JPS58100688A - Electrolytic cell for generating fluorine - Google Patents

Abstract

PURPOSE:To reduce a chance of the contact of bubbles of gaseous F2 with bubbles of gaseous H2 and to attain enhanced current efficiency by making the cathode of an electrolytic cell provided with no diaphragm open so as to lead a gas produced by electrolysis to the rear side of the cathode. CONSTITUTION:A skirt 3 for preventing gaseous F2 and gaseous H2 from mixing with each other is set on the surface of an electrolytic soln. in the electrolytic chamber 5 of an electrolytic cell for generating F2. HF and a salt contg. F are fed to the chamber 5 and electrolyzed to produce F2 and H2. Most of the F2 produced on the open cathode 2 is led to the rear side of the cathode 2 through the openings of the cathode 2. The cathode 2 has 0.1-5cm thickness in the horizontal direction, and it is formed with louverlike or expanded metal. By making use of the electrolytic cell provided with the open cathode and no diaphragm, enhanced current efficiency is attained.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an electrolytic cell for fluorine generation, and particularly to an electrolytic cell for fluorine generation that can generate fluorine and hydrogen by electrolyzing hydrofluoric acid with high current efficiency and low electrolysis voltage.

Various companies have proposed so-called hydrofluoric acid electrolytic cells for producing fluorine by electrolyzing hydrofluoric acid, and the present invention relates to a diaphragmless electrolytic cell among them.

A non-diaphragm electrolytic cell does not have a diaphragm between the anode and the cathode and supplies hydrofluoric acid and fluorine-containing salt to the decomposition chamber for electrolysis. Fluorine and hydrogen may combine in the electrolytic chamber and return to hydrofluoric acid, which may reduce the current efficiency or cause a large amount of generated gas (fluorine gas and hydrogen gas) to be on or near the electrode surface. This method has the disadvantage that it shields the electrode surface and causes an increase in electrolytic voltage due to a decrease in the apparent effective electrode area. In contrast,
In addition to providing a skirt between the anode and cathode to prevent hydrogen and fluorine from mixing, it is also possible to increase the distance between the anode and cathode, increase the immersion depth of the electrode, or use highly corrosion-resistant material such as moil between the anode and cathode. Measures have been taken to prevent the mutual diffusion of air bubbles, such as by providing a metal mesh.

However, in the former method, the production volume of unit electrolytic inspection wheels decreases because the distance between the electrodes becomes narrower, increasing the sliding voltage, and the effective electrode surface value decreases due to the smaller electrode immersion depth. There was a drawback.

Furthermore, in the case of the latter method, even if the metal mesh is made of a highly corrosion-resistant material such as Monel, its service life is short and it is rarely necessary to replace it frequently.

As a result of various studies on ways to overcome the above-mentioned drawbacks of conventional electrolytic cells, the present inventors discovered that these problems could be solved by devising a special method for the cathode, and completed the present invention. In this invention, a partition wall (skirt) is provided on the electrolytic solution surface to prevent mixing of fluorine gas and hydrogen gas, and hydrofluoric acid and a fluorine-containing salt are supplied to an electrolytic chamber formed between anode and cathode. A fluorine generation electrolytic cell that generates fluorine and hydrogen by electrolyzing fluorine and hydrogen, is characterized in that the cathode is open-pored and most of the gas moves to the back side (the opposite side to the anode). The main topic is an electrolytic cell for fluorine generation.

It is something that

The cathode used in the present invention is different from the flat cathode used in the past (in the past, the wall of the electrolytic cell was often used as the cathode). (to the opposite side of the anode).

That is, hydrogen generated on the cathode surface happens to move to the back door f1 of the cathode through the opening of the cathode, so that 7? +
Fewer bubbles remain or diffuse to the anode side, and therefore, fluorine gas bubbles rising or floating on or near the anode surface and diffused water (gas bubbles are less likely to associate and react, maintaining high current efficiency. be able to.

Furthermore, hydrogen moves to the back surface of the cathode, and between the anode and cathode,
The gas area filled with oil near the cathode surface of the bamboo is reduced to dust supply, and the sliding voltage is lower than that of the J and A combinations of J and A, as this reduces the amount of gas that accumulates in the vicinity of the cathode surface. It can also be seen that there is a decreasing effect on

The inventors of the present application have made four changes to the history of cathodes having the above-mentioned effects, and have found that the above object can be preferably achieved when the cathode has specific geometrical characteristics.

This point will be explained below with reference to the drawings.

FIG. 1 is a half-mounted sectional view of an example of the electrolytic cell of the present invention. 1id is an anode made of carbon, for example, and - is a cathode. 3 is a partition wall (skirt), 4 is a cooling jacket, and 5 is an electrolysis chamber. 2 shows a case in which the cathode has a louver shape, and FIG. 2 shows a partially enlarged view of the cathode in FIG. 1. In the cathode shown in Figure 2, the louver blades are arranged at an angle of 45° with the horizontal plane, the interval between the blades is the same as the vertical thickness of the blades, and the width of the blades is three times the above interval. shows. Fig. 3 shows another preferred embodiment of the louver shape of the cathode in the electrolysis of the present invention, where 6 indicates the cathode, which is slightly inclined toward the back surface. In this case, gas is more likely to escape to the back side of the cathode. Hydrogen generated at the M pole escapes to the back surface of the cathode along the gap between the blades t4j
) M will be explained below.

That is, the hydrogen gas generated at the portion 7 in FIG. 2 moves toward the upper right in the figure, and the electrolyte also moves toward the upper right due to the gas lift effect. At this time, the hydrogen gas generated at the part 6 enters the gap between the blades due to the suction effect and moves to the upper right part.

The present inventors have found that when the geometrical arrangement of the blades is specific, hydrogen is preferably desorbed to the back surface, which is suitable for improving current efficiency and reducing electrolysis voltage.

In other words, the area of the visible part when looking at the cathode from the anode side (the sum of the vertical part 6 and the inclined part 7 shown by the bold line in FIG. 2) is the reference area, and the angle is 45 degrees or more with respect to the horizontal plane.
When the area of the cathode surface below 0' is 50% or more of the reference area, and the area of the cathode surface at 45° or more and less than 90' with respect to the horizontal plane is 20% or more of the reference area, hydrogen is added to the back surface of the cathode. Gas easily moves effectively, and if the above range is exceeded, hydrogen gas will not necessarily escape to the back surface of the cathode.

Here, the angle between the horizontal plane and the horizontal plane is measured by the angle between the horizontal plane and the upward slope of the cathode surface toward the back of the cathode.

The above relationship will be specifically shown in the case of FIG. Here, if the width of the blade in the vertical direction of the drawing is b, (A) Cathode area of the visible part seen from the anode = (a
+E a ) b (B) Area of the cathode surface at 45° or more and 90° or less with respect to the horizontal plane = (a+v/T a ) b (C) Area of the cathode surface at 45° or more and 9-00 unsalted relative to the horizontal plane iab, so the ratio of (B) to (A) is 100%,
The ratio of (0) to (A) is fab/(a+[a)b
That is, it becomes 58.5%.

4 to 7 are cross-sectional views showing other embodiments of the cathode used in the electrolytic cell of the present invention, and both show the case of expanded metal.

FIG. 4 is a front view of the extended metal cathode from the M h< side.

5, 6, and 7 show a cross section [>1] taken along the line AA in FIG. 4.

Figure 5 shows a case where the member forming the opening in the expanded metal has a square cross-sectional shape with one side a, and Figure 6: The above member has a rectangular cross-sectional shape with one side 2a and the other side 3a. However, the case where the surface of the long side 3a slopes upward toward the back surface of the cathode is shown.

Using the same calculation method as in the case of Fig. 2 above, in the case of Fig. 5, the ratio of the area of one pole surface of 45° or more and 90° or less - 50 factor of the cathode surface of 45° or more and less than 90° ■” It ° ratio =
In the case of FIG. 6, the ratio of the area of the cathode surface between 45° and 90' is 60 cm.The ratio of the area of the cathode surface between 45° and 90° is 60 cm.

FIG. 7 shows a case where the ratio of the two sides of the member obtained by making a wide slit in a thin plate and pulling it is even larger than that in FIG. 6.

The larger the thickness of the cathode in the horizontal direction, the greater the effect of drawing in air bubbles, but if the cathode is too thick, air bubbles and electrolyte will pass through. Since the resistance becomes thicker and the amount of bubbles that escape to the back surface of the cathode decreases, the thickness
3a in case of figure.

5 a in the case of Figure 5, 55 a / in the case of Figure 6
2) is preferably about 0.1 to 5α, and 05 to 3σ for history.
degree is more preferable.

This electrode can be used in various types of electrolytic cells, but the
In the electrolytic cell of the type shown in the figure, a strong upward flow occurs in the passage formed in the cathode sleeve, which also enhances the suction effect.

In addition, the shape of the cathode of the electrolytic cell of the present invention needs to be porous, and its porosity is 30 to 90.
%, preferably 40 to 80 inches. Further, when the openings are arranged with regularity, the repeating unit is preferably 3 to 25 meters, and more preferably 5 to 15 meters.

In the electrolytic cell of the present invention, the distance between the back of the cathode and the wall of the cell does not have to be particularly limited, but if this distance is too large, the suction effect described above will be lost, and the cooling effect from the cell wall will simply be due to natural convection. The cooling effect is not great because the cooling effect is only due to The above distance is 0.3 to 4.0 cm, more preferably 0.5 to 2.0 cm, depending on the amount of current applied (that is, the amount of hydrogen gas generated), the immersion depth of the cathode, etc. It is preferable to set it to about cm.

Further, it is necessary to provide a partition wall (skirt) above the electrolytic solution to prevent the generated fluorine gas and hydrogen gas from mixing. In the electrolytic cell of the present invention, it is extremely rare for fluorine gas and hydrogen gas to be mixed in the electrolytic solution, but by extending the partition wall slightly into the electrolytic solution, the above effects can be achieved even better. sell.

It is preferable that the partition wall be immersed to a slight depth below the electrolyte surface. In the case of the electrolytic cell of the present invention, the fluorine gas generated at the anode rises almost along the electrode surface, but near the liquid surface it rises. Diffusion to the cathode side occurs. In addition, most of the hydrogen gas generated at the cathode moves to the back surface of the cathode, but a portion of the hydrogen gas remaining between the anode and the anode diffuses to the anode side as it rises in the electrolyte and combines with fluorine gas. do. The reason why the partition walls are slightly immersed in the electrolyte is to effectively prevent these problems.

Even in the case of the electrolytic cell of the present invention, when the depth of obstruction of the cathode is large, out of the hydrogen gas generated from the bottom of the cathode,
A large proportion of the hydrogen gas that is not sucked backwards diffuses toward the anode side 1 while moving up the front surface of the cathode. In this case,
In order to increase the suction effect to the back surface of the cathode, it is preferable to have a ridge protruding from the front surface of the cathode.

FIG. 8 shows a partial cross-sectional view of the electrolytic cell of the present invention in which a casing is installed on the cathode.

In FIG. 8, the rib 8 is attached to the lower surface of the louver blade so as to protrude in front of the cathode. This area is not necessarily the bottom surface of the louver blade, but it is also possible to attach it to the top surface, but since the top surface of the louver blade functions more effectively as an electrode surface compared to the bottom surface, the area is It is best to attach it to the underside of the blade. Unfortunately, there is no need to limit the material for this part, but
From the viewpoint of heat resistance, chemical resistance, etc., it is preferable to use a fluororesin coating. Alternatively, it may be made of metal, and its surface may be covered with a sheet or coated.

This fluororesin sheet can be bonded to the blade using an adhesive, for example. In addition, it is practical to identify by inserting one piece into one and by tightening bolts. Even if the immersion depth of the cathode is large, it is of course necessary to provide this area for each blade, and under normal operating conditions where the electrolytic current density is 15 A/dm2 or less, it is necessary to provide 1 area per immersion depth of 25 crn. One or two pieces is enough.

If the number of legs is large, the effective area of the electrode will be reduced, so it is not preferable to provide more than bi.

In addition, if the negative electrode is a perforated member such as expanded metal or punched metal, a fitting with a connecting part that can be fitted into the member constituting the perforation is fitted into the member. You can attach it with.

Next, the present invention will be explained in more detail with reference to Examples.

Example I In the center of an iron container lined with PTIFEli resin (inner volume: 25 crn in length, 30 crr in width, 100 z in height), a container measuring 5 cm in length, 20 m in width, and 6 in height was connected to a positive power source.
A 5- carbon plate was installed as an anode.

Next, a louver like the one shown in Figure 2 was installed as a shade. In other words, an iron blade with a thickness of 511II11 and a parallelogram cross section cut out from an iron plate with a thickness of 5cm is 45mm.
They were arranged at 7.07 inertia intervals so as to have an inclination angle of .degree. (
In Fig. 2, a = 7.07 M) A louver was installed as a cathode, separated by 10 mm from the inner surface of the iron container. The thickness of the cathode (louver 1) was 15 haze.

Based on the area of the visible part of this cathode when viewed from the sun, the ratio of the area that is 45° or more and 90° or less with respect to the horizontal plane is 100 cm, and the ratio of the area that is 45° or more and less than 90° is 58.5%.

Next, as a partition wall, a flat plate made of Monel was placed exactly in the middle between the anode and the cathode so that the immersion depth in the electrolyte was 7 cW1.

In the electrolysis described above, the molar ratio of hydrofluoric acid and potassium fluoride is 2.
:1 double salt (melting point 70°C) was immersed in the cathode at a depth of 55°C.
Then, the temperature of the electrolytic cell was set to 90°, and the current density was 12A/dn? between the anode and cathode. Direct current was applied to perform hydrofluoric acid electrolysis.

The current efficiency was 99% and the sliding voltage was 9.8 .

Example 2 As a cathode, the major diameter of the opening is 20wn, and the minor diameter of the opening is 1011
A test was carried out in the same manner as in Example 1, except that an iron expanded metal with a linear shape of 2wI x 5gours was used.

Furthermore, based on the area of the visible part of this cathode as seen from the cathode, the ratio of the area that is 45° or more and 90° or less with respect to the horizontal plane is approximately 66 degrees, and 45° or more and less than 90°. The area ratio is about 52%.

Further, the current efficiency was 98 cm, and the sliding voltage rp was 9.9 V.

Example 3 In Example 1, the immersion depth of the cathode was 55 Crn,
In addition, a thin Teflon plate is placed on the lower surface of the cathode louver blade in front of the cathode. Oc1n protrusion, ・As shown in the figure, there are 2 points at about 5 crn and about 20 crn from the lower end of the cathode.
Electrolysis was carried out in the same manner as in Example 1, except that it was attached with bolts at the following locations.

Further, the current efficiency was 100%, and the sliding voltage was 9.8V.

Further, when the current density was increased to 18A/1i, 5, the current efficiency was 98chi. Next, the Teflon thin plate was removed and comparative measurement was performed using current density I BA/dmj, and the current efficiency was 93.5%.

The effect of the thin mounting plate is noticeable in areas with high current density.

Comparative Example As a conventionally used electrolytic cell, an iron container (inner volume 2
2.5crnX 30mX 100m) as a cathode,
A carbon plate measuring 20 cm x 650 cm was prepared as an anode. (The distance between the anode and cathode was made to be the same as in Example 1.) When electrolysis was otherwise carried out in the same manner as in Example 1, fluorine and hydrogen association occurred in the electrolytic chamber, resulting in a large amount of residual gas. As a result, the current efficiency was as low as 83%, and the sliding voltage was as high as 103V.

[Brief explanation of drawings]

FIG. 1 is a half-cut sectional view of an example of the electrolytic cell of the present invention. FIG. 2 is a partially enlarged view of the cathode in FIG. 1. Third
The figure is an enlarged partial sectional view of another preferred cathode of the electrolytic cell of the present invention. FIG. 4 is a front view from the anode side when the cathode of the electrolytic cell of the present invention is made of expanded metal. FIGS. 5, 6, and 7 are partially enlarged cross-sectional views of the section AA in FIG. 4 when the cathode used in the electrolytic cell of the present invention is an expanded metal. Figure 8 is a partially enlarged cross-sectional view of the cathode when a louvered shade of the electrolytic cell of the present invention is provided with a sill. 1... Anode 2... Cathode 3... Partition wall (skirt) 4... Cooling jacket 5... Electrolytic chamber 6... Visible part of the cathode seen from the anode side Unit 7... From the anode side Visible part of the cathode seen 8... 异sai / sai 'circumference 73 1 n 1 bowl; 5° 5! 3 - j@C1688 (6) sai 4r
I sai, closing 7 otrr t7■／ ／ ／ 3 sae

Claims (1)

[Claims] (1) Hydrofluoric acid and a fluorine-containing salt are supplied to an electrolytic chamber formed between an anode and a cathode in which a partition wall (skirt) is provided on the surface of the electrolytic solution to prevent mixing of fluorine gas and hydrogen gas. An electrolytic cell for fluorine generation characterized in that the electrolytic cell moves to the back side (the side opposite to the anode). (2) The cathode should be placed at an angle of 45° or more with respect to the horizontal plane, with the area of the cathode in the visible part when viewed from the anode side being the standard area.
The area of the cathode surface at 0° or less is 50% or more of the reference area, and the area of the cathode surface at 45° or more and less than 90° with respect to the horizontal plane is 20% or more of the reference area. The electrolytic cell for fluorine generation described in (1). (8) The electrolytic cell for fluorine generation according to claim 1 or 2, wherein the cathode is louvered or expanded metal. (4) The electrolytic cell for fluorine generation according to claim (2), wherein the horizontal thickness of the cathode is 0.1 to 5 mm. (6) The electrolytic cell for fluorine generation according to claim (1), wherein a partition wall (skirt) between the anode and cathode is immersed in an electrolytic solution between the anode and cathode. (6) Any one of claims (1), (4), or (5) in which the space behind the cathode (distance between the cathode/back surface and the tank wall) is 0.3 to 2 cm. Electrolytic cell for fluorine generation. ('7) The electrolytic cell for fluorine generation according to any one of claims (1) to (8), wherein an eave is provided at the cathode or below the cathode.