Title:
BIPOLAR HYPOCHLORITE CELL
United States Patent 3849281
Abstract:
Disclosed is a substantially vertical bipolar electrolytic cell especially suited to the production of alkali metal hypochlorites, divided into a plurality of cell units by horizontal partitions and featuring a bipolar electrode design wherein a foraminous, U-shaped cathode portion adapted to receive a sheet-like anode and a sheet-like anode portion are joined around a horizontal partition by a conductive portion.
US Patent References:
Electrolytic cell
Hartman et al. - June 1925 - 1541947
PRODUCTION OF SODIUM CHLORATE
Goens et al. - July 1972 - 3676315
ELECTROLYTIC CELL FOR THE MANUFACTURE OF OXYHALOGENS
Loftfield - December 1973 - 3779889
Electrolytic cell
Hartman et al. - June 1925 - 1541947
PRODUCTION OF SODIUM CHLORATE
Goens et al. - July 1972 - 3676315
ELECTROLYTIC CELL FOR THE MANUFACTURE OF OXYHALOGENS
Loftfield - December 1973 - 3779889
Inventors:
Bennett, John E. (Painesville, OH)
Burkhardt, James W. (Mentor, OH)
Loftfield, Richard E. (Chardon, OH)
Burkhardt, James W. (Mentor, OH)
Loftfield, Richard E. (Chardon, OH)
Application Number:
05/381730
Publication Date:
11/19/1974
Filing Date:
07/23/1973
View Patent Images:
Export Citation:
Assignee:
Diamond Shamrock Corporation (Cleveland, OH)
Primary Class:
Other Classes:
204/269, 204/284
International Classes:
C25B9/06; B01K3/04
Field of Search:
204/95,268,269,289,286
Primary Examiner:
Mack, John H.
Assistant Examiner:
Solomon I, W.
Attorney, Agent or Firm:
Tinkler, Timothy E.
Claims:
We claim
1. An electrolytic cell comprising:
2. a sheet-like, foraminous, anode portion,
3. a U-shaped, foraminous, cathode portion adapted to receive and encompass a sheet-like anode, and
4. a conductive connecting portion joining said anode and cathode portions;
5. said anode portion is encompassed by a next-adjacent cathode and is parallel to said partition,
6. said cathode portion encompasses a next-adjacent anode and is parallel to and spaced apart from the opposite side of said partition and the next-adjacent partition, and
7. said connecting portion is held between an edge of said partition and a container sidewall; and
8. A cell as in claim 1 wherein the bipolar electrode comprises a continuous sheet of expanded titanium mesh, the anode portion of which bears an electrocatalytic coating on the surface thereof.
9. A cell as in claim 1 wherein spacers are provided to space said cathode and cathode portions apart from said partitions.
10. A cell as in claim 1 wherein spacers are provided between each anode and its encompassing cathode to maintain an anode-cathode gap.
11. A cell as in claim 1 wherein a gasket is provided between said container sidewall and a partition edge so that the connecting portion of the bipolar electrode is held between said partition edge and said gasket in a sealing arrangement.
12. A cell as in claim 1 wherein the bipolar electrode comprises an anode portion of expanded titanium metal coated with an electrocatalytic material and joined to connecting and cathode portions from the group of foraminous stainless steel, nickel, and palladium-titanium alloy.
1. An electrolytic cell comprising:
2. a sheet-like, foraminous, anode portion,
3. a U-shaped, foraminous, cathode portion adapted to receive and encompass a sheet-like anode, and
4. a conductive connecting portion joining said anode and cathode portions;
5. said anode portion is encompassed by a next-adjacent cathode and is parallel to said partition,
6. said cathode portion encompasses a next-adjacent anode and is parallel to and spaced apart from the opposite side of said partition and the next-adjacent partition, and
7. said connecting portion is held between an edge of said partition and a container sidewall; and
8. A cell as in claim 1 wherein the bipolar electrode comprises a continuous sheet of expanded titanium mesh, the anode portion of which bears an electrocatalytic coating on the surface thereof.
9. A cell as in claim 1 wherein spacers are provided to space said cathode and cathode portions apart from said partitions.
10. A cell as in claim 1 wherein spacers are provided between each anode and its encompassing cathode to maintain an anode-cathode gap.
11. A cell as in claim 1 wherein a gasket is provided between said container sidewall and a partition edge so that the connecting portion of the bipolar electrode is held between said partition edge and said gasket in a sealing arrangement.
12. A cell as in claim 1 wherein the bipolar electrode comprises an anode portion of expanded titanium metal coated with an electrocatalytic material and joined to connecting and cathode portions from the group of foraminous stainless steel, nickel, and palladium-titanium alloy.
Description:
BACKGROUND OF THE INVENTION
Alkali metal hypochlorites, especially sodium hypochlorite, are extensively employed for bleaching and disinfecting applications, e.g., in sewage treatment facilities. To avoid the expensive transportation of hypochlorite solutions, which are predominantly water, and further to avoid premature decomposition on storage, it is desirable to generate the needed hypochlorate at the site of use. Therefore, there is considerable demand for a compact, efficient, electrolytic cell for the generation of hypochlorite, which cell is operable for extended periods of time with a minimum of maintenance.
STATEMENT OF THE INVENTION
Therefore, it is an object of the present invention to provide a compact electrolytic cell for the production of hypochlorites at high current efficiencies.
This and further objects of the present invention will become apparent to those skilled in the art from the specification and claims that follow.
There has now been found an electrolytic cell comprising:
A. a substantially vertically disposed container having electrolyte inlet means in the lower portion thereof and electrolysis product outlet means in the upper portion;
B. a plurality of horizontally disposed, electrically nonconductive, partitions dividing said container into a plurality of cell units;
C. a terminal, foraminous, sheet-like, monopolar anode horizontally disposed in the first of said cell units;
D. a terminal, foraminous, monopolar cathode, horizontally disposed in the last of said cell units and comprising a U-shaped construction adapted to receive and encompass a foraminous, sheet-like anode;
E. means for impressing an electrolyzing current across said monopolar electrodes;
F. at least one bipolar electrode comprising
1. a sheet-like, foraminous, anode portion,
2. a U-shaped, foraminous, cathode portion adapted to receive and encompass a sheet-like anode, and
3. a conductive connecting portion joining said anode and cathode portions;
G. said bipolar electrode being horizontally disposed in adjacent cell units on opposite sides of a partitiion so that
1. said anode portion is encompassed by a next-adjacent cathode and is parallel to said partition,
2. said cathode portion encompasses a next-adjacent anode and is parallel to and spaced apart from the opposite side of said partition and the next-adjacent partition, and
3. said conductive connecting portion is held between an edge of said partition and a container sidewall; and
H. means for passing electrolyte and products of electrolysis from the bottom to the top of the container through the cell units in sequence.
Such a cell has a primary advantage of high current efficiency operation, apparently owing to the relationship of two cathodes for each anode created by the fact that each anode is encompassed by a U-shaped cathode. A further advantage relates to the long, useful life of the cell in continuous operation, at least in part due to the elimination of gas-liquid interface corrosion (since the cell is operated in a flooded condition). Ease of disassembly, replacement, and repair of component parts when required is also found.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a perspective view showing the relationship between the electrodes and partitions of a cell according to the present invention.
FIG. 2 is a vertical cross-section of a typical cell of the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Basically, the invention contemplates a vertically disposed electrolytic cell, divided by horizontal partitions and employing bipolar electrodes that parallel opposite sides of said partitions, the positive ends of said electrodes being foraminous sheets and the negative, or cathodic ends, also being foraminous and sheet-like but bent back on themselves to form a "U-shape" that encompasses the next-adjacent anode sheet. Thus, each cell unit defined by adjacent partitions contains a U-shaped cathode encompassing a sheet-like anode. Since the flow sequence of electrolyte and products of electrolysis is from the bottom to the top of the entire cell, each unit is operated in a substantially flooded condition.
The cells of the present invention may conveniently be used to produce alkali metal, especially sodium and potassium, hypochlorites in concentrations within the range of from 1 to 20 grams per liter by the direct electrolysis of alkali metal chloride solutions, typically having a concentration of from 5 to 100 g/l. Since the problem of cathodic deposits when employing impure alkali metal chloride solutions is well known, and in view of the fact that cells of the present invention contemplate two cathodes for every anode, it is desirable to employ an alkali metal chloride feed of high purity, thus avoiding the need for excessive backwashing or the like. Conditions of operation are typical, for example involving a pH on the order of 7 to 10, temperatures within the range of 5° to 50° C, etc.
The invention may be understood most readily by reference to the attached drawings wherein the vertical cell container is indicated generally at 1 and is provided with electrolyte inlet means 3 near the bottom thereof and an outlet 5 in the upper portion for unreacted electrolyte and products of electrolysis. The container 1 is divided into a plurality of cell units 7 by a plurality of electrically nonconductive partitions 9. Materials of construction for both the container and the partitions may be any mechanically sound, electrically nonconductive and corrosion resistant material, such as, polyvinyl chloride, chlorinated polyvinyl chloride, Lucite, and the like. Each partition 9 joins with the four container walls in a substantially sealing engagement to prevent current and electrolyte leakage. As explained more fully hereinafter, one, and generally a corresponding, edge of each partition engages the container wall in such a manner as to accommodate a bipolar electrode connecting portion. Each partition 9 is provided with a means for passing electrolyte and products of electrolysis from the cell container bottom to its top through each unit 7 in sequence. Typically and conveniently this means simply comprises one or more holes 11 placed in diagonally opposite corners of partitions 9 to provide a tortuous flow path, thus insuring adequate circulation and mixing with a minimum of current leakage.
In the first cell unit 7' is horizontally disposed a foraminous dimensionally stable monopolar terminal anode 13 connected to current supply means 15. Correspondingly, in the last cell unit 7" is a horizontally disposed, foraminous, U-shaped, monopolar terminal cathode 17, spaced apart from partition wall 9 and connected to current withdrawal means 19. Thus, an electrolyzing current may be impressed across current means 15 and 19. It will be readily apparent that the polarity of the terminal electrodes in cell units 7'and 7" may be reversed, that is, the monopolar anode 13 may be disposed in the last cell unit 7". Further, it is not necessary that the first and last cell units be defined by two adjacent partitions 9 since the first partition and the bottom of the container can as well define the first cell unit 7', with the last partition 9 and the cell container top defining the last cell unit 7".
In the embodiments shown, the terminal anode 13 and terminal cathode 17 are joined to current means 15 and 19 around a partition edge by conductive connecting portions 33 and 35, respectively. Other arrangements, such as direct extension through container wall 29 to external current means are possible.
Intermediate the terminal electrodes is at least one bipolar electrode comprising a foraminous, sheet-like, anode portion 21, a U-shaped, foraminous, cathode portion 23 adapted to receive and encompass a sheet-like anode, and a conductive connecting portion 25 joining said anode and cathode portions.
From the drawings, it will be seen that the U-shaped cathode portion 23 of the bipolar electrode in the first cell unit 7' encompasses the terminal anode 13, both said terminal anode 13 and cathode portion 23 being substantially parallel to the partitions 9 that form cell unit 7'. Cathode portion 23 is spaced apart from partitions 9, conveniently by spacing members 27 formed of an electrically insulating material. In the next-adjacent cell unit 7, bipolar anode portion 21 is encompassed by cathode portion 23 of the next bipolar electrode in the series, both again being spaced apart from and horizontal to partitions 9. It will be understood that if only two cell units, e.g., cell units 7' and 7", are employed in the particular cell, anode portion 21 of the bipolar electrode will be encompassed by terminal U-shaped cathode 17. At this point, it may be mentioned that the number of cell units, and hence bipolar electrodes, is limited only by practical mechanical considerations and the desired production to be obtained from the entire cell, containers having from 2 to 25 cell units being typical.
The anode and cathode portions of each bipolar electrode are joined by electrically conductive connecting portions 25 which are essentially perpendicular to the horizontally disposed anode and cathode portions and are held between an edge of the partition 9, on opposite sides of which said anode and cathode portions are disposed, and a container sidewall 29. Conveniently, and to insure a sealing (i.e., substantially liquid-tight) engagement, gasket 31 may be provided between wall 29 and partition edge 9. Alternately, each partition edge may be slotted to receive the connecting portion 25, any leakage resulting being negligible.
A variety of materials of construction for the bipolar electrodes are contemplated. Generally, these will be dimensionally stable electrodes, necessarily foraminous to insure proper electrolyte circulation and gas release and essentially planar or sheet-like in configuration. The anode portion may be of any conductive, resistant material bearing a coating electrocatalytic to the desired reaction, for example, expanded titanium metal covered with a platinum group metal, platinum group metal oxide, or similar, known, coating. The cathodic portion must also have appropriate physical and electrochemical characteristics and may be, for example, expanded titanium metal or palladium-titanium alloy (0.2 percent Pd), perforated stainless steel or nickel, or any of the foregoing or other metals, coated with an electrocatalytic material (e.g., a platinum group metal) or uncoated. The connecting portion may be any conductive, corrosion resistant combination of the foregoing but need not be electrocatalytic. For mechanical simplicity, the bipolar electrode may be formed from a continuous sheet of expanded (e.g., titanium) metal bent to the appropriate "S-shape", bearing an electrocatalytically active (e.g., platinum group metal oxide) coating on the anode portion and being uncoated on the cathode portion. On the other hand, the electrode may be discontinuous in the sense that the anode portion may be coated expanded (titanium) metal butt welded to perforated stainless steel connecting and cathodic portions. Other variations will suggest themselves to those skilled in the art.
In order to maintain the minimum anode-cathode gap necessary for efficient operation, e.g., 0.02-0.1, preferably about 0.03, inch, without the electrical short circuiting that would occur on anode-cathode contact, spacers to maintain this gap are suggested. A simple and effective spacer may be comprised merely of a flexible "shoestring" of inert polymer which may be interwoven in the foraminous electrodes to maintain the gap without substantially interfering with electrolyte circulation.
Alkali metal hypochlorites, especially sodium hypochlorite, are extensively employed for bleaching and disinfecting applications, e.g., in sewage treatment facilities. To avoid the expensive transportation of hypochlorite solutions, which are predominantly water, and further to avoid premature decomposition on storage, it is desirable to generate the needed hypochlorate at the site of use. Therefore, there is considerable demand for a compact, efficient, electrolytic cell for the generation of hypochlorite, which cell is operable for extended periods of time with a minimum of maintenance.
STATEMENT OF THE INVENTION
Therefore, it is an object of the present invention to provide a compact electrolytic cell for the production of hypochlorites at high current efficiencies.
This and further objects of the present invention will become apparent to those skilled in the art from the specification and claims that follow.
There has now been found an electrolytic cell comprising:
A. a substantially vertically disposed container having electrolyte inlet means in the lower portion thereof and electrolysis product outlet means in the upper portion;
B. a plurality of horizontally disposed, electrically nonconductive, partitions dividing said container into a plurality of cell units;
C. a terminal, foraminous, sheet-like, monopolar anode horizontally disposed in the first of said cell units;
D. a terminal, foraminous, monopolar cathode, horizontally disposed in the last of said cell units and comprising a U-shaped construction adapted to receive and encompass a foraminous, sheet-like anode;
E. means for impressing an electrolyzing current across said monopolar electrodes;
F. at least one bipolar electrode comprising
1. a sheet-like, foraminous, anode portion,
2. a U-shaped, foraminous, cathode portion adapted to receive and encompass a sheet-like anode, and
3. a conductive connecting portion joining said anode and cathode portions;
G. said bipolar electrode being horizontally disposed in adjacent cell units on opposite sides of a partitiion so that
1. said anode portion is encompassed by a next-adjacent cathode and is parallel to said partition,
2. said cathode portion encompasses a next-adjacent anode and is parallel to and spaced apart from the opposite side of said partition and the next-adjacent partition, and
3. said conductive connecting portion is held between an edge of said partition and a container sidewall; and
H. means for passing electrolyte and products of electrolysis from the bottom to the top of the container through the cell units in sequence.
Such a cell has a primary advantage of high current efficiency operation, apparently owing to the relationship of two cathodes for each anode created by the fact that each anode is encompassed by a U-shaped cathode. A further advantage relates to the long, useful life of the cell in continuous operation, at least in part due to the elimination of gas-liquid interface corrosion (since the cell is operated in a flooded condition). Ease of disassembly, replacement, and repair of component parts when required is also found.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a perspective view showing the relationship between the electrodes and partitions of a cell according to the present invention.
FIG. 2 is a vertical cross-section of a typical cell of the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Basically, the invention contemplates a vertically disposed electrolytic cell, divided by horizontal partitions and employing bipolar electrodes that parallel opposite sides of said partitions, the positive ends of said electrodes being foraminous sheets and the negative, or cathodic ends, also being foraminous and sheet-like but bent back on themselves to form a "U-shape" that encompasses the next-adjacent anode sheet. Thus, each cell unit defined by adjacent partitions contains a U-shaped cathode encompassing a sheet-like anode. Since the flow sequence of electrolyte and products of electrolysis is from the bottom to the top of the entire cell, each unit is operated in a substantially flooded condition.
The cells of the present invention may conveniently be used to produce alkali metal, especially sodium and potassium, hypochlorites in concentrations within the range of from 1 to 20 grams per liter by the direct electrolysis of alkali metal chloride solutions, typically having a concentration of from 5 to 100 g/l. Since the problem of cathodic deposits when employing impure alkali metal chloride solutions is well known, and in view of the fact that cells of the present invention contemplate two cathodes for every anode, it is desirable to employ an alkali metal chloride feed of high purity, thus avoiding the need for excessive backwashing or the like. Conditions of operation are typical, for example involving a pH on the order of 7 to 10, temperatures within the range of 5° to 50° C, etc.
The invention may be understood most readily by reference to the attached drawings wherein the vertical cell container is indicated generally at 1 and is provided with electrolyte inlet means 3 near the bottom thereof and an outlet 5 in the upper portion for unreacted electrolyte and products of electrolysis. The container 1 is divided into a plurality of cell units 7 by a plurality of electrically nonconductive partitions 9. Materials of construction for both the container and the partitions may be any mechanically sound, electrically nonconductive and corrosion resistant material, such as, polyvinyl chloride, chlorinated polyvinyl chloride, Lucite, and the like. Each partition 9 joins with the four container walls in a substantially sealing engagement to prevent current and electrolyte leakage. As explained more fully hereinafter, one, and generally a corresponding, edge of each partition engages the container wall in such a manner as to accommodate a bipolar electrode connecting portion. Each partition 9 is provided with a means for passing electrolyte and products of electrolysis from the cell container bottom to its top through each unit 7 in sequence. Typically and conveniently this means simply comprises one or more holes 11 placed in diagonally opposite corners of partitions 9 to provide a tortuous flow path, thus insuring adequate circulation and mixing with a minimum of current leakage.
In the first cell unit 7' is horizontally disposed a foraminous dimensionally stable monopolar terminal anode 13 connected to current supply means 15. Correspondingly, in the last cell unit 7" is a horizontally disposed, foraminous, U-shaped, monopolar terminal cathode 17, spaced apart from partition wall 9 and connected to current withdrawal means 19. Thus, an electrolyzing current may be impressed across current means 15 and 19. It will be readily apparent that the polarity of the terminal electrodes in cell units 7'and 7" may be reversed, that is, the monopolar anode 13 may be disposed in the last cell unit 7". Further, it is not necessary that the first and last cell units be defined by two adjacent partitions 9 since the first partition and the bottom of the container can as well define the first cell unit 7', with the last partition 9 and the cell container top defining the last cell unit 7".
In the embodiments shown, the terminal anode 13 and terminal cathode 17 are joined to current means 15 and 19 around a partition edge by conductive connecting portions 33 and 35, respectively. Other arrangements, such as direct extension through container wall 29 to external current means are possible.
Intermediate the terminal electrodes is at least one bipolar electrode comprising a foraminous, sheet-like, anode portion 21, a U-shaped, foraminous, cathode portion 23 adapted to receive and encompass a sheet-like anode, and a conductive connecting portion 25 joining said anode and cathode portions.
From the drawings, it will be seen that the U-shaped cathode portion 23 of the bipolar electrode in the first cell unit 7' encompasses the terminal anode 13, both said terminal anode 13 and cathode portion 23 being substantially parallel to the partitions 9 that form cell unit 7'. Cathode portion 23 is spaced apart from partitions 9, conveniently by spacing members 27 formed of an electrically insulating material. In the next-adjacent cell unit 7, bipolar anode portion 21 is encompassed by cathode portion 23 of the next bipolar electrode in the series, both again being spaced apart from and horizontal to partitions 9. It will be understood that if only two cell units, e.g., cell units 7' and 7", are employed in the particular cell, anode portion 21 of the bipolar electrode will be encompassed by terminal U-shaped cathode 17. At this point, it may be mentioned that the number of cell units, and hence bipolar electrodes, is limited only by practical mechanical considerations and the desired production to be obtained from the entire cell, containers having from 2 to 25 cell units being typical.
The anode and cathode portions of each bipolar electrode are joined by electrically conductive connecting portions 25 which are essentially perpendicular to the horizontally disposed anode and cathode portions and are held between an edge of the partition 9, on opposite sides of which said anode and cathode portions are disposed, and a container sidewall 29. Conveniently, and to insure a sealing (i.e., substantially liquid-tight) engagement, gasket 31 may be provided between wall 29 and partition edge 9. Alternately, each partition edge may be slotted to receive the connecting portion 25, any leakage resulting being negligible.
A variety of materials of construction for the bipolar electrodes are contemplated. Generally, these will be dimensionally stable electrodes, necessarily foraminous to insure proper electrolyte circulation and gas release and essentially planar or sheet-like in configuration. The anode portion may be of any conductive, resistant material bearing a coating electrocatalytic to the desired reaction, for example, expanded titanium metal covered with a platinum group metal, platinum group metal oxide, or similar, known, coating. The cathodic portion must also have appropriate physical and electrochemical characteristics and may be, for example, expanded titanium metal or palladium-titanium alloy (0.2 percent Pd), perforated stainless steel or nickel, or any of the foregoing or other metals, coated with an electrocatalytic material (e.g., a platinum group metal) or uncoated. The connecting portion may be any conductive, corrosion resistant combination of the foregoing but need not be electrocatalytic. For mechanical simplicity, the bipolar electrode may be formed from a continuous sheet of expanded (e.g., titanium) metal bent to the appropriate "S-shape", bearing an electrocatalytically active (e.g., platinum group metal oxide) coating on the anode portion and being uncoated on the cathode portion. On the other hand, the electrode may be discontinuous in the sense that the anode portion may be coated expanded (titanium) metal butt welded to perforated stainless steel connecting and cathodic portions. Other variations will suggest themselves to those skilled in the art.
In order to maintain the minimum anode-cathode gap necessary for efficient operation, e.g., 0.02-0.1, preferably about 0.03, inch, without the electrical short circuiting that would occur on anode-cathode contact, spacers to maintain this gap are suggested. A simple and effective spacer may be comprised merely of a flexible "shoestring" of inert polymer which may be interwoven in the foraminous electrodes to maintain the gap without substantially interfering with electrolyte circulation.