EP0610946A1 - Cathode activée pour cellules chlore-alcali et son procédé de fabrication - Google Patents

Cathode activée pour cellules chlore-alcali et son procédé de fabrication Download PDF

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Publication number
EP0610946A1
EP0610946A1 EP94102148A EP94102148A EP0610946A1 EP 0610946 A1 EP0610946 A1 EP 0610946A1 EP 94102148 A EP94102148 A EP 94102148A EP 94102148 A EP94102148 A EP 94102148A EP 0610946 A1 EP0610946 A1 EP 0610946A1
Authority
EP
European Patent Office
Prior art keywords
cathode
mesh
sheet
cathode assembly
diaphragm
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP94102148A
Other languages
German (de)
English (en)
Inventor
Carlo Traini
Giovanni Meneghini
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
De Nora SpA
Original Assignee
Permelec SpA
De Nora Permelec SpA
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Permelec SpA, De Nora Permelec SpA filed Critical Permelec SpA
Publication of EP0610946A1 publication Critical patent/EP0610946A1/fr
Withdrawn legal-status Critical Current

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    • 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
    • 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
    • C25B9/00—Cells or assemblies of cells; Constructional parts of cells; Assemblies of constructional parts, e.g. electrode-diaphragm assemblies; Process-related cell features
    • C25B9/17—Cells comprising dimensionally-stable non-movable electrodes; Assemblies of constructional parts thereof
    • C25B9/19—Cells comprising dimensionally-stable non-movable electrodes; Assemblies of constructional parts thereof with diaphragms

Definitions

  • Chlor-alkali electrolysis is certainly the electrolytic process of greatest industrial interest.
  • said electrolysis process may be illustrated as the splitting of a starting reactant, which is an aqueous solution of sodium chloride (hereinafter defined as brine), to form gaseous chlorine, sodium hydroxide in an aqueous solution and hydrogen.
  • brine sodium chloride
  • This splitting is made possible by the application of electrical energy which may be seen as a further reactant.
  • Chlor-alkali electrolysis is carried out resorting to three technologies: with mercury cathodes cells, with porous diaphragms cells or with ion exchange membranes cells. This latter represents the most modern development and is characterized by low energy consumptions and by the absence of environmental or health drawbacks.
  • the mercury cathodes cells are probably destined for a sharp decline in use because of the severe restrictions adopted by most countries as regards the release of mercury to the atmosphere and soil.
  • the most modern cell designs allow one to meet the severe requirements of the present regulations, but the public opinion rejects "a priori" any process which could lead to the possible release of heavy metals in the environment.
  • the diaphragm process has also problems as the main component of the diaphragm is asbestos fibers, which is recognized to be a mutagenic agent.
  • the most advanced technology foresees a diaphragm made by depositing a layer of asbestos fibers mixed with certain polymeric binders onto cathodes made of iron meshes. The structure thus obtained is then heated whereby the fusion of the polymeric particles permits the mechanical stabilization of the agglomerate of asbestos fibers.
  • the release of fibers during operation is minimized, as well as the release to the atmosphere due to various expedients adopted during manipulation of the asbestos in the deposition step.
  • the anode electrode surfaces are released and are moved towards the surfaces of the diaphragms by suitable spreading means or extenders. Spacers may be introduced between said electrode surfaces and the diaphragms.
  • the novel cathode assembly of the invention for use in monopolar or bipolar diaphragm or membrane electrolysis cells comprises pairs of interleaved anodes and cathodes having openings, said cathodes being provided with a corrosion resistant ion exchange membrane or a porous diaphragm, said cells being provided with inlets for feeding brine and outlets for the withdrawal of chlorine, hydrogen and caustic.
  • Said cathode assembly comprises a thin and flexible corrosion resistant, perforated or expanded sheet or mesh provided with an electrocatalytic coating for hydrogen evolution in an alkaline environment, applied between each of said cathodes and said diaphragm, the cathode and the sheet or mesh being in electrical and mechanical contact, preferably by a plurality of contact points.
  • Fig. 1 is a cross sectional longitudinal view of a conventional diaphragm cell for chlor-alkali electrolysis comprising anodes of the expandable type and the cathode assemblies of the present invention.
  • Fig. 2 a cross sectional view of a detail of fig. 1 illustrating the cathode assemblies of the present invention.
  • the diaphragm electrolysis cell comprises a base (A) on which expandable anodes (B) are secured by means of conductor bars (D).
  • the cathode (C) is made of a perforated or expanded sheet or mesh of interwoven iron wire so shaped as to form a multiplicity of rather flat parallelepipeds (so called fingers).
  • the thickness of the sheet or mesh is such as to ensure a sufficient rigidity to the cathode structure.
  • the dimensions of the openings in the sheet or mesh have suitable values so as to permit easy deposition of the diaphragm starting from a suspension of fibers and possibly of a polymeric binder as well as good adhesion of the diaphragm after deposition.
  • the anodes are interleaved with the fingers.
  • Said fingers (C) are provided with a diaphragm (not shown in the figure). Spacers (not shown in the figure) may be optionally inserted between the surfaces of said anodes and the diaphragms.
  • the cover (G) is made of corrosion resistant material with outlets (H) for chlorine and brine inlets (not shown). Hydrogen and caustics are released through (I) and (L) respectively.
  • the fingers (C) are provided with the thin, foraminous sheet or mesh (F) of the present invention, coated with the diaphragm (E) constituted by fibers and possibly by a polymeric binder.
  • the cathode assembly of the invention is provided with catalytic properties to ensure a decrease of the cell voltage to 3.10-3.15 V and allows for utilizing the cathode structures of existing cells made of interwoven iron wires or of a perforated sheet, thus minimizing the financial investment cost.
  • the application to the fingers (C) of the cathode structure of conventional chlor-alkali cells of a fine and flexible, foraminous screen (F) made of a mesh or expanded or perforated sheet provided with an electrocatalytic coating for hydrogen evolution in an alkaline environment gives unexpected advantages.
  • the improved cathode of the invention is characterized by a composite layer structure, wherein the more internal layer is formed by the fingers (C) of the conventional cells, while the more external layer is formed by the mesh or sheet (F), provided with the electrocatalytic coating, which is mechanically and electrically connected to the fingers.
  • the fingers therefore act both as supports and current distributors.
  • the mesh or sheet (F) of the present invention may be made of iron, chromium, nickel, copper and alloys thereof.
  • the materials most commonly used, due to their availability on the market, are iron, stainless steel and nickel.
  • a thin layer of nickel, some microns thick is applied by galvanic deposition.
  • the dimensions of the openings are not critical but must be suitably selected in order not to interfere with the deposition of the diaphragm or not to spoil the adhesion of the diaphragm to the cathode.
  • the mesh or sheet of the present invention must be thin to permit the greatest flexibility, which is necessary during fixing to the cathode structures (fingers) of conventional cells.
  • the electrocatalytic coating must be advantageously capable of resisting current reversals and to minimize the deposition of metallic iron or electrocondutive compounds of iron, such as magnetite when the fresh brine is polluted by some parts per million of iron.
  • the current reversals occur whenever a monopolar cell of a production line must be excluded from operation. The exclusion is carried out by short-circuiting the cell with a suitable jumper switch means and the cell is then removed from the production line and sent to the service area, while copper rods are inserted in its place. In this way the production is not interrupted. During short-circuiting, the cell is crossed by high reverse current which may easily damage the cathode coating.
  • An alternative method consists in providing the cathodes with coatings capable of undergoing even strong currents reversals.
  • coatings are made of a substrate of nickel metal containing a dispersion of electrocatalytic particles as described in BE 848458, obtained by galvanic deposition from a bath containing suitable nickel salts and particles of electrocatalytic material held in suspension by mechanical stirring with the possible addition of suitable suspending agents.
  • a similar coating obtained by galvanic deposition comprises a nickel matrix having suspended therein particles of electrocatalytic material and particles of a material capable of absorbing high quantities of hydrogen in the form of hydrides, as described in US 5,035,790.
  • the said coatings are also capable of resisting the aggressive attack by the active chlorine dissolved in the brine which flows and diffuses through the diaphragm during the first minutes of the shut-down of the cells.
  • a first obvious alternative solution is represented by subjecting the fresh brine to a suitable pre-treatment and excluding from the circuit any steel component which with time and with the formation of defects may become a continuous source of poisoning of the brine. It is evident that these countermeasures involve high costs.
  • a second alternative is to resort to very active electrocatalytic coatings, which operate at such a potential that the formation of metal iron or magnetite, if not impossible, is at least strongly slowed down.
  • the method of preparation of the cathode assembly of the present invention comprises preparation of the perforated or expanded sheet or fine mesh screen provided with the electrocatalytic coating, and the pre-treatment of the cathode structure of conventional cells.
  • the original diaphragms must be carefully removed to eliminate even the minimum residue of fibers and polymeric binder. This removal may be efficiently carried out in compliance with the current health regulations by using strong water jets under pressure and collecting the liquid which is to be sent to a treatment section.
  • the polished structure thus obtained must be free of any rust or deposits of any nature. This may be obtained by hydrosand-blasting or chemical pickling using acid solutions added with suitable filming corrosion inhibitors.
  • the pre-treatment is limited only to hydrosand-blasting or chemical pickling.
  • the fine electrocatalytic expanded sheet or mesh must be readily applied.
  • the mesh or sheet is cut into strips of suitable dimensions and the strips are then pressed carefully onto the surface of the fingers of the cathode structure.
  • the strips are then mechanically fixed so as to make the electrical continuity between the electrocatalytic sheet or mesh and the cathode structure as extended as possible.
  • the activated sheet or mesh must be particularly flexible and capable of conforming to the profile of the cathode structure, which may certainly present distorsions of various kinds. Further, the number of contact points must be very high.
  • the most advantageous fixing method is electrical spot welding. It must be noted that the weldings spots are only to ensure electrical continuity and a particular mechanical resistance is not required.
  • the activated sheet or screen applied to the external of the cathode structure are subjected to a hydraulic head during operation which tends to keep them pressed against the cathode structure themselves.
  • the composite cathode assembly thus obtained is then subjected to deposition of the diaphragm, which is carried out according to the conventional techniques, without particular variations, if the dimensions of the openings in the sheet or mesh are suitably selected.
  • cathode assembly of the present invention may apply also for membrane cells of the so called bag cell type, which are obtained from existing chlor-alkali diaphragm cells using ion exchange membranes in the form of a bag capable of enveloping the cathode fingers.
  • the fingers of the two cells were readily provided respectively with an activated nickel mesh and an activated expanded sheet prepared according to the teachings of Example 1 of US patent 4,724,052.
  • the mesh was made of nickel wire having a diameter of 0.3 mm and forming square openings of 2 x 2 mm and the expanded, flattened sheet had square openings having dimensions of 5 x 5 mm. After flattening, the thickness of the sheet was 0.5 mm.
  • the application was carried out by maintaining the activated mesh and the sheet pressed against the surfaces of the fingers and then spot welding with a portable welding machine. The welding points formed a square reticulate with a distance among the points of 30 mm.
  • the two composite cathode structures were then coated with a diaphragm comprising asbestos fibers and a suitable fluorinated polymeric binder of the type MS2, forming up to a thickness of 3 mm.
  • the coated cathode structures were then treated in oven according to the conventional technique to obtain mechanical stabilization of the fibers by the polymeric binder.
  • the two cells were re-inserted in the production line, with the following average parameters:
  • the voltage of the two cells equipped with the composite cathode assembly of the present invention detected once stationary operating conditions were reached, was about 3.07 Volts, that is 0.28 Volts lower than the average value typical of the production line. The voltage then slowly increased to 3.10 V in 15 days and remained thereafter constant. No noticeable variations in current efficiency or oxygen content in chlorine were detected.
  • Example 1 The cell of Example 1, provided with the same activated mesh made of a nickel wire, was fed with fresh brine containing 0.01 grams/liter of iron. For comparison purposes, also a reference cell from the production line having an operating lifetime of 50 days, was also fed with the same polluted brine. The reference cell was shut down after 28 days of operation when the hydrogen content in the chlorine reached 0.8%.
  • the cell equipped with the cathode assembly of the invention showed a hydrogen content in chlorine of 0.2% substantially unvaried during the whole operation.

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Electrochemistry (AREA)
  • Materials Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Electrolytic Production Of Non-Metals, Compounds, Apparatuses Therefor (AREA)
  • Electrodes For Compound Or Non-Metal Manufacture (AREA)
EP94102148A 1993-02-12 1994-02-11 Cathode activée pour cellules chlore-alcali et son procédé de fabrication Withdrawn EP0610946A1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
ITMI930255 1993-02-12
ITMI930255A IT1263898B (it) 1993-02-12 1993-02-12 Catodo attivato per celle cloro-soda e relativo metodo di preparazione

Publications (1)

Publication Number Publication Date
EP0610946A1 true EP0610946A1 (fr) 1994-08-17

Family

ID=11364983

Family Applications (1)

Application Number Title Priority Date Filing Date
EP94102148A Withdrawn EP0610946A1 (fr) 1993-02-12 1994-02-11 Cathode activée pour cellules chlore-alcali et son procédé de fabrication

Country Status (11)

Country Link
EP (1) EP0610946A1 (fr)
JP (1) JPH06340991A (fr)
CN (1) CN1090893A (fr)
BG (1) BG98449A (fr)
BR (1) BR9400498A (fr)
CA (1) CA2114757A1 (fr)
IL (1) IL108489A0 (fr)
IT (1) IT1263898B (fr)
NO (1) NO940458L (fr)
PL (1) PL302210A1 (fr)
ZA (1) ZA94915B (fr)

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5961795A (en) * 1993-11-22 1999-10-05 E. I. Du Pont De Nemours And Company Electrochemical cell having a resilient flow field
CN102031534A (zh) * 2010-12-29 2011-04-27 蓝星(北京)化工机械有限公司 一种氧阴极制碱离子膜电解槽装置

Families Citing this family (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US6051117A (en) * 1996-12-12 2000-04-18 Eltech Systems, Corp. Reticulated metal article combining small pores with large apertures
WO2009070938A1 (fr) * 2007-12-03 2009-06-11 Bluestar (Beijing) Chemical Machinery Co., Ltd. Cellule électrolytique à membrane ionique de type à électrodes multiples avec cathodes à oxygène
DE102009004031A1 (de) * 2009-01-08 2010-07-15 Bayer Technology Services Gmbh Strukturierte Gasdiffusionselektrode für Elektrolysezellen
ITMI20091719A1 (it) * 2009-10-08 2011-04-09 Industrie De Nora Spa Catodo per processi elettrolitici
ITMI20111938A1 (it) * 2011-10-26 2013-04-27 Industrie De Nora Spa Comparto anodico per celle per estrazione elettrolitica di metalli
CN103046071B (zh) * 2012-12-13 2015-02-18 苏州市启扬商贸有限公司 离子膜电解单元槽
CN106148992A (zh) * 2015-04-20 2016-11-23 李坚 离子膜催化法或电渗析催化法水制氢及其应用

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4409085A (en) * 1981-12-15 1983-10-11 Olin Corporation Diaphragm cells employing reticulate cathodes
FR2606794A1 (fr) * 1986-11-19 1988-05-20 Permelec Spa Electrode remplacable pour cellules electrochimiques
EP0405559A2 (fr) * 1989-06-30 1991-01-02 Asahi Glass Company Ltd. Cathode très durable présentant une basse surtension à l'hydrogène et son procédé de fabrication

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4409085A (en) * 1981-12-15 1983-10-11 Olin Corporation Diaphragm cells employing reticulate cathodes
FR2606794A1 (fr) * 1986-11-19 1988-05-20 Permelec Spa Electrode remplacable pour cellules electrochimiques
EP0405559A2 (fr) * 1989-06-30 1991-01-02 Asahi Glass Company Ltd. Cathode très durable présentant une basse surtension à l'hydrogène et son procédé de fabrication

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5961795A (en) * 1993-11-22 1999-10-05 E. I. Du Pont De Nemours And Company Electrochemical cell having a resilient flow field
CN102031534A (zh) * 2010-12-29 2011-04-27 蓝星(北京)化工机械有限公司 一种氧阴极制碱离子膜电解槽装置
CN102031534B (zh) * 2010-12-29 2013-04-10 蓝星(北京)化工机械有限公司 一种氧阴极制碱离子膜电解槽装置

Also Published As

Publication number Publication date
BR9400498A (pt) 1994-08-23
BG98449A (en) 1994-11-15
IL108489A0 (en) 1994-05-30
JPH06340991A (ja) 1994-12-13
CN1090893A (zh) 1994-08-17
PL302210A1 (en) 1994-08-22
NO940458D0 (no) 1994-02-10
ITMI930255A1 (it) 1994-08-12
NO940458L (no) 1994-08-15
CA2114757A1 (fr) 1994-08-13
IT1263898B (it) 1996-09-05
ITMI930255A0 (it) 1993-02-12
ZA94915B (en) 1994-08-22

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