EP3899101A2 - Procédé d'électrolyse à membrane de solutions de chlorures alcalins en ayant recours à une électrode à diffusion gazeuse - Google Patents

Procédé d'électrolyse à membrane de solutions de chlorures alcalins en ayant recours à une électrode à diffusion gazeuse

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Publication number
EP3899101A2
EP3899101A2 EP19818094.5A EP19818094A EP3899101A2 EP 3899101 A2 EP3899101 A2 EP 3899101A2 EP 19818094 A EP19818094 A EP 19818094A EP 3899101 A2 EP3899101 A2 EP 3899101A2
Authority
EP
European Patent Office
Prior art keywords
electrolysis
anolyte
cell
cathode
catholyte
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Withdrawn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
EP19818094.5A
Other languages
German (de)
English (en)
Inventor
Andreas Bulan
Michael Grossholz
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.)
Covestro Deutschland AG
Original Assignee
Covestro Intellectual Property GmbH and Co KG
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 Covestro Intellectual Property GmbH and Co KG filed Critical Covestro Intellectual Property GmbH and Co KG
Publication of EP3899101A2 publication Critical patent/EP3899101A2/fr
Withdrawn legal-status Critical Current

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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
    • C25B1/00—Electrolytic production of inorganic compounds or non-metals
    • C25B1/01—Products
    • C25B1/34—Simultaneous production of alkali metal hydroxides and chlorine, oxyacids or salts of chlorine, e.g. by chlor-alkali electrolysis
    • C25B1/46—Simultaneous production of alkali metal hydroxides and chlorine, oxyacids or salts of chlorine, e.g. by chlor-alkali electrolysis in diaphragm cells
    • 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
    • C25B11/032—Gas diffusion 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
    • C25B11/00—Electrodes; Manufacture thereof not otherwise provided for
    • C25B11/04—Electrodes; Manufacture thereof not otherwise provided for characterised by the material
    • C25B11/051—Electrodes formed of electrocatalysts on a substrate or carrier
    • C25B11/073—Electrodes formed of electrocatalysts on a substrate or carrier characterised by the electrocatalyst material
    • C25B11/075—Electrodes formed of electrocatalysts on a substrate or carrier characterised by the electrocatalyst material consisting of a single catalytic element or catalytic compound
    • C25B11/081—Electrodes formed of electrocatalysts on a substrate or carrier characterised by the electrocatalyst material consisting of a single catalytic element or catalytic compound the element being a noble metal
    • 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
    • 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
    • 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
    • C25B15/02—Process control or regulation
    • C25B15/023—Measuring, analysing or testing during electrolytic production
    • C25B15/025—Measuring, analysing or testing during electrolytic production of electrolyte parameters
    • C25B15/027—Temperature
    • 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
    • C25B15/02—Process control or regulation
    • C25B15/023—Measuring, analysing or testing during electrolytic production
    • C25B15/025—Measuring, analysing or testing during electrolytic production of electrolyte parameters
    • C25B15/029—Concentration
    • C25B15/031—Concentration pH
    • 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
    • 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
    • C25B9/60—Constructional parts of cells
    • C25B9/65—Means for supplying current; Electrode connections; Electric inter-cell connections

Definitions

  • the invention relates to a method for the electrolysis of aqueous solutions of alkali chlorides by means of gas diffusion electrodes while maintaining certain operating parameters.
  • the invention is based on electrolysis processes known per se, e.g. for the electrolysis of aqueous alkali metal chloride solutions by means of gas diffusion electrodes, which usually comprise an electrically conductive support and a gas diffusion layer with a catalytically active component.
  • gas diffusion electrodes which usually comprise an electrically conductive support and a gas diffusion layer with a catalytically active component.
  • the arrangement is such that there is a narrow gap between the gas diffusion electrode and the ion exchange membrane, through which an electrolyte flows.
  • Various proposals for operating the gas diffusion electrode as oxygen consumption electrodes in electrolytic cells of a technical size are known in principle from the prior art. The basic idea is to replace the hydrogen-developing cathode of the electrolysis (for example in chlor-alkali electrolysis) with the oxygen-consuming electrode (cathode).
  • the gas diffusion electrode - hereinafter also called GDE for short - must meet a number of requirements in order to be used in technical electrolysers.
  • the catalytic converter and all other materials used must be chemically stable against the electrolyte used and the gases supplied to the electrode and the compounds formed on the electrode, such as hydroxide ions or hydrogen, at a temperature of typically up to 90 ° C.
  • a high degree of mechanical stability is also required so that the electrodes can be installed and operated in electrolyzers with a size of usually more than 2 m 2 (technical size).
  • Other desired properties are: high electrical conductivity, a low layer thickness, a high inner surface and a high electrochemical activity of the electrocatalyst.
  • Suitable hydrophobic and hydrophilic pores and a corresponding pore structure for conducting gas and electrolyte are necessary. Long-term stability and low manufacturing costs are further special requirements for a technically usable oxygen consumption electrode.
  • a toe for chlor-alkali electrolysis is described, in which the liquid from top to bottom via a flat porous element, a so-called percolator, attached between the gas diffusion electrode and the ion exchange membrane, in a kind of free-falling liquid film, called falling film for short , is guided along the gas diffusion electrode (mini-gap arrangement). With this arrangement only one is loaded very small liquid column on the liquid side of the gas diffusion electrode, and it does not build up a high hydrostatic pressure profile over the overall height of the cell.
  • micro gap Another arrangement, which is sometimes also referred to as “zero gap” but more precisely termed “micro gap”, is described in JP3553775 and US6117286A1.
  • this arrangement there is another layer made of a porous hydrophilic material between the ion exchange membrane and the GDE, which absorbs the resulting alkali lye due to its suction power and from which at least part of the lye can flow downwards.
  • the possibility of draining the alkali solution is determined by the installation of the GDE and the cell design.
  • An oxygen consumption electrode typically consists of a carrier element, for example a plate made of porous metal or a woven fabric made of metal wires, and an electrochemically catalytically active coating.
  • the electrochemically active coating is microporous and consists of hydrophilic and hydrophobic components.
  • the hydrophobic constituents make it difficult for electrolyte to penetrate and thus keep the corresponding pores in the GDE free for the transport of oxygen to the catalytically active centers.
  • the hydrophilic constituents enable the electrolyte to penetrate to the catalytically active centers and to remove the hydroxide ions from the GDE.
  • a fluorine-containing polymer such as polytetrafluoroethylene (PTFE) is generally used as the hydrophobic component, which also serves as a polymeric binder for particles of the catalyst.
  • PTFE polytetrafluoroethylene
  • the silver serves as a hydrophilic component.
  • Platinum has a very high catalytic activity for the reduction of oxygen. Because of the high cost of platinum, it is only used in a supported form.
  • the preferred carrier material is carbon.
  • the durability of carbon-based, platinum-based electrodes in continuous operation is insufficient, presumably because platinum also catalyzes the oxidation of the carrier material. Carbon also favors the undesirable formation of H2O2 , which also causes oxidation.
  • Silver also has a high electrocatalytic activity for the reduction of oxygen. Silver can be used in carbon-supported form and also as finely divided metallic silver. Although the carbon-supported silver catalysts are more durable than the corresponding platinum catalysts, their long-term stability under the conditions in one of the oxygen-consuming electrodes, in particular when used for chlor-alkali electrolysis, is also limited.
  • the silver is preferably introduced at least partially in the form of silver oxides, which are then reduced to metallic silver.
  • the reduction usually takes place when the electrolysis toe is started up for the first time.
  • the silver compounds are reduced, there is also a change in the arrangement of the crystallites, in particular also a bridge formation between individual silver particles. Overall, this leads to a solidification of the structure.
  • the membrane is permeable to cations and water and largely impermeable to anions.
  • the ion exchange membranes in electrolysis cells are exposed to heavy loads: they must be resistant to chlorine on the anode side and strong alkaline loads on the cathode side at temperatures around 90 ° C.
  • Perfluorinated polymers such as PTFE usually withstand these loads.
  • the ion transport takes place via acid sulfonate groups and / or carboxylate groups polymerized into these polymers. Carboxylate groups show a higher selectivity, the carboxylate group-containing polymers have a lower water absorption and have a higher electrical resistance than sulfonate group-containing polymers.
  • multilayer membranes are used with a thicker layer containing sulfonate groups on the anode side and a thinner layer containing carboxylate groups on the cathode side.
  • the membranes are provided with a hydrophilic layer on the cathode side or on both sides.
  • the membranes are reinforced by inserting woven or nonwoven fabrics, the reinforcement is preferably incorporated in the layer containing sulfonate groups.
  • the ion exchange membranes are sensitive to changes in the media surrounding them. Different molar concentrations can create strong osmotic pressure drops between the anode and cathode sides. When the electrolyte concentrations decrease, the membrane swells due to increased water absorption. When the electrolyte concentrations increase, the membrane releases water and shrinks as a result. In extreme cases, water removal can lead to the precipitation of solids in the membrane or mechanical damage such as cracks in the membrane. Changes in concentration can cause faults and damage to the membrane. The layer structure can be delaminated (blistering), which worsens the mass transfer or the selectivity of the membrane.
  • holes pinholes
  • cracks can occur, which can lead to undesired mixing of the anolyte and catholyte.
  • An inhomogeneity of the water and / or ion distribution in the membrane and / or the gas diffusion electrode can lead to local peaks in the current and mass transport upon recommissioning and consequently damage to the membrane or the gas diffusion electrode.
  • the precipitation of alkali metal chloride salts on the anode side also presents problems.
  • the strong osmotic gradient between anolyte and catholyte results in water transport from the anode to the cathode compartment.
  • the electrolysis is in operation, there is a loss of chloride and alkali ions from the water transport from the anode compartment, so that the concentration of alkali chloride in the anode compartment drops under common electrolysis conditions.
  • the electrolysis is switched off, the water transport caused by the osmotic pressure remains from the anode to the cathode compartment.
  • the concentration in the anolyte rises above the saturation limit.
  • precipitation of alkali chloride salts especially in the border area to the membrane or even in the membrane, which can lead to damage to the membrane.
  • electrolysis cells are desirably operated for periods of several years without being opened in the meantime. Due to fluctuating quantities and disruptions in the electrolysis upstream or downstream production areas, however, electrolysis cells in production plants must inevitably be repeatedly shut down and restarted. When the electrolysis cells are switched off and put back into operation, conditions occur which lead to damage to the cell elements, such as anode, ion exchange membrane, gas diffusion electrode or other components used in the cell, and which can considerably reduce their service life and furthermore impair the performance of the electrolysis. In particular, oxidative damage in the cathode compartment, damage to the gas diffusion electrode and damage to the membrane were found.
  • the published patent application JP 2004-300510 A describes an electrolysis process using a micro-gap arrangement, in which corrosion of the cathode space is to be prevented when the cell is switched off by flooding the gas space with sodium hydroxide solution. Covering the gas space with caustic soda therefore protects the cathode space from corrosion, but offers insufficient protection against damage to the electrode and the membrane during shutdown and start-up or during standstill.
  • US 4578159A1 describes for an electrolysis process using a “zero gap” arrangement that by rinsing the cathode compartment with 35% sodium hydroxide solution before starting the cell, or by starting the cell with a low current density and gradually increasing the current density, damage to the membrane and electrode is avoided become. This procedure reduces the risk of damage to the membrane and gas diffusion electrode during commissioning, but does not offer any protection against damage during decommissioning and standstill.
  • the anode side is first filled with brine, water and nitrogen are entered on the cathode side.
  • the cell is then heated to 80 ° C.
  • the gas supply is switched to oxygen and a polarization voltage with low current flow is applied.
  • the current density is increased and the pressure in the cathode is increased, the temperature rises to 90 ° C.
  • the brine and water supply are subsequently adjusted so that the desired concentrations on the anode and cathode sides have been reached.
  • the volume flow and / or the composition of the catholyte supplied to the gap is set before the electrolysis voltage is applied between the anode and cathode in such a way that the aqueous solution of alkali hydroxide leaving the cathode gap has a chloride ion content of at most 1000 ppm and after the introduction of the anolyte and an oxygen-containing gas into the cathode compartment, the electrolysis voltage is applied.
  • EP 2639337 A2 humidified oxygen is added before starting up a cell with a finite gap arrangement of the catholyte circuit and an excess pressure is set in the cathode half-cell according to the configuration in the cell, generally in the amount of 10-100 mbar compared to the pressure in the anode.
  • the object of the present invention is to find suitable improved operating parameters for commissioning and decommissioning, in particular for decommissioning and temporary stoppages of an electrolytic cell for chlor-alkali electrolysis using a gas diffusion electrode with a mini-gap arrangement and silver catalyst as an electrocatalytic substance, which are simple to carry out and if they are observed, damage to the membrane, electrode and / or other components of the electrolysis toe can be avoided.
  • Mini-gap arrangement in the sense of the invention means any arrangement of an electrolysis toe which has an electrolyte gap through which the catholyte flows, between the oxygen-consuming electrode and the membrane, the gap having a gap width of at least 0.01 mm and in particular having a gap width of at most 3 mm.
  • electrolysis toe based on the principle of the falling film cell, catholyte flows from top to bottom in a vertically arranged electrolysis toe following gravity.
  • Other arrangements with an alternative flow direction or horizontally arranged electrolysis toe are also intended to be encompassed by the invention.
  • electrolysers containing a gas diffusion electrode with a silver catalyst can be put into operation and taken out of operation repeatedly without damage due to the improved sequence of these steps, and are not damaged even when the machine is at a standstill.
  • the process is particularly suitable for the electrolysis of aqueous sodium chloride and potassium chloride solutions.
  • the invention relates to a method for chlor-alkali electrolysis with an electrolytic cell in a gap arrangement, in particular with a distance of 0.01 mm to 3 mm between the ion exchange membrane and the gas diffusion electrode, the toe having at least one anode space with anode and an alkali metal chloride-containing anolyte, an ion exchange membrane, a cathode compartment with a gas diffusion electrode as the cathode, which has a silver-containing catalyst and, in particular, 0.01 mm to 3 mm thick, porous element through which catholyte flows, between the gas diffusion electrode and the membrane, characterized in that at the end of the electrolysis process, in particular For decommissioning, at least the following steps are carried out in this sequence: a) Lowering the electrolysis voltage and removing chlorine from the anolyte, so that less than 10 mg / L active chlorine is present in the anolyte by maintaining an electrolysis voltage per element of 0.1 to 1.4 V and a current density which is greater
  • a measure known from conventional membrane electrolysis is the maintenance of a polarization voltage, which means that when the electrolysis ends, the voltage is not reduced to zero, but a residual voltage is maintained, so that a residual current flows in the usual direction of electrolysis, so that a constant low current density results and electrolysis occurs to a small extent. If the electrolysis is to be taken out of operation, the electrolytes have to be cooled down, which changes the potential. Therefore, this measure alone is not sufficient to prevent damage to the electrode when the gas diffusion electrodes are used when it is being put into operation or out of operation.
  • the alkali metal chloride is preferably sodium chloride or potassium chloride, particularly preferably sodium chloride.
  • the alkali hydroxide is preferably sodium hydroxide or potassium hydroxide, particularly preferably sodium hydroxide.
  • the gas diffusion electrode is exposed to oxygen gas during operation on its side facing away from the catholyte.
  • the oxygen gas flow to the gas diffusion electrode is preferably maintained when the electrolysis is switched off in accordance with the new method.
  • the purity of the oxygen corresponds to the concentrations and purity requirements customary in electrolysis with a gas diffusion electrode; oxygen with a content of over 98.5% by volume is preferably used.
  • the temperature of the catholyte supplied is regulated in operation such that a temperature of 70-95 ° C., preferably 75-90 ° C., is established in the discharge from the cathode compartment.
  • a temperature difference between the anolyte outlet and the catholyte inlet of less than 20 ° C. is preferably set during operation and when the unit is taken out of operation. Such a small temperature difference avoids damage to the ion exchange membrane.
  • a brine is fed to the anode compartment, the NaCl content of which is 180 g / L (3.07 mol / L) to 330 g / L (5.64 mol / L ) is.
  • the chlorine gas is removed from the anode compartment and the content of dissolved / dispersed chlorine is reduced.
  • concentrations disclosed in this application are determined in particular by titration or another analysis method which is fundamentally known to the person skilled in the art.
  • a current density of greater than zero up to 20 A / m 2 preferably from 0.1 A / m 2 up to 20 A / maintain m 2 .
  • the electrolysis is operated under these conditions until the anolyte is CU-free, ie the chlorine content with oxidation level zero and> 0 is less than 10 mg / L.
  • the chlorine-free content in the anolyte is measured in particular by means of redox titration such as iodometry or by checking the anolyte using iodine-strength paper. Maintaining the brine pH in the range from 2 to 12, preferably pH 6 to 9, during step a) is necessary in order to avoid any chlorine development at a lower pH.
  • the temperature of the anolyte in steps a) and b) is preferably at least 65 ° C., particularly preferably at least 70 ° C.
  • the anolyte is cooled in step d) to a temperature below 70 ° C. while maintaining an electrolysis voltage of 0.1 to 1.4 V. This is another difference from the prior art - this is done here cooling without maintaining the electrolysis voltage.
  • the electrolysis voltage is switched off in step e) at a temperature of the electrolytes of ⁇ 55 ° C., preferably at a temperature of ⁇ 50 ° C.
  • step f the cathode gap (mini-gap) is emptied in step f) (e.g. by switching off the pump for the catholyte feed).
  • mini-gap is only emptied after the anode compartment has been emptied.
  • the anode compartment is emptied in step g) by draining off the anolyte and in particular subsequent rinsing h) of the anode compartment with alkali chloride solution with a maximum of 4 mol / l or with demineralized water (fully demineralized water).
  • step i) the cathode gap (mini gap) is finally rinsed with dilute sodium hydroxide solution or demineralized water to remove chloride residues and to empty the cathodic mini gap.
  • the cathode gap is rinsed again after the anode space has been emptied in order to remove chloride. This avoids, for example, corrosion on the nickel connecting flanges of the cell due to excessive chloride values in the lye remaining in the cathode compartment.
  • the anode compartment can then be emptied particularly preferably.
  • the gas diffusion electrode is efficiently protected by the process according to the invention. Thanks to the potentiostatic operation, the cell can also be cooled below 70 ° C without chlorine being developed on the anode side. This is important from a safety point of view if the electrolysis elements are to be opened later for maintenance or repair.
  • the electrolysis voltage is reduced.
  • the voltage is regulated down to a value of 0.1 to 1.4 V.
  • a temperature of the analyte of> 65 ° C. and a concentration of greater than 200 g / L (3.41 mol / L) NaCl and an alkali hydroxide concentration in the catholyte of ⁇ 28% by weight (9.1 mol / L) at one Catholyte temperature of> 65 ° C the chlorine content in the anode compartment is reduced to ⁇ 10 mg / 1, preferably less than 1 mg / 1.
  • the pH of the anolyte in the outlet from the electrolysis cell is 2 to 12, preferably 6 to 9.
  • Chlorine content is understood to mean the total content of dissolved chlorine in the oxidation state 0 and higher.
  • the remaining chlorine is preferably removed from the anode compartment in such a way that chlorine-free anolyte is supplied with the simultaneous removal of chlorine-containing anolyte, or by pumping around the anolyte in the anode circuit with simultaneous removal and removal of chlorine gas.
  • the voltage is set such that a current density of 0.01 to 20 A / m 2, preferably 10 to 18 A / m 2, is established. Under these conditions the electrolysis is not operated below a temperature of 70 ° C, otherwise the chlorine development will start again.
  • the electrolysis can be cooled by the process according to the invention if the electrolysis voltage is not more than 1.4 V below a temperature of 70 ° C., the pH of the brine being between 2 and 12. In this state, the electrolysis can linger for many hours without damaging the gas diffusion electrode. Compared to the prior art, the electrolysis voltage remains applied.
  • the load can be increased again at any time. If the electrolytic cell is to be emptied, the following further steps are carried out with particular preference:
  • the cathode compartment After the cathode compartment has been emptied, the anode compartment is emptied within 0.01 to 200 minutes; if necessary, the cathode compartment and anode compartment can be emptied in parallel after the power supply has been switched off
  • the rinsing is carried out with highly dilute brine with an alkali chloride content of 0.01 to 4 mol / 1, with water or, preferably, with deionized water.
  • the rinsing is preferably carried out by filling the anode compartment once or only partially filling the anode compartment and immediately draining the rinsing liquid.
  • the rinsing can also be carried out in two or more stages, for example by first filling and draining the anode compartment with a dilute brine with an alkali metal chloride content of 1.5-2 mol / 1 and then further with highly diluted brine with a NaCl - Content of 0.01 mol / 1 or filled with deionized water and drained.
  • the rinsing solution can be drained off immediately after the anode compartment has been completely filled, or can remain in the anode compartment for up to 200 minutes and then be drained off. After draining, a small amount of rinsing solution remains in the anode compartment. The anode compartment then remains piped or cordoned off without direct contact with the surrounding atmosphere.
  • the brine corresponds to the purity requirements of chlor-alkali electrolysis that are common for membrane electrolysis.
  • the cathode compartment is rinsed with an alkali lye with a concentration of max. 12 mol / L, preferably 0.01 to 4 mol / L, which is fed to the cathode compartment for 0.01 min to 60 min and then drained off again.
  • Alkaline hydroxide solution from regular production is preferably used for rinsing the cathode compartment. Lye from shutdown processes is less suitable for rinsing, primarily because of contamination with chloride ions. It can also be rinsed with deionized water. After the rinsing process, the cathode compartment is emptied.
  • the oxygen supply can be switched off in particular when the voltage is switched off.
  • the oxygen supply is preferably shut off after the cathode compartment has been emptied and rinsed.
  • the electrolysis cell with the wet membrane can be kept ready for a short period of time in the installed state for a short time without impairing the performance of the electrolysis cell.
  • the concentration of the diluted alkali chloride solution used for rinsing or wetting is 1 - 4.8 mol / L.
  • the rinsing solution can be drained off immediately after the anode compartment has been completely filled, or can remain in the anode compartment for up to 200 minutes and then be drained off.
  • the concentration of the alkali hydroxide solution used for rinsing or wetting is 0.1 to 10 mol / 1, preferably between 1 and 4 mol / 1.
  • the temperature of the brine or the alkali hydroxide solution can be between 10 and 80 ° C, but preferably 15 to 40 ° C.
  • the mini-gap cathode dishes can be rinsed for a period of 0.01 to 10 minutes.
  • the invention also relates to a method for commissioning, in particular for restarting following the new method for decommissioning.
  • the electrolysis is restarted in particular as follows:
  • Anolyte is filled into the anode compartment of the toe in accordance with step j) and, in particular, heated to at least 50 ° C. in a circuit with a heat exchanger
  • step k) the catholyte is outside the toe, e.g. in a circuit with storage tank and heat exchanger, heated to a temperature of at least 50 ° C.
  • the cathode gap (mini-gap) according to step 1) is filled by filling the preheated alkali solution into the gap at a temperature of at least 50 ° C .
  • This procedure differs from the prior art, in this case first the cathode compartment is filled and then the anode compartment - the procedure according to the invention avoids excessive chloride values in the alkali and thus any corrosion problems.
  • an electrolysis voltage of at least 0.4 V is preferably applied in step m), in particular within 0.01 to 10 min, so that a current density of at least 0.2 A / m 2 is established.
  • Anolyte and catholyte are then heated according to step n) to a temperature of at least 70 ° C. and the current density is then preferably increased.
  • the increase in the current density to the production current density in step q) is particularly preferably carried out with a gradient of 0.018 kA / (m 2 * min) to 0.4 kA / (m 2 * min) until the current density at the electrolysis element is at least 2 kA / m 2 .
  • the concentrations are determined by titration or another method known in principle to the person skilled in the art.
  • the electrolysis cell which is put out of operation according to the above new method is put into operation again according to the new method described above. If the described method steps are followed, the electrolysis cell can go through a large number of start-up and shutdown cycles without the cell's performance being impaired.
  • the gas diffusion electrode used in the examples was produced according to EP1728896B1 as follows: A powder mixture consisting of 7% by weight of PTFE powder, 88% by weight of silver I-oxide and 5% by weight of silver powder was placed on a network of nickel wires applied and pressed to an oxygen consumption electrode.
  • the electrode was installed in an electrolysis unit with an area of 100 cm 2 with an ion exchange membrane of DuPONT type N982 (manufacturer Chemours) and a distance between the gas diffusion electrode and the ion exchange membrane of 3 mm.
  • the electrolysis unit When assembled, the electrolysis unit has an anode space with an anolyte inlet and outlet, with an anode consisting of a titanium expanded metal, which is coated with a commercially available DSA coating for the chlorine production from Denora, consisting of a mixed oxide of ruthenium / iridium oxide was and a cathode space with the gas diffusion electrode as a cathode and with a gas space for the oxygen and oxygen supply and discharge lines, a liquid drain and an ion exchange membrane, which are arranged between the anode and cathode space.
  • the pressure in the anode compartment was lower than in the cathode compartment, so that the ion exchange membrane was pressed onto the anode structure by a higher pressure in the cathode chamber with a pressure of approximately 30 mbar.
  • the electrolysis cell was operated with a brine concentration of approx. 210 g / L (3.58 mol / L) NaCl and a sodium hydroxide solution concentration of approx. 31% by weight (10.4 mol / L) at electrolyte temperatures of approx. 85 ° C .
  • the cell voltage was corrected to 32% by weight (10.79 mol / L) sodium hydroxide solution and 90 ° C. using standard methods.
  • the electrolytes were introduced into the cell from below and removed again from the top of the cell.
  • Oxygen was supplied to the gas space of the cathode.
  • An oxygen with a quality of more than 99.5 vol .-% oxygen was used here.
  • the oxygen was moistened with water at room temperature.
  • the amount of oxygen was regulated in such a way that 1.5 times the stoichiometric excess of the required amount of oxygen was always supplied on the basis of the set current.
  • the oxygen is fed into the gas space from above and discharged below.
  • the electrolysis unit had a gap of approx. 3 mm between the oxygen consumption electrode and the ion exchange membrane. This gap was filled with a porous PTFE fabric as a percolator and spacer. The production current density was 6 kA / m 2 .
  • Example 1 Commissioning Before starting the catholyte circuit, oxygen saturated with water was fed to the cathode compartment at room temperature, so that the pressure in the cathode gas chamber was 59 mbar. The hydrostatic pressure of the sodium hydroxide solution at the lowest point in the cell was 32 mbar.
  • the anolyte circuit was put into operation according to the invention and the anode compartment was filled with an anolyte with a concentration of approx. 210 g NaCl / 1 (3.58 mol / L). While the anode circuit was maintained and the anolyte was passed through the cell, the anolyte was heated to 50 ° C by a heat exchanger in the anode circuit.
  • the 50 ° C. hot sodium hydroxide solution was passed into the cell and, after the cathode gap had been filled, an electrolysis voltage of 1.08 V was applied within 30 seconds. A current density of 10 mA / cm 2 was established . The pH of the anolyte running off was 8.
  • the electrolytes were heated from 50 ° C to 70 ° C within 1 hour. After the temperature of the running anolyte and catholyte reached 70 ° C., the electrolysis voltage was increased, the electrolysis voltage being increased so that the current density was increased by 50 mA / cm 2 every 2 min to a current density of 600 mA / cm 2 . After start-up, the concentrations were adjusted in such a way that the concentration of the brine running off was approx. 210 g / 1 (3.59 mol / L) and that of the sodium hydroxide solution was approx. 31.5% by weight (10.6 mol / L) .
  • the electrolysis unit was operated at a current density of 600 mA / cm 2 .
  • the current density was reduced to 1.5 mA / cm 2 for decommissioning.
  • the main rectifier was switched off and the polarization rectifier switched on.
  • the polarization rectifier then maintains a current density of 1.5 mA / cm 2 .
  • Operation at the low current density was maintained for 1.5 hours.
  • the anolyte is then chlorine-free. This process is carried out in technical electrolysers for safety reasons.
  • One of the reasons for this is that chlorine or chlorine compounds, for example, hypochlorite will not diffuse from the anolyte into the catholyte via the ion exchange membrane and there lead to corrosion of cell components or the gas diffusion electrode.
  • the phase of chlorine-free rinsing takes about 1.5 hours in technical electrolysers.
  • Electrolyte circuits remained in operation with the same volume flows as in electrolysis operation at 600 mA / cm 2 .
  • the 02 supply was also maintained.
  • the temperature of the anolyte and catholyte is reduced from 85 ° C to 70 ° C.
  • the cell voltage in this phase was approximately 1.16 V and the pH of the anolyte running out of the cell was pH 8.2.
  • the temperature of the anolyte and catholyte is reduced to 50 ° C., the polarization rectifier being operated potentiostatically.
  • the voltage remains at 1.16V and the current is reduced accordingly.
  • the polarization rectifier is switched off and the catholyte is immediately let out of the cathode compartment. This takes about 30 seconds.
  • the cathode compartment has been emptied, the anode compartment is drained off within 1 hour. The anode compartment is opened from below up to a height of max. 50% of the cell height is filled with deionized water and drained off immediately.
  • the cathode gap was also rinsed by switching the catholyte pump on again and feeding catholyte into the cathode compartment.
  • the catholyte pump was switched on for approx. 10 seconds.
  • the catholyte gap then ran empty within 15 s. The cell was then left to stand for 10 hours.
  • the cell voltage was 2.48 V at a current density of 600 mA / cm 2
  • the cell voltage was 2.48 V at a current density of 600 mA / cm 2
  • the cell voltage remained unchanged, the gas diffusion electrode and other components were not damaged.
  • Electrolyte circuits remained in operation with the same volume flow as in electrolysis operation, also the 02 supply
  • the temperature of the electrolytes was reduced to 75 ° C. in the course of 1.5 hours, a current density of 1.8 mA / cm 2 being maintained.
  • the power supply was switched off
  • the cathode compartment was emptied.
  • the anode compartment was filled from below with demineralized water, the anode compartment being filled only halfway and immediately drained again.
  • the cathode gap was further rinsed with catholyte. After the anolyte was drained, the catholyte was also drained from the cathode gap.
  • the cell was then left to stand for 10 hours.
  • the cell voltage was 2.11 V at a current density of 400 mA / cm 2
  • the cell voltage was 2.14 V at a current density of 400 mA / cm 2
  • the cell voltage increased by 30mV, the gas diffusion electrode was damaged.

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Electrochemistry (AREA)
  • Materials Engineering (AREA)
  • Automation & Control Theory (AREA)
  • Analytical Chemistry (AREA)
  • Inorganic Chemistry (AREA)
  • Electrolytic Production Of Non-Metals, Compounds, Apparatuses Therefor (AREA)
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Abstract

L'invention concerne un procédé d'électrolyse de chlorures alcalins en ayant recours à des électrodes consommatrices d'oxygène aux paramètres fonctionnels spéciaux pour la mise hors service et la remise en service
EP19818094.5A 2018-12-18 2019-12-16 Procédé d'électrolyse à membrane de solutions de chlorures alcalins en ayant recours à une électrode à diffusion gazeuse Withdrawn EP3899101A2 (fr)

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EP18213272.0A EP3670706B1 (fr) 2018-12-18 2018-12-18 Procédé d'électrolyse à membrane de solutions de chlorure alcalin à l'aide d'une électrode à diffusion gazeuse
PCT/EP2019/085312 WO2020127021A2 (fr) 2018-12-18 2019-12-16 Procédé d'électrolyse à membrane de solutions de chlorures alcalins en ayant recours à une électrode à diffusion gazeuse

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EP19818094.5A Withdrawn EP3899101A2 (fr) 2018-12-18 2019-12-16 Procédé d'électrolyse à membrane de solutions de chlorures alcalins en ayant recours à une électrode à diffusion gazeuse

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KR20210103482A (ko) 2021-08-23
EP3670706B1 (fr) 2024-02-21
EP3670706A1 (fr) 2020-06-24
JP2022510916A (ja) 2022-01-28
US20220056594A1 (en) 2022-02-24
CN113166952A (zh) 2021-07-23
CN113166952B (zh) 2023-05-23
WO2020127021A2 (fr) 2020-06-25

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