DE2006660B2 - METHOD OF ELECTROLYZING AN AQUATIC ALKALINE SOLUTION - Google Patents

Description

The invention relates to a method for electrolyzing an aqueous alkali halide solution or of hydrochloric acid in an electrolytic cell consisting of three compartments, which has a neutral diaphragm and contains a cation exchange membrane.

There are already various methods of electrolyzing an aqueous electrolyte solution using an ion exchange membrane is known. However, it is very difficult to apply these methods on an industrial scale because they are various have technical disadvantages.

For example, U.S. Patents 3,017,338 and 3,135,673 teach methods of making of sodium hydroxide solution by electrolyzing an aqueous sodium chloride solution in one of three compartments existing electrolytic cell described, which a cation exchange membrane and a contains highly water-permeable, neutral diaphragm. These known methods exhibit the inevitable Disadvantage that caustic soda is poor quality, d. H. Containing impurities Caustic soda, forms as a by-product. Since the entire electrolyte solution supplied through the neutral If the diaphragm has to be led into the corresponding compartment, there is a risk of clogging of the neutral diaphragm, so that the process cannot be carried out in a stationary and stable manner for a long time can. There is also the risk of polymerization of the cation exchange membrane, which is a An increase in the required electrolysis voltage.

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

It has now been found that the., Reach each other Kisses. if the electrolysis is carried out in a three-compartment electrolytic cell, which • in a neutral diaphragm with very low water permeability and a cation exchange membrane contains, whereby the electrolyte solution under certain Conditions.

The concentration of chloride ions in the prepared by the refinement method Sodium hydroxide can be extracted to as low as 20 to 30 parts per million.

The Elcktrolysc-IcIIe used in the invention consists of at least one cell unit. “Calibrate a cathode, an anode, a cation exchange membrane and contains a neutral diaphragm with very low water permeability, wherein Cation exchange membrane and the neutral diaphragm so at a distance between the cathode and the anode are arranged that the cation exchange membrane on the cathode side and the neutral diaphragm on the anoclen * cite; in this way an anode compartment delimited by the anode and the neutral diaphragm, an intermediate compartment delimited by the neutral diaphragm and the cation exchange membrane and a cathode compartment defined by the cation exchange membrane and the cathode is formed. According to the invention an aqueous electrolyte solution is passed through the anode compartment and the intermediate compartment and a cathode solution through the cathode compartment at a flow rate of at least each; 3cm / sec. passed through, the internal pressure of the intermediate compartment being higher than the internal pressure of the Anode compartment is held.

The invention will now be based on the drawing!

ίο further explained. In the drawings shows

F i g. 1 shows a schematic longitudinal section through the electrolytic cell used according to the invention and a flow diagram of an embodiment of the invention,

F '\ g. FIG. 2 is a graph showing the relationship between the flow rate in an electrolytic cell and the voltage of the cell according to Example 3. FIG.

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 arranged 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 on the cathode side are arranged. In this way 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 strength of each compartment is usually several millimeters. In Fig. 1

is only one of a unit cell for the sake of simplicity existing electrolytic cell shown; in the practical embodiment there is the electrolytic cell but from a composite of several such cell units.

As the material for the anode 1, conventional materials for electrolytic cells can be used, e.g. B. Graphite. Platinum, as well as a noble metal such as platinum or rhodium, plated titanium or tantalum.

The material for the cathode 2 can be conventional

4. 'Materials for Flektrolvsezellen. such as B. Fken stainless steel or nickel.

In the invention, the neutral diaphragm 3 must have the lowest possible water permeability, which is expediently not more than 5 ml / min. / Cm2, preferably not more than 2 ml / min. / Cm ² , at a pressure difference of 1 kg cm- ' target. A neutral diaphragm with such properties can easily be manufactured in a manner known per se, e.g. B. made of acid and chlorine-containing materials such as blue asbestos, polytetrafluoroethylene ("Teflon") and polyesters; If necessary, the neutral diaphragm can be reinforced by surface treatment, the introduction of net-like material in the form of polyvinylidene chloride (saran), polyester or polyethylene as the core or on the surface of the diaphragm. For example, a neutral diaphragm made of blue asbestos is obtained by dispersing a binder such as, for. B. a latex made of polyvinylidene chloride (saran), in an aqueous slurry of blue asbestos, then processing the slurry to a diaphragm and pressing the diaphragm, and if necessary, applying a suitable material,

y \ c Di \ iny'ibenzo |, on the surface of the preserved pjaphnmmas. One can also manufacture a diaphragm of piunsisiifl by a plastic, _w per polytetrafluoroethylene, polyvinylidene chloride, or with a plasticizer polyäthvlenterephthalat vermisciu. the mixture is then formed into a film and the plasticizer is extracted from the film.

Ais cation-exchange membrane 4 can be 'apply ¹ to: Preferably, however, applies ι üie such a membrane to which a low pilTiiiiiiicrbarkeit of alkali from the cathode compartment Γι in the intermediate compartment 8 as well as a good jCatii', any Hlcmt prepared in manner known per se "i'cntransportzahl has.

Bl] of the invention consist of the supplied electricity trol ·. I ions of alkali halide, such as sodium chloride or potassium chloride, as well as hydrochloric acid. If alkali is introduced, im \ vi>: nilichen a solution of the corresponding H \ d; \ i \ ids. gaseous water and chlorine. If a feed consisting of hydrochloric acid is introduced is essentially gaseous π hydrogen and chlorine.

electrolysis process according to the invention is sec. A small amount of the solution can be used transferred from the intermediate compartment 8 into the anode compartment 9 through the neutral diaphragm 3 will.

If a neutral diaphragm with high water permeability is used, a large one will work Amount of the intermediate compartment solution in the lower part of the electrolytic cell into the anode compartment 9; it occurs hardly over in the upper part of the electrolysis cell.

For this reason, part of the anode suture solution flows into the intermediate compartment 8 in the upper part of FIG Electrolytic cell and it is therefore impossible to carry out the process with the help of the neutral diaphragm 3 to execute. It is therefore impossible to use a chlorine-free aqueous salt solution on the surface of the supply cation exchange membrane 4. Furthermore, there is almost no flow of the intermediate solution at the surface d-τ cation exchange membrane resulting in an increase in tension. If, on the other hand, one applies according to the invention neutral diaphragm 3 with very low water permeability, so practically no transfer occurs the solution from the intermediate compartment 8 into the node compartment 9 through the neutral diaphragm 3

now explained with reference to Fig. 1 for the case that 25 through. Furthermore, there is practically no fluctuation the flow rate between the upper and lower TeTl of the intermediate compartment 8. A very small amount of the intermediate compartment solution is only poured into the anode compartment, corresponding to the total

Kme to electrolytic aqueous salt solution 5 3 "th surface of the neutral diaphragm 3, transferred. In this way, clogging of the neutral diaphragm 3 and a does not occur in the invention Vcrunreiniäung by anode compartment solution .n the intermediate compartment. The characteristics of the neutral

A small proportion of the intermediate compartment solution sometimes 35 diaphragms 3 and the cathode exchange mem- bers in the intermediate compartment due to the neutral diaphragm 4 also deteriorate with longer periods; hranma 3 migrates into the anode compartment 9, driebszcit does not migrate.

load all the interdepartmental solution into the tank 6 In the invention, the flow rate is

return. Part of the solution returned in this way becomes the respective departmental solution within the electronics department a tank 7 for returning the anode compartment lysis cell at least 3 cm / sec. This will make the

Flow velocity ve.t ^ iluitg of the solution improved, polarization of the cation exchange membrane 4 is completely prevented and the removal of the Gases at the anode 1 and the cathode 2 from the

an alkali halide is used as the feed solution and the solution from each compartment between ι1 .. ·: ι return tanks and the electrolytic cell refilled.

v. ! p.l into a tank 6 for recycling the intermediate solution brought in. The Zwischencnabieillösung ν ird from the tank 6 in the intermediate compartment 8 with Introduced using a pump 17. Although a very

solution transferred. The anode compartment solution is drawn from the tank 7 with a pump 16 into the anode compartment 9 introduced and again returned to the tank 7 after the gas formed at the anode

'tKrri'trpnii ^ u / ^r i-rlr »Pm Toil rlf ¹ *' πιι <; rlpr F-'lfVtrol vcr »_ ■ L - - · - · ■ - - - - · - .._, ..«.

cell recirculated anode compartment solution is, after removal of the remaining anodic gas in a Anodising gas removal apparatus no 10, with the as The salt and water used as the starting material combine stable feasibility of the process at low levels Tension is guaranteed.

In the foregoing, the invention was explained for the case that the respective Abteillöscn

Purifying an aqueous salt

mixed and returned to tank 6 as solution 5 via Hne 5c between the electrolytic cell and the tanks will. But it is also possible to completely dispense with the tanks in the invention.

The process according to the invention of the decomposition of alkali halide or hydrochloric acid into the dehydrogenator explained.

Apparatus 11 for
solution transferred.

The Kathci.lcnabtillösung is in an analogous way / wipe a tank 12 to return the

Kathodenabteillör.ung unti the cathode compartment 13 35 speaking free "halogen, metal hydroxide and water circulated with the aid of a pump 18. Hydrogen is now based on the following examples
Oases becomes part of the electrolytic cell
Coming cathode compartment solution üüä the Elektrolysesystcm discharged as a product to Gifäß 14. 60
Water IS is introduced into the tank 12 separately.

With the invention, the pressure in the intermediate abbey! S higher than in this solution cycle

_{the r D} in the anode compartment 9 of the electrolytic cell

Seeing pressure lie, furthermore it is important for a 65 not to be described within the scope of the invention. Operation at low voltage, as can be seen from the An electrolytic cell of the following

The following examples show that the flow rate calculation is applied: dif''cit of the respective compartment solution at least 3 cm / anode: electrode made of platinum-plated titanium.

example 1

In this example, the electrolysis of sodium chloride is carried out using a neutral diaphragm with great water density, which

Cathode: stainless steel electrode.

Neutral diaphragm: polyester fabric with a water permeability of 20 ml / min. / Cm- 'for a Pressure difference of 1 kg / cm'- '.

Cation exchange membrane: Homogeneous membrane made by interpolymerizing a phenyl ester of vinylsulfonic acid, styrene and divinylbenzene as main components and subsequent hydrolysis of the copolymer thus obtained.

The available area of the membranes and the diaphragm for the passage of current between the electrodes was 500 cm ² (5 cm ' 100 cm). The distance between the electrodes was 8 mm. The thickness of the anode compartment was 2.5 mm. the thickness of the intermediate compartment was 2.0 mm and the thickness of the cathode compartment was 2.8 mm. The thickness of the neutral diaphragm was 0.5 mm and the thickness of the cation exchange membrane was 0.2 mm. A 5 η NaCl solution was circulated both as an anode compartment solution and as an intermediate compartment solution. An aqueous 5 η NaOH solution was recycled as the cathode compartment solution. The solution temperature was 60 ° C. and the strength of the direct current was 75 A (15 A / dm ² ). The flow rate of the compartment solutions was in each case 4 cm sec. At the inlet of the electrolytic cell and the pressure in the intermediate compartment was about 0.10 kg cm ² higher than the pressure in the anode compartment. When the electrical current was passed through, most of the intermediate compartment solution was transferred through the neutral diaphragm in the lower part of the electrolytic cell into 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. Although the cell voltage was 4.85 V, a current efficiency, based on the alkali, of 92 "η was obtained.

The procedure was then continued by setting the flow rate of the anode compartment solution to 1 cm sec and the flow rate of the intercompartment solution to 7 cm sec at the inlet of the electrolytic cell. The process could be carried out without any transfer of the anode compartment solution to the intermediate compartment of the electrolytic cell, but the recycled intermediate compartment solution only has a flow rate of 1.0 cm sec. The cell voltage was 4.40 V and the alkali current yield was still 92 ⁰ O. In this case, however, the purified salt solution could not be introduced in time into the tank 6 for the return of the intermediate compartment solution and part of the returned anode drain solution had to go into the tank 6 for the return of the intermediate compartment solution be recycled: there was contamination by chlorine gas in the intermediate compartment solution.

Due to the contamination of the intermediate compartment solution with chlorine gas deterioration of the cation exchange membrane and tension occurred increased after 100 hours of continuous execution de? Procedure by about 0.2 V; also verrincerie the alkali current yield increased by 4 ° ο and was therefore 88 ° n.

The purity of the sodium hydroxide solution obtained in this example was not satisfactory; the chloride ion content the caustic soda was a few thousand parts per million.

Example 2

In this example the electrolysis of sodium chloride is carried out using a neutral Diaphragms with low water permeability explained.

The electric current was through the same electrolytic cell as passed through in example 1 under the conditions described there, with the exception,

ίο that a neutral diaphragm made of a blue asbestos film was used, the surface of which had been treated with divinylbenzene to reduce the porosity and reinforced with a saran net along the surface; this diaphragm had a water permeability of 5 ml / min. / cm ² at a pressure difference of 1 kg / cm. The flow rate of each compartment solution was adjusted to 4 cm sec. At the inlet of the electrolytic cell. The transfer of the interdepartmental solution

into the anode compartment through the neutral diaphragm was about 50 ml / min, and the return Intermediate solution had a flow rate of about 3.1 ml sec. After 100 hours of continuous The cell voltage was 4.20 V and it was stable while passing an electric current. It there was no deterioration of the cation exhaust membrane and the alkali current yield was 93 "'Ό.

The concentration of chloride ions in the according to

The caustic soda obtained in this example was 20 parts per million.

Example 3

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, wherein the results shown in FIG. 2 were obtained. The electrical conditions are in given the following:

Anode and intermediate compartment solutions: 5 η NaCl.

Cathode compartment solution: 5 η NaOH solution.

Temperature: fiO C. Electric current density. 75 A (15Adm ² ).

Example 4

An electrolytic cell consisting of 7 cell units was used, each cell unit having an available area of 70 drn ² (70 cm · 100 cm) for the flow of current and all cell units being clamped in a filter press. The AK anode was a platinum-plated titanium electrode, the cathode an ice electrode. an asbestos film made with polyester fabric as the core, which has been surface-treated with divinylbenzene to reduce the porosity, is used as the neutral diaphragm; a vinylsulfonic acid-divinylbenzene membrane was used as the cation exchange membrane. The inter-electrode distance was 8 mm. An aqueous 5 η NaCl solution was used as the anode and intermediate compartment solution. An aqueous 5 η sodium hydroxide solution was used as the cathode compartment solution. A saturated NaCl solution as a purified aqueous solution

Saline solution was placed in the tank 6 for recycle of the intermediate compartment solution. The electrolysis was carried out at a solution temperature of 70 "C and a current density of 7350 A (15 A / dm ² ) at

1806

a flow rate of the respective compartment solution of about 40 lit./min. and a flow rate of about 7 cm / sec. carried out inside the electrolytic cell, the pressure being within the The anode compartment was kept, there was no contamination of the intermediate compartment solution by chlorine gas and the amount of intercompartment solution transferred into the anode compartment through the neutral diaphragm was about 5 lit. min. and practically did not change at all. The cell voltage was 3.80 V and the alkali current efficiency was 94.5%. The concentration of chloride ions in the The caustic soda obtained in this way was 20 to 50 parts per million.

There was no deterioration of the cation exchange membrane one and there was no change in water permeability and electrical Resistance of the neutral diaphragm observed. The process lasted 93 days under stable conditions are executed.

Example 5

In the same device as in Example I, a cation exchange membrane was arranged, which had been produced by polymerizing acrylic acid, divinylbenzene and styrene to form a film and then grinding the polymer with sodium hydroxide solution; the neutral membrane was made by a papermaking process from "an aqueous slurry of shredded tusks of asbestos containing saran latex as a binding agent, and then pressing under a pressure of 80 kg cm-"; this gave a neutral membrane which had a water permeability of 2 ml min. cm ² with a pressure difference of 1 kg cm ² . A saturated aqueous solution of potassium chloride was placed in the intermediate • compartment and the anode compartment; An aqueous solution of a 5 η KOH 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 ° C. and a direct current density of 75 A (15 A dm- ').

The pressure inside the intermediate compartment was about 0.1 kg cm ² higher than inside the anodic part.

In this procedure, the transfer of the interstitial solution was through the neutral diaphragm into the anode compartment about 18 ml min. The flow rate of the recirculated intermediate compartment solution was about 3.7 cm sec. Gaseous contamination of the intermediate compartment solution Chlorine was not observed. After the electrolysis was carried out continuously for 25 days was. the cell voltage was stable at 3.8 V and there was no deterioration of the cation exchange membrane and the neutral diaphragm. The alkali yield was 94 ° 0.

The concentration of the caustic soda obtained in this example did not exceed 40 parts per million

Example 6

The electrolysis of an aqueous hydrochloric acid was carried out using the same electrolytic cell ion exchange membrane and the same neutral diaphragm. A 10N aqueous HCl solution was introduced both into the anode compartment and into the intermediate compartment. An aqueous 5 η HCl solution was introduced into the compartment. The linear flow rate of the liquid at the inlet of the respective compartment was 4 cm sec. The temperature was 60 ° C. and the electrical current density was 15 A, dm ² . The pressure within de; Intermediate compartment was about 0.05 kg / cm * higher than: inside the anode compartment. In this process, the transfer of the intermediate compartment through the neutral diaphragm into the anode compartment was ml / mm .; the recirculated intermediate compartment had a flow rate of about 3.6 cm sec. There was no contamination of the intermediate compartment solution by gaseous chlorine. N: U: continuous electrolysis derr 100 hours urn passworder led was. the cell voltage was> abi 3.20 V. There was practically no difference:; int the cation exchange membrane and the mi,:,; iler diaphragm observed.

Claims (1)

Claim: Process for the electrolysis of a water alkali halide solution or of aqueous acid in an electrolysis cell, consisting of at least one cell unit, which has a cathode, an anode, a cation exchange, and a neutral diaphragm. '■■■> in the case of the cation exchange membrane and there- ·.:' Central diaphragm opposite each other in ο ·:.! - such a distance between the cathode and the anode that the Katuv, n exchange membrane on the cathode side and the neutral diaphragm on the anode side be :. · The and form an anode compartment delimited by the anode and the internal diaphragm. an intermediate compartment bounded by the neutral diaphragm and Ow cation exchange membrane, and a Kathr.cl.yi compartment supported by the cation exchange membrane and the cathode. characterized in that an aqueous F n <\ nz to be electrolyzed through the anode compartment and the intermediate aH.-i: and a cathode solution through the cathode compartment at a flow rate of at least 3 cm in each case, a neutral diaphragm with a water permeability of not more than 5m [/ min./cm ² ] at a pressure difference of 1 ke / cm ² and keeps the internal pressure in the intermediate compartment higher than in the anode compartment 1 sheet of drawings 109 549/515 18 0 6