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
  • C25B13/08—Diaphragms; Spacing elements characterised by the material based on organic materials

Definitions

• the present invention relates to a permeable diaphragm for an electrochemical cell, in particular for an electrolysis cell for aqueous solutions of alkali metal halides.
• It relates more particularly to a permeable diaphragm for an electrochemical cell, made of fibrous organic polymeric material.
• This known diaphragm has the disadvantage of requiring the incorporation of a surfactant in the aqueous medium used to manufacture it, so as to allow sufficient dispersion of the polymeric material therein. It has the additional disadvantage of requiring the addition of an additive wettable by aqueous electrolytes to the fibrous polymeric material, to make the diaphragm sufficiently wettable by these electrolytes.
• an additive wettable such as asbestos fibers, mica, talc, or particles of titanium dioxide
• the diaphragm is generally too hydrophobic to allow its normal use in electrochemical cells for the treatment of aqueous electrolytes, in particular in cells for the electrolysis of aqueous solutions of alkali metal halides.
• the known diaphragm described above also has the disadvantageous feature of being only achievable from a very specific and costly variety of polymer fibers, namely fibers obtained by extrusion of a polymer in the molten state. , subjected to an intense shearing force in an auxiliary liquid medium.
• This particular feature of the known diaphragm has the disadvantageous effect of adversely affecting its cost.
• porous sheets in which a fibrous polymeric material, generally a fluoropolymer, is dispersed in an organic liquid , for example, a halogenated hydrocarbon, and a felt is separated from the resulting organic suspension.
• an organic liquid for example, a halogenated hydrocarbon
• porous sheets of fibrous organic polymeric material obtained by this known process have the advantageous characteristic of having excellent behavior when they are used as permeable diaphragms in electrochemical cells, and more particularly in cells for electrolysis of aqueous solutions of alkali metal halides.
• the object of the invention is therefore to provide a permeable diaphragm made of fibrous organic polymeric material for an electrochemical cell, which simultaneously exhibits excellent wettability by aqueous electrolytes, in particular brines, and optimum permeability to these aqueous electrolytes during electrolysis.
• the invention relates to a diaphragm made of fibrous organic polymeric material for an electrochemical cell, said diaphragm consisting of a porous sheet obtained from a suspension of the fibrous polymeric material in an organic liquid.
• the organic fibrous polymeric material used in the context of the invention may be in the form of fibers or fibrils.
• fibrils is intended to denote a specific structure of the polymeric material.
• the fibrils consist of an aggregate of a multitude of very fine filaments, with a dandruff appearance, connected together so as to form a three-dimensional network.
• the fibrillated aggregates In appearance flaky, the fibrillated aggregates have an oblong shape; their length varies from approximately 0.5 to 50 mm and their diameter from a few microns to approximately 5 mm. They are characterized by a high specific surface, greater than 1 m 2 / g and even, in many cases, 10 m 2 / g .
• the fibrils used in the context of the invention can, for example, be produced by subjecting a mixture of a polymer in the molten state and of a solvent, to a sudden expansion through an appropriate orifice, as described in particular in French patents 1,596,107 of December 13, 1968, 2,148,449 and 2,148,450 of August 1, 1972 and in Belgian patents 811,778 of March 1, 1974 and 824,844 of January 17, 1975, all in the name of the Applicant.
• the fibrils used in the context of the invention can also be manufactured by other methods, for example by one or other of the methods described in French patents 1,214,157 of June 10, 1958 and 1,472 989 of September 24, 1965, in the name of EI du Pont de Nemours and Co. In these manufacturing processes, continuous fibrillated wicks are obtained, which must then be shredded, for example by grinding.
• the fibrous organic polymeric material is in the form of fibers
• fibers whose diameter is substantially between 0.1 and 25 microns are those having a diameter of between 1 and 15 microns.
• the choice of the polymer of the fibrous organic polymeric material is dictated by the need to obtain a diaphragm which resists the chemical and thermal conditions normally prevailing in electrochemical cells.
• thermoplastic polymers chosen from polyolefins, polycarbonates, polyesters, polyamides, polyimides, polyphenylenes, polyphenylene oxides, polyphenylene sulfides, polysulfones and mixtures of these polymers.
• fluorinated polymers are preferably used, according to the invention.
• Polymers containing fluorinated monomer units derived from ethylene or propylene are advantageously chosen, preferably polymers containing at least 50%, and more particularly at least 75%, of such monomer units.
• Particularly suitable polymers are those containing only monomeric units derived from ethylene or propylene in which all the hydrogen atoms have been substituted by chlorine or fluorine atoms.
• polymers which are suitable in the case where the diaphragm according to the invention is intended for the electrolysis of sodium chloride brines are those chosen from polytetrafluoroethylene, polychlortrifluoroethylene, polyvinylidene fluoride , copolymers of ethylene and chlorotrifluoroethylene, copolymers of ethylene and tetrafluoroethylene, copolymers of tetrafluoroethylene and perfluoralkylvinylether, copolymers of chlorotrifluoroethylene and vinylidene fluoride, copolymers of hydropentafluorpropylene and vinylidene fluoride, copolymers hexafluoroisobutylene and vinylidene fluoride, copolymers of tetrafluoroethylene and perfluorvinylether sulfonyl.
• the organic liquid used in the manufacture of the diaphragm according to the invention can be any organic product which, in the working conditions used to manufacture the porous sheet, is liquid and does not substantially modify the fibrous structure of the organic polymeric material, in particular the structure of the fibrils in the case where the fibrous organic polymeric material consists of fibrils.
• the organic liquid can therefore consist of an organic product which is normally liquid or gaseous under normal conditions of pressure and temperature. In the case where an organic product is used which is gaseous at the working temperature used to manufacture the porous sheet, it is obviously advisable to work under pressure, in an autoclave.
• halogenated hydrocarbons are advantageously used, according to the invention, for example chlorinated or fluorinated hydrocarbons.
• the halogenated hydrocarbons are advantageously chosen from saturated acyclic hydrocarbons and ethylene hydrocarbons, such as for example, trichlorethylene, perchlorethylene, 1,1,1-trichloroethane, methylene chloride, carbon tetrachloride, trichloro-trifluoroethane .
• the organic liquid can be used in pure form or, alternatively, it can be slightly diluted with water or another miscible medium. Generally, the amount of water or other miscible medium mixed with the organic liquid cannot exceed 10% of the weight of pure organic liquid; it is preferably less than 5% of the weight of the pure organic liquid.
• a fibrous organic polymeric material and an organic liquid whose respective solubility parameters are different from each other by less than 5 (cal / cm 3 ) 1/2
• the solubility parameter of a substance being, by definition, the square root of its cohesion energy per unit of volume (Kirk-Othmer - Encyclopedia of Chemical Technology - 1971 - Supplement Volume - p.889).
• the fibrous polymeric material and the organic liquid are advantageously chosen so that the difference between their parameters respective solubility is between 1.5 and 3 (cal / cm 3 ) 1/2 , the solubility parameter of the organic liquid being preferably greater than that of the fibrous polymeric material.
• the ability of the diaphragm according to the invention to be wetted by aqueous electrolytes, in particular by sodium chloride brines, is considerably improved when an organic liquid is chosen whose surface tension does not does not exceed 40 dyn / cm and is preferably less than 30 dyn / cm, such as, for example, carbon tetrachloride or 1,1,2-trichloroethane.
• the dispersion of the fibrous organic polymeric material in the organic liquid is between 0.2 and 25%, preferably between 0.5 and 15 X.
• Weight contents which are suitable are those between 1 and 10 X.
• the suspension it is also advantageous to subject the suspension to a beating which has the function of dispersing the fibrous polymeric material in the organic liquid and of conferring, using the organic liquid, an intrinsic mechanical cohesion to the porous sheet. obtained after decantation or filtration of the organic liquid.
• the intensity of the threshing is adjusted so that the sheet thus obtained has sufficient cohesion to allow its use as a diaphragm in an electrolysis cell.
• Values which are suitable for the intensity of threshing are those which give the suspension of fibrous polymeric material in the organic liquid, a state of dispersion corresponding to a Schopper-Riegler number of between 20 and 80, preferably 30 and 75, as defined in standards SCAN-M3: 65 and TAPPI T227m-58.
• the threshing intensities required to obtain these Schopper-Riegler number values depend on various factors, including the nature of the fibrous polymeric material and the organic liquid, as well as the concentration and temperature of the suspension subjected to threshing. They can be easily determined, in each particular case, by routine work.
• the organic suspension of fibrous polymeric material can be kept at a temperature lower, equal to or higher than room temperature.
• the temperature of the suspension should be kept at all times above the melting point of the organic liquid and below the softening temperature of the fibrous polymeric material.
• the temperature and pressure should also be adjusted during threshing to avoid vaporization of the organic liquid.
• temperatures which are very suitable are those between 15 and 100 ° C.
• porous sheet it suffices, in a manner known per se, to decant or filter the suspension which has been subjected to threshing.
• the sheet by filtering the above suspension directly through an openwork support of the diaphragm by applying a technique of the type commonly used for the manufacture of asbestos diaphragms and described in particular in United States patents 1 865 152 in the name of KE STUART, of June 28, 1932, and 3 344 053 in the name of NEIPERT et al., Of May 4, 1964.
• the perforated support of the diaphragm can advantageously be the perforated cathode of a diaphragm electrolysis cell .
• This embodiment has the advantage of allowing manufacturing diaphragm in situ on cathodes of complicated shape, with non-developable surface, for example of the type equipping the electrolysis cells described in French patents 2 223 083 of 28.3.1973 and 2 248 335 of 14.10.1974 in the name of the Applicant.
• the threshing of the suspension of fibrous polymeric material is carried out then its filtration through the perforated support, in a unique device, known per se for the manufacture asbestos diaphragms, of the type described in French patent 2,308,702 of 25.4.1975, in the name of the Applicant.
• any known drying technique can be used for this purpose, such as drying at room temperature, in a calm atmosphere or by vacuum.
• the duration of the drying must be sufficient for the residual content of organic liquid in the sheet to be reduced to 5%, preferably to 2% by weight.
• the sheet after having dried the sheet, it is subjected to an annealing at a temperature higher than 100 ° C., but lower than the softening temperature. of the fibrous polymeric material.
• the annealing is advantageously carried out at at least 200 ° C. for at least 1 hour, preferably at least 10 hours.
• Well suited annealing temperatures are those which are about 5 to 15 ° C lower than the softening temperature of the fibrous polymeric material.
• the diaphragm according to the invention has the advantage of having good mechanical cohesion and of being of stable dimensions during its use in an electrochemical cell. It has the advantageous property of an excellent wettability by aqueous electrolytes, in particular by sodium chloride brines.
• the aforementioned porous sheet resulting from drying and annealing is subjected to a treatment with a liquid whose surface tension does not exceed 40 dyn / cm and is preferably less than 30 dyn / cm.
• the diaphragm according to this particular embodiment of the invention is characterized by optimum wettability by aqueous electrolytes, in particular aqueous solutions of alkali metal halides such as sodium chloride brines.
• the treatment of the porous sheet with the liquid at low surface tension can be carried out by any known impregnation technique, for example by washing or immersion. However, it is preferred to percolate the treatment liquid through the porous sheet.
• the treatment of the sheet with the liquid at low surface tension can be carried out at low temperature, at ambient temperature or at high temperature, under a pressure less than, equal to or greater than atmospheric pressure.
• the liquid with low surface tension can be any organic or inorganic liquid which, under the conditions of treatment of the sheet, has a surface tension not exceeding 40 dyn / cm and does not substantially modify the fibrous structure of the organic polymeric material of the sheet.
• Liquids with low surface tension which are particularly suitable, in the context of the invention, are those whose surface tension is between 10 and 30 dyn / cm, for example acetone, ethyl alcohol, methyl alcohol , isopropyl alcohol, chloroform, diethyl ether, carbon tetrachloride, ammonia.
• aqueous solutions having the required surface tension for example water containing a surfactant in an amount sufficient to bring its surface tension to 40 dyn / cm maximum, and preferably below 30 dyn / cm.
• the diaphragm according to the invention has the particularly advantageous characteristic of generally having a permeability to aqueous electrolytes of the same order of magnitude as that of the asbestos diaphragms normally fitted to the brine electrolysis cells.
• sodium chloride so that it is well suited to be substituted for the asbestos diaphragms of existing electrolysis cells, for example of the type described in French patents 2 164 623 of 12.12.1972, 2 223 083 of 28.3. 1973, 2 230 411 of 27.3.1974 and 2 248 335 of 14.10.1974, all in the name of the Claimant.
• the diaphragm according to the invention also has the interesting and surprising feature of having, from the start of its use, the optimum characteristics required for wettability and permeability.
• This feature of the diaphragm according to the invention provides the appreciable advantage that the electrochemical installations, in particular the electrolysis cells of sodium chloride brines, are henceforth capable of operating in normal regime, with optimum energy efficiency, from the start of putting them into service with a new diaphragm.
• the diaphragm according to the invention is suitable both for equipping electrochemical batteries used for the production of electrical energy and for equipping electrolysis cells. It finds an interesting application in diaphragm cells for the electrolysis of aqueous solutions of alkali metal halides, in particular sodium chloride brines.
• the specific surface of the porous sheet of the diaphragm is between 0.5 and 40 m 2 / g, preferably between 1.5 and 20 m 2 / g; its permeability is also advantageously between 0.02 and 1 h -1, preferably between 0.05 and 0.5 hl, the permeability of the porous sheet being defined by the flow rate (in cm 3 / h) of saturated brine in sodium chloride at 80 ° C, which crosses a surface of the sheet of 1 cm 2 , under hydrostatic pressure corresponding to a brine column of 1 cm. Values between 5 and 15 m 2 / g for the specific surface and between 0.07 and 0.3 h -1 for the permeability are particularly suitable when the diaphragm is intended for the electrolysis of concentrated brines of sodium chloride.
• the appropriate values of the specific surface and the permeability of the sheet forming the diaphragm can easily be obtained by a judicious choice of the dimensions of the fibers or of the fibrils forming the fibrous polymeric material, of the nature of the organic liquid, of the concentration of the suspension subjected to threshing and threshing energy used.
• the diaphragm according to the invention may optionally contain, in addition to the fibrous polymeric material, other usual constituents of permeable diaphragms, such as inorganic fibers (for example asbestos fibers) or additives intended to reinforce certain properties of the diaphragm or to give it additional properties, for example particles of titanium dioxide or barium titanate, or surfactants, preferably fluorinated, such as acids fluorinated or perfluorinated fats, fluorinated or perfluorinated sulfonic acids or salts of these acids.
• inorganic fibers for example asbestos fibers
• additives intended to reinforce certain properties of the diaphragm or to give it additional properties for example particles of titanium dioxide or barium titanate, or surfactants, preferably fluorinated, such as acids fluorinated or perfluorinated fats, fluorinated or perfluorinated sulfonic acids or salts of these acids.
• these additional constituents into the diaphragm according to the invention, it is possible, for example, to introduce them as they are in the particulate state into the suspension of the fibrous polymeric material after or, preferably, before subjecting the latter to threshing.
• a fibrous polymeric material can be used which already contains such additives as a filler.
• Examples 1 to 6 which follow relate to diaphragms based on fibrils made from Halar brand polymers (sold by Allied Chemical Corp.), which are copolymers of ethylene and chlorotrifluoroethylene.
• the fibrils used were obtained by subjecting a biphasic mixture of the polymer in the molten state and of an appropriate solvent, to a sudden expansion through an orifice of small section, as described in French patents 1,596,107 of 13 December 1968, 2,148,449 and 2,148,450 of August 1, 1972 and in the Belgian patents 811,778 of March 1, 1974 and 824,844 of January 17, 1975, all in the name of the Applicant.
• the fibrils obtained as described above, were dispersed in perchlorethylene so as to form 9 l of a suspension containing 1% by weight of fibrils.
• the suspension was subjected, at ambient temperature and atmospheric pressure, to threshing in a conventional paper industry sogger, for 1 min. 30.
• the organic suspension of polymeric material exhibited, after threshing, a state of dispersion corresponding to a Schopper-Riegler number between 55 and 60.
• the suspension was then filtered through a circular perforated fabric of 113 cm 2 , causing for this purpose a depression of 50 mm under the trellis, for 3 minutes.
• the porous sheet collected on the canvas was dried thereon, by heating at 90 ° C for one hour.
• One of the diaphragms thus obtained was subjected to an electrolysis test in a laboratory cell.
• the distance between the anode and the cathode was 5 mm and the diaphragm was placed as it was on the cathode, facing the anode.
• Example 1 The test of Example 1 was repeated, with the only difference that after drying, the diaphragm sheet was annealed at 200 ° C for 24 h.
• Example 2 Was produced, as described in Example 1, a diaphragm containing 30% by weight of fibrils and 70% by weight of titanium dioxide particles. After the hype, which lasted
• the organic suspension of fibrous polymeric material and titanium dioxide had a state of dispersion corresponding to a Schopper-Riegler number equal to 43.
• a diaphragm was made by applying the method described in Example 1, but this time using, in contrast to the invention, water instead of perchlorethylene to form the suspension of fibrils.
• the water used contained 1% by weight of product FLUORAD FC-170 (3M Company), which is a fluorinated surfactant.
• FLUORAD FC-170 (3M Company)
• the duration of the beating of the aqueous suspension of fibrils was 1 min 30, as in the tests of Examples 1 to 3.
• the diaphragm collected after drying was characterized by a breaking load equal to 0.2 kg / cm 2 .
• Example 4 The test of Example 4 was repeated, but by extending the duration of the threshing which, here, was one hour.
• the diaphragm collected at the end of the drying did not exhibit a higher breaking load than that of the diaphragm of Example 4.
• Example 4 The test of Example 4 was repeated, except that after the drying, the diaphragm sheet was annealed at 200 ° C for 24 hours.
• the diaphragm obtained exhibited a tensile breaking load equal to 1.2 kg / cm 2 .

Landscapes

• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Electrochemistry (AREA)
• Materials Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Manufacture Of Macromolecular Shaped Articles (AREA)
• Primary Cells (AREA)
• Addition Polymer Or Copolymer, Post-Treatments, Or Chemical Modifications (AREA)
• Electrolytic Production Of Non-Metals, Compounds, Apparatuses Therefor (AREA)
• Organic Insulating Materials (AREA)
• Micro-Organisms Or Cultivation Processes Thereof (AREA)
• Cell Separators (AREA)
• Secondary Cells (AREA)
• Hybrid Cells (AREA)
• Diaphragms For Electromechanical Transducers (AREA)

Priority Applications (1)

Applications Claiming Priority (2)

Publications (2)

Family

ID=9211536

Family Applications (1)

Country Status (12)

Cited By (1)

Families Citing this family (5)

Citations (3)

Family Cites Families (5)

• 1979
  • 1979-07-13 ZA ZA00793535A patent/ZA793535B/xx unknown
  • 1979-07-19 AT AT79200411T patent/ATE14025T1/de not_active IP Right Cessation
  • 1979-07-19 DE DE7979200411T patent/DE2967474D1/de not_active Expired
  • 1979-07-19 EP EP79200411A patent/EP0007674B1/de not_active Expired
  • 1979-07-23 AU AU49151/79A patent/AU4915179A/en not_active Abandoned
  • 1979-07-30 ES ES482970A patent/ES482970A1/es not_active Expired
  • 1979-07-30 NO NO792501A patent/NO156295C/no unknown
  • 1979-07-30 BR BR7904891A patent/BR7904891A/pt unknown
  • 1979-07-30 PT PT69996A patent/PT69996A/pt unknown
  • 1979-07-31 JP JP9803779A patent/JPS5521598A/ja active Pending
  • 1979-07-31 FI FI792390A patent/FI64816C/fi not_active IP Right Cessation
• 1980
  • 1980-10-17 US US06/197,826 patent/US4302303A/en not_active Expired - Lifetime

Patent Citations (3)

Also Published As

Similar Documents

Legal Events