Classifications

• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
  • C25B13/00—Diaphragms; Spacing elements
  • C25B13/04—Diaphragms; Spacing elements characterised by the material
• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
  • C25B13/00—Diaphragms; Spacing elements
  • C25B13/04—Diaphragms; Spacing elements characterised by the material
  • C25B13/05—Diaphragms; Spacing elements characterised by the material based on inorganic materials
  • C25B13/06—Diaphragms; Spacing elements characterised by the material based on inorganic materials based on asbestos
• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
  • C25B11/00—Electrodes; Manufacture thereof not otherwise provided for
  • C25B11/02—Electrodes; Manufacture thereof not otherwise provided for characterised by shape or form
  • C25B11/03—Electrodes; Manufacture thereof not otherwise provided for characterised by shape or form perforated or foraminous
  • C25B11/031—Porous electrodes
• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
  • C25B15/00—Operating or servicing cells
  • C25B15/08—Supplying or removing reactants or electrolytes; Regeneration of electrolytes

Definitions

• the present invention relates to a diaphragm capable of being used in cells for the electrolysis of solutions of alkali halides.
• aqueous solutions of alkaline halides generally electrolyzed are those of sodium chloride to obtain chlorine and soda.
• Diaphragms based on asbestos fibers known and obtained by this process do not have all the qualities of mechanical and chemical resistance required for optimal electrolysis conditions. Indeed, these diaphragms can either have unsatisfactory hydraulic and / or electrical performance due in particular to a hydrophobic nature of the diaphragms, and this from the start of their use in electrolysis, or deteriorate over time, in particular by deconsolidation of the structure , when using these diaphragms in electrolysis, inducing a decrease in hydraulic and / or electrical performance.
• An object of the present invention is therefore to provide microporous diaphragms having, when used in the electrolysis of aqueous solutions of alkali halides, satisfactory transport of the soluble species present in the electrolyte, while having a reduced flux of soda to through the separator of given geometry.
• Another object of the present invention is to provide microporous diaphragms having, during their use in electrolysis, a uniform flow of the electrolyte from one compartment to another.
• Another object of the invention is to provide a method for manufacturing microporous diaphragms whose hydraulic and electrical performance in electrolysis are satisfactory, while respecting the energy consumption of the system in kilowatt hours.
• a diaphragm comprising: - 100 parts by weight of asbestos fibers,
• Another subject of the invention consists of a diaphragm comprising: - 100 parts by weight of asbestos fibers,
• the present invention likewise relates to a process for the preparation of a diaphragm essentially comprising the following steps: a) preparation of an aqueous suspension comprising, in addition if necessary, a thickening agent:
• the suspension prepared having a specific weight ratio of the fluoropolymer to the silica derivatives, such that the diaphragm prepared has a weight ratio of the fluoropolymer to the silica derivatives after step c), inclusive between 0.6 and 1.2, and preferably between 0.6 and 0.9, with the exception of a diaphragm obtained by depositing a suspension comprising 100 parts by dry weight of asbestos fibers, 30 parts by dry weight of silica-based derivatives, 25 parts by dry weight of fluoropolymer, 1.5 parts by dry weight of a thickening agent.
• the invention also relates to a process for the preparation of a diaphragm essentially comprising the following steps: a) preparation of an aqueous suspension comprising:
• the suspension prepared having a specific weight ratio of the fluoropolymer to the silica derivatives, such that the diaphragm prepared has a weight ratio of the fluoropolymer to the silica derivatives after step c), inclusive between 0.6 and 1, 2, and preferably between 0.6 and 0.9.
• the subject of the present invention is a diaphragm comprising:
• the diaphragm comprises - 100 parts by weight of asbestos fibers, - 30 to 70 parts by weight of silica-based derivatives,
• the diaphragms according to these two embodiments of the invention comprise
• the diaphragms are obtained by depositing a suspension comprising, in addition to the other constituent elements described below, 0 to less than 1.5 parts by dry weight and more particularly from 0 to 1 part in dry weight of a thickening agent per 100 parts by dry weight of asbestos fibers
• the diaphragms according to the present invention preferably comprise at least one surfactant.
• This surfactant is present in amounts of between 0.5 and 10, preferably between 0.6 and 5 parts by weight per 100 parts by dry weight of asbestos fibers.
• a nonionic surfactant is used.
• nonionic surfactant it is possible in particular to use ethoxylated alcohols or fluorocarbon compounds with functionalized groups alone or as a mixture, these alcohols or these fluorocarbon compounds generally have carbon chains from C6 to
• ethoxylated alcohols are used which are ethoxylated alkylphenols, such as in particular octoxynols
• the diaphragms according to the present invention advantageously have a weight per unit area of between 0.4 and 3 kg / m 2 and, preferably, 0.7 and
• the present invention also relates to a method for preparing a diaphragm.
• the process is suitable for the preparation of diaphragm, with the exception of that obtained from a suspension comprising 100 parts by dry weight of asbestos fibers, 30 parts by dry weight of silica-based derivatives, 25 parts by dry weight of fluoropolymer, 1.5 parts by dry weight of a thickening agent.
• the method according to this first mode essentially comprises the following steps: a) preparation of an aqueous suspension comprising, in addition if necessary, a thickening agent:
• the suspension of step a) has a specific weight ratio of the fluoropolymer to the silica derivatives, so that the diaphragm prepared has a weight ratio of the fluoropolymer to the silica derivatives, after step c), between 0.6 and 1.2, and preferably between 0.6 and 0.9.
• the method according to the invention essentially comprises the following steps: a) preparation of an aqueous suspension comprising:
• the suspension prepared having a specific ratio by weight of the fluoropolymer to the silica-based derivatives, such that the diaphragm prepared has a weight ratio of the fluoropolymer to the silica-based derivatives, after step c) , between 0.6 and 1.2, and preferably between 0.6 and 0.9.
• the suspension prepared in each of the two embodiments mentioned has a weight ratio of the fluoropolymer to the silica-based derivatives which is to be adjusted so that the diaphragm obtained after 1 step c) has such a ratio of between 0.6 and 1.2, and preferably between 0.6 and 0.9. Indeed, this ratio can vary depending on the respective stopping rate of these two compounds on the material with high porosity.
• a person skilled in the art will be able to determine, by means of simple tests, the quantity of dry matter to be dispersed in the suspension as a function of the rate of stopping observable on the porous material through which the dispersion is filtered under the conditions vacuum programmed.
• the preparation of an aqueous suspension according to step a) of the process of the present invention essentially comprises, in addition to the thickening agent if one is used : - 100 parts by dry weight of asbestos fibers, - 35 to 50 parts by dry weight of silica-based derivatives,
• the method according to the present invention preferably uses a suspension comprising at least one surfactant.
• This surfactant is generally present in amounts of between 0.5 and 10, preferably between 0.6 and 5, parts by weight per 100 parts by weight of asbestos fibers.
• this surfactant is nonionic.
• the surfactants advantageously usable are those mentioned above.
• microporous diaphragms whose electrical and hydraulic performance are satisfactory and stable over time; and this is advantageously observed when these diaphragms obtained are used, in brine electrolysis cells under high current densities of up to 40 A / dm 2 and more.
• the diaphragms thus obtained also make it possible to work with high sodium hydroxide concentrations (of the order of 140 to 200 g / l, or even more) in the catholyte, which limits the energy consumption useful for the subsequent concentration of sodium hydroxide.
• the suspension prepared during step a) may include a thickening agent.
• the amount of thickening agent can vary between 0 and less than 1.5 parts by dry weight per 100 parts by dry weight of asbestos fibers.
• the amount of thickening agent varies between 0 and 1 part by dry weight relative to the above reference.
• the thickening agents are chosen from polysaccharides of natural or synthetic origin.
• the thickening agents are chosen from natural polysaccharides, such as biogums, obtained by fermentation of a carbohydrate under the action of a microorganism.
• natural polysaccharides such as biogums
• biogums obtained by fermentation of a carbohydrate under the action of a microorganism.
• xanthan gum such as xanthan gum, gellan, rhamsan and welan.
• these contents of thickening agent if however the suspension comprises one, make it possible to stabilize the suspension to be deposited, and therefore to obtain homogeneous diaphragms, while keeping a time necessary for the deposition, compatible with industrial objectives.
• the asbestos fibers used in the composition of the suspension to be deposited are advantageously those commercially available. Mention may in particular be made of chrysotile asbestos fibers of length between 1 to 5 mm and chrysotile asbestos fibers of length less than 1 mm.
• the material binder according to the invention consists of fluorinated polymers.
• fluorinated polymers is meant homopolymers or copolymers derived at least in part from olefinic monomers substituted pa: fluorine atoms, or substituted by a combination of fluorine atoms and at least one of chlorine atoms , bromine or iodine per monomer.
• homopolymers or fluorinated copolymers can be constituted by polymers and copolymers derived from tetrafluoroethylene, hexafluoropropylene, chlorotrifluoroethylene, bromotrifluoroethylene.
• Such polymers can also comprise up to 75 mol% of units derived from other ethylenically unsaturated monomers containing at least as many fluorine atoms as carbon atoms, such as for example vinylidene (di) fluoride, esters vinyl and perfluoroalkyl, such as perfluoroalkoxyethylene.
• the fluoropolymer is advantageously according to the invention in the form of an aqueous dispersion containing, in general, from 30 to 70% of dry polymer, with a particle size between 0.1 and 5 micrometers and preferably between 0.1 and 1 micrometer.
• the fluoropolymer used is a polytetrafluoroethylene.
• sica derivatives is meant according to the invention precipitated silicas and combustion or pyrogenic silicas.
• the silicas have a BET specific surface area between 100 m 2 / g and 300 m 2 / g and / or a particle size evaluated with the COULTER® counter between 1 and 50 microns and, preferably, between 1 and 15 microns.
• the aqueous suspension prepared in step a) of the process according to the present invention comprises 500 to 10,000 parts of water per 100 parts by weight of asbestos fibers.
• the diaphragm When the diaphragm is used in electrolysis, the diaphragm should preferably be in the form of a microporous diaphragm, that is to say a diaphragm substantially devoid of silica-based derivatives.
• the process of the present invention then comprises a step e) corresponding to the elimination of the silica-based derivatives.
• the elimination of the silica-based derivatives can be carried out by attack in an alkaline medium. This elimination of the silica-based derivatives can be done before the use of the diaphragm in electrolysis, but, in a practical and advantageous manner, the silica-based derivatives can be eliminated "in situ" in the electrolyser, by dissolution in the medium. alkaline, especially during the first hours of electrolysis.
• the treatment is advantageously carried out in contact with an aqueous solution of sodium hydroxide whose concentration is between 40 and 200 g / l and at a temperature between 20 and 95 ° C.
• the web is therefore formed by filtration under programmed vacuum of said suspension through a porous material.
• porous materials can in particular be fabrics and / or grids whose void, the perforations or the porosity can be between 1 ⁇ m and 5 mm, and preferably between 20 ⁇ m and 2 mm.
• the porous material may correspond to a porous metallic surface which then constitutes the elementary cathode of the cell d 'electrolysis.
• This elementary cathode may have one or more planar or cylindrical surfaces, commonly called "thimble", having an open surface.
• the cathode prior to the deposition of the diaphragm, is covered with a precathode sheet.
• This preliminary step is carried out by programmed vacuum filtration through the elementary cathode, consisting of a metal surface having a mesh vacuum or perforations of between 1 ⁇ m and 5 mm, and preferably between 20 ⁇ m and 2 mm, d '' an aqueous suspension of fibers at least part of which is electrically conductive, of a binder based on a fluoropolymer in the form of particles and optionally additives, followed by the elimination of the liquid medium, the possible drying of the sheet thus formed and any sintering of this sheet.
• the sintering of the precathode layer is preferably carried out at this stage of the process only insofar as the binder of this layer is different from the binder of the suspension prepared in step a) of the process according to the present invention.
• the precathode layer thus obtained then constitutes the porous material through which the suspension prepared in step a) of the process according to the present invention can be filtered.
• the additives can in particular correspond to derivatives based on silica, as described above for the diaphragm, or else to electrocatalytic agents chosen from the group consisting of Raney metals and Raney alloys, the major of which will be eliminated. easily removable part (s) of metal (s), and mixtures thereof.
• the different vacuum programs described above, whether for depositing the precathode layer or the diaphragm according to the invention, can be carried out continuously or in stages, from atmospheric pressure to final pressure (0.01 to 0.5 bar). absolute).
• the above-mentioned sintering (or consolidation) steps are generally carried out at a temperature above the melting or softening point of the fluoropolymers, binders of said layers. .
• a suspension is prepared, with stirring, of:
• a - deionized water the amount of which is calculated to obtain approximately 4 liters of suspension and an extract of approximately 4.5%;
• the suspension is allowed to stand for at least 24 hours.
• the suspension is stirred for 30 minutes before use.
• the volume of solution required is withdrawn so that it contains the quantity of dry extract which it is intended to deposit to form the diaphragm (of the order of 1 to 2 kg / m 2 ).
• Filtration is carried out under programmed vacuum on a cathode on which a precathode sheet has been previously deposited which will be described below.
• the depression is established and increases by 50 mbar per minute to reach approximately 800 mbar.
• the vacuum is maintained for 15 minutes at 800 mbar.
• the assembly is then sintered, after optional drying at approximately 100 ° C., bringing the cathode and diaphragm assembly to 350 ° C., with a bearing at a temperature of approximately 315 ° C., the whole for approximately 1 hour and a half. .
• silica is then eliminated by an alkaline attack with electrolytic soda during the first moments of the electrolysis (elimination "in situ").
• the precathode layer is prepared in the following manner: In 7 liters of deionized water, 30 g of asbestos fibers less than 1 mm in length are introduced with stirring, 82 ml of triton X 100® at 40 g / l of Rohm and Haas company.
• the depression is established and increases by 10 mbar per minute to reach around 200-300 mbar.
• the vacuum is maintained for 15 minutes at 200-300 mbar. It is dried for 1 hour at 120 ° C.
• the electrolysis cell for measuring performance has the following characteristics and operating conditions: - expanded metal anode coated with Ru0 2 - Ti0;
• the cell temperature 85 ° C.
• the permeability corresponds to the flow of the electrolyte from one compartment to another, this flow is evaluated by the simple difference in heights observed between the anode and cathode compartments;
• the stop rates on the precathode layer which constitutes the porous material are 100% (stop rate observed by simple material balance: determination of the elements F, Mg and Si by fluorescence with X-rays and / or by weighing).
• the stop rates on the precathode layer which constitutes the porous material are 100% (stop rate observed by simple material balance: determination of the elements F, Mg and Si by fluorescence with X-rays and / or by weighing).
• Comparative Examples 1, 2 and 3 show that the hydraulic and / or electrical performance is unsatisfactory.
• Examples 6 and 7 corresponding to 15 g of PTFE per 100 g of asbestos fibers in the suspension and Examples 10 and 11 corresponding to a PTFE / Silica ratio equal to 1.33 are comparative examples.
• the stop rates on the precathode layer which constitutes the porous material are 100% (stop rate observed by simple material balance: determination of the elements F, Mg and Si by fluorescence with X-rays and / or by weighing).
• the low PTFE content in Examples 6 and 7 induces a high and unstable permeability, but above all there is the risk of a deconsolidation of the diaphragm after a few hours of operation in electrolysis (result found, but not apparent from the table), this which is incompatible with industrial development.
• the diaphragm has a hydrophobic character (high tension and low permeability), the soda yield is low and energy consumption is high.
• the stop rates on the precathode layer which constitutes the porous material are 100% (stop rate observed by simple material balance: determination of the elements F, Mg and Si by fluorescence with X-rays and / or by weighing).
• the deposited weight is 1.59 kg / m2.
• the concentration of sodium hydroxide produced is gradually varied from 2 to 5 moles. M during the first 300 hours of operation.
• the test is extended for 2500 hours and a production of sodium hydroxide concentration of 5N ⁇ 0.2N is maintained.
• the newt is replaced entirely or partially by sodium dioctyl sulfosuccinate (sulfimel) which is an anionic surfactant.
• sulfimel sodium dioctyl sulfosuccinate
• the stop rates on the precathode layer which constitutes the porous material are 100% (stop rates observed by simple material balance: determination of the elements F, Mg and Si by fluorescence with X-rays).
• Sulfimel therefore contributes to the joint increase in flow resistance and electrical resistance.
• the dry matter content in the suspension is approximately 4.1%.
• the compositions, the conditions and the results are collated in the following table 4.
• the deposited weight corresponds to the dry weight of the precathode (approximately 5 kg) and that of the deposited diaphragm.
• the examples "bis" correspond to the examples having the same number, the only difference lies in the weight deposited.
• Y varies: 30, 50 and 70 g of silica
• the stop rates on the precathode layer which constitutes the porous material are 100% (stop rate observed by simple material balance: determination of the elements F, Mg and Si by fluorescence with X-rays and / or by weighing).
• the example corresponding to the diaphragm with 50 g of PTFE and 30 g of silica is therefore a comparative example, the PTFE / Silica ratio being 1.7.
• the low silica content compared to PTFE induces a very low permeability and a very high tension.
• the soda yield is very low and the production of a soda with a titre of between 3.3 and 4.5 N is impossible (for a deposited weight of
• a suspension is prepared, in accordance with Example 1, with stirring, of:
• Example 34 also comprises 1.5 g of xanthan gum, that of Example 35 does not contain any.
• the filtration of the suspension is carried out under programmed vacuum on a volume cathode prepared according to example 7 of European patent application no. 296,076, as follows:
• the flow time measured is 40 minutes for Example 34 and 5 minutes for Example 35.

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• Chemical & Material Sciences (AREA)
• Organic Chemistry (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Electrochemistry (AREA)
• Materials Engineering (AREA)
• Metallurgy (AREA)
• Engineering & Computer Science (AREA)
• Inorganic Chemistry (AREA)
• Compositions Of Macromolecular Compounds (AREA)
• Electrolytic Production Of Non-Metals, Compounds, Apparatuses Therefor (AREA)
• Manufacture Of Macromolecular Shaped Articles (AREA)
• Paints Or Removers (AREA)
• Manufacture Of Porous Articles, And Recovery And Treatment Of Waste Products (AREA)
• Chemical Or Physical Treatment Of Fibers (AREA)

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• 1993
  • 1993-03-26 FR FR9303486A patent/FR2703075B1/fr not_active Expired - Fee Related
• 1994
  • 1994-03-28 US US08/343,450 patent/US5547550A/en not_active Expired - Fee Related
  • 1994-03-28 RU RU94046344/04A patent/RU94046344A/ru unknown
  • 1994-03-28 EP EP94911227A patent/EP0642602A1/fr not_active Withdrawn
  • 1994-03-28 CN CN94190153A patent/CN1106615A/zh active Pending
  • 1994-03-28 PL PL94306376A patent/PL306376A1/xx unknown
  • 1994-03-28 CA CA002136763A patent/CA2136763A1/fr not_active Abandoned
  • 1994-03-28 KR KR1019940704275A patent/KR950701692A/ko not_active IP Right Cessation
  • 1994-03-28 JP JP6521744A patent/JPH08505189A/ja active Pending
  • 1994-03-28 WO PCT/FR1994/000342 patent/WO1994023093A1/fr not_active Application Discontinuation
  • 1994-11-26 KR KR94704275A patent/KR970007100B1/ko active
  • 1994-12-23 BG BG99292A patent/BG61878B1/bg unknown

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