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
  • C25B1/28—Per-compounds
  • C25B1/29—Persulfates
• • 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

Definitions

• the invention relates to a method for producing Alkali metal, especially sodium and potassium as well as Ammonium peroxodisulfate by anodic oxidation of a Alkali metal or ammonium sulfate or hydrogen sulfate containing aqueous solution.
• sodium peroxodisulfate is produced with a current efficiency of 70 to 80% in an electrolysis cell with a cathode protected by a diaphragm and a platinum anode by adding a neutral aqueous anolyte solution with an initial content of 5 to 9% by weight sodium ions, 12 to 30% by weight of sulfate ions, 1 to 4% by weight of ammonium ions, 6 to 30% by weight of peroxodisulfate ions and a potential-increasing agent, a so-called promoter, such as in particular thiocyanate, using a sulfuric acid solution as catholyte at a current density of at least 0.5 to 2 A / cm 2 is electrolyzed.
• a so-called promoter such as in particular thiocyanate
• the mother liquor is mixed with the cathode product, neutralized and fed back to the anode.
• Disadvantages of this method are 1. the need to use a promoter to reduce oxygen evolution, 2. the need for a high current density and thus a high anode potential in order to obtain an economically acceptable current efficiency and 3. the problems associated with the production of the platinum anode with a view to obtaining a current efficiency that is acceptable for technical purposes and a long service life of the anode.
• EP-B 0 428 171 describes an electrolysis cell from Filter press type for the production of peroxo compounds, including ammonium peroxodisulfate, sodium peroxodisulfate and Potassium peroxodisulfate known.
• peroxo compounds including ammonium peroxodisulfate, sodium peroxodisulfate and Potassium peroxodisulfate known.
• anodes are here hot isostatically applied to a valve metal Platinum foils used.
• the anolyte becomes a promoter and sulfuric acid containing solution of the corresponding Sulfate used. This procedure also shows the previous problems mentioned.
• the anodes which are usually covered with platinum over their entire surface always require a high current density. This is what happens a high current load of the anolyte volume, the Separators and the cathode, which means additional measures to reduce the cathodic current density by a three-dimensional structuring and activation is required. In addition there is a high thermal Loading of the labile peroxodisulfate solution. Around To minimize stress, constructive measures must be taken be taken, and the cooling effort increases. Because of the limited heat dissipation, the Electrode area are limited, and this increases the Installation effort per cell unit. To the high As a rule, to cope with electricity load additionally electrode support materials with high Heat transfer properties can be used in turn are prone to corrosion and expensive.
• the object of the present invention is a technical Process for the preparation of ammonium and To demonstrate alkali metal peroxodisulfates, the disadvantages of the known methods at least to a lesser extent having.
• the Manufacture of ammonium and alkali metal peroxodisulfates with high current efficiency is possible by using as an anode diamond thin-film electrode doped with a trivalent or pentavalent element is used.
• Surprisingly can completely dispense with the use of a promoter and electrolysis at low current density be carried out, which results in further advantages.
• the present invention accordingly relates to a Process for the preparation of a peroxodisulfate from the Series of ammonium, sodium and potassium peroxodisulfate, by anodizing a salt from the series Ammonium, sodium and potassium sulfate or / and des corresponding aqueous bisulfate-containing Electrolyte in an electrolytic cell, comprising at least an anode, a cathode and an anolyte space, this is separated from a catholyte space by a separator or adjacent to a gas diffusion cathode, thereby is characterized - that as an anode one on one arranged conductive carrier and by doping with a trivalent or pentavalent element made conductive Diamond layer used and the anolyte no promoter adds.
• the subclaims are directed towards preferred Embodiments of this method.
• the conductive diamond layer which acts as an anode is used for their manufacture by doping with one or more trivalent or pentavalent elements with such a quantity endowed that sufficient conductivity results.
• the doped diamond layer is thus an n-conductor or a p-conductor.
• the conductive one is expediently located Diamond layer on a conductive carrier material, wherein this can be selected from the series silicon, Germanium, titanium, zirconium, niobium, tantalum, molybdenum and Tungsten and carbides of the elements mentioned. Alternatively can also have a conductive diamond layer on aluminum be applied.
• Particularly preferred carrier materials for the diamond layer are silicon, titanium, niobium, tantalum and tungsten and carbides of these elements.
• a particularly suitable electrode material for the anode is a boron-doped diamond thin film on silicon.
• the manufacture of diamond electrodes can be done in two special CVD process (chemical vapor deposition technic). It is the microwave plasma CVD and the hot wire CVD process. In both The gas phase that arises through cases Microwave radiation or thermal through hot wires activated to plasma, from methane, hydrogen and possibly other additives, especially a gaseous one Connection of the dopant.
• a Boron compound such as trimethylboron
• a gaseous phosphorus compound as An n-type dopant is obtained.
• Deposition of the doped diamond layer on crystalline Silicon becomes a particularly dense and non-porous layer obtained - a film thickness around 1 ⁇ m is common sufficient.
• the deposition can also be carried out on a crystalline material on a self-passivating metal like titanium, tantalum, Tungsten or niobium.
• a self-passivating metal like titanium, tantalum, Tungsten or niobium.
• the production of ammonium and sodium peroxodisulfate can in conventional electrolysis cells, which are also in the form of a Filter packages can be summarized, performed become.
• the anode compartment and cathode compartment are through separated a separator.
• the separator can for example, a common porous material from a act oxidic material, but one is preferred Ion exchange membrane.
• Ion exchange membrane Such are suitable as cathodes Materials as already known in the prior art are like lead, carbon, tin, zircon, platinum, nickel and their alloys, with lead being preferred.
• the Electrolysis cell is the cathode in the form of a Gas diffusion electrode is formed, and the cathode supplied with an oxygen-containing gas. So that Electrolysis with much lower cell voltages operated, which makes a significant contribution to Saving energy means.
• the Electrolysis cell a circuit for the liquid anolyte and another circuit for a liquid Catholytes.
• the anolyte can be sulfurized or be neutral and contains ammonium and / or Alkali metal cations, sulfate and / or Hydrogen sulfate anions, preferably also Peroxodisulfate anions, but no polarizer.
• the anolyte composition can correspond to that as described in the documents cited at the beginning on the status of Technology are mentioned, but with the difference that no Promoter is added or is otherwise present.
• the starting anolyte preferably contains 300 to 500 g of ammonium sulfate and 0 to 0.2 mole of sulfuric acid per mole of ammonium sulfate per liter.
• a substantially neutral starting anolyte is preferred.
• the catholyte is a sulfuric acid ammonium sulfate solution.
• the anodic oxidation is expediently carried out at an anodic current density in the range from 50 to 1000 mA / cm 2 , preferably 400 to 900 mA / cm 2 .
• Ammonium peroxodisulfate is obtained in a manner known per se from an anolyte stream discharged from the anolyte cycle, the workup preferably comprising vacuum crystallization and separation of the crystals from the mother liquor.
• the anolyte mother liquor is recirculated into the electrolysis after increasing the ammonium sulfate or hydrogen sulfate content. This can be done by mixing with the catholyte produced and adding a base if necessary.
• Sodium peroxodisulfate can either be obtained directly by anodic oxidation of an anolyte containing sodium bisulfate, the anolyte preferably containing 500 to 600 g NaHSO 4 per liter.
• an aqueous solution containing 300 to 400 g H 2 SO 4 per liter and 300 to 500 g Na 2 SO 4 per liter is used as the catholyte.
• sodium peroxodisulfate can also be obtained in a manner known per se by reacting an anolyte containing ammonium peroxodisulfate from an anodic oxidation of ammonium sulfate or ammonium hydrogen sulfate with sodium hydroxide solution, in order to subsequently crystallize out sodium peroxodisulfate and separate it from the mother liquor - examples are given for the embodiments relating to this the DE-OS 199 13 820 and the DE-PS 27 57 861 referenced.
• Figure 1 shows the course of the current yield depending the current density in the manufacture of Ammonium peroxodisulfate using a Platinum electrode (comparative examples) and one to be used according to the invention doped with boron Diamond electrode.
• Figure 2 shows the example of sodium peroxodisulfate average current density the dependence of the current yield of the concentration of sodium peroxodisulfate with a Diamond or platinum electrode.
• Figure 2 shows that the current efficiency at a diamond electrode to be used according to the invention increasing content of sodium peroxodisulfate in the anolyte only slowly decreases - under the test conditions can be for example with a current efficiency equal to or higher 75% anolyte solutions with a sodium peroxodisulfate content of about 400 g / l.
• a current efficiency equal to or higher 75% anolyte solutions with a sodium peroxodisulfate content of about 400 g / l.
• Using a conventional platinum anode and the use of a promoter in contrast in the anolyte only Peroxodisulfate concentrations of about 300 g / l, namely obtained with a current efficiency of about 25%.
• the electrolytic cell contains a lead cathode and a diamond anode doped with boron on a Si wafer.
• the diamond anode was connected to a metal plate (power distributor).
• the diamond anode was replaced by a mirror-finished platinum sheet ground with diamond powder.
• the electrolyte chambers were separated by an ion exchange membrane (DuPont, Nafion 430) in the anode compartment and cathode compartment. The distance between the electrodes was 2.2 cm.
• the round electrode area was 38.48 cm 2 .
• the table shows the comparison of the electrolysis results with Pt and a diamond anode.
• Figure 1 shows the dependence of the current yield on the Current density.
• NaHSO 4 was anodized.
• the anolyte consisted of a NaHSO 4 solution with 610 g NaHSO 4 / l. After setting the current density, samples were taken and analyzed after a predetermined time. A linear decrease in volume was assumed when calculating the current yield.
• the curves according to FIG. 2 show the current yield in Dependence on the sodium peroxodisulfate obtained (NaPS) concentration in the anolyte using a Diamond electrode (B2) or a Pt anode (VB2).
• NaPS sodium peroxodisulfate obtained

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• Chemical & Material Sciences (AREA)
• Inorganic Chemistry (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)
• Organic Low-Molecular-Weight Compounds And Preparation Thereof (AREA)

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• 2000
  • 2000-04-20 DE DE10019683A patent/DE10019683A1/de not_active Withdrawn
• 2001
  • 2001-04-04 US US09/825,352 patent/US6503386B2/en not_active Expired - Lifetime
  • 2001-04-11 CZ CZ20011317A patent/CZ20011317A3/cs unknown
  • 2001-04-14 AT AT01109242T patent/ATE297477T1/de active
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  • 2001-04-14 EP EP01109242A patent/EP1148155B2/fr not_active Expired - Lifetime
  • 2001-04-14 DE DE50106427T patent/DE50106427D1/de not_active Expired - Lifetime
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• 2013
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