Chemistry: electrical and wave energy – Apparatus – Electrolytic
Patent
1994-12-15
1996-08-20
Gorgos, Kathryn
Chemistry: electrical and wave energy
Apparatus
Electrolytic
204296, 427243, 427245, 4273855, 4273977, 427379, C25B 1304, C25B 1306
Patent
active
055475507
DESCRIPTION:
BRIEF SUMMARY
The present invention concerns a diaphragm for use in electrolyzer units for alkali halide solutions.
It also concerns a process for the preparation of a diaphragm which may optionally be microporous. The diaphragm mentioned above can be produced by this process.
Finally, it concerns the use of the diaphragm in an electrolyzer unit for aqueous alkali, halide solutions.
The aqueous alkali halide solution which is most frequently electrolyzed is sodium chloride, to produce chlorine and caustic soda.
This type of material is generally prepared by depositing asbestos fibers on a support, consolidating them with a polymer which is inert towards the electrolyte and optionally adding a pore forming agent which is decomposed at the end of the operation to produce the required porosity.
Known asbestos-based diaphragms produced by that process do not possess all the mechanical and chemical properties required for optimal conditions of electrolysis. The diaphragms either have unsatisfactory hydraulic and/or electrical properties from the outset when used in electrolysis, mainly due to the hydrophobic nature of the diaphragms, or they degrade with time during use of those diaphragms in electrolysis, mainly by structural weakening, reducing the hydraulic and/or electrical properties.
French patent no 73 18805, filed on 18 May 1973 by RHONE-PROGIL, describes a process for the preparation of porous diaphragms from an aqueous suspension of asbestos fibers, a fluorinated resin latex, a pore forming agent and anionic sulphonic surfactants. Specified amounts of fluorinated resin, pore forming agent and asbestos are preferred, which result in microporous diaphragms with electrolysis properties which have been shown to be unsatisfactory; the unsatisfactory properties are due to poor flow of the electrolyte from one compartment to another in the system and/or an increase in tension with no increase in the yield of caustic soda. In addition, the anionic surfactants in the diaphragms react with the cations present during manufacture when the diaphragms are used for electrolysis, reducing their hydraulic and electrical properties
One aim of the present invention is thus to provide a microporous diaphragm which, during use in the electrolysis of aqueous solutions of alkali halides, satisfactorily transports the soluble species present in the electrolyte, along with a reduced flow of caustic soda across a separator of given geometry.
A further aim of the present invention is to provide a microporous diaphragm which, during use in electrolysis, has a uniform electrolyte flow from one compartment to another.
A still further aim of the invention is to provide a process for the preparation of a microporous diaphragm with satisfactory hydraulic and electrical properties with regard to the energy consumption of the system in kilowatt hours.
These and other aims are achieved by the present invention which provides a diaphragm comprising:
100 parts by weight of asbestos fibers;
30 to 70 parts by weight of silica-based derivatives;
20 to 60 parts by weight of fluorinated polymer; silica-based derivatives is between 0.6 and 1.2 by weight, preferably between 0.6 and 0.9, with the exception of a diaphragm obtained by depositing a suspension containing 100 parts by dry weight of asbestos fibers, 30 parts by dry weight of silica-based derivatives, 25 parts by dry weight of fluorinated polymer and 1.5 parts by dry weight of a thickening agent.
The invention also concerns a diaphragm comprising:
100 parts by weight of asbestos fibers;
30 to 70 parts by weight of silica-based derivatives;
20 to 60 parts by weight of fluorinated polymer; silica-based derivatives is between 0.6 and 1.2 by weight, preferably between 0.6 and 0.9, obtained by depositing a suspension whose nature and constituents will be defined below, said suspension optionally including a thickening agent in an amount of less than 1.5 parts by dry weight per 100 parts by dry weight of asbestos fibers.
The present invention also concerns a process for the preparation of a diaphragm, subs
REFERENCES:
patent: 4665120 (1987-05-01), Hruska et al.
patent: 5092977 (1992-03-01), Bachot et al.
Kuntzburger Fr ed eric
Magne Jean-Claude
Gorgos Kathryn
Rhone-Poulenc Chimie
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