US716804A - Apparatus for producing caustic soda by electrolysis. - Google Patents

Description

flu. 7|6.804. Pa'iented Dec. 23, I902.

E. A. ALLEN & H;-

Moons. APPARATUS FOR PRODUCING cAusm: souA BY ELEGTROLYSIS.

(Application filed Dem 27, 189B. Renewed. May 14, 1902.)

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m. 716,804; Patented Dec. 23, 1962.

E. A. ALLEN & H. K. mouse.

APPARATUS FOR PRODUCING CAUSTC SUDA. BY ELECTROLYSS.

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g E g g (Application filed Dec 27, I898. Renewed may 14, 1902.)

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E. A. ALLEN & H. K. MOORE. v APPARATUS FOR PRODUCING GAUSTIC SODA BY ELECTROLYSIS.

(Application filed Dec. 27, 1898. Renewed. May 14, 1902.)

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UNITED STATES PATENT OFFICE.

EDWARD A. ALLEN, OF RUMFORD FALLS, MAINE, AND HUGH K. MOORE, OF LYNN, MASSACHUSETTS, ASSIGNORS, BY MESNE ASSIGNMENTS, TO MOORE ELECTROLYTIC COMPANY, OF PORTLAND, MAINE, AND BOSTON, MASSACHUSETTS, A CORPORATION OF MAINE.

APPARATUS FOR PRODUCING CAUSTlCSODA BY ELECTROLYSIS SPECIFICATION forming part of Letters Patent No. 716,804, dated December 23, 1902. 7

Application filed December 27, 1898. Renewed May 14, 1902. Serial No. 107,313. (No model.)

To all whom it may concern.-

Be it known that we, EDWARD A. ALLEN, of Rumford Falls, in the county of Oxford and State of Maine, and HUGH K. MOORE, of Lynn, in the county of Essexand State of Massachusetts, have invented certain new and useful Improvements in Methods of and Apparatus for Producing Caustic Soda byElectrolysis, of which the following is a specification. This invention has relation to apparatus for producing chlorin and caustic sodaby electrolysis from a saturated solution of sodium ohlorid, although, so far as the apparatus itself is concerned, it may be employed :5 for the production of any other hydrate or sulfid of an alkali metal.

The first and primary object'of the invention is to produce caustic soda and chlorin for commercial use in large quantities at a low cost.

A second object of the invention is to provide an improved cell by means of which the caustic soda or other hydrate or sulfid may be formed at its point of discharge therefrom,

so that it will not be difiused through the electrolyte, but will be carried off in fluidv form to a receptacle provided for its reception without the aid of foreign matter.

A third obj ect of the invention is to provide an improved cell by means of which the saline solution may percolate through the dia phragm and be subjected to continued electrolysis before the solution of caustic soda, salt, and water reaches the receptacle pro- Vided for it.

Reference is to be had to the accompanying drawings, and to the letters marked thereon, forming a part of this specification, the same letters designating the same parts or features, as the case may be,wherever they occur.

Of the drawings, Figure 1 represents in plan view a plurality of cells embodying our invention. Fig. 2 represents a section on the line 2 2 of Fig. 1. Fig. 3 represents in perspective view one of the cells. Fig. a represents an end view of the same. Fig. 5 represents a longitudinal section through the cell.

Figs. 6 and 7 represent transverse sections through the cell.

As heretofore constructed cells for the production of caustic soda have been formed with a semiporous diaphragm and an exterior electrode, the diaphragm being so constructed as to permit osmotic action, whereby the caustic soda was formed on the cathode; but the construction of said cells required the employment of jets of water or steam to carry away the caustic soda as it formed on the cathode, necessitating, therefore, an expensive plant and intricate arrangement of the cells and pi pes,besides causing deleterious results from the heat generated by the steam.

In carrying out our process we employ a non conducting vertical diaphragm which permits the solution to percolate through it in considerable quantities and a suitable cathode formed of wire sponge, steel wool, or other suitable substance which can be arranged in a porous layer of such thickness that by capillary attraction it will hold a considerable body of the solution of sodium chlorid and caustic soda and cause the continuation of the electrolysis as it passes downward through the sponge, whereby it reaches the receptacle prepared for it in a fluid condition with a 'minute percentage of sodium chlorid. The

metallic sodium is deposited in the cathode and the water contained in the undecomposed solution which passes through the diaphragm converts the said metallic sodium into sodium hydrate, and the electrolytic decomposition of the sodium salt which passes through the diaphragm into the pores of the cathode is continued to completion as thesolution flows slowly through the cathode to the receptacle prepared for it. By arranging the cathode substantially vertical the liquid which passes thereinto through the diaphragm flows gradually from edge to edge thereof and drops out when it reaches the lower part, and thereby the solution is subjected to continued electrolysis for the greatest possible length of time. In describing the cathode as substantially vertical we desire to be understood as meaning that it is inclined from the l1orizontal, so as to be out of the liquid and unsubmerged, in contradistinction to the cathode in those cells in which itis substantially horizontal and is submerged in the caustic solution. Where the cathode is horizontally arranged and is not submerged, but is raised above the solution, the liquid passes through it from face to face very rapidly and the electrolysis is continued for a short time. By permitting the liquid to flow entirely through the cathode from edge to edge instead of directly through it from face to face the resultant liquid contains a maximum percentage of the hydrate. In this way we obviate the necessity of employing jets of steam or water and are enabled to use the resultant liquid directly for various manufactures, as will be readily understood by those skilled in the art.

The cell consists of two end walls a a, rabbeted at their upper ends, as shown. to receive two side bars a at, thus leaving the longitudinal sides of the cell open. The ends are secured to a bottom plate a and they may be all formed of wood, although we prefer slate, since it lasts for many years without being affected by the process. The open sides are closed by a diaphragm b, of asbestos paper or other substance which will permit of the free percolation of the saline solution therethrough in aqueous or liquid form. On the outside of each diaphragm is the cathode e, which consists of a plurality of layers of wire-cloth or a bed of steel wool to form a comparatively thick sponge which will hold the solution suspended therein. The asbestos paper and the wire sponge are bent underthe bottom plate 0L2, as shown, so as to form an electrical contact with the elongated iron plate 01, upon which the cells rest side by side. The ends of the sponge and diaphragm are secured to the end walls a by strips a through which screws are passed into the said end walls, and consequently when the cell is made of slate holes are formed in it and are filled with lead to receive the screws. Longitudinal strips a are secured to the side of the cell and overlap the asbestos paper to secure it in place, as shown, there being similar strips 01, at the ends of the cells, and said strips are rabbeted' to form a continuous groove a outside of the walls ct a Theanode consists of a plurality of pieces of gas-carbon e e, which are cast in a lead plate 6, which rests loosely upon the top of the cell and overlaps the walls a a, as shown in Figs. 3 and 4. On top of the plate e is a jacketf, formed of sheet-lead, having its continuous edges bent downward, so as to fit in the groove a. The groove a is filled with any suitable non-volatile hydrocarbon, such as coal-tar, to form a lute and prevent the escape of theliberated chlorin gas which results from the electrolytic action. The plate a is formed with an aperture 6 which registers with a similar aperture in the lead jacketf. The latter is formed with a grooved annular ring f, surrounding the aperture therein, in the groove of which is luted a glass dome g,

having luted in the upper portion thereof a pipe g, which conducts away the chlorin gas.

We use the glass dome of the cell as an indication of the condition thereof, for as chlorim is yellowish green in color it can be seen in the dome when it is given off. Hence if the cell be out of order and carbonic-acid gas is being formed it can be detected by the change of color in the dome. We prefer to use the glass dome for another reason, t0o namely, to insulate each cell. Where the pipes lead from a plurality of cells to a common duct, the electric current is liable to be short-circuited,and hence the presence of the dome prevents it.

The electrolyte is introduced into the cell through an aperture a in the upper portion of the end wall, said aperture being normally closed by a valve or plug, and in order to maintain the electrolyte in a saturated condition the lead jacket is provided with a funnel 72, connected with a curved glass pipe 71, which forms a trap and which is introduced into the cell through an aperture in the lead pipe e, so that brine with salt in suspension may be poured through it, the brine remaining in the trap to form a seal.

The plate d, on which a plurality of the cells are placed side by side and with which they are all electrically connected,is inclined,

as shown, and is provided with a trough d on its lowest edge to receive the fluid resulting from the electrolysis and to conduct it to a suitable receptacle.

The reason for employing a substantially flat pan or plate is that it is necessary to withdraw the hydrate as it flows fromthe cathode and prevent its accumulation, and hence if a tank were employed to receive the cell and were provided with outlets at or near its bottom to discharge the hydrate solution as it accumulated its side walls would not perform the usual function of retaining the accumulated hydrate, and we would therefore regard such a tank as accomplishing the same result as the fiat pan or plate and as being included within our invention.

The anodethat is, the gas-carbon eis connected with the electric circuit through the medium of a mercury-cup t', while the cathode is connected with the other branch of the circuit through its contact with the iron plate which is in the circuit through a similar mercury-cup t".

The cell is partially filled with the electrolyte or saturated solution of sodium chlorid, the level of the liquid being above the lowest edge of the side walls ct-that is, above the exposed portion of the diaphragm. As the saline solution percolates through the diaphragm it is held in suspension by capillary attraction in the metallic sponge, free chlorin being given off in the interior of the cell at the anode and caustic soda being formed in the cathode and on the surface thereof.

As previously stated, the electrolyte perand the balance of the sodium chlorid is converted by the water of the undecomposed solution in the pores of the cathode into caustic soda, the chlorin atom migrating through the diaphragm to the anode, and the resultant fluid reaches the plate din the'consistency of molasses and consists of caustic soda and water with a minute percentage of sodium chlorid, the sodium chlorid, however, being in such small proportion that the solution given off is to all intents and purposes fairly free from it for commercial use. If desired, afterward the solution may be passed through an evaporating-pan and a centrifugal machine and freed from the last traces of the sodium chlorid.

We have found that a current density of not less than four hundred and forty-four nor over five hu ndred and ten am peres per square meter of the cathode-surface produces the best results, and the diaphragm should preferably be made to permit the percolation in one hour of substantially three liters to each square meter of diaphragm surface. This percolation or flow is easily regulated by varying the height of the column of liquid in the cell, but when the percolation is greater than three liters per square meter an hour the current density is increased proportionately.

By means of this cell and method which we have described we are enabled to produce caustic soda commercially at a very low cost and without the employment of steam or water jets. The chlorin may of course be conducted into contact with lime water or treated in any other known way for forming a bleach.

We provide means for withdrawing the liquid when the cell is in use, the same consisting of an aperture j, normally closed by a valve or plugj'. Whenever the cell is not in use-as, for instance, when the dynamo is not being usedthe chlorin which is dissolved in the liquid percolates with it through the diaphragm and attacking the caustic soda neutralizes it, forming sodium hypochlorite, and then the chlorin attacks the iron and destroys the sponge, with the formation of ferric chlorid. Hence it is important that we should provide means for withdrawing the electrolyte when the cell is not working.

We regard it as desirable that the temperature of the cell should not be increased beyond 80 centigrade, as above that point oxygen is given off from the water, which, uniting with the carbon of the anode,'gives off carbonic-acid gas with some carbon monoxid and renders the chlorin gas unfit for bleach ing purposes. It is well known that chlorin gas in a heated condition has a bad eifect upon the cell and piping connected therewith The temperature may be kept below 80 centigrade by regulating the electric current or by providing a very porous diaphragm through which the solution may freely flow,

whereby the fresh cool solution may be introduced in its place.

We also regard it as desirablethat the electrolyte should be always saturated with salt, for otherwise the solution around the anode becomes impoverished of salt, whereby the water is electrclyzed, giving oif oxygen on the anodein nascent condition, which unites with the carbon of the anode, forming carbon dioXid and carbon monoxid.

Vi e do not herein claim the herein-described process of producing chlorin and sodium hydrate, as it forms the subject-matter of a divisional application, Serial No. 6,4:80, filed February 26, 1900.

Having thus explained the nature of the invention and described a way of constructing and using the same, although without attempt-ing to set forth all of the forms in which it may be made or all of the modes of its use,

we declare that what we claim'is- 1; A cell of the character described, comprising a nou conducting substantially vertical diaphragm, sufficiently porous to permit the percolation of a considerable quantity of liquid, a suitable anode, and a cathode in contact with the outer face of the diaphragm, said cathode being formed of a porous layer of such thickness as to retain a considerable body of liquid in its pores, whereby the sodium deposited in the cathode is converted into hydrate by the water of theundecomposed solution which has passed through the diaphragm,

and the electrolyzing of the undecomposed solution in the pores of the cathode is completed as it flows therethrough from edge to edge.

2. A cell of the character described, comprising a receptacle forming the anode-compartment having a bottom, end walls, and longitudinal side strips or bars connecting the upper portions of the end walls, to leave the sides of the receptacle open, a porous diaphragm stretched across each of the open sides of the receptacle, and a spongy cathode outside each diaphragm, said parts being constructed and arranged whereby the entire body of electrolyte is confined within the receptacle and is allowed to percolate slowly through the diaphragm so as to saturate the cathode, and gravitate therethrough, in combination with a substantially flat pan or plate on which the receptacle rests, and from which the cathion solution flows as it is discharged from the cathode.

3. A cell of the character described, comprising a receptacle having end walls, and an open side, a vertical porous diaphragm closing said side, an anode in said receptacle, a

' substantially vertical cathode outside said diaphragm, and having its lower edge folded under the bottom of the receptacle, and an inclined flat metallic pan orplatein metallic connection with the cathode and upon which the receptacle and the folded part of the cathode rest, said parts being constructed and arranged whereby the undecomposed electrolyte percolates through the diaphragm and is decomposed, and the hydrate gravitates down the cathode to the plate, and flows off of the plate.

4. A cell of the character described, comprising end walls, a diaphragm closing one or more of the sides, an anode, a cathode outside the diaphragm, a cover, a lute ext-ending entirely around the upper part of the cell, and a false cover having its edges taking into the lute.

5. The combination of a metallic pan or plate, a plurality of receptacles resting removably on said plate, each receptacle having an anode, and a cathode at the side of and bent under the receptacle and adapted to make electrical contact with the pan or plate, and an electric circuit including said anodes, cathodes, and said pan or plate.

6. The combination of a plurality of receptacles each having an anode, and an unimmersed cathode, a substantially fiat metallic plate upon which the receptacles removably rest having provisions for continuously discharging the cathion solution, and an electric circuit having one terminal connected with the plate and the cathodes, and the other terminal connected in multiple with the anodes.

7. A cell of the character described, comprising a receptacle forming an anode-compartment having a bottom, end walls, and longitudinal side strips or bars connecting the upper portions of the end walls so as to have the sides of the receptacle open, an anode in said receptacle, a porous diaphragm stretched across each of the open sides of the receptacle, and a cathode outside of and in contact with said diaphragm, said cathode being formed of alayer of metalhaving pores to receive and hold a considerable body of liquid by capillary action, said elements being constructed and arranged whereby the entire body of electrolyte is confined within the receptacle and is allowed to percolate slowly through the diaphragm and after saturating the cathode to gravitate therethrough to the lower edge thereof.

In testimony whereof we have aflixed our signatures in presence of two witnesses.

EDWARD A. ALLEN. HUGH K. MOORE. Witnesses:

M. B. MAY, A. D. HARRISON.

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