DE2263883C3 - Process for the preparation of a particulate silver catalyst by electrodeposition of silver - Google Patents

Description

The present invention relates to a method for at a current density in the range from 2 to 100 mAm production of catalysts based on SiI- pere / cm ² and at temperatures between 10 and

ber, which are suitable for the synthesis of Ethyienoxid. 95 50 ⁰ C and removal of the silver to the extent of its

In particular, the present invention relates to a mixture of the cathode, which is characterized in Process for the preparation of catalysts on the that an electrolyte solution of silver salts in Electrochemical basis of silver. complex form used with ammonia.

There are many methods of making cataly- The detachment of the deposited silver from the ca-

Sators on the basis of silver for the production of 30 thode can u «:. h mechanical methods or known by ethylene oxide. On the other hand, it is known that ultrasonic vibrations occur,
the structure of the silver and the working conditions, the following mechanical techniques can be used favorably

where it can be obtained an essential one can be applied: use of brushes that Significant for achieving high activities and sliding back and forth on the cathode, using a

Possess selectivities. The previously proposed vibrating or oscillating cathode, spraying by chemical methods consist essentially of the liquid under pressure on the cathode, vigorous decomposition of silver salts or compounds, to stir the electrolytic solution.
To be kept in a finely divided state. Which are useful in the process according to the invention

Such methods have the essential silver compounds that can be used as electrolyte solution

Partly that they are difficult to reproduce and that in the case of salts such as silver nitrates, silver sulphate, silver acetate, silver halides, silver oxalate, complex salts, which are unavoidable in the treatment processes, occur, whereby expensive recovery compounds, such as ammoniacal ones, can occur
driving will be necessary. Silver hydroxides.

On the other hand, the production of silver would be with high levels of energy. In addition, the silver salts are preferably in

and in a reproducible manner using complex forms with ammonia or fluoborate ions generation of systems for electrochemical appearance (fluoboric ions).

generation of this metal is possible. On the other hand, however, it is also advantageous to use a buffer

also known that the electrolysis of silver solutions increases the pH of the solution in the range of 10-14 leads and holds to a metal with a compact shape.

in each case too large particle sizes, which make it possible to 50. The electrolysis is generally carried out in the presence of use in industrial processes for the production of protective colloids, such as cellulose derivatives, for example of ethylene oxide by oxidation of ethylene, not carboxymethyl cellulose,
make suitable. In the electrolysis process according to the invention can

So it is from the German Auslegeschrift 1 048 422 the current density vary in a wide range, however

known, silver powder by electrochemical deposition, values in the range of 2 to 3 deposition of silver on a silver cathode and deposition 50 mAmpere / cm * are preferably used. Provide the following working strips of the kömigen silver precipitate. examples serve to explain the invention.
The silver powder produced in this way, however, scatters in one

wide grain range and maximum particle size

Ben of 440,000 A, which have no catalytic activity 60

did in the oxidation of ethylene to ethylene oxide 100 g AgNO ₃ , 750 g borax (Na ₁ B ₄ O ₇ · 10H ₁ O)

sit. Furthermore, from the German patent specification and 400 g of NaOH were ge-1060151 in distilled water an electrochemical process for manufacturing dissolves and dilutes to a volume of 1001. For this Treatment of silver powder from a slurry of 600 cm * of an aqueous ammonia solution

Ag ₃ O known, which is primarily used for 65 (28 Βέ) and 10 g of carboxymethyl cellulose (previously used in the manufacture of sintered materials. Dissolved from Chem. Elsewhere). 3.5 liters of the above on-Techn. 1957, Heftll, p.645b! S649, is the electrolyte! 8th solution, shown in the single figure, was known to produce metal powders. In the case of the stand, an electrolytic cell is poured in that has an anode

Graphite in compact form 1 and a cathode at a temperature of 18 ⁰ C

a silver plate 2. Apparent current density '!', 70 mA / cm »

The cell was equipped with a system for mechanical cathode potenüa! -1000 mV against

Removal of the deposited silver equipped, the SCE

consisted of two plastic brushes 3,3 ', whose Rota- 5 cathode Silbemetz with

tion speed in a wide range through a mesh of 1 mm *

with a gear provided Motoi 4 can be controlled brush speed,. ZOO revolutions

can. _{per minute}

The brushes were attached so, 'leave them the voltage 12 volts

Kaüwden surface overlapped, ok

A peristaltic pump S outside the cell. The energy consumption was about 3 kWh per Ug sucked the electrolytic solution, conducted it through begotten silver.

a heat exchanger 6 and returned it to the cell coated on a ceramic material. The silver produced was placed in a reactor under the im

During the electrolysis of the Silbertiter was introduced through _ls Example 1 specified conditions. At periodic additions of complex overall with ammonia 22O ⁰ C was obtained in the reaction of ethylene to tied-silver nitrate in excess kept constant ethylene oxide, conversion and Sdektivitätswertc th. From 20 and 80%. The silver obtained had crystal

The electrolysis was carried out with a constant current of 700 A.
carried out by means of an amperostat. A load a ₀

drawing electrode (saturated calomel) was in contact.

with the cathode for measuring the electrode potential - example 3

% ' The electrodeposition was carried out under the following Using the same solution of Example 1, a

s; Conditions carried out: a ₅ electrolysis using ultrasound for

s ^ Removal of the silver carried out, Bs were fol-

Sj, temperature 2O ⁰ C, the following experimental conditions are observed:

ij cathode surface 80 cm ²

ή Anode surface 80 cm ² Position of the transducer near the cathode

Current density 6 mA / cm ² 30 temperature 15 ° C

I ^ distance between the electro-cathode Ag plate

k the 3 cm cathode area 50 cm ²

Cathode potential -1000 mV against anode of compact graphite

for SCE *) anode surface 100cm ²

* 'Brush speed 60 revolutions 35 current density 50 mA / cm ²

per minute voltage 10 V

Chip cathode potential applied to the cell -1300 mV

\ nung 3 V

[' The transducer for the ultrasound was nait the

t *) Standard calomel electrode. _{4 <J} Cathode electrically connected to avoid possible corrosion

s to avoid sion processes.

The electrical energy consumption was about 0.7 kWh.

per kg of silver produced, the yield was 80%. The silver obtained in mental conditions had sizes

The silver produced had an average of about 800 Å and gave conversion and

Γ size of 800 Å, was washed with water by ion free-45 Selektrivitätswerte in the ethylene-ethylene oxide Reakgewaschen, in the oven at 8O ⁰ C and dried tion of 25% and 78%.

■ then using suitable techniques on a

ceramic carrier deposited to test the B e i s ρ i e 1 4

; perform catalytic activity.

The one made of a carrier and silver in an amount of 5 "> This example refers to a possible in-15% existing catalyst was put into a pipe by an industrial process for the production of catalyst-2,4 cm, which is formed with an outer jacket based on silver by means of electrical deposition was equipped with a thermostatic fluid of silver nitrate solution with continuous flow could circulate. The height of the catalytic bed and continuous detachment of the electrically depleted about 1 m. 55 different materials in an electrolytic cell

In the reactor was at atmospheric pressure of the bipolar type.

A gaseous mixture was fed in, which had the following It was an electrolyte of the following composition: 5% ethylene, 6.5% CO ₂ , composition used:
5% O ₂ , 83.5% N ₂ . The flow rate was 210 Nl / h and the contact time was about 4.6 seconds. 60 AgNO ₃ 0.5 to 10 g / C

At 220 ^° C., conversion and selectivity borax 5 to 20 g / C were obtained

efficiency values of 30 and 80%. Carboxymethyl cellulose .. 0.04 to 0.5 g / C

NH ₂ 5 to 100 g / C

B e i s ρ i e 1 2 NaOH 3 to 100 g / C

A bipolar type cell was used with the same solution as in Example 1.

Electrolysis under the following experimental conditions The electrodes were made of silver plates (or rust conditions carried out: free stem plates) and made of compact graphite. the

O 5.75 509 622/268

Bipolarity was established by tight coupling of a graphite plate realized with a silver plate (or a stainless steel plate).

The separation of the electrodeposited material from the cathode was carried out as above done with brushes.

The electrolytic solution was withdrawn from the bottom of the electrolytic cell, cooled with respect to the Corrected the silver titer and the pH value to separate the metallic silver from the electrolyte placed in a centrifuge and then pumped back into the electrolytic cell.

1 sheet of drawings

Claims (2)

In this case, the extraction of silver leads to particles whose grain sizes are broadly based on the patent application. Scatter range, the upper limit of which exceeds 1. Process for making a particle 600,000 A is located. The particles thus obtained are therefore inactive in the form of a silver catalyst by electrochemical 5 in the oxidation of ethylene to ethylene oxide. Deposition of silver on a silver cathode. The aim of the present invention is to produce silver catalysts by electrolyte, an aqueous electrolyte, with a density in the range from 2 to 100 mAmpere / cm * whose particle sizes are below 1500 A and preferably and at temperatures between have 10 and 5O ⁰ C between 300 and 1500 A, the η et at their arrival and removal of the silver in the extent of its formation to turn for the synthesis of ethylene oxide by the cathode Oxidavon, dadurchgekennzeich- tion of ethylene, high activities and selectivities in that an electrolyte solution made from silver salt. ...... "., zen used in a complex form with ammonia. It has now been found that it is possible to use silver 2. Use of the suitable for the synthesis of ethylene oxide according to the method of And whose Claim 1 produced catalyst when producing 15 crystal aggregates sizes between 300 and 1500 A. have of ethylene oxide from ethylene by reaction, by electrolysis of Silberverbindunmit Air or oxygen can be produced, with silver depending on its formation removed from the cathode.
The invention therefore relates to a method for producing to position a particulate silver catalyst by electrochemical deposition of silver on a silver cathode from an aqueous electrolyte