JPH06104185B2 - Hydrogen isotope separation method by electrolysis - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an isotope of hydrogen, that is, H by electrolysis of water.
It relates to a method for separating D (deuterium) and T (tritium).

[Prior Art] Separation of hydrogen isotopes is carried out for the purpose of concentrating and recovering heavy water, concentrating tritium, removing tritium in heavy water, or removing tritium in light water. The main means for that purpose is the electrolysis of water and the chemical isotope conversion reaction, and both are often used in combination.

For example, when removing tritium in light water, as shown in the attached drawing, natural water and treated water are supplied to the exchange reaction tower (1) to generate hydrogen gas (HT) generated from the cathode of the electrolytic cell (2). (Including H) and the exchange reaction is carried out, and bottom water (including HTO) is supplied to the electrolytic cell (2). Tritium in the treated water is released as depleted hydrogen with a reduced tritium concentration.

On the other hand, some oxygen gas (1-10
It is unavoidable that hydrogen gas and water (steam) of about vol.%) are mixed in, and HT and HTO are concentrated in them at a high concentration. If oxygen gas is released without sufficiently removing them, not only the concentrated tritium will be released out of the system, but also the reflux ratio to the concentration step will be low, and as a result, the degree of concentration may not reach a predetermined value. . This is also a problem in the case of heavy water concentration in a heavy water system. Therefore, it is important to efficiently remove hydrogen gas and water vapor in the oxygen gas generated by the electrolytic cell and to circulate the hydrogen gas to the electrolytic cell as needed in order to industrially carry out the separation of hydrogen isotopes by electrolysis. Is essential.

The inventors examined various processes with the intention of the probability of the technology satisfying such requirements. First, the oxygen gas generated from the electrolyzer is passed through a connected reactor called a recombiner or converter to oxidize the hydrogen contained in the oxygen gas into water (including hydrogen isotopes) and generate it. A process for cooling the oxygen gas containing water to condense and separate water is established. However, in the oxygen gas after the produced water has been condensed and separated, the amount of water that remains saturated under the conditions of temperature and pressure of condensation still remains, and unless these are recovered, it is not possible to meet the above requirements. I found it difficult.

The first method I thought of as a means of recovering this trace amount of water was adsorption by molecular sieves (TSA method).
However, the molecular sieve has a drawback that the adsorption capacity is not high, a large adsorption tower is required, and the frequency of desorption, that is, regeneration is high, so that the molecular sieve is rapidly deteriorated. Furthermore, hydrogen isotopes containing tritium are often industrially separated at nuclear fuel reprocessing plants, and the high temperatures (more than 200 ° C) during molecular sieve regeneration use a solvent at the reprocessing plant. In the atmosphere, you need to avoid.

From this point of view, what was next considered was adsorption at a low temperature of −70 ° C. or lower. This is a process in which adsorption is carried out at a low temperature and desorption is carried out at a normal temperature, but a low temperature such as −70 ° C. is apt to cause clogging of the device due to freezing, and is disadvantageous in that energy cost for cooling increases.

After going through the above process, the inventors finally used an adsorbent having high hygroscopicity, and performed adsorption under a relatively high pressure and desorption under a relatively low pressure at an almost constant temperature. It has been found that the so-called PSA (Pressure Swing Adsorption) method for carrying out the method is most advantageous for industrial implementation.

[Problems to be Solved by the Invention] An object of the present invention is to utilize the above-mentioned findings in a method for separating hydrogen isotopes by electrolysis, and in an oxygen gas generated from an electrolytic cell, water and hydrogen containing hydrogen isotopes. Hydrogen isotope separation that efficiently and safely collects hydrogen and eliminates the risk of releasing concentrated deuterium and tritium to the outside of the system, while increasing the reflux ratio to the electrolytic cell to achieve a predetermined concentration. To provide the law.

[Means for Solving the Problems] As shown in the drawings, the method for separating hydrogen isotopes by electrolysis according to the present invention is a method for separating hydrogen isotopes by electrolysis of water. Through the recombiner, the hydrogen and hydrogen isotopes contained therein are converted into water, and before or after the recombination,
Oxygen gas is pressurized by a compressor, and most of the produced water is separated by cooling and condensation, and then the remaining water is removed by adsorbing it through an adsorption tower, and then the dried oxygen gas is removed from the adsorption pressure above. Is characterized in that the oxygen gas containing the desorbed water is recovered by being desorbed through the adsorption tower under a low pressure and circulated to the suction side of the compressor.

[Operation] The illustrated example is an apparatus for removing tritium in light water as described above.

Natural water and treated water, that is, light water containing tritium, are supplied to the exchange reaction tower (1), where a system containing hydrogen gas (including HT) from the electrolytic cell (2) is formed, and chemical reaction is performed. Let the exchange reaction take place. The bottom water (including HTO) is sent to an electrolytic cell and used for electrolysis, whereby tritium is concentrated. Depleted hydrogen is released from the top of the column.

As is well known, such exchange reaction is mainly carried out between hydrogen and water vapor and between water and water vapor, and for the former gas reaction, a platinum group precious metal supported on Teflon or the like is used. A sex catalyst is used. A packing is used for the latter gas-liquid opposition. Various attempts have been made to efficiently carry out the entire exchange opposite.
The multi-stage exchange counter tower proposed in No. 62-46484 is a typical example.

The oxygen gas in question generated from the electrolyzer (2) passes through a reactor (4) called a recombiner or exchanger, and hydrogen (including HT) in the oxygen gas is present in a large amount in the surroundings. And becomes water (including HTO). The recombiner (4) is also a contact counter filled with a noble metal catalyst, and is used while being kept at room temperature or usually at a slightly elevated temperature, for example, 40 to 50 ° C. The pressure is about 4 to 10 kg / cm ² G if pressurization of the oxygen gas by the compressor (3) is performed prior to passing through the recombiner as shown in the example, and if the pressure is applied after passing through the recombiner, it is, of course, normal. The pressure is around 0 kg / cm ² G.

In any case, the pressurized oxygen gas containing water generated by recombination reaches the condenser (5) and is cooled to a temperature of about 5 to 10 ° C, and most of the water vapor is separated as water (including HTO). To be done.

In the oxygen gas from which most of the water has been separated, there is still 1% or less of water remaining, so the first adsorption tower (6A)
To adsorb water under a pressure of 6 kg / cm ² G, for example. The temperature ranges from the condensation temperature to room temperature.

About half of the dehydrated oxygen gas is sent to the second adsorption tower (6B) where water has already been adsorbed and the pressure has returned to around normal pressure, and the water is desorbed.

When the first adsorption tower (6A) approaches saturation, oxygen gas is sent to the second adsorption tower (6B) by switching the valve, and the first adsorption tower (6A) lowers the pressure to normal pressure. ,
This time, conversely, about half of the dehydrated oxygen gas is sent from the second adsorption tower (6B) to desorb adsorbed water.

Oxygen gas containing desorbed water is circulated to the suction side of the compressor (3) according to the broken line in the figure,
It is combined with oxygen gas from the recombiner (4) and the water (including HTO) therein is cooled and condensed. Since the water obtained in the condenser (5) contains concentrated HTO, it is circulated in the electrolytic cell to achieve the required reflux ratio, and is sent to the concentrated water tank (7).

[Example] An apparatus having the flow shown in the drawing was assembled to remove tritium in light water. 150m of natural water in the exchange reaction tower (1)
l / hr and 150 ml / hr of treated water were supplied, and almost the total amount of column bottom water was supplied to the electrolytic cell (2), and hydrogen gas containing HT was returned to the exchange counter column. Depleted hydrogen of 0.369 Nm ³ / hr was released from the top of the exchange counter column.

Oxygen gas was 0.187 Nm ³ / hr, which was pressurized to 6 kg / cm ² G with a compressor (3) and recombined (4).
Sent to. The compressor (3) is a diaphragm type and has a capacity of 0.4 Nm ³ / hr. The recombiner is a solid bed contact counter packed with about 20 g of 0.5% Pt on alumina catalyst.

From oxygen gas cooled to about 5 ° C with a condenser (5) 2.
Although 9 ml / hr of water was decomposed, a little less than 1% of water remained in the oxygen gas. Subsequently, this oxygen gas was used for PS in two towers and one set.
A adsorption tower (6A, 6B) sent to one side (6A) 6kg / cm ² G, 40
Adsorption was carried out for 5 minutes under the condition of ° C. The adsorbent is activated alumina particles with a diameter of 3 mm prepared for water vapor adsorption, and it has been activated at 40 ° C. in advance.

After the adsorption of the first column (6A) was completed, the oxygen gas destination was switched to the second column (6B), and the removal of water was continued. First tower (6A)
Is a part of the adsorbed and dehydrated oxygen gas at normal pressure of 0.18 Nm ³ /
Water was supplied at a rate of hr to cause desorption of water, and oxygen gas containing the desorbed water was returned to the suction side of the compressor (3). Hereinafter, the switching of the adsorption tower was repeated every 5 minutes cycle.

Moisture in oxygen gas released from the adsorption tower to the outside of the system is 1ppm
It was below.

[Advantages of the Invention] According to the present invention, in the separation of hydrogen isotopes by electrolysis, hydrogen and water (both containing hydrogen isotopes) contained in oxygen gas from the electrolytic cell are removed to achieve the degree of enrichment. If necessary, it can be refluxed to the electrolytic cell by an operation accompanied by slight pressurization at room temperature. The fact that high temperature is not required means that it can be safely carried out even in a flammable atmosphere, and the fact that there is no need for low temperature and that a slight pressurization is sufficient means that energy consumption is small.

High-performance adsorbents are available at low cost, and because they are used without temperature changes, they can withstand repeated use, so the equipment is compact and the cost is low.

[Brief description of drawings]

The drawing is a flow chart showing an example in which the hydrogen isotope separation method of the present invention is applied to tritium removal recovery performed by combining electrolysis with an isotope exchange reaction. 1 ... Exchange reaction tower 2 ... Electrolyzer 3 ... Compressor 4 ... Reactor (recombiner, converter) 5 ... Condenser 6A, 6B ... Adsorption tower 7 ... Concentrated water tank

Claims (5)

[Claims] 1. A method of separating hydrogen isotopes by electrolysis of water, wherein oxygen gas generated from an anode of an electrolytic cell is passed through a recombiner to convert hydrogen and hydrogen isotopes contained therein into water, Prior to or after recombining, oxygen gas is pressurized by a compressor, most of the produced water is separated by cooling condensation, and the remaining water is removed by adsorption through an adsorption tower. ,
Then, the dried oxygen gas is recovered by desorbing it by passing it through an adsorption tower under a pressure lower than the adsorption pressure, and an oxygen gas containing desorbed water is circulated to the suction side of the compressor. Hydrogen isotope separation method. 2. The hydrogen isotope separation method according to claim 1, wherein the hydrogen isotope exchange reaction is performed in combination with water electrolysis. 3. The hydrogen isotope separation method according to claim 1, wherein water separated by cooling condensation is circulated and used for electrolysis. 4. A continuous operation by using at least two adsorption towers and alternately performing adsorption and desorption.
Hydrogen isotope separation method. 5. Adsorption and desorption are performed at around room temperature and 0-10.
The hydrogen isotope separation method according to claim 1, which is carried out by a PSA (Pressure Swing Adsorption) method in a pressure range of kg / cm ² G.