US20130334059A1 - Apparatus for electrolyzing sulfuric acid and method for electrolyzing sulfuric acid - Google Patents

Apparatus for electrolyzing sulfuric acid and method for electrolyzing sulfuric acid Download PDF

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US20130334059A1
US20130334059A1 US14/001,636 US201214001636A US2013334059A1 US 20130334059 A1 US20130334059 A1 US 20130334059A1 US 201214001636 A US201214001636 A US 201214001636A US 2013334059 A1 US2013334059 A1 US 2013334059A1
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sulfuric acid
anode side
cathode side
anode
cathode
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Hiroki Domon
Kouji Fujii
Junko Kosaka
Masaaki Kato
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De Nora Permelec Ltd
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Chlorine Engineers Corp Ltd
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Assigned to CHLORINE ENGINEERS CORP., LTD. reassignment CHLORINE ENGINEERS CORP., LTD. ASSIGNMENT OF ASSIGNORS INTEREST (SEE DOCUMENT FOR DETAILS). Assignors: DOMON, HIROKI, FUJII, KOUJI, KATO, MASAAKI, KOSAKA, JUNKO
Publication of US20130334059A1 publication Critical patent/US20130334059A1/en
Assigned to PERMELEC ELECTRODE LTD. reassignment PERMELEC ELECTRODE LTD. ASSIGNMENT OF ASSIGNORS INTEREST (SEE DOCUMENT FOR DETAILS). Assignors: CHLORINE ENGINEERS CORP., LTD.
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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
    • C25B1/00—Electrolytic production of inorganic compounds or non-metals
    • C25B1/01—Products
    • C25B1/28—Per-compounds
    • 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
    • C25B1/22—Inorganic acids
    • 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
    • C25B11/042—Electrodes formed of a single material
    • C25B11/043—Carbon, e.g. diamond or graphene
    • 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
    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
    • C25B15/00—Operating or servicing cells
    • C25B15/08—Supplying or removing reactants or electrolytes; Regeneration of electrolytes

Definitions

  • the present invention relates to an apparatus for electrolyzing sulfuric acid and a method for electrolyzing sulfuric acid for producing oxidizing agent-rich electrolytic sulfuric acid through electrolysis of sulfuric acid.
  • the present invention relates to the apparatus for electrolyzing sulfuric acid and the method for electrolyzing sulfuric acid for producing electrolytic sulfuric acid containing oxidizing agent at a high efficiency and safely in such a manner that dilute sulfuric acid for which temperature and concentration are controlled is formed in the apparatus for electrolyzing sulfuric acid and the temperature- and concentration-controlled dilute sulfuric acid is electrolyzed.
  • persulfuric acid has been used in various manufacturing and inspection processes as chemical agent, such as pre-treatment agent for electrolytic metal plating, etching agent, oxidizing agent in chemical and mechanical polishing treatment for semiconductor device manufacturing, oxidizing agent for organic substance in wet analyses, and cleaning agent for silicon wafer.
  • chemical agent such as pre-treatment agent for electrolytic metal plating, etching agent, oxidizing agent in chemical and mechanical polishing treatment for semiconductor device manufacturing, oxidizing agent for organic substance in wet analyses, and cleaning agent for silicon wafer.
  • oxidizing agent which is called “oxidizing agent”
  • the “oxidizing agent” indicates persulfuric acid which names generically peroxodisulfuric acid and peroxomonosulfuric acid and hydrogen peroxide and the “electrolytic sulfuric acid” indicates the substance which contains oxidizing agent produced through the electrolysis of sulfuric acid and unreacted sulfuric acid.
  • the oxidizing agent and the electrolytic sulfuric acid containing unreacting sulfuric acid (hereinafter, simply called “electrolytic sulfuric acid”) formed by a system to electrolyze sulfuric acid are applied to remove resist, pollutant organic matter or metals in the semiconductor manufacturing process.
  • electrolytic sulfuric acid unreacting sulfuric acid
  • it is required for the apparatus for electrolyzing sulfuric acid to have such features that electrolytic sulfuric acid containing oxidizing agent is formed at a higher concentration, the current efficiency to form oxidizing agent through electrolysis is higher and the degradability of formed oxidizing agent is low.
  • sulfuric acid commercially available is concentrated sulfuric acid at the density of 98% or 96%, and therefore when sulfuric acid diluted to that of a low density, which is called dilute sulfuric acid is to be supplied to the apparatus for electrolyzing sulfuric acid, the chemicals supply equipment of the plant must have an exclusive storage tank as additional unit and supply piping, requiring a large amount of equipment cost.
  • sulfuric acid of a low concentration is larger in volume compared with concentrated sulfuric acid, and the transportation cost of the chemical will be increased compared with that of concentrated sulfuric acid.
  • the concentration of sulfuric acid can be controlled at a high efficiency within the apparatus for electrolyzing sulfuric acid, sulfuric acid electrolysis to obtain oxidizing agent at a high efficiency through electrolysis of sulfuric acid of a low concentration is realized, with the costs for equipment, transportation, etc. for preparing dilute sulfuric acid being reduced to a minimum. Moreover, if the equipments and lines for generating dilute sulfuric acid from concentrated sulfuric acid are made in common use with those for generating electrolytic sulfuric acid containing oxidizing agent from dilute sulfuric acid as much as possible, downsizing and simplification of the apparatus for electrolyzing sulfuric acid are achieved.
  • Paragraph 0011 of PTL 1 which describes generation of persulfuric acid through electrolysis of sulfuric acid in an electrolytic cell discloses, “the current efficiency of persulfuric acid can be enhanced by specifying the concentration range of sulfuric acid to be used for generation of persulfuric acid at a low sulfuric acid concentration of 2 ⁇ 11 mol/L.”
  • Paragraph 0026 of PTL 2 proposing a persulfuric acid supply system discloses, “regarding the range of sulfuric acid concentration in the electrolyte supplied to the electrolysis system, the current efficiency of persulfuric acid can be enhanced by controlling the concentration of sulfuric acid to as low as 10 ⁇ 18M (mol/L).”
  • Paragraph 0012 and Paragraph 0018 of PTL 3 disclose, “a method to enhance the current efficiency to form electrolytic sulfuric acid and form oxidizing agent efficiently and stably by applying sulfuric acid of a different concentration as electrolyte.”
  • PTL 4 discloses an application of gas liquid separation means as a removing method of sulfuric acid containing electrolytically generated gas generated from the electrolysis system.
  • PTL 4 discloses neither the removal of vapor or mist occurring at controlling the sulfuric acid concentration nor the method for controlling the sulfuric acid concentration in spite that the quantity of the sulfuric acid in the vapor or mist generated at controlling the sulfuric acid concentration in the system is larger than that of the sulfuric acid contained in the electrolytically generated gas.
  • PTL 5 discloses the method of generating persulfuric acid in which the sulfuric acid used for cleaning is re-concentrated, and re-electrolyzed after dilution and cool down. In this method, however, sulfuric acid used for cleaning supplied at a low concentration is re-concentrated and therefore, the cleanliness is not uniform and the safety is problematic.
  • the present invention aims to provide an apparatus for electrolyzing sulfuric acid and a method for electrolyzing sulfuric acid by which oxidizing agent is electrolytically produced at a high current efficiency, safely and stably for a long time of operation in such a manner that the heat of dilution occurring at the time of diluting concentrated sulfuric acid to sulfuric acid of a low concentration and the heat occurring at the time of electrolysis are removed, electrolysis conditions for producing oxidizing agent at a high current efficiency are prepared, generation of mist or vapor caused by the heat of dilution is suppressed, and condensate droplet of sulfuric acid derived from the mist or vapor got mixed with the exhaust line is removed.
  • the present invention provides an apparatus for electrolyzing sulfuric acid characterized in that in the apparatus for electrolyzing sulfuric acid 1 comprising the anode side electrolysis part 20 and the cathode side electrolysis part 23 ,
  • the anode side dilute sulfuric acid generation loop A in which concentrated sulfuric acid, as feed material, is diluted and controlled to a specified temperature and concentration, and the anode side electrolytic sulfuric acid generation loop B in which the dilute sulfuric acid generated in the anode side dilute sulfuric acid generation loop A is electrolyzed to form electrolytic sulfuric acid and the formed electrolytic sulfuric acid is controlled to a specified temperature and concentration are provided at least in the anode side electrolysis part 20 ;
  • the anode side tank 31 , the anode side concentrated sulfuric acid supply part 32 and the anode side cooler 34 are disposed in this order constituting a loop being connected by the anode side by-pass pipe 36 , to which the anode side pure water supply pipe 10 is connected to feed pure water to the anode side dilute sulfuric acid generation loop A at any point wherever in the anode side dilute sulfuric acid generation loop A;
  • the anode side concentrated sulfuric acid supply pipe 27 is connected to feed concentrated sulfuric acid to the anode side concentrated sulfuric acid supply part 32 ;
  • the anode side tank 31 and the anode compartment 4 provided internally with the anode 3 of the electrolytic cell 2 comprising the anode compartment 4 and the cathode compartment 7 separated by the diaphragm 5 constitute a loop being connected by the anode side circulation pipe 37 ;
  • the concentrated sulfuric acid supplied to the anode side concentrated sulfuric acid supply part 32 from the anode side concentrated sulfuric acid supply pipe 27 is diluted with pure water supplied by the anode side pure water supply pipe 10 ;
  • the diluted sulfuric acid of a low concentration is controlled to a specified temperature and concentration while being circulated in the anode side dilute sulfuric acid generation loop A to form dilute sulfuric acid of the specified temperature and concentration;
  • the formed dilute sulfuric acid is supplied to the anode compartment 4 of the electrolytic cell 2 via the anode side circulation pipe 37 constituting the anode side electrolytic sulfuric acid generation loop B to form electrolytic sulfuric acid in the anode compartment 4 ;
  • the formed electrolytic sulfuric acid is controlled to a specified temperature and concentration while being circulated in the anode side electrolytic sulfuric acid generation loop B;
  • the present invention provides the apparatus for electrolyzing sulfuric acid, characterized in that:
  • the cathode side tank 38 , the cathode side concentrated sulfuric acid supply part 39 and the cathode side cooler 41 are disposed in this order, constituting a loop being connected by the cathode side by-pass pipe 43 , to which the cathode side pure water supply pipe 12 is connected to feed pure water to the cathode side dilute sulfuric acid generation loop A′ at any point wherever in the cathode side dilute sulfuric acid generation loop A′ and the cathode side concentrated sulfuric acid supply pipe 29 is connected to feed concentrated sulfuric acid to the cathode side concentrated sulfuric acid supply part 39 ;
  • the cathode side tank 38 and the cathode compartment 7 provided internally with the cathode 6 of the electrolytic cell 2 comprising the anode compartment 4 and the cathode compartment 7 separated by the diaphragm 5 constitute a loop being connected by the cathode side circulation pipe 44 ;
  • the concentrated sulfuric acid supplied to the cathode side concentrated sulfuric acid supply part 39 from the cathode side concentrated sulfuric acid supply pipe 29 is diluted with pure water supplied via the cathode side pure water supply pipe 12 ;
  • the diluted sulfuric acid of a low concentration is controlled to a specified temperature and concentration while being circulated in the cathode side dilute sulfuric acid generation loop A′ to form dilute sulfuric acid of the specified temperature and concentration;
  • the formed dilute sulfuric acid is supplied to the cathode compartment 4 of the electrolytic cell 2 via the cathode side circulation pipe 44 constituting the cathode side electrolysis loop B′;
  • the dilute sulfuric acid controlled to the specified temperature and concentration is electrolyzed while being circulated in the cathode side electrolysis loop B′
  • the present invention provides the apparatus for electrolyzing sulfuric acid, featuring that above the anode side tank 31 , the anode side gas-liquid separator 91 and the anode side mist separator 92 are connected sequentially in series via the anode side gas vent pipe 102 , and the respective bottoms of the anode side gas-liquid separator 91 and the anode side mist separator 92 are provided with a draining means of a communicating vessel structure for the common use by the anode side gas-liquid separator 91 and the anode side mist separator 92 to drain liquid accumulated at the bottom of the respective separators.
  • the present invention provides the apparatus for electrolyzing sulfuric acid, featuring that above the anode side tank 31 , the anode side gas-liquid separator 91 and the anode side mist separator 92 are connected sequentially in series via the anode side gas vent pipe 102 , and the respective bottoms of the anode side gas-liquid separator 91 and the anode side mist separator 92 are provided with a draining means of a communicating vessel structure for the common use by the anode side gas-liquid separator 91 and the anode side mist separator 92 to drain liquid accumulated at the bottom of the respective separators,
  • the cathode side gas-liquid separator 96 and the cathode side mist separator 97 are connected sequentially in series via the cathode side gas vent pipe 103 , and the respective bottoms of the cathode side gas-liquid separator 96 and the cathode side mist separator 97 are provided with a draining means of a communicating vessel structure for the common use by the cathode side gas-liquid separator 96 and the cathode side mist separator 97 to drain liquid accumulated at the bottom of the respective separators.
  • the present invention provides the apparatus for electrolyzing sulfuric acid featuring that the ozone decomposition mechanism 93 is connected to the anode side mist separator 92 .
  • the present invention provides the apparatus for electrolyzing sulfuric acid featuring that the hydrogen treatment mechanism is provided to the cathode side mist separator 97 .
  • the present invention provides the apparatus for electrolyzing sulfuric acid featuring to have such configuration that more than one of anode side tank are installed in parallel in the anode side dilute sulfuric acid generation loop A, generated electrolytic sulfuric acid containing oxidizing agent is once stored in one of the tanks, and then, the valve is switched to other anode side tanks where electrolytic sulfuric acid containing oxidizing agent of the specified concentration is formed.
  • the present invention provides the apparatus for electrolyzing sulfuric acid featuring to have such configuration that while electrolytic sulfuric acid containing oxidizing agent of the specified concentration stored in one anode side tank is being transferred to a location of use outside the apparatus for electrolyzing sulfuric acid, electrolytic sulfuric acid containing oxidizing agent of the specified concentration is formed in another anode side tank.
  • the present invention provides the apparatus for electrolyzing sulfuric acid featuring that the anode 3 is a conductive diamond electrode.
  • the present invention provides the apparatus for electrolyzing sulfuric acid featuring that the diaphragm 5 is a fluororesin type cation exchange membrane or a hydrophilically treated porous fluororesin membrane.
  • the present invention provides a method for electrolyzing sulfuric acid characterized in that electrolytic sulfuric acid controlled to a specified temperature and concentration is formed by applying any one of the afore-mentioned apparatuses for electrolyzing sulfuric acid
  • the present invention provides a method for electrolyzing sulfuric acid characterized in that any one of the afore-mentioned apparatuses for electrolyzing sulfuric acid is applied, a porous fluororesin membrane is applied as the diaphragm 5 , and overflowing of the cathode side tank 38 is prevented by draining periodically or draining by the specified quantity when the liquid level of the cathode side tank 38 has reached the specified point because of an increase of the dilute sulfuric acid solution circulating in the cathode side electrolysis loop B′ of the cathode side electrolysis part 23 due to entrained water brought by cation at the time of passing through the porous fluororesin membrane.
  • the present invention provides the method for electrolyzing sulfuric acid characterized in that any one of the afore-mentioned apparatuses for electrolyzing sulfuric acid is applied, a porous fluororesin membrane is applied as the diaphragm 5 , and concentrated sulfuric acid is replenished to the cathode side concentrated sulfuric acid supply part 39 in order to maintain a certain range of dilute sulfuric acid concentration when the sulfuric acid concentration of the cathode side dilute sulfuric acid solution formed in the loop A′ of the cathode side electrolysis part 23 has decreased to or below the specified level of concentration due to entrained water brought by cation at the time of passing through the porous fluororesin membrane.
  • the present invention provides any one of the afore-mentioned methods for electrolyzing sulfuric acid featuring that the temperature of dilute sulfuric acid before electrolysis in the anode side dilute sulfuric acid generation loop A of the anode side electrolysis part 20 or in the cathode side dilute sulfuric acid generation loop A′ of the cathode side electrolysis part 23 is controlled to 30 degrees Celsius or less.
  • the present invention provides any one of the afore-mentioned methods for electrolyzing sulfuric acid featuring that the temperature of electrolyzed electrolyte in the anode side electrolytic sulfuric acid generation loop B of the anode side electrolysis part 20 or in the cathode side electrolysis loop B′ of the cathode side electrolysis part 23 is controlled to 30 degrees Celsius or less.
  • the present invention provides any one of the afore-mentioned methods for electrolyzing sulfuric acid featuring that the sulfuric acid concentration of dilute sulfuric acid before electrolysis in the anode side dilute sulfuric acid generation loop A of the anode side electrolysis part 20 or in the cathode side dilute sulfuric acid generation loop A′ of the cathode side electrolysis part 23 is controlled to the range of 2 ⁇ 10 mol/L.
  • the apparatus for electrolyzing sulfuric acid and the method for electrolyzing sulfuric acid by the present invention can form dilute sulfuric acid controlled to an intended specification of temperature and concentration in the apparatus for electrolyzing sulfuric acid; by performing electrolysis of dilute sulfuric acid under controlled temperature, oxidizing agent-rich electrolytic sulfuric acid can be produced at a high current efficiency and safely; and electrolyte containing oxidizing agent at a high concentration can be produced at a high current efficiency, which has not been able to be accomplished by the prior art.
  • FIG. 1 An overall view of an example of the apparatus for electrolyzing sulfuric acid by the present invention
  • FIG. 2 A process drawing explaining each process of temperature control, concentration control, electrolysis, supply, drain treatment, etc. of sulfuric acid carried out by the apparatus for electrolyzing sulfuric acid in FIG. 1
  • FIG. 3 A block diagram showing the anode side electrolysis part 20 of another example of the apparatus for electrolyzing sulfuric acid by the present invention
  • FIG. 4 A process drawing explaining each process of temperature control, concentration control, electrolysis, supply, drain treatment, etc. of sulfuric acid carried out by the apparatus for electrolyzing sulfuric acid in FIG. 3
  • FIG. 1 shows an example of the apparatus for electrolyzing sulfuric acid 1 by the present invention.
  • the apparatus for electrolyzing sulfuric acid 1 comprises the anode side electrolysis part 20 and the cathode side electrolysis part 23 , incorporating the electrolytic cell 2 .
  • the electrolytic cell 2 is divided into the anode compartment 4 and the cathode compartment 7 by the diaphragm 5 .
  • the anode 3 is installed in the anode compartment 4
  • the cathode 6 is installed in the cathode compartment 7 .
  • the anode compartment 4 is provided in the anode side electrolysis part 20 of the apparatus for electrolyzing sulfuric acid 1 .
  • the present invention is characterized in that the anode side electrolysis part 20 is configured in the following way.
  • the anode side electrolysis part 20 comprises the anode side dilute sulfuric acid generation loop A and the anode side electrolytic sulfuric acid generation loop B.
  • the anode side tank 31 , the anode side concentrated sulfuric acid supply part 32 , the anode side circulation pump 33 , and the anode side cooler 34 are disposed in this order in the anode side dilute sulfuric acid generation loop A, being connected by the anode side by-pass pipe 36 , constituting a loop. It is configured in such a way that the circulation of the anode side dilute sulfuric acid generation loop A can be suspended by the anode side by-pass valve 35 provided between the anode side cooler 34 and the anode side tank 31 .
  • the anode side pure water supply pipe 10 is connected to the anode side tank 31
  • the anode side concentrated sulfuric acid supply pipe 27 is connected to the anode side concentrated sulfuric acid supply part 32 .
  • Concentrated sulfuric acid supplied from the anode side concentrated sulfuric acid supply pipe 27 to the anode side concentrated sulfuric acid supply part 32 via the anode side concentrated sulfuric acid supply valve 28 is diluted with pure water supplied from the anode side pure water supply pipe 10 via the anode side pure water supply valve 11 to sulfuric acid of a low concentration in the anode side tank 31 .
  • Diluted sulfuric acid is controlled to the specified temperature and concentration while being circulated in the anode side dilute sulfuric acid generation loop A.
  • the dilute sulfuric acid controlled to the specified temperature and concentration in the anode side dilute sulfuric acid generation loop A is supplied to the anode compartment 4 of the electrolytic cell 2 forming the anode side electrolytic sulfuric acid generation loop B, and electrolyzed.
  • the anode side electrolytic sulfuric acid generation loop B is to be described in the latter part.
  • anode side dilute sulfuric acid generation loop A pure water is supplied to the anode side tank 31 , after quantitation by an integrating flow meter or the level gauge provided to the tank, which are not shown in FIG. 1 .
  • Applicable types of the integrating flow meter include those of ultrasonic wave, electromagnetic and coriolis.
  • Supply or cease of supply of pure water is controlled by a controller based on the measurements or signals from the integrating flow meter or the liquid surface sensor.
  • the anode side pure water supply pipe 10 can be connected at any part within the anode side dilute sulfuric acid generation loop A, not limited to the exemplified case of FIG. 1 .
  • Dilute sulfuric acid is circulated respectively in the anode side dilute sulfuric acid generation loop A or the anode side electrolytic sulfuric acid generation loop B by the open-close operation of the anode compartment inlet valve 21 , the anode compartment outlet valve 22 and the anode side by-pass valve 35 .
  • cathode compartment inlet valve 24 and the cathode compartment outlet valve 25 function.
  • the anode compartment 4 of the electrolytic cell 2 is connected with the anode side tank 31 by the anode side circulation pipe 37 , constituting a loop.
  • Dilute sulfuric acid formed in the anode side dilute sulfuric acid generation loop A is circulated in the anode side electrolytic sulfuric acid generation loop B by the valves provided midway on the respective piping.
  • Dilute sulfuric acid subjected to the temperature and concentration control in the anode side dilute sulfuric acid generation loop A is electrolyzed to form electrolytic sulfuric acid in the anode side electrolytic sulfuric acid generation loop B, and the formed electrolytic sulfuric acid and the dilute sulfuric acid prepared in the anode side dilute sulfuric acid generation loop A are mixed while being circulated in the anode side electrolytic sulfuric acid generation loop B so that the electrolytic sulfuric acid is controlled to the specified temperature and concentration.
  • materials which have corrosion-resistance to sulfuric acid or sulfuric acid containing oxidizing agent are required. Those include fluororesin such as polytetrafluoroethylene (PTFE) and tetrafluoroethylene-perfluoroalkylvinylether copolymer (PFA) and quartz.
  • the cathode side electrolysis part 23 of the apparatus for electrolyzing sulfuric acid 1 shown in FIG. 1 comprises, as with the anode side electrolysis part 20 , the cathode side dilute sulfuric acid generation loop A′ which dilutes concentrated sulfuric acid to dilute sulfuric acid of the specified temperature and concentration and the cathode side electrolysis loop B′ which circulates the dilute sulfuric acid prepared in the cathode side dilute sulfuric acid generation loop A′ through the cathode compartment 7 .
  • the cathode side dilute sulfuric acid generation loop A′ of the apparatus exemplified in FIG. 1 comprises the cathode side tank 38 , the cathode side concentrated sulfuric acid supply part 39 , the cathode side circulation pump 40 , the cathode side cooler 41 , the cathode side by-pass valve 42 , the cathode side by-pass pipe 43 , and valves provided midway on respective pipe lines.
  • the cathode side pure water supply pipe 12 is connected to the cathode side tank 38
  • the cathode side concentrated sulfuric acid supply pipe 29 is connected to the cathode side concentrated sulfuric acid supply part 39 .
  • Concentrated sulfuric acid supplied from the cathode side concentrated sulfuric acid supply pipe 29 to the cathode side concentrated sulfuric acid supply part 39 via the cathode side concentrated sulfuric acid supply valve 30 is diluted with pure water supplied from the cathode side pure water supply pipe 12 to the cathode side tank 38 via the cathode side pure water supply valve 13 in the cathode side tank 38 to be dilute sulfuric acid of a low concentration.
  • the dilute sulfuric acid is controlled to the specified temperature and concentration while being circulated in the cathode side dilute sulfuric acid generation loop A′, supplied to the cathode compartment 7 of the electrolytic cell 2 provided in the cathode side electrolysis loop B′ and electrolyzed.
  • the cathode side pure water supply pipe 12 can be connected at any part within the cathode side dilute sulfuric acid generation loop A′.
  • materials which have corrosion-resistance to sulfuric acid or sulfuric acid containing oxidizing agent are required. Those include fluororesin such as PTFE and PFA, and quartz.
  • the cathode side electrolysis loop B′ comprises the cathode compartment 7 of the electrolytic cell 2 , the cathode side circulation pipe 44 , the cathode side tank 38 and valves provided midway on each pipe line, constituting a loop.
  • electrolysis of dilute sulfuric acid is performed, but the electrode reaction generates only hydrogen gas, without forming electrolytic sulfuric acid.
  • dilute sulfuric acid controlled to the intended temperature and concentration is circulated.
  • the anode side concentrated sulfuric acid supply part 32 and the cathode side concentrated sulfuric acid supply part 39 are able to be provided at any side of the inlet or outlet of the anode side circulation pump 33 and the cathode side circulation pump 40 .
  • concentrated sulfuric acid is added to pressurized pure water, considerable heat and bubble will be generated at the point where pressure is built up due to dilution of concentrated sulfuric acid, leading to a possible further build up of pressure.
  • the anode side concentrated sulfuric acid supply part 32 and the cathode side concentrated sulfuric acid supply part 39 are preferably provided at the inlet side of the anode side circulation pump 33 and the cathode side circulation pump 40 .
  • the concentration of sulfuric acid can be controlled by means of the volume ratio of the pure water supplied to the anode side dilute sulfuric acid generation loop A and the cathode side dilute sulfuric acid generation loop A′ to the concentrated sulfuric acid whose concentration is known.
  • the volume of the respective liquids is controlled by an integrating flow meter, etc. through quantitation.
  • conductive diamond electrode As the anode 3 , it is preferable to use conductive diamond electrode as the anode 3 .
  • conductive diamond electrode has advantages: a high current efficiency of persulfuric acid due to high oxygen overvoltage, chemically and mechanically high durability, and free from contamination by the anode, leading to formation of highly clean sulfuric acid solution, which is electrolyte and electrolytic sulfuric acid, which is product of electrolysis. From the reasons described, a conductive diamond electrode is preferably applied for the anode 3 of the electrolytic cell 2 .
  • the conductive diamond electrode which is superior in corrosion resistance, is preferable in view of cleanliness, but also applicable are such electrodes comprising platinum metal like platinum, valve metals such as titanium, zirconium, tantalum, and niobium, and carbon materials like graphite and glassy carbon, having corrosion resistance to sulfuric acid.
  • the present invention applies such manner that liquid is not supplied to the electrolytic cell 2 while the concentration of sulfuric acid is being controlled, but is circulated and cooled in the anode side dilute sulfuric acid generation loop A, which allows the flow through the anode side by-pass pipe 36 in the anode side electrolysis part 20 .
  • liquid is not supplied to the electrolytic cell 2 , but is circulated and cooled in the cathode side dilute sulfuric acid generation loop A′, which allows the flow through the cathode side by-pass pipe 43 , in order to control the concentration and temperature.
  • the anode side gas-liquid separator 91 and the anode side mist separator 92 downstream of the anode side gas vent pipe 102 connected to the anode side tank 31 in order to prevent the scrubber of electrolytically generated gas or units outside the apparatus from being corroded by vapor or mist entrained by the gas generated by electrolysis.
  • the cathode side gas-liquid separator 96 and the cathode side mist separator 97 are installed preferably downstream of the cathode side gas vent pipe 103 connected to the cathode side tank 38 .
  • Anode gas generated in the anode compartment 4 of the electrolytic cell 2 may contain toxic ozone. Therefore, it is desirable that the ozone decomposition catalyst is provided as the ozone decomposition mechanism 93 in the downstream of the anode side mist separator 92 so that ozone is reduced to harmless oxygen, or is vent outside the apparatus after being sufficiently diluted with air or inert gas.
  • the ozone decomposition catalyst manganese dioxide is most commonly used, but manganese dioxide will dissolve when it comes in contact with acid solutions such as sulfuric acid of a low pH and ozone resolving power may be lost.
  • the gas conducting piping is commonly made with metal pipes such as stainless steel. In this case, the pipes will be corroded in contact with sulfuric acid mist or condensate, and therefore, basically, it is necessary for the electrolytically generated gas containing such mist or condensate not to be drained outside the apparatus.
  • Hydrogen which is the cathode gas occurring at the cathode compartment of the electrolytic cell 2 is inflammable and explosive. Therefore, it is necessary that the hydrogen gas is transformed into harmless water vapor by mixing with air for burning with the help of hydrogen combustion catalyst provided downstream of the cathode side mist separator 97 or to be sufficiently diluted with air or inert gas before discharging outside the apparatus.
  • Hydrogen combustion catalyst has a function to eliminate hydrogen by burning hydrogen with air.
  • the catalyst containing precious metal as an active ingredient for combustion is widely used. In general, if the surface of the catalyst is covered with liquid like water, hydrogen gas cannot get in contact with the catalyst and the combustion ability of hydrogen will be lost.
  • the gas conducting piping is commonly made with metal pipes such as stainless steel.
  • the pipes will be corroded in contact with sulfuric acid mist or condensate, and therefore, basically, it is necessary for the electrolytically generated gas containing such mist or condensate not to be drained outside the apparatus.
  • the equipment is used with such mechanism that sulfuric acid is separated from the electrolytically generated gases by utilizing the difference of gravity between the electrolytically generated gas and the fluid in the electrolytically generated gas in the vessels like pipe or tank, or such mechanism that enough retention time is provided for the electrolytically generated gas in the vessel so that the mist falls down in the vessel.
  • Applicable units for the anode side mist separator 92 and the cathode side mist separator 97 include a cylindrical vessel in which chemical-resistance mesh or porous material exists, or a unit in which the retention time of electrolytically generated gas is long enough for the mist to fall.
  • effective means include that the saturated vapor pressure is lowered by cooling the gas-liquid separator system, the mist separator or piping connecting to these units; thereby moisture in the electrolytically generated gas is coagulated to enhance the moisture removal efficiency at the gas-liquid separator system or the mist separator so that the quantity of carrying over to the downstream lines is reduced.
  • the gas passage will be blocked by the internally accumulated liquid and the gas may not be vented from the anode side tank 31 , and the cathode side tank 38 .
  • the internally accumulated liquid should be periodically drained from the anode side gas-liquid separator 91 , the cathode side gas-liquid separator 96 , the anode side mist separator 92 , and the cathode side mist separator 97 .
  • Drain of the fluid from the anode side gas-liquid separator 91 and the anode side mist separator 92 is carried out via the anode side drain pipe 95 by opening the anode side gas pipe drain valve 94 .
  • Drain of the fluid from the cathode side gas-liquid separator 96 and the cathode side mist separator 97 is carried out via the cathode side drain pipe 100 by opening the cathode side gas pipe drain valve 99 .
  • gas liquor separation in particular, the functions of the respective equipment and the status at the operation of the apparatus for electrolyzing sulfuric acid.
  • the anode side cooler 34 is provided in the anode side dilute sulfuric acid generation loop A, but when sulfuric acid is diluted, the solution temperature rises higher than the room temperature. At this time, it is possible for the gas (air) at a water vapor pressure which is in equilibrium position in the concentration and temperature of the dilute sulfuric acid stored in the anode side tank 31 to exist in the gas space of the anode side tank 31 , which is larger than that of the piping. In contact with the tank wall or piping wall, the gas containing water vapor is cooled down below the room temperature to form condensate of water drop.
  • a specified quantity of pure water is provided first in the anode side tank 31 or the piping, to which a specified quantity of sulfuric acid is supplied and mixed during circulation.
  • the liquid surface in the anode side tank 31 rises with the amount of supplied sulfuric acid, and the gas in the anode side tank 31 is gradually expelled outside the anode side tank 31 , that is, the upper part of the anode side gas vent pipe 102 , generating flow of air.
  • water droplet attached to the wall surface move in the anode side gas vent pipe 102 .
  • the anode side mist separator 92 connected to the upper part of the anode side gas-liquid separator 91 is able to separate the mist from the gas, which is droplet floating in the gas because of fineness, by means of the micro porous separation membrane preventing the mist from passing through. As the mist separated by the separation membrane increases, it becomes droplet, which can flow as liquid.
  • the liquid a separated by the anode side gas-liquid separator 91 flows down the gas-liquid separator system 91 by gravity (self-weight).
  • the mist separated by the anode side mist separator 92 collects to be droplet, flows down the anode side mist separator 92 by self-weight and moves to the anode side gas-liquid separator 91 .
  • the liquid b separated by the anode side mist separator 92 flows down the anode side gas-liquid separator 91 as with the liquid a.
  • the liquid a and the liquid b having flown down the anode side gas-liquid separator 91 collect before the anode side gas pipe drain valve 94 and drain out of the apparatus by self-weight when the anode side gas pipe drain valve 94 is opened.
  • relations of height among units are important. It is necessary, at least, to do it sequentially with the anode side mist separator 92 , the anode side gas-liquid separator 91 , and the anode side gas pipe drain valve 94 from the upper part.
  • Anode side gas pipe drain valve 94 can be opened and closed at any arbitrary timing. The same is preferably applied to the cathode side mist separator 97 connected at the upper part of the cathode side gas-liquid separator 96 .
  • liquid of sulfuric acid in the gas-liquid separator system and the mist separator can be efficiently drained by providing a pressure reducer (not shown in the figures) to the anode side drain pipe 95 and the cathode side drain pipe 100 to reduce the pressure in the gas-liquid separator system and the mist separator so that the gas flow in an opposite direction to the flow of the anode gas and the cathode gas is created.
  • a pressure reducer not shown in the figures
  • the inert gas supply part (not shown in the figures) is provided at the outlet side of the anode side mist separator 92 and the cathode side mist separator 97 .
  • inert gas nitrogen gas, for example, is applicable.
  • hydrophilically treated porous fluororesin membrane or fluororesin type cation exchange membrane is desirable.
  • fluororesin type cation exchange membrane is applied, such phenomena are observed that the concentration of sulfuric acid at the anode will increase with lapse of electrolysis time by the effect of water entrained when cation permeates through the ion exchange membrane from the anode side to the cathode side; the quantity of liquid at the anode side will decrease; the concentration of sulfuric acid at the cathode will decrease by dilution with entrained water; and the quantity of liquid at the cathode will increase.
  • the quantitative control of liquid at the cathode side is performed by open close operation of the cathode tank drain valve 113 .
  • the liquid is drained by self-weight outside the apparatus by opening the cathode tank drain valve 113 in the both cases of periodical drain and regulating by the height of the liquid surface of the tank.
  • a variety of method can be applied to administrate the quantity of drain. For instance, a liquid surface sensor to measure the low position is provided to the cathode side tank 38 and by using it, the cathode tank drain valve 113 is closed when the liquid surface of draining liquid has reached the sensor position.
  • the valve is opened when the entrained water volume calculated from the electrolysis time and electric current supply has reached the preset level or that the liquid surface of accumulated entrained water has reached the sensing position preset in a liquid surface sensor to measure the high position provided to the cathode side tank 38 .
  • the balancing gas for the space in the cathode side tank 38 can be introduced from the cathode gas scrubber 98 through the cathode side gas vent pipe 103 .
  • the cathode tank drain valve 113 opens when the liquid surface of the cathode side tank 38 has reached the preset height and drains the specified quantity of liquid through the cathode tank drain pipe 112 .
  • the liquid surface of the cathode side tank 38 is regulated by means of the liquid surface sensor, etc., which are not shown in the figures.
  • the overflow of the cathode side tank 38 can be prevented by discharging a specified quantity of liquid periodically or at the time when the liquid surface of the cathode side tank 38 has reached the predetermined height.
  • the sulfuric acid of the cathode is further diluted with entrained water and lowered concentration leads to significantly poor conductivity.
  • the concentration can be controlled to a constant level in such a manner that the sulfuric acid concentration of catholyte is monitored by a sulfuric acid concentration meter, which is not shown in the figures and concentrated sulfuric acid is supplemented as required from the cathode side concentrated sulfuric acid supply part 39 .
  • the concentration of sulfuric acid in catholyte can be regulated in such a way that the volume of entrained water is calculated from the measurements of electrolysis time and electric current; the concentration of sulfuric acid of electrolyte at the time when the volume of calculated entrained water is added to the volume of electrolyte in the cathode side tank 38 prepared before the electrolysis is calculated; when the calculated sulfuric acid concentration is lower than the specified range, the quantity of sulfuric acid to be added to restore in the specified range is calculated; and concentrated sulfuric acid is supplied to the cathode side electrolysis loop B′ in operation from the cathode side concentrated sulfuric acid supply 39 with quantitation of the calculated sulfuric acid quantity by a flow meter.
  • the electrolytic sulfuric acid in the anode side tank 31 which has reached the specified concentration of oxidizing agent after the specified time of electrolysis is supplied to the location of use outside the apparatus via the anode tank drain pipe 110 and the anode tank drain valve 11 .
  • electrolyte in the cathode side tank 38 after the specified time of electrolysis is drained outside the apparatus via the cathode tank drain pipe 112 and the cathode tank drain valve 113 .
  • the concentration of the catholyte is controlled and the characteristic values, such as the concentration or the conductivity of the catholyte are monitored so that the catholyte is repeatedly used as far as the characteristic values stay within the specified values.
  • the administration of the temperature and the concentration at the cathode side are not directly related with the current efficiency of persulfuric acid, but still the administration of them is preferable for the following reasons.
  • the catholyte transfers heat to the anolyte through the diaphragm 5 , which is cation exchange membrane and impedes the anolyte temperature from staying within the specified range; in case that the concentration of anolyte is different from that of catholyte, the diaphragm 5 , which is cation exchange membrane becomes the interface of the concentration difference of two electrolytes at which heat of dilution occurs, affecting the current efficiency of persulfuric acid due to difficulty in temperature control of the electrolyte; the diaphragm 5 , which is cation exchange membrane degrades or dimensionally changes due to overheat; and bubbles of water vapor occur due to overheat, leading to a larger resistance of the cell.
  • the administration of the temperature and the concentration at the cathode side are necessary.
  • FIG. 2 shows the processes for controlling the concentration of sulfuric acid and the electrolysis of the apparatus for electrolyzing sulfuric acid 1 as shown in FIG. 1 .
  • the processes in the anode side electrolysis part 20 comprise the processes as follows, as shown in FIG. 2 .
  • Pure water is supplied to the anode side tank 31 from the anode side pure water supply pipe 10 .
  • Pure water is circulated by the anode side circulation pump 33 . At this time, pure water is circulated in the anode side dilute sulfuric acid generation loop A via the anode side by-pass pipe 36 , without being supplied to the anode compartment 4 .
  • Concentrated sulfuric acid is supplied from the anode side concentrated sulfuric acid supply part 32 to the pure water circulating in the anode side dilute sulfuric acid generation loop A, in which the concentrated sulfuric acid and pure water is being mixed by continuous circulation.
  • the solution enters the anode side cooler 34 right after the concentrated sulfuric acid is mixed with the pure water, and therefore, heat of dilution which occurs when concentrated sulfuric acid is mixed with pure water is immediately removed so that generation of vapor or mist is suppressed.
  • Drainage of the anode side gas-liquid separator 91 and the anode side mist separator 92 is carried out by opening the anode side gas pipe drain valve 94 via the anode side drain pipe 95 .
  • This process is performed on an as-needed basis in the processes: 3) Concentrated sulfuric acid supply process, 5) Sulfuric acid temperature and concentration control process and 6) Electrolysis process.
  • Dilute sulfuric acid solution is being circulated and mixed while being cooled down to the specified temperature or less, preferably to 30 degrees Celsius or less within the anode side dilute sulfuric acid generation loop A.
  • the solution with the sulfuric acid temperature at 30 degrees Celsius or less gives a high current efficiency of oxidizing agent formation.
  • the sulfuric acid temperature is cooled down to 30 degrees Celsius or less before electrolysis.
  • the sulfuric acid concentration is preferably controlled to 2 ⁇ 10 mol/L.
  • the sulfuric acid concentration should preferably be controlled to the range of 2 ⁇ 10 mol/L.
  • Pure water is supplied to the cathode side tank 38 from the cathode side pure water supply pipe 12 .
  • Pure water is circulated in the cathode side dilute sulfuric acid generation loop A′ by the cathode side circulation pump 40 . At this time, pure water is circulated in the cathode side tank 38 via the cathode side by-pass pipe 43 , without being supplied to the cathode compartment 7 .
  • Concentrated sulfuric acid is supplied from the cathode side concentrated sulfuric acid supply part 39 to the pure water circulating in the cathode side dilute sulfuric acid generation loop A′, in which the concentrated sulfuric acid and pure water are being mixed by continuous circulation.
  • the solution enters the cathode side cooler 41 right after the concentrated sulfuric acid is mixed with the pure water, and therefore, heat of dilution which occurs when concentrated sulfuric acid is mixed with pure water is immediately removed so that generation of vapor or mist is suppressed.
  • Drainage of the cathode side gas-liquid separator 96 and the cathode side mist separator 97 is carried out by opening the cathode side gas pipe drain valve 99 via the cathode side drain pipe 100 .
  • This process is performed on an as-needed basis in the processes: 3) Concentrated sulfuric acid supply process, 5) Sulfuric acid temperature and concentration control process and 6) Electrolysis process.
  • Dilute sulfuric acid solution is being circulated and mixed till it becomes evenly while being cooled down to a specified temperature or less, preferably to 30 degrees Celsius or less within the cathode side dilute sulfuric acid generation loop A′.
  • the solution with the sulfuric acid temperature at 30 degrees Celsius or less gives a high current efficiency of oxidizing agent formation.
  • the sulfuric acid temperature is cooled down to 30 degrees Celsius or less before electrolysis.
  • the sulfuric acid concentration is preferably controlled to 2 ⁇ 10 mol/L.
  • the sulfuric acid concentration should preferably be controlled to the range of 2 ⁇ 10 mol/L.
  • the processes 1)-5) carried out in the anode side and the cathode side are the same and are performed completely independently.
  • Dilute sulfuric acid controlled to the specified temperature and the concentration in the anode side dilute sulfuric acid generation loop A of the anode side and in the cathode side dilute sulfuric acid generation loop A′ of the cathode side is electrolyzed in the electrolysis process of the anode side electrolytic sulfuric acid generation loop B and the cathode side electrolysis loop B′.
  • Electrolysis process is the process to electrolyze dilute sulfuric acid solution which is carried out after the completion of the processes: 1 ⁇ 5) at the both sides of the anode and the cathode. Electrolysis is performed by circulating dilute sulfuric acid solution in the both anode side electrolysis part 20 and cathode side electrolysis part 23 . A high current efficiency is achieved when the temperature of the solution is at 30 degrees Celsius or less. Therefore the temperature of the solution during the electrolysis is preferably controlled to 30 degrees Celsius or less.
  • Electrolytic sulfuric acid formed in the electrolysis process is controlled to the specified temperature and the specified concentration in the anode side electrolytic sulfuric acid generation loop B of the anode side electrolysis part 20 and supplied to a location of use outside the system. This is called the electrolytic sulfuric acid solution supply process. More specifically, after electrolysis is performed in the electrolysis process for the specified time, the electrolytic sulfuric acid solution supply process transfers anolyte to the location of use outside the system when the concentration of oxidizing agent, which is being observed by a concentration monitor not shown in the figures, has reached to the specified level.
  • Electrolytic sulfuric acid is supplied to a resist stripping apparatus, an etching apparatus or the like, but the apparatus or equipment to be connected are not specifically restricted.
  • a concentration monitor to measure the concentration of oxidizing agent or sulfuric acid can be built in the apparatus or provided on the external piping through which electrolytic sulfuric acid flows. Measurements obtained from the concentration monitor are able to be used to control electric current supplied to the electrolytic cell or to determine the timing of the output of operation signal, solution transfer signal or alarms supplied to the equipment, such as cleaning units, to which electrolyte sulfuric acid is sent from the apparatus for electrolyzing sulfuric acid.
  • the measuring method of the concentration monitor is not specifically restricted.
  • the cathode tank drain valve 113 is temporarily opened to drain a small amount of catholyte.
  • the catholyte formed in the electrolysis process is drained from the cathode side electrolysis loop B′ of the cathode side electrolysis part 23 , which is called the catholyte drain process.
  • the catholyte drain process drains the full amount of catholyte diluted by entrained water from the cathode side tank 38 . Drainage may be performed when the time of use of catholyte has reached the pre-determined time or may be performed when the concentration of sulfuric acid of the catholyte as measured by the sulfuric acid concentration meter, which is not shown in the figures, is known to have decreased to the specified value. Whereas, the cathode drain process can be performed at the same time as the anolyte supply process, but not as the electrolysis process.
  • two or more of anode side tanks can be installed in the anode side electrolysis part 20 .
  • an individual function can be assigned to each tank, such as the tank exclusively used for transferring the solution outside the apparatus, the tank exclusively used for controlling the dilute sulfuric acid, and the tank exclusively used for the electrolysis, or differently such as the tank exclusively used for transferring the solution outside the apparatus and the tank exclusively used for the control of the dilute sulfuric acid and the electrolysis process, so that sulfuric acid including oxidizing agent can be efficiently formed in a large amount for a short period of time.
  • the cathode side electrolysis part 23 also, it is similarly possible to provide such system having multiple tanks.
  • the apparatus for electrolyzing sulfuric acid 1 two or more of the electrolytic cell 2 are allowed to be installed. Also possible is that two or more of the anode-cathode pairs can be installed to one electrolyzer to form a bipolar configuration.
  • FIG. 3 shows an example of installing plural anode side tanks in the anode side electrolysis part 20 .
  • the cathode side electrolysis part 23 is not shown, the configuration is same as the cathode side electrolysis part 23 shown in FIG. 1 .
  • FIG. 3 shows the apparatus for electrolyzing sulfuric acid in which the first anode side tank 49 and the second anode side tank 50 are installed in parallel in the anode side dilute sulfuric acid generation loop A. After Electrolytic sulfuric acid containing formed oxidizing agent is stored once in the first anode side tank 49 , electrolisys process is switched to the second anode side tank 50 by the change-over valves 51 ⁇ 58 , where electrolytic sulfuric acid containing oxidizing agent at the specified concentration is formed.
  • electrolyzed sulfuric acid is stored in the first anode side tank 49 and while electrolytic sulfuric acid is similarly being manufactured in the second anode side tank 50 with related valves switched, electrolytic sulfuric acid can be supplied to the location of use from the first anode side tank 49 .
  • electrolytic sulfuric acid can be kept supplied continuously, and at the same time, (2) it is possible to manufacture and store electrolytic sulfuric acid with different concentration of sulfuric acid•oxidizing agent separately in the first anode side tank 49 and the second anode side tank 50 and to supply to two different locations of use, or to supply to application processes which require a different oxidizing power from one apparatus.
  • multiple cathode side tanks are able to be installed in the cathode side electrolysis part 23 as with the case of the anode side tank.
  • FIG. 4 shows the processes of the sulfuric acid concentration control and the electrolysis in the apparatus for electrolyzing sulfuric acid 1 of FIG. 3 , in which the case is given that only one cooler and one sulfuric acid mixer are provided for common use. First, the process shown at the left side of FIG. 4 is explained.
  • Pure water is supplied to the anode side tank 49 via the anode side pure water supply pipe 10 by opening the change-over valve 55 .
  • Quantitation of supply water volume is available by closing the change-over valve 55 which operates on the signals from the liquid surface sensor provided to the first anode side tank 49 or from the integrating flow meter provided to the anode side pure water supply pipe 10 .
  • the change-over valves 52 and 54 belonging to the anode side tank 50 are closed.
  • Pure water is circulated by operating the anode side circulation pump 33 .
  • the anode side by-pass valve 35 is opened, and the anode compartment outlet valve 22 and the anode compartment inlet valve 21 are closed.
  • Pure water circulates in the anode side dilute sulfuric acid generation loop A via the anode side by-pass pipe 36 , without being sent to the anode compartment 4 .
  • Concentrated sulfuric acid is supplied from the anode side concentrated sulfuric acid supply part 32 to the pure water circulating in the anode side dilute sulfuric acid generation loop A, in which the concentrated sulfuric acid and pure water are being mixed by continuous circulation.
  • the solution enters the anode side cooler 34 right after the concentrated sulfuric acid is mixed with the pure water, and therefore, heat of dilution which occurs when concentrated sulfuric acid is mixed with pure water is immediately removed so that generation of vapor or mist is suppressed.
  • temperature rise of the anode side concentrated sulfuric acid supply part 32 derived from heat of dilution is suppressed, which leads to the protection of piping, pumps, and valves in the vicinity from damage or deformation due to high heat.
  • Drainage of the anode side gas-liquid separator 91 and the anode side mist separator 92 is carried out by opening the anode side gas pipe drain valve 94 via the anode side drain pipe 95 .
  • This process is performed on an as-needed basis in the processes: 3) Concentrated sulfuric acid supply process, 5) Sulfuric acid temperature and concentration control process and 6) Electrolysis process.
  • Dilute sulfuric acid solution is being circulated and mixed while being cooled down to a specified temperature or less, preferably to 30 degrees Celsius or less within the anode side dilute sulfuric acid generation loop A.
  • the solution with the sulfuric acid temperature at 30 degrees Celsius or less gives a high current efficiency of oxidizing agent formation.
  • it is preferable that the sulfuric acid temperature is cooled down to 30 degrees Celsius or less before electrolysis.
  • the sulfuric acid concentration is preferably controlled to 2 ⁇ 10 mol/L. If it exceeds 10 mol/L, the current efficiency of oxidizing agent sharply decreases to 60% or less; whereas, if it becomes below 2 mol/L, sulfuric acid ion, as raw material for oxidizing agent, in the solution decreases and the current efficiency degrades to 60% or less. Therefore, the sulfuric acid concentration should preferably be controlled to the range of 2 ⁇ 10 mol/L.
  • Dilute sulfuric acid controlled to the specified temperature and the concentration in the anode side dilute sulfuric acid generation loop A of the anode side is electrolyzed in the electrolysis process of the anode side electrolytic sulfuric acid generation loop B.
  • Electrolysis process is the process to electrolyze dilute sulfuric acid solution carried out in succession of the processes of 1) ⁇ 5).
  • FIG. 4 does not include the cathode side, the processes of 1) ⁇ 5) are performed also on the cathode side similarly to the anode side, which is same as in FIG. 2 .
  • Electrolysis is performed in the anode side electrolysis part 20 by circulating dilute sulfuric acid solution. High current efficiency is achieved when the temperature of the solution is at 30 degrees Celsius or less. Therefore the temperature of the solution during the electrolysis is preferably controlled to 30 degrees Celsius or less.
  • Dilute sulfuric acid solution is circulated between the anode side tank 49 and the anode compartment 4 by closing the anode side by-pass valve 35 , and opening the anode compartment outlet valve 22 and the anode compartment inlet valve 21 .
  • Direct current is supplied to the electrolytic cell 2 and electrolysis is carried out at the specified supply current for the specified time duration to obtain electrolytic sulfuric acid containing oxidizing agent of the specified concentration. With the change-over valves 51 and 53 being closed, the formed electrolytic sulfuric acid containing oxidizing agent of the specified concentration is stored in the first anode side tank 49 .
  • Electrolytic sulfuric acid formed in the electrolysis process is controlled to the specified temperature and the specified concentration in the anode side electrolytic sulfuric acid generation loop B of the anode side electrolysis part 20 and supplied to a location of use outside the system. This is called the electrolytic sulfuric acid solution supply process. More specifically, after electrolysis is performed in the electrolysis process for the specified time, the electrolytic sulfuric acid solution supply process supplies anolyte to the location of use outside the system when the concentration of oxidizing agent, which is being observed by a concentration monitor not shown in the figures, has reached to the specified level.
  • Electrolytic sulfuric acid is supplied to a resist stripping apparatus, an etching apparatus or the like, but the apparatus or equipment to be connected are not specifically restricted.
  • Pure water is supplied to the anode side tank 50 via the anode side pure water supply pipe 10 by opening the change-over valve 56 .
  • Quantitation of supply water volume is available by closing the change-over valve 56 which operates on the signal from the liquid surface sensor provided to the second anode side tank 50 or the signal from the integrating flow meter provided to the anode side pure water supply pipe 10 .
  • the change-over valves 52 and 54 belonging to the anode side tank 50 are opened.
  • Pure water is circulated by operating the anode side circulation pump 33 .
  • the anode side by-pass valve 35 is opened, and the anode compartment outlet valve 22 and the anode compartment inlet valve 21 are closed.
  • Pure water circulates in the anode side dilute sulfuric acid generation loop A via the anode side by-pass pipe 36 , without being sent to the anode compartment 4 .
  • Concentrated sulfuric acid is supplied from the anode side concentrated sulfuric acid supply part 32 to the pure water circulating in the anode side dilute sulfuric acid generation loop A, in which the concentrated sulfuric acid and pure water are being mixed by continuous circulation.
  • the solution enters the anode side cooler 34 right after the concentrated sulfuric acid is mixed with the pure water, and therefore, heat of dilution which occurs when concentrated sulfuric acid is mixed with pure water is immediately removed so that generation of vapor or mist is suppressed.
  • temperature rise of the anode side concentrated sulfuric acid supply part 32 derived from heat of dilution is suppressed, which leads to the protection of piping, pumps, and valves in the vicinity from damage or deformation due to high heat.
  • Drainage of the anode side gas-liquid separator 91 and the anode side mist separator 92 is carried out by opening the anode side gas pipe drain valve 94 via the anode side drain pipe 95 .
  • This process is performed on an as-needed basis in the processes: 3) Concentrated sulfuric acid supply process, 5) Sulfuric acid temperature and concentration control process and 6) Electrolysis process.
  • Dilute sulfuric acid solution is being circulated and mixed while being cooled down to the specified temperature or less, preferably to 30 degrees Celsius or less within the anode side dilute sulfuric acid generation loop A.
  • the solution with the sulfuric acid temperature at 30 degrees Celsius or less gives a high current efficiency of oxidizing agent formation.
  • it is preferable that the sulfuric acid temperature is cooled down to 30 degrees Celsius or less before electrolysis.
  • the sulfuric acid concentration is preferably controlled to the range of 2 ⁇ 10 mol/L.
  • the current efficiency of oxidizing agent is higher than the sulfuric acid of 10 mol/L or more; whereas, if it becomes below 2 mol/L, sulfuric acid ion, as raw material of oxidizing agent, in the solution decreases and the current efficiency degrades.
  • Dilute sulfuric acid controlled to the specified temperature and the concentration in the anode side dilute sulfuric acid generation loop A of the anode side is electrolyzed in the electrolysis process of the anode side electrolytic sulfuric acid generation loop B.
  • Electrolysis process is the process to electrolyze dilute sulfuric acid solution carried out in succession of the processes of 1) ⁇ 5).
  • FIG. 4 does not include the cathode side, the processes of 1) ⁇ 5) are performed also on the cathode side similarly to the anode side, which is same as in FIG. 2 .
  • Electrolysis is performed in the anode side electrolysis part 20 by circulating dilute sulfuric acid solution. High current efficiency is achieved when the temperature of the solution is at 30 degrees Celsius or less. Therefore the temperature of the solution during the electrolysis is preferably controlled to 30 degrees Celsius or less.
  • Dilute sulfuric acid solution is circulated between the anode side tank 50 and the anode compartment 4 by closing the anode side by-pass valve 35 , and opening the anode compartment outlet valve 22 and the anode compartment inlet valve 21 .
  • Direct current is supplied to the electrolytic cell 2 and electrolysis is carried out at the specified supply current for the specified time duration to obtain electrolytic sulfuric acid containing oxidizing agent of the specified concentration. With the change-over valves 52 and 54 being closed, the formed electrolytic sulfuric acid containing oxidizing agent of the specified concentration is stored in the first anode side tank 50 .
  • electrolytic sulfuric acid is supplied to a location of use from the second anode side tank 50 ; whereas, pure water supply process starts again at the first anode side tank 49 and repeated.
  • the experiment was conducted using the apparatus for electrolyzing sulfuric acid and the method for electrolyzing sulfuric acid shown in FIG. 1 and FIG. 2 .
  • a conductive diamond electrode was applied, which was prepared in such a way that diamond provided with conductivity by boron doping was coated on a 200 mm ⁇ silicon substrate. Current density was 100 A/dm 2 .
  • the sulfuric acid temperature and concentration control process was as follows, in which concentrated sulfuric acid was diluted with pure water to prepare dilute sulfuric acid of the specified temperature and the specified concentration.
  • the anode compartment inlet valve 21 and the anode compartment outlet valve 22 were opened and the anode side by-pass valve 35 was closed in the anode side to configure the anode side electrolytic sulfuric acid generation loop B;
  • the cathode compartment inlet valve 24 and the cathode compartment outlet valve 25 were opened and the cathode side by-pass valve 42 was closed to configure the cathode side electrolysis loop B′; and electrolysis is carried out with dilute sulfuric acid solution being circulated and direct current being supplied to the electrolytic cell to form electrolytic sulfuric acid containing oxidizing agent.
  • the sulfuric acid concentration before the electrolysis was controlled to the range of 1.8 ⁇ 16.7 mol/L by the sulfuric acid concentration control process.
  • the same method was applied to catholyte of the cathode side to control the concentration. After cooling dilute sulfuric acid solution, electrolysis was carried out.
  • the applied conditions were as follows.
  • Diaphragm For sulfuric acid conc. in electrolyte: 10.0 mol/L or more, hydrophilically treated porous PTFE membrane applied. For sulfuric acid conc. in electrolyte: 9.2 mol/L or less, cation exchange membrane applied.
  • Dilute sulfuric acid electrolyzed by the afore-mentioned procedures under the afore-mentioned conditions was sampled from the sampling pipe branching at the electrolysis part not shown in the figures and the total quantity of the oxidizing agent formed in the dilute sulfuric acid was measured by the KI titrimetry.
  • Table 1 shows measurements of the concentration of total oxidizing agent at the same volume capacity density at the temperature of the dilute sulfuric acid applied to the electrolysis.
  • the concentration of sulfuric acid was 3.7 mol/L. When the temperature excelled 30 degrees Celsius, the concentration decreased.
  • Table 2 gives the concentration of the total oxidizing agent and the current efficiency obtained from the sulfuric acid concentration of 1.8 ⁇ 16.7 mol/L, where applied current density was 100 A/dm 2 and the volume capacity density was 25 Ah/L.
  • the current efficiency obtained from the concentration of total oxidizing agent was 60% or more in the range of 2.0 ⁇ 10.0 mol/L of the sulfuric acid concentration. It is found that in the range outside 2.0 ⁇ 10.0 mol/L, the current efficiency sharply drops.
  • Table 3 shows the case in which the electrolyte was being cooled to keep 30 degrees Celsius even during electrolysis and the case in which cooling was stopped during the electrolysis and the electrolyte heated up to 51 degrees Celsius by the heat of electrolysis.
  • the concentration of oxidizing agent was 1.51 mol/L in the case that cooling at 30 degrees Celsius was continued; whereas in the case that cooling was suspended during electrolysis and the temperature of electrolyte rose up to 51 degrees Celsius by heat generated by electrolysis, the concentration of oxidizing agent was only 0.72 mol/L, not achieving efficient electrolysis.
  • Comparative Example 1 shows the case that the mixing point of concentrated sulfuric acid and pure water was inside the anode side tank, and neither the gas-liquid separator system nor the mist separator were provided. In the process of dilute sulfuric acid formation of Comparative Example 1, cooling was not performed as required, and troubles of the apparatus occurred.
  • Comparative Example 1 2.6 L of ultrapure water was supplied from the top of the tank and 5.9 L of 98 mass % sulfuric acid was supplied from the bottom of the tank in order to prepare 6 mol/L of dilute sulfuric acid solution. Both solutions were at room temperature.
  • the flow rate for the supply of ultrapure water was 3 L/min and that of 98 mass % sulfuric acid was 0.2 ⁇ 1 L/min.
  • the pump Upon completion of supplying 98 mass % sulfuric acid, the pump was operated and the solution was circulated between the tank and the heat exchanger to cool down the dilute sulfuric acid solution to 25 degrees Celsius.
  • electrolysis was started by circulating the solution between the tank and the electrolytic cell.
  • the temperature of the solution during electrolysis was 27 degrees Celsius and the gas pressure in the gas vent piping of the anode and the cathode was 3 ⁇ 5 kPa.
  • the gas pressure in the cathode tank sharply rose to an abnormal level of 200 kPa and circulation of the solution between the tank and the electrolytic cell was ceased.
  • the cell After releasing the remaining pressure, the cell was disassembled, during which through-holes were found in cation exchange membranes.
  • sulfuric acid containing oxidizing agent can be formed at a high efficiency and safely by the electrolysis of dilute sulfuric acid prepared to the specified temperature and concentration in the apparatus, under the controlled temperature condition. Furthermore, the present invention provides the apparatus for electrolyzing sulfuric acid and the method for electrolyzing sulfuric acid which can produce highly concentrated oxidizing agent solution at a high current efficiency, which was not able to achieve by the conventional technologies, and can form oxidizing agent stably.

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US11505871B2 (en) * 2017-04-24 2022-11-22 Hoeller Electrolyzer Gmbh Method for operating a water electrolysis device
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TW201243109A (en) 2012-11-01
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CN103518007A (zh) 2014-01-15
KR101551049B1 (ko) 2015-09-18

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