JPS6119790A - Manufacture of porous diaphragm - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a new diaphragm, particularly for electrolysis, and to a method of manufacturing the same.

Japanese Patent Application No. 49-54987 (French Patent Application No. 2229739) for use in nuclear power plants discloses that a fluororesin latex and a pore-forming agent are added to an aqueous suspension of asbestos fibers in the presence of a sulfonic anionic surfactant. The pore-forming agent is decomposed by adding it to form a stable, homogeneous suspension, applying the suspension to a filter mold, drying and melting at a temperature above the melting point of the fluororesin in its crystalline state. A method is described for producing a porous diaphragm of asbestos deposited and consolidated with a fluororesin, which is characterized in that it is finally removed by.

The diaphragm of an electrolytic barrel is known to behave like a porous medium, i.e. on the one hand it allows flow with a small ohmic drop, and on the other hand it allows for a uniform flow of electrolyte from one compartment to another. enable.

There is therefore a set of mechanical, electrical and hydraulic conditions which are now increasingly critical, requiring electrolytic cells to work at high current density, provided that they withstand prohibitive ohmic drops.

The necessary properties are rather contradictory. Thus, from a mechanical point of view, this diaphragm must have a well-defined and lasting shape. This diaphragm is in use! 1iIvl and deformation must be prevented.

In other words, such a diaphragm must have good mechanical strength. However, it must also have good wettability to allow gases to be liberated and to circulate the electrolyte while preventing the diffusion of OH- ions towards the opposite direction of the liquid flow. Such diffusion causes the formation of chlorate leading to a decrease in yield.

In order to separate this, the electrolytic diaphragm must have a low relative resistance. The relative resistance number is understood as the quotient of the resistance of a medium consisting of an electrolyte-impregnated diaphragm/the resistance of the same medium consisting of N.

It is observed that this relative resistance is constrained by the porosity of the diaphragm, but also in the form of flow channels.

Attempts have therefore been made to combine several elements in order to simultaneously meet all of the above requirements.

Thus, U.S. Pat. No. 3,694,281 discloses a plastic filament which forms a mechanical support mounted on at least one surface of the diaphragm or which is inserted at the interface between the asbestos and the substrate. It is proposed to make laminates with threads, fibers or particles.

French [4 Special Edition No. 2170247] proposes a simple arrangement in which a support made of cloth, for example polypropylene J, is used.

Belgian patent No. 814,510 proposes to improve the hardness of the diaphragm by applying it to at least one sheet of olivine.

In a particular embodiment of this diaphragm, the sheet of diaphragm is sandwiched and bonded between two sheets of olivine asbestos.

However, the difficulty encountered is to retain the advantages of an open structure, such as in diaphragms for nuclear power plants, while improving mechanical properties. When such diaphragms are used industrially, it has been found that they actually have the disadvantage of exhibiting structural deformation, especially local loss of bonding, and result in a performance that cannot be completely regenerated.

This disadvantage arises if the diaphragm obtained according to the nuclear power plant application is combined with a reinforcing element by integrating the reinforcing element with the anode surface of the porous membrane (this reinforcing element is porous for the passage of liquid in electrolysis). It has been found that membranes with at least an open structure can be avoided.

Surprisingly, it has been found that the above-mentioned disadvantages are still encountered if the same reinforcing element is placed on the cathode side rather than on the anode side.

This reinforcing element consists quite simply of a cloth or sheet of asbestos fibers.

A 0.5 part 1 m thick and 500 g/m2 heavy asbestos fabric is advantageously combined with a microporous membrane according to the original invention, the ratio of pore former charge to weight of asbestos being greater than 100% and preferably is 250-600%.

In a preferred embodiment, the diaphragm according to the invention is 0.5 to 1 mm thick, weighs less than 500 g/TrL2 and is incorporated into the anode side of the microporous membrane and comprises IC asbestos, with a proportion of calcium carbonate. is 250 to 600% of the weight of asbestos. This diaphragm has a relative resistance of less than 4, 509/
at 20 °C in cm2.

with a liquid flow rate through the diaphragm of 0.25-0.02 d/min/cm2 under a liquid charge of 2.5-5IIIR and preferably a thickness of 3''/4#.

Such a diaphragm can be obtained by applying the same method as described in the original invention.

In practice, asbestos suspensions are prepared by dispersing by stirring a mixture containing 11 parts of asbestos, 5 to 100 parts of water, and 0.015 to 0.1 parts of anionic surfactant by weight. Ru.

The asbestos used is preferably made of 0.5 to 50 cocoon fibers. The surfactant, preferably sodium sulfosuccinate, is used pure or as an alcoholic solution.

Vigorous agitation provides a stable, well-dispersed asbestos suspension.

The fluororesin latex and pore-forming agent are added to the suspension in the following proportions by weight: 100 parts asbestos, 60-200 parts fluororesin (dry) -ioo- 1400 parts pore-forming agent. be done.

Stirring is then carried out for 1 to 20 minutes, especially under certain conditions of speed.
Preferably it lasts for 5 to 10 minutes.

The final volume of the suspension is adjusted by adding water at the end of the stirring process in a proportion that best suits the observed deposition conditions.

Polytetrafluoroethylene latex is generally a suspension of about 60% Bottetrafluoroethylene in water.

This may be substituted with other latexes of fluororesins (mixtures of di-1-la-fluoroethylene-hegizafluoro[1-but-1-copylene, polychloro-1-lifluoroethylene, etc.).

The pore-forming agent used may be calcium carbonate, colioid alumina, metal oxides or any material suitable to be removed by solvent or decomposition at the end of the operation.

It must have a well-defined particle size.

Preference is given to using calcium carbonate consisting of particles having an average diameter of 2N25μ.

When a flat diaphragm is made, a stable, homogeneous mixture of the various components is poured onto the reinforcing component in such amounts as to obtain the desired thickness. This is then filtered and then vacuum dried. Drying at a temperature exceeding 100℃, approx.
It is carried out at 50°C for 3 to 24 hours.

Seams 1 to 1 are then melted by placing them in an oven at a temperature above the melting point of the fluororesin, preferably 25 DEG to 75 DEG C. above, for 2 to 20 minutes and preferably about 6 to 10 minutes. The temperature chosen will vary depending on the melting time, but
However, it also depends on the thickness and composition of the diaphragm.

Once the diaphragm has cooled, place it in the presence of a wetting agent for 10~
24-72 depending on the thickness in a 20% by weight aqueous solution of a weak acid.
Soaked for a period of time. Acetic acid is preferred, but other weak acids may also be used.

The resulting diaphragm is then rinsed in water to remove acid and kept in water.

However, the invention will be better understood from the following examples. These illustrate the invention! This is not intended to be limiting in any way.

Example 1 This example is a control experiment different from the method of the invention in which reinforcing elements were placed on the cathode side of the diaphragm.

In this experiment, a suspension of asbestos fibers, -100q, asbestos 1-valt with an average length of 1-2 mm.

-250047 hours of water, -2.5 hours of a 75% alcoholic solution of sodium-dioctyl sulfosuccinate.

Dispersion is carried out by stirring for 60 minutes using a drum roller type stirrer.

Next, the following six items are added.

-300 in latex form with 60% dry extract
ri's polytetraful A mouth] Nijilene, -560g of calcium carbonate (registered trademark BLEOHY8)
.

Stir the mixture for 5 minutes.

Using the following vacuum program, 17 (l) of suspension was
Drain onto dn+2 asbestos fabric.

-1 minute decantation 12 minutes at 200mmH (l) -2 minutes at 300 mH (I 10 minutes at 740mmHQ.

The asbestos cloth used had a weight of 255g/TrL2 and
．． It has a thickness of 76mm. It has warp and weft threads of 111 tex (weight of 1000 meters of thread, g) and 13 threads/cm in the warp and 7 threads/cm in the weft.
has.

The mold thus obtained in combination with asbestos cloth was heated to 150°C.
Dry in Owan for 5 hours. This reinforced mold is next 36
Melt in an oven kept at 0° C. for 7 minutes. The carbonate is removed in 72 hours in a 20% by weight aqueous acetic acid solution. The diaphragm thus obtained is washed with water.

This gives a die frame with the following properties:

Weight, s/dm2 170 Thickness, standard 3.55 Liquid flow rate, mQ
191 cm2 (50'; under charge of i/cm2) 0.15 relative resistance, R/Ro 2. The diaphragm is used as a zeparator for the electrolysis of a solution of sodium chloride under the following conditions:

The asbestos cloth placed on the electrode side is formed by a grid (titanium with platinum plated on the anode side and iron on the cathode side) separated by 7 mm. It is observed that

- Loss of binding on the anode surface - 3, 4, 4 volt equilibrium cell voltage - Liquid composition - Soda 9# 125 - Chlorate SF/j! 1 - Liquid charge on the diaphragm of 15 cm of water (H).

Example 2 This example is the same as above except that the same asbestos fabric is arranged on the anode side.

It can be seen that the liquid has the same composition of soda and chlorate, but the equilibrium voltage has been reduced to 3.17 volts. That is, the resistivity is 2.1 and the liquid charge on the diaphragm is 12 cm of water.

Examples 3-14 In all of these examples, the ratios of the various components are as follows.

Asbestos fiber “tooy water 250CIPTFE
Other conditions and results of electrolysis under the same conditions as in Examples 1 and 2 are shown in the table below.

This table shows the effects and advantages of the diaphragm according to the invention.

It can thus be seen that the charges for Examples 10-14 were either too high or too large, rendering the diaphragms virtually unusable for electrolysis.

Example 9 is an example of a diaphragm that withstands high proportions of chlorate, which makes the diaphragm unsuitable.

These examples show that structures that are too closed give poor results in electrolysis.

On the other hand, it's too open! [The structure gives quite good results in electrolysis, but the resulting diaphragm is brittle, meaning that thicker diaphragms must be used.]
However, as can be seen from Example 3, this is detrimental to the application to electrolysis.

It can be seen from Examples 1 to 8 that there is a preferred range that gives overall excellent results.

Example 15 This example is carried out under the same conditions as above and with the preferred ranges above. This illustrates an experiment with reinforcing elements on the cathode surface different from those described in Example 1.

In this example, the preparation of the morning assembly forming agent (CaCO3> is 560
CJ and the amount of filter material is 120 g.

The thickness of the diaphragm is 3.10 m.

The relative resistance is 2.25, the equilibrium voltage is 3.30 volts, the liquid charge H is 2.5 cm and the liquid composition is 1 soda 116 g/j! -Chlorate 1.7s, 1.

These conditions are not acceptable for electrolysis, the liquid loading is too low and the chlorate content is too high. Furthermore, the cell voltage corresponds to that in Example 5, and the amount of filtered material is 20
0 g, liquid charge is 24 and amount of chlorate is 0.9.

A solution and appropriate liquid charge that increased the amount of solids in the porous membrane to obtain a low chlorate content could lead to high equilibrium pressures, while a larger amount of filtrate material, 120 g (Example 4
According to the invention, using 140 g instead of 140 g, as the liquid charge on the diaphragm becomes larger, the rate ratio decreases and the cell voltage becomes weaker.

Even with higher amounts of pore-forming filler, better results are obtained in electrolysis (Examples 2 and 3).

These examples demonstrate the new and advantageous effects of the present invention, such as the absence of bond loss and the very significant improvement in electrolytic performance.

It should likewise be pointed out that the following effects are observed with the diaphragm according to the invention.

- The diaphragm has a greater resistance to wear by the gas on the anode side.

One diaphragm has greater resistance to bending and impact operations sometimes required by cell technology, and is also less susceptible to damage from handling, especially during molding.

- In situ (in situ) removal operations are facilitated.

In particular, it should be pointed out that, contrary to what happens to irises, the mechanical, hydraulic and electrochemical demands of electrolysis are surprisingly all better met by the diaphragm according to the invention.

Claims (7)

[Claims] (1) Form a stable homogeneous suspension by adding a fluoropolymer latex and a pore-forming substance to a suspension of asbestos fibers in water in the presence of a sulfonic anionic surfactant; A fluorine-containing resin in which the suspension is shaped by filtration, dried, melted at a temperature exceeding the melting point of the fluororesin in its crystalline state, and the pore-forming substances removed by decomposition. In a process for producing a porous diaphragm of consolidated deposited asbestos, the microporous membrane thus obtained is combined with a reinforcing element by integrating the reinforcing element with the anode side of the membrane, and the reinforcing element is integrated with the anode surface of the membrane. A method characterized in that the element has a structure that is at least open as a porous membrane for the passage of liquid in electrolysis. (2) The reinforcing element is 0.5-1mm thick and 500g/m^
A method for manufacturing a porous diaphragm according to item (1) above, characterized in that it consists of an asbestos fabric having a weight of less than 2. (3) In the microporous membrane in which the reinforcing elements are combined, the ratio of pore-forming filler to the weight of asbestos is 100.
% and preferably from 250 to 600%. (4) The method according to any one of the above items (1) to (3), wherein the surfactant is sodium dioctyl sulfosuccinate. (5) The method according to any of the above items (1) to (4), wherein the pore-forming agent is calcium carbonate. (6) The method according to any one of the above (1) to (5), wherein the fluororesin latex is polytetrafluoroethylene. (7) Asbestos weight of a diaphragm consisting of an asbestos cloth with a thickness of 0.5 to 1 mm, a weight of less than 500 g/m^2 and integrated with the anode surface of the microporous membrane, with a filler consisting of calcium carbonate. The diaphragm has a relative resistance of less than 4 and a liquid flow rate of 0.25 to 0.02 ml/min/cm^2 passing through the diaphragm under a liquid charge of 50 g/cm^2 at 20°C. A diaphragm for electrolysis, characterized in that it has a flow rate and a thickness of 2.5 to 5 mm, preferably 3 to 4 mm.