This invention relates to the electroltic preparation of perchlorates directly from sodium
chloride using lead dioxide anode.
Hitherto it has been the practice to employ a two stage 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 desintegrated 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 of the liquor 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 thoses 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 effluent 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 levels 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 currint 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
(i) The said fluoride ions may be provided by adding sodium fluoride ou hydrogen fluoride to the bath.
(ii) About 0.5 to 5 grams per liter of sodium fluoride may be added; but about 2g/L is ok.
(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 a massive lead dioxide or a GSLD.
(v) The current density may be in range 5 to 40 amps per square decimeter.
(vi) The electrolyte 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 being maintained constant at predetermined levels throughout the process.
The following Table 1. gives the particulars of three different examples illustrating the invention.
|Concentration of electrolite (initial) g/L NaCl||290.8||291||308.1|
|Sodium fluoride g/L||2||2||2|
|Current density (amps /dm^2)||10||25||19|
|Current concentration (amp/L)||18.75||25||10|
|Cell voltage ( volts)||3.0 to 3.9||3.7 to 4.5||3.9 to 4.5|
|Current efficiency %||52.2||53.2||57.5|
|Energy consumption (kwh/kg of NaClO4)||13.3||13.9||13.2|
|Current passed Amps||15||20||800|
|Quantity of NaClO4 present in solution (gms)||544||546||61KG|
Table II shows other benificeal effects of using NaF.
|Experimental conditions||Without NaF||With NaF|
|Anode current density (amps / dm squared)||20||20|
|Current concentration (amp/L)||25||25|
|Temperature C.||35 TO 38||35 TO 40|
|Current efficienct y% (with ref. to NaClO4 formed)||39.5||53.4|
|Energy consumption (kwh/kg of NaCl04)||16.2||12.3|
Snip of most of the text repeating the claims above except:
Claim (3): Current density is in the range 5 to 40 Amps per dm^2.
Claim (4): Temperature is in the range 30 to 60 C.
Other patents sited:
2,813,825 11/1957 Miller et al
2,840,519 6/1958 Stern et al
2,872,405 2/1959 Miller et al
3,020,124 2/1962 Bravo et al
The present studies reveal that both NaF and
Na3AlF6 catalyze the anodic oxidation of Chlorate ion
to Perchlorate ion at a Beta-PbO2 coated Titanium electrode.
Na2SiF6 and Na2TiF6 do not affect the reaction.
However, NaBF4 and NaPF6 retard the reaction. It is demonstrated that the Fluorocompounds influence the overpotential of the Chlorate oxidation reaction more than that of oxygen evolution, thus resulting in either electrocatalysis or retardation of the reaction.
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