US3350286A - Process for producing alkali chlorate or alkali perchlorate - Google Patents

Description

G. J. CRANE PROCESS FOR PRODUCING ALKALI CHLORATE OR ALKALI PERCHLORATE Oct. 31, 1967 2 SheetsSheet 1 Original Filed April 27, 1964 3,350,286 PROCESS FOR PRODUCING ALKALI CHLORATE OR ALKALI PERCHLORATE Original Filed April 27, 1964 v G. J. CRANE Oct. 31, 1967 2 Sheets-Sheet 2 FIG. 2 Z

United States Patent 3,350,286 PROCESS FOR PRODUCING ALKALI CI-ILORATE 0R ALKALI PERCHLORATE George J. Crane, Islington, Ontario, Canada, assignor to Huron Nassau Limited, Nassau, Bahama Islands, a corporation of The Bahama Islands Continuation of application Ser. No. 362,719, Apr. 27, 1964. This application Jan. 23, 1967, Ser. No. 611,173 Claims priority, application Canada, Nov. 5, 1963, 888,375 3 Claims. (Cl. 20495) This application is a continuation of Ser. No. 362,719, filed Apr. 27, 1964, which is now abandoned.

This invention relates to an improved process of manufacturing alkali chlorates and perchlorates by means of multipolar electrolytic cells.

The most economic manufacture of sodium chlorate and perchlorate is usually performed in multipolar electrolytic cells. These cells comprise a series of parallel electrodes mounted in a box and sealed at their edges and bottom to prevent leakage of solution or electric current, the solution to be electrolyzed being maintained between each set of electrodes. A brine such as NaCl is electrolyzed in the cells through a number of intermediate reactions to form the sodium chlorate, with hydrogen gas evolved as a by-product when oxygen from the water is freed to enter into the reaction. The overall chemical reaction is represented by 3H O+NaCl NaClO -|-3H The brine solution containing NaCl and some NaClO circulates between the electrodes and at each pass some of the NaCl is converted to NaClO Fresh solution enters each electrode compartment at the lower edge of the electrode through an inlet pipe, and the natural circulation of the liquor between the electrodes is caused by the generation of hydrogen gas between the cell plates. This reduces the average specific gravity of the material between the electrodes. The heavier dense fresh liquor from the tank enters into the bottom inlet pipes and forces out the mixture of liquid and gas through upper pipes positioned at the top of the electrodes. In addition a minor circulation force is caused by a temperature increase of the electrolyte in the cells between the electrodes.

The efiiciency of the electrolysis and overall operating economy is sensitive to a number of operating conditions such as temperature, pH, uneven flow rate of electrolyte, bubble formation and variations in specific gravity of the liquid gas material between the electrodes. Also, under poor circulation conditions hydrogen bubbles produce a froth at the surface of the electrolyte which further interferes with the free discharge of the solution from the effluent pipes. In addition this froth constitutes an explosive hazard. Maintaining a sufficiently large flow rate necessitates increasing the diameter of the inlet and effluent pipes but this consequently increases the current leakage. For maximum efliciency it is desirable to independently vary the flow rate of the electrolyte between the electrodes to compensate for the increasing space between the electrodes as they Wear away, and also variations in the electrode surface. In addition changes in the chemical nature of the electrolyte and changes in current density require independent variation for the flow rate.

It is an object of the invention to control the conditions of the electrolyte between the electrodes.

It is a further object of this invention to decrease stray current losses.

Other objects of this invention will be made apparent from the description to follow.

The objects of this invention are attained in a process for the production of compounds selected from the group 3,350,286 Patented Oct. 31, 1967 ice consisting of alkali chlorates and alkali perchlorates by the electrolysis of an alkali chloride brine which comprises: electrolyzing said brine in a multipolar electrolytic cell, providing inlet and outlet means for said cell, pumping fresh electrolyte into the inlet means of said cell at a positive and controlled pressure, and removing electrolyzed solution from the outlet means.

The invention is more suitably understood by reference to the diagrams in which:

FIGUREI is a perspective view of a multipolar cell;

FIGURE 2 is a perspective view of a multipolar cell bearing constant pressure means; and I FIGURE 3 is a perspective view of a multipolar cell positioned in a tank.

In the drawings a typical cell of the prior art type is shown in FIGURE 1 having an outer wall 1, monopolar electrodes 2, and multipolar intermediate electrodes 3. The multipolar electrodes are sealed into grooves in the side wall to form individual and separate compartments 5. Adjacent cell compartments are separated from each other by insulating elements 4. Inlet pipes 9 and outlet pipes 8 provide a path for fresh brine to enter the electrolyzed brine to leave the cell. The cell box is placed in a large tank to a depth below the inside level of liquor in the tank shown at 7. In normal operating conditions a normal inside level will be as shown at 6. This diflference in hydrostatic levels between 6 and 7 will produce the outflow of liquor from the cell box.

One form of the inventive feature of this apparatus is shown in FIGURE 2 in which manifolds 11 are shown surrounding each set of inlet tubes. This is more completely illustrated in FIGURE 3 in which the cell is shown in a normal operating condition placed in a large tank. Fresh electrolyte from the tank is supplied through pipe 13 by pump 12 into pipes 10 and then to manifolds 11 surounding the inlet pipes 9. A valve 14 regulates the amount of electrolyte which may be forced through the system. Only two monopolar electrodes are shown in FIGURE 1 but more parallel circuits may be assembled in the cell box in which case the number of monopolar electrodes must be increased. Only four cell compartments are shown in series but this number can be increased to fifty or greater depending on the total voltage available. The inlet tubes 9 not only distribute fresh electrolyte evenly across the entire width of the cell but they also have a greater resistance to leakage of electric current than tubes usual for this type of circulation. This is because their length can be increased and the diameter decreased, the greater resistance to flow of liquid being compensated for by pump 12.

By maintaining a positive circulation of electrolyte in the interelectrode space the semi stationary foam that forms with certain liquid electrolyte compositions is eliminated. In addition a more uniform consumption of the graphite electrodes is attained due to the reduced temperature, denser uniform electrolyte mixture, more electrolyte conductivity and even laminar flow between the electrodes. Furthermore the concentration of unwanted by-products is reduced thus lessening the loss of chemicals through gaseous intermediates. Consequently, the output of a given size of electrolyti multipolar cell may be significantly increased with only a small expenditure of capital.

Iclaim:

1. A process for the production of compounds selected from the group consisting of an alkali chlorate and alkali perchlorate by the electrolysis of an alkali chloride brine comprising electrolyzing said brine in a multipolar electrolytic cell consisting of a plurality of spaced multipolar electrodes dividing said cell into a plurality of compartments having insulating means separating adjacent compartments, each of said compartments being rovided with inlet conduit means adjacent the bottom thereof, each of said inlet conduit means opening intermediate spaced opposed electrode faces, and with outlet conduit means adjacent the top thereof, each said outlet conduit means discharging intermediate said spaced electrode faces, introducing electrolyte through said inlet conduit means through manifold means into the space between said electrode faces thereby evenly distributing said electrolyte throughout the lower portion of each compartment, withdrawing electrolyzed material and maintaining a positive pressure on the electrolyte introduced through said inlet conduit means by a pump connected to said manifold means.

2. The process of claim 1 including containing said cell in a tank provided with electrolyte, maintaining the level of electrolyte in said tank at a depth below the outlet conduit means of said cell whereby the hydrostatic level within said cell produces an outflow of electrolyte References Cited UNITED STATES PATENTS 718,249 1/1903 Haas 204268 2,350,669 6/1944 Boller 204237 FOREIGN PATENTS 531,803 1/1941 Great Britain.

JOHN H. MACK, Primary Examiner.

D. R. JORDAN, Assistant Examiner.

Claims (1)

1. A PROCESS FOR THE PRODUCTION OF COMPOUNDS SELECTED FROM THE GROUP CONSISTING OF AN ALKALI CHLORATE AND ALKALI PERCHLORATE BY THE ELECTROLYSIS OF AN ALKALI CHLORIDE BRINE COMPRISING ELECTROLYZING SAID BRINE IN A MULTIPOLAR ELECTROLYTIC CELL CONSISTING OF A PLURALITY OF SPACED MULTIPOLAR ELECTRODES DIVIDING SAID CELL INTO A PLURALITY OF COMPARTMENTS HAVING INSULATING MEANS SEPARATING ADJACENT COMPARTMENTS, EACH OF SAID COMPARTMENTS BEING PROVIDED WITH INLET CONDUIT MEANS ADJACENT THE BOTTOM THEREOF, EACH OF SAID INLET CONDUIT MEANS OPENING INTERMEDIATE SPACED OPPOSED ELECTRODE FACES, AND WITH OUTLET CONDUIT MEANS ADJACENT THE TOP THEREOF, EACH SAID OUTLET CONDUIT MEANS DISCHARGING INTERMEDIATE SAID SPACED ELECTRODE FACES, INTRODUCING ELECTROLYTE THROUGH SAID INLET CONDUIT MEANS THROUGH MANIFOLD MEANS INTO THE SPACE BETWEEN SAID ELECTRODE FACES THEREBY EVENLY DISTRIBUTING

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