Patented July 12, 1932 1866,969

UNITED STATES PATENT OFFICE EARL FREDENHAGEN, OE GREESWALD, GERMANY ELECTROEYERC PRODUCTIOr OE FLUORNE No Drawing. Application filed July 11, i829, serial No. 377,808, and in Germany July 17, 1928. The present invention relates to the elec ing chamber with the electrolysis vessel, so trolytic production of fluorine. that the dried sals can be brought from the It is known that fluorine can be produced drying chamber to the electrolysis vessel electrolytically from fused alkali metal bi without.coming into contact with the atmos 5 fluorides or from solutions of alkali metal phere. Accordingly the drying chamber is fluorides in hydrogen fluoride. In the begin to be regarded as part of the electrolysis ning of the process oxygen is first obtained, systéra, since the electrolyte always contains some Since in the course of the electrolysis the water. At the same time the water present electrolyte becomes poorer in hydrogen it therein causes the electrolysis to proceed in fluoride whereby the solidification point of 8 a very irregular manner and also the volt age varies considerably. Attempts have been theand electrolyte, accordingly the the internal decomposing electric voltage resistance are made to remove the traces of water present increased, it is necessary for a continuous op by the electrolysis itself, but this requires eration to replace the hydrogen fluoride in s facili for many hours, whereby the va the electrolyte solution or melt. If hydro riations of the voltage are reduced but not gen fluoride prepared in the usual manner completely removed. and containing more or less water is used for I have now found that fluorine can be pro this purpose, the disengagement of fluorine duced directly in a uniform manner and with is decreased and unfavourably influenced in 20 out the undersirable generation of oxygen by the aforesaid manner and the anodic volt subjecting the alkali metal bifluorides prior age, is increased. In order to continue the to their serving as the electrolyte in the elec electrolysis without trouble, the hydrogen trolysis vessel itself to a severe drying oper fluoride in the electrolyte is replaced by such ation, preferably bypassing a current of d hydrogen fluoride as contains only an ex 25 air or other dry inert gas through the sufi tremely small amount of water, namely such 75 ciently cemminuted salt at an elevated tem that the condensed hydrogen fluoride has a perature, but below the melting point of the specific conductivity at 0°C. of less than 0.02 salt, until the hydrogen fluoride given off by reciprocal ohm. the alkali metal bifluoride when occasionally The following example will further illus 30 heated to decomposition, has a specific con trate the nature of this invention which, how- 80 ductivity, after condensation, at 0 C. of less ever, is out limited thereto. than 0.2 reciprocal ohm. Preferably the elec trolysis vessel is tight to the air so that no Eaample water vapour can enter the electrolytic cham Potassium bifluoride dried in the usual 5 ber. For this purpose every opening of the manner is subjected to electrolysis in an elec- 85 vessel must be avoided and an insulating trolyzing vessel, between a copper cathode tightening between the anode and the metallic and a graphite anode. Electrolysis takes diaphragm and another one between the ves place very irregularly. The voltage varies sel serving as the cathode and the diaphragm between 10 and more than 30 volts whereby 40 or the anode must be provided. In case the the current intensity decreases with increas diaphragm consists of copper it is not abso sing voltage. With an increasing current lutely necessary that the tightening between E. nsity, the variations of the voltage occur the anode and the diaphragm is an insulat more readily and with a type of apparatus ing One used for these experiments it was not possible he same result is obtained when the elec to increase the current density to substantial trolyte salt is dried outside the electrolysis ly more than 0.1 ampere per square centi vessel and in that case prevented from taking meter. The said variations of the voltage R even traces of water vapour while it is occur very often at the beginning of the filled into the electrolysis vessel. This re electrolysis but less often after a longer time, 59 sult is best obtained by connecting the dry but even after 15 hours of operation they are 100 2 1,886,989 not entirely avoided and the disengagement trolysis system at an elevated temperature, of fluorine is very irregular. but below the melting point of the salt, until In accordance with the present invention the hydrogen fluoride given off by the salt the same Salt is dried within the electrolysis when occasionally heated to decomposition vessel by means of a current of dry air passed has a specific conductivity at 0° C. of less 70 through at a temperature below the melting than 0.02 reciprocal ohm, and carrying out point of the salt. When the salt thus treated electrolysis with the salt in a liquid condi is electrolyzed, the electrolysis proceeds in a tion while avoiding access of moisture. very uniform manner and without variations 4. The process of producing fluorine which 10 of the voltage. When operating with a ten comprises passing a current of a dry inert 75 sion below 10 volts the current density can be gas through potassium bifluoride in the elec increased, in the case of the apparatus above trolysis vessel at an elevated temperature, referred to, to more than 0.3 ampere per but below the melting point of the salt until square centimeter without the voltage being the hydrogen fluoride given off by the salt 5 substantially increased or the electrolysis when occasionally heated to decomposition 80 becoming irregular. - has a specific conductivity at 0° C. of less After a long time of operation the melt than 0.02 reciprocal ohm, carrying out elec becomes lower in hydrogen fluoride and in trolysis with the salt in a liquefied condition order to continue the electrolysis without in while avoiding access of moisture, adding 20 terruption, hydrogen fluoride is added. hydrogen fluoride free from water and hav. When this is carried out by producing hy ing a specific conductivity at 0° C. of not drogen fluoride from potassium bifluoride more than 0.02 reciprocal ohm to the elec and absorbing it in the melt, very great vari trolyte, in order to maintain its liquid con ations of voltage and current density take dition and continuing electrolysis. 25 place in electrolysis, and it was found that In testimony whereof I have hereunto set 90 the water content of the added hydrogen my hand. fluoride is the cause. The said variations of KARL FREDENHAGEN. current density and tension are not observed, if care is taken that the added hydrogen fluoride is practically free from water, that is that it has the specific conductivity indi cated above. When adding to a used up melt hydrogen fluoride of this kind the elec trolysis can be continued without variations. 35 What I claim is: 100 1. The process of producing fluorine which comprises passing a current of a dry inert gas through an alkali metal bifluoride in the electrolysis system at an elevated tempera 40 ture, but below the melting point of the 05 salt, until the hydrogen fluoride given off by the salt when occasionally heated to decom position has a specific conductivity at 0°C. of less than 0.02 reciprocal ohm, and carry 45 ing out electrolysis with the salt in a liquid O condition while avoiding access of moisture. 2. The process of producing fluorine which comprises passing a current of a dry inert gas through an alkali metal bifluoride in the 50 electrolysis vessel at an elevated tempera ture, but below the melting point of the salt until the hydrogen fluoride given off by the salt when occasionally heated to decomposi tion has a specific EE at 0° C. of less 55 than 0.02 reciprocal ohm, carrying out elec 120 trolysis with the salt in a liquefied condition while avoiding access of moisture, adding hydrogen fluoride free from water and hav. ing a specific conductivity at 0°C., of not 60 more than 0.02 reciprocal ohm to the electro 25 ... tionlyte, andin ordercontinuing to maintain, electrolysis. its liquid condi 3. The process of producing fluorine which comprises passing a current of a dry inert gas through potassium bifluoride in the elec 30