Patent Publication Number: US-3876520-A

Title: Electrolytic cell for generating chlorine

Description:
United States Patent [1 1 Blue et al.  
 [ Apr. 8, 1975 ELECTROLYTIC CELL FOR GENERATING CHLORINE [75] Inventors: Robert D. Blue; John A. Van  
 Westenburg; James J. Leddy, all of Midland, Mich.  
 [73] Assignee: The Dow Chemical Company,  
 Midland, Mich.  
 [22] Filed: June 17, 1971 [21] Appl. No.: 154,197  
 Related U.S. Application Data 3] Continuation of Ser. No. 780,711, Dec. 3, 1968,  
 Primary E.\&#39;aminer.lohn H. Mack Assistant Examiner-R. L. Andrews Attorney, Agent, or Firm-Earl D. Ayers [57] ABSTRACT The invention relates to the design parameters for diaphragm type chlorine cells. Specifically, the invention relates to the discovery that, in the design of cells in which the effective electrode height is greater than 3.5 feet, it is necessary for the efficient operation of the cells both with respect to current utilization and distribution, that anolyte brine recirculation rates be employed between the bottom and top of the anode(s) such that the ratio of recirculated anolyte brine flow in a given compartment of the electrolyzer to the amount of current passed through that compartment be in the range of 5l0 (preferably 7) GPM per kiloampere through that compartment. The preferred method for achieving this circulation is by providing an electrolyte redistibution flow means adjacent to and at right angles to the electrode faces, and whose cross sectional area, measured in a horizontal plane, is determined by the relationship: Area in sq. inches is equal to or greater than the kiloampere loading in that compartment of the electrolyzer. This preferred recirculation may also be achieved by the pumping of anolytye brine external to the cell. The flow distribution means is, if disposed adjacent to the electrodes, preferably prohibited from conducting current.  
 4 Claims, 4 Drawing Figures ELECTROLYTIC CELL FOR GENERATING CHLORINE This application is a continuation-in-part of Robert D. Blue et al., application Serial No. 780,711 filed December 3, 1968, for Improved Electrolytic Cell and Method of Operation Thereof, and now abandoned.  
 BACKGROUND OF THE INVENTION This invention relates to chlorine cells and particularly to so-called diaphragm type electrolytic cells used in the production of chlorine. In diaphragm type electrolytic cells of electrode height greater than 36 inches in which a gas is produced at either or both anode and cathode, it has long been assumed in the practice of the art that as larger cells were built, there existed a serious limitation in cell height, due to the blockage of electrode area in the upper region of a cell by so-called gas blinding as a result of the gas discharged in the cell, leading to poor current distribution and concomitant inefficient operation of the cell.  
  Such conclusions are also reached by Motonobu Minagawa and Tadas Ueda in their publication Studies on Electrolysis in Diaphragm Cells (Part III), Denki Kagaku (Electro-Chem., Japan) 35, 2l0-2l5 1967).  
  Accordingly, a principal object of this invention is to provide an improved diaphragm type electrolytic cell.  
  Another object of this in.vention is to provide an improved, more efficient diaphragm type electrolytic cell.  
  A further object of this invention is to provide a diaphragm type electrolytic cell having improved current distribution.  
  Yet another object of this invention is to provide a diaphragm type electrolytic cell having improved means for recirculating electrolyte which during cell operation rises between an electroactive anode &#39;face and an adjacent diaphragm surface.  
  In accordance with this invention, there is provided a diaphragm type electrolytic cell having an effective anode height in excess of three and one-half feet which is provided with anolyte redistribution flow means, whereby anolyte circulation between the bottom and top of the anode(s) in a given compartment of the electrolyzer is between five and ten gallons per minute per ,kiloampere applied through that compartment.  
 The anolyte redistribution means may be internal or external f the electrolyzer structure.  
  The invention, as well as additional objects and advantages thereof, will best be understood when the following detailed description is read in connection with the accompanying drawing, wherein:  
  FIG. 1 is a side elevational view, partly broken away and in section of apparatus in accordance with this invention;  
  FIG. 2 is a sectional view taken along the line 2-2 of FIG. 1;  
  FIG. 3 is a sectional view taken along the line 33 of FIG. 2, and  
  FIG. 4 is a fragmentary sectional view, similar to FIG. 2, showing external anolyte redistribution means.  
  Referring to the drawings, and particularly to FIGS. 1, 2 and 3, there is shown a diaphragm type chlorine cell, indicated generally by the numeral 10, including an electrolyzer housing 12 comprising bottom 14, top  
 16, sides 19, 20, and ends 18a, 18b, each made of conventional cement formulations, as is well known to those skilled in the art.  
  Disposed within the housing is an anode back plate 28, usually made of graphite, to which the graphite (for example) anodes 30 are rigidly mechanically and electrically coupled, the anodes 30 usually being substantially perpendicular to the back plate 28 which lies against the side wall 19 and extending across the housing towards the opposite side wall.  
  The top wall 16 has a port 22 through which chlorine is withdrawn from the cell. Brine is added to the electrolyzer unit through a port 24 in the top 16 and catholyte is withdrawn through the port 26 at the bottom of the cell. A trap, not shown, is used to adjust the catholyte level of the cell. The anolyte level 38 is maintained above the catholyte level during the operation of the cell.  
  An array of cathode pockets 32, which extend outwardly from a back screen 34, form the cathodediaphragm structure of the cell. As seen in FIG. 2, studs 36, extending from the cement side wall 20, provide means for making the cathode-diaphragm screen structure less subject to flexing.  
  Leads 40, 42 are used to apply direct current to the anode and cathode, respectively.  
  The upper end of the back screen 34 is protected from attack by chlorine by the cement ridge 62 into which the back screen 34 is. bonded. The ridge 62 extends below the anolyte level 38 of the cell.  
  As is shown in FIG. 3, a greater than normal space is provided between the outer ends of the pockets 32 and the back plate 28. The general area, designated 48, bounded by the end part of pockets 32, the end plate 28 and the inner end part of the adjacent anodes 30, forms an anolyte redistribution means in accordance with this invention.  
  Alternatively, increased space may be provided between the outer end 64 of any anode and the adjacent part of back screen 34 to provide increased anolyte redistribution means. Also, a combination of the two above described means may be used in a single electrolyzer cell.  
  It is desirable that the anolyte redistribution means be relatively free from electrolytic activity, and to help achieve this aim, a coating of insulating material, such as phenol formaldehyde, for example, may be applied, as at 46 and/or 66.  
  The invention is based on the discovery that, in the design of diaphragm type electrolytic cells in which the effective electrode height is greater than 3.5 feet, it is necessary for the efficient operation of the cells both with respect to current utilization and distribution, the anolyte brine circulation rates be employed between the bottom and top of the anode(s) such that the ratio of anolyte brine flow in a given compartment of the electrolyzer to the amount of current passed through the compartment be in the range of 5-10 (preferably 7) gallons per minute per kiloampere through the compartment. The preferred method of achieving this circulation is by providing an electrolyte redistribution flow means adjacent to and at right angles to the electrode faces, and whose cross sectional area, measured in a horizontal plane, is determined by the relationship: Area in sq. inches is equal to or greater than the kiloampere loading in that compartment of the electrolyzer. This preferred circulation may also be achieved by the pumping of anolyte brine external to the cell.  
 The flow distribution means is, if disposed adjacent to the electrodes, preferably prohibited from conducting current.  
  As used in this application, a compartment is defined as the space between two adjacent anodes less the space occupied by the interleaved cathode pocket.  
  The current loading of each compartment is between 0.25 ampere and about 5 amperes per sq. inch of electro-active anode surface.  
  It should be noted that a hydrogen vent 61, shown in FIG. 2, is provided at the upper end of the catholyte compartment.  
  While the brine throughput in an electrolyzer unit may be only a few gallons per minute, the recirculation in the electrolyzer may be upwards of several hundreds of gallons per minute because of the gas lift pump action between the anodes and the adjacent cathode pockets. Providing the required recirculation paths in accordance with this invention enables the maintenance of the massive liquid flow between the anodes and cathodes which enables the rapid removal of chlorine from the electroactive anode-cathode area while keeping an adequate supply of liquid even at the upper parts of the anodes and cathodes and thus permitting efficient operation of cells having anodes up to 8, l0, 12 or more feet in height.  
  An alternative means of achieving brine recirculation through a compartment in a series type chlorine cell is shown in FIG. 4.  
  A tubular recirculation loop 48 having a pump 58 incorporated therein extends through bores 50, 56 in the upper and lower parts of wall 19a and through the graphite back plate 28a. The bore 50 is above and the bore 58 is below the anode 30a. Each bore lies between an anode and its adjacent pocket.  
  Chlorine escapes through port 22a and is collected in hood 44. The bottom 14a is the same as bottom 14 shown in FIGS. 1 and 2.  
  External redistribution flow loops 48 disposed along the electrolyzer body supplement the limited internal anolyte recirculation return path of each compartment found in prior art chlorine cells.  
  Thus. the anolyte recirculation means in accordance with this invention may be accomplished internally, externally, or a combination of both with respect to the housing of the electrolyzer.  
 What I claim is:  
  l. A diaphragm type electrolytic chlorine cell having an enclosed housing including top, bottom, ends and sides, an array of interleaved anode and cathode elements having a height in excess of 42 inches disposed within and supported from the sides of said housing, each anode havingan outer end and having an inner end supported from said side of said housing, said an-- odes being supported from the side of said housing opposite the side from which said interleaved cathodes are supported input and output means for circulating brine through said housing, means for applying direct current across said anode and cathode elements, means for withdrawing chlorine from above said anode elements, and flow channel means defined by two adjacent anode inner ends, said housing and the interleaved unsupported cathode end and including within said flow channel means at least one vertically disposed electroinactive area at and between said inner ends of said adjacent anodes and extending along adjacent facing sides of said anodes, for circulating substantially gas-free brine downwardly between each pair of adjacent anode element and the cathode element interleaved therewith.  
  2. A chlorine cell in accordance with claim 1, wherein said anode and cathode height is between 42 inches and 15 feet.  
  3. A chlorine cell in accordance with claim 1, wherein said cell contains additional flow channel means disposed between the outer end of an anode element and the adjacent semi-surrounding cathode structure, said outer end of said anode element being substantially inactive electrolytically.  
  4. A diaphragm type electrolytic chlorine cell having an enclosed housing including top, bottom, ends and sides, and array of interleaved anode and cathode elements having a height in excess of 42 inches disposed within and supported from the sides of said housing, each anode having an outer end and having an inner end supported from said side of said housing, said anodes being supported from the side of said housing opposite the side from which said interleaved cathodes are supported, input and output means for circulating brine through said housing, means for applying direct current across said anode and cathode elements, means for withdrawing chlorine from above said anode elements, and flow channel means defined by two adjacent anode inner ends, said housing and the interleaved unsupported cathode end and including within said flow channel at least one vertically disposed electroinactive area at and between said inner ends of said adjacent anodes and extending along adjacent facing sides of said anodes for circulating substantially gasfree brine downwardly between each pair of adjacent anode element and the cathode element interleaved therewith, said flow channel means having an effective cross sectional area in square inches whereby brine is recirculated between each anode face and the adjacent cathode surface because of the gas lift action therebetween during operation of said cell at a rate of between 5 and 10 gallons per minute per thousand amperes applied between said anode face and said adjacent cathode surface.