JPS6355973B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a high-purity hydrogen permeable filter with a high permeation rate and a high-performance hydrogen gas separation device. More specifically, the present invention relates to a hydrogen gas separation device comprising a hydrogen permeable filter obtained by forming a palladium thin film on a porous support with high gas permeability, and a hydrogen permeable filter obtained by using hollow fibers as the support.

Since hydrogen does not undergo harmful oxidation or nitridation, it has recently been used in metal metallurgy and electronic material manufacturing, and is also being reconsidered as an energy source and for chemical industry applications.

In particular, for the production of high-purity hydrogen, it is purified by passing through palladium foil produced by roll rolling or hammering.

Palladium foil manufactured by conventionally used roll rolling or hammering methods has a thickness of around 20μ at the thinnest, and the hydrogen gas permeation rate, which is important for filters, is low, making it difficult to produce large amounts of ultra-pure hydrogen. On the other hand, it required a long time to reach the saturation overpotential, and had the disadvantage that the potential could not be measured quickly using a hydrogen electrode. Further, palladium metal in excess of the necessary amount is expensive and is not preferred from the viewpoint of resource conservation. Furthermore, palladium foil is somewhat brittle, and when it absorbs hydrogen, it undergoes significant volumetric expansion, making it even more brittle.For these reasons, it is difficult to handle, and pure hydrogen is required for a wide range of industrial applications. However, it is not used much because it has become expensive to purify.

The inventor of the present invention made extensive studies to make palladium foil thinner and to facilitate the purification of hydrogen.
Rather than using palladium foil alone,
As a new filter, we succeeded in forming a thin vapor-deposited film on a porous support made of organic polymer that has gas permeability and is difficult to handle, and we have created a composite filter with this surface vapor-deposited film for hydrogen gas permeation. We succeeded in developing a module that can be used as a filter to increase the permeation rate of hydrogen gas and to produce large amounts of industrially usable pure hydrogen.

That is, the present invention has a porosity of 110% or more, and a hydrogen gas permeability coefficient of 5×10 ^-7 (cc・cm/cm ² , sec・cm) at 20°C.
cmHg) or more, and a hydrogen permeable filter formed by forming a thin film of palladium or palladium alloy with a thickness of 0.03μ to 15μ on the surface of an organic polymer porous hollow fiber support with a through-hole diameter of less than 200Å. In addition, two or more hollow fiber filters obtained in 2 1) are bundled together and fixedly sealed at both ends, raw hydrogen gas is fed from the outer surface of the filter or from the inside of the filter, and purified hydrogen is passed through the hollow part of the filter. Hydrogen gas is obtained from the end of the filter or from the outer surface of the filter.

The present invention will be explained in more detail below.

One of the features of the present invention is that the thickness of the palladium membrane is reduced in order to increase the hydrogen permeation rate, and in order to maintain the strength of the membrane, a thin film is formed on the support to create a composite membrane. .

The support must be strong and have high gas permeability. The inventor is
As a result of studying this support, the porosity was 10%.
or more and the permeability coefficient of hydrogen gas is 5×10 ^-7 at 20℃
(cc·cm/cm ² , sec·cmHg) or more, it has been found that it is necessary to use an organic polymer porous hollow fiber.

Here, the porosity is expressed by the following formula.

Porosity =
Volume of pores included in unit volume of support/unit volume of support (1) In the case of the organic polymer porous hollow fiber support used in the present invention, the pores in the support are They need to be connected. The porosity of such a support can be determined by immersing the filter in a low-viscosity liquid that is not absorbed by the support base material, and calculating the porosity using equation (1) from the weight change of the filter before and after immersion and the density of the base material and liquid. Porosity can be determined. Gas permeability can also be determined by a membrane module as shown in FIG. In the case of hollow fibers, if the gas permeability is high, the pressure loss in the hollow conduit becomes large, so the length of the hollow fibers is kept constant (20
cm), bent it into a U-shape as shown in Figure 1, fixed both ends, and measured.

The support used in the present invention can be produced by a known method. For example, it can also be obtained by stretching a semipermeable membrane or hollow fiber obtained by a wet film forming method, or a hollow fiber obtained by melt molding.

In order to form a uniform and thin palladium film on the surface of the support, it is necessary that the pores present on the surface of the support have a small pore diameter. This hole diameter is 200
When the palladium film is exposed to Å, it collapses at the hole.
It is not possible to create a film as thin as 0.03μ. For such purposes, semipermeable membranes obtained by wet membrane forming methods serve as effective supports. That is, the semipermeable membrane generally has a structure having a thin dense layer (small pore size) on the membrane surface and a sponge layer (large pore size) inside the membrane.

Since the present invention uses hollow fibers as a support, the membrane area per device volume can be significantly increased.

The size of the porous hollow fibers of the present invention is not particularly limited, but usually has an inner diameter of 10 μm or more and a wall thickness of 5 μm or more. The inner diameter is preferably 20μ or more, and when processing a large amount of gas, the pressure loss of gas feeding dominates economic efficiency, so the thicker the better, and a tube shape of 5.0 mmφ may also be used. However, considering that if the inner diameter is large and the wall thickness is small, it will become mechanically weak, and if it is made into a module, the surface area will be reduced, a diameter of about 0.2 to 2 mm is preferable. Since the wall thickness controls the gas permeability, it is preferable that it be as thin as possible to withstand force, so it is preferably 5μ or more, preferably 8μ or more, and 100μ or less, preferably 50μ or less.

Recently, due to advances in technology, hollow fibers with a non-uniform structure have been developed, with only the surface layer having a dense membrane structure and the inside having a porous structure. In this case, even if the wall thickness is thick, it will not be a resistance to gas permeability, and the handleability of the hollow fiber may be used as a criterion. In any case, in order to maintain good hydrogen permeability, the support should be 5×10 ^-7 cc・cm/cm ² , sec,
It is preferable that the transmittance is greater than cmHg. In order to form a good deposited film, it is necessary that there be no holes penetrating the inner surface of 200 Å or more.

The material of the organic polymer porous hollow fiber used as the support is not particularly limited, and may include cellulose, cellulose diacetate, cellulose triacetate, polyethylene, polypropylene,
Polyfluorinated polymers such as polytetrafluoroethylene, polyester-based polyethylene terephthalate, polybutylene terephthalate, polyamide-based nylon 6, nylon 6,6, polyacrylonitrile-based polymers, polyvinyl chloride, polyvinyl alcohol, polysulfon, polyben Duimidazole,
Hollow fibers made of commercially available polymeric materials such as heat-resistant polymers such as polymetaphenylene isophthalamide can be used. 1% to obtain ultra-pure hydrogen
It is preferable that the amount of volatile low molecular weight compounds (per weight) not included.

There are no particular limitations on the manufacturing method of hollow fibers, and gas permeability of 5×10 ^-7 cc・cm/cm ² , sec, cm
It is good if it is Hg or more.

Next, a method for forming a palladium thin film on these supports will be explained.

In order to form a uniform and thin film, a known vacuum evaporation method can be used. These methods include electron beam evaporation, resistance heating evaporation, and high frequency heating evaporation. That is, the support and palladium or palladium alloy are placed in a vacuum evaporation chamber, evacuated, and then the metal is heated to near its melting point, whereby the evaporated metal uniformly adheres to the surface of the support and forms a thin film. The thickness of the thin film is determined by the degree of vacuum, the temperature of the metal, and the deposition time. A thickness of 0.03 to 15 μm is useful for the thin film in view of hydrogen permeation rate, uniformity of the thin film, absence of defects such as pinholes, etc.

In the case of hollow fibers, by vapor deposition, strength is no longer an important factor, and the film thickness can be made significantly thinner, and the minimum thickness that can prevent the occurrence of pinholes is sufficient, as long as it is 300 Å or more. good. If the thickness of the deposited film becomes too thick, peeling from the surface of the hollow fiber will occur, which will easily result in defects, and will be disadvantageous to the desired improvement in permeability and economical efficiency, so it is preferably 15 μm or less.

For vapor deposition, it is necessary to remove volatile gases as impurities in the support, and it is preferable to perform vacuum drying in advance using a separate device, but in the case of a small amount, a vapor deposition device may be used. The degree of vacuum during vapor deposition may be varied depending on the thickness of the deposited film, but it is necessary to have a degree of vacuum of at least 1×10 ⁻⁵ Torr or higher. Preferably, a pressure of about 5×10 ⁻⁶ Torr provides a uniform film.
The temperature of the support is usually 70° C. or lower and preferably room temperature or higher.

When depositing hollow fibers, palladium or its alloys require a relatively high degree of vacuum, and the deposition particles usually do not go around to the back side of the hollow fibers.
It is preferable to repeat the vapor deposition twice, to use an apparatus having two or more metal evaporation sources at the same time, or to rotate the hollow fiber within the vapor deposition chamber. Palladium and palladium alloys can be used as metals for deposition.

Here, the palladium alloy is, for example, palladium and silver, and since it is the palladium portion that permeates hydrogen, it is not necessarily necessary to use palladium alone, and palladium alloys can also be used in the present invention.

Next, a gas separation device using a hollow fibrous hydrogen permeable filter will be explained.

Figures 1 and 2 are conceptual diagrams of this device. In FIG. 1, a hollow fiber 4 having a palladium thin film on its surface is bent into a U-shape, both ends are fixed to 6 with adhesive, and the fiber is placed in a container 3. The adhesive part 6 also serves to separate purified gas and crude gas. That is, crude hydrogen gas is sent from 2 or 5 and brought into contact with the outer wall of the hollow fiber 4. Hydrogen gas 7 that has passed through the hollow fiber membrane and been purified can be taken out from 8. The gas to be treated is discharged to the outside from 5 or 1. In the case shown in Figure 2, the hollow fibers are arranged in parallel and the openings of the hollow fibers are made in two places and fixed with adhesive. In this case, crude gas is sent to the inner wall of the hollow fiber, and purified hydrogen is taken out from the outer wall. This is the case. It is even more effective to provide a pressure difference between the crude gas side and the purified gas side. With this device, a large amount of purified hydrogen can be obtained with a small module.

A detailed explanation will be given below using examples.

Example 1 Hollow fibers made from polypropylene were produced by a melt spinning method and stretched to obtain porous hollow fibers. The shape of the hollow fiber is 200μ in outer diameter and 160μ in inner diameter, and the gas permeability coefficient of this hollow fiber is 20℃ for hydrogen gas.
The porosity was 40%, ^{and the} maximum pore diameter measured by the bulb point method in ethanol was 190 Å.

Palladium was deposited onto this hollow fiber using a resistance heating evaporation method, maintaining the degree of vacuum at 6 × 10 ^-6 Torr during deposition, and varying the time so that the thickness of the deposited film was 300 angstroms, 500 angstroms, and 1000 angstroms. . The vapor deposition was carried out simultaneously from above and below while keeping the hollow fiber in the center and moving it.

Each of the palladium-deposited hollow fibers thus obtained was cut to a length of 25 cm, and 10 fibers were bundled and both ends were glued with epoxy adhesive.
We prototyped a module as shown in the figure. The outer surface area will be 12.56 cm ² . A 1:1 mixture of gas and air obtained from a hydrogen gas cylinder was poured into this module from the outside and led to the hydrogen electrode. The battery was composed of a platinum electrode with black platinum and a molten metal electrode, and a PH buffer solution of 0.2M potassium hydrogen phthalate and 0.2N hydrochloric acid was used. When purified hydrogen gas was passed through the module to the hydrogen electrode, the electromotive force of the cell reached an equilibrium value after a few seconds for all modules. As a result, hydrogen gas was purified, and excellent gas separation and permeability were confirmed.

Example 2 Hollow fibers made of an acrylonitrile copolymer were obtained by a wet-dry spinning method. The inner diameter of the hollow fiber is 180μ,
The film thickness was 80μ. When the cross section of this hollow fiber was observed with an electron microscope, a dense layer with a thickness of 0.2 μm or less was present on the outer wall, and no pores with a pore diameter of 200 Å or more were present in this dense layer. On the other hand, there were many pores with a pore size of 0.1 to 10 μm inside the membrane other than the dense layer. The porosity of this membrane was 65%, and the hydrogen gas permeability coefficient was 5.3×10 ^-4 (cc·cm/cm ² ·sec·cmHg). While maintaining the degree of vacuum at 5 × 10 ^-6 Torr using resistance heating evaporation method, palladium-silver alloy (silver content is 50% or less) is deposited on the surface of the dense layer side of this film until the thickness of the evaporated film is 500 Å. It was deposited so that Using the obtained palladium thin film coated hollow fibers, modules were prepared in the same manner as in Example 1 (effective length: 15 cm, 10 fibers,
Membrane outer surface area: 16.0 cm ² ), and the electromotive force of the battery was measured in the same manner as in Example 1, and the electromotive force was
Equilibrium value was reached after 7.3 seconds. Hydrogen gas was purified in a short time, and excellent gas separation and permeability were confirmed.

Comparative Example 1 Polypropylene was melt-spun into hollow fibers, and after annealing, it was stretched 1.2 times at room temperature, and then
It was hot stretched at 140°C to give a total stretching ratio of 2.0 times, and then heat set at 145°C. The obtained porous polypropylene hollow fibers have an inner diameter of 200μ, a film thickness of 25μ, and pores are uniformly opened in the film thickness direction.The average pore diameter measured by mercury intrusion method is 1200Å, the porosity is 43%, and the hydrogen gas The permeability coefficient is 1.5×10 ^-3 cc at 20℃. cm/ ^cm2 . sec.cmH
It was hot at g. Palladium was deposited at 500 Å and 1000 Å in the same manner as in Example 1 except that this hollow fiber was used.
Vacuum deposition was performed to a film thickness of 2000 Å.

A module was made in the same manner as in Example 1 using the obtained hollow fiber coated with a palladium thin film, and the time taken for the electromotive force of the battery to reach an equilibrium value was measured in the same manner as in Example 1. It was found that the film thickness was 500 Å. It belongs to
The filters were 32 seconds long, 27 seconds for the 1000 Å filter, and 23 seconds for the 2000 Å filter, which were inferior to the filter of the present invention.

[Brief explanation of the drawing]

FIGS. 1 and 2 are conceptual front views of a module using a hollow hydrogen filter. 1...Hydrogen-containing crude gas, 2...Gas inlet, 3...
Module outer cylinder, 4... Palladium vapor-deposited hollow fiber, 5
...Gas outlet, 6...Hollow fiber bonding part, 7...Pure hydrogen gas, 8...Pure gas outlet.

Claims (1)

[Claims] 1. Has a porosity of 10% or more, and has a hydrogen gas permeability coefficient of 5×10 ^-7 (cc・cm/cm ²・sec・cm
A hydrogen-permeable filter comprising a thin film of palladium or a palladium alloy having a thickness of 0.03 to 15 μ and formed on the surface of an organic polymer porous hollow fiber support having a through-hole diameter of less than 200 Å. 2 It has a porosity of 10% or more, and the hydrogen gas permeability coefficient is 5×10 ^-7 (cc・cm/cm ²・sec・cm
A hydrogen permeable filter is made by forming a membrane of palladium or palladium alloy with a thickness of 0.03μ to 15μ on the surface of an organic polymer porous hollow fiber with a through-hole diameter of less than 200 Å. Gas that is made to bundle two or more bottles and securely seal both ends so that raw hydrogen gas is sent from the outer surface of the filter or the inner surface of the filter, and purified hydrogen is obtained from the end passing through the hollow part of the filter or from the outer surface of the filter. Separation device.