FI73009B - INSTALLATION AV IONBYTARMEMBRAN I EN ELEKTROLYSCELL. - Google Patents

Abstract

A method of installing an ion-exchange membrane in an electrolytic cell in which the membrane is expanded by stretching to increase the surface area per unit weight of the membrane and the expanded, stretched membrane is secured to the electrolytic cell or to a part thereof. The stretching is preferably effected at elevated temperature and the expansion produced by stretching may be <<locked>> into the membrane by cooling the expanded, stretched membrane to a lower temperature prior to installation of the membrane in the electrolytic cell.

Description

73009

The present invention relates to a method for installing an ion exchange film in an electrolytic cell.

Electrolytic cells are known which comprise a plurality of anodes and cathodes, in which each anode is separated from an adjacent cathode by an ion exchange membrane which divides the electrolytic cell into a large number of anode and cathode states. The anode compartments of such a cell are provided with means for supplying electro-10 to the cell, preferably from a common source, and with means for removing electrolysis products from the cell. Correspondingly, the cathode compartments of the cell are provided with means for removing electrolysis products from the cell and possibly with means for supplying water or other liquid to the cell. The electrolytic cells can be single-pole or bipolar.

For example, filter press type electrolytic cells may contain a large number of alternating anodes and cathodes, e.g., fifty anodes si-20 alternately with fifty cathodes, although the cell may contain more than one anode and cathode, e.g., up to one hundred and fifty alternately located anodes and cathodes.

In such an electrolysis cell, the membranes are substantially impermeable to liquid, and during electrolysis, ions, for example hydrated ions, pass through the membrane between the anode and cathode states of the cell. Thus, when electrolysing an aqueous alkali metal chloride solution in a cell equipped with cation exchange membranes, the solution is fed to the anode compartments of the cell and the chlorine and electrolysis solution used are removed from the anode solutions. the hydrogen formed in the reaction between the alkali metal ions and the hydroxyl ions and the 2,7009 alkali metal hydroxide solution are removed from the cathode states of the cell.

Electrolytic cells of the type described can be used in particular for the production of chlorine and sodium hydroxide by electrolysis of aqueous sodium chloride solution.

In the case of such an electrolytic cell, the film is attached to the cell, for example by squeezing it between seals. It is desirable that the membrane be installed in the cell under tension and that the membrane remain approximately 10 tension when the cell is filled with electrolyte and the cell is in operation. However, if the membrane is installed in the electrolysis cell dry and fastened to it tightly, it is found that in use, when the electrolyte touches the membrane in the cell, the membrane swells and expands and loosens and may even become wrinkled. This may result in uneven gas release and an increase in cell voltage. This is particularly detrimental when the cell is designed to operate with a small or zero anode-cathode gap.

To reduce this problem of swelling of the film in use, it has been proposed to pre-expand the film before installing it in an electrolytic cell, for example by immersing the film in water, aqueous sodium chloride solution or aqueous sodium hydroxide solution. Ideally, the film should be pre-pressurized to approximately the same extent as the dry film swells upon contact with the electrolyte in the electrolytic cell.

U.S. Patent No. 4,000,057 describes the pre-expansion of a film prior to its installation in an electrolytic cell 30, the method comprising treating the film with a liquid in which the curve of film expansion as a function of time runs approximately horizontally for at least four hours after liquid treatment. Suitable liquids include, for example, aqueous solutions of ethylene glycol, glycerol and high molecular weight fatty alcohols.

3 73009

Although the above methods help to solve the problem of the film swelling when it comes into contact with the electrolyte in the electrolysis cell, they themselves have significant drawbacks. Thus, the pre-expanded films are wet and remain wet during installation in the electrolytic cell, and are therefore difficult to handle. Special handling precautions may be necessary, for example, when the film is pre-expanded by treatment with a corrosive liquid, such as sodium hydroxide solution. It may also be difficult to attach the wet film to the electrolytic cell so that it does not leak, for example between a pair of seals.

The present invention relates to a method for installing an ion exchange film in an electrolytic cell, which method does not suffer from the above-mentioned disadvantages.

In the method of the present invention for installing an ion exchange film made of an organic polymer containing exchangeable groups or derivatives thereof which can be converted into exchangeable groups in an electrolytic cell, the ion exchange film is expanded, and the expanded film is attached to an electrolytic cell or a portion thereof. the film is expanded by stretching to increase the surface area of the film per unit weight.

In the method of the invention, the ion exchange membrane in the form of a plate or film is expanded by stretching to increase the surface area to weight ratio of the membrane.

Expansion of this membrane does not require the use of a liquid to expand and thus expand the membrane.

In fact, the expansion by stretching is generally and preferably carried out using a dry film, thus avoiding the considerable disadvantages associated with the use of the liquid. In addition, expansion is not accomplished by simply compressing the film at elevated pressure and temperature.

35 Stretching the film should be done carefully, 4 73009 to prevent the film from tearing. Using an elevated temperature during film stretching greatly helps to avoid film tearing.

Another embodiment of the present invention is a method of installing an ion exchange film on an electrolytic cell, the method comprising heating the ion exchange film to stretch the film at an elevated temperature and attaching the expanded stretched film to the electrolytic cell or a portion thereof.

In addition, it is preferable to stretch the film at an elevated temperature and cool it to a lower temperature, to or near ambient temperature, while maintaining the film in the expanded stretched state, and then attach the expanded stretched film to the electrolysis cell or portion thereof.

Stretching can be done, for example, by allowing the film to pass around and between rollers rotating at different circumferential speeds, and the expanded stretched film can be cooled to a lower temperature. Alternatively, the film can be stretched by applying a stretching force to opposite edges of the film, and the expanded stretched film can be cooled to a lower temperature. Stretching of the film can be performed using a stretching frame or machine.

The film can be stretched in one or two directions. 25 Bidirectional stretching can occur in two directions simultaneously or sequentially.

When stretching the film in one direction, strips of relatively rigid material may be attached to opposite edges of the film to prevent the film 30 from shrinking transversely to the stretching direction of the film.

When the film is stretched, for example, at an elevated temperature, and in particular when the film is cooled to a lower temperature, for example at or near ambient temperature, after the film is kept in the expanded stretched state, at least part of the stretching-induced expansion "locks" 5 73009 the diaphragm. When the expanded stretched film is mounted and attached to the electrolytic cell and when the film comes into contact with the electrolyte, especially at an elevated temperature, for example an aqueous solution of alkali metal chloride 5 at a temperature of up to 95 ° C, in a chlor-alkali cell, the film is completely or partially released. and the membrane tends to shrink towards its original state, although the membrane, of course, remains attached to the electrolytic cell. This tendency to shrink 10 is counteracted by the expansion of the membrane due to swelling when the membrane comes into contact with the electrolyte, with the result that the membrane mounted on the electrolytic cell remains taut and does not wrinkle in use.

It is preferred that the amount of expansion provided by stretching be approximately equal to or greater than the expansion caused by the swelling of the film upon contact with the electrolyte in the electrolytic cell so that the film remains taut in the cell upon contact with the electrolyte. However, some benefit can also be obtained, although the amount of expansion provided by stretching is somewhat less than the expansion caused by the swelling of the film upon contact with the electrolyte. The appropriate amount of expansion by stretching can be determined by a simple experiment.

In general, the expansion of the film obtained by stretching should increase the surface area of the film per unit weight by at least 2%, preferably by at least 5%. By stretching, a large expansion of the film can be achieved, for example an increase of at least 50% or 100% or even ten times or even more in the surface area of the film per unit weight. When the amount of stretching is considerable, additional advantages are obtained. Thus, when the stretching results in a large expansion of the film, the use of the film in the electrolytic cell results in a lower operating voltage, resulting in energy cost savings. In addition, electrolysis products can be manufactured with a higher current efficiency of 6,7009.

In order to make most of the expansion of the film caused by the yenutroot "locked" into the film, the film can be cooled from an elevated temperature to a lower temperature-5 while keeping it in an expanded stretched state during that time. However, when such a film is used in an electrolytic cell, the shrinkage of the film upon contact with the electrolyte at an elevated temperature may be much greater than the expansion caused by the swelling of the film due to the action of the electrolyte, and the film may tend to tear. Whether or not there is a tendency to tear will naturally depend on the amount of film expansion caused by the stretching.

When the amount of expansion of the film 15 produced by stretching is considerable, it is preferable, for example, to harden the expanded stretched film 20 by heating it at an elevated temperature to obtain a film having a large increase in surface area per unit weight which can be used in an electrolytic cell at a significantly reduced voltage. and then cooling it to a lower temperature. In this way, sufficient expansion can be "locked" to the film to keep the film taut and wrinkled during use in the electrolytic cell, and also to avoid any tendency of the film to tear during use.

The membrane which is expanded by stretching is generally in the form of a film and may have a thickness of, for example, 0.2 to 2 mm.

Although stretching can result in very thin films, the expanded stretched film should not be so thin that it is very prone to damage when used in an electrolytic cell. In general, the thickness of the expanded stretched film is at least 0.02 mm, preferably at least 0.1 mm.

35 The elevated temperature at which the film is stretched depends on the nature of the film. In general, however, it is higher than 40 ° C, preferably higher than 55 ° C.

A suitable temperature for use in stretching each particular film can be determined by a simple experiment. The temperature should not be so high that the 5 film organic polymer melts or decomposes significantly. In general, the elevated temperature at which the stretching is performed does not exceed 150 ° C.

When tempering an expanded stretched film, the tempering temperature may be the same or approximately the same as the elevated temperature at which the film is stretched.

The quenching temperature may be higher than the stretching temperature. The duration of hardening of the expanded stretched film determines the amount of expansion of the film that "locks" into the film as it is cooled to a lower temperature; the longer this hardening time, the less amount of expansion remains "locked" in the films. Generally, the tempering time is at least 1 minute, but usually does not exceed 5 hours.

The lower temperature to which the film is cooled is the temperature at which the film does not recover rapidly when any limiting force is removed. It is most convenient to cool the film to or near ambient temperature.

In another preferred embodiment, which is useful when the film needs to be significantly expanded by stretching, the film is stretched at an elevated temperature, the film is cooled to a lower temperature, e.g., ambient temperature, while maintaining the film in an expanded stretched state, and the expansion step is stretched at an elevated temperature. and the cooling step is repeated at least once. In this way, the desired amount of film expansion can be achieved by performing stretching in several batches, and there is less chance that the film will be damaged, e.g., torn, during stretching.

The ion exchange membrane is preferably a cation exchange membrane.

73009 Containing acidic groups or their derivatives which can be converted into acidic groups. In order to withstand the corrosive conditions found in many electrolytic cells, especially chlor-alkali cells, the film is preferably a fluoropolymer, and even more preferably a perfluoropolymer containing such acidic groups or derivatives thereof.

Suitable acidic groups include sulfonic acid, carboxylic acid or phosphoric acid groups. The film may contain two or more different acidic groups. Suitable derivatives of acidic groups are the salts formed by these groups, for example metal salts, in particular alkali metal salts. Suitable derivatives are in particular those which can be converted into acidic groups by hydrolysis, for example acid halide groups, for example -SO 2 F and -COF, nitrile groups -CN, acid amide groups -CONI 4, where R is H or alkyl, and acid ester groups, for example -COOR, where R is an alkyl group.

Suitable cation exchange films include, for example, those disclosed in GB Patent 1,184,321, 1,402,920, 1,406,673, 1,455,070, 1,497,748, 1,497,749, 1,518,387 and 1,531,068.

It is preferable to use films containing derivatives of acidic groups which can be converted into exchangeable groups by hydrolysis, since films containing such groups are generally more easily stretchable. For example, when the film is a fluoropolymer containing carboxylic acid groups as alternating groups, it is preferable to stretch the film in a form in which the carboxyl groups are esterified, for example, in the methyl ester form.

When the film contains groups that can be converted to exchangeable groups by hydrolysis, the hydrolysis can be performed, for example, by treating the calyo with an aqueous alkali metal hydroxide solution, for example, an aqueous sodium hydroxide solution. Since the film may tend to swell upon hydrolysis, it is preferable to perform said hydrolysis after the expanded stretched film is attached to the electrolysis cell or a part thereof.

For example, the film can be reinforced with a fluoropolymer mesh, although such reinforced films are not preferred because stretching of the reinforcing mesh may be difficult. The film may be in the form of a laminate, or it may be coated with electrode materials or other materials.

The expanded stretched ion exchange membrane is attached to the electrolysis cell or a part thereof. Once the film has been expanded by stretching at an elevated temperature, it can be attached to the electrolytic cell or a part thereof while at an elevated temperature. However, since the expanded stretched film tends to cool to ambient temperature and thus shrink during this attachment operation, it is preferable to "lock" the expansion into the film before attaching the film to the electrolytic cell or portion thereof. Thus, it is preferred to expand the ion exchange film by stretching at an elevated temperature 25 and to keep the film in an expanded stretched state while cooling the film to a lower temperature, preferably ambient temperature, at which temperature the film retains a substantial portion of its expanded stretched state.

The expanded stretched film may be attached to the electrolytic cell or part thereof by any suitable means. For example, the membrane may be clamped between a pair of seals in the electrolytic cell or attached to a frame which is then mounted to the electrolytic cell, or the membrane may be attached to the electrode.

The method of the present invention is particularly suitable for an ion exchange film to be installed in an electrolytic cell of the filter press type. The filter-5 cross-type electrolytic cells may contain a large number of alternating anodes and cathodes, and an ion exchange membrane is interposed between each anode and its adjacent cathode. Such cells may contain, for example, fifty anodes located alternately with fifty cathodes, although the cell may contain even more anodes and cathodes, for example up to one hundred and fifty alternating anodes and cathodes.

The electrodes of the electrolytic cell are generally made of a metal or alloy. The quality of the metal or alloy depends on whether the electrode is to be used as an anode or a cathode, and on the nature of the electrolyte to be electrolysed in the cell.

When an aqueous solution of alkali metal chloride is electrolysed and the electrode is to be used as an anode, it is convenient to make the electrode from a film-forming metal or a mixture thereof, for example zirconium, niobium, tungsten or tantalum, but it is preferable to make it from titanium. with a conductive, electrocatalytically active substance. The coating may contain one or more platinum group metals, i. platinum, rhodium, iridium, ruthenium, osmium or palladium, and / or oxides of one or more of the above metals. The platinum group metal or oxide-containing coating thereof may be a mixture of one or more base metal oxides, in particular one or more film-forming metal oxides, for example titanium dioxide.

Electrically conductive, electrocatalytically active 11,7009 substances used in electrolytic cells as anode coatings for the electrolysis of an aqueous alkali metal chloride solution, and methods for forming such coatings are known in the art.

When electrolyzing an aqueous solution of an alkali metal chloride and when the electrode is to be used as a cathode, it is expedient to make the electrode of iron or steel or another suitable metal, for example nickel. The cathode may be coated with a material suitable for reducing the hydrogen overvoltage of the electrolysis.

Any suitable electrode structure can be used in the electrolytic cell. For example, the electrode may comprise a plurality of elongate bodies, for example rods or strips, or it may comprise a perforated surface, for example a perforated plate, a mesh or a metal mesh.

The invention is illustrated by the following examples.

Example 1

A rectangular piece, 35 cm 20 x 30 xm, 280 μm thick, made of a thick cation exchange membrane sheet made of a copolymer of tetrafluoroethylene and perfluorovinyl ether was cut; the ion exchange capacity of the film was 1.3 milliequivalents / gram.

Strips of flexible PVC tape were attached to both 35 cm long edges of the Kap-25 piece, and aluminum strips were attached to both 30 cm long edges of the piece. The body was then placed in a Bruckner Karo 11 ori entrainer, and the body temperature was raised to 67 ° C in an oven associated with the orientator.

30 The aluminum strips were pulled farther apart at a rate of 1 / min until the distance between the aluminum strips attached to the part had increased 1.5-fold, with flexible PVC strips helping to prevent the part from narrowing. The body 35 attached to the orientation device was then removed from the oven and cooled to ambient temperature 12,7009 in an air stream.

The above operations, stretching the body at 67 ° C and cooling it to ambient temperature, were repeated twice, with the first strip treatment increasing the distance of the aluminum strips 2.5 times from the original and the second 4.2 times from the original.

The resulting cation exchange membrane was then removed from the orientation device. The film returned slightly to the original dimensions of 10 pieces. The film thickness after this small recovery was 80 μm.

The cation exchange membrane prepared as described above was carefully and tightly clamped between the EPDM rubber-seal pair and installed in an electrolytic cell equipped with a 7.5 cm diameter nickel mesh cathode and a 7.5 cm titanium mesh anode coated with RuO 2. and TiCl 2 (in a weight ratio of 35 RuO 2: 65 TiCl 2).

A 310 g / l concentrated aqueous solution of 20 NaCl, pH 8.0, was fed to the anode space of the cell. Water was fed to the cathode space of the cell, and NaCl was electrolyzed in the cell at 90 ° C with a NaCl concentration in the anode space of 200 g / l during electrolysis.

Chlorine and dilute NaCl solution were removed from the anode space, and water and aqueous NaOH (35 wt%) were removed from the cathode space.

2

Electrolysis was performed at a current density of 1 kA / m and a cell voltage of 3.01 V.

After a total of 20 days of electrolysis, the cell was opened and the cation exchange membrane was examined. Film 30 was found to be taut and wrinkle-free.

For comparison, the above-mentioned electrolysis was otherwise repeated in the same manner, but by installing a 280 cation thick cation exchange membrane plate in the electrolysis cell, i. unstretched membrane.

2 35 At a current density of 1 kA / m, the voltage was 3.1 V, and the membrane removed from the lift was found to be wrinkled and loose.

Example 2

The electrolysis according to Example 1 was repeated at a current density of 2 kA / m 2. In this case, the voltage was 3.24 V and, as in Example 1, the film was found to be taut and wrinkle-free when removed from the cell.

for comparison, the above electrolysis was repeated by installing a 280 μm-thick cation exchange membrane plate in the cell, i. unstretched membrane.

2

At a current density of 2 kA / m, the voltage was 3.4 V, and the membrane removed from the cell was found to be wrinkled and loose.

Example 3 The electrolysis according to Example 1 was repeated 2 at a current density of 3 kA / m. In this case, the voltage was 3.52 V and, as in Example 1, the film removed from the cell was found to be taut and wrinkle-free.

For comparison, the above-mentioned electrolysis was repeated by installing a 280 μm-thick cation exchange membrane plate in the electrolysis cell, i. unstretched membrane.

2

At a current density of 3 kA / m, the voltage was 3.7 V, and the membrane removed from the cell was found to be wrinkled 25 and loose.

Example 4 A 11.5 cm x 11.5 cm piece of cation exchange film made of a copolymer of tetrafluoroethylene and perfluorynyl ether containing sulfonic acid groups in the form of a potassium salt was taped at the edges with PVC tape and thus taped to a tightening frame. The film was heated to 180 ° C and stretched in one direction at a speed of 0.85 m / min until the film was stretched to twice its length. The film 35 was then cooled to ambient temperature and removed from the clamping frame.

14 73009

The membrane was installed in the electrolysis cell of Example 1 and electrolysed according to Example 1, i.

The aqueous NaCl solution was electrolyzed at a current density of 2 2 kA / m. A NaOH solution with a concentration of 25% by weight was formed with an efficiency of 50%. The cell voltage was 2.95 V.

When the electrolysis cell was opened, the film was found to be taut and wrinkle-free.

For comparison, the electrolysis was repeated using the above-mentioned but unstretched film. The cell voltage 10 was 3.1 V and NaOH was generated at a current efficiency of 57%.

When the cell was opened, the film was found to be wrinkled and loose.

Example 5

The stretching according to Example 4 was repeated with the change that the film used was a copolymer of tetrafluoroethylene and perilovinyl ether containing carboxylic acid methyl ester groups, and the temperature to which the film was heated during stretching was 80 ° C.

The membrane was mounted in the electrolysis cell of Example 1, hydrolyzed by treatment with NaOH solution, and the electrolysis was performed according to Example 3, i.

The aqueous NaCl solution was electrolyzed at a current density of 2 3 kA / m. A 35% NaOH solution was formed with a current efficiency of 94%. The cell voltage was 3.32 V.

25 When the electrolytic cell was opened, the film was found to be taut and wrinkle-free.

For comparison, the electrolysis was repeated using the above-described but unstretched film. The cell voltage was 3.4 V, and NaOH was generated at a current efficiency of 94%.

30 When the cell was opened, the membrane was found to be wrinkled and loose.

Example 6

A piece of ion exchange film, a copolymer of tetrafluoroethylene and perfluorovinyl ether containing carboxylic acid methyl ester groups, i.e. the film of Example 5 of Mark 5, was heated to 67 ° C and stretched in one direction in a tensioning frame according to Example 4, except that the tensile speed was 4.3-fold, i.e. it was stretched at a length of 5 to 430% of the original as measured in the direction of stretch.

After stretching, the film was rapidly cooled to ambient temperature in an air stream and removed from the frame.

After standing for 15 minutes, the film was found to shrink by 15% in the direction of stretch, so that its length measured in this direction was 365% of the original.

Electrolysis was performed according to Example 1 using the membrane described above. After 20 days of electrolysis, the film was found to be taut and wrinkle-free. Examples 7-9 The procedure of Example 6 was repeated for three different film samples with the difference that before cooling and removing from the clamping frame, the samples were hardened after stretching by holding at 67 ° C for 1 min (e.g. 7), 2 min (Example 8) and 20 3 min. (Example 9), respectively.

After standing for 15 min after removal from the frame, the films were found to shrink in the stretching direction by 11% (Example 7), 10% (Example 8) and 9% (Example 9), respectively, thus the film lengths measured in this direction were 383. % (Example 7), 387% (Example 8) and 391% (Example 9) of the original.

Electrolysis was performed according to Example 1 using each of the above membranes. After 20 days of electrolysis, each membrane was found to be 30 taut and wrinkle-free.

Claims (11)

73009 A method for installing an ion exchange film made of an organic polymer containing variable groups or derivatives thereof which can be converted into variable groups in an electrolytic cell, the method comprising expanding the ion exchange film and attaching the expanded film to the electrolytic cell or a portion thereof, characterized in that the film is expanded 10 to increase the area of the film per unit weight. Method according to Claim 1, characterized in that the film is expanded by stretching at an elevated temperature. A method according to claim 2, characterized in that the film is expanded by stretching at an elevated temperature, the expanded stretched film is cooled to a lower temperature while maintaining the film in the expanded stretched state, and the film is then attached to the electrolysis cell or a part thereof. Method according to any one of the preceding claims, characterized in that the film is stretched in one direction. Method according to any one of claims 1 to 3, characterized in that the film is stretched in two directions. Method according to any one of the preceding claims, characterized in that the amount of film expansion produced by stretching is equal to or greater than the amount of film expansion caused by the film coming into contact with the electrolyte. Method according to any one of the preceding claims, characterized in that the stretching of the film causes an increase of at least 5% in the surface area of the film per unit weight. Method according to Claim 7, 73009, characterized in that the stretching of the film causes an increase of at least 100% in the surface area of the film per unit weight. Method 5 according to any one of claims 2 to 8, characterized in that the film is expanded by stretching at a temperature of at least 55 ° C. A method according to any one of claims 2 to 9, characterized in that the expanded stretched film is hardened by heating at an elevated temperature. A method according to any one of the preceding claims, characterized in that the film is expanded by stretching at an elevated temperature and the film is cooled to a lower temperature while maintaining the film 15 in the expanded stretched state, and in that both the expansion step and the cooling step are repeated at least once. 73009