DE1277216B - Process for promoting the reoxidation of cathodically reduced metal compounds in the electrolysis of aqueous hydrochloric acid - Google Patents

Description

FEDERAL REPUBLIC OF GERMANY

GERMAN

PATENT OFFICE

EDITORIAL

Int. Cl .:

COIb

German class: 12 i- 7/06

Number:
File number:
Registration date:
Display day:

P 12 77 216.6-41 (F 48078)

January 3, 1966

September 12, 1968

The invention relates to a method for promoting the reoxidation of cathodically reduced ones Metal compounds in the electrolysis of aqueous hydrochloric acid, in which the electrolyte compounds of metals are added, which in several, easily convertible oxidation stages may occur.

It is known from hydrochloric acid, in particular from waste acid, such as those used in organic chlorination Compounds accrues to obtain chlorine and hydrogen by electrolytic means. An essential one The advantage of this process is that the investment costs are relatively low. To the To make electrolysis of aqueous hydrochloric acid even more economical, however, it is desirable that the required Lower cell voltage.

From British patent specification 834 640 it is known that the electrolyte metals, in particular Metals of the platinum group, whereby the hydrogen overvoltage is lowered. The achieved Tension gain is beneficial but not sufficient. A disadvantage of this known method consists in the fact that the metal initially deposited on the cathodes is mainly at Business interruption drops. As a result, a bottom sludge collects in the cathode spaces of the cells, which can hardly be brought into solution. It is therefore necessary to have the cell in certain Open and clean at intervals, which causes considerable costs.

From the American patents 2,468,766 and 2,666,024 it is known not to subject hydrochloric acid directly to the electrolysis, but to first convert it into the chloride of a metal, which can occur in several oxidation stages that can easily be converted into one another, the redox potential Me " ⁺ i = »Me ⁽ " ~ ^{1) +} must be more positive than the redox potential H «= * H ⁺ , and to electrolyze these metal chloride solutions. Copper and iron have primarily been suggested as metals to be used. The process enables the cell voltage to be reduced considerably. In many cases, the elimination of hydrogen production is economically negligible.

A sensitive disadvantage of the process, however, is that the cathodically reduced metal has to be oxidized to the greatest possible extent in an additional and expensive process stage in which hydrogen chloride is also fed in. It is known that the oxidation to the higher level with air or oxygen only proceeds at an acceptable rate at the beginning and slows down as the process of promoting reoxidation decreases
of cathodically reduced metal compounds
in the electrolysis of aqueous hydrochloric acid

Applicant:

Farbwerke Hoechst Aktiengesellschaft
formerly Master Lucius & Brüning,
6000 Frankfurt

Named as inventor:

Dr. Ernst Dönges, 6000 Frankfurt;

Dr. Hans-Georg Janson,

6230 Frankfurt-Unterliederbach

Content of oxidizable substance. But if solutions are returned to the electrolysis, the. another one contain substantial metal content in the lower oxidation stage, this leads to a considerable chlorine consumption in the cell and thus a significant reduction in the power yield, so that the gain in energy achieved by the voltage reduction is reduced by the loss Power yield is largely lost again. The large amount of air required for reoxidation drives hydrogen chloride out of the solution, which is reabsorbed in an additional process step must become.

Finally, the above-mentioned method makes it necessary to have the electrolyte in rapid flow through the - horizontally arranged - to pump the cell so that the cathodically reduced metal compound is discharged and does not reach the anode by diffusion, where they in turn consume chlorine and thus too Electricity yield losses.

There has now been a method for promoting the reoxidation of cathodically reduced metal compounds, which can occur in several oxidation stages that can easily be converted into one another, by means of an oxidizing gas in the electrolysis of aqueous hydrochloric acid in electrolysis cells, whose anode and cathode compartments are separated by the diaphragms, found that thereby is characterized in that a nonionic, non-foaming wetting agent is added to the electrolyte.

According to the invention, the electrolysis of aqueous hydrochloric acid is carried out in cells with vertical electrodes through whose anode and cathode

809 600/523

spaces are separated by diaphragms, where the anolyte and catholyte are solutions that relate to of hydrochloric acid are 4 to 8 molar, and the 0.5 to 2 mol per liter of copper chloride or iron chloride contains, leads to hydrogen chloride in the anolytes during the electrolysis according to the consumption and an oxidizing gas in the catholyte and maintains the differential pressure between the Anode compartment and the cathode compartment to zero.

The limiting current density is determined by the rate of reoxidation of the cathodically reduced Metal connection determined. As soon as the cathodic reduction due to excessive current density occurs faster than reoxidation, the cell voltage gradually rises to the deposition voltage of hydrogen.

In order to increase the rate of reoxidation, non-ionic, non-foaming wetting agents added. Butyl diglycol and in particular have proven particularly useful for this purpose Dibutyl diglycol, which are added to the electrolyte in amounts up to about 1 g / l.

Air can be used as the oxidizing gas.

Reoxidation is considerably accelerated if oxygen is used as the oxidizing gas. Using oxygen as the oxidizing gas and adding about 1 g / 1 dibutyl diglycol to the Electrolytes one gets to current densities, as they are also achieved with conventional operation, v where current yields of over 90% are possible at about half the cell voltage.

The amount of oxidizing gas introduced into the catholyte is measured so that always at least about 40% of the metal ions present are in the higher-valued form and that at The water formed by the oxidation is blown out of the cell with the gas stream. By using the Concentration of the hydrochloric acid approximately on that of the azeotropic mixture, one can do the simultaneous To a large extent suppress or completely prevent the blowing out of hydrogen chloride.

Particularly favorable results are obtained according to the method according to the invention if the Concentration of the electrolyte with respect to the hydrochloric acid by replenishing hydrogen chloride in the Anolyte holds 22 to 23%, the electrolyte about 1 g / l dibutyl diglycol and 1 to 2 moles per liter of copper ions adds, and for reoxidation of the cathodically formed copper (I) oxygen in the cathode compartment feeds in such a way that the gas bubbles in fine distribution brush along close to the cathode surface.

When carrying out the method according to the invention, the electrode spaces can be on the liquid side be closed and only facilities for feeding in hydrogen chloride and oxygen or air and for discharging chlorine and air or oxygen and water vapor.

If it is necessary to dissipate the heat, the electrolyte can be in the cathode compartment or in the The anode compartment or in both electrode compartments are pumped around and passed through external coolers.

A test cell with an electrode surface of 2 dm ^{2 was used} to carry out the examples described below. The electrode spacing was 2 mm. There was a diaphragm between the electrodes. Hydrogen chloride was blown into the anolyte through a frit at the lower edge of the anode, and air or oxygen was blown into the catholyte through a frit at the lower edge of the cathode.

example 1

Table 1 shows the results of the electrolysis in the conventional operating mode (experiment 1) and in Operating mode according to the invention, using oxygen and with the addition of dibutyl diglycol (Experiment 2) placed side by side.

Tabel

Electrolyte-
composition additive
Dibutyl
diglycol
(g / i) Current density
(A / dm ² ) tension
(V) T
Γ C) oxygen
(Vh) Chlorine electricity
yield
(%) 1. Anolyte - 23% hydrochloric acid
Catholyte - 23% hydrochloric acid
2. Anolyte = 22% hydrochloric acid with
1.5 Mol / l Cu ²⁺ : ... 1
1 } -
1 ²²
[maximum 1.85
0.96 80
80 50 97
92.5 ■ Catholyte = 23% hydrochloric acid with
0.7 mol / l Cu ²⁺ ; 0.3 mol / l Cu ¹⁺
Test duration = 100 hours.

Example 2

Table 2 shows the result of an experiment which, under otherwise identical conditions as experiment 2 in example 1, but was carried out without the use of a wetting agent.

Tabel

Electrolyte _k
composition additive
(g / i) Current density
(A / dm ² ) tension
(V) T
cc) oxygen
(l / h) Chlorine electricity
yield
(%) Anolyte = 22% hydrochloric acid with
1.5 mol / l Cu ²⁺ 8th
maximum 0.77 80 20th 85

continuation

Electrolyte-
composition additive
(g / 1) Current density
(A / dm ² ) tension
(V) T
( ⁰ C) oxygen
(l / h) Chlorine electricity
yield
( ⁰ Io) Catholyte = 23% hydrochloric acid with
0.7 mol / l Cu ²⁺ ; 0.3 mol / l Cu ^{1 +}
Test duration = 10 hours. - 8th
maximum 077 80 20th 82

Example 3
Table 3 shows the result of comparative tests using air as the oxidizing gas.

Table 3

Electrolyte-
composition additive
Dibutyl
diglycol
(g / l) Current density
(A / dm ² ) tension
(V) T
Γ C) air
(l / h) Chlorine electricity
yield
(%) 1. Anolyte = 22% hydrochloric acid with
1.5 mol / l Cu ²⁺ 1
1 1 π
[maximum
3 0.81
0.70 70
70 25th
10 85
about 60 Catholyte = 23% hydrochloric acid with
0.7 mol / l Cu ^{2 +} ; 0.3 mol / l Cu ^{1 +}
2. Like 1 Test duration = 9 hours.

Example 4

Table 4 shows the results of an experiment carried out under the same conditions as in Example 1, however using butyl diglycol as a wetting agent.

Table 4

Electrolyte-
Composition" additive
Dibutyl
diglycol
(»D Current density
(A / dm ² ) tension
(V) ' T
( ⁰ C) oxygen
(1 / h) Chlorine electricity
yield
(%) ' Anolyte = 22% hydrochloric acid with
1.5 mol / l Cu ²⁺ 1
1 I «
maximum 0.89 80 40 84 Catholyte = 23% hydrochloric acid with
0.7 mol / l Cu ²⁺ ; 0.3 mol / l Cu ^{1 +}
Test duration = 8 hours.

Example 5

Table 5 shows the results of an experiment in which iron chloride was used instead of copper chloride became.

Table 5

Electrolyte-
composition additive
Dibutyl
diglycol
(g / i) Current density
(A / dm ² ) tension
(V) T
r ο oxygen
(l / h) Chlorine electricity
yield
(%) Anolyte = 24.8% hydrochloric acid with
1.2 mol / l Fe ³⁺ 1
1 11
maximum 0.95 74 40 92.2 Catholyte = 19.8% hydrochloric acid with
0.53 mol / l Fe ²⁺ ; 0.47 mol / l Fe ³⁺ ....
Test duration = 8 hours.

The examples show that in particular using copper salts, oxygen and a Addition of dibutyldiglycol current yields of over 90% can be achieved, with the achievable current density is just as high as with conventional operation. Without the addition of the wetting agent it works achievable current density and thus the current yield.

Claims (3)

Patent claims: 1. Process for promoting the reoxidation of cathodically reduced metal compounds, which can occur in several oxidation stages that can easily be converted into one another, by means of a oxidizing gas in the electrolysis of aqueous hydrochloric acid in electrolysis cells, whose Anode and cathode compartments are separated by diaphragms, characterized is that you add a non-ionic, non-foaming wetting agent to the electrolyte. 2. The method according to claim 1, characterized in that the electrolyte is used as a wetting agent Butyl diglycol or dibutyl diglycol added. 3. The method according to claim 2, characterized in that the electrolyte is butyl diglycol or adding dibutyl diglycol in amounts of about 1 g / l. Considered publications:
French patents No. 1 208 508,
1304448;
U.S. Patent No. 1,746,542.