 5 hours. It was used by sintering under. The treated support is washed with distilled water and sodium hydroxide to remove foreign substances, and then activated to the surface by 5% acid treatment, and then the pore size is reduced to have a suitable structure as a support and 1A to enhance adhesion between the support and the plating layer. Copper plating was carried out for 2 minutes at. Palladium alloy plating was performed for 20 minutes at a current density of 40 하였으며. The composite film was evenly plated, and hydrogen gas was selectively permeated, but a silica layer was formed to act as a barrier to prevent the diffusion of metallic acids at high temperatures. After the hydrogen gas permeation experiment was conducted at 450 ° C. for about 20 days, the separation performance rapidly decreased. Table 1 shows the permeability of nitrogen and hydrogen gas, and the stability test results of the membrane are shown in FIG. 2A.

Comparative Example 2

In the same manner as in Example 1, but the palladium alloy plating was prepared by the electroless plating method composite film. The permeation performance of the prepared composite membrane, the thickness of the plating layer, and the use conditions are shown in Table 1 below.

Comparative Example 3

In the same manner as in Example 1, palladium alloy plating was prepared by a sputtering composite film. The permeation performance of the prepared composite membrane, the thickness of the plating layer, and the use conditions are shown in Table 1 below.

Comparative Example 4

In the same manner as in Example 1, but the palladium alloy plating was prepared by a composite film by chemical vapor deposition. The permeation performance of the prepared composite membrane, the thickness of the plating layer, and the use conditions are shown in Table 1 below.

Comparative Example 5

The permeation performance of the Pd / Ag alloy membrane having a thickness of 25.4 μm was measured at a pressure difference of 100 psi between the both ends of the membrane.

According to the results of Table 1, it can be seen that the hydrogen-nitrogen separation performance of the composite membrane according to the present invention is superior to the membranes prepared by other conventional methods. This phenomenon becomes more pronounced in view of the phenomenon that the permeability increases by increasing the working pressure.

In addition, Figures 1a and 1b shows the results of EPMA experiments for a composite film not containing a silica layer and a silica layer developed to improve the thermal and chemical stability. In the composite film including the silica layer according to Figure 1b, it was observed that the silica layer serves as a barrier to prevent the intermetallic diffusion between the palladium alloy layer and the support. That is, in the case of the composite membrane including the silica layer prepared by the manufacturing method according to Example 1, the palladium plated layer did not diffuse under the silica layer even after 40 days of hydrogen gas permeation experiment. However, the composite membrane containing no silica layer by the manufacturing method of Comparative Example 1 was observed after 20 days of hydrogen gas permeation experiment at 450 ℃ as a result of the phenomenon that the palladium plating layer gradually diffused to the support layer. Could.

2a and 2b likewise compares the results of the permeation experiment for the composite membrane prepared in Comparative Example 1 and Example 1 and supports the above results well.

As a result, it can be seen that the hydrogen gas separation membrane developed in the present invention not only has a very good performance for selective separation of hydrogen gas, but also has thermal stability at high temperature, so that it can be applied to hydrogen gas separation for a long time. .

Claims (6)

In the hydrogen gas separation composite membrane in which a plating layer of palladium alloy is introduced on the porous metal support, a thin layer of silica is formed between the porous metal support and the plating layer of the palladium alloy. Alloy composite membrane. In the method for producing a hydrogen gas separation composite membrane wherein a plating layer of a palladium alloy is introduced on the porous metal support, a) modification of the surface of the support, which is heat-treated after dispersion coating nickel fine powder on the surface of the porous metal support; b) forming a silica thin film layer by coating a silica sol precursor prepared by hydrolyzing tetraethyl orthosilicate (TEOS) on the modified porous metal support; c) preparing a palladium alloy composite membrane for hydrogen gas separation, comprising: forming a plating layer of palladium alloy on the other side of the support while applying a reduced pressure of 700 Torr or less on one side of the support on which the silica thin film layer is formed; Way. The method of claim 2, wherein the porous support has a pore size of 0.2 to 0.5 µm and is a flat membrane, hollow fiber membrane, or tubular membrane. The method of claim 2 or 3, wherein the porous support material is a conductive metal material, or a ceramic or glass material coated with a conductive material. The palladium alloy composite membrane of claim 2, wherein the plating layer contains a Group VIII element, a Group Ib element, a Group VIa element, a Group IVa element, and a Group Va element in addition to the alloy of palladium and nickel. Way. The method for producing a hydrogen gas separation palladium alloy composite membrane according to claim 2 or 5, wherein the plating layer contains 40 wt% or more of palladium.