JPS59229487A - Electrolytic cell for generating fluorine - Google Patents

Abstract

PURPOSE:To electrolyze a hydrofluoric acid to fluorine and hydrogen with excellent electrolytic current efficiency by constituting the cathode in a diaphragm-less type electrolytic cell which electrolyzes the hydrofluoric acid to fluorine and hydrogen into a specific shape so that the re-reaction of the formed fluorine and hydrogen is prevented. CONSTITUTION:A hydrofluoric acid and a salt contg. fluorine are supplied into an electrolytic cell which has an anode 1 formed of carbon and a cathode 2 formed of a louver-shaped or expanded metal, has a skirt 3 between the anode and cathode and above the cathode and is provided with a porous diaphragm consisting of a woven sheet of C or Al in proximity to the cathode. Electricity is conducted to the anode 1 and the cathode 2 to electrolyze the hydrofluoric acid so that gaseous fluorine is generated at the anode and gaseous hydrogen at the anode. The cathode inclines to 45- 90 deg. relative with the horizontal plane. The gaseous hydrogen generated at slopes 8 and perpendicular surfaces 7 ascends on the outside of the cathode along the slopes. Since the contact of said gas with the gaseous fluorine is prevented by the skirt 3 when the gaseous hydrogen diffuses on the liquid surface, the fluorine is recovered from the anode with high electrolytic current efficiency without inducing the reaction to return the fluorine and hydrogen again to the hydrofluoric acid.

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

A non-diaphragm electrolytic cell supplies hydrofluoric acid and a fluorine-containing salt to an electrolytic chamber without a diaphragm between the anode and cathode, and electrolyzes it. However, in conventional electrolytic cells, the generated fluorine and hydrogen may combine in the electrolytic chamber and return to hydrofluoric acid, resulting in a decrease in current efficiency and a large amount of generated gas (fluorine gas and hydrogen gas) on or near the electrode surface. This has the disadvantage that it "shields" the surface and causes an increase in electrolytic voltage due to a decrease in the apparent effective electrode area. To deal with this, it is necessary to install a skirt between the anode and cathode to prevent hydrogen and fluorine from mixing, to increase the distance between the anode and cathode, to shorten the immersion depth of the electrode, or to install a skirt such as monel between the anode and cathode. A metal mesh with high corrosion resistance was provided to prevent the mutual diffusion of air bubbles.

However, in the former method, the sliding voltage increases due to the large distance between the electrodes, and the effective electrode area decreases due to the small immersion depth of the electrodes. The disadvantage was that it was less.

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

As a result of various studies on ways to overcome all of the above-mentioned drawbacks of conventional electrolytic cells, the inventors of the present invention 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. In an electrolytic cell for fluorine generation, in which fluorine and hydrogen are generated by electrolysis, the cathode is open-pored and most of the gas moves to the back side (opposite the anode); The object of the present invention is to provide an electrolytic cell for fluorine generation, characterized in that a diaphragm is provided close to or in contact with the cathode surface.

Of course, the purpose can be fully achieved even without the above-mentioned diaphragm, so a patent application for an electrolytic cell without a diaphragm has already been filed in 1988-1983.
Although the invention was filed as No. 477, the present invention was made based on the discovery that the effect can be greatly increased by further using a diaphragm in combination with this invention.

The cathode used in the present invention differs from the flat cathode that has been used in the past (in the past, the wall of the electrolytic cell was often used as the cathode). It is characterized by being like moving to the opposite side).

In other words, since hydrogen generated on the cathode surface quickly moves to the back surface of the cathode through the openings in the cathode, fewer bubbles remain near the cathode and diffuse toward the anode, resulting in hydrogen rising on or near the anode surface. Alternatively, floating fluorine gas bubbles and diffused hydrogen gas bubbles are less likely to associate and react, making it possible to maintain high current efficiency.

Furthermore, hydrogen moves to the back surface of the cathode, and between the anode and cathode,
In particular, the amount of gas remaining in the vicinity of the cathode surface is extremely reduced, and the sliding voltage does not increase due to the adhesion of bubbles on the cathode surface or shielding, so the effect of lowering the sliding voltage can be obtained compared to the conventional case.

The inventors of the present application further investigated the cathode having the above effect 1, and found that the above object is 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. 1 is an anode made of carbon, for example, and 2 is a cathode.

3 is a partition wall (skirt), 4 is a cooling jacket, 5 is an electrolysis chamber, and 6 is a diaphragm.

In FIG. 1, the cathode has a louver shape, and FIG. 2 shows a partially enlarged view of the cathode in FIG. 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. Figure 3 shows the louver shape of the cathode in the electrolysis of the present invention.
Another preferred embodiment is shown in which 7 is slightly inclined toward the back of the cathode.

In this case, gas is more likely to escape to the back side of the cathode.

The mechanism by which hydrogen generated at the cathode escapes to the back surface of the cathode along the gaps between the blades will be explained below.

That is, the hydrogen gas generated at the portion 8 in FIG. 2 moves toward the upper right in the figure, and the stain-resolving solution also moves toward the upper right due to the gas lift effect. At this time, most of the hydrogen gas generated at the part 7 enters the gap between the blades due to the suction effect and moves to the upper right part of tl.

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.

That is, the area of the visible part when looking at the cathode from the anode side (the sum of the vertical part 7 and the inclined part 8 shown by the thick line in FIG. 2) is the reference area, and the area is 45 degrees or more with respect to the horizontal plane.
When the area of the cathode surface at 0° or less is 50 times or more of the standard area, and the area of the cathode surface at 45 degrees or more and less than 90' with respect to the horizontal plane is 20 times or more of the standard area, hydrogen is added to the back surface of the cathode. It is easy for gas to move most effectively, and if the above range vh deviates, hydrogen gas will not necessarily escape to the back surface of the cathode.

Here, the angle between the cathode surface and the horizontal plane is measured by the angle between the cathode surface and the horizontal surface of the upwardly sloped 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, (4) Cathode area of the visible part seen from the anode - (a + Q
l) b φ) Area of the cathode surface that is 45° or more and 90° or less with respect to the horizontal plane = (a + 0 - a) b (0) Area of the cathode surface that is 45° or more and less than 900 with respect to the horizontal plane = 51b However, Ratio of (B) to (A) tiloO%
, the ratio of (0) to France) is fab/(a+1a)b
In other words, it is 58.5 yen.

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 expanded metal cathode viewed from the anode side.

5, 6, and 7 show cross-sectional views taken along the line AA in FIG. 4.

Fig. 5 shows a case where the member forming the opening in the expanded metal has a square cross-sectional shape with one side of a, and Fig. 6 shows the case where the member is mm2! L1 other side 31! It has a rectangular cross-sectional shape consisting of L, and the long side (9) 3a is inclined upward toward the back surface of the cathode.

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 the cathode surface of 45' or more and 90° or less = 50%.
The ratio of the area of the cathode surface that is 45° or more and less than 90' = 50 factor, and in the case of Figure 6, the ratio of the area of the cathode surface that is 45° or more and less than 90° = 60 factor 45° or more, 90 The ratio of the area of the cathode surface less than 60 degrees is calculated.

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 greater the thickness of the cathode in the horizontal direction, the greater the effect of drawing in bubbles, but if the cathode is too thick, the resistance to passage of bubbles and electrolyte increases, and the amount of bubbles that escape to the back of the cathode decreases. Therefore, the thickness is 3a in the case of FIG.

σa in the case of M5 diagram sJa/2 in the case of Figure 6) Fi
o, preferably about 1 to 5 etn, more preferably 0.5 to 3 (
10) A good level of preparation is preferred.

This electrode can be used in various types of electrolytic cells, but in the electrolytic cell of the type shown in Figure 1, a strong upward flow occurs in the passage formed on the back of the cathode, which also increases the suction effect. be.

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.
11, preferably 40 to 80 inches. Also,
When the openings are arranged with regularity, the number of repeating units is preferably 3 to 25 squares, more preferably 5 to 15 squares.

In the electrolytic cell of the present invention, the distance between the back surface of the cathode and the cell wall does not need to be particularly limited, but if this distance is too large, the above-mentioned suction effect will be reduced, and the cooling effect from the cell wall will be due to mere natural convection. If the cooling effect is too small, the resistance to the rise of hydrogen gas discharged to the backside of the cathode will increase, inhibiting the suction effect of gas bubbles and electrolyte. Therefore, the above distance is 0.3 to 4.5 mm, depending on the amount of current flow (that is, the amount of hydrogen gas generated), the immersion depth of the cathode, etc.
It is preferable to set it to about 0-1, and more preferably about 0.5 to 2.0.

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 electrolyte, but extending the partition wall slightly into the electrolyte can achieve the full effect described above. sell.

It is preferable that the partition wall be immersed to a slight depth below the surface of the electrolytic solution.In the case of the electrolytic cell of the present invention, the fluorine gas generated at the anode rises along the electrode surface, but does not reach the surface of the electrolyte. Diffusion toward the cathode occurs in the vicinity. 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 cathode diffuses toward the anode as it rises in the electrolyte and combines with fluorine gas. The reason why the partition walls are slightly immersed in the electrolytic solution is to prevent these problems.

Even in the case of the electrolytic cell of the present invention, when the immersion depth 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 while moving up the front surface of the cathode. In this case, in order to increase the suction effect to the back of the cathode, a wall (
It is best to make the eaves protrude.

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 louver blade 9Fi is attached to the lower surface of the louver blade so as to protrude in front of the cathode. This area is not necessarily attached to 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. Further, the material of this part is not particularly limited, but it is preferably made of fluororesin from the viewpoint of heat resistance, chemical resistance, etc. Alternatively, a material made of metal 03) whose surface is covered with a sheet or coated may also be used.

This fluororesin sheet can be bonded to the blade using an adhesive, for example. In addition, fixing by insertion and fixing by bolting are also practical. Moreover, even if the immersion depth of the cathode is large, it is of course not necessary to provide this area for each blade.
Is the electrolytic current density 15A/dfr? Under the following normal operating conditions, one to two pieces per immersion depth of 25 tM1 are sufficient.

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

In addition, if the cathode is a perforated member such as expanded metal or punched metal, a connecting part that can be fitted into the member constituting the perforation should be provided, and the nine legs should be fitted into the member. All you have to do is attach it.

Even in an electrolytic cell that takes into account the various considerations described above, in order to further increase the current efficiency, it is necessary to provide a diaphragm near or in contact with the anode side surface of the cathode. This diaphragm can almost completely block out fluorine that may approach the cathode, albeit in a small amount.

This diaphragm needs to be able to allow the electrolyte to flow through it, and for that purpose it is preferably porous. Furthermore, since this diaphragm may come into contact with generated fluorine gas, it is preferably fluorine-resistant.

As such a porous and fluorine-resistant diaphragm, carbon cloth, aluminum wire mesh, etc. are preferable, and in some cases, fluororesin fabrics such as polytetrafluoroethylene cloth can also be used.

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

Example I Iron container lined with FTIFm resin (inner volume, length 25
A carbon plate connected to a positive power supply and measuring 5 mm long, 20 mm wide, and 65 mm high was installed as an anode in the center of the test tube.

α5) Next, a louver as shown in FIG. 2 was installed as a cathode. In other words, a 5 m thick iron blade with a parallelogram cross section cut out from an iron plate with a thickness of 511II++ is
They were arranged at intervals of 7.07° so that the angle of inclination was 7.07°. (
In Fig. 2, a = 7.07 van) A louver was used as a cathode and was placed 10 flllfi away from the inner surface of the iron container. The thickness of the cathode (width of the louver) was set to #1155w.

Based on the area of the visible part of this cathode as seen from the anode, 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 It is 58.5%.

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

Next, a carbon cloth measuring 21 m x 67 cy++ and having a thickness of 1 mm (porosity: 35 mm) was placed in contact with the anode side surface of the cathode.

In the electrolytic cell as described above, the molar ratio of hydrofluoric acid and potassium fluoride is 2:
The double salt No. 1 (melting point 70°C) was added so that the immersion depth of the cathode 06) was 55cm In, and the temperature of the electrolytic cell was raised to 90°C.

Next, a direct current is passed between the anode and cathode at a current density of 14 A/-,
Hydrofluoric acid electrolysis was performed.

In addition, current efficiency Fi9991, sliding voltage #'i9.8V"
There was t'.

Example 2 As a cathode, the major diameter of the opening is 20 mm, and the minor diameter of the opening is 10111.
A single-wire 2m x 5mm iron expanded metal is used as a diaphragm with a wire diameter of 0.5mm. ．． Hydrofluoric acid electrolysis was carried out in the same manner as in Example 1 except that a 20-mesh aluminum wire mesh was used.

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

Further, the current efficiency was 98% and the sliding voltage was 969v.

Example 3 In Example 1, the immersion depth of the cathode? 55111α7) Attach a thin Teflon plate to the bottom of the cathode louver blade so that it protrudes 1.0cn1 from the front of the cathode, and bolt it to two places, one about 5ctn and about 20crn from the bottom end of the cathode. Electrolysis was carried out in the same manner as in Example 1, except that the same carbon cloth diaphragm as in Example 1 was placed at a distance of 1 cIn from the cathode surface.

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

Further, when the current density was increased to 22 A/-, the current efficiency was 98 cm. Next, when the Teflon thin plate was comparatively measured at a current density of 18 A/- after removing the sediment force, the current efficiency was 93.51.

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
2.53X 30tMX 100f
A fiX 20crnX 65m carbon plate as an anode was prepared. (The distance between the anode and cathode was set to be the same as in Example 1a8). ) Other than that, electrolysis was carried out in the same manner as in Example 1, but due to association of fluorine and hydrogen in the electrolysis chamber and a large amount of retained gas, the current efficiency was as low as 83% and the sliding voltage was 10.3V. it was high.

[Brief explanation of the drawing]

FIG. 1 is a half-mounted 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 of the electrolytic cell of the present invention when the cathode is made of expanded metal when viewed from the anode side. 5, 6, and 7 are partially enlarged cross-sectional views taken along the line A-A in FIG. 4 when the cathode used in the electrolytic cell of the present invention is an expanded metal. FIG. 8 is a partially enlarged sectional view of the looper-type cathode of the electrolytic cell of the present invention in which a rim is provided. 1... Anode 2... Cathode 3... Partition wall (skirt) (19) 4... Cooling jacket 5... Electrolytic chamber 6. ...Diaphragm 7... Visible part of the cathode viewed from the anode side 8...
...Visible part of the cathode seen from the anode side 9...20 (20), For t4 Kawasai 5 Kawa O6 For off. Age 8) Shoulder. Procedural amendment format) % formula % 1. Indication of the case Patent Application No. 102883 filed in 1988 2. Name of the invention Electrolytic cell for fluorine generation 3. Person making the amendment Relationship to the case Patent applicant address Chiyoda, Tokyo Ward Marunouchi 2-1-2 Name
(004) Asahi Glass Co., Ltd. 8, Contents of the amendment: Reprint of the specification and drawings (no changes to the contents), as shown below: 439-

Claims (9)

[Claims] (1) Hydrofluoric acid and a fluorine-containing salt are supplied to an electrolytic chamber formed between an anode and a cathode, which is provided with a partition wall (skirt) on the surface of the electrolytic solution to prevent mixing of fluorine gas and hydrogen gas, and is electrolyzed to produce fluorine gas. In the electrolytic cell for fluorine generation that generates hydrogen, the cathode is open-pored and most of the gas moves to the back side (the opposite side to the anode), and the cathode is close to or near the cathode side facing the anode. An electrolytic cell for fluorine generation, characterized in that a diaphragm is provided in contact with the cell. (2) The cathode shall be placed at an angle of 45° or more and 90° with respect to the horizontal plane, using the visible area of the cathode when viewed from the anode side as the reference area.
The area of the following cathode surfaces is 50% or more of the reference area, and the area of the cathode surfaces at an angle of 45 degrees or more and less than 90 degrees with respect to the horizontal plane is 20 times or more of the reference area.
) Electrolytic cell for fluorine generation. (3) The electrolytic cell for fluorine generation according to claim (1) or (2), wherein the cathode is looper-shaped or expanded metal. (4) The electrolytic cell for fluorine generation according to claim (2), wherein the cathode has a horizontal thickness of 0.1 to 5 cn1. (5) 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) Space behind the cathode (distance between the back of the cathode and the tank wall)
Claim (1), wherein is 0.3 to 2 crR;
The electrolytic cell for fluorine generation according to either paragraph (4) or paragraph (5). (7) The electrolytic cell for fluorine generation according to any one of claims (1) to (3), wherein the cathode has an eaves provided at its lower part. (8) The electrolytic cell for fluorine generation according to claim (1), wherein the diaphragm is a porous diaphragm having fluorine resistance. (9) Claim No. 8, wherein the fluorine-resistant porous diaphragm is a woven carbon or aluminum sheet.
Electrolytic cell for fluorine generation.