JP4403463B2 - Single / bipolar electrolyzer - Google Patents

Description

The present invention relates to a large-scale bipolar molten salt electrolyzer for obtaining gas from an anode and metal from a cathode mainly by electrolysis.

Metal extraction by electrolysis is currently widely performed by aqueous solution electrolysis of sulfates represented by zinc and copper and aqueous solution electrolysis of chlorides such as cobalt and nickel. In titanium production, metal production by electrolytic reduction of magnesium chloride produced by using titanium salt for reduction is performed by molten salt electrolysis. Well-known aluminum is produced by high temperature molten salt electrolysis of aluminum oxide. In recent years, as a low-cost production method for silicon, which has been tightened with the demand for solar cells, a production method by reduction of silicon tetrachloride with zinc has been studied. For this purpose, the recycling of zinc used is an important factor in determining the process. It is an element, and molten salt electrolysis of zinc chloride is indispensable, and studies for that purpose are being conducted. In these electrolysis, various electrolysis methods are performed by changing the conditions depending on the electrolysis conditions.

In many industrial electrolytic cells, an electrolytic solution tank and an electrode / electrolytic part are integrated, and in general, leakage current associated with electrolysis is solved in the entire system. In small metal sampling electrolyzers, it is often the case that electrolysis is performed by immersing the electrode / electrolysis part in the electrolytic bath, but in most cases a plurality of electrodes are connected in parallel, and there is no leakage current. Electrolysis is performed in a polar manner. In the case of molten salt electrolysis, even if there are usually multiple anodes in the electrolytic cell, the cathode should have a relatively simple configuration such as the bottom only, and the distance between the electrodes is also relatively large. there were.

However, in the case of the electrolytic process to be put into the chemical process, the chemical process itself is relatively small, but the electrolytic cell is inevitably large and the unbalanced area is unbalanced. In particular, in hot molten salt electrolysis, there are major problems such as heat retention in the liquid feeding section and pump selection. In reality, however, energy loss is large, but electrolysis is performed by electrolysis alone and connected to other processes. Therefore, continuous operation is not performed.

The present inventors have proposed a bipolar electrolysis apparatus that incorporates a new electrolysis method for electrolysis of molten zinc chloride. Patent Document (1) Here, leakage current which is a problem in a bipolar electrolytic cell is prevented by attaching an electrode frame around the electrode, and the electrode frame serves as a heat insulating material, so that the temperature of the electrolysis portion is substantially increased and the electrolyte solution In addition to reducing the liquid resistance of the electrolytic portion of the electrolyte, it is possible to minimize electrolyte vapor and mist, which are the most problematic in molten salt electrolysis, by relatively lowering the electrolyte surface temperature. In the bipolar electrolyzer, the shape of the current-carrying body is relatively simple, but the voltage applied to the electrodes increases, and there is a problem that the leakage current increases rapidly as the number of bipolar electrodes increases. In order to prevent this, the electrode frame inevitably becomes larger, and depending on the conditions, there is a problem that it becomes larger than the electrode itself.

For this reason, in the case where the electrode portion is immersed in the liquid tank, a large bipolar system has not been performed. In particular, in aqueous solution electrolysis, metal electrodes are often used, and since the power feeding body is relatively simple, power feeding is complicated, but the monopolar method has been widely used. On the other hand, even in molten salt electrolysis, since the scale is usually small, there are many cases where a single-pole method is used. It wasn't. Although the leakage current is reduced by attaching an electrode frame as a technique by the inventors as described above, there is a trade-off between the size of the electrode and the current in order to minimize the leakage current. There is a need to keep it 10 or less, and the voltage between the electrodes at both ends is often 30 V or more, and there is a problem that the electrode frame has to be enlarged in order to suppress the leakage current.

In molten salt electrolysis, it is important to control the electrolyte mist generated along with the electrolysis, and the present inventors attach a large mist catcher particularly when the electrodes are densely present in the molten salt electrolysis and the gas corresponding to the mist catcher. Proposes to control the ascent rate. (Patent Document 2) The use of this technique is particularly important. Particularly, when a large number of electrodes are concentrated, such a technique is essential because a large amount of gas is generated while entraining mist. However, in order to use such a mist catcher, it is necessary to make the conductive member around the electrode, especially above the electrode as simple as possible, and for that purpose, it is necessary to simplify the structure for energizing the electrode.

JP 2005-200759 A JP-A-2005-200758

In the present invention, the electrolytic cell is mainly used for performing large-scale electrolysis by immersing the electrolytic unit in the liquid, minimizing the leakage current and simplifying the current-carrying structure on the electrode, thereby reducing the size of the electrolytic cell. In addition, another object of the present invention is to provide an electrolytic unit structure for minimizing the influence of mist generated by electrolysis .

In the present invention, electrolysis is performed by immersing an electrode group formed by connecting a plurality of multipolar units as a single electrode and an electrolytic unit composed of an electrode frame structure around the electrode in one electrolytic bath or by attaching it to a bath . a electrolytic cell for electrolytic processes, side plate electrode frame structure with connecting electrodes in the electrolytic unit is to be connected in parallel electrically a plurality of units connected to the bipolar consists blind plate And an electrode frame for regulating the current provided above and below the electrode body , which is a single / bipolar type electrolytic cell that prevents leakage current and keeps the electrolytic part warm. While simplifying the connection, the leakage current, which is a problem when a large number of electrodes are installed in one electrolytic bath, is minimized, and the electrolytic cell itself is made compact and large-scale electrolysis is possible. I was able to do it.

This will be described in detail below.
In other words, when the metal produced mainly by molten salt electrolysis, especially metal extraction electrolysis, has a higher specific gravity than the electrolytic bath, the metal produced by electrolysis falls downward in the liquid and the gas produced at the anode escapes upward. In addition, no electrolytic product remains around the electrode. Further, in the direct electrolysis of molten salt, since the electrolytic bath itself is an electrolyte, the electrolytic reaction itself does not change because the electrolyte is always supplied even if the product falls vertically. Of course, when a supporting electrolyte is used, since the viscosity of the liquid is generally reduced, the supply of the electrolytic substance becomes very fast, and the problem of supply of the electrolytic substance between the electrodes hardly occurs. In addition, in the case of aqueous solution electrolysis, for example, in the case of copper powder production, the copper powder as the cathode product falls down without staying on the cathode surface, and the anode generation gas escapes upward, so that it is the same as in molten salt electrolysis. It can be handled. In order to perform electrolysis most efficiently for these, it is necessary to optimize the electrolysis current density and minimize the voltage. For this purpose, it is essential to minimize the distance between the electrodes, keep the electrolysis voltage low with an appropriate current density, and minimize the re-reaction of the electrolysis product to increase the electrolysis efficiency.

In order to achieve these, the electrolytic cell of the present invention includes a large number of small electrodes to keep the electrolytic current density properly, to simplify the conductive structure to the electrodes, and to add more electrodes. The aim was to improve the energy efficiency by minimizing the expansion of the electrolytic cell size and minimizing the escape of heat, especially in the case of high-temperature molten salt electrolysis. As a matter of course, we aimed to further improve the current efficiency by minimizing the leakage current. In order to achieve this, here, a large number of electrodes with a small distance between the electrodes are incorporated in one electrolytic cell. In other words, a plurality of multipolar connections in which the number of multipolar stages is limited with respect to electrode connection so that the leakage current is minimized while miniaturizing the electrode frame around the electrodes, and the plurality of multipolar units are connected in a single pole, The electrolytic cell structure of the present invention was completed by providing a simple conductive structure so as to be arranged in one electrolytic cell.

For example, it is assumed that the total current is 4500A in the case of molten zinc chloride direct electrolysis, and the size of one electrode is regulated to a width of 10 cm and a height of 30 cm. This capacity corresponds to 45 tons / year of chlorine production, and in the case of zinc reduction silicon production, it corresponds to 9 tons / year of silicon production capacity. At this time, if the current density is 50 A / dm 2, 30 stages of electrolysis are required. Here, when the temperature of the zinc chloride is 550 ° C., the electrical resistance of the zinc chloride is about 8 Ωcm, and when the electrode height is 30 cm and the distance between the electrodes is 5 mm, the electrolysis voltage is 2. at the current density of 50 A / dm2. It is 5-2.7V. Considering a 10-stage double pole at this time, the leakage current can be reduced to about 3% by providing a frame having a gap of 5 mm above and below the electrode and an electrode frame height of 10 cm, that is, a total of 20 cm above and below the electrode. At this time, when the electrode frame having the same height is used in the case where the whole is integrated into 30 stages, the leakage current becomes about 10% or more. In order to make this leakage current the same as in the case of 10 stages, the frame height is about 60 cm above and below, and an electrode frame much larger than the electrode is required. You will have problems with the supply.
In order to avoid this, it is necessary to reduce the electrode frame to about 10 cm and to conduct a large current electrolysis with a large number of electrodes. For this purpose, the problem can be solved by arranging three sets of 10- pole multipolar units so that the electrodes having the conductors at the ends (end electrodes) are shared. In other words, if there are 30 stages as shown here, by connecting three 10-stage multipolar units in parallel, two of the end electrodes are common to the two units, so the end electrodes, that is, the electrodes having a conductor are 4 In other words, the electrode frame may be sufficiently small.
On the other hand, if all are single poles, the number of electrodes is 31, and 31 conductors are required.
Also, in the case of a 30-stage double pole, there are two end electrodes having a conductor, and although the structure is simple, the electrode body with the electrode frame as described above becomes extremely large. There is a problem that handling becomes very difficult. Here, 10-stage double pole x 3 single-pole connection is used, but this is only an example, and it goes without saying that the number of stages and division into single poles may be performed as necessary.

For example, in this example, molten zinc chloride is used. However, when an alkali with a small electrical resistance is used as the supporting electrolyte, the leakage current increases by a small amount corresponding to the electrical resistance. Although it is necessary to reduce the number of unit stages , this may be determined depending on the electrolytic bath used and the electrode scale. As an example, when a mixture of potassium chloride and sodium chloride is added to this, the electric resistance of the electrolytic bath can be reduced to about 4 Ωcm by half. Or double the height of the frame to prevent this case leakage current, the purpose can be achieved if as halve the number of bipolar unit stage. In normal electrolysis, it is desirable that the electrolytic bath resistance is small, but this also leads to the result that it is desirable to have an appropriate electrical resistance in terms of leakage current.
Of course, these are the same in aqueous electrolysis, and by making good use of the relationship with the liquid resistance, electrolysis can be performed with the minimum leakage current.

Such connection is particularly effective when the electrode is relatively low in electrical conductivity, such as graphite or conductive ceramics, and the conductive member is large and easily complicated.
Of course, even in such a case, it is necessary for each electrolytic unit to satisfy the usual electrolysis conditions. For example, in order to prevent the anode generation gas and the cathode product from contacting each other and causing a reverse reaction, the anode must be connected. It is also useful to tilt the entire electrode 5-10 degrees from the vertical with the top side. A large mist catcher is attached to the upper part of the electrolytic cell to liquefy the electrolytic bath component gas accompanying the rising gas and return it to the bath, and to prevent the mist coexisting with the generated gas from coming out. This is particularly important in high-temperature molten salt electrolysis, and the steam and mist that rises above often solidify as the temperature drops, causing gas pipes to become clogged. The mist catcher is not particularly specified, but if possible, it is desirable to directly attach the mist catcher so as to cover the upper part of the electrolytic cell with a large size having a cross-sectional area of 1/2 to 1/1 of the electrolytic cell opening.

By combining a bipolar type and a monopolar type in an electrolytic bath in which an electrolytic unit is immersed in or attached to an electrolytic bath used for metal extraction, particularly metal generation by molten salt electrolysis, according to the present invention. A large number of electrodes can be incorporated into a small electrolytic cell with a minimum conductive structure, and maximum production can be performed with a minimum electrolytic cell scale while maintaining high efficiency.

An embodiment of the invention will be described with reference to the drawings. In other words, FIG. 1 is an example of the arrangement of electrodes placed in an electrolytic cell, having 30 electrolysis units divided into 10 units , connected as a bipolar unit , and having a common end electrode having a conductor. This is a case where the three parts are connected in a single pole type. Although this single-pole unit is 3 to which may be increased further, also it may of course be increased or decreased the number of connections bipolar units as required. Here, it demonstrates along this figure.

Here, 1 indicates the main body of the electrolytic cell, in which a bipolar unit including a plurality of electrodes is placed. This electrolysis unit consists of a combination of a thin electrode group 2 and an end electrode 3 having a thickness and a conductor 5, and each of the thin electrode groups 2 contains nine electrodes for bipolar electrolysis. Together with the end electrodes, it becomes a unit of electrolysis of 10 stages and is connected in a bipolar manner. Since both ends of the central end electrode are used for electrolysis, the number of conductors 5 is increased because a current twice as large as that of the end electrodes at both ends flows.

Here, the end electrodes are connected to each other by the wiring 6 and are connected to the power source 4. In this case, a total of 30 electrolysis parts are provided, but the electrolysis voltage corresponds to 10 cells in the electrolysis part. That is, if 1 cell is 3V, it becomes 30V. With this arrangement, an electrode frame for preventing leakage current is attached to each electrode. Considering the case of the same leakage current, the height of the electrode frame can be reduced to 1/3 or less only at both ends as compared with the case of using a double pole as it is. Moreover, it is no longer necessary to handle dangerous high-voltage direct current. Certainly, the arrangement of the conductors is complicated, but the degree is small and acceptable. Course here to be three side-by-side model view it as a bipolar 10-stage, depending on the liquid resistance of the electrolyte to be able to increase or decrease the number of bipolar stage, can increase or decrease the number of end electrodes by a scale . For example, in the direct electrolysis of molten zinc chloride, the resistance of the electrolytic solution is about 8 Ωcm, which is relatively large and about 10 steps are suitable. However, if a supporting electrolyte such as a mixed salt of potassium chloride and sodium chloride is added to this, it is markedly different. since liquid resistance drops, it is necessary to take a method such as attaching to or greater pole frame increases the number of end electrodes by reducing the number of bipolar stage accordingly.
Examples will be described in detail below.

Example 1
An electrolytic cell arranged as shown in FIG. 1 was produced. That is, the electrolytic cell main body was made of a dense graphite plate having a thickness of 30 mm, coated with ceramic cement prepared by kneading mullite powder for insulation and water glass inside, and fired at 600 ° C. to form an insulating coating. Dense graphite produced by CIP method was processed and used for the electrode for electrolysis. The size was 30 cm in height and 10 cm in width, and three 10-stage bipolar units were connected in parallel with the end electrodes in between. In addition, an electrode frame having a height of 10 cm and a gap of 5 mm as the distance between the electrodes was provided above and below the electrodes. The electrolytic bath was made of molten zinc chloride and the temperature was maintained at 550 ° C. When electrolysis was performed at a current density of 50 A / dm 2, the cell voltage was 26 V (for 10 stages), and the leakage current was estimated from the generated chlorine efficiency, and it was found that the leakage current was about 5%. . For comparison, the electrode was left as it was, the conductor was removed, and electricity was applied from both ends to conduct electrolysis as a practically 30-stage multipolar unit. As a result, the electrolysis voltage was 78-79 V, which was measured in the same manner. The leakage current increased to about 30%. Although it should be lower in calculation, it was estimated that the leakage due to the increase in the number of tanks in the middle and the leakage due to the voltage increase were added, resulting in a large leakage current. As a result, it can be seen that by connecting a suitable number of multipole stages and dividing them into single poles, it is possible to perform electrolysis with a sufficiently low leakage current while simplifying the conductor and without enlarging the electrode frame. It was.

"Example 2"
Electrolysis was performed using an electrolytic bath in which mixed alkaline chloride of KCl: NaCl = 1: 1 (mol) was added to zinc chloride as a supporting electrolyte. The electric resistance of this electrolyte is 4 Ωcm at 500 ° C., and the leakage current may become too large under the conditions of Example 1. Therefore, a small electrolytic cell having a small and 10-stage double pole was created and the leakage current was examined. went. The electrolysis up to 10 stages was performed under the same conditions as in Example 1, with the height of the electrode frame for preventing leakage current being 15 cm. Electrolysis was performed using the same size electrode and a current density of 40 A / dm2. The distance between the electrodes was 5 mm. The electrolytic cell current was 120A. The cell voltage was 24 V in 10 steps because the electric resistance was low. The leakage current was about 2A in the upper and lower directions only at both ends, and the total was 2 × 2 × 3 = 12A, which is about 3 times the upper and lower, and the leakage current was about 10%. This changed to the same as the end electrodes of the central electrode relative, was relocated and the electrode such that the bipolar units of five stages on either side, the electrolytic voltage is halved, the leakage current in accordance with the this Decreased to about 3%. Further, here, the measurement was performed by replacing the electrode frame with a lower one of 10 cm, but even in that case, it was found that the leakage current was practically about 4%.

This is a small, high-efficiency, large-capacity electrolytic cell that is most suitable for metal extraction electrolysis, particularly metal extraction by molten salt electrolysis, and also zinc and chlorine gas extraction by zinc chloride electrolysis. Achieved and fully connected to the continuous line for zinc recycling for the production of high-purity silicon by zinc reduction, it is possible to achieve full continuous operation, and it is widely used as energy issues are discussed. I think that it will become.

  It is an example of the electrolytic cell electrode arrangement | positioning of this invention, and is a schematic diagram of a plane.

Explanation of symbols

1 Electrolyzer can body 2 Bipolar unit part 3 End electrode (electrode with conductor)
4 DC power source for electrolysis 5 Conductor connection structure 6 Conductor connection structure of electrolysis electrode and power supply for electrolysis

Claims (8)

For electrolytic treatment in which an electrode group formed by connecting a plurality of multipolar units as a single electrode and an electrolytic unit composed of an electrode frame structure around the electrodes are immersed in a single electrolytic bath or mounted in a bath for electrolysis a electrolytic cell, the side plates and the electrode body electrode frame structure with connecting electrodes in the electrolytic unit is to be connected in parallel electrically a plurality of units connected to the bipolar consists blind plate A monopolar / bipolar electrolytic cell that consists of electrode frames for regulating the current provided above and below the battery, and that is designed to prevent leakage current and keep the electrolytic part warm . The single / bipolar electrolytic cell according to claim 1, wherein the integrated electrolytic unit is fixed in the electrolytic bath. The single / bipolar electrolytic cell according to claim 1 or 2 , wherein the integrated electrolytic unit is immersed in an electrolytic bath. Single-bipolar type electrolytic cell of any of claims 1 to 3, wherein the electrolytic cell is an electrolytic cell for molten salt electrolysis. The adjacent electrode frame has a gap that is equal to or slightly narrower than the distance between adjacent electrodes, and the gap is placed above and below the electrodes so as to substantially match the distance between the electrodes. Item 5. A monopolar / bipolar electrolytic cell according to any one of items 1 to 4 . 6. The monopolar / bipolar electrolytic cell according to any one of claims 1 to 5 , wherein the electrodes are attached in parallel with the electrode frame so as to prevent mixing of the anode product and the cathode product. Single-bipolar type electrolytic cell of claim 1, wherein the electrolytic cell is provided with a mist catcher having a large enough to remove the electrolytic bath vapor and mist in the electrolytic cell top. Melting with chlorine by electrolysis using molten zinc chloride as an electrolytic bath using the single / bipolar electrolytic cell of claim 1 Electrolytic method for obtaining metallic zinc.

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