US3493478A - Electrolytic preparation of perchlorates - Google Patents

Description

United States Patent Ofi 3,493,478 Patented Feb. 3, 1970 3,493,478 ELECTROLYTIC PREPARATION OF PERCHLORATES Handady V. K. Udupa, Srinivasa Sampath, Kapisthalam C. Narasimham, and Muthia Nagalingam, all Central Electrochemical Research Institute, Karaikudi, (S. Rl y.), India; Chakkalakkal J. Raju, Fertilizer Corporation of India Ltd., Trombay Unit, Bombay, India; and Govinda Rao, Madras Rubber Factory, Tiruvottiyur, Madras, India N Drawing. Filed Dec. 2, 1966, Ser. No. 598,609

Int. Cl. B01k 1/00; C01b 11/26, 11/18 US. Cl. 20482 11 Claims ABSTRACT OF THE DISCLOSURE Sodium perchlorate is prepared electrolytically from sodium chloride solutions in one step by passing a direct current through the solution, in the presence of fluoride ion. A stainless steel cathode and a lead dioxide anode are satisfactory.

This invention relates to the electrolytic preparation of perchlorates directly from sodium chloride using lead dioxide anode.

Hitherto it has been the practice to employ a twostage process for the production of perchlorates from chlorides, the first stage being the oxidation of chloride to chlorate using graphite, magnetite or lead dioxide anodes and the second stage consisting of the oxidation of chlorate to perchlorate, using platinum or lead dioxide anodes. This conventional process has various drawbacks, such as: (i) that in between the two stages the solutions have to be processed to isolate the chlorate and recover the unconverted chloride; (ii) that graphite gets disintegrated to a considerable extent and magnetite to a lesser extent when used in the production of chlorates; and (iii) that there is an inevitable loss of platinum due to corrosion in the perchlorate cell.

With a view to avoiding the intermediate step of the processing the liquors after. the said first stage of the conventional process, it has been proposed that the effluent from the chlorate cell should be treated under different electrolytic conditions from those in which the sodium chloride solution was treated in the chlorate cell during the first stage of the process. But this proposed process also is a two stage process and the processing of the eflluent from the chlorate cell introduces complications in the method.

This invention has for its main object an improved method which will obviate the drawbacks of known methods, and whereby the perchlorates may be prepared directly from sodium chloride in a single step of electrolytic oxidation, the conditions of electrolysis being maintained constant at predetermined levles throughout the period. Another object of this invention is to avoid the use of graphite, magnetite or platinum as the anode.

With these and other objects in view, this invention broadly consists of a process of preparing sodium perchlorate directly from sodium chloride in a single step of electrolytic oxidation, which consists in passing a direct current through a bath of sodium chloride solution containing fluoride ions.

The improved process according to this invention may be carried out into practice under the following conditions:

(i) The said fluoride ions may be provided by adding sodium fluoride or hydrogen fluoride to the bath.

(ii) About 0.5 to 5 g./l. of sodium fluoride may be added; but about 2 g./l. would give satisfactory results.

(iii) The electrolytic oxidation may be carried out in a cell having a stainless steel cathode and a lead dioxide anode.

(iv) The said anode may consist of massive lead dioxide or an electrode having lead dioxide electrodeposited on a substrate like graphite.

(v) The current density may range from 5 to 40 amp/dm.

(vi) The electrolytic oxidation may be carried out at a temperature of 30 to 60 C.

(vii) The process may be carried until all the chloride is converted into perchlorate, the conditions of electrolysis being maintained constant at predetermined levels throughout the process.

The following Table I gives the particulars of three different examples illustrating the invention:

TABLE I Example I II III Concentration of electrolyte (initial) (g. NaCl 0 8 291 308. 1 Addition agents N 9.13 (g./l) 2 2 2 Anode Cathode Current density (amp./dm. 10 25 19 Current concentration (amp./l) 18. 25 10 Temperature of electrolyte C 40 45 Cell voltage (volts) 3. 0-3. 9 3. 7-4. 5 3. 9-4. 5 Current etficiency percent 52. 2 53. 2 57. 5 Energy consumption (kWh/kg. of

NaClOr) 13. 3 13. 9 13.2 Current passed (amps.) 15 20 800 Duration (hrs) 78 223 Quantity of sodium perchlorate present in solution (gms) 544 546 4 61. 0

1 Carbon substrate lead dioxide.

2 Graphite substrate lead dioxide. 3 Stainless steel.

4 Kgs.

The following Table II shows other beneficial effects resulting from the addition of fluoride to the bath.

1 Graphite substrate lead dioxide. 2 Stainless steel.

Although this invention has been particularly described with reference to the preparation of sodium perchlorate, it is to be understood that it is applicable also to the preparation of other perchlorates by the conversion of the sodium perchlorate prepared by this process, into the required perchlorates by processes already known for such conversion.

What we claim is:

1. A process of preparing sodium perchlorate directly from sodium chloride in a single step of electrolytic oxidation, which consists in passing a direct current through a bath of sodium chloride solution containing fluoride ions.

2. A process as claimed in claim 1, wherein the said fluoride ions are provided by adding hydrogen fluoride to the said bath.

3. A process as claimed in claim 1, wherein the electrolytic oxidation is carried out using a current density range of 5 to 40 amp./dm.

4. A process as claimed in claim 1, which is carried out at a temperature of 30 to 60 C.

5. A process as claimed in claim 1, wherein the conditions of electrolysis are maintained constant at predetermined levels throughout the process.

3 6. A process as claimed in claim 1, wherein the said fluoride ions are provided by adding sodium fluoride to the said bath.

7. A process as claimed in claim 6, wherein about 0.5 to 5 g./1. of sodium fluoride is added to the sodium 5 chloride solution.

8. A process as claimed in claim 7 wherein the sodium fluoride added is about 2 g./ 1.

9. A process as claimed in claim 1 wherein the electrolytic oxidation is carried out in a cell having a stainless steel cathode and a lead dioxide anode.

10. A process as claimed in claim .9, wherein the said anode consists of massive lead dioxide.

11. A process as claimed in claim 9, wherein the said 4 anode consists of an electrode having lead dioxide electro-deposited on a substrate like graphite.

References Cited UNITED STATES PATENTS 2,813,825 11/1957 Miller et a1 20482 2,840,519 6/1958 Stern et al. 204-S2 2,872,405 2/1959 Miller et a1. 204-290 3,020,124 2/1962 Bravo et a1. 20482 XR JOHN H. MACK, Primary Examiner D. R. JORDAN, Assistant Examiner U.S. C1. X.R. 20495