JPH0474045B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a hydrogen separation membrane. More specifically, the present invention relates to a hydrogen separation membrane that separates ultra-high purity hydrogen from hydrogen-containing gas with high permeability even at low temperatures and has excellent durability.

In recent years, the demand for high-purity hydrogen has increased with the development of the semiconductor industry, optical fiber manufacturing industry, etc. Hydrogen is produced from fossil fuels such as natural gas and naphtha using steam reforming or partial oxidation methods. Hydrogen is also produced as a byproduct of the oil refining process or salt electrolysis, and by water electrolysis. Hydrogen gas produced by these methods contains impurities such as CO, CO ₂ , water vapor, and hydrocarbons, so it is necessary to separate and refine the hydrogen in order to obtain high-purity hydrogen. be.

Conventional technology Conventional hydrogen purification methods include diffusion methods using palladium alloy membranes, chemical absorption methods using caustic soda, diisopropanolamine, etc., physical absorption methods using water, deep-chilled methanol, etc., activated carbon, alumina gel, and Molecule. Adsorption methods using liquid nitrogen, liquid air, etc., separation methods using polymer membranes using polydimethylsiloxane, polyimide, etc. have been used.

However, the only way to obtain ultra-high purity hydrogen of 99.99999% or higher is the diffusion method using the palladium alloy membrane described above. A typical palladium alloy film is an alloy film in which several tens of percent silver is added to palladium. However, this alloy has a low hydrogen permeability at low temperatures, so it must be used at temperatures above 300°C in order to increase its hydrogen separation ability, and it is also expensive.

Problems to be Solved by the Invention The present invention aims to solve the problems with conventional hydrogen separation membranes made of palladium alloy membranes, and is capable of separating ultra-high purity hydrogen with high permeability even at low temperatures. The purpose is to provide a durable hydrogen separation membrane at low cost.

Means for Solving the Problems Hydrogen permeability in a hydrogen separation membrane can be expressed as the product of hydrogen diffusion coefficient and hydrogen solid solubility.
The hydrogen diffusion coefficient of vanadium is more than five times larger than that of palladium at temperatures of 200 to 300°C, and the solid solubility of hydrogen is also large. Therefore, the hydrogen permeability of vanadium is significantly higher than that of palladium.

The present inventors conducted research to use vanadium as a material for hydrogen separation membranes, and found that vanadium absorbs a large amount of hydrogen at low hydrogen pressures, and forms hydrides at temperatures below 200°C, which tends to cause hydrogen embrittlement. In addition, it is easily oxidized, forming an oxide film on the surface that impedes hydrogen permeation. Therefore, it cannot be used as a hydrogen separation membrane as it is.

Therefore, by adding 5 to 20 atomic percent of nickel or cobalt, or both, to vanadium to form an alloy film, it is possible to improve the hydrogen embrittlement without significantly reducing the hydrogen permeability of vanadium. It has been found that it can be used as a membrane.

Additionally, if the surface of this alloy film is coated with palladium or palladium alloy, it will become oxidation resistant, and if used at temperatures above 200°C, the alloy components will diffuse into the palladium film, which will harden and make it less likely to cause hydrogen embrittlement. I gained new knowledge. The present invention was completed based on these findings.

The gist of the present invention is that 5 to 20 atomic % of one or two of Ni and Co;
A hydrogen separation membrane consisting of an alloy membrane whose remainder is vanadium and whose surface is coated with palladium or a palladium alloy.

If the amount of Ni, Co, or both elements in the vanadium alloy in the present invention is less than 5 atomic %, hydrogen embrittlement cannot be improved, and if it exceeds 20 atomic %, the solid solubility of hydrogen in the alloy decreases. As the hydrogen permeability decreases, it hardens significantly and becomes difficult to process. Therefore, their amount is suitably in the range of 5 to 20 atomic percent.

Coating with palladium or palladium alloy can be performed by a plating method, a vapor deposition method, a sputtering method, or the like. As a palladium alloy, palladium-
Examples include silver alloy (20 to 30 atomic % silver), palladium-yttrium alloy, and the like.

Effects of the Invention The hydrogen separation membrane of the present invention has the following effects.

1. It exhibits high hydrogen permeability even at low temperatures such as 200°C, so hydrogen separation can be performed with energy savings.

2. Hydrogen permeability is greater and superior to membranes made only of palladium.

3. Since no hydride is formed, hydrogen embrittlement does not occur, and no plastic changes occur during the hydrogen absorption/release process, resulting in excellent durability.

4 Since the alloy membrane surface is coated with palladium or palladium alloy membrane, deterioration of hydrogen separation performance due to adhesion of carbon, oil mist, etc.
It can be recovered by baking treatment that introduces air at 200 to 300°C, and high efficiency operation is possible.

5 Vanadium is about 1/10th the value of palladium, so it is cheaper than existing palladium alloy membranes.

Example 1 A V-15 atomic% Ni alloy and a V-15 atomic% Co alloy were produced by arc melting in argon,
A film with a thickness of about 1 mm was obtained by hot rolling. The surfaces of these films were coated with palladium to a thickness of 10 nm by electrolytic plating. The temperature dependence of hydrogen permeation is shown in curve 1 (V-Ni alloy) and curve 2 (V-Co alloy) in FIG. 1. Note that curve 3 shows the case of a film made only of palladium for comparison. As shown by these results, the hydrogen permeability of the hydrogen separation membrane of the present invention is greater than that of the palladium membrane.

Hydrogen permeation tests were repeatedly conducted on the hydrogen separation membrane of the present invention under several atmospheres of hydrogen pressure, but no cracks were found. Furthermore, deterioration in hydrogen separation performance due to carbon or oil mist was recovered by baking treatment at 200-300°C by introducing air.

Example 2 V-15 atomic% by arc melting method in argon
A Ni alloy was melted and its hydrogen pressure-composition isotherm curve was measured. The results are shown in FIG. The curves in the figure are the absorption curve (1-a) and release curve (1-b) at 175°C, and the absorption curve (2-a) at 250°C.
and release curve (2-b), absorption curve (3-a) and release curve (3-b) at 350°C. In any of the pressure-composition isothermal curves, there is no so-called plateau in which the hydrogen concentration rapidly increases at a constant hydrogen pressure, indicating that no hydride is formed within the measured temperature and pressure range. In other words, it can be seen that this alloy is less likely to cause hydrogen embrittlement.

Furthermore, there is no significant difference in the hydrogen absorption/release curves at the same temperature. In other words, since the hysteresis is small, almost no plastic deformation occurs during the hydrogen absorption/release process, indicating good durability.

[Brief explanation of the drawing]

Figure 1: Hydrogen permeability and temperature of Pd film (curve 3), V-15 atomic% Ni alloy film (curve 1) and V-15 atomic% Co alloy film (curve 2) with 10 nm palladium plating on the surface. Relationship diagram, Figure 2 shows V-15 atomic%
The hydrogen pressure-composition isotherm curve diagram of Ni alloy is shown. Absorption curve (1-a) and release curve (1-b) at 175°C,
Absorption curve (2-a) and release curve (2-b) are 250
°C, absorption curve (3-a), and release curve (3-b) are
The case at 350℃ is shown.

Claims (1)

[Claims] 1. A hydrogen separation membrane consisting of an alloy membrane consisting of 5 to 20 atomic percent of one or two of Ni and Co, with the balance being vanadium, and the surface of the membrane is coated with palladium or a palladium alloy.