US3311550A

US3311550A - Cell for the electrolysis of aqueous solutions of hydrogen chloride

Info

Publication number: US3311550A
Application number: US321766A
Authority: US
Inventors: Schoberle Robert; Stijnen Gerardus Nicolaas
Original assignee: Solvay SA
Current assignee: Solvay SA
Priority date: 1962-11-29
Filing date: 1963-11-06
Publication date: 1967-03-28
Anticipated expiration: 1984-03-28
Also published as: DE1467138A1; CH408877A; BE640396A; NL120628C; NL286119A

Description

March 28, 1967 R SCHOBERLE T CELL FOR THE ELECTROLYSIS OF AQUEOUS SOLUTIONS OF HYDROGEN CHLORIDE Filed Nov. 6, 1963 Ill ll wild] GAIN/Tilli- 3 l u b m II II J W W 6 INVENTORY ROBERT SC-HQBERLE GERARDUS NICOLAAS STl-JNEN FRANCIS M. CRAWFORD United States Patent 3,311,550 CELL FOR THE ELECTROLYSIS 0F AQUEOUS SOLUTIONS OF HYDROGEN CHLORIDE Robert Schoherle and Gerardus Nicolaas Stijneu, Roermond, Netherlands, assigmors to Solvay & Cie, Brussels, Belgium Filed Nov. 6, 1963, Ser. No. 321,766 Claims priority, application Netherlands, Nov. 29, 1962,

,119 8 Claims. (Cl. 204-256) The present invention relates to an improved cell for the electrolysis of aqueous solutions of hydrogen chloride.

It is known that during the substitutional chlorination of organic compounds and during the dehydrochlorination of chlorinated hydrocarbons hydrogen chloride is obtained as a byproduct. On account of the small demand for this compound, it is highly desirable to recover the chlorine. Two procedures have generally been used for this purpose, namely the oxidationof the hydrogen chloride by the oxygen of the air in the presence of a catalyst, and the electrolysis of aqueous solutions of hydrogen chloride. The latter method is generally preferred because it requires only a relatively simple and convenient apparatus and in addition has satisfactory adaptability.

Cells for the electrolysis of aqueous solutions of hydrogen chloride are generally constructed in a manner similar to -a filter press, that is, a plurality of electrolytic units combined into a single block and held between two end members by tie-rods. Each electrolytic unit carries a bipolar graphite electrode mounted in an acid-resistant frame.

The electrode can be formed either of a graphite plate deeply grooved on both sides or of a composite graphite plate grooved on the cathode side and covered with graphite granules on the anode side. In the latter case the consumption of the graphite from the anode side by the formation of CO can be compensated by the addition of graphite granules during the process.

Each electrolytic unit also comprises a diaphragm for separating the gases collected in the gas spaces above the level of the electrolyte and devices for keeping the electrolyte in circulation, and for evacuating the gaseous products.

In such cells the electrolyte circulates as follows: The concentrated solution enters into the anodic compartment of each element, then passes through the diaphragm and is removed from the cathodic compartment. The concentr-ation of the hydrogen chloride, which is about 30% by weight at the entrance, is at the outlet from the cathode compartment. greater current densities, for example, at 2000 to 3500 amperes/nfl, the electrolyte in the anode compartment is put into forced circulation through a refrigerant in order to control the thermal equilibrium in the cell.

Although such cells are of simple design, they present inconveniences which are sometimes serious.

Thus the graphite granules have a high ohmic resistance because of poor contact of the granules with one another and with the plate, which causes much loss of electric energy per ton of chlorine produced.

Electrodes formed of a single graphite :plate do not present this difiiculty, but since they are gradually consumed, their distance from each other gradually increases with 'a resulting increase of electric energy consumed, it not being possible to readjust the distance between the electrodes since the latter are fixed in frames that are pressed against one another. This is an inconvenience for both kinds of electrodes. In fact, since a junction is present between each frame, and since this junction is more or less compressed by necessity, some freedom of movement between the electrodes is to be expected, in

When such cells operate with o 3,311,559 Patented Mar. 28, 1967- view of the impossibility of moving them toward one another sufiiciently for optimum functioning of the cell, even when new. Furthermore, the cells and the frames must be manufactured with utmost precision in order to reduce the free play between the electrodes.

When the cells have to be reconditioned, and especially when it is necessary to replace one of the diaphragms which have only a limited life, it is necessary to completely dismantle the cell, even when only one element is defective. It naturally follows from this that the expense of upkeep of cells of the filter-press type is very great.

The design of these cells requires the presence of a tight joint between the electrolytic elements, which joint must extend around the entire frame of which the dimensions are generally of the order of 1.5 m. x 1.2 m. A cell with 30 frames must also have that many perfectly tight joints. The presence here of any leaks would be very detrimental because hot chlorinated solutions of hydrogen chloride are very corrosive. Also, it is difiicult to make these joints perfectly tight and especially to maintain them tight during the operation of the cell. It is necessary sometimes to resort to costly measures, such as the provision of a chamber of acid-resistant material under each cell.

The cells of this invention for the electrolysis of aqueous solutions of hydrogen chloride make it possible to remedy the above inconveniences. Such cells are characterized by: (1) an electrically insulated and covered trough in which are placed, without any attachment, the decomposition elements, (2) means for adding concentrated aqueous solution of hydrogen chloride to the decomposition elements, (3) the means for evacuating the gases formed and the diluted aqueous solution of hydrogen chloride, and (4) means for delivering the electric current necessary for electrolysis.

Other features of this invention will be presented here inafter and particularly in the drawings which show the invention in detail. The drawings are merely illustrative and not limiting, as the invention is capable of many variations.

FIGURE 1 shows a transverse section of a cell constructed according to this invention. FIGURE 2 is a longitudinal section of the same. FIGURE 3 is a vertical section of -a modified construction. FIGURE 4 is a longitudinal section of another modification.

In these figures, the trough 1 is of generally uniform internal cross-section and is made of material that is acid resistant and a nonconductor of electricity. It is closed by a cover 2, held down by flanges and bolts 3 and rendered fluid tight by a gasket 4. The cover is provided with an outlet 5 for the removal of chlorine gas. Each decomposition element is transversely positioned in the trough and comprises a bipolar graphite electrode 7 .grooved on both sides. The electrode is mounted in a frame 6 made of synthetic material or of steel protected by an acid-resistant coating. In the upper part of the frame is a gas chamber 8 for collecting liberated hydro gen. The frame carries a diaphragm 9. The gas liberated in the cathode compartment is collected by conduit 10 and delivered to gas chamber 8, from which it is delivered by conduit :11 to the collector 12. Conduit 11 is flexible, being either made of several removable elements or of flexible material. The gas obtained in the anodic compartment is collected in the chamber 13 formed by the cover 2 above the level of the electrolyte. Each frame is longitudinally moveable and provided with a packing 15 around that portion of its periphery which dips into the electrolyte, the purpose of this packing being to prevent extraneous currents. At the ends of the cell are two mono polar electrodes 16 connected to electric terminals 17. In the drawings the electric polarities have been indicated in accordance with the locations of the anodic and cathodic compartments, but it is obvious that the polarities could be reversed, in which case it would be the chlorine which would collect in gas chambers 8 of frames 6 and which would be delivered to the collector 12 while the hydrogen would collect in gas chamber 13 and would be evacuated through 5.

The circulation of the electrolyte can be effected in various ways. The fresh acid is introduced by the conduit 18 and is distributed by conduits 19 to the various compartments. It can be introduced into these compartments from either above or from below. In FIGURES l and 2 the addition of acid has been shown arbitrarily as being from below.

The evacuation of spent acid can be through the overflow conduit 21 in which there is an automatic valve 22 connected to a timer for permitting escape of the acid at regular intervals with concurrent lowering of the acid level in the trough, so as to permit renewal of the acid in the cathode compartment shown in the drawing. The liquid level can also be controlled by an automatic valve (not shown) on the collector 12 into which the gases from chambers 8 escape.

The removal of spent acid can also be accomplished by the methods shown in FIGURES 3 and 4.

In FIGURE 3 the gas chambers 8 are connected with one another through a collector 23 which is of such a construction that it will permit the distances between the gas chambers to change, as explained above. In FIGURE 4 each gas chamber 8 is connected by a flexible conduit 24 to a collector 25. In both of these cases the fresh acid can be introduced by means of the conduit 18 into the compartments outside the diaphragm, namely between the electrode and the diaphragm carried by two successive frames (which compartment can be anodic or cathodic according to the direction of the current), the other compartment being supplied by passage through the diaphragm. The acid then passes through the gas chambers and is carried away by collectors 23 or 26.

The advantages of such a cell are obvious. First of all, the fact that the decomposition elements are merely placed in the trough makes it possible to move them toward one another as much as possible at the start of the operation, and, since the connections to the collectors are all flexible, it is possible to adjust the distance between the electrodes during operation to compensate for their consumption on the anode side. The voltage drop then remains low, and consequently the energy consumption per ton of chlorine produced will be proportionately low. The frames are inexpensive to manufacture because their dimensions do not need to be exact when lateral looseness can be taken up by inexpensive packing which does not need to fit tight.

The design of this cell simplifies considerably the work of upkeep. In fact, to replace a diaphragm, it is sufficient to disconnect the cover from the cell and to pull out the defective element which can then be replaced or repaired.

The cell of this invention remains perfectly tight under all conditions because it has only one cover which is secured to the trough by a tight joint above the level of the electrolyte. Loss of chlorinated acid need not be feared, and it is furthermore possible to conduct the electrolysis under pressure with all the advantages which are incidental to this method of operation.

Finally the total length of this cell depends only on the thicknesses of the electrodes and not on the frames as in filter presses. 7

It is therefore possible to reduce the length to the minimum determined only by the thicknesses of the electrodes.

This results in but little crowding and reduces the cost to a minimum.

We claim:

1. A cell for the electrolysis of aqueous solutions of hydrogen chloride comprising (1) an electrically insulated trough of generally reinforced internal cross-sectional form tran-sversally closed by a cover and in which are positioned, without any fixed attachment, a plurality of longitudinally positioned decomposition elements each comprising a bipolar graphite electrode grooved on both of its faces, the electrode being mounted in a frame provided with a diaphragm and in the upper part of it with a gas chamber connected through flexible conduits to a collector for evacuation of the gas formed between the inner side of the electrode and the diaphragm, the lower part of the frame immersed in the electrolyte being provided peripherally with a packing engaging the inside of the trough, (2) means for delivering aqueous hydrogen chloride solution to the decomposition elements, (3) means for evacuation of the gas generated on the outer side of the electrode and also of the diluted solution of hydrogen chloride, and (4) means for conducting to the cell the electric current necessary for electrolysis.

2. The cell of claim 1 in which the means for evacuating the diluted hydrogen chloride solution comprises an overflow conduit and an automatic valve for regulating the level of the electrolyte in the trough.

3. The cell of claim 1 in which the means for evacuating the diluted solution of hydrogen chloride comprises an overflow conduit and the means for regulating the level of the electrolyte in the trough comprises an automatic valve positioned in the collector for the produced gas.

4. The cell of claim 1 in which the means for evacuating the diluted solution of hydrogen chloride comprises a flexible collector connected between the gas chambers in the frames.

5. The cell of claim 1 in which the means for evacuating the diluted solution of hydrogen chloride solution comprises flexible conduits connecting the individual gas chambers in the frames with a common collector.

6. The cell of claim 1 in which the means for deliver ing fresh electrolyte to the cell comprises a collector and conduits leading therefrom to the anodic compartments of the said cells.

7. The cell of claim 1 in which the means for evacuating the diluted hydrogen chloride solution comprises an overflow conduit and an automatic valve for regulating the level of the electrolyte in the trough, and the means for delivering fresh electrolyte to the cells comprise a collector and conduits leading therefrom to .the anodic compartments of the. cells.

8. The cell of claim 1 in which the means for delivering fresh electrolyte to the cell comprises a collector delivering fresh electrolyte to the compartment outside the diaphragm, the electrolyte passing into the compartment between the diaphragm and electrode attached to the same frame.

References Cited by the Examiner UNITED STATES PATENTS 3,242,065 3/1966 De Nora et al. 2042S6 FOREIGN PATENTS 585,596 9/1933 Germany. 201,267 8/ 1923 Great Britain.

JOHN H. MACK, Primary Examiner.

D. R. JORDAN, Assistant Examiner.

Claims

1. A CELL FOR THE ELECTROLYSIS OF AQUEOUS SOLUTIONS OF HYDROGEN CHLORIDE COMPRISING (1) AN ELECTRICALY INSULATED TROUGH OF GENERALLY REINFORCED INTERNAL CROSS-SECTIONAL FORM TRANSVERSALLY CLOSED BY A COVER AND IN WHICH ARE POSITIIONED, WITHOUT ANY FIXED ATTACHMENT, A PLURALITY OF LONGITUDINALLY POSITINED DECOMPOSITION ELEMENTS EACH COMPIRSING A BIPOLAR GRAPHITE ELECTRODE GROOVED ON BOTH OF ITS FACES, THE ELECTRODE BEING MOUNTED IN A FRAME PROVIDED WITH A DIAPHRAGM AND IN THE UPPER PART OF IT WITH A GAS CHAMBER CONNECTED THROUGH FLEXIBLE CONDUITS TO A COLLECTOR FOR EVACUATION OF THE GAS FORMED BETWEEN THE INNER SIDE OF THE ELECTRODE AND THE DIAPHRAGM, THE LOWER PART OF THE FRAME IMMERSED IN THE ELECTROLYTE BEING PROVIDED PERIPHERALLY WITH A PACKING ENGAGING THE INSIDE OF THE TROUGH, (2) MEANS FOR DELIVERING AQUEOUS HYDROGEN CHLORIDE SOLUTION TO THE DECOMOSITIN ELEMENTS, (3) MEANS FOR EVACUATION OF THE GAS GENERATED ON THE OUTER SIDE OF THE ELECTRODE AND ALSO OF THE DILUTED SOLUTION OF HYDROGEN CHLORIDE, AND (4) MEANS FOR CONDUCTING TO THE CELL THE ELECTRIC CURRENT NECESSARY FOR ELECTROLYSIS.