Method for producing fluorine gas

A method for producing fluorine gas comprising:

• reacting 1,2,3,4-tetrachlorobutane or 1,1,2,2-tetrafluoroethane as a raw material compound with fluorine gas to perform fluorination and obtaining a reaction mixture containing 1,1,2,3,4,4-hexafluoro-1,2,3,4-tetrachlorobutane or perfluoroethane which is a major fluorinated substance as a target component generated by the fluorination of the 1,2,3,4-tetrachlorobutane or 1,1,2,2-tetrafluoroethane, a minor fluorinated substance as a non-target component generated as a by-product by the fluorination of the 1,2,3,4-tetrachlorobutane or 1,1,2,2-tetrafluoroethane, and by-product hydrogen fluoride generated as a by-product in the fluorination;
• separating the reaction mixture to obtain a main product component containing the 1, 1,2,3,4,4-hexafluoro-1,2,3,4-tetrachlorobutane or perfluoroethane as a majority component and a by-product component, the by-product component being a component other than the main product component and containing the by-product hydrogen fluoride;
• purifying the by-product component to obtain a recovered hydrogen fluoride component in which a concentration of an organic substance contained in the by-product component is reduced and a concentration of the by-product hydrogen fluoride is increased;
• performing electrolysis using the recovered hydrogen fluoride component as at least a part of an electrolyte to produce fluorine gas;
• and
• introducing the fluorine gas obtained in the electrolysis into a reaction field for the fluorination in performing the fluorination to use the fluorine gas obtained in the electrolysis as at least a part of fluorine gas used in the fluorination;
• wherein, the by-product component is purified such that a total concentration of the organic substance in the recovered hydrogen fluoride component becomes 200 mass ppm or less.