JPS63506B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for electrolyzing an aqueous alkali chloride solution by installing a cation exchange membrane between the anode and anode electrodes at a low electrolysis voltage. More specifically, the method involves electrolyzing an aqueous alkali chloride solution by fixing and holding the cation exchange membrane between negative and anode electrodes, thereby shortening the distance between the two electrodes as much as possible. The so-called ion exchange membrane method has been carried out in which an aqueous solution is electrolyzed by leaving a cation exchange membrane between the cathode and anode to form a cathode chamber and an anode chamber, but the ion exchange membrane used is Generally, for example
It is a thin film of about 100μ to 300μ and generally has no self-supporting properties. Therefore, during electrolysis, the ion exchange membrane often sways due to the flow of the electrolyte, and if the distance between the negative and anode electrodes is short, a part of the ion exchange membrane will come into contact with the electrode, and a large current will flow through that part, causing ions to flow. Easy to damage the exchange membrane. Therefore, there is a limit to the reduction in electrolytic voltage caused by shortening the distance between both electrodes, and various solutions to this problem have been proposed. That is, there is a method in which a head difference is provided between the electrolytes in the anode and negative polarity chambers, and the ion exchange membrane is pressed against one of the electrodes to eliminate the fluctuation of the ion exchange membrane (JP-A-51-68477, JP-A-51-103099). ), a method of stacking an ion exchange membrane on the surface of one electrode and filling the space between the ion exchange membrane and another electrode with conductive loose particles to stably fix the position of the ion exchange membrane (Unexamined Japanese Patent Publication No. 17375 (1973), a method for sandwiching an ion exchange membrane by improving the precision of smooth finishing of the electrode plate surface (Japanese Patent Laid-Open No. 54-1737)
47877, JP-A-54-60295, JP-A-54-88898), and a method in which a spacer made of synthetic resin is interposed between the ion exchange membrane and the electrode surface (JP-A-54-77285). However, even if these methods are implemented, the desired reduction in electrolytic voltage is not sufficient, and there are various problems with the method of fixing the ion exchange membrane, so it cannot be said that the intended purpose has been fully achieved. . That is, in the method using the pressure difference, there is a difference in the pressure applied to the ion exchange membrane between the upper and lower parts of the electrolytic solution, and it is difficult to maintain a constant pressure difference, and the pressure difference fluctuates. There is a limit to how much the distance between the electrodes can be shortened since this tends to cause agitation of the ion exchange membrane. In addition, the method of filling loose particulates has the disadvantage that it is complicated to handle small pieces of loose parts when assembling and dismantling the electrolytic cell, and when filling the particulates densely, there is a problem in the direction of shifting the ion exchange membrane. Wrinkles are likely to occur in the membrane due to the force acting on it; if the gap to be filled is narrow, it is difficult to uniformly fill the gap with the particulate matter; and the gas generated is likely to form on the back side of the particulate filling layer. There are many problems such as an increase in electrolytic voltage due to a gas gap because the electrolytic gas exits the packed bed without passing through. On the other hand, in the method of sandwiching the electrodes, especially when the electrode surface area is large, it is difficult in practice to improve the finishing accuracy so that both electrodes can be evenly butted together and to prevent twisting deformation of both electrodes. Furthermore, when using the spacer, the current density on the electrode surface may vary depending on the area occupied by the spacer, and it is not possible to interpose a non-conductive material such as a synthetic resin net over the entire ion exchange membrane and electrode surface. There are problems in that the generated gas tends to remain and the electrolytic voltage reduction effect decreases due to the widening of the distance between the electrodes. As a result of research taking these problems into consideration, the present inventor succeeded in easily shortening the distance between electrodes and effectively lowering the electrolysis voltage in the so-called ion exchange membrane method, thereby completing the present invention. I reached it. The gist of the present invention is to provide a method for electrolyzing an aqueous alkali chloride solution by installing a cation exchange membrane between an anode and a cathode, in which a thin layer of an aggregate of conductive fibrous materials entangled with each other is used as an anode and/or a cathode. A method for electrolyzing an aqueous alkali chloride solution includes disposing a current collector on the outer surface of the thin layer and clamping both electrodes, a cation exchange membrane, and the current collector together for electrolysis. The present invention will be explained in detail below. Normally, a box-shaped metal electrode made of valve metal or coated with valve metal oxide is used as the anode, and a steel wire mesh is used as the cathode, but in the present invention, the anode and/or cathode can be used to prevent mutual entanglement. This method uses a thin layer of conductive fibrous aggregates, and by sandwiching the ion exchange membrane and tightening the two electrodes, the two electrodes become extremely close to each other. If the current is uniform, the current through the ion exchange membrane is not uniform locally, which is undesirable because it causes non-uniformity in the current distribution within the assembly. This problem can be solved by applying a conductive current collector such as a wire mesh or lattice-like perforated plate that allows the generated gas to pass through the back side on the outer surface of the assembly, and if necessary, reinforcing this with a bending-resistant reinforcing material. We have found that the problem can be solved by tightening the two poles together. By using the current collector, current flows over the entire surface of the current collector, so that non-uniformity in current distribution within the assembly does not occur. The conductivity of the current collector is at least not worse than that of the above-mentioned aggregate. For example, in the case of the anode side, platinum, palladium, rhodium, ruthenium, or iridium is used on a base material made of titanium or other valve metal. Alternatively, these oxides may be used alone or coated with a mixture thereof, and in the case of the cathode side, nickel, iron, stainless steel, titanium, platinum group metals, etc. may be used. The thin layer of an aggregate of conductive fibers entangled with each other used in the present invention is made of a single conductive material that is resistant to corrosion by the electrolyte in contact with it or the gas generated by electrolysis, or a composite coated with these materials. The aggregate is a thin layer of an aggregate of fibrous materials, and examples of the aggregate include elastic sheet-like materials such as cotton-like webs, felts, low-density web sintered bodies, woven fabrics, and nets. Note that the web referred to herein refers to fibers cut to a suitable length and spread out to form a cotton-like material, and felt is the web made by needle punching or the like to strengthen the intertwining. Furthermore, the low-density web sintered body refers to an elastic sintered body in which the web is sintered in a lightly compressed state and fibrous materials are bonded to each other. In this case, the performance of the thin layer is controlled by the basis weight (g/cm ² ) and the thickness after tightening (mm), but if the thickness after tightening is small, the uniformity of the ion exchange membrane will be affected if the basis weight is too small. If it is too large, a large tightening force is required and the ion exchange membrane is likely to be damaged. On the other hand, if the thickness after tightening is large and the basis weight is too small, gas gaps are likely to occur and the electrolysis voltage will increase. However, on the other hand, making it too large is meaningless both technically and economically. That is, an increase in the amount of fibrous material used and the occurrence of a gas gap are unavoidable. in the end,
Appropriate basis weight must be selected so that the thickness after tightening is not too large or too small, but the thickness after tightening is usually preferably 0.1 to 5 mm. In order to keep the thickness constant with good reproducibility, it is convenient to place a spacer made of a corrosion-resistant metal or synthetic resin around the aggregate. Further, as the conductive material suitable for the fibrous material, when used as a cathode, a material selected from the group consisting of iron, nickel, an alloy containing at least one of iron and nickel, and platinum group metals is suitable. However, the surface of the fiber made of these materials may be coated or plated with a known material having a low hydrogen overvoltage. On the other hand, when used as an anode, materials such as platinum group metals, oxides of these metals, and carbon are suitable. The anode may also be coated or plated with a known material that is corrosion resistant to the anolyte and has a low chlorination voltage. The material of the cation exchange membrane is not particularly limited, but commonly used ones include cation exchange membranes containing fluorinated vinyl, divinylbenzene polymers, and the like. Various methods can be used to integrate both electrodes, ion exchange membranes, and current collectors as described above, such as tightening each unit with a spring, or tightening them using a filter press instead of each unit. The method is not particularly limited. By adopting the configuration described above, the present invention allows the cation exchange membrane to be brought uniformly and extremely close to the electrode, and this approach method can be easily carried out, and ultimately electrolysis can be carried out at a low electrolytic voltage. It has been found that this method is effective. The effects of the present invention will be explained below with reference to Examples. Example 1 The anode of an expanded metal screen made of titanium coated with ruthenium oxide and the current collector for the cathode of an expanded metal screen made of stainless steel are separated by a fluorine resin cation exchange membrane (trade name Nafion #315), and the cathode A thin layer of various conductive fibrous aggregates shown in Table 1 was interposed between the current collector and the ion exchange membrane, and the whole was tightened over the entire surface to provide an electrolytic cell. Supply 310g/saline solution to the anode chamber of the electrolytic cell,
Ion-exchanged water was supplied to the cathode chamber, and electrolysis was carried out at a temperature of 80° C. and a current density of 20 A/dm ² . In this case, the catholyte had a 20wt% NaOH concentration, and the anolyte and catholyte levels were almost the same. The results of electrolysis under these conditions are shown in Table 1. In addition, in the example, the results were compared when the conductive fibrous material aggregate thin layer was not used, the cathode current collector was used as the cathode, the distance between the electrodes was 5 mm, and the ion exchange membrane was fixed in the middle. Examples are shown in the same table.

【table】

[Table] Example 2 A thin layer of various conductive fibrous aggregates shown in Table 2 was interposed between the cathode current collector and the ion exchange membrane, and the thickness of the thin layer was kept constant around the thin layer. In order to
An electrolytic cell was constructed and electrolyzed in the same manner as in Example 1, except that a Teflon spacer having the thickness shown in Table 2 was placed. The results of the electrolysis are shown in Table 2. Comparative Example 2 shown in Table 2 is obtained by transcribing the values of Comparative Example 1.

[Table] Example 3 The anode current collector of a titanium expanded metal screen coated with ruthenium oxide and the cathode current collector of a stainless steel expanded metal screen were replaced with a fluororesin-based cation exchange membrane (product name Nafion #315). ) between the anode current collector and the ion exchange membrane, and a carbon fiber web (wire diameter
0.01mmφ, fabric weight 0.026g/cm ² ), iron fiber web (wire diameter 0.025mm) between the cathode current collector and ion exchange membrane.
mmφ, basis weight 0.27 g/cm ² ), both current collectors were pressed toward the ion exchange membrane to form an electrolytic cell. Supply 310 g of salt water to the anode chamber of the electrolytic cell,
Ion-exchanged water was supplied to the cathode chamber, and electrolysis was carried out at a temperature of 80° C. and a current density of 20 A/dm ² . In this case, the catholyte had a NaOH concentration of 20 wt%, and the anolyte and catholyte levels were almost the same. As a result of electrolysis under these conditions, the electrolysis voltage is
It was 3.35V.

Claims (1)

[Claims] 1. In a method of electrolyzing an aqueous alkali chloride solution by installing a cation exchange membrane between an anode and a cathode, a thin layer of an aggregate of conductive fibrous materials entangled with each other is used as an anode and/or a cathode. A method for electrolyzing an aqueous alkali chloride solution, characterized in that a current collector is disposed on the outer surface of the thin layer, and both electrodes, a cation exchange membrane, and the current collector are integrally tightened for electrolysis. 2. Claims in which a cation exchange membrane, a thin layer of conductive fibrous aggregates intertwined with each other, and a cathode current collector are layered in this order on the smooth surface of an anode plate and are integrally tightened for electrolysis. The method for electrolyzing an aqueous alkali chloride solution according to item 1. 3. The fibrous material constituting the thin layer of the interconnected conductive fibrous material aggregate used as the cathode is made of a material selected from the group consisting of iron, nickel, and an alloy containing at least one of iron and nickel. The method for electrolyzing an aqueous alkali chloride solution according to claim 1 or 2, wherein the fibrous material is a single or mixed fibrous material.