DE1667597A1 - Hydrogen-permeable element for the production of high-purity hydrogen - Google Patents

Description

concerning

Hydrogen-permeable element for the production of high-purity hydrogen ... . . - .--. '.

The "invention relates to the manufacture of Hydrogen, in an electrolysis cell with a cathode made of palladium or a hydrogen-permeable cathode Palladium alloy with activated Surface, so that the essentially entire © in The 2-cell electrolytic unit produces hydrogen in ultra-pure form can be obtained.

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Although hydrogen is considered to be the best carrier gas for gas chromatography, it has not found further application because of the dangers associated with storing and handling hydrogen from cylinders. In addition, the contamination of hydrogen W from bottles is often too high for gas chromatographic purposes. Electrolysis cells have therefore already been proposed for the production of ultra-pure hydrogen, one or more tubes made of palladium alloy being used as the cathode. During electrolysis, the electrolytically separated hydrogen diffuses through the walls of the hydrogen-permeable pipes made of palladium alloy and can thus be obtained from the cell in a highly pure form.

Of which forms in solohen duties waters fuel pressure resulting from the Kernst'sehen ⁷ equation, the voltage of the gas pressure occurring at the aero electrolyte surface facing the cathode to the cathode 3 *, n ^ brings relationship "Matt.Kann; generally! '^ say that a considerably high pressure can occur which exceeds offc70 atü (lüOOpsi) without this

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to a noticeable reduction in hydrogen decomposition comes. The maximum pressure only results from the mechanical strength of the cathode Tube. .-

To operate a cell in practice, most of the hydrogen deposited by electrolysis must penetrate the palladium alloy drill hole and be able to be extracted from it in a highly pure form. It is known that the proportion of hydrogen absorbed on the drilling walls - and consequently also the amount of pure hydrogen to be recovered - can be increased if the surface of the drilling is coated with palladium black to increase its activity. Thus coated tubes absorb at least .6.0) 'o of at 90 ⁰ C and a current density of 6.5 A / dm ² (UEO amperes.per square foot) operating electrolytic cell. Other methods for activating drilling cathodes made of palladium have also been proposed, but no drilling cathodes have yet been used.

the
firgable that allow / recovery of the essentially total amount of hydrogen developed in an ultra-pure form.

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166759?

The invention thus relates to a method for activating an area of pallet. ium or a hydrogen permeable palladium alloy, preferably in "contact was with a melt of an alkali metal or Erdalkaiihydroxyd · ,. by this surface, which is at a temperature of at least about 450 G ^0, e iner oxy dl he ends At mo sphere , except where - through it is covered with an activated coating.

The invention also relates to a hydrogen permeable one

Component, in particular an electrode for electrolysis, made of palladium or palladium alloy, its surfaces by an activated coating, which is produced according to the above procedure has been obtained, is characterized. The application this electrode for electrolytic hydrogen production allows the extraction of so good. like the total amount of hydrogen evolved in ultra-pure form and moreover shows a service life - the uninterrupted operability for Obtaining essentially all of the electrodeposited hydrogen in ultra-pure form the operating times of known electrodes in the form of 1 alladium alloy in hydrogen-generating Cells far outperforms.

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The invention also relates to an electrolyte for a Hydrogen generating cell, this one is made by an aqueous solution of an alkali or alkaline earth metal hydroxide from electrolysis at a current strength of at least lö A / l is exposed for at least 1 h, creating an electrolyte for a hydrogen generating one Cell. Is formed which is essentially free of Impurities and shows improved effectiveness when used in such cells »

According to the invention, an electrolysis cell is obtained for the production of ultra-pure hydrogen, which is achievable in terms of its effectiveness It is characterized by purity and in this it is considerably above the known hydrogen-producing cells is laying.

Before the surface is exposed to hydrogen permeable palladium or palladium alloy to produce a suitable electrode for the alkali metal or alkaline earth metal hydroxide WasBerstoffgewinnung one, it should be carefully cleaned of dirt and grease. This is achieved by washing with a customary solvent, such as carbon tetrachloride or acetone, after drying, for example in an oven at an elevated temperature

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on the order of 200 ⁰ G for a sufficiently long time to remove all moisture and the solvent, the surface is subjected to the activation treatment. It should be noted that the cleaning and drying of the electrode surface prior to activation is essential in order to be able to use the

essentially the total amount of hydrogen evolved

to win ultra-pure.

After cleaning and drying the electrode surface, these are a melt of an alkali or Exposed to alkaline earth hydroxides, e.g. by immersing the electrodes in a bath of molten hydroxides * Of course you can also click the electrode surface other way to match with the hydroxide melt, e.g. spraying or applying. It is only necessary to ensure that the entire electrode surfaces with melted Hydroxide come into contact for optimal extraction of ultra-pure hydrogen from the electrolysis cell. Used as a hydrogen-evolving electrode Palladium or a hydrogen permeable palladium alloy when used in the form of tubes, it is preferred to seal the tube with the hydroxide scrim melt before its end to bring into contact, so that their inner surfaces be perfectly wetted with the melt. '

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In the case of the method according to the invention, one can call it Hydroxyd melt use the hydroxides of alkali and alkaline earth metals, such as potassium, sodium, Lithium, ßubidium, cesium, strontium * and barium hydroxide " Of course, one or more hydroxyae can be used to activate the palladium electrode or a hydrogen-permeable palladium alloy. Calcium and magnesium hydroxide cannot be used turn as they decompose before melting; However they can be used together with the melt of other hydroxides.

UIe temperature of the hydroxide melt, the naGh. the erfinet unpsgemä SEN method for treating the palladium or palladium! egierungsflächen applies insofar should be at least k ^ O ° G G are ⁰ to ¹ J ^ O, preferably 4-50. It showed you that such a thing

Pretreatment at elevated temperatures faster ei "- M

foils can and dai-3 the speed of activation varies with egg tenroeratur egg melt. Was a melt auπ Matriumhydroxyd with a temperature of 45u. C applied as an activating bath, so was an exposure time; on the electrodes made of palladium or palladium ^{alloy of L} j min for optimal activation of the electrodes in eggs nachfölgenö_en oxydie-

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treatment required. If the temperature of the melt ■■ However ca, 700 °, so only a few seconds are required. Longer exposure times in a bath at a higher temperature only lead to excessive etching and losses of palladium or palladium alloy. The time to be used in each case at a certain temperature of the melt for complete activation can easily be determined by simple experiments. The exposure time can range from a few seconds at temperatures of the order of 700 ⁰ G and vary a few minutes at temperatures of at least about G.

The surface of palladium or the palladium alloy which has been treated with the melt of an alkali or ErE alkali hydroxide is then exposed to an oxidizing atmosphere in the form of oxygen-enriched air or air in accordance with the process according to the invention in order to achieve activation It is essential that the temperature of the surface to be treated in this way is at least approximately 450 ^° C. Surface temperatures up to

at 75O ° G and above are permissible. Extreme temperatures should be avoided, as otherwise the ability of the _t surface zone may be lost.

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When the melt of the hydroxides is in contact with the atmosphere, the contact occurs Electrode surface with oxygen once the electrode taken from the melt and exposed to the ambient air. As a result, it immediately comes across the

entire electrode area to form an activated one Surface according to the invention.

After the palladium or palladium alloy surfaces So treated, they are demineralized with Rinsed off water to remove all traces of the hydroxides to remove. You have to work extremely carefully so as not to contaminate the activated electrode surfaces and also not to destroy the active layers. .

The invention is explained in more detail with reference to the accompanying figures. :. - ... M

Fig. 1 shows a cross section through the inventive Electrolytic cell.

. Fig. 2 shows the section through 2-2 of the electrolytic cell of Fig. 1 and a

Fig. 3 shows schematically the application of the cell for the production of hydrogen.

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The electrolysis cell 10 for the production of hydrogen according to FIG. 1 comprises an electrolysis chamber 11 made of nickel or otherwise material resistant to the ambient conditions. As the electrolyte in the chamber an aqueous solution of l6 wt serves -.% Sodium hydroxide, which is up to the level of the 12th The electrolyte level is maintained by an appropriate supply of water via the supply line from a storage container, as can be seen from FIG. 3. The electrolyte volume of the cell 10 comprises a quarter of the total volume of the electrolysis chamber including the storage container. An initial filling of a k% sodium hydroxide solution is already enriched to 16% NaOH after a short operating time of the cell.

Before the electrolyte is fed into the cell this is preferably overnight in a separate electrolysis cell with a current of 15 A / l. electrolyzed to remove all impurities from the solution to be deposited and only thereby to make the electrolyte suitable for use in the hydrogen cell 10.

In the cell 10, the electrolysis chamber 11 forms the anode and is therefore connected to a corresponding power supply connected to a DC power source (not shown) across terminals I ^. About the current density

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Balancing between anode and cathode is a
Mckelstab 15 provided; it is z ', B _e connected by welding to the upper end of the chamber l6. 11

The rod 15 extends into the electrolysis chamber 11 and, through its connection with the chamber wall, also provides one
Part of the anode of the cell

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A number of palladium tubes 17, the surfaces of which are activated by the method according to the invention, serve as the cathnode. The bores are arranged parallel to one another and in a circle around the anode rod 15, as can be seen from FIG they are waterproof, sealed, for example welded or pressed together. In the electrode chamber 11 are by means of insulating spacers 19, for example of polytetrafluoroethylene, which are fixed to the m Anodeiistab 15 held.

The lower ends of the drilling 17 are on the upper one Splash 20 of the cathode chamber 21 is welded. Of the

Flange 20 is made of nickel or another material. The electrical connection of the cathode chamber 21 to a ΰ -leiehstromquelle is done via ^ the terminal 22, which is on

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the cathode chamber is fixed by means of a rent or screw 22a.

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Before assembling the cell 10 x, the tubes 17 are carefully cleaned, degreased and ^{dried in an oven of approx. 105 0} G (220 ⁰ E) until all traces of moisture

and cleaning agents have been removed. The thus cleaned and dried Drill are then dipped into a melt of, for example, sodium hydroxide at a temperature of, for example 675 'to 700 ^D C and therein ca. left for 3 min, it is particularly important to ensure that no part of nickel from the cathode chamber comes into contact with the molten liquor. Now the whole thing is removed from the melt, cooled in the air and carefully rinsed off with deionized water. The pipes activated in this way are now carefully closed to prevent further contamination

™ protect. Now the pipes, the ends of which have been closed, are inserted into the cell and the splash connection is closed. As can be seen from Fig. 1, the flange 20 of the cathode chamber 21 is via insulators 23, Zk made of, for example, polypropylene from the plan 25 of the

Electrolysis chamber 11, which serves as an anode, separated. The . The two pools, which are isolated from each other, are

Clamping screws 26, 27 and the hexagon nut 28, 29 are tightened. The screws 26, 2? are insulated from the Katuodeiif laiisch 20, namely with üilie of sheaths 30 ', 31 made of, for example, rubber. "■ / '", "

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To avoid leakage of the electrolyte, For example, rings 32 made of a resilient material such as polypropylene are provided. This material must be opposite be resistant to the action of the electrolyte. the

in rings 32 there are 4 »· around each tube 17 / more immediately Near the flange insulators 23, 2 ^. When the mounting screws 2o, 2? are tightened, the Ü-einge 32 are pressed together with a tight fit and thus an excellent liquid seal all around the pipes in close proximity to contact with the Reached isolator 23.

The cell 10 operates at about room temperature. 2 or 3V =. By using the cathode tubes 17 made of palladium or palladium alloy according to the invention one achieves an almost one hundred percent Extraction of the separated hydrogen in ultra-pure form, it diffuses through the cathose tubes and collects in the cathode chamber 21, from there it becomes supplied to its use via the pipe socket 32a,.

The oxygen formed by the anode, i.e. at the Inside v / and the electrolysis chamber 11 and on the anode tab 15, is blown off via the pipe socket 33. How out

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As shown in Figure -3, oxygen line 33 is preferred made of a flexible electrolyte resistant material, such as polyethylene, and with a Electrolyte reservoir connected to restore all of the electrolyte entrained by the oxygen to catch.

From the arrangement of FIG. 3 it can be seen, that the Vi assers to ff cell 10 with its cathode in the form of the invention activated palladium * tubes with direct current operated from a DC power source (not shown). The connection is made via the current leads 40, 4-1 « The level in the cell is usually always the same adhered to electrolyte, with the help of the storage container 35 »from which the electrolyte via line 42 from electrolyte-resistant, flexible material such as polyethylene is fed. A contact 43 in the line 4l is opened with the help of a spring 44 to interrupt the power supply to the cell 10 when the electrolyte level in the storage container to a predetermined lower Value has decreased *

In the cell 10 is hydrogen with a. Speed of approx. 7 ecm / A of the applied current electrodeposited. He is about Bohr 32a and

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Recovered line 45 with valve ^ i-6 in ultra-pure form. To stop the electrolysis when the hydrogen pressure in the cell has reached a predetermined maximum value, a pressure valve 4? with control switch in the circuit between the direct current source and the cell in line 45 is provided. Xterw. now the predetermined maximum hydrogen pressure has been reached at the cell outlet, the pressure valve 47 interrupts the power supply to the cell and thus terminates the electrolysis and, at the same time, the hydrogen production. In line 45 there is also a safety valve 49 to allow hydrogen to be blown off in the event that the pressure valve 4? fails. In general, the safety valve 49 will respond at a predetermined hydrogen pressure which is higher than that. Control pressure for the actuation of the pressure valve 47.

in Figures 1 to 3 the cathodes are in the form of Tubes made of palladium or hydrogen-permeable palladium alloys shown with activated surfaces, of course the cathodes can also have a different shape, e.g. sheets arranged in series or double wire tubes, so that the formed on the cathode surface

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Hydrogen can diffuse through this jacket into the interspace and "-" can be obtained from it. It should be noted that ^; naon of the invention in the electrolytic production of hydrogen on ■ - '■ "cathodes in the form of a membrane made of palladium or

en wasserstof fpermeablen Pallädiumlegierung / the top "· ■ '■■ surfaces are activated and only one side of the membrane is exposed to the electrolyte.

If a palladium alloy is used, it is a prerequisite that it is permeable to hydrogen but not permeable to the electrolyte. As . For example, a silver-palladium alloy with 75 / S-JPcL "'- and 25 % Ag or a ternary alloy with silver and gold proved to be suitable. Cathodes made of pure palladium are preferred, since the palladium alloys usually have a higher working temperature for the cells Require effectiveness. Ralladium cathode tubes with surfaces activated according to the invention can be operated with a current strength of 15 A, a temperature of approx. 65 ° G (150 ° I <\) being established in the cell. Under these working conditions, the generation of ultra-pure hydrogen is already equivalent to that of silver-palladium alloys as cathoic

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with additional heating possible.

After two months of operation, the yield of ultra-pure hydrogen with palladium-silver alloys as cathode has fallen by approx. 10% , whereas the supply of hydrogen with pure palladium

remains the same. The resistance of pipes made of palladium ti

is only about a third of the resistance of

the end
such / PaTLadium silo alloys. It has also been found that the resistance of pipes made of palladium-silver alloys, and also of palladium, can be substantially reduced by inserting a conductive wire into the pipe.

In the hydrogen-donating cell of the invention NaCN can use a variety Anoaenmaterialien, Üickel is preferred "but are also suitable platinum and Kohlej platinum is very expensive, coal Anoaen disintegrate over time, you can also Silver Jt'alladium anodes apply ; however, this does not appear to be very two-dimensional as they slowly dissolve and form thick deposits of palladium black on the cathode surfaces, making diffusion of hydrogen through the cathode walls difficult. '

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According to the invention, any electrolyte can be used in the hydrogen-generating cells. Basic electrolytes are preferred to acidic electrolytes. Optimal results can be achieved with an electrolyte in the form of an aqueous solution of an alkali or alkaline earth metal hydroxide. Of the basic electrolytes, sodium hydroxide solution is preferred, since the ohm ¹ losses during hydrogen separation are low, an undetectable amount of ozone is developed and no noticeable decrease in hydrogen development can be observed with increasing operating time.

The concentration of alkali or alkaline earth metal hydroxide in the electrolyte can fluctuate within wide limits. With sodium hydroxide solution, a concentration of 15 % NaOH achieves optimal results with regard to the evolution of hydrogen.

It could be established that the istromaüsbeute in aqueous solutions of alkali or alkaline earth metal! hydroxy the can be increased noticeably if the

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Solutions in a separate cell, with one current intensity of at least 10 A / l. at least 1 h before the Use as an electrolyte in hydrogen generating, electrölysiert the cell in order to. almost completely rid them of impurities. Die.se electroly- ' table pretreatment is expediently carried out in a different unit than in the. Cell, which .then should be used for the development of pure hydrogen. It it should be noted that the time for this electrolytic pretreatment of the electrolyte per se is not is critical, but to some extent depends on the Current density and the original purity of the pretreatment Electrolytes. .

The ¥ oräektroiyse of the electrolyte is in general achieved by feeding the electrolyte to be treated to a special electrolysis cell and then at a current of at least 10 A / l electrolyte volume and a voltage of approx. 3-V = across the. Cellular

'- ■' ■ 'becomes

clamp electrolyzed / nickel electrodes for at least 1 h can be used in such a pre-electrolysis. However, others are also suitable Materials like carbon or platinum. Generally speaking, Any inert material can be used as the electrode material to serve*

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The invention thus relates to a new and improved one Process for the activation of palladium or hydrogen-permeable palladium alloys, which are used as Cathodes in electrolysis cells are used to produce hydrogen. In this way, the hydrogen is obtained in high yield with high purity. The salary The amount of impurities in the hydrogen is less than 10 "parts (10 parts per billion).

The evolution of hydrogen in known cells with untreated areas of palladium or palladium-le-. alloy cathode drops by approx. 25 * £ in a few days

In the case of cathodes treated according to the invention, essentially 100 % ultra-pure hydrogen is obtained, whereby this efficiency does not experience any significant reduction over long periods of up to a year.

latent stimulus eh e

BAD ORlGIMAL

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Claims (2)

iCHEN 9 SCHWEKJEHSTOASSE 22 06 51 TEiKOEAMMADHESSB; ΡΒΟΤΕΟΤΡΑΤΕΝΤ MttNQHEN lA-32 793 P A T E M T A E S P H U G H E - 1. Hydrogen-permeable element - characterized by an activated membrane Palladium or palladium alloy, with the activation ^w tion is achieved by a 'coating, which by treatment of the membrane surface at a temperature of at least approx. 450 ° G in an oxidizing atmosphere has been. 2. Process for the production of the hydrogen permeable Element according to claim 1, characterized in that ge k e η that you can get the surface of a palladium or palladium alloy cleans, dries, given ((| optionally pre-treated in a melt of alkali metal or alkaline earth metal hydroxide at a temperature of at least 50 ^ ⁰ G and finally subjected to oxygen-containing atmosphere exposes. - '■ 109827/1139 Empty ropes