DE2006660A1 - Method for electrolyzing an aqueous electrolyte solution - Google Patents

Description

PATENT LAWYERS

-iNG. H. LEINWEBER dipl-ing. H. ZIMMERMANN

PO S- 1 ~ j 3 b 2 8 MUnehen 2, Rosental 7, 2nd exercise.

Part addr. Lelnpat HQndien Telefon (OSII) 2 <1f »

February 13, 1970

Our sign Lw / XIIl / C

ASAiII ^ ASEI KOGYO KAßUSHIKI "KAI SHA, Osaka / Japan rot to electrolyze an aqueous electrolyte solution

l) The invention relates to a method for electrolyzing an aqueous electrolytic solution in which an aqueous solution of an alkali halide or hydrochloric acid is one of three Compartments of the existing electrolytic cell, which contains a neutral diaphragm and a cation exchange membrane, are electrolyzed will.

There have already been various methods of electrolyzing an aqueous electrolyte solution using an ion exchange device -known. It is however difficult to do this i / re-apply on an industrial scale as they are different technical guard parts on v / iron sen.

in U.S. Patents 3,017,333 and 5,135,673 for example processes for the production of caustic soda by Electrolysis of an aqueous water chloride solution in a fjuij wrote three parts of the existing electrolytic cell, which

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a cation exchange membrane and a highly water-permeable one contains neutral diaphragm, iuese known process have the unavoidable disadvantage that caustic soda lasts poor quality, i.e. containing impurities Caustic soda, forms as a by-product. As the entire supplied Electrolyte solution must be passed through the neutral diaphragm into the appropriate compartment, there is Risk of clogging of the neutral diaphragm, so that the process cannot be stationary and stable for a long time can perform. There is also the risk of polymerization of the cation exchange membrane, which increases the required electrolytic voltage.

The object of the invention is to eliminate the disadvantages these known methods of electrolysis of an aqueous electrolyte solution by using an ion exchange membrane and a neutral diaphragm. The invention provides a method in which the electrolysis of a Alkali halides or hydrochloric acid at high current and low voltage in an extremely stable manner over one can be run for a long period of time.

It has now been found that this can be achieved if the electrolysis is carried out in one of three compartments Electrolysis cell runs, which has a neutral diaphragm with very low water permeability and a Contains cation exchange membrane, whereby the electrolysis solution is passed through under certain conditions.

The electrolytic cell used in the invention consists of at least one cell unit, which a Cathode, an anode, a cation exchange membrane and a

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neutral diapnragma with very low water permeability contains, being the cation exchange membrane and the neutral diaphragm are so at a distance between the cathode and the anode that the cation exchange membrane on the cathode side and the neutral diaphragm on the anode side are located; In this way, an anode compartment, delimited by the anode and the neutral diaphragm, becomes a duren The neutral diaphragm and the cation exchange membrane are limited Intermediate compartment and a cathode compartment delimited by the cation exchange membrane and the cathode, According to the invention, an aqueous electrolyte solution is through the Anode compartment and the intermediate compartment and a cathode solution pass through the cathode compartment at a flow rate of at least 3 cm / sec. passed through, the internal pressure of the intermediate compartment is higher than the internal pressure of the anode compartment.

The invention will now be further explained with reference to the drawings.

In the drawings:

Fig. 1 is a schematic longitudinal section through the invention applied electrolytic cell and a flow sheet of an embodiment of the invention;

2 is a graph showing the relationship between the flow rate in an electrolytic cell and the voltage of the cell according to the example

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In FIG. 1, the electrolytic cell 19 consists of an anode 1, a cathode 2, and a neutral diaphragm 3 and a cation exchange membrane 4; the neutral diaphragm 3 and the cation exchange membrane are at a distance of about 1 to 10 mm between the anode 1 and the cathode 2, so that the neutral diaphragm on the anode side and the cation exchange membrane is arranged on the cathode side. This way you become an anode compartment 9 through the anode 1 and the neutral diaphragm 3, an intermediate compartment 8 through the neutral diaphragm 3 and the Cation exchange membrane 4 and a cathode compartment 13 formed by the cation exchange membrane 4 and the cathode 2. The thickness of each compartment is usually several mm. In Fig. 1 is only for the sake of simplicity an electrolytic cell consisting of a cell unit is shown; in the practical embodiment the electrolytic cell, however, consists of a composite of several such cell units.

Conventional materials can be used as the material for the anode 1 for electrolysis cells, e.g. graphite, platinum, as well as those plated with a noble metal such as platinum or hhodium Titanium or tantalum.

Usual materials can be used as the material for the cathode 2 for electrolysis cells such as iron, stainless steel or Jückel.

in the invention, the diaphragm must neutral 'j having a möglictiot luearige Wasserdurchiässigkeit that · Lvveukriiii'.i'-.' rweüie at a pressure differential of;

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I kr / cm '"not notir im:' j ml / min. ^{Cm L} , preferably not

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SAD ORIGINAL

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should be more than 2 ml / min, cm. A neutral diaphragm. One with such properties can easily be left in itself . Manufacture in a known manner, for example from acid and chlorine-resistant materials such as blue asbestos, polytetrafluoroethylene _; ("Teflon"), as well as polyesters; are by-netzartigem'Material in the form of polyvinylidene chloride (saran), polyester or polyethylene as the core or at the surface of the diaphragm, reinforced - spectral diaphragm by surface treatment, introducing _': optionally, the newly arrived. For example, a neutral blue asbestos diaphragm is obtained by dispersing a binder, such as a latex made of polyvinylidene chloride (saran), in an aqueous slurry; of blue asbestos, then processing the slurry to a diaphragm and presses the diaphragm, and optionally applying a suitable material such as divinylbenzene, to the surface of the resulting diaphragm \ -Man can AuCN a diaphragm made of plastic manufacture, domestic; by mixing a plastic such as polytetrafluoroethylene, polyvinylidene chloride or polyethylene terephthalate with a plasticizer, "then forming the wipe into a film and extracting the plasticizer from the film.

Any membrane produced in a manner known per se can be used as the cation exchange membrane 4; Preferably, however, such a membrane is used, which has a low diffusibility for alkali from the Cathode compartment 13 in the intermediate compartment 8 as well as a good one Has cation transparency number.

BATH ORIGINAL

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In the invention, the supplied electrolyte solutions exist from alkali halide, such as i) sodium chloride or potassium chloride, as well as hydrochloric acid. If alkali halide is introduced, then essentially a solution of the corresponding is obtained Hydroxides, gaseous hydrogen and chlorine. If a hydrochloric acid feed is introduced essentially gaseous hydrogen and chlorine are obtained.

! The electrolysis process according to the invention is; now explained with reference to Fig. 1 for the case that one as Feed solution applies an alkali halide and the! Solution from each compartment between the recovery tanks and the Electrolysis cell recirculates.

An aqueous salt solution 5 to be electrolyzed becomes j introduced into a tank 6 for returning the intermediate solution j. The interdepartmental solution is from the tank j 6 introduced into the intermediate compartment 8 with the aid of a pump 17. Although a very small proportion of the inter-compartment

Solution sometimes migrates from the intermediate compartment 8 through the neutral diaphragm 3 into the anode compartment 9, almost all of the intermediate compartment solution migrates back into the tank 6. Part of the solution thus recirculated is transferred to a tank 7 for recirculation of the anode compartment solution. The anode compartment solution is introduced from the tank 7 by a pump 16 in the anode compartment \) and recycled back into the tank 7 after the anode formed on the G-as was separated. A portion of the anode compartment solution returned from the electrolytic cell is mixed with the salt used as the starting material after the remaining anode gas has been removed in an anode gas removal apparatus 10

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and water mixed and into the tank 6 as a solution 5 via a Transferred apparatus 11 for cleaning an aqueous salt solution.

The. Eathode solution is in an analogous manner between a tank 12 for "returning the cathode compartment solution and the cathode compartment 13 with the aid of a pump 18 in the circuit guided. After the gas formed at the cathode has been deposited, part of the cathode compartment solution coming from the "electrolytic cell" becomes discharged from the electrolysis system as a product. Water 15 is introduced into the tank 12 separately.

In the invention, the pressure in the intermediate compartment b higher in this solution cycle than that in the anode compartment 9 of the electrolytic cell are the prevailing pressure. It is also important for low voltage operation, such as can be seen from the following examples that the flow rate the respective departmental solution at least 3 cm / sec. amounts to. A small amount of solution can be removed from the intermediate compartment 8 can be transferred into the anode compartment 9 through the neutral diaphragm 3.

If a neutral diaphragm with high water permeability is used, a large amount of the intermediate compartment solution in the lower part of the electrolytic cell passes into the anode compartment 9; it / ab'er occurs hardly in the upper part _of: about Elektrolyszelle. For this reason, part of the anode compartment solution flows back into the intermediate compartment 8 in the upper part of the electrolytic cell, and it is therefore impossible to carry out the process with the aid of the neutral diaphragm 3. So it is impossible to find an aqueous salt water free from galorgas; solution to the surface of the cation exchange membrane '4 feed.

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Furthermore, almost no flow of the intercompartment solution occurs on the surface of the cation exchange membrane causes an increase in tension.

If, on the other hand, e ± n is used in accordance with the invention, neutral Diaphragm 3 with very low water permeability, so practically no transfer of the solution from the intermediate compartment occurs 8 into the anode compartment 9 through the neutral diaphragm 3. Furthermore, there is practically no fluctuation in the Flow rate between the upper and lower part of the intermediate compartment 8 on. A very small amount of the interdepartmental solution is only in the anode compartment, corresponding to the entire surface of the neutral diaphragm 3, convicted. In this way, the invention does not cause clogging of the neutral diapnragma 3 and contamination by anode compartment solution in the intermediate compartment. The properties of the neutral diaphragm 3 and the cathode exhaust membrane 4 do not deteriorate even with prolonged operation.

In the invention, the flow velocity is respective departmental solution in the electrolytic cell at least 3 cm / sec. This will increase the flow velocity distribution of the solution, a polarization of the cation exchange membrane is improved 4 is completely prevented and the removal of the gases at the anode 1 and the cathode 2 from the surface the electrode is accelerated, so that the method can be carried out stably at a low voltage is.

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BATH ORIGINAL

In the foregoing, the invention has been explained for the case that the respective departmental solutions between the electrolytic cell and the tanks. But it is also possible, "- the tanks" in the invention completely, to be omitted.

The inventive method of decomposing Alkalinalogenld or hydrochloric acid in the corresponding free Halogen, metal hydroxide and hydrogen is now based on further explained in the following examples. "

This example uses the electrolysis of sodium chloride using a neutral diaphragm with high water permeability, which is not within the scope of the Invention is described.

An electrolytic cell of the following composition was used; ·
Anode: electrode made of platinum-plated titanium. Cathode: stainless steel electrode .. Neutral diaphragm: polyester fabric with a water

2 permeability of 20 ml / min, cm at a pressure drop

2
differed from 1 kg / cm /. ■

Category exchange membrane: Homogeneous membrane, manufactured by means of a mixed polymer of a phenyl ester of vinyl sulfonic acid, Styrene and divinylbenzene as the main components and then hydrolyzing the j thus obtained Mixed polymers.

The available! 'Pool of the membranes and the "diaphragm for the passage of current between the electrodes

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500 cm ^ (5 cm χ 100 cm). The distance between the electrodes was 8 mm. The thickness of the anoderi abbey was 2.3 mm, the thickness of the intermediate compartment was 2.0 mm and the thickness the cathode compartment was 2.8 mm. The thickness of the neutral diaphragm was 0.5 min and the thickness of the cation exchange membrane was 0.2 mm. A 5 η NaCl solution was also used circulated as an anode compartment solution as well as an intermediate compartment solution. An aqueous 5 η iNaOH solution was recycled as a cathode compartment solution. The solution temperature

was 6O ⁰ C and the amperage of the DC current was 75 A (15 A / dm). The flow rate of the compartment solutions was in each case 4 cm / sec. at the inlet of the electrolytic cell

ρ and the pressure in the intermediate compartment was about 0.10 kg / cm higher than the pressure in the anode compartment. When passing the electric current, most of the intermediate ^was: compartment solution through neutral diaphragm in the lower part of the electrolysis cell transferred to the anode compartment. At the same time, the anode compartment solution in the upper part of the electrolytic cell was transferred to the intermediate compartment. The recirculated intermediate compartment solution had a flow rate of only 0.5 cm / sec. on. Although the cell voltage was x 4, & 5 'x V, a current efficiency based on the alkali of $ 92 was obtained.

The process was then continued by the flow speed of the anode compartment solution to 1 cm / sec. and the flow rate of the intermediate solution to 7 cm / sec. ;

were set at the inlet of the electrolytic cell. The VeroTme

could drive / some transfer of the anode compartment solution into the intermediate compartment of the electrolytic cell could be carried out,

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however, the recirculated interdepartmental solution only knows one Flow rate of 1.0 cm / sec. The cell voltage was 4.40 V and the alkali current yield was still $ 92. However, the purified saline solution could not in this case timely in the tank 6 for recirculation of the intermediate compartment solution are introduced and part of the recycled anode compartment solution had to be returned in the tank 6 to return the intermediate solution; an impurity occurred by Ghlorgas in the intermediate compartment solution.

The contamination of the intermediate compartment solution with chlorine gas resulted in deterioration of the cation exchange membrane one and the tension increased after 100 hours continuous execution of the process by about 0.2 V; furthermore, the alkali current yield decreased by $ 4 and was therefore $ 88 .. '.

Example_.2 ■ '"..'^;

This 'example' is taking the electrolysis of sodium chloride. Use of a neutral diaphragm with low Water permeability explained.

The electric current was passed through the same electrolytic cell as in Example 1 under the conditions described therein, except that a neutral diaphragm: was used from a blue asbestos sheet "whose _surface; treated to reduce porosity with ^{divinylbenzene:} and a Sarannetζ had been reinforced along the surface; this diaphragm had a water permeability of

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5 ml / min, cm at a pressure difference of 1 kg / cm. The \ flow rate of the respective departmental solution was set to \

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4 cm / sec. set at the inlet of the electrolytic cell. ■ The transfer of the intermediate compartment solution to the anode compartment

part of the neutral diaphragm was about j 50 ml / min, and the recirculated intermediate solution showed ! a flow rate of about 3. ΐ ml / sec «on.- After 100 hours of continuous passage of electrical Current, the cell voltage was 4.20 V and was stable j. There was no deterioration in the cation exchange S membrane and the alkali current yield was $ 93

The relationship between the flow rate in each compartment at the outlet and the voltage were examined in the same electrolytic cell under the same conditions as in Example 2, and the results shown in Fig. 2 were obtained. The electrolytic conditions are given below:
Anode and intermediate solutions: 5 η KaCl. Cathode compartment solution: 5 η WaOü solution. Temperature: 6O ⁰ C, Electric current density: 75A (15A / dm).

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An electrolytic cell made up of 7 cell units was used, each cell unit having an available area of 70 dm (70 cm × 100 cm) for the flow of stroni and all cell units being clamped in a filter press. Alis anocie was a platinum-plated titanium electrode, an iron electrode as the cathode, an asbestos film made with polyester fabric as the core material as the neutral diaphragm, which was

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BATH ORIGINAL

benzene .zut reduction in porosity oberflächeiibehandelt ^ was used as Eationenaustausehmembran%, a [membrane of Vinjlsulfonsaure ^ divinylbenzene used. The distance between the two electrodes was 8 mm. An aqueous 5 η LaCl solution was used as the anode and second compartment solution. An aqueous 5 η sodium hydroxide solution was used for the cathode compartment solution. A saturated LaCl solution as a purified aqueous salt solution was used in the tank 6 is mounted for Eückfuhrung the Zwisehenabteillösung. the i Elektroljse was conducted at a solution temperature of 7O ⁰ G j and a current density of 7350 a (15 a / dm) at a stream have · of the respective compartment solution of about 40 Lit./Min speed . and a flow rate of about 7 cm / sec. within! ' of the electrolytic cell, keeping the pressure inside the intermediate compartment about 0.1 kg / cm higher than that inside the anode compartment. There was no contamination of the intermediate compartment solution by chlorine gas and the amount of that in the anode compartment through the neutral diaphragm The interstitial solution was about 5 liters per minute and practically did not change at all. The cell voltage was 3.80 V and the alkali current yield was 94.5 $. There was no deterioration of the cation exchange membrane and there was no change in the Wasserdurchlässigk ^e i "t and observing the electrical resistance of the neutral diaphragm. The process could be carried out under stable conditions for 93 days. .... ■■

Example 5 ■

In the same device as in Example 1, a Cation exchange membrane arranged, which by polymerizing from acrylic acid, divinylbenzene and styrene to one

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Film and subsequent saponification of the polymer with matron lye had been made; the neutral membrane was made by a papermaking process from an aqueous slurry of fiberized blue asbestos containing saran latex as a binder, and then Pressing under a pressure of 80 kg / cm; a neutral membrane was obtained, which is permeable to water

ρ
speed of 2 mm / min, cm at a pressure difference of 1 kg / cm. A saturated aqueous solution of potassium chloride was placed in the intermediate compartment and the anode compartment; An aqueous solution, a 5 η KOM, was introduced into the cathode compartment. The linear flow rate ^{: of} the liquids in each compartment was 4 cm / sec.

The electrolysis was carried out at a solution temperature of 60 G;

2 ■ and a direct current density of 7 !? A (15 A / dm).

The pressure inside the intermediate compartment was about 0.1 kg / cm higher than that inside the anode compartment.

In this procedure, the transfer of the intermediate compartment solution through the neutral diaphragm into the Anode compartment about 18 ml / min. The "recirculated intermediate solution" flow rate was about 3.7 cm / sec. No contamination of the intermediate compartment solution by gaseous chlorine was observed. After the electrolysis was carried out continuously for 25 days, the cell voltage was stable at 3.8 V and there was no deterioration the cation exchange membrane and the neutral diaphra mas. The alkali yield was 94 #.

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The electrolysis of an aqueous hydrochloric acid was carried out using the same electrolytic cell, ion exchange membrane and the same neutral diaphragm. A 10 η HCl aqueous solution was introduced into both the anode compartment and the intermediate compartment. In the cathode compartment, a 5 η HCl aqueous solution was introduced. solution introduced. the linear Flioßgeschwindigkeit of the fluids at the inlet of each compartment was 4 cm / sec., the temperature was 6O ⁰ C and

■ 2 - the electric. Current density, 15 A / dm. The pressure inside the intermediate compartment was about 0.05 kg / cm higher than inside the anode compartment. In this method, the transfer of the intermediate compartment solution through the neutral diaphragm into the anode compartment was 22 ml / min; the recirculated intermediate solution had a flow rate of about 3.6 cm / sec. on. There was no contamination of the intermediate compartment solution: by gaseous chlorine. After the electrolysis was carried out continuously for 100 hours, the cell voltage was stably 3.20 V. Practically no deterioration of the ion exchange membrane and the neutral diaphragm was observed.

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Claims (2)

- 16 - Patent claims: Process for electrolyzing an aqueous Alkali alogenide solution or aqueous hydrochloric acid in one Electrolysis cell, consisting of at least one cell unit, which has a cathode, an anode, a cationic membrane and a neutral diaphragm, where the cation exchange menir and the neutral diaphragm are arranged opposite each other at such a distance between the cathode and the anode that the cation exchange membrane on the cathode side and the neutral diaphragm on the anode side and a form the anode compartment delimited by the anode and the neutral diaphragm, one by the neutral diaphragm and the intermediate compartment delimited by the cation exchange membrane, and an intermediate compartment defined by the cation exchange membrane and The cathode compartment delimited by the cathode, characterized in that there is an aqueous compartment to be electrolyzed Solution through the anode compartment and the intermediate compartment and a cathode solution through the cathode compartment with a at least Flow rate of / 3 cm / sec. directs, whereby a neutral diaphragm with a water permeability of no more than 5 ml / min, cm at a pressure 2
difference of 1 kg / cm and keeping the internal pressure in the intermediate compartment higher than that in the anode compartment. - 17th 009834/1710 2Ö0666Ö 2. Electrolysis process according to claim -I ₁ characterized ^;,. .that one as aqueous .Elektrciljselösiiiag. -einaa aqueous, MkalihalogeiiidlosiMg used .. Electrolysis proceed according to spray 1 * by doing this metj- that is called "aqueous electrolysis solution apply aqueous hydrochloric acid. 00983471710