Bipolar type ion exchange membrane electrolytic cell

Abstract: A bipolar type ion exchange membrane electrolytic cell has gas-liquid separating chambers which minimizes a pressure fluctuation in compartment frame units, deterioration of ion exchange membranes and a voltage variation in the compartment units. Upper portions of back plates 5, 3a are outwardly bent at a higher position than meshed electrode plates of each of anode and cathode compartment frames to form inversed U-shape portions; U-shaped channel members 10 are respectively placed in and fixed to the inversed U-shape portions so that spaces are formed, as passages 12, in association with the back plates, and areas defined by the inversed U-shape portions and the U-shaped channel members are gas-liquid separating chambers.

Description: The present invention relates to a bipolar type ion exchange membrane electrolytic cell. Ion exchange membrane electrolytic cells which have been widely used, are of a filter press (fastening) type electrolytic cell wherein, as shown in Figure 4, a number of ion exchange membranes 20 and compartment frame units 21 are alternately arranged by interposing gaskets 22 (the thickness is drawn exaggeratedly), and the arranged elements are fastened from both sides by using a hydraulic press or the like. The electrolytic cell of this type is generally classified into a monopolar type electrolytic cell of a parallel connection type and a bipolar type electrolytic cell of a serial connection type, which are distinguishable from the difference in electrical connection. In the bipolar type ion exchange membrane electrolytic cell, as shown in Figure 5, a compartment frame unit 21 is formed by connecting an anode compartment frame 30 and a cathode compartment frame 40 back to back. The anode compartment frame 30 for forming an anode compartment 31 comprises a back plate 32 and a meshed electrode plate 33 which is disposed in substantially parallel the back plate 32 with a certain space to the back plate 32 wherein supporting members or ribs 34 are disposed between the back plate 32 and the anode plate 33 to maintain the above-mentioned space therebetween. Each of the supporting members 34 is provided with a plurality of openings through which electrode liquid or electrolyte can flow in the left and right directions in Figure 5. The construction of the cathode compartment frame 40 for providing a cathode compartment 41 is the same as that of the anode compartment frame 30. Namely, it comprises a back plate 42, a meshed cathode plate 43 and supporting members or ribs 44. The back plate 32 is connected integrally with the back plate 42 to form a partition wall for conducting an electric current. A peripheral edge portion of each of the back plates 32, 42 is bent and fixed to a hollow body or a square pipe 24. Figure 6 is a front view of the compartment frame unit 21, i.e., a view observed from the cathode side, wherein numeral 27 designates an inlet at the side of the cathode compartment frame 40 through which a cathode liquid or a catholyte, is introduced. Numeral 28 designates an outlet for a catholyte and hydrogen gas. Similarly, an inlet 27a and an outlet 28a for an anode liquid are formed in the anode compartment frame 30. In a case of an electrolytic cell for chlor-alkali manufacture, chlorine gas is generated in the anode compartment 31, and hydrogen gas is generated in the cathode compartment 41. Each of gas is mixed with the liquid respectively to form a gas-liquid mixed phase stream. The stream goes up in each of the compartments to reach each gas-liquid separator 29 provided at the upper portion of the compartments where the gas-liquid mixture stream is separated into a gaseous phase and a liquid phase to be discharged from compartments through the outlets 28, 28a, respectively. The gas-liquid separator may be such one as disclosed in United States Patent No. 5,225,060 that a gas-liquid separating chamber is formed in a non-electrolysis area which is in an upper portion of each of the electrode plates wherein at least one opening is formed at the bottom of the gas-liquid separating chamber so that the gas-liquid mixed phase stream passing upwardly in the compartments enters into the chamber through the opening. Further, the gas-liquid separator may be such one as disclosed in Japanese Examined Patent Publication No. 46191/1985 that an L-shaped channel body is disposed in a electrolysis area to thereby form a gas-liquid separating chamber, so that the gas-liquid mixed phase stream enters into the chamber from the electrode side and is discharged therethrough. In such bipolar type ion exchange membrane electrolytic cell, when the discharging of the gas-liquid mixed phase stream is not smooth, there causes stagnation of gas at an upper portion of the compartments which results in fluctuation of pressure in the compartments, hence, a cause of voltage variation. Further, fluctuation of pressure in the compartments causes vibrations of adjacent ion exchange membranes and frequent times of their contact to the electrode whereby the ion exchange membranes may deteriorate. Accordingly, it is necessary to separate quickly gas from liquid in the gas-liquid separators and to discharge them outside of the compartments. For this, the function of the gas-liquid separator is important. In the gas-liquid separator formed in a non-current conductive, electrolysis, area as disclosed in United States Patent No. 5,225,060, the stagnation of gas easily takes place near the opening formed at the bottom portion of a gas-liquid separating chamber, whereby the fluctuation of pressure in the compartment, the deterioration of ion exchange membrane and the variation of voltage in the compartment take place. Further, in the gas-liquid separator formed in a current conductive area as disclosed in Japanese Examined Patent Publication No. 46191/1985, wherein the gas-liquid mixed phase stream enters into a gas-liquid separating chamber through a gap or space, between an electrode plate and gas-liquid separating chamber, the stagnation of gas is easily formed between the electrode and the ion exchange membrane because the electrode is in a meshed form, whereby there causes the fluctuation of pressure in the compartment, the deterioration of ion exchange membrane and the variation of voltage. It is a primary object of the present invention to provide a bipolar type ion exchange membrane electrolytic cell having a gas-liquid separator which suppresses the fluctuation of pressure in the compartments, the deterioration of ion exchange membranes and the variation of voltage. In accordance with the present invention, there is provided in a bipolar type ion exchange membrane electrolytic cell having a plurality of compartment frame units which are arranged by interposing ion exchange membranes therebetween and are fastened together, wherein each of the compartment frame units is formed by connecting back to back an anode compartment frame and a cathode compartment frame which respectively comprise a back plate and a meshed electrode arranged in substantially parallel with a certain space, the bipolar type ion exchange membrane electrolytic cell being characterized in that an upper portion of the back plate is outwardly bent at a higher position than the meshed electrode plate of each of the anode and cathode compartment frames to form an inversed U-shape portion; a U-shaped channel member is placed in and fixed to the inversed U-shape portion so that a space or gap is formed, as a passage for electrolyte and gas, in association with the back plate, and an area defined by the inversed U-shape portion and the U-shaped channel member or part, is a gas-liquid separating chamber. In the present invention, a holding member, a supporting plate, having dispersed openings is disposed substantially horizontally in the U-shaped channel member so that an upper portion with respect to the holding member provides a gaseous phase chamber in the gas-liquid separating chamber, and a lower portion with respect to the holding member provides a liquid phase chamber. Further, in the present invention, the width of the passage between the U-shaped channel member and the back plate is preferably 5-20% of the width of the electrode compartment frame. Further, in the present invention, the size A of an inlet for the gas-liquid separating chamber, which is formed at the upper end of the U-shaped channel member at the side of the passage, is preferably 5-30% of the height of the gas-liquid separating chamber. In drawings: Figure 1 is a longitudinal sectional view of a part of a bipolar type ion exchange membrane electrolytic cell in accordance with an embodiment of the present invention; Figure 2 is a longitudinal cross-sectional view showing a gas-liquid separator and related portions thereof in accordance with an embodiment of the present invention; Figure 3 is a perspective view partly broken of the gas-liquid separator; Figure 4 is a longitudinal cross-sectional view of the bipolar type ion exchange membrane electrolytic cell, which is observed from a side; Figure 5 is a transverse sectional view taken along a line B-B in Figure 4; and Figure 6 is a front view of a compartment frame unit. Preferred embodiments of the present invention will be described in more detail with reference to the drawings. In Figures 1 to 3, a compartment frame unit 1 of the bipolar type ion exchange membrane electrolytic cell of the present invention comprises an anode compartment frame 2 and a cathode compartment frame 3 which are connected back to back each other. The anode compartment frame 2 is composed of a back plate 5, a meshed anode plate 6 arranged in substantially parallel to the back plate 5 and supporting members, ribs 7 arranged between the back plate 5 at the anode side and the anode plate 6 to maintain a space therebetween. Each of the supporting members 7 is provided with openings 7a at desired locations so as to communicate an anolyte in the compartment. On the other hand, the cathode compartment frame 3 comprises a cathode side back plate 3a, a cathode plate 3b and supporting members or ribs 3c. Numerals 4 designate gaskets and numerals 1a designate ion exchange membranes. The back plate 5 and the supporting members 7 of the anode compartment frame 2 are made of, for instance, titanium or a titanium alloy, and the anode plate 6 is composed of an electric-conductive meshed titanium plate as substrate on which a titanium oxide or an oxide of precious metal (e.g., ruthenium oxide, iridium oxide or the like) is coated. The construction of the cathode compartment frame 3 is similar to that of the anode compartment frame 2. The cathode plate 3b is composed of an electric-conductive meshed plate having corrosion resistance to alkalis, such as, for instance, iron, nickel, stainless steel or the like, as substrate, on which Raney nickel or precious metal is coated. The back plate 3a and the supporting members 3c are made of a material such as iron, nickel, stainless steel or the like. The presence of the electrode plates 6, 3b in the electrolytic cell forms a electrolysis area. A gas-liquid separator 8 is provided in the non-electrolysis area at an upper portion of each of the anode compartment frames 2 or the cathode compartment frames 3. In the gas-liquid separator 8, an outer frame 9 is formed by bending outwardly an upper portion of the back plate 5 of the anode compartment frame 2 to form an inversed U-shape portion. A U-shaped channel member or part 10 is disposed in the outer frame 9. A portion defined by the outer frame 9 and the channel member 10 constitutes a gas-liquid separating chamber 11. The outer frame 9 of the gas-liquid separator 8 has an inner side portion 9a, an upper portion 9b and an outer side portion 9c. The lower end 9d of the outer side portion 9c of the outer frame 9 is firmly attached to an outer side portion 10b at a position near the lower end of an outer side portion 10b of the channel member 10 by means of Tig welding or the like. In case that the outer side portion 9c of the outer frame 9 covers only the upper end of the outer side portion 10b of the channel member 10, welding has to be carefully made in a linear form so as not to cause liquid leaking which may result in the distortion of the compartment frame. As shown in Figure 2, however, when the outer side portion 9c of the outer frame 9 is extended to a position near the lower end of the outer side portion 10b of the channel member 10, there is no danger of liquid leaking, and use of spot welding is sufficient. A gap or space is formed as a passage 12 for the gas-liquid mixed phase stream between an inner side portion 10a of the channel member 10 and the inner side portion 9a of the outer frame 9. As shown in Figure 3, spacers 13 are disposed at desired locations in the passage 12 whereby a predetermined distance can be maintained for the gap when a number of the compartment frame units 1 each comprising the anode compartment frame 2 and the cathode compartment frame 3 are pressed through the gaskets 4 from both sides. The channel member 10 and the spacers 13 may be made of the same material as the back plates, for instance. It is preferable that the inner side portion 10a of the channel member 10 is made higher than the outer side portion 10b. A gap is formed as an inlet 14 for introducing the gas-liquid mixed phase stream going up through the passage 12 into the gas-liquid separating chamber, between the upper end of the inner side portion 10a of the channel member 10 and the upper portion 9b of the outer frame 9. A holding member or a supporting plate 15 is disposed substantially horizontally at substantially middle position in each of the channel members 10. The holding member 15 has dispersed openings 16. The holding member 15 can maintain the width of the channel member 10 when the compartment frame units are pressed from both sides, and also can function as a separating plate for separating a gaseous phase from a liquid phase in the gas-liquid separating chamber 11 wherein a gas phase chamber is formed in an upper portion 17 with respect to the holding member 15 and a liquid phase chamber is formed in a lower portion 18 with respect to the holding member 15. The size of each of the compartment frame units 2, 3 is, for instance, about 240 cm wide, about 120 cm high and about 2 cm thick when it is observed from the front (Figure 6). The size of the gas-liquid separating chamber 11 is such that, for instance, the length of the outer side portion 9c of the outer frame 9 is about 60 mm and the width of the upper portion 9b is about 20 mm. The dimension A of the gap as the inlet 14 formed between the upper end of the inner side portion 10a of the channel member 10 and the upper portion 9b of the outer frame 9 is about 10 mm. The dimension A is preferably 5-30% of the height of the gas-liquid separating chamber 11, more preferably, 10-20%. The height of the outer side portion 10b of the channel member 10 may be almost same as that of the inner side portion 10a. By increasing the height of the outer side portion 10b, however, the outer side portion 10b having a reduced height facilitates operations for arranging the holding member 15 in the channel member 10. The width of the passage 12 is made to be about 2 mm. The width of the passage 12 is preferably 5-20% of the width of the compartment frame 2,3, more preferably, 7-15%. In the bipolar type ion exchange membrane electrolytic cell of the present invention, when the gas-liquid mixed phase stream which has passed upwardly in each of the anode compartment frames 2 further goes up the narrow passage 12 at the side of the back plate 5, the mixed phase stream becomes a bubble flow wherein small bubbles disperse in a liquid phase, and the bubble flow enters into the gaseous phase chamber 17 of the gas-liquid separating chamber 11 through the inlet 14. The liquid phase in the bubble stream in the gaseous phase chamber 17 enters into the liquid phase chamber 18 through the opening 16 of the holding member 15. Since the gas-liquid mixed phase stream passing upwardly through the passage 12 is first fed to the gaseous phase chamber of the gas-liquid separating chamber, separation between the gaseous phase and the liquid phase can rapidly be carried out. The gaseous phase and the liquid phase separated in the gas-liquid separating chamber 11 are moved laterally (the back and forth directions in Figure 2 or the left and right directions in Figure 6) to be discharged through the outlets 28 in Figure 6. The same flow are obtainable in the cathode compartment frames 3. The back plates 5, 3a may be made of material different from the gas-liquid separator 8. However, use of the same material is advantageous because the number of welding may be small and processing may become easy. Further, in place of the U-shaped channel member 10, an L-shaped member, which is a modification of the U-shaped member, may be used to form the passage 12 at the side of the back plates 5, 3a with respect to the gas-liquid separating chamber 11. Now, the present invention will be described in further detail with reference to Examples. However, it should be understood that the present invention is by no means restricted by such specific Examples. EXAMPLE 1 Electrolysis tests were carried out by using the bipolar type ion membrane electrolytic cell having compartment frame units each comprising anode and cathode compartment frames and provided with a gas-liquid separators of the present invention to measure values of pressure change in the anode compartment frames. The dimensions of the electrode plate in each of the compartment frames were 240 cm wide and 120 cm high. An expanded meshed titanium plate of a thickness of 1.7 mm was used for each anode plate, and a punched meshed nickel plate of a thickness of 1.2 mm was used for each cathode plate. Titanium plates of a thickness of 1.2 mm were used for anode side back plates and titanium plates of a thickness of 2.0 mm and a width of 30 mm were used for supporting members or ribs. The number of supporting members or ribs used was 24 which were arranged in the longitudinal direction at equal intervals and were fixed to the back plates and the electrode plates by welding. Nickel plates of a thickness of 1.2 mm were used for the cathode side back plates, and nickel plates of a thickness of 1.0 mm and a width of 30 mm were used for the supporting members. The number of the supporting members or ribs used was 24 which were arranged at equal intervals in the longitudinal direction with respect to the electrolysis area cell, and were fixed to the back plates and the electrode plate by welding. Of each of the gas-liquid separators, the height, the width, the dimension A of the inlet 14 and the width of the passage 12 were 60 mm, 30 mm, 10 mm and 2 mm respectively. 24 Pieces of spacers 13 having a thickness of 2 mm, a width of 5 mm and a height of 50 mm were arranged at equal intervals in order to assure the distance of the passage 12. In each of the U-shaped channel members, the holding member or the supporting plate was horizontally fixed to a position 25 mm apart from the upper end of the outer frame 9. 24 Openings having a diameter of 12 mm were formed in the holding member 15 at equal intervals. The chamber frame units each comprising the anode compartment frame and the cathode compartment frame and the ion exchange membranes were arranged alternately by interposing the gaskets, and thus formed assembly was fastened from both sides by a cell frame made of iron thereby forming a bipolar type ion exchange membrane electrolytic cell. For the ion exchange membranes, Flemion membrane F-893 (manufactured by Asahi Glass Company Ltd.) were used. An aqueous solution of NaCℓ of 300 g/ℓ was introduced through an inlet 27 at a lower portion of the compartment frame units so that the concentration of the solution of salt at an outlet 28 for the anode compartments was 210 g/ℓ, and dilute sodium hydroxide aqueous solution was introduced through an inlet 27a at a lower portion of the compartment frames so that the concentration of sodium hydroxide aqueous solution at an outlet 28a for the cathode compartments was 32 wt%. Electrolysis tests were carried out under the conditions of a temperature of electrolyte of 90°C and a current density of 5 KA/m 2 to measure values of pressure fluctuation. Results are shown in Table 1. After the operations of 6 months, the electrolytic cell was disassembled to observe and inspect the ion exchange membranes. As a result, there was found no abnormality in the appearance and the membrane strength. Current density (KA/m 2 ) Voltage (V) Values of pressure fluctuation in anode compartment (mmH 2 O) Example 1 5 3.22 24 Example 2 4 3.04 18 Example 3 3 2.86 10 EXAMPLE 2 Electrolysis tests were conducted in the same condition as Example 1 except that the current density was 4 KA/m 2 . A result of the measurement of the value of pressure fluctuation is shown in Table 1. After the operations of 6 months, the electrolytic cell was disassembled. However, no abnormality was found. EXAMPLE 3 Electrolysis tests were conducted under the same condition as Example 1 except that the current density was 3 KA/m 2 . A result of the measurement of the value of pressure change is shown in Table 1. After the operations of 6 months, the electrolytic cell was disassembled. However, no abnormality was found. COMPARATIVE EXAMPLE 1 A bipolar ion exchange membrane electrolytic cell in which the size of the electrode plates, the material for the electrode plates, the back plates and the ion exchange membranes were the same as those in Example 1, was used. However, the gas-liquid separating chambers were respectively formed within compartment frames constituted by the electrode plates and the back plates at the electrolysis area. Each of the gas-liquid separating chambers was formed by fixing an L-shaped member to the back plate at an upper portion of the compartment frame constituted by the electrode plate and the back plate so that the gas-liquid mixed phase stream passing upwardly in the compartment frame was passed through the passage between the L-shaped member and the electrode plate and entered into the gas-liquid separating chamber through a space as an inlet formed between an upper portion of the L-shaped member and an upper portion of the compartment frame. The width of the passage was 10 mm; the height of the L-shaped member was 60 mm and the height of the space as the inlet was 10 mm. Electrolysis tests were conducted under the same conditions as Example 1 to measure values of pressure fluctuation. A result obtained is shown in Table 2. After the operations of 3 months, the electrolytic cell was disassembled to observe and inspect the ion exchange membranes. An upper portion of the membranes exhibited a white color owing to the stagnation of gas, and the strength of that portion of the membranes was clearly lower than that of an intermediate portion or a lower portion. Current density (KA/m 2 ) Voltage (V) Values of pressure fluctuation in anode compartment (mmH 2 O) Comparative Example 1 5 3.30 70 Comparative Example 2 4 3.10 45 Comparative Example 3 3 2.90 24 COMPARATIVE EXAMPLE 2 Electrolysis tests were conducted under the same conditions as Comparative Example 1 except that the current density was 4 KA/m 2 to measure values of pressure change. A result obtained is shown in Table 2. COMPARATIVE EXAMPLE 3 Electrolysis tests were conducted under the same conditions as Comparative Example 1 except that the current density was 3 KA/m 2 to measure values of pressure change. A result obtained is shown in Table 2. The results in Table 1 and Table 2 show that the values of pressure fluctuation in the anode compartments of the ion exchange membrane bipolar type electrolytic cell in Examples 1 to 3 are lower than those of the electrolytic cell in Comparative Examples 1 to 3, and there is less influence to the ion exchange membranes. In accordance with the present invention, there is a small possibility of stagnation of gas at a lower portion of the outer side of the gas-liquid separating chambers since gas-liquid mixed phase streams passing upwardly in the compartment frames are sucked by siphon action to be introduced into the gas-liquid separating chambers through the passages formed in a side portion of the gas-liquid separating chambers. Further, when the gas-liquid mixed phase stream is passed through the narrow passage, the mixed phase stream becomes a bubble flow wherein small bubbles are dispersed, whereby separation of a gaseous phase from a liquid phase can be smooth and the separated phases can be discharged quickly out of the compartment. Accordingly, there is almost no pressure fluctuation or voltage variation in the compartment frames, and stable operations can be obtained at a high current density of 4 KA/m 2 or higher even under a high temperature condition. Since each of the gas-liquid separators is disposed in each of non-electrolysis areas of the electrolytic cell and the passage to each of the gas-liquid separators is formed at the back plate side, there is no stagnations of gas at the side of the meshed electrode plates, in particular, between the electrode plates and the ion exchange membranes, whereby there is a small possibility of the deterioration of the ion exchange membranes. Each of the gas-liquid separators is formed by outwardly bending an upper portion of the back plate of each of the compartment frames in a form of an inversed U-shape in which a U-shaped channel member is disposed and fixed to the outwardly bent portion to provide a space as a passage between the U-shaped channel member and the back plate, the number of Tig welding can be reduced and manufacturing process is simple while the compartment frames having a high rigidity can be obtained. Further, a holding member is disposed in each of the gas-liquid separating chambers so as to extend in its longitudinal direction wherein a gaseous phase chamber is formed in an upper portion with respect to the holding chamber and a liquid phase chamber is formed in a lower portion with respect to the holding member in the gas-liquid separating chamber. Accordingly, there is no danger of the deformation even when the gas-liquid separating chambers are pressed from both sides. Further, since the gaseous phase chamber and the liquid phase chamber are formed by the presence of the holding member, the discharge of a gaseous phase and a liquid phase to the outside of the compartment can be smooth, and a pressure fluctuation in the compartment is minimized. Further, since the bubble flow going up through the passage is firstly introduced into the gaseous phase chamber of the gas-liquid separating chamber, the separation of the gaseous phase from the liquid phase is effectively carried out.

Claims: A bipolar type ion exchange membrane electrolytic cell having a plurality of compartment frame units (1) which are arranged by interposing ion exchange membranes (1a) therebetween and are fastened together, wherein each of the compartment frame units (1) is formed by connecting back to back an anode compartment frame (2) and a cathode compartment frame (3) which respectively comprise a back plate (5) and a meshed electrode plate (6) arranged in substantially parallel with a certain space, the bipolar type ion exchange membrane electrolytic cell being characterized in that an upper portion of the back plate (5) is outwardly bent at a higher position than the meshed electrode plate (6) of each of the anode and cathode compartment frames (2,3) to form an inversed U-shape portion; a U-shaped or L-shaped channel member (10) is placed in and fixed to the inversed U-shape portion so that a space is formed, as a passage (12), in association with the back plate (5), and an area defined by the inversed U-shape portion and the U-shaped or L-shaped channel member (10) is a gas-liquid separating chamber (11), which is located in the non-electrolysis area above the electrodes. A bipolar type ion exchange membrane electrolytic cell according to Claim 1, wherein a holding member (15) having dispersed openings (16) is disposed substantially horizontally in the U-shaped or L-shaped channel member (10) so that an upper portion (17) with respect to the holding member (15) provides a gaseous phase chamber in the gas-liquid separating chamber (11), and a lower portion (18) with respect to the holding member (15) provides a liquid phase chamber. A bipolar type ion exchange membrane electrolytic cell according to Claim 1 or 2, wherein the width of the passage (12) between the U-shaped or L-shaped channel member (10) and the back plate (5) is 5-20% of the width of the compartment frame. A bipolar type ion exchange membrane electrolytic cell according to anyone of Claims 1 to 3, wherein the size of an inlet (14) for the gas-liquid separating chamber (11), which is formed at the upper end of the U-shaped or L-shaped channel member (10) at the side of the passage (12), is 5-30% of the height of the gas-liquid separating chamber (11).

Inventors: KIMURA TATSUHITO, SUZUKI MIKIO, UCHIBORI TAKAHIRO, KIMURA, TATSUHITO, SUZUKI, MIKIO, UCHIBORI, TAKAHIRO, Kimura, Tatsuhito Asahi Glass Company Ltd., Suzuki, Mikio Asahi Glass Company Ltd., Uchibori, Takahiro Asahi Glass Company Ltd.
Applicants: ASAHI GLASS CO LTD, ASAHI GLASS COMPANY LTD.
Application year: 1995
Main classification: C25B9
IPC codes: C25B9, C25B11