JPS6037877B2 - How to process diaphragms for electrolysis - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a method for obtaining an asbestos diaphragm for aqueous electrolysis that is dimensionally stable, has low electrical resistance, and exhibits little change in water permeability over time.

As is known, asbestos is widely used as a diaphragm for aqueous solution electrolysis, especially saline solution electrolysis.

Although asbestos membrane has many advantages, it has the disadvantage that it has low physical strength and swells considerably during the initial stage of electrolysis, so it can be damaged by the generated gas and the resulting liquid flow. In addition, the amount of water permeable at the initial stage of electrolysis is large, and for example, when producing caustic soda by saline solution electrolysis, it takes a long time until the concentration of caustic soda becomes appropriate. Because of these drawbacks, it has been impossible to reduce the electrical resistance of the diaphragm by making it thinner, thereby lowering the electrolytic voltage. It is also known that starch and chloroprene rubber are used as binders for asbestos paper, but when these asbestos papers are used as diaphragms, their physical strength is still insufficient, so the corneal membrane may be damaged under high current densities. You can finally see it getting damaged. In order to compensate for these drawbacks, research has been carried out on using organic polymers, especially flouten-based resins, as binders and visual agents during the production of asbestos corneal membranes.

However, fluorine-based resin is expensive, and in order to be used as a binder, it requires high-temperature treatment at a temperature of 28,000 or higher, which changes the properties of the asbestos fibers and makes them brittle. A diaphragm reinforced with a diaphragm has drawbacks such as, for example, the amount of water permeable at the initial stage of electrolysis of saline water is 10% lower than when it is stable, and the amount of water permeable changes greatly over time, making it difficult to adjust the concentration of caustic soda. Furthermore, the knee membrane reinforced with fluororesin has drawbacks such as lowering current efficiency and requiring hydrophilic treatment because the resin is hydrophobic. The present inventors have found that by using chloroprene rubber latex, which is known as an asbestos paper binder, under special conditions, it is dimensionally stable, has high physical strength, has low electrical resistance, and has little change in water permeability over time. We succeeded in obtaining a diaphragm with performance that could not be expected from conventional asbestos diaphragms.

The configuration and effects of the present invention will be explained in detail below.

{1' Asbestos fibers are deposited on a cathode in the form of a wire mesh or a perforated plate from a well-defined asbestos slurry aqueous solution by vacuum suction or the like to form a diaphragm. This process is known as the deposit method. {2' Wash the diaphragm by immersing it in running water or passing water from one side of the diaphragm to the other to remove as much caustic soda and salt contained in the fly's membrane as possible.

[3} Dry the membrane.

The degree of dryness is good, at least to the extent that it is not damp to the touch. The drying temperature may be room temperature, but it is desirable to dry at 60 to 150 q○ in a short time. {4' A latex liquid containing chloroprene rubber particles, or a liquid to which water glass or a nonionic surfactant is further added, is passed through the diaphragm using a vacuum method, etc., and the diaphragm adsorbs the chloroprene rubber particles over the entire layer. .

The amount of chloroprene rubber particles adsorbed is adjusted by adjusting the latex concentration and permeation amount. '5} Air is passed through the diaphragm under reduced pressure, etc. to drain water well, and then heat and dry.

A diaphragm with good performance can be obtained by the above method, but in order to minimize the amount of electrolytes such as caustic soda and salt in the diaphragm, the distance from one side of the diaphragm to the ground must be approximately 0.005 to 0.01/
It is desirable that water permeates for 10 minutes or more at a flow rate of 1/min.

However, the above flow rate does not limit the configuration of the present invention.
Further, drying after washing with water is preferably carried out for a short period of time at a temperature that does not damage asbestos, for example, 60°C to 150°C. Next, in order to improve the performance of the diaphragm, it is important to infiltrate a sufficient amount of chloroprene rubber particles into the diaphragm and to uniformly adsorb chloroprene rubber both on the surface and inside the diaphragm. In other words, if there is too much chloroprene rubber on the surface of the diaphragm, a film will form only on the surface when it dries, and when a current is passed through, gas leakage will occur due to insufficient gas escape, and this will reduce the strength of the diaphragm and cause an increase in voltage. Since the amount of chloroprene rubber particles is small, the reinforcing effect is only on the surface, and since the diaphragm has a double layer structure, gas accumulation occurs, the voltage increases, and the strength of the diaphragm does not improve substantially. Therefore, the concentration of the chloroprene rubber latex is preferably adjusted to 0.01 to 2% by weight, preferably 0.06 to 0.3% by weight. By using such a latex, the amount of chloroprene latex deposited on asbestos is about 2 to 25% by weight. As mentioned above, in order for the polymer particles in the latex to sufficiently penetrate into the inside of the diaphragm, the permeability of the latex liquid into the corneal membrane must be good.

As mentioned above, as a result of repeated research, the present inventors found that drying the diaphragm before letting the latex liquid pass through it is very effective for improving the permeability of the latex liquid. Furthermore, it has been found that the permeability is good or bad depending on the type of latex, and when the permeability is poor, it is effective to add a nonionic surfactant or water glass. For example, neoprene latex (Showa Neoprene Company product 0)
#736 has relatively good permeability and can be used simply by adjusting the concentration, but #400 has poor permeability and requires the addition of a surfactant or water glass. However, by adding a surfactant or water glass to #736, the permeability was further improved, and the performance of the diaphragm was improved. The alkali is generally Na20 or K20.Nonionic surfactants include both polyethylene glycol type and polyhydric alcohol fatty acid ester type.

Next, if the concentration of chloroprene rubber particles in the latex is too low, it is necessary to pass a large amount of latex liquid through the diaphragm in order to impregnate the diaphragm with the chloroprene rubber necessary for reinforcement, but in this case, it is necessary to pass a large amount of latex liquid per unit time. Since there are few chloroprene rubber particles, chloroprene rubber is adsorbed by asbestos near the surface and does not penetrate into the interior.

On the other hand, if the concentration is too high, the permeability will be poor, and therefore a good diaphragm will not be obtained because a film will be formed when the diaphragm surface comes into contact with air at the end of permeation. In order to obtain a good diaphragm, it is necessary to balance the penetration and adsorption of chloroprene latex particles into asbestos. That is, the purpose of the present invention is to improve the performance of the diaphragm by optimizing the concentration of chloroprene rubber and improving the permeability. The inside of the tube is washed with water, dried, and then immersed in a diaphragm treatment solution containing chloroprene rubber latex and dried again. Next, the effects of the present invention will be explained with reference to Examples. Example 1 Asbestos fibers were deposited from a slurry solution containing asbestos fibers dispersed in 20 wt% NaOH adjusted to 32 days/day onto a cathode wire mesh with an effective area of 1.0 under a reduced pressure of -50 tons of Hg, A corneal membrane with a thickness of 2 skins was formed, washed with 1 layer of water, and then dried at 70q○ for 3 hours.

Next, neoprene latex ■ Latex #736 (chloroprene rubber latex brand name manufactured by Showa Neoprene Co., Ltd.)
with water to 0. A solution diluted to 6% by weight of asbestos was permeated under reduced pressure of -45% Hg. A round weight percent of chloroprene rubber particles were adsorbed. Thereafter, air was passed through it for 30 minutes under a reduced pressure of 140% Hg, and then it was dried for a short time at 7,000 degrees Celsius. This diaphragm was installed in a dew tank and an electrolytic test was conducted. The conditions are as shown below. Saline concentration:
Table 1 shows the results after 3 weeks of operation at 310 mm anolyte head; 50 mm bath temperature: 70 CC; anode: ruthenium oxide coated titanium wire mesh anode; ld gap: 7; skin current: 20 A/d.

Example 2 A diaphragm with a thickness of 1 was made using the same method as in Example 1, and the thickness was 0.06.
% neoprene latex #736 was used to adsorb 2.1% by weight of chloroprene rubber particles on asbestos.

Other conditions were the same as in Example 1. The results are shown in Table 1. Example 3 The thickness of the corneal membrane was set to 1.9 cm, and 0% of Emalgen 920 (polyethylene glycol type nonionic surfactant manufactured by Kao Atlas Co., Ltd.) was added to neoprene latex diluted with water to 0.0% by weight. 02% by weight was used, and 4% by weight of chloroprene rubber particles were adsorbed on asbestos.

Other conditions include drying at 120q before passing through the latex liquid.
The procedure was the same as in Example 1, except that the drying was carried out at C for 3 hours and the subsequent drying was carried out at 120° C. for one period. The results are shown in Table 1. Example 4 The thickness of the diaphragm was 1.9 ribs, and the water was 0.0% by weight
Neoprene latex #736 diluted with 0.05% by weight of water glass was used, and the amount was 4% by weight based on asbestos.

Loprene rubber particles were adsorbed. Other conditions are the same as in Example 3. The results are shown in Table 1.

Comparative Example 1 A corneal membrane with a thickness of 2 ribs was deposited in the same manner as in Example 1,
It was used for electrolysis without water treatment, drying treatment, chloroprene treatment, or drying treatment.

The results are shown in Table 1.

Comparative Example 2 The same treatment as in Example 1 was carried out except that the drying performed before the latex liquid permeation in Example 1 was not performed.

In this case, gas leakage occurred in the diaphragm after several hours of electrolysis, and the voltage was 0.2 V or more higher than in the example, making long-term operation impossible. Table 1 compares the operational data of Examples 1 to 4 and Comparative Example 1 after 3 weeks, and the amount of electrolyte extracted immediately after the start of electrolysis.

Table 1 Electrolysis experimental data (20A/2,70°C) From Table 1, the following conclusions can be drawn.

'1} According to Example 1 and Comparative Example 1, the voltage was lowered by 0.1 V and the caustic soda concentration was increased by a series of steps of water treatment, drying treatment, chloroprene treatment, and drying treatment.

In particular, the amount removed immediately after electrolysis is 38+/mjn without the above treatment, which is more than 8 times the stable value (values taken after 3 weeks), but with the above treatment, it is about twice as high. , there is little change in the amount removed over time. ■ As shown in Example 2, even if the diaphragm is set to the level of one barrier, the Na○ maternity, CI2 purity, and CI
There is no problem with the concentration of day 2 in 2, and the voltage is 3.02V.
This is a decrease of 0.22V compared to Example 1.

When a diaphragm with a thickness of 1 bar was used for electrolysis without any treatment as in Comparative Example 1, the ratio in CI2 exceeded 2%, making stable operation impossible. [3} According to Examples 3 and 4, by using neoprene latex and a nonionic surfactant or water glass in combination, it became possible to further reduce the voltage.

'4) The disadvantage of asbestos diaphragms is that they swell significantly in the early stages of electrolysis and have virtually no strength. However, after about 3 weeks of operation, they become stable and strong, and are resistant to disturbances in operating conditions. It is said that it will also have resistance.

The neoprene latex-treated diaphragm has a strength more than three times that of a stable untreated diaphragm, and even in the early stages of electrolysis, when the untreated diaphragm has no strength, it has a strength of lk9' or more, and its reinforcing effect is sufficient.

The condition and tensile strength of the diaphragm at the end of three weeks of electrolysis were as follows.

Examples 1 to 4: Almost no swelling, 0.74 to 1.1k9/Negative Comparative Example 1: Swelled approximately twice as much as 0.2k9/Negative As in Comparative Example 2, drying before permeation of the latex liquid was carried out. When this was not done, the voltage was 0.2 V or more higher than in the example, and gas leakage occurred in the diaphragm.

Claims (1)

[Scope of Claims] 1. After depositing asbestos fibers from an asbestos slurry onto the surface of an electrolytic cathode to form a diaphragm, the inside of the diaphragm is washed with water and dried, and then placed in a diaphragm treatment solution containing chloroprene rubber latex. A method for treating an electrolytic diaphragm, which comprises immersing it in water and drying it again. 2. The method for treating an electrolytic diaphragm according to claim 1, wherein the diaphragm treatment liquid further contains water glass. 3. The method for treating an electrolytic diaphragm according to claim 1, wherein the diaphragm treatment liquid further contains a nonionic surfactant.