DD207814A3 - METHOD FOR PRODUCING DIMENSION STABILIZED ANODES - Google Patents

Abstract

D. INVENTION A METHOD FOR THE PRODUCTION OF DIMENSIONAL STABILIZED ANODES (DSA) WITH USED CONSTRUCTION (TITANIUM BASED BODY, INTERMEDIATE LAYER, ELECTROCHEMICALLY ACTIVE LAYER) FOR ELECTROCHEMICAL PROCESSES, ESPECIALLY FOR CHLORINE CALAnIE ELECTROLYSIS. THE OBJECTIVE OF THE INVENTION IS TO PROVIDE DSA WITH A COST-SAVING INTERMEDIATE LAYER AND THEREFORE TO MEET A SIGNIFICANT IMPROVEMENT IN ELECTRODEAL PROPERTIES SUCH AS REDUCING CHLORINE VOLTAGE, INCREASING CONDUCTIVITY, EXTENDING DURABLE LIFE. ERFINDUNGSGEMAESS WILL D. TITANGRUNDKOERPER ANGEAETZT, WITH A SOLUTION OF A AMINOPOLYKARBONSAEURE AND / OR ITS SALTS WASHED U. WITH A PRAEPARATIONSLOESUNG THAT RUTHENIUMTRIS-ETHYLENEDIAMINE trichloride, A thermally decomposable TITAN LINK ANOTHER thermally decomposable metal compound and a complexing agent, PREFERABLY A AMINOPOLYKARBONSAEURE AND / OR THEIR SALTS INCLUDES COATED. AFTER BURNING IN THIS INTERMEDIATE LAYER, OTHER LAYERS WILL BE SPRAYED WITH A KNOWN RU / TI PREPARATION SOLUTION MIXED WITH THE SAME LAYERED COMPLEX FILTER, THROUGH SUBSEQUENT THERMAL TREATMENT INTO THE ELECTROCHEMICAL ACTIVE LAYER. THE INTERMEDIATE LAYER PROTECTS THE BASIC BODY EFFECTIVELY FROM OXYDATION DUE TO ELECTRODE MANUFACTURE, STRICTLY LIMITS THE DIFFUSION OF OXYGEN TO THE BASIC BODY IN ELECTROLYSIS OPERATION, AND GUARANTEES VERY GOOD ELECTRICAL CONDUCTIVITY BETWEEN BASIC BODY AND ACTIVE LAYER.

Description

Process for the preparation of dimensionally stable anodes

Field of application of the invention

The invention; relates to a process for producing dimensionally stable anodes for electrochemical processes, in particular for chloralkali electrolysis, in which a substantial improvement in the electrochemical parameters of the electrodes is achieved by applying an intermediate layer having a different composition to a titanium base. The invention is applicable in the chemical industry.

-2JUH. 1982 * 013 691

2403 8 5 6

Characteristic of the known technical solutions

In the past ten years, dimensionally stable anodes (D3A) for chloroalkylene electrolysis have prevailed over the standard graphite anodes on a world scale. More than half of the chlorine produced in the world today is produced with dimensionally stable anodes, which applies both to the diaphragm and to the eco-silver process »

Dimensionally stable anodes are made of a support metal, generally titanium, and one by thermal decomposition; manufactured electrochemically active coating of ruthenium dioxide and titanium dioxide in a suitable molar ratio with the addition of other suitable substances' produced. These anodes are therefore also referred to as composite electrodes. (K.Hass, Chem-Ing-Techn 47 (1975), 121; V.de Nora, 3.W.Kühn von Burgsdorff, Chem-Ing-Techn. 47 (1975) 125)

Dimensional stability of anodes has the following essential advantages over graphite anodes:

1. A high mechanical strength and a life, which is specified with about 2-3 years ¹ .

2. Good catalytic activity with low chlorine overvoltage.

3. Good electrical conductivity.

4. One at high positive electrode potentials, inert., Material, i. a little corrosion.

5 ". A quick detachment of the gas bubbles from the electrical surface.

The lifetime of a DSA is essentially limited by two factors:

i. The corrosion of the electrochemically active layer with RuO ₉ as d _: he decisive. Component",

2, The diffusion of oxygen through the electrochemical-a 'tive layer and formation of a poorly conductive TiOp layer at the phase boundary titanium metal /' ·, ruthenium oxide-titanium dioxide layer.

As a result of the formation of this titanium dioxide layer, the resistance of the electrode gradually increases, which results in an increase in the upper voltage and thus in energy losses (Journal of Applied Electrochemistry, 1981) (144-44 T. Louis).

For this reason, it was suggested between thea Tir-s. tangential body and the aktiyen layer another

Layer, a so-called barrier or intermediate layer ein- ) . This has the task of preventing the oxidation of the base material during the production of the electrodes and for the duration of the electrolysis and to guarantee a very good electrical conductivity between the active layer and the base material. In this case, compounds of the following metal were used as an intermediate layer: Cd, Ag, Au, Pt, Ru, Pd. (US-PS 40S6 157).

Other patents recommend the incorporation of thin layers of Ru and Ir, which, under the later production conditions, convert into their oxides or the incorporation of layers with a much higher proportion of noble metal compared to the active layer. , ·.

DE-PS 2 947 316 - DE-PS 2S15 955 DE-PS 3 COI 240

Although high concentrations of noble metal oxides cause excellent conductivity, on the other hand, the conductivity of RuG ₂ / Ti0 is -, - layers "with only 30-4G s RuO ₇ already very high, so DAS3 an even higher precious metal proportion is in the intermediate layer represents an economic 'Machteil.'

2403 8 5 6

For prevention; The diffusion of oxygen into the body and the resulting growth of a poorly conducting TiQ ₂ layer were recommended in the patent literature as oxides for the intermediate layer. To; include: MnO ₂ , Co ₃ O ₄ , CdO * Ag ₂ Oj SnO ₂ - * TiO.

(DE-PS 2619 670, 2532 553,

2714 605, 2342 663,

2729 272 DD-PS 131 048).

These oxide additives limit the diffusion of oxygen to the body and thus prevent the formation of a poorly conductive TiO ₂ layer. This extends the service life of the anodes. By means of these inorganic additives, however, complete protection of the titanium basic body during the preparation of the electrodes is not achieved. Especially during the preparation, where the base metal is repeatedly exposed to temperatures above 400 ⁰ C, it is very susceptible to oxidation processes.

In summary, it can be estimated that both a high noble metal content of the intermediate layer and the incomplete protection of the main body during preparation represent principal disadvantages of the previously described electrode production processes.

Z4U j ö b b

Object of the invention

The aim of the invention is, for electrochemical prozes.se, especially for the Chloralkalielektrolyse a dimensionally stable anode of conventional composition with Ti metal as the main body and an electrochemically active layer composition 20-40 mbl RuO ₂ to 80-60 mol ^ TiO ₂ , in which achieved by incorporating a cost-saving intermediate layer, a substantial improvement in the electrode properties, especially increases the electrical conductivity of the electrode and thus reduces the chlorine overvoltage, the electrode, extends the life of the electrode and the use of anodes energy saving is effected. ,

240385 6

Explanation of the essence of the invention

The invention has for its object to develop a process for the preparation of dimensionally stable anodes, wherein the electrodes have a conventional structure with Titangrund-, body * one; Intermediate layer and an electrochemically active layer should have, however, differ from known DSA by a different, built-up intermediate layer, which in turn are characterized by a high electrical conductivity and an oxidation of the titanium in the production: the DSA should prevent.

According to the invention, the known, defatted and mechanically roughened titanium basic body with an acid, preferably with concentrated hydrochloric acid for a few minutes up to 3 hours at 6C-lOO ⁰ C etched. During etching, any existing titanium dioxide dissolves and the titanium surface is activated and roughened.

The base body pretreated in this way is washed immediately with an aqueous solution of an aminopolycarboxylic acid and / or its salts, for example with a solution of ethylenediaminetetraacetic acid and its mono- and / or dialkali salt, and left in this solution. By means of this treatment, titanium ions which are still present on the titanium surface are dissolved in a complex manner and thus removed from the surface, the substrate remains in this solution. The complexing agent acts as a corrosion inhibitor and prevents oxidation and dissolution of the titanium.

On such treated base body, a preparation solution is applied to produce an intermediate layer ,, which a thermally decomposable ruthenium compound, preferably ruthenium-tri-ethylendiamintrichlorid, sine thermally zarsetzbars titanium compound and a thermally decomposable compound ä§r metals Fs, Cq ,. Mn, Sn, -Sb, Te, Ce or Ag or a mixture of at least two of these metal compounds and a complexing agent. For

the latter is particularly suitable an aminopolycarboxylic acid and / or salts thereof, for example ethylenediaminetetraacetic acid and / or its mono and / or dialkali salt.

The preparation solution for the intermediate layer is prepared by mixing the solutions of the individual components, whereby, for example, the following solutions are combined:

1. ruthenium tris-ethylenediamine trichloride prepared according to patent COIC / 228651/1 in a solution of methanol. and / or isopropanol.

2. titanium tetra-δ-butylate in. Isopropanol.

"3. Compounds of the metals Fe, Co * Mn, Sn, Sb, Te, Ce

^ 'or Ag in alcoholic solution.

4. complexing agent in aqueous solution

The preparation solution prepared by combining the individual solutions has the following metal content:

5-50 mol% Ru 20-90 mol% Ti 0.2-30 mol% Fe, Co, Mn, Sn, Sb, Te, Ce or Ag.

The preparation solution is applied once or several times to the prepared titanium base. After each coating, drying takes place at temperatures up to 10O ⁰ C and then baking at temperatures between 350 - 500 C. By the addition of a complexing agent for Präparatiönslösung to achieve a homogeneous distribution of the same on the surface of the body and a uniform decomposition of the corresponding metal oxides , The good properties of the intermediate layer are achieved neither by the presence of metal oxides nor by the complexing agent alone, but only by the interaction of all components. The intermediate layer consists of 1-5 layers.

Very advantageous is the use of a Präparatiönslösung with a precious metal content up to 40 mol ^ Ru.

On the intermediate layer produced according to the invention is

a known Ru / Ti preparation solution applied, through which the electrochemically active layer is formed. This preparation solution according to the invention the same as used for the intermediate layer complexing agent, preferably ethylenediaminetetraacetic ^ whose mono- and / or dialkali added as an aqueous solution. Thereafter, the active layer is baked in a known manner.

Due to the presence of the aminopolycarboxylic acid or its salts, an unexpectedly favorable homogeneous distribution of said coating reagents is achieved, in particular in the intermediate layer, but also in the electrochemically active layer, so that the organometallic compounds and metal complex salts which are applied during the separation process are converted very uniformly into their corresponding oxides.

The intermediate layer produced by the process according to the invention increases the adhesive strength of the electrochemically active layer, it distinguishes itself even at low noble metal content by a high electrical conductivity, and thus improves the electrical conductivity of the electrode and reduces the diffusion of oxygen into the electrode body. As a result, the oxidation of the base metal, which has a detrimental effect on the quality of the DSA, is prevented, in particular during the electrode production itself and the necessary separation process. The surprisingly advantageous properties of the intermediate layer, which exceed those of known intermediate layers of DSA, are not achieved by the resulting metal oxides and not by the complexing agent itself, but only by the interaction of all applied components, '

The. The biodisintenable anodes prepared by the process according to the invention are characterized by the following advantages:

240385 δ

1. Especially at high current densities, as in the chlor-alkali industry. are common »the electrodes have very good chemical, electrical and mechanical parameters.

2 .. The high electrical conductivity of the intermediate layer, the noble metal content can be reduced in this layer, thereby the cost of producing the electrode is lowered.

3. Furthermore, the high electrical conductivity of the intermediate layer and its effect on the electrochemically active layer, the chlorine overvoltage of the electrode is reduced, resulting in energy savings.

, the chloralkali electrolysis result.

4. The intermediate layer protects the base metal from oxidation during electrode production, where it is exposed to temperatures between 350 and 5QO ⁰ C for an extended period of time.

5. The lifetime of the electrode is increased because the transport of oxygen through the intermediate shanks is also decisively inhibited. .

6. The proposed method is economical, simple. and cost-saving.

Example 1:

The defatted titania base etched in concentrated hydrochloric acid is thoroughly washed after etching with acetone and immediately coated twice with a preparation solution as described below. The completely applied preparation solution for the intermediate layer contains'

7 2

4.3 x 10 ~ mol of Ti per cm geometric electrocene top

surface.. '

3.1 x 1C ~ ⁷ mcl Ru per cni "geometric top electrode

flow.

4.1 χ 10 ~ mol Ce per c'm "" geometric electrode surface

flat, as well

2403 8 5 6

0.0χ10 "mol of the disodium salt of ethylenediaminetetra

acetic acid per cm geometric electrode surface.

Titanium is produced in the form of Ti (OC ₄ Hg) ₄ , ruthenium in the form of Ru (en) ₃ Cl ₃ (from patent Wp COlc / 228651/1 from commercially available, insoluble RuCl ₃ , ethylene diamine), and cerium in the form of Ce (NO ₃ )., Used. After the 1st painting on the preparation solution; The titanium basic body is added for 10 min. 8O ⁰ C dried, cooled, coated a second time and dried again at 80 ⁰ C for 10 min. Subsequently, this intermediate layer is baked in an electric resistance oven at 420 ⁰ C for about 2 min. After cooling, the further coating is carried out with a known Ri ^ thenium zTitanpräparationslösung to which the disodium salt of ethylenediaminetetraacetic acid in a molar ratio 1: 1 is added. Thermal decomposition causes the ruthenium and titanium compounds to pass into the electrocatalytically active RuO ₂ / TiO ₂ layer.

The thus prepared anodes were used for the electrolysis of an aqueous 4-molar sodium chloride solution (pH = 3).

; 2

puts. At an anodic current density of 500 mA / cm, the anode potential betrüg at 25 ⁰ C with respect to the hydrogen reference electrode from 1.35 to 1.37 volts.

Example 2:.

The surface of the titania base is rubbed thoroughly with sandpaper, degreased with carbon tetrachloride and added in concentrated hydrochloric acid for one hour. Etched SO ⁰ C This is followed by cooling for one hour in an aqueous solution saturated with CHELAPLEX III (disodium salt of ethylenediaminetetraacetic acid). Subsequently, as. Zwi.c he η layer a 'solution on die'Tit.sn.ob.erf smile.e applied having the following metal content:

240385 6

4,8 χ ΙΟ "" ⁷ mol Ti, 3,2 χ ΙΟ " ⁷ mol Ru, 2,4 χ 1O ~ mol Sn and 0,02 ml saturated CHELAPLEX III -" solution

2 on 1 cm geometric surface.

Titanium is in the form of Ti (OC ₄ Hg) ₄ , ruthenium in the form of 'Ru (en)' Cl, and tin in the form of tin tetraethyl 'Sn (C ₂ H ₅ ) . used.

The applied with the help of a brush layer is dried in air. It is applied immediately another layer, which is also dried first and then baked in an electric heater at 420 ⁰ C for 5 min. After cooling, the further coating joins with the composition of a ruthenium-titanium preparation solution known from other patents. The thus-obtained electrodes were used for the electrolysis of a 4-molar sodium chloride solution (pH = 3).

2 At an anodic current density of 600 mA / cm, the anode potential with respect to the saturated calomel electrode was 1.12 volts at 25 ^° C. and 1.09 volts at 80 ^° C.,

Example 3:.

The titanium base body pretreated as in Example 2 is coated twice with a preparation solution. The completely applied preparation solution contains for the -'intermediate layer

-7 2 '

4.3 x 10 moles of Ti per cm of geometric surface

-7 2

3.2 χ 10 mol Ru per cm geometric electrode surface

-P '   · 1 2

2.4 χ 10 ~ ' ^J mol Fe per cm geometric electrode surface as well

8.0 X 10 ~ mol of the disodium salt of ethylenediamine tetra-

acetic acid per cm geometric electrode surface. Titanium is in the form of TiCl ^ χ 2 acetonitrile, ruthenium in the form of Ru (s) -. C1-. and iron in the form of FeCl- χ 6 i-UO used. '

- ¹² - / £ iU JO 3 U

The application is carried out according to the technology described in Example 1, but without prior drying. The electrodes prepared in this way were used for the electrolysis of an aqueous 4-molar sodium chloride solution (pH = 3).

2 sets. At an anodic current density of 500 mA / cm, the anodic upper voltage at 25 ° C. was about 80 mV *

Example 4:

The titanium basic body is pretreated according to Example 2. The completely applied preparation solution for the

^! 2

Interlayer contains per cm geometric electrode surface:

4.8 x 10 ^-7 mol Ti, 3.2 χ 10 ^-7 mol Ru, 2,4 χ 10 ^-8 mol Mn and "χ 3.0 10." mol of the disodium salt of ethylenediaminetetraacetic acid. ;

Titanium is used in the form of Ti (OC ₄ Hg). Ruthenium in the form of Ru (en) -7Cl ₃ and manganese in the form of Mn (II) acetate. The application is carried out according to the method described in Seispiel 1, but without previous drying.

The anodes prepared in this way were used for the electrolysis of an aqueous 4-molar sodium chloride solution (pH = 3).

2 sets. At an anodic current density of 500 mA / cm, the anode potential at 25 ⁰ C compared to the hydrogen comparison electrode was 1.36 volts.

Claims (3)

Erf inciungsan claim (1 I> 240385 6 3. The method according to item 1, characterized in that the thermally decomposable ruthenium tris-ethylenediamine trichloride Ru (en), Cl, is dissolved in methanol and / or isopropanol. 4. The method according to item 1, characterized in that before preferably titanium tetrachloride * 2 acetonitrile (TiCl _4, 2 CH ₃ CN) or titanium tetra-o-butylate (Ti (OC ₄ Hg) _{4 is used} as a thermally decomposable titanium compound. 5 * method according to item 1, characterized in that at least one inorganic or organic salt or an organometallic compound of ^l metals Fe, Co, Mn, Sn, Sb, Te, Ce or Ag, for example manganese (II) acetate as a thermally decomposable metal compound Mn (CH ₃ CuO) ₂ . Tin tetraethyl Sn (C ₉ H ^) ₄ or Car (III) - nitrate Ca (NO ₃ ) ^ are contained in the preparation solution. 6. Method according to point 1 », characterized in that the preparation solutions for the intermediate layer and for the electrochemically active layer as complexing agent ethylenediaminetetraacetic acid disodium salt is mixed in aqueous solution« 7. The method according to item 1, characterized in that the preparation solution for the intermediate layer has a metal content of 5 to 50 Taol% Ru, 20 to 90 mol% Ti, 0.2-30 molfij Fe, Mn, Sn, Sb, Te, Ce or Ag and containing the aminopolycarboxylic acid in a molar ratio of the total metals to acid of from 1: 1 to 1: 0.5 '. 1. A process for the preparation of dimensionally stable anodes for electrochemical processes-such as the chloralkali electrolysis, consisting of a titanium basic body, an intermediate layer and an electrochemically active layer, wherein the titanium basic body degreased, mechanically roughened, etched with an acid and washed, then with a Preparation solution, the intermediate layer applied, treated one or more times with intermediate drying at temperatures up to 10C ⁰ C and then baked and finally the electrochemically active layer by treatment with a Ru / Ti-preparation solution is applied and baked, characterized '' ^y net characterized in that the titanium basic body is washed with an aqueous solution of an amino polycarboxylic acid and / or its mono and / or dialkali salt, the preparation solution for the intermediate layer, a thermally decomposable Ru-Mon, preferably ruthenium tris-ethylenediamine tri chloride, a thermally decomposable Ti compound "a thermally decomposable compound of the metals Fe ₁ Co ₁ Mn ₁ Sn ₁ Sb ₁ TeJCe or Ag or a mixture of at least two of these compounds and a complexing agent, preferably an amino-oligo-carboxylic acid and / or its Mono and / or their dialkali salt ,. contains and by mixing the Autolube in a suitable solvent, is preferably prepared in lower alcohols, water or mixtures thereof, dissolved Komoonenten and Ru / Ti preparation solution for electrochemically activators layer in a mixture with a wäSrigen solution thereof complexing agent is applied. 2. Method according to item 1, characterized in that an aqueous solution of the disodium salt of ethylenediaminetetraacetic acid is preferably used for washing de3 freshly etched titanium basic body » 3. The method according to item 7, characterized in that the preparation solution preferably contains up to 40 mol% Ru, up to 60 mol; a Ti and up to 5 n \ ol% additional metal.