JPH0571671B2 - - Google Patents

Description

[Detailed description of the invention]

(Field of Application of the Invention) The present invention relates to an electrolytic cell, and more particularly to an electrolytic cell with improved current efficiency. (Background of the invention) The energy efficiency of an electrolytic cell is mainly determined by the overvoltage and current efficiency of the electrolytic reaction, excluding parts not directly related to the electrolytic reaction, such as pump power and energy consumption for heating. . Of these, current efficiency losses include losses due to side reactions that are not the intended electrolytic reactions, and losses due to leakage current flowing through the solution inflow and outflow holes of the stacked electrolytic cell.
The loss due to this leakage current is particularly significant in an electrolytic cell in which single cells are electrically stacked in series. In other words, considering the ease of power supply in this type of electrolytic cell, it is preferable to use high voltage and low current, but if you try to match the electrolytic cell with this, it will require a considerable number of series stacks of single electrolytic cells. (for example, 100 to 500), and as the voltage increases, the proportion of leakage current increases significantly. Some calculations show that increasing the number of layers from 10 to 20 increases the leakage current rate by nearly 2.5 times. Therefore, in order to reduce this leakage current as much as possible and increase the energy efficiency of electrolysis, methods such as inserting air bubbles in the solution inflow and outflow holes, installing a barrier plate, and partially reducing the hole diameter are used. Therefore, attempts have been made to increase the electrical resistance of the solution inflow and outflow holes to reduce the rate of leakage current. However, these measures only reduce the leakage current ratio by half,
No fundamental solution has been reached. In general, in industrial electrolytic cells, the effective electrode area is increased to reduce leakage current and reduce costs by increasing scale. There is. Conventionally, in order to solve this problem, (1) increasing the amount of liquid sent into the tank, (2) installing a pressure plate to distribute the liquid evenly within the electrode chamber, and (3) using only one electrode chamber. Measures such as providing multiple liquid inflow holes are being taken. However, treatment (1) involves an increase in pump power due to an increase in the liquid flow rate, treatment (2) complicates the structure inside the tank, and providing an effective diagonal plate is difficult due to hydraulic problems. It is also difficult. In addition, the measure (3) actually increases the area of the inlet hole relative to the effective electrode area, increasing the leakage current ratio.
This is not a desirable method. On the other hand, as for the structure of an electrolytic cell, it is known that a stack is made up of only a few single electrolytic cells stacked on top of each other, and a large number of these cells are made, and each stack is provided with an inlet and an outlet for each solution. However, this electrolytic cell has problems in terms of efficiency and cost in terms of piping and wiring, as well as the complexity and cost increase in manufacturing the main body. (Objective of the Invention) An object of the present invention is to provide an electrolytic cell that prevents a decrease in efficiency of electrolytic energy due to the above-mentioned leakage current and has excellent equidistribution between the electrolytic cells and within the electrolytic cell. The present invention provides a stacked electrolytic cell in which single electrolytic cells having a positive electrode chamber and a negative electrode chamber surrounded by a frame are electrically stacked in series, in which a plurality of solutions flow into the frame portions of the positive electrode chamber and the negative electrode chamber, respectively. Place the exit hole,
The present invention is characterized in that a pump for causing a solution to flow into the solution inflow/output hole and the solution inflow hole is provided independently for each lamination range whose number is smaller than the total number of laminations. Briefly stated, the present invention is based on a conventional electrolytic cell (cell stack) as shown in FIG. On the other hand, as shown in Fig. 2, a plurality of cells (three in this case) are provided for each of a, b, c, and d, and the total number of cells is divided corresponding to the plurality of holes, and each divided cell is Each part has an inlet and an outlet for liquid. That is,
In the case of the conventional type, a single cathode liquid inflow hole distributes the liquid evenly to 100 cells, but in the present invention, if for example four of the same holes are provided, each hole distributes the liquid equally to 25 cells. It would be a good thing to do. Here, if the cell voltage applied to one cell is 2V, in the conventional type, the voltage applied to both ends of the hole is 200V (one line), which increases the leakage current passing through the hole, but in the present invention, the voltage applied to both ends of the hole is 50V (four lines). Therefore, the leakage current is significantly reduced. The leakage current flowing through this manifold increases at a rate of more than double when the number of cells stacked in series with a common hole doubles, but in the present invention, since the number of stacked cells passing through one hole decreases, The leakage current is reduced accordingly. Furthermore, since the amount of liquid flowing through a single hole is reduced to a fraction of that of the conventional type, the cross-sectional area of the hole can be reduced. These two effects make it possible to significantly reduce the leakage current of the cell stack. As described above, the present invention has a plurality of solution inflow and outflow holes for each of the positive and negative electrodes, so that the number of stacked layers of the single electrolytic cell is effectively kept small. This is the most effective way to reduce leakage current, and if the number of single electrolytic cells stacked in one liquid inflow/output hole is, for example, 10 and the total number of stacks is 100, the conventional method of providing only one liquid inflow/outflow hole is recommended. In comparison, it is possible to prevent a drop in efficiency due to leakage current of 80% or more. In the present invention, pumps are provided respectively corresponding to the plurality of positive and negative electrode solution inflow and outflow holes. This makes it possible to timely adjust the amount of liquid sent by each pump to overcome problems such as increased electrical resistance of the electrolytic cell due to imbalance. That is,
Providing separate pumps for each positive and negative electrode liquid has the effect of preventing leakage current and facilitating equal distribution between single electrolytic cells. In the present invention, a positive pump, each equipped with a pump,
It is preferable to provide separate solution tanks corresponding to the negative electrode liquid inflow and outflow holes. This allows the solution systems to be separated into separate lines, so
In addition to thoroughly preventing leakage current, even if one tank is damaged, the remaining tanks can sufficiently compensate by simply changing the piping. In the present invention, the electrodes in the positive electrode chamber and the negative electrode chamber in the electrolytic cell are preferably made of a conductive material through which a solution can flow, such as carbon cloth, carbon felt, metal net, or the like. (Embodiment of the Invention) An embodiment of the electrolytic cell of the present invention will be described below with reference to FIGS. 3 and 4. FIG. 3 is a sectional view of an electrolytic cell according to the present invention. The components of the single electrolytic cell 1 include a positive electrode chamber 2 having a positive electrode 3, a negative electrode chamber 4 having a negative electrode 5, and a diaphragm 7 provided between the positive electrode chamber 2 and the negative electrode chamber 4. They are stacked in series with a bipolar partition plate 6 in between to form an electrolytic cell. Each electrode chamber is formed by stacking frames, and both sides of the electrolytic cell in which these frames are stacked are fixed by holding plates 12. The frames of the positive electrode chamber 2 and the negative electrode chamber 4 have a positive electrode liquid inflow hole (line) 8 and a positive electrode liquid outflow hole (line), respectively.
9, a negative electrode liquid inflow hole (line) 10, and a negative electrode liquid outflow hole (line) 11 are provided. The electrolytic cell shown in Fig. 3 has a structure in which each of the three single electrolytic cells has one solution inflow hole and one outflow hole. pumps 13A-D and tanks 14A-D are provided. Although each tank and pump can operate independently, it is preferable to have compatibility and common use in consideration of accidents such as breakdowns. The electrodes 3 and 5 in the positive and negative electrode chambers are uniform,
In addition, a liquid-permeable conductor having some resistance to solution permeation is used, specifically, carbon cloth, carbon felt, metal net, sintered porous metal, conductive plate on which metal crystals are precipitated, etc. are used. As mentioned above, by providing separate liquid inflow lines and pumps in the positive and negative electrodes, equal distribution of liquid between the single electrolytic cells is achieved, and by using liquid permeable conductors as electrodes, It is also possible to distribute the liquid evenly within the single electrolytic cell, and most of the leakage current can be prevented. (Effects of the Invention) According to the present invention, solution inflow and outflow holes are provided in the frames of the positive electrode chamber and the negative electrode chamber of a single electrolytic cell, respectively, without providing solution flow holes in the partition plate, the frame of the diaphragm, etc. as in the conventional case. (line), the leakage current flowing through the solution inflow and outflow holes can be significantly reduced.
In addition, by using liquid-permeable conductors as the electrodes in the positive and negative electrode chambers, and by using separate pumps to flow the solution into the positive and negative electrode chambers, it is possible to maintain the same level of liquid within and between the single electrolytic cells. The leakage current caused by the flow of liquid can be minimized. Example 1 The performance of the electrolytic cell having the configuration shown in FIGS. 3 and 4 and two conventional techniques was compared. That is, in an electrolytic cell in which felt-like carbon was used for the positive and negative electrodes of the electrolytic cell, a carbon powder binding plate was used as the bipolar partition plate, a cation exchange membrane was used as the diaphragm, and the number of stacked single electrolytic cells was 20, Conventional electrolytic cell (hereinafter referred to as type) with one solution inlet and one outlet hole each
A conventional electrolytic cell (hereinafter referred to as An electrolytic cell (hereinafter referred to as a mold), which is an embodiment of the present invention, has one hole for every five laminated layers, and is provided with a separate pump and tank corresponding to each solution inflow and outflow hole. We conducted a performance comparison experiment on the following. The flows of the catholyte in the mold (Comparative Example 1), the mold (Comparative Example 2), and the mold (Example of the present invention) are shown in FIGS. 5 to 7, respectively. Note that the flow of the negative electrode liquid is omitted because it is the same as that of the positive electrode liquid. Using each electrolytic cell with such a configuration, the solution contains:
For both the positive and negative electrode solutions, a 0.2 mol/ethylenediamine etracarbonate iron (bivalent, trivalent) aqueous solution adjusted to pH 4 with a phosphoric acid-sodium phosphate buffer solution was used in circulation. A constant current with a current density of 50 mA/cm ² was passed through the electrolytic cell. Table 1 shows the ratio of the amount of change in composition of the positive and negative electrode liquids to the amount of electricity applied after 25 minutes of energization. Note that a polarograph was used to measure the amount of change in the composition of the solution.

[Table] The percentage (%) in the table indicates the current efficiency, and the closer it is to 100%, the better the performance of the electrolytic cell or electrolytic cell system. From this result, an example of the present invention in which solution inflow and outflow holes were provided separately for every five laminated layers, and a separate pump and tank were provided for each solution inflow and outflow hole (
It can be seen that the current efficiency of type ) is the best. In the electrolytic cell of this embodiment, if at least the solution inlet/outlet and the pump are separate, similar effects can be obtained. The present invention can be applied not only to electrolytic cells but also to battery bodies of secondary battery systems using a solution as an active material. Therefore, the electrolytic cell in the scope of the claims of the present application also includes batteries.

[Brief explanation of the drawing]

1 and 2 are schematic perspective views of conventional and inventive electrolytic cells, FIG. 3 is a sectional view of an electrolytic cell showing an embodiment of the present invention, and FIG. 4 is a pump for pumping the liquid. FIG. 5 and FIG. 6 are diagrams showing the flow of the cathode solution in the prior art, and FIG. 7 is a diagram showing the flow of the cathode solution in an embodiment of the present invention. . DESCRIPTION OF SYMBOLS 1... Laminated electrolytic cell, 2... Positive electrode chamber, 3... Positive electrode, 4... Negative electrode chamber, 5... Negative electrode, 6... Multipolar partition plate, 7... Diaphragm, 8... Positive electrode liquid inflow hole, 9... Positive electrode liquid outflow hole, 10... Negative electrode liquid inflow hole, 11... Negative electrode liquid outflow hole, 12... Presser plate.

Claims (1)

[Scope of Claims] 1. In a stacked electrolytic cell in which single electrolytic cells each having a positive electrode chamber and a negative electrode chamber surrounded by a frame are electrically stacked in series, a solution inlet/outlet communicating with the positive electrode chamber and the negative electrode chamber and An electrolytic cell characterized in that a pump for causing a solution to flow into the solution inflow hole is provided independently for each lamination range whose number is smaller than the total number of laminations. 2. The electrolytic cell according to claim 1, wherein the electrodes in the positive electrode chamber and the negative electrode chamber of the single electrolytic cell are made of a conductor through which a solution can flow.