DE2312297C3 - Process for the production of elemental fluorine - Google Patents

Description

Fluorine, its industrial importance in the recent Has increased significantly in the past, is technically made by electrolysis of a solution of a fluoride in anhydrous hydrogen fluoride shown. The addition of fluorides is necessary to increase the conductivity increase, lower the vapor pressure of hydrogen fluoride and the occurrence of so-called anode effects largely to prevent. Potassium fluoride is preferred as fluoride, among other things those of lithium, sodium and ammonium are used. To the raw materials for the electrolyte high purity requirements are made, for example with regard to the content of water, sulfur, Silicon and heavy metal compounds. The upper limit for the water content is usually 0.1% for still considered permissible.

The electrolytic cell is known in various embodiments. The cell trough mostly exists made of steel or monel and serves as a cathode. The anodes are electrically isolated on the cell cover attached and also protruding into the electrolyte elements for separating the cathode gas space from the anode gas compartment. The separating elements (aprons) usually consist of Monel or a magnesium alloy.

Corrosion, particularly on the aprons, is a serious problem with the operation of the cells occur and lead to contamination of the electrolyte by dissolved apron material. If the As corrosion progresses to the perforation of the aprons, the hydrogen enters the cathode compartment with the An explosive reaction of fluorine in the anode space. Frequent checks of the aprons are therefore necessary. To do this, the cell must be put out of operation and dismantled.

In the explosions, the anodes are usually partially destroyed, leaving the electrolyte with carbon contaminated and thereby useless. With violent explosions it happens that the pressure increase Lifting the cell lid causes hot electrolyte to escape from the cells a serious danger for the operating personnel. It can also cause considerable damage to the surrounding parts of the system.

The average life of the electrolytic cells is between 1 and 12 months of operation (see A. J. R u d g e in A. T. Kuhn Industr. Electrochemical Processes, chap. 1, Elsevier Publishing Co, Amsterdam, New York, London [1971]).

It has now surprisingly been found that by adding barium and / or strontium ions to the electrolyte the corrosion can be largely limited, so that the life of the cell ίο is increased many times over.

The inventive method for production

of elemental fluorine by electrolysis of a mixture of hydrogen fluoride with a fluoride characterized in that the electrolyte contains barium and / or strontium ions.

It has been shown that amounts of 0.05 to 0.9%, preferably 0.10 to 0.35%, of barium and / or Strontium ions reduce the corrosion rate by a factor of 10 to 100.

The barium or strontium ions can be in the form of barium or strontium compounds, preferably as fluoride.

example

In a new electrolysis cell of the Allied Chem. Corp. type, as described, for example, in K i r k - O t h m e r: Encyclopedia of Chemical Technology 2nd Ed., Vol. 9, p. 513, an electrolyte was the Composition KF-2.0 HF and with a barium content of 0.15% barium ions, which are in the form of Barium fluoride were added to the electrolyte, with the continuous supply of hydrogen fluoride with an average HF content of 99.90% and an average water content of 0.02% under the operating conditions described in the above-cited reference on p. 514 over a period of time electrolyzed corresponding to 26 months of operation. After this time, an examination of the Electrolyte composition has a magnesium content of 0.008%. Also the look of the aprons and the underside of the lid indicated that practically no corrosion had occurred.

If 0.12% strontium ions in the form of strontium fluoride are used instead of 0.15% barium ions If electrolytes were added, there was also virtually no corrosion after the specified operating time to be established.

The experiment was only repeated under the same conditions, also in a new electrolysis cell except that the electrolyte did not contain barium or strontium ions. After 2 months of operation the magnesium content of the electrolyte was already 0.81% and the aprons were very strong Signs of corrosion.

Already based on the comparison of those from the aprons and the inside of the lid Magnesium impurities in the two experiments can significantly reduce corrosion detectable by the presence of barium or strontium ions in the electrolyte.

Claims (2)

Patent claims: 1. Process for the production of elemental fluorine by electrolysis of a mixture of Hydrogen fluoride with a fluoride, characterized in that the electrolyte is barium and / or contains strontium ions. 2. The method according to claim 1, characterized in that the content of the electrolyte to Barium and / or strontium ions between 0.05 and 0.9%, preferably between 0.10 and 0.35%.