Catalyst for oxidation of hydrogen in the atmosphere containing hydrogen, oxygen and water vapor

 

(57) Abstract:

Proposed catalyst for oxidation of hydrogen in the atmosphere containing hydrogen, oxygen and water vapor containing palladium or its alloys or platinum and media respectively - ferrite stainless or steel, or Monel metal, made in the form of sheet material, fabric, mesh or granulate and resistant to the corrosive action of water vapor. As an alloy of palladium catalyst contains palladium - nickelmania alloy at mass. the ratio of palladium to Nickel and copper, respectively, 95 : 4 : 1, or pallidipennis or paradiseby alloy. 1 C.p. f-crystals, 2 tab.

The invention concerns a catalyst for oxidation of hydrogen in the atmosphere containing hydrogen, oxygen and water vapor. The catalyst consists of a metal, influencing the oxidation of hydrogen, or an appropriate alloy in the form of a catalytic layer is applied to the carrier material.

The removal of hydrogen from containing oxygen and hydrogen, and therefore, explosive gas mixtures, especially of great importance in case of accidents at nuclear power plants. Such gas mixtures are formed by faults of different types of nuclear reactors. In addition t the e are oxygen and its isotopes, that is always associated with a certain risk.

Known catalytic systems (DE 3725290), consisting of a Pd-Cu-Ni alloys. It turned out that such catalysts of Pd, Ni, Cu and Pd-Ag or Pd-Cu deposited on a carrier material, very effective when used in emergency situations at nuclear power plants. These alloys are characterized by high catalytic activity in the presence of catalyst poisons such as Co, J and S. the Alloys show a very small time delay before the catalytic reaction.

In accordance with theoretical data on developments in the nuclear reactor accidents can be expected that the hydrogen evolution begins with the selection of a small number of CO2and CO. There was also a substantial amount of steam. In this case, steam is formed partially in the cooled, partially in the overheated state. Steam release depends mainly on developments in the accident. However, even with the same sequence of emergency water vapor content in different parts of the protective casing may be different. It was found that the steam release should take into account almost since the beginning of the accident. In different parts of the space sterzi the rate of release of vapors. Water vapor content in some parts of the safety casing for a short time can reach less than 20% and more than 95%

While the allocation of steam can be provided from the start of the accident, the first signs of hydrogen appear with a certain delay of about half an hour. Education maximum concentrations of hydrogen at the failure of the reactor system can be expected in the first hours after the start of discharge in the middle and lower parts of the installation. Later in the safety case can accumulate high concentrations of flammable gas mixtures with hydrogen burning threaten the security of the safety case.

The analysis of the development of a variety of emergency situations has shown that in these cases with great certainty you can count on long-term allocation of steam. I.e. catalysts for the elimination of hydrogen for a long time can be used in the steam flow. It should be borne in mind that in some types of reactors used deionized water, known for its particularly aggressive.

The present invention is to develop a catalyst to remove hydrogen from the atmosphere containing hydrogen and color the In accordance with the invention the task is solved by a catalyst for the oxidation of hydrogen in the atmosphere, containing hydrogen, oxygen and water vapor containing catalytically active component on the basis of a platinum group metal and a carrier, having almost the same coefficient of linear expansion and thermal conductivity.

Known catalyst for oxidation of hydrogen, consisting of catalyzing the oxidation of hydrogen and metal carrier having almost the same coefficient of linear expansion, providing thermally compatible connection between them (C. A. Reuter. Catalytic properties of substances. Naukova Dumka, Kiev, 1968, S. 1082).

According to the above technical solution of the catalyst for oxidation of hydrogen consists of a catalyzed oxidation of hydrogen metal palladium and media nichrome.

Known catalyst has a low catalytic activity and resistance to corrosion in an atmosphere of saturated water vapor.

The catalyst according to the invention overcomes these disadvantages due to the fact that as the active component, the catalyst contains palladium or its alloys, or platinum, and as a carrier, respectively, or stainless ferritic steel, or Monel metal, made in the form of sheet material, fabric, mesh illocal as an alloy of palladium paradigmically alloy when the mass ratio of palladium to Nickel and copper, 90 99 4 9 1, respectively, or pallidipennis or paradiseby alloy when the mass ratio of palladium to copper or silver equal to 99 1 respectively.

The resistance of the medium to corrosion prevents its oxidation in the presence of water vapor, resulting in even with the collapse of the catalytic layer of the catalyst does not produce harmful oxidation products. The catalytic activity of the catalyst is retained in atmospheres containing water vapor. Very significant also that due to the good temperature compatibility of the material of the carrier and the catalytic layer provides good adhesion. The delamination is eliminated.

As the material of the carrier can be used, in particular, low-alloyed ferrous steel with low content of chromium and Nickel, noble alloy steel, conforming to German industrial standard, for example 1.5732, 1.5755, and other stainless steel this series, as well as austenesque steel, characterized by a lower corrosion resistance compared to carbon steel.

For improving thermal compatibility between the active component of the catalyst and the carrier provides additional comfo what I Pd

Ni Cu coatings can be used for media expansion coefficient 11,710-6cmoC.

In the presence of water vapor from the decay products are formed solutions containing both oxygen and alkali, can affect the catalyst, especially at elevated temperatures.

In accordance with the invention applied materials-carriers providing stability of the catalyst in the presence of the solutions of these substances, and toxic substances, such as boric acid or carbon monoxide.

In order to avoid structural changes in the media during the work, and as a consequence possible deformations of surfaces, which may cause cracking catalytic layer, it is preferable to use media that are in the process of increasing temperature and steady-state during operation temperature range do not form mixed crystals or phases with hydrogen and oxygen, can lead to dangerous changes in the lattice parameter. Thus the carrier material and the catalytic layer remain compatible in the process of increasing temperatures, and the formation of mixed crystals and phase.

To select the material of the carrier bol is due to the surface roughness). Best of all, if the media is only slightly dissolves the hydrogen, resulting in a slight release of hydrogen during cooling media. The oxide layers between the material carrier and the catalyst layer impede the connection surfaces of the carrier and coating and cause cracking catalytic layer. Therefore, the oxide layers on the base material before application of the catalytic layer was removed and the catalytic layer is applied on the treated sand the way the media. This treatment increases the surface of the catalyst, i.e., during the coating of the vapor resulting from the evaporation catalytic layers are deposited in grooves machined with the sandblasting method the surface of the carrier and stored inside the microscopic voids when forming the rough surface of the material carrier.

Thus, the subject invention eliminates the possibility of dissolution of the catalyst material of the carrier under the influence of heat in the process of catalysis, resulting in possible to avoid the dispersion of the catalytic layer.

As the catalyst according to the invention may use:

palladium-nickelodeo of Staley as carriers, namely steel and 1.5755 1.5732.

As a catalytically active component used:

palladium-nickelmania alloys with

90 wt. Pd, 9 wt. Ni, 1 wt. Cu

94 wt. Pd, 5 wt. Ni, 1 wt. Cu

93 wt. Pd-6 wt. Ni, 1 wt. Cu

99 wt. Pd, 1 wt. Ag (silver)

99 wt. Pd, 1 wt. Cu,

clean palladium or pure platinum.

All of the above alloys rich in palladium and pure palladium have only slightly different coefficients of thermal expansion and teploprovodnostyu. As catalysts, they are equally suitable. Platinum is different from the lower coefficient of thermal expansion.

As media were tested along with ferritic steels steel grade 304 and 316 on a scale ASTM, steel with low content of carbon in an amount of 0.6 wt. and Monel-metal (Cu-Ni alloy).

The invention is illustrated in the following examples and data are given in table. 1 and 2.

Example 1.

We investigated the catalytic action PdNiCu alloy, containing 85 Pd, 4 wt. Ni, 1 wt. Cu supported on a carrier of ferrous steel 1,5755 on both sides (linear coefficient of expansion of steel 11,710-6cmoC with actionnow the camera was simulated conditions, the corresponding real environment during the accident at the nuclear power station, filling the chamber with appropriate gas mixtures. The camera was installed catalyst sheet with the active surface 48 cm2.

Before the catalytic reaction, the catalyst surface was immersed in an atmosphere of saturated steam at 100oC and a pressure of 1 bar. The exposure time was 3.25 hours Determined whether saturated steam acts on the carrier material, causing the formation of cracks on the surface of the catalytic layer. After that, the reaction chamber was applied air pressure 1,29 bar and hydrogen under pressure of 0.11 bar. The following composition of the atmosphere: 44 about. pair, 51,6 about. air and 4,4 about. H2. Due to the starting catalytic oxidation of hydrogen after passing the pressure in the chamber for 2 min falling off of 2.51 bar to 2.45 bar. Then the pressure continued to slowly and constantly falling. From this it followed that the oxidation reaction was quickly started and after 2 minutes ended, i.e., the hydrogen is present in the bound form.

Simultaneously, the temperature at the catalyst layer for 1 min was up with the 100oC to the maximum level 220oC. After idle the end of the catalytic reaction, the catalyst surface was glossy. Crack formation on the catalytic layer could not be determined.

Example 2.

Used alloy PdNiCu, similar in composition to the alloy described in example 1. Alloy deposited on both sides of the media from ferrous steel 1.5732. Linear coefficient of expansion of steel 11,710-6cmoC fully contribute to the expansion coefficient PdNiCu-alloy. The layer thickness of the carrier is 0.5 mm, the size of the catalytic surface 48 cm2.

The difference between example 2 is that the catalytic layer with the carrier of steel before the catalytic reaction was aged in an atmosphere of saturated gas at 100oC for 72 h

In this example, the atmosphere gas consisted of the following components: water vapor 42,2 about. air 53,6 about. In a gas mixture such composition missed 4,2 about. of hydrogen.

In the same way as in example 1, the catalytic reaction was started immediately after the transmission of hydrogen gas atmosphere.

With increasing pressure in the reaction chamber when hydrogen begins to rise and the temperature in the catalytic layer.

Catalytic oxidation of hydrogen leads to a pressure drop. The pressure in the chamber for several minutes UP>oC from the initial temperature 100oC. After this temperature for 4 min drops again to its original value of 100oC. Hydrogen is completely transformed into water vapor.

Visual and microscopic examination after the experiment showed that the metal surface of the catalyst remained without any cracks and deposits.

Example 3.

This example demonstrates the catalytic ability of the oxidation in the atmosphere with high hydrogen content. In the same way as in example 2, take the sheet with double-sided coating PdNiCu-alloy on a carrier of ferrous steel 1.5732. The size of the catalytic surface is 48 cm2. The atmosphere of the gas mixture has the following composition: 57,6 about. water vapor, 32,9 about. air and 9.5 about. of hydrogen.

As in the examples described above, in this case, the catalytic reaction begins immediately after the transmission of hydrogen gas atmosphere. After submission of hydrogen under pressure 0,165 bar catalytic oxidation of hydrogen causes a drop in pressure, the pressure in the reaction chamber is reduced from 1.85 to bar up to 1.60 bar for several minutes. The temperature of the catalyst layer for 1 min increases to a maximum of the Jana pairs.

Example 4.

This example reflects the course of the reaction with catalytic oxidation using the same PdNiCu-alloy in an atmosphere of gas enriched with water vapor. The size of the catalyst corresponded to the previous examples. As the material of the carrier used ferrous steel 1.5732.

Reaction chamber filled with a gas mixture having the following composition: 79,2 about. water vapor, 15,9 about. air and 4.9 about. of hydrogen. Before the experiment the catalyst sheet was placed at 3.75 h in an atmosphere of saturated steam at 100oC. Immediately after the transmission of hydrogen in an atmosphere containing steam or gas, began catalytic oxidation. With increasing pressure in the reaction chamber when the hydrogen is also the temperature at the catalyst layer. Catalytic oxidation of hydrogen caused the pressure drop, the pressure in the reaction chamber for 4 min was decreased from 1.27 bar to 1.2 bar. The temperature at the catalyst layer increased from 100oC to a maximum of 180oC for 2 minutes and Then the temperature started to fall and after 6 minutes returned to the original value of 100oC. In the catalytic oxidation of hydrogen is fully turned in the El 1.5732 gases in the atmosphere, enriched with hydrogen. The dimensions of the catalyst layer corresponded described in examples 2, 3 and 4. In the reaction chamber was created atmosphere gas of the following composition: 42,5% vol water vapor, 43,5 about. air and about 14. of hydrogen.

Before catalytic reaction catalyst layer was placed at 2.5 h in an atmosphere of saturated steam at 100oC.

Due to the outbreak of the catalytic oxidation of hydrogen after passing the pressure in the reaction chamber for 3 min decreases with 2,77 bar 2.4 bar.

Due to the high concentration of hydrogen temperature for 1 min increases with the 100oC up to a maximum value 145oC. After 3 min, the temperature of the catalyst layer decreases again almost to its original value and is held at 115oC.

After the catalytic reaction surface of the sheet remains smooth, cracking or damage is not detected even when the study under the microscope.

1. Catalyst for oxidation of hydrogen in the atmosphere containing hydrogen, oxygen and water vapor containing catalytically active component on the basis of a platinum group metal and a carrier, having almost the same coefficients lyderic palladium or its alloys, or platinum, and as a carrier, respectively ferrite stainless or steel, or Monel metal, made in the form of sheet material, fabric, mesh or granulate and resistant to the corrosive action of water vapor.

2. The catalyst p. 1, characterized in that as an alloy of palladium it contains paradigmically alloy when the mass ratio of palladium, Nickel and copper, respectively 95 4 1 or pallidipennis or paradiseby alloy.

 

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