Ion exchange membrane electrolyzer

The present invention provides an electrolyzer, which comprises vertical type electrolyzer units with irregular surfaces formed on partition walls on anode side and on partition walls on cathode side, said irregular surfaces being overlapped on each other and integrated, and electrode plates being connected to convex portions of the partition walls, whereby said irregular surfaces are formed as troughs and ridges extending in vertical direction of the electrolyzer units, said irregular surfaces are divided into a plurality of sectors in height direction, said trough in each sector extends along the same straight line as the ridge of another sector, a liquid junction is provided to connect adjacent troughs in the same sector in the connecting portion of the adjacent sector and to connect the troughs in adjacent sectors, and an internal circulation member is provided between the partition wall and the electrode surface, using inclined surfaces of the trough on the partition wall or a member parallel to the inclined surface of the trough of the partition wall as dividing walls, thereby forming an internal circulation passage where the electrolytic solution flows down.

BACKGROUND OF THE INVENTION
 The present invention relates to a filter press type electrolyzer, and in
 particular, to an electrolyzer characterized by circulation of
 electrolytic solution.
 The electrolyzer of filter press type is widely used in various
 applications such as manufacture of chlorine and caustic soda by
 electrolysis of salt, or electrolytic manufacture of organic substances,
 electrolysis of seawater, etc.
 In a typical electrolysis method using the filter press type electrolyzer
 for electrolysis of salt, a bipolar type filter press type electrolyzer is
 used, in which a plurality of electrolyzer units are placed one upon
 another via cation exchange membrane, and anode chamber and cathode
 chamber adjacent to each other are connected electrically and mechanically
 via partition walls in the electrolyzer units. On both ends, end type
 electrode chamber units each having anode or cathode on each side thereof
 are placed on each other, and these are fixed by hydraulic press or other
 means.
 On the other hand, in this bipolar type electrolyzer unit, partition walls
 are provided to separate the anode chamber from cathode chamber and also
 to transmit electric current for electrolysis. On the partition wall to
 separate anode chamber from cathode chamber, anode and cathode are mounted
 respectively. Depending upon each individual electrolysis reaction, one of
 the anode chamber and the cathode chamber is in acidic environment, while
 the other is in reducing environment. In particular, in the electrolysis
 of salt, i.e. typical electrolysis method utilizing ion exchange membrane,
 chlorine is generated at anode, and high concentration sodium hydroxide
 and hydrogen are generated at cathode. In this respect, thin film forming
 metal such as titanium, tantalum, zirconium, etc. with high
 corrosion-resistant property, resistant to chlorine, or alloy of these
 metals are used in the anode chamber. In the atmosphere of the cathode
 chamber, titanium absorbs hydrogen and is embrittled, and even highly
 corrosion resistant titanium cannot be used for the cathode chamber. For
 this reason, ferrous metal such as nickel, stainless steel, etc. or alloy
 of these metals are used for the cathode chamber. By forming each of these
 electrode chambers by partition walls made of metal materials and by
 connecting these chambers together, electrical connection can be achieved.
 However, if it is tried to connect titanium on the anode chamber side
 directly with iron, nickel, stainless steel, etc. on the cathode side by
 welding, intermetallic compound is formed by titanium and ferrous metal on
 the anode chamber side, and it is not possible to obtain a bonded system,
 which has sufficient strength suitable for practical application.
 To solve these problems, the present applicant filed JP-A-03249189,
 disclosing a bipolar electrolyzer, which comprises partition walls with
 irregular surfaces engaged with each other and produced by press
 procedure, and a structure of electrolyzer units with electrode connected
 on a convex portion and a method to manufacture the electrolyzer units.
 Further, the present applicant proposed an electrolyzer with improvement
 in circulation of electrolytic solution within the bipolar electrolyzer in
 JP 5005195A (U.S. Pat. No. 5,314,591), JP 5005196A (U.S. Pat. No.
 5,314,591), or JP 5009774A (U.S. Pat. No. 5,314,591), etc.
 In particular, by the method proposed in JP 5009774A (U.S. Pat. No.
 5,314,591), it is possible to achieve better electrical connection through
 the irregular surfaces on the partition walls. By improving circulation of
 electrolytic solution in the electrolyzer, even distribution of
 concentration of the electrolytic solution can be attained, and efficient
 operation of electrolyzer can be realized.
 In the electrolyzers of this type, a system for circulation of electrolytic
 solution in the electrolyzer is adopted with the purpose of supplying
 electrolytic solution evenly over the extensive electrode area.
 FIG. 6 is a drawing to explain a method to circulate the electrolytic
 solution by external circulation of electrolytic solution.
 From an electrolytic solution inlet 18 on the lower portion of an
 electrolyzer unit 1, electrolytic solution 31 is introduced into an
 electrode chamber 4, and the electrolytic solution containing electrolysis
 products is discharged from a discharge port 32 on the upper portion of
 the electrolyzer and this is collected in a circulation tank 33. In the
 circulation tank 33, gas products 34 are separated, and a part of the
 discharged electrolytic solution is sent to an electrolytic solution
 preparation process 35, and at least a part of the electrolytic solution
 in the circulation tank 33 is mixed with a supplementary or make-up
 solution 36, and this is supplied through the electrolytic solution inlet
 18 on the lower portion of the electrolyzer into the electrolyzer using a
 circulation pump 37, and the solution is circulated.
 In case the electrolytic solution is brine or salt water, brine with
 concentration of 200 g/l is mixed with saturated brine with concentration
 of 300 g/l at volume ratio of 1:1, and if it is supplied as brine with
 concentration of 250 g/l, difference in the concentration of the
 electrolytic solution between the electrolytic solution inlet 18 and the
 discharge port 32 is 50 g/l.
 In order to reduce the concentration difference of the electrolytic
 solution between the inlet and the discharge port, there is a method to
 increase the circulation volume of the electrolytic solution and to
 circulate a larger quantity of electrolytic solution. However, when flow
 rate is increased, pressure fluctuation in the upper portion of the
 electrode chamber is increased, and ion exchange membrane dividing anode
 chamber from cathode chamber is vibrated, and this leads to deterioration
 of the ion exchange membrane.
 Further, FIG. 7 is a schematical drawing to explain a method to circulate
 electrolytic solution, utilizing the difference in specific gravity of the
 electrolytic solution caused by electrolysis.
 An electrolytic solution tank 38 is provided, which is connected to a
 discharge port 32 of the electrolyzer in the upper portion of an
 electrolyzer unit 1, and a pipe on the lower portion of the electrolytic
 solution tank is connected to an electrolytic solution inlet 18.
 Electrolysis products containing gases generated in the electrolyzer are
 moved upward in the electrolyzer because of the difference in specific
 gravity and reach the electrolytic solution tank 38. In the electrolytic
 solution tank 38, gas products 34 are separated, and a part of the
 electrolytic solution is sent to electrolytic solution preparation process
 35, and a supplementary solution 36 is added to a part of the electrolytic
 solution to adjust concentration of the electrolytic solution, and this
 solution is supplied from the electrolytic solution inlet 18 into the
 electrode chamber 4.
 When the electrolytic solution is supplied to the lower portion of the
 electrolyzer equipped with an electrolytic solution circulation system as
 described above, the electrolytic solution is diluted. The concentration
 of the electrolytic solution at a position away from the electrolytic
 solution inlet cannot be evenly distributed. Thus, distribution of
 electric current becomes uneven near the electrolytic solution inlet of
 the electrode chamber, and this adversely affects voltage for
 electrolysis.
 In case brine is electrolyzed, hydrochloric acid is often added to the
 brine in order to reduce pH value of the electrolytic solution. Because of
 uneven distribution of concentration in the electrolytic solution, lower
 pH occurs near the electrolytic solution inlet, and this often leads to
 deterioration of ion exchange membrane.
 It is an object of the present invention to prevent uneven distribution of
 concentration and temperature in the electrolytic solution in electrode
 chambers, to improve voltage and current efficiency and to provide longer
 service life of ion exchange membrane. In particular, the invention
 provides an electrolyzer, by which sufficiently high electrolysis
 performance can be attained in a large size electrolyzer with larger
 electrode area.
 SUMMARY OF THE INVENTION
 The present invention provides an electrolyzer, which comprises vertical
 type electrolyzer units with irregular surfaces formed on partition walls
 on anode side and on partition walls on cathode side, the irregular
 surfaces being overlapped on each other and integrated, and electrode
 plates being connected to convex portions of the partition walls, whereby
 the irregular surfaces are formed as troughs and ridges extending in
 vertical direction of the electrolyzer units, the irregular surfaces are
 divided into a plurality of sectors in height direction, the trough in
 each sector extends along the same straight line as the ridge of another
 sector, a liquid junction is provided to connect adjacent troughs in the
 same sector in the connecting portion of the adjacent sector and to
 connect the troughs in adjacent sectors, and an internal circulation
 member is provided between the partition wall and the electrode surface,
 using inclined surfaces of the trough on the partition wall or a member
 parallel to the inclined surface of the trough of the partition wall as
 dividing walls, thereby forming an internal circulation passage where the
 electrolytic solution flows down.
 Also, the present invention provides an electrolyzer as described above,
 wherein the internal circulation member is formed by a member of triangle
 pole type having a surface in contact with an inclined surface of the
 trough in each sector.
 Further, the present invention provides an electrolyzer as described above,
 wherein the internal circulation passage is formed by an inclined surface
 of a trough in each sector and an internal circulation member, one lateral
 end of the internal circulation member extending in longitudinal direction
 of the electrode chamber is in contact with a ridge on the partition wall,
 and a lateral portion in contact with the partition wall, extending in the
 direction of the partition wall, and defining the trough and the liquid
 junction is provided on a lateral end of the longitudinal member opposite
 to the portion in contact with the ridge of the partition wall.
 The present invention provides an electrolyzer as described above, wherein
 the internal circulation passage is formed by an inclined surface of a
 trough in each sector and by an internal circulation member, the internal
 circulation member comprises a longitudinal member extending in
 longitudinal direction of the electrode chamber, and a lateral member
 extending from a lateral end of the longitudinal member and defining the
 trough and the liquid junction, and in a sector adjacent to a sector where
 the entire surface of the trough is covered with the longitudinal member,
 the central portion of the longitudinal member is positioned on a ridge of
 the partition wall in a second sector adjacent to a first sector, and
 there are provided two lateral portions extending from the lateral end of
 the longitudinal member toward the partition wall and in contact with the
 partition wall.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
 In the following, description will be given on the electrolyzer of the
 present invention referring to the attached drawings.
 FIG. 1 is a drawing to show an embodiment of a unit electrolyzer of an
 electrolyzer of the present invention. It is a partially cutaway view seen
 from anode side, showing a part of electrodes and electrode chamber frame.
 As a partition wall 2 on anode side of an electrolyzer unit 1, thin plate
 made of a material selected from thin film forming metal such as titanium,
 zirconium, tantalum, etc. or alloy of these metals is molded in form of a
 pan, and this is engaged with a partition wall (not shown) on cathode side
 produced by the same molding procedure, and these are mounted on an
 electrolyzer frame 3. On both partition walls in an electrode chamber 4,
 concave and convex portions engaging with each other are formed, and a
 concave portion 5 and a convex portion 6 are installed on the partition
 wall on anode side, and a groove-like concave portion and a convex portion
 are also provided on the partition wall on cathode side at such position
 as to engage with irregular surfaces on anode side.
 On the convex portion of the partition wall on anode side, an anode is
 bonded directly or via a conductive spacer (not shown) as an electrode 7
 by welding. The anode is made of expanded metal, porous plate, etc.
 covered with anode active covering, which comprises oxides of metal of
 platinum family. On the convex portion of the partition wall on cathode
 side, a cathode is attached by welding or other means. It is made of
 expanded metal, porous plate etc. covered with cathode active covering,
 which comprises metal of platinum family, and it is bonded directly or via
 a conductive spacer.
 The irregular surfaces are divided into four sectors, i.e. a first sector
 11, a second sector 12, a third sector 13, and a fourth sector 14 from the
 above in this order. Concave portion and convex portion in each sector are
 formed as a trough 15 and a ridge 16 respectively extending in vertical
 direction of the electrolyzer unit. Adjacent troughs are connected with
 each other, and a liquid junction 17 connecting the adjacent troughs with
 each other and also connecting the troughs in upper and lower sectors with
 each other is provided in each sector. The sectors arranged in vertical
 direction on the electrolyzer unit are not limited to four sectors, i.e.
 the first sector to the fourth sector, but there may be 3 sectors or 5 or
 more sectors.
 Electrolytic solution is introduced through an electrolytic solution in let
 18 through an electrolytic solution supply pipe 19 installed inside the
 electrolyzer frame 3 into internal space of the electrode chamber 4 from
 an electrolytic solution blow port 20 arranged on lower portio n of the
 electrode chamber. The electrolytic solution goes up along the troughs of
 the electrode chamber together with gas generated in the electrolyzer, and
 it further goes up from the liquid junction toward left or right troughs
 while changing the flow passage. While it is going up, mixing of the
 electrolytic solution proceeds, and concentration of the electrolytic
 solution becomes even.
 Further, in the electrolyzer of the present invention, an internal
 circulation member 21 is provided between the partition wall 2 and the
 electrode 7. In the sector between the partition wall 2 and the internal
 circulation member 21, the electrolytic solution containing bubble s
 generated at the electrode does not flow in. With the bubbles separated in
 t he upper portion of the electrode chamber, the electrolytic solution
 flows downward, and it is circulated in the electrode chamber.
 Even when the partition walls 2 are not designed in the same shape from
 below to the above as in the electrolyzer of the present invention, an
 internal circulation passage for electrolytic solution can be formed from
 above toward below by designing the internal circulation member 21 in such
 form as to match the irregular surfaces of the partition wall.
 The electrolyzer of the present invention comprises ridges, troughs and
 liquid junctions to promote even distribution of concentration of the
 electrolytic solution on the partition wall 2, and the internal
 circulation member for the electrolytic solution is provided. In this
 respect, as shown in FIG. 1, even in case of a large size electrolyzer
 with longer depth from the inlet of electrolytic solution, the
 electrolytic solution can be circulated to full extent inside the
 electrode chamber, and electrolysis can be achieved in efficient manner.
 FIG. 2 is a drawing to explain a partition wall having irregular surfaces
 as used in a unit electrolyzer of the electrolyzer of the present
 invention.
 The electrolytic solution flows from a trough 15a formed by inclined
 surfaces 22a and 22b and from a trough 15b formed by an inclined surface
 22c into a liquid junction 17, and these streams of solution join together
 at the liquid junction 17, and then, this flows to a trough 15c, which is
 formed by an inclined surfaces 22d and 22e of the next sector. As a
 result, the streams of the electrolytic solution coming from the adjacent
 troughs join together at the liquid junction, and the solutions are mixed
 together and concentration is evenly distributed.
 FIG. 3 shows perspective views to explain an embodiment of an internal
 circulation member in the electrolyzer of the present invention.
 FIG. 3 (A) is a partially cutaway views of electrodes and partition walls
 in different sectors above and below. FIG. 3 (B) shows an internal
 circulation member in form of a triangle pole.
 The partition wall 2 is designed in such manner that troughs and ridges are
 deviated by a half pitch from one sector to another. The triangle pole
 type internal circulation member 21a with its two surfaces touches
 alternately the inclined surfaces 22f and 22g (inclined in different
 directions) of the partition wall. As a result, even in case the troughs
 are not aligned along a straight line as in the electrolyzer of the
 present invention, the triangle pole type internal circulation member can
 be mounted. Outside the internal circulation member, ascending flow is
 generated by the flow of the electrolytic solution coming from the lower
 portion of the electrolyzer and also by bubbles generated from
 electrolysis. Then, descending flow of the electrolytic solution is
 generated in an internal electrolytic solution circulation passage 23a of
 the internal circulation member, and the electrolytic solution is
 circulated.
 In the electrolyzer of the present invention, the electrode 7 may be
 directly attached to the ridges of the partition wall 2, while it may be
 designed in such manner that a conductive spacer 8 made of a metal bar is
 attached to the ridge and the electrode is bonded to the conductive spacer
 by welding. In so doing, the bonded portion of the electrode is also
 present at a position on the partition wall, i.e. on a plane of projection
 from the troughs, and this makes it possible to provide the better
 electric current distribution to the electrode and the better condition to
 maintain electrode shape. Further, the conductive spacer forms a gap
 between the electrode and the internal circulation member, and this is
 helpful to create the better condition to form the circulation passage of
 the electrolytic solution.
 FIG. 4 is a perspective view to explain an embodiment of the internal
 circulation member to be arranged on the electrolyzer of the present
 invention.
 FIG. 4 (A) is a partially cutaway view of the electrode and the partition
 wall, showing the partition walls in upper and lower sectors and an
 internal circulation member 21b. In the upper sector, a lateral end in
 longitudinal portion of the internal circulation member 21b is brought
 into contact with a ridge 16. On the lateral end not in contact with the
 ridge, a lateral portion is formed, and an internal electrolytic solution
 circulation passage 23b is formed by an inclined surface 22h of the trough
 of the partition wall 2 and the lateral portion 25a. This indicates that a
 ridge is formed on an extension of the trough of the upper sector. In the
 lower sector, an internal electrolytic solution circulation passage 23b is
 formed by an inclined surface 22i of the partition wall and a lateral
 portion 25d of the internal circulation member 22b.
 FIG. 4 (B) is a perspective view to explain the internal circulation member
 21b. From a lateral end opposite to the lateral end, which is in contact
 with the ridge of the partition wall of the longitudinal portion when the
 partition wall is installed in the electrode chamber unit, lateral
 portions 25a, 25b, 25c and 25d are extended from a longitudinal portion
 24a alternately in a first direction and in another direction
 perpendicular to the first direction, and an internal circulation passage
 is formed by the longitudinal portion 24, the lateral portion and the
 inclined surface of the partition wall.
 FIG. 5 is a perspective view to explain another embodiment of the internal
 circulation member to be installed in the electrolyzer of the present
 invention.
 FIG. 5 (A) is a partially cutaway view of the electrode and the partition
 wall, showing inclined surfaces of the partition wall and the internal
 circulation member. An internal circulation passage 23d is formed by
 inclined surfaces 22j and 22k of a trough of the partition wall 2 and by a
 planar portion 24b of an internal circulation member 21d.
 On an extension of the trough formed by the inclined surfaces 22j and 22k,
 a ridge is positioned, which is formed by inclined surfaces 22m and 22n as
 shown in the figure. An internal electrolytic solution circulation passage
 23e is formed by the inclined surface 22m and a lateral portion 25g of the
 internal circulation member 21d. Also, an internal electrolytic solution
 circulation passage 23f is formed by the inclined surface 22n and a
 lateral portion 25h of the internal circulation member 21d. The internal
 electrolytic solution circulation passages 23e and 23f are communicated
 with the internal electrolytic solution circulation passage 23d formed in
 the upper sector, and this provides a circulation passage where descending
 flow of the electrolytic solution goes down.
 FIG. 5 (B) is a perspective view to explain the internal circulation member
 21d. On the internal circulation member 21d, lateral portions 25e, 25f,
 25g and 25h are extended alternately in different directions, i.e. in a
 first direction and in a different direction perpendicular to the first
 direction, from the longitudinal portion 24b, which faces to the electrode
 surface when installed in the electrode chamber unit. An internal
 circulation passage is formed by the partition wall and the longitudinal
 portion 24b, and the lateral portions 25e, 25f, 25g and 25h of the
 internal circulation member 21b. Also, by providing a connecting hole 26
 to connect a conductive spacer to the ridge, conductive connection
 resistance between the conductive spacer and the partition wall can be
 reduced.
 In the electrolyzer of the present invention, the internal circulation
 member is not designed with the purpose of maintaining the strength of the
 electrolyzer within the electrolyzer or of supplying electric current, and
 it can be manufactured using materials formed by thin metal plate of the
 same type as the material used in the partition wall by welding or other
 means. For example, on the anode chamber side, titanium thin plate of 0.5
 to 0.3 mm in thickness may be used. On the cathode chamber side, nickel
 thin plate of 0.5 to 0.3 mm in thickness may be used.
 To mount the internal circulation member, it is mounted by welding or other
 means on the partition wall before mounting the electrode. The triangle
 pole type internal circulation member as shown in FIG. 3 can be mounted in
 a space after the electrode has been mounted.
 The material to form the internal circulation member is not limited to the
 material of planar shape and it may be a member with curved surface as far
 as it can form a space between irregular inclined surface of the partition
 wall in the electrode chamber and itself.
 The number of the internal circulation members to be mounted and the
 mounting position can be determined arbitrarily depending upon the size of
 the electrolyzer. Regarding the structure of the internal circulation
 member, one type or several types of the members as shown in FIG. 3 to
 FIG. 5 may be mounted.
 According to the electrolyzer of the present invention, electrolytic
 solution can be supplied evenly from the lower portion of the electrode
 chamber frame. By the irregular surfaces on the partition wall, it is
 possible to circulate the electrolytic solution in more satisfactory
 manner. Because the internal circulation member is designed to suit the
 irregular surfaces, the electrolytic solution can be circulated within the
 electrode chamber in more satisfactory manner, and this leads to even
 distribution of concentration and temperature of the electrolytic
 solution.
 Because the circulation of the electrolytic solution in the electrode
 chamber can be improved, uneven distribution of concentration and
 temperature of the electrolytic solution in the electrode chamber can be
 avoided, and this makes it possible to provide higher efficiency in
 voltage and current and to guarantee longer service life of the ion
 exchange membrane.