US 2219342 A
Description (OCR text may contain errors)
Oct. 29, 1940. H, L STEWART 2,219,342
APPARATUS FOR ELECTROLYSIS Filed June 26, 1936 2 Sheets-Sheet l 'l Il IlI "lll Oct. 29, 1940. H L STEWART 2,219,342
APPARATUS FOR ELECTROLYSIS Filed June 26, 1936 2 Sheets-Sheet 2 @EBM f8 i6 i? Patented Oct. 29, 1940 APPARATUS F B. ELECTBOLYSIS Hubert L.- stewart, Pittsburgh, rs., assigner, by
mesne assignments, to Koppers Gompany, a corporation of Delaware Application June' 26,
This invention relates to improvements in apparatus for electrolysis. More particularly, the invention relates to cells employed for the electrolysis of solutions of materials to generate useful products therefrom.
In the accompanying drawings which serve to illustrate the present invention, and in which like reference characters denote like parts in the apparatus.
Figure 1 is a sideelevational view of an elec trolyzer having a plurality of cells;
Fig. 2 is a view of one side of a plate used as an electrode inan electrolyzer comprising the present invention;
Fig. 3. is a vertical sectional view showing the relative positioning of two plates to form a cell;
Fig. 4 is an elevational view of a vertical edge of a. plate;
Fig. 5 is a view of one side of a modified form 20 of plate;
Fig. 6 is a sectional view of a plate on line 8 8 of Fig. 5 in the direction of the arrows;
Fig. 'I is a sectional view of a portion of a plate showing one form of a structural detail thereof;
Fig. 8 is a view on line 8-8 of Fig. 3 showing the structure of means provided between the plates.
Referring to Fig. 1 of the drawings, the appara- 30 tus shown by way of example includes a bipolar electrolyzer of the multi-cell, lter-press type designated generally by the numeral I, means for .introducing liquids into the cells, and means for withdrawing materials therefrom in a particular 35 manner to be described below.
The electrolyzer I comprises a series of metalli plates or electrodes 2 clampedtogether in a heavy frame 3, electrically insulated from one another and separated by diaphragms 4 (described in 4fur- 0 ther detail below) of porous fabric, such as asbestos fabric or canvas. The plates 2 are recessed centrally to form a cell between opposing faces, each cell being divided by the diaphragm material into an anolyte chamber and a. catholyte cham- 45 ber. In the drawings, the electrolyzer is shown with twenty-.one intermediate plates each centrally recessed on both sides, and two end plates, the master anode 5 and the master cathode 6, each centrally recessed on the inner side only.
The frame 3 may be of any type suitable for clamping the plates tightly against each other. Channel bolting strips 'I may be welded on the outer side of both the master anode 5 and the master cathode 6. Tie bolts 8 are provided which 55 are properly insulated from the channels at both 193e, serial No. 37,569
(ci. s-25s) ends. For instance, a fiber bushing 9 and a. ber washer III may be provided to insulate the ends of the tie bolts 8 from the channel strips l.
Figs. 2 to 8 inclusive illustrate the construction of the plates or electrodes 2. Each plate is provided with passag'eways in the body thereof for conveniently introducing an electrolyte into the cells and for `withdrawing solutions and gases therefrom. 'I'he plate, shown in Figs. 2, 3 and 4, is an intermediate plate. It is recessed centrally on both sides, shoulders II and I2 being formed at and around the edges. Passages I3 and Il extend through the shoulders II and I2 respectively and communicate with the recess on op posite sides of the plate. The passage I3 leads to a passage I5 and the passage Il leads to a passage I6. The passages I5 and I6 extend through the thickness of the plate in spaced projections Il and I8 extending from the upper edge of the said plate. When a plurality of plates are brought together, the passages I5 and I6 coincide with corresponding passages in each plate and form gas oiftakes I5' and I6' through which gases from opposite sides of the plates are withdrawn.
An important feature of the present invention is the provision of passages in the plates for the introduction and withdrawal of liquids. As illustrated by way of example, passages I8 and 20 extend into the body of a plate preferably in the portions of the shoulders II and I2 on the lower edge of the plate and substantially parallel with said edge. The passages I9 and 20 may extend from either of the normally vertical edges of a plate (Fig. 2), but preferably from the same edge (Fig. 6) to the opposite edge at which the passages xnay be dead-ended or they may extend part of the way through as shown. Ports 2| connect the central recessed portion on one side of a plate `2 to the passage I9, and ports 22 connect the central recessed portion on the other side of the plate to the passage 20.
- In Fig. 3, two plates 24 and 25 similarly constructed are shown assembled to form a cell 26 of an electrolyzer. Passages 21 and 28 near the level 29 of the electrolyte extend into each of the plates 24 and 25 from either one of the outer edges. In Fig. 2, the passage 2l is shown extending into the electrode from one edge, and the passage 28 is shown extending into the electrode from the opposite edge of a plate.
The passage 2l is connected to the surface of one face 30 of a plate by ports 3i. The passage 28 is connected to the surface of the opposite face 32 of the plate by ports 2l. The face 38 of a Y between the plates.
plate is preferably provided with a nickel plating 34 that serves as the anode. The iron surface of face 32 serves as the cathode of a cell.
lThe diaphragm 4, referred to above, is clamped On either side of the diaphragm, gaskets 36 and 31 are fitted to provide for the proper insulation of the plates from one another and to prevent leakage of the electrolyte solution. A preferred form of gasket is shown in Fig. 8. This gasket made of rubber, forv example, frames a central portion of the diaphragm 4 which is left exposed to the electrolyte. The gasket extends inwardly from the outer edge of a plate and beyond the inner edges of the shoulders II and I2. The upper horizontal portion of a gasket extends downwardly from` thetop of a cell to slightly below the liquid level (see Fig. 3) to prevent, by highly effective means, the mixing of gases, that is, to keep gas generated at the anode separate from the gas generated at the cathode.
'Ihe lower horizontal portion and the vertical-side portions of the gasket prevent current from passing through the diaphragm between the edges of adjacent electrodes. Openings 38 andy 39 in the gasket, register with the passages I5 and I6 respectively in a plate. Insulating tubular sections 48 and 4I are providedas linings for the passages I5 and I6 respectively to prevent any escape of current in case entrained electrolyte collectsvin the gas oltakesfl and I6 (Fig. 1).
Nipples 42 are provided at the outlets of each of the passages I9, 20, 21 and 28, to which nipples, i'lexible tubular means are removably con! nected. The tubular means are preferably made of insulating material such as rubber. In Fig. 1, the tubular means 43 are shown connecting the passages 21k of each plate 2 to a manifold `44. Tubular means 45 connect the passages 28 of each plate 2 to a manifold 46. Tubularmeans 41 connect the passages I9 of each plate 2 to a manifold 48. Tubular means 49 connect the passages 20 of each plate 2 to a manifold 50. The manifolds 44, 46, 48, and 59' are each at 5I, 52, 53, and 54 respectively.
The manifold pipe 44 is provided with a vertical extension 55 and a branch pipe 56. The manifold pipes 46 and 48 are both connected to a vertical pipe 51 provided with a branch pipe 58 extending downwardly into'a tank 59. A pipe 60 leads from the tank 59 to a pump 6I. vThe pump 6I is connected to the open end 62 of the pipe 51 by means of a pipe 63.
The manifold pipe 50 is connected to a vertical extension 64 provided with a branch pipe 65( In the modified electrode plate shown in Figs. 5, 6 and' 7, instead of a plurality of ports such as 2I, 22, 3I and 33 connected to the passages I9, 20, 21 and 28 respectively, slots 66, 61, 68 and 69 may be provided for ingress or egress of liquids through the passages 10, 1I, 12 and 13 respectively. The slots may extend part of the way or entirely across the central surfaces of the electrodes and are preferably narrower than the diameter of the passages, thereby forming constricted apertures as shown in Fig. 7.
The electrode plates described above for a filter-press type -of electrolyzer make it possi,
ble to introduce electrolyte solution or withdraw products of electrolysis or both simultaneously,
in a highly efficient manner. If a product of electrolysis formed in a-cell, has a specific gravity less than that of the electrolyte, the use of the electrode makes it possible to withdraw the product directly from the upper portion of the surface of the electrode at which the product dead-ended is formed while introduction of the electrolyte is accomplished at a lower level in the cell. Also, if a product of electrolysis has a. specific gravity greater than that of the electrolyte, means are provided in the electrode at whichthe heavier product is formed, for introducing electrolyte solution at an upper level in a cell at the surface of the electrode while withdrawal of the said heavier electrolysisproduct is accomplished at a lowerlevel in the rcell. The electrode plate employed makes it possible to withdraw products of electrolysis, from zones in a. cell in which they are most concentrated.
The tubular connections between the cells and the several manifolds may be interchangeable to provide-for feeding electrolyte and lwithdrawing 4electrolysis products at the desired levels depending upon their relative specific gravities. The manifolds 44, 46, 48 and 50 are preferably spaced some distance from the cell (as much as ve feet in some cases) to prevent, as much as possible, any current flow through the liquids in the manifolds. To further prevent any possible loss of current through the insulating tubular, connections and the manifolds, suitable means may be provided by which, the resistance of the electrolyte in the tubular` means is increased. For instance the installation of overvoltage dams may 4'be provided. Such dams may consist of two nickel screen discs placed transversely in the insulating tubular connections spaced apart and connected by a Wire of low resistancesuch as iron or copper. The voltage necessary in such a construction to overcome the resistance of the electrolyte in the said tubular connections is increased in amount equal to the hydrogen and oxygen overvoltages on nickel in view of which the ow of current through the said connections and manifolds will be decreased. A dam comprising two screen discs d and d' held inspaced relation, and a. connecting wire w is shown in Fig.- 2 in a tubular connection c, a portion of which is enlarged for purposes of illustration.
Avmethod of operating the electrolyzer shown in the accompanying drawings may be illustrated in connection with the electrolysis of certain chemicals. Sodium carbonate (Na2CO3) solution, for instance, is electrolyzed to produce sodium hydroxide (NaOH) and sodium bicarbonate (NaHCO).
Sodium carbonate in an aqueous solution containing about 1.8 lbs. sodium carbonate per gallon to about 2 lbs. per gallon is pumped from the tank 59 by means of the pump 6I into the pipe 51. They solution may, if desired, be preheated to about 60 C. to 80 C. by means of a steam coil 14 in the tank 59. The level 29 of the electrolyte in the cells is maintained con-` stant by means of the overow pipe 58 which returns surplus electrolyte solution toA the tank 59.L The solution entering the pipe 51 flows through the manifold' 46, the flexible tubular.
means 45, the passage 28ports 33 (or passages 1I and slots 61) and into the upper zone of the cathode chamber of each cell 26. The electrolyte also flows through the manifold 48, the exible tubular means l41', the passages I9, ports 2| (or passages 12 and slots 68) and into the bottom oftheanode chamber of each cell 26.
Upon flow of current from a generator 15 (diagrammatically shown in Fig. 1) sodium bicarbonate is generated at the anode of each cell, and sodium hydroxide is generated at the cathode of each cell.l The bicarbonate solution generated, having a lower specific gravity than the sodium carbonate solution being electrolyzed, rises in the cells in the anode chambers and is Withdrawn near the level of the electrolyte or as close 4to the liquid-gas interface as is practicable through ports 3l, passages 21 (or slots 68 and passages l0) exible tubular means 43, and manifold pipe 44; and overflows through the pipe 56. The generated sodium hydroxide solution, having a higher specific gravity than the sodium carbonate solution being electrolyzed, is withdrawn from the bottom of the cathode chamber of each cell through ports 22, passages 20, (slots 59 and passages 13) flexible tubular means 49, and manifold pipe 50; andoverfiows through the pipe 65.
As indicated in the drawing, (Fig. 1), the overow pipe 56 is at a silghtly lower level than the overow pipe 58, and the overflow pipe is at a slightly lower level than either pipes 56 or 58. By means of this arrangement a difference of the static heads of the various solutions is maintained depending upon the specific gravities thereof. The levels at which the electrolysis products are withdrawn will depend upon their relative specific gravities. For thispurpose, pipes 55 and 64 may be constructed so as to be extensible. Alternatively, a swivel pipe connection 85 such as that shown connected to the pipe 65 may be provided which may be turned any angle. 'I'he pipe 85 is shown in full line in a position at which the liquid is withdrawn at the level of the pipe 65. Sodium bicarbonate solution preferably has a hydrostatic head greater than that of the caustic soda in order to prevent infiltration of caustic soda from the cathode chamber into the anode chamber. Such infiltration tends to neutralize the eil'ects of electrolysis.
A substantial space between the level of the electrolyte and the tops of the cell chambers is preferred so that no liquid is carried with either the hydrogen or oxygen through the passages I3 or I4 respectively.
As indicated above, the electrode plates are bipolar, nickel plating being provided on the anode side and iron on the cathode side. Stainless steel containing 18% chromium and 8% nickel may be used in the anode, if desired. Copper, cadmium, or Monel metal may be substituted for the iron as the cathode. Iron for the cathode is preferred because of its low over-voltage. One or more leads are attached to the master plates. More than one lead to each of the said plates is used to provide for proper distribution of current.
The cell temperature and current density are maintained fairly constant by regulating the voltage. A cell or electrolyzer may be operated with a current density of about 50 amperes per squarev foot to about amperes per squarefoot. The cell temperature rangesy preferably from about 60 C. to about 80 C. 'Ihe temperature should not be so high as to produce too violent an evolution of gases and should not be so low as to raise the resistance of electrolyte too high. The use of the form of plate provided with passages described above is advantageous in that it preheats the electrolyte as the solution flows through the passages. v
The rate of introduction of sodium carbonate solution into the cells depends on the concentration of solutions that are to be withdrawn. The feed to the cathode chambers may differ, if desired, from the feed to the anode chambers. In the electrolysis of the sodium carbonate solution, the feed to the cathode chamber may be about 1.0 gallon per hour per kilowatt hour and to the anode chamber about 1.2 gallons per hour per kilowatt hour. For the purpose of thus controlling the feed, ,valves 80 and 8| may be provided in pipes 48 and 48 respectively. A feed of approximately twenty per cent faster through the anode chamber is found advantageous in preventing the accumulation 0f solid sodium bicarbonate. The cell feed is preferably at such a rate as to convert from about 40% to about 48% of the sodium present as sodium carbonate into sodium hydroxide, and from about 40% to about 48% of the sodium present as sodium carbonate into sodium bicarbonate leaving sodium carbonate unchanged to the extent of about from 4% to 20%.
Throughout the operation of a cell the cell feed-current density ratio is controlled in such a manner as to give maximum yields of electrolysis products. Periodical analyses of the electrolysis products may be made from time to time to determine the concentrations of sodium Ahydroxide and sodium bicarbonate.
In the commercial operation of the cell, a current eiliciency of between 92 and 98% and an energy efliciency of between 46 and 52% are obtainable. The yields of 0.71l to 0.79 pound of sodium hydroxide per kilowatt hour can be obtained.
Besides electrolyzing sodium carbonate the process may be applied to solutions of potassium carbonate, and of borax. Borax will produce sodium hydroxide and boric acid. Potassium carbonate will be converted into potassium hydroxide and bicarbonate. Disodium phosphate is converted into sodium hydroxide and monosodium phosphate.
It is apparent from the above description that various changes maiy be made in the form, construction and arrangement of parts without departing from the spirit and scope of the invention or sacrificing all of its material advantages, the forms hereinbefore cited by way of illustration being merely the preferred embodiments thereof.`
What I claim is:
1. In apparatus for electrolysis, comprising a generator of the filter-press type having a plurality of electrode plates clamped together face to face and centrally recessed to provide a cell between each pair of plates; manifold means, and connecting means constructed of insulating material between each -of the cells and the said manifold means for the passage of solution to Aor from the cells,` and an overvoltage dam in each of the said connecting means, the said dam comprising spaced screens positioned transversely in the said connecting means, and a wire of low resistance connecting the said screens.
2. In apparatus for electrolysis comprising a plurality of cells which cells connect-with each other by passage means for conducting liquid to or from the said cells, the said passage means having a wall constructed of insulating material, an overvoltage dam in such passage means, the said dam comprising spaced metallic, foraminate means positioned transversely in the said passage means, and an electrical conductor of low resistance connecting the said spaced foraminate means.
3. Apparatus comprising means for inhibiting the flow of current through a passage having a wall constructed of insulating material and containing an electrolyte, the s'aid means comprising spaced metallic, foraminate means positioned transversely in the said passage, and an electrical conductor of low resistance connecting the said foraminate means.
4. In apparatus for electrolysis, a solid electrode plate for a bipolar electrolyzer of the multicell, iilter press type, having separate anolyte and catholyte chambers and a separate gas oitake for each chamber, a plurality of unconnected passages of relatively small cross section in said plate l@ each extending from an outer edge of the plate into the body thereof to a working face of the plate, one of said passages extending to the surface of the plate at points extending across a workingface of the plate adjacent butl below the 15 normal level of electrolyte solution in the electrolyzer, and another of said passages extending to the surface of the plate at points extending across a working face of the plate adjacent the lower edge of the working face of the plate, each g@ of the said passages serving alternatively for the introduction of electrolyte solution or for the withdrawal of a. solution of a product of electrolysis at the said levels.
5. In apparatus for electroylsis, a solid elec'- 25 trode plate for a bipolar electrolyzer of the multicell, lter press type, having separate analyte and catholyte chambers and a separate. gas oitake for each chamber, a plurality of unconnected passages of relatively small cross section in said plate a@ each extending from an outer edge of the plate into the body thereof to a Y,Working :face of the plate, one of said passages extending to the surface of the plate at points extending across one Y working `face of the plate adjacent but below the 35 normal level of electrolyte solution in the electrolyzer, another of said passages extending to.
the surface o1' the plate at points extending across the said one working face of the plate adjacent the lower edge of the said face, a third of said passages extending to'the surface of the plate at points extending across the opposite Working face 5 of the plate adjacent the level of the said rstnamed points, and a fourth of said passages e'xtending to the surface of the plate at points extending across the said opposite working face of the plate adjacent the level of the said secondnamed points, each nof the said passages serving alternatively for the introduction of electrolyte solution or for the withdrawal of a solution of a product of electrolysis at the said levels.
6. In apparatus for electrolysis, a solid electrode plate for a bipolar electrolyzer of the multicell, iilter press type having separate anolyte and catholyte chambers and a. separate gas 01T- take for each chamber, a plurality of unconnected passages of relatively small cross section in said plate each extending from an outer edge of the plate into the body thereof, a plurality of elongated slots extending substantially completely across a working face ofthe plate, one of said passages extending to a slot in the working 'face 25 of the plate adjacent but below the normal level of electrolyte solution in the electrolyzer, and another of said passages extending to a slot adjacent the lower edge of the Working face of the plate, a portion of each of the said passages adjacent the said slots tapering toward the latter and each of the said\ passages serving altertively for the introduction of electrolyte solution or i'or the withdrawal -of a solution of a product of electrolysis at the said levels. l 35 HUBERT L. STEWART.