DE1071789B - Process for the electrochemical oxidation of carbon monoxide or carbon monoxide mixtures in fuel elements with aqueous alkaline electrolytes - Google Patents

Description

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GERMAN Mrmm < PATENT OFFICE

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EDITORIAL NOTICE 1071789

R 25100 IVa / 21b

REGISTRATION DATE: MARCH 5, 1959

4-98 NOTICE
THE REGISTRATION
AND ISSUE OF THE
EDITORIAL:

DECEMBER 24, 1959

The present invention is a carbon monoxide electrode, in particular for the electrochemical Electricity generation through reversible oxidation of CO or CO-containing gas mixtures (e.g. Furnace gas, water gas, generator gas, synthesis gas) in connection with an oxygen or air cathode in a fuel element with an alkaline electrolyte is intended. For the electrochemical utilization of the CO uses elements that can be divided into two groups:

1. Galvanic elements that work with aqueous electrolytes at temperatures below the boiling point of the electrolyte work at atmospheric or elevated pressure,

2. Galvanic elements that use solid or molten electrolytes at temperatures above of 500 ° C and atmospheric pressure work.

The invention belongs to the first group.

A method for the electrochemical actuation of CO has already been described in which the au CO gas is fed to a copper electrode located in the alkaline aqueous electrolyte. From the The fact that this electrode, with -1.04 V against the oxygen electrode, has a potential in the vicinity of the reversible hydrogen potential, from which it deviates by up to + 6OmV depending on the test conditions, it is concluded that the process determining the potential is the solution of the preceding one Conversion reaction formed hydrogen.

More recently , the processes involved in the electrochemical actuation of CO on electrodes containing Raney copper and Raney nickel in alkaline solution have been examined more closely and the existence of a potential-determining hydrogen dissolution has been inferred, the hydrogen originating from an upstream conversion reaction.

A direct electrochemical dissolution of the CO in such an electrode was therefore previously for held impossible.

By contrast, it was found that this inference therefore is not mandatory because the reversible potential of Kohlenmonoxydelektrode in a strongly alkaline medium by more than 200 mV more negative than the reversible hydrogen potential. In addition to anodic carbon monoxide dissolution, cathodic hydrogen deposition must therefore inevitably occur on the electrode body, the greater the more negative the potential of the electrode body and the lower the hydrogen overvoltage on the electrode material used. So you can use a known nickel double skeleton catalyst electrode, which works as a reversible hydrogen electrode, when operating with CO, only a potential in the vicinity process
K for electrochemical oxidation

of carbon monoxide
or carbon monoxide mixtures

in fuel elements
with aqueous alkaline electrolytes

Applicant:

Ruhrchemie Aktiengesellschaft,

Oberhausen (RhId.) - Holten,

and coal electricity

Corporation,

eat

Dipl.-Phys. Peter Jacob, Dr. Eduard Justi,

and Dr. August Winsel, Braunschweig,

have been named as inventors

of the reversible hydrogen potential. Any negation of the potential leads to a significantly increased hydrogen separation and thus to an increased anodic load on the electrochemical CO dissolution taking place on the same electrode body. Such an electrode therefore inevitably converts CO electrochemically with the formation of H ₂ , with carbon monoxide and thus chemical energy being constantly consumed.

This behavior is shown schematically in Fig. 1. Curve 1 denotes the current-voltage characteristic of a reversible CO electrode, curve 2 the characteristic of the reversible hydrogen electrode realized in the same electrode body, the performance of which is significantly greater than that of the CO electrode. The potential U ₁ characterizes the mixed potential from both electrode processes that is established at the electrode in the unloaded state.

From this consideration it follows that the reversible CO potential can only be seen on electrode bodies with a large hydrogen overvoltage, i.e. with materials that are used for the production of Hydrogen electrodes are particularly unfavorable.

The aim of the invention consisted in the choice of suitable electrodes carbon oxide without upstream Conversion to be implemented electrochemically directly.

3 4

There has been a method of extracting electrical sinters in a reducing atmosphere. Afterward

The Al is derived from energy through direct electrochemical oxidation by means of concentrated alkali lye

of carbon monoxide with an oxidizing gas, dissolved out of the sintered body and thereby the

preferably oxygen or air, in alkaline Raney structure of the catalyst metal within the

Electrolytes found with which this goal was set. 5 pores of the electrode. The electrode is

is rich. It consists of being activated and operational as fuel. Instead of Al you can

electrode uses an electrode that is at least one base for the Raney alloys and others

Metal of VI. Subgroup of the Periodic System Metals such as Zn, Si, Mg, etc., are used that

of the elements, preferably tungsten and / or dissolved out by alkali or acid or in

Molybdenum, as a catalyst for the electrochemical io can be removed in other ways.

Activation of carbon monoxide contains. For the support frame material, in addition to

The principle of the invention is shown by curve 3 in the condition of the electronic conductivity, the requirements

Fig. 1 illustrates. The hydrogenation shows that it is resistant to the activating solution

deposition curve on an electrode with a large must be. Furthermore, it is from that described above

Overload. The potential U ₂ is favorable for the same reason if the hydrogen overvoltage

The mixed potential that occurs on the support frame material is greater than or equal to the CO characteristic curve

such an electrode with a high hydrogen overvoltage according to the invention on the respectively used

Hydrogen overvoltage. Raney metal VI. Subgroup is. This

However, if there is a large hydrogen overvoltage, the potential-reducing hydrogen is only prevented from a necessary, not yet sufficient, deposition on the support structure. This circumstance can be taken into account for the suitability as a CO electrode material by making the support and also the specific catalytic active framework from the same metal from which the activating Raney was used to dissolve and activate the CO gas -Metal is made up; however must show. Mercury z. B. experience has shown that some other materials are also suitable for the support structure despite its extremely high overvoltage of> 0.57 V 25, e.g. B. the carbides of metals of VI. In addition to the CO electrode unsuitable, while group and other metals and compounds were found that metals of VI. Subgroup, especially if they are cheaper than tungsten and molybdenum, which are used as catalysts, a sufficiently high level of VI metal used. Subgroup.
Show hydrogen overvoltage and at the same time as the electrode, namely with one of the CO. These two metals are catalyst sieve electrodes. The catalytically active Raney metals have been included in this hitherto only low catalytic activity. In this case, meshes can be arranged on one or two electronically conductive microsieves or wire compartments from this, during operation, which realize the more than 70 mV 35 tric charges in order to dissipate the electrical CO potentials, which are more negative in the electrochemical than the reversible hydrogen potential. Reaction of the CO on the catalyst are released, tial under atmospheric pressure in the same elec- tron. The sieves should, if possible, contain a larger trolyte solution. Have hydrogen overvoltage than that between

A significant improvement in the process is the fact that Raney metal has been arranged for them. One can go to this

by increasing the load capacity 40 purpose, for example, amalgamated copper sieves are given.

such CO electrodes. This was made by using, but also microsieves from any other

Turning the relevant metals into the finest metals with correspondingly for the hydrogen separation

division or in a strongly disordered state, in front of a poisoned surface,

preferably in the form of Raney metals. It is advantageous to use strong electrolytes as electrolyte

In particular, electrodes have proven to be useful which contain alkaline lye with a concentration of 1 to 10 normal. However

Has a known double skeleton catalyst structure - one is also in equilibrium alkaline

show and for the production of such materials hydrolyzed alkali carbonate-alkali-bicarbonate-electrolyte

serve, the 10 to 80 percent by weight, preferably trolyte at or a little below the boiling point

20 to 40 percent by weight of a Raney alloy is suitable. The pressure here can be up to 50 kg / cm ²

of at least one metal of the VI. Subgroup in 50.

an electronically conductive support structure embedded with the ones used in the method according to the invention

keep. The latter is used for low resistance electrodes are potentials up to -1200 mV against

guidance of the ionization of the carbon dioxide to achieve the 0, lnormal calomel electrode. There

developing electrical charges. it has been observed that tungsten and molybdenum are among

In order to produce such electrodes, certain conditions are met in alkaline media Preferably from the powdered alloys potentials above - 800 mV against the calomel electrode Metals made with aluminum, which can be dissolved through access, is the limit of anodic melting of these metals or also powder load capacity given by this potential limit, metallurgically by reaction of the mixed and The process according to the invention can also be used with Then pressed metal powder at temperatures below 60 CO-containing gas mixtures, such as synthesis gas, water below the melting temperature of the respective alloy, gas, furnace gas, etc. The CO contains. Alloys have proven particularly useful, regardless of the hydrogen that is also present of the composition W: Al = (7 to 90): (93 to 10) and nitrogen with delivery of electrical Percentage by weight, preferably W: Al = 66: 34 Ge energy from the gas mixture consumed. These weight percentage, furthermore the alloys of the composition is particularly important in view of the fact Mo: Al = (9 to 90): (91 to 10), the preferred thing is that the pure preparation of CO is very inconvenient 50: 50 percent by weight. One mixes the powder which is high and expensive. The operation of the invention shaped Raney alloy with the electronically electrode with such CO-containing gas mixtures conductive scaffold powder in the desired ratio can be carried out particularly advantageously so that the nis, presses the powder mixture in the form of electrodes and 70 during the current draw in the pores of the gas

Electrode due to CO consumption creating inert gas cushion be flushed continuously or periodically into the electrolyte in a known manner.

If the CO content of the mixed gas is high (80 ¹ Vo), periodic purging is preferable. For this purpose, the electrode according to the invention is designed as a double-layer electrode. The narrow-pored layer with a mean pore radius r _t faces the electrolyte, the wide-pored layer with a mean pore radius r ₂ > r ₁ faces the gas space. The normal operating pressure is set so that the wide-pored layer is pressed free against the capillary pressure of the electrolyte, but the narrow-pored, electrolyte-side layer remains filled with electrolyte. The CO-depleted gas cushions in the pores become noticeable through an increase in polarization and are flushed through the fine-pored layer into the electrolyte by temporarily increasing the gas pressure to a value above the capillary pressure of the fine-pored layer. ao

For the conversion of heavily contaminated CO, the electrode according to the invention is known Way designed as a diffusion electrode with the most uniform (homeoporous) pore structure possible and operated with a suitable pressure in such a way that a proportion of the inert gas in the fresh gas corresponds Gas flow constantly bubbling through the electrode.

The method according to the invention is particularly advantageous for generating electrical energy from the known CO-H ₂ mixtures, such as furnace gas, water gas, generator gas and synthesis gas, with maximum utilization of the gas constituents being achieved. Since the CO electrode used in the process according to the application can _{not process H 2} because of its necessary high hydrogen overvoltage, the electrochemical conversion of CO-H ₂ -GaS mixtures is carried out by removing the residual gas, which has largely been freed of CO and which is produced from H. ₂ and inert, bubbled through the electrolyte and implemented in a known manner in a fuel element with a nickel double skeleton catalyst electrode with further power generation. It was found here that only such a small CO residue remains in the gas that the Ni diffusion electrodes are not destroyed by carbonyl formation if a sufficiently predominant H ₂ concentration is present.

example 1

To produce the molybdenum alloy , 10 g of aluminum and 10 g of molybdenum, both metals in the form of small, compact "pieces, are placed in a carbon crucible containing calcium chloride as a protective melt. The metals are alloyed at 1400 ° C for a few minutes while stirring and then the melt The regulus obtained in this way contains η ο ch_ £ fcH £ as_Ca 1 ei umghl ό r13, which by

Washing with distilled What he ser out solved

can be. The Regulus is then dried in a drying cabinet and then ground in a ball mill to a grain size of about 70 μ.

1.5 g of this alloy powder are then thoroughly mixed with 3 g of pure molybdenum powder in a mixer and then pressed in a die under a pressure of 4 t / cm ² to form a circular, approximately 2 mm thick electrode. This is in a tungsten belt furnace at 1000 ° C in H _? -Atmos phere sintered for two and a half hours, whereby a mechanically sufficiently strong body is obtained.

The electrode is then placed in about 4.6 normal potassium hydroxide solution, initially at room temperature, later at about 100 ° C the Al is leached out of the electrode. The electrode is now pyrophoric and must be protected from the ingress of atmospheric oxygen.

The electrode activated in this way is clamped in a plexiglass holder and immersed in the electrolyte consisting of 4,6n KOH, which should have an operating temperature of around 85 ° C. At a CO pressure of 2 atm. a constant resting potential of -1200 mV is established against the saturated calomel electrode. In such an experiment, the CO electrode was subjected to stationary anodic loading up to a current density of i = 30 niA / cm ² , the polarization increasing by a maximum of 130 mV, so that the electrode potential was set at -1062 mV. After the discharge, the original resting potential of -1200 mV was restored. Fig. 2 shows the polarization of this real CO electrode as a function of the current density i.

Example 2
Tungsten DSK electrode

The Raney tungsten alloy is produced by mixing 10 g of pulverulent tungsten and 5 g of pulverulent aluminum p ut and pressing again in disk form at 4 t / cm ^2; this body is then sintered in a tungsten belt furnace at 1600 ° C. in an H ₂ atmosphere for about 30 minutes and thereby alloyed. The alloy was ground to a powder of 150 μ in a ball mill.

2 g of this alloy powder were then mixed well again with 6 g of pure tungsten powder of approximately the same grain size in a mixer and the mixture was ^{pressed in a die at 5 t / cm 2} to form an electrode also 20 mm in diameter and 2 mm in height. The electrode was then sintered in a tungsten belt furnace for V2 hours at 1600 ° C. in a reducing hydrogen atmosphere.

The aluminum was then leached out in 4.6 normal potassium hydroxide solution at 100 ° C.

The electrode was then clamped tightly to the edge in a plexiglass holder, as is described for the molybdenum electrode in Example 1. At a temperature of 83 ° C of the 5normal potassium hydroxide electrolyte and a carbon monoxide pressure of 0.5 atmospheres, it showed a potential of -1211 mV against the saturated calomel electrode. The electrode was operated with a stationary anodic load of 25 mA / cm ² , its polarization increasing to 350 mV, that is to say the electrode potential was set at -861 mV against calomel. An interruption of the exercise brought back the old resting potential of -1211 mV against the saturated calomel electrode.

The electrodes from both examples retained their mechanically stable properties even after the load operation Condition at.

Example 3

Two fine-meshed copper wire networks with a mesh size of 35 μ and a wire thickness of 50 μ, provided with welded copper wires _{for making contact, were cleaned and dissolved in a solution of 100 g of NH 4} Cl, 0.17 g of HgCl ₂ , 10 cm '3, 5% HCl and 1000 cm ^{3 of} distilled water amalgamated for 5 minutes.

The iietze were placed in a holding device Polyethylene clamped plane-parallel with a mutual distance of 3 mm so that between formed a pocket-shaped space for them to hold the activated Raney molybdenum. The Raney

Molybdenum was formed by the action of 5 normal potassium hydroxide solution on the molybdenum-aluminum alloy of Example 1 obtained at temperatures up to 100 ° C.

In the pocket-shaped space filled with Raney molybdenum, carbon monoxide gas was introduced with a slight overpressure of up to 0.1 atm using thin capillary probes. In 5 normal potassium hydroxide solution as the electrolyte, a potential of −1.2 V against the saturated calomel electrode was established, which at 0.3 V polarization could be loaded ^{up to 20 mA / cm 2.}

Claims (11)

Patent claims: 1. A method for the electrochemical oxidation of carbon monoxide or carbon monoxide mixtures in fuel elements with aqueous alkaline electrolytes, characterized in that an electrode is used as the fuel electrode which contains at least one metal of V I. Subgroup of the Periodic Table of the Elements, preferably Wolf ram and / or ^ molybdenum, contains. - ~ ~ " 2. The method according to claim 1, characterized in that the implementation at an electrode is made in which the metal of VI. Subgroup in finely divided or strongly disordered Form, preferably in the form of the Raney metal, is present. 3. The method according to claim 2, characterized in that the implementation at an electrode is made in which the metal of VI. Subgroup is present in a double skeleton catalyst structure and made from a material that is 10 to 80 percent by weight, preferably 20 to 40 percent by weight, of a Raney alloy of at least one metal of VI. Subgroup Contains embedded in an electronically conductive support structure. 4. The method according to claim 2, characterized in that the implementation at an electrode is made, which is in the form of a catalyst sieve electrode in which the metal the VI. Subgroup preferably in the form of the Raney metal or with a Raney double skeleton structure between two_electronically conductive Mw crosieben or wire netting is arranged. 5. The method according to claim 1 to 4, characterized in that that the reaction is carried out on an electrode which, in addition to the metal of VI. Subgroup of the periodic system of Elements only those metals or electronic semiconductors in contact with the electrolyte solution contains whose hydrogen overvoltage is greater than or equal to the overvoltage of hydrogen on the metals used of the VI. Subgroup of the Periodic System of the Elements is. 6. Process for generating electrical energy using carbon monoxide alongside other gas mixtures containing combustible gases, characterized in that first Carbon monoxide according to the process of any one of claims 1 to 5 with the production of electrical Energy converts and then the residual gas, largely freed from carbon monoxide, that from Combustible gases and inert components consists, in a manner known per se, in a fuel element implemented with a nickel double skeleton catalyst electrode with further power generation. 7. Electrode for generating electrical energy through direct conversion of carbon monoxide with an oxidizing gas, preferably oxygen or air, in a fuel element alkaline electrolytes, characterized in that they contain at least one metal of VI. Subgroup of the Periodic Table of the Elements, preferably tungsten or molybdenum, as a catalyst for the electrochemical activation of carbon monoxide. , 8. Electrode according to claim 7, characterized in that it is the metal of VI. Subgroup in finely divided or highly disordered form, preferably in the form of the Raney metal. 9. Electrode according to claim 7 and 8, characterized in that it is the metal of VI. Subgroup Contains in double skeleton catalyst structure. 10. Electrode according to claim 7 and 8, characterized in that it is in the form of a catalyst sieve electrode is trained. 11. Electrode according to claim 7 to 10, characterized in that it is next to the metal of the VI. Subgroup of the periodic system of the elements only those metals or electronic Contains semiconductors in contact with the electrolyte solution, the hydrogen overvoltage of which is greater or equal to the overvoltage of the hydrogen on the metals used in VI. Subgroup of the Periodic Table of the Elements. 1 sheet of drawings