JPS5919733B2 - Catalyst for water-hydrogen exchange reaction - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an effective catalyst for enriching hydrogen isotopes by a water-hydrogen exchange reaction.

Hydrogen isotope enrichment technology is extremely important in the production of heavy water used in heavy water-moderated nuclear reactors and in the removal of tritium from wastewater at nuclear fuel reprocessing plants.

One of the promising methods for enriching hydrogen isotopes is pt
This is a double temperature exchange method in which water and hydrogen are exchanged using precious metals such as catalytic converters as catalysts.

In the double temperature exchange method, the reaction expressed by the following formula is the reaction of formula (1), which is carried out in the low-temperature side exchange column at about 25°C.
) The reaction of the formula is carried out in an exchange column on the high temperature side of about 200° C. in the presence of a catalyst.

In a water-hydrogen exchange reaction, the catalyst surface must be constantly in contact with fresh water or water vapor and hydrogen.

However, if liquid phase water adheres and remains on the catalyst surface, it will prevent hydrogen from coming into contact with the catalyst surface, which will not only inhibit its function as an exchange reaction catalyst (it may even lead to a decrease in the activity of the catalyst itself).

Therefore, in order to industrialize the water-hydrogen exchange reaction,
It is necessary to develop a water-repellent catalyst that does not allow liquid phase water to adhere directly to the catalyst.

However, covering the entire surface of the catalyst with a water-repellent film after supporting the catalyst on the carrier may prevent even water vapor and hydrogen gas from coming into contact with the catalyst, and may even impede the action of the catalyst.

Therefore, it is desired to develop a water-repellent treatment method in which a preferable water-repellent catalyst is not wetted by liquid and only gas can freely contact the surface of the catalyst.

On the other hand, regarding the pore structure of the catalyst carrier, in order to have a high specific surface area like that used in general catalysts, the pore size is λ~
In a porous water-repellent membrane with several hundred micropores, it is difficult to cover the surface of the catalyst supported within the micropores of the carrier with a thin water-repellent film, and the reaction rate of 200 kg/crrt during the exchange reaction is difficult to cover.
Under a certain pressure, the surface of the catalyst 3 within the micropores of the carrier a becomes completely wetted with water 4, as shown in FIG.

Therefore, even though the surface area of the carrier is increased by a large number of micropores, most of the surface area can only exhibit the same effect as without D-4 water repellent treatment.

Furthermore, even if the inside of the pores is made water repellent by using a carrier made of a water-repellent material, water and hydrogen move more easily on the catalyst surface inside the pores than on the catalyst surface outside the pores. Since it is not easy, is left in a state close to equilibrium.

That is, in any case, almost nothing other than the catalyst attached to the surface of the carrier can contribute to the exchange reaction, and no effect can be expected from having a high specific surface area even though the carrier is porous.

In other words, it is more effective to make the carrier structure complex and increase the surface area due to large pores than to increase the specific surface area of the carrier used for a water-hydrogen exchange reaction catalyst using micropores.

The present invention has focused on the above points, and aims to provide a water-hydrogen exchange reaction catalyst that has an effective high specific surface area and favorable water repellency.

That is, we have discovered that a porous material with a three-dimensional irregular network structure is excellent as a catalyst carrier for a water-hydrogen exchange reaction, and have provided a water-repellent catalyst using the porous material as a carrier.

The three-dimensional irregular network structure porous material used as the catalyst carrier of the present invention has a structure in which fine skeletons form an irregular three-dimensional network, as shown in Figure 2, and has a porosity of 90 to 98%.
Because of its tall and intricate skeletal structure, the surface area per unit volume is extremely large, and the pores are completely connected.

There are various manufacturing methods for such a porous body having a three-dimensional irregular network structure depending on the material.

For example, in the case of resin, the usual manufacturing method for foamed resin can be applied as is.

In the case of metal, it is manufactured by, for example, applying nickel chemical plating or the like to the surface of a foamed resin skeleton such as polyurethane foam having continuous pores to impart conductivity, and then electroplating.

Further, after electroplating, the resin skeleton can be removed by incineration if necessary.

Furthermore, as a method that can be applied to metals or ceramics,
There is a method in which a slurry of metal or ceramic powder is dip-coated onto a foamed resin skeleton, and then the resin skeleton is removed by incineration and the metal or ceramic powder is sintered.

Any of the above-mentioned methods can be used as a method for producing the three-dimensional irregular network structure porous material of the present invention, and the method is not limited to these methods.

This three-dimensional irregular network structure porous body has a diameter of several tens of micrometers to several tens of micrometers.
The skeleton with a thickness of 0μ forms a three-dimensional irregular network, so it has a high specific surface area, and the effective pore diameters of almost all of them exceed several 100μ.

Therefore, all the catalysts supported on the surface of the carrier can come into contact with the object to be exchanged evenly, and there is no part that would adsorb liquid, and all the catalysts can effectively absorb water.
Involved in hydrogen-based exchange reactions.

The material used as the catalyst carrier of the present invention is not particularly limited as long as it can withstand up to the operating temperature and has appropriate mechanical strength.

That is, not only ceramic materials but also various materials can be used.

Group 1 noble metals are used as catalyst materials, and it is well known that platinum is superior.

As for the method of supporting the catalyst, it is important to control the amount and distribution of the catalyst to be uniform, and usually a method is adopted in which the support is immersed in a solution of chloroplatinic acid and thermally decomposed.

Further, as another supporting method, there is a method of electroplating using chloroplatinic acid.

The inventors discovered that it is useful to coat the catalyst with a water-repellent porous membrane as a water-repellent method that prevents water from condensing on the catalyst and allows free contact with the objects to be exchanged. I found out.

As shown in FIG. 3, the catalyst surface according to the present invention includes a carrier 1 made of a three-dimensional irregular network structure porous body, a catalyst 20 supported on this, and a porous water-repellent membrane 3 having thin micropores. It has a structure covered with

By selecting the diameter of the micropores to a size that does not allow water to be adsorbed under the pressure during the exchange reaction, only gas can freely contact the catalyst.

A specific example of such a water-repellent film 3 that can selectively pass only gas is a fluorocarbon copolymer represented by the following formula.

The fluorocarbon copolymer represented by the above formula is soluble in an organic solvent such as acetone.

That is, if a carrier and a catalyst thereon are simultaneously coated with a solution of the copolymer, traces of the solvent left behind by drying will remain as fine pores.

According to this method, the thickness and pore diameter of the water-repellent film can be easily controlled by adjusting the concentration of the copolymer.

Example A three-dimensional irregular network structure porous body made of nickel with an average pore diameter of 0.5 m and a thickness of 5 mm was used as a carrier.The carrier was immersed in an acetone solution of hexachloroplatinic acid and dried to coat hexachloroplatinic acid on the carrier skeleton. After sufficient deposition, reduction treatment was performed in a hydrogen stream at 250° C. for 3 hours to obtain a catalyst supported with 1.0% by weight of platinum.

Furthermore, it was immersed in an ethyl alcohol solution of the fluorocarbon copolymer to be destroyed, dried, and covered with a porous water-repellent membrane that only allows gas to pass through.

This catalyst was packed in a packed column for hydrogen isotope exchange reaction, and the catalytic activity was measured. As a result, 9.5 x 103 mol
A specific activity of e/H@, 3 was obtained.

The present invention is not limited to the above-mentioned fluorocarbon copolymer, and it is of course possible to use a water-repellent film having micropores made of other water-repellent materials such as silane and silicone.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram of a conventional water-repellent catalyst surface, FIG. 2 is an explanatory diagram of a three-dimensional irregular network structure porous carrier used in the present invention,
FIG. 3 is an explanatory diagram of the surface state of the water-repellent catalyst of the present invention. 1...Carrier, 2...Catalyst, 3...
...Water repellent film.

Claims (1)

[Claims] 1 is a carrier made of a porous material having a three-dimensional irregular network structure in which all the effective pores have a size of several hundred μm or more, and is made of a metal selected from Group 8 of the periodic table. 1. A catalyst for a water-hydrogen exchange reaction, characterized in that the carrier and the catalyst are both coated with a porous water-repellent membrane that allows only gas to pass through. 2. The water-hydrogen exchange reaction catalyst according to claim 1, which is a porous membrane of a fluorocarbon copolymer forming a water-repellent membrane. 3. The water-hydrogen exchange reaction catalyst according to claim 1 or 2, wherein the catalytic metal is platinum.