Fluorine cell

Details Fluorine cell Fluorine cell

1996-04-01

1997-11-18

Valentine, Donald R.

Chemistry: electrical and wave energy

Apparatus

Electrolytic

204266, 204286, 204290R, 204294, 204241, 204247, C25B 900, C25B 1112

Patent

active

056883846

DESCRIPTION:

BRIEF SUMMARY
The present invention relates to a fluorine cell and particularly, though not exclusively, to an on-demand type of fluorine cell for the production of fluorine gas.
Electrochemical cells for the production of fluorine are known in the art. Many large-scale fluorine producing cells and employing currents in the region of 1000 amps and above are operated substantially continuously or at least have the hydrogen fluoride electrolyte maintained in a permanently molten condition to prevent damage to the electrodes on freezing. Such fluorine producing plants are used for supplying fluorine to large-scale production processes which are normally operated continuously and where the fluorine production rate can be accurately matched to the demand.
A particular problem arises when small-scale production cells are contemplated using production currents of less than about 1000 amps and where the fluorine demand is intermittent and/or cannot be accurately predicted. Such users frequently require fluorine at irregular intervals and in relatively small quantities. Examples of such use may be research environments such as in Universities or in industrial research laboratories. If the cell is shut down after each use, lengthy start-up procedures are usually required to generate fluorine again which gives rise to inconvenience and inefficiency.
Frequently, conventional small-scale fluorine cells are simply left running between uses so as to ensure a prompt fluorine supply. An on-line lute pot or seal pot sometimes being employed. Thus, fluorine and consequently hydrogen fluoride electrolyte is wasted due to the necessity of blowing-off fluorine.
Conventional fluorine cells tend to be either troublesome or wasteful, due to the difficulties in matching fluorine output to need. If the cell is set below the fluorine needs of the process, insufficient fluorine is produced, and if the output is set above the process requirement, fluorine is wasted due to blow-off. Due to these difficulties many users opt for their supply of fluorine in pressurised cylinders.
Another problem which arises with known cells is in the construction of their anodes which are generally made from hard carbon which is attached to an anode hanger by means of copper pressure plates which sandwich the carbon therebetween by means of bolts. This method had been found to be unreliable due to corrosion products degrading the electrical contact between the carbon anode and copper pressure plates.
A further problem which arises is that generally known as stud-fires and stud-leaks. Known cells have their anode hangers passing through the cell lid and insulated therefrom by plastics material seals. A considerable amount of heat can be generated during operation of a fluorine cell due to the passage of electrical current and the resultant resistance heating. This problem can also be exacerbated by the above noted problem of poor electrical contact between the anode and anode connector or hanger. Such heating greatly increases the chances of a runaway reaction between the seal material, often a fluoroelastomer rubber, and the generated fluorine, thus causing a fluorine leak. In extreme cases, the seal and the metal of the electrical connection stud actually burn in the stream of fluorine gas producing a stud-fire.
A yet further problem with known fluorine cells is that of ensuring accurate vertical alignment of the anode within the anode compartment so as to guarantee even separation of anode and cathode and, in the extreme case, that no electrical contact whatsoever is made with the surrounding cell walls which may constitute the cell cathode. A consequential problem of the inaccuracy of anode mounting with known cells is that fluorine bubbles sometimes find their way into the hydrogen side of the cell and results in a violent reaction during recombination of the fluorine and hydrogen.
GB 1 561 212 describes a hydrogen generating cell by the electrolysis of water, the generation of hydrogen being controlled merely by the pressure thereof depressing the water level belo

REFERENCES:
patent: 3616436 (1971-10-01), Haas
patent: 3773644 (1973-11-01), Tricoli et al.
patent: 4002552 (1977-01-01), Bunn, Jr. et al.
patent: 4144161 (1979-03-01), Bourgeois
patent: 5037518 (1991-08-01), Young et al.
patent: 5154813 (1992-10-01), Dill
patent: 5160415 (1992-11-01), Kondo et al.
patent: 5290413 (1994-03-01), Bauer et al.

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