EP0332394A1 - Elektrolytische Darstellung von Natriumhydrosulfit - Google Patents

Elektrolytische Darstellung von Natriumhydrosulfit Download PDF

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Publication number
EP0332394A1
EP0332394A1 EP89302255A EP89302255A EP0332394A1 EP 0332394 A1 EP0332394 A1 EP 0332394A1 EP 89302255 A EP89302255 A EP 89302255A EP 89302255 A EP89302255 A EP 89302255A EP 0332394 A1 EP0332394 A1 EP 0332394A1
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Prior art keywords
solution
catholyte
cathode
compartment
anode
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EP89302255A
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English (en)
French (fr)
Inventor
Leonard L. Diaddario, Jr.
Mark A. Schroeder
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CNA Holdings LLC
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Hoechst Celanese Corp
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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
    • C25B1/14—Alkali metal compounds

Definitions

  • This invention relates to dithionites and more particularly relates to electrochemical preparation of dithionites from bisulfites.
  • Dithionites commonly termed hydrosulfites, have been used for years to bleach a wide variety of materials including straw, feathers, glue, textiles, and wood pulps.
  • hydrosulfites For many such commercial uses in the past, zinc dithionite has been preferred because of its stability in aqueous solution, but ecological considerations in recent years have caused sodium dithionite to be used almost exclusively.
  • two-compartment cells are used for the electrolysis in which anode and cathode compartments are separated by a diaphragm or an ion-exchange membrane.
  • aqueous sulfur dioxide is reduced to dithionite by the following half reaction: 2SO2 + 2e ⁇ ⁇ S2O42 ⁇ (1)
  • the electrolyte serves two functions. It is the source of sodium ions which are transported through a cation-exchange membrane to the cathode compartment, and it provides a source of easily oxidizable anions. Either a sodium chloride or a sodium hydroxide solution has been used to produce chlorine or oxygen, respectively, by one of the following half reactions: 2NaCl ⁇ Cl2+ 2Na+ + 2e ⁇ (2) 4NaOH ⁇ O2 + 4Na+ + 2H2O + 4e ⁇ (3)
  • half-reaction 1 with either half-reaction 2 or 3 yields a sodium dithionite solution by either of the following overall reactions: 2SO2 + 2NaCl ⁇ Na2S2O4 + Cl2 (4) 4SO2 + 4NaOH ⁇ 2Na2S2O4 + O2 + 2H2O (5)
  • aqueous sodium bisulfite solutions can be used as the source of sulfur(IV).
  • Bisulfite is reduced to dithionite at the cathode by the following half-reaction: 2NaHSO3 + 2e- -- ⁇ Na2S2O4 + 2OH- (6)
  • U.S. Patent No. 2,273,799 describes a process for producing sodium hydrosulfite from sodium bisulfite at a porous carbon cathode formed from comminuted solid carbonaceous material and a porous carbonaceous binder.
  • the anode compartment contained a graphite anode and saturated brine electrolyte.
  • the cathode compartment contained a catholyte of NaHSO3, Na2SO3, and NaCl and, selectively, a graphite cathode.
  • U.S. Patent No. 3,523,069 describes an electrolytic process for converting a solution of SO2 in water to an acidic solution of Na2S2O4 in the cathode compartment, the anode compartment containing an NaOH solution as anolyte and the cathode and anode compartments being separated by a cation-permeable membrane.
  • Careful control of catholyte temperature of 0-40°C, catholyte SO2 concentration at 2-25 wt.%, pH at 0.5-3.0, catholyte velocity at 1-40 meters/minute and other variables is required.
  • U.S. Patent 3,748,238 describes a process for preparing sodium dithionite from sodium bisulfite or sodium metabisulfite in an electrolysis apparatus provided with a special spongy, porous lead electrode used therein as a cathode and substantially filling the catholyte compartment of the apparatus.
  • the porous lead electrode is produced from alkali metal plumbites in the same electrolysis apparatus and remains in place for electrochemical preparation of sodium dithionite.
  • U.S. Patent No. 3,920,551 describes a process for making dithionites electrolytically by adding gaseous SO2 to the cathode compartment of an electrolytic cell in which the anode and cathode compartments are separated by a cation permselective membrane.
  • the anode compartment contains an alkali metal chloride anolyte solution.
  • hydroxyl ions are reacted with SO2 to produce sulfite.
  • a process for continuous manufacture of concentrated sodium dithionite solutions by cathodic direct reduction of solutions containing sulfite/bisulfite is also described in U.S. Patent 4,144,146, within two-compartment cells divided by a chlorine-resistant cation exchanger membrane consisting of a copolymer of tetrafluoroethylene and a perfluorovinylsulfonic acid containing ether groups.
  • an anode/cathode redox reaction system in which sodium bisulfite is reduced to sodium dithionite at the cathode according to reaction 6 while water is oxidized to oxygen under acidic conditions at the anode according to the following half reaction: 2H2O -- ⁇ O2 + 4H+ + 4e ⁇ (10)
  • Reaction 11 produces dithionite at the cathode and oxygen gas at the anode. There is no net production or consumption of protons or hydroxide ions. The number of moles of protons produced at the anode are equal to the number of moles of hydroxide ions produced at the cathode. To maintain charge balance, the protons produced at the anode migrate through the cation-exchange membrane which separates the anode compartment from the cathode compartment. Thus, the catholyte pH should remain constant throughout the electrolysis. By using reaction 11, the catholyte pH should remain in the range for optimum electrolysis, and dithionite decomposition is controlled because the catholyte pH is not highly acidic.
  • the membrane which is to separate the anode compartment from the cathode compartment is a Nafion® membrane which is a permselective membrane of sulfonated fluorocarbon polymer, designed to permit selective passage of cations.
  • Nafion® membrane which is a permselective membrane of sulfonated fluorocarbon polymer, designed to permit selective passage of cations.
  • the Nafion cation-exchange membrane used is not 100% efficient. Some proton-for-sodium ion exchange takes place across the membrane even when no potential is applied to the electrodes. This dialysis causes the catholyte pH to become more acidic, but it has been discovered that the catholyte can be maintained at a constant pH by small additions of a base, such as sodium hydroxide.
  • This process for the electrolytic formation of a dithionite salt comprises the following steps:
  • these steps be preceeded by the step of admixing gaseous SO2 with dilute sodium hydroxide solution to form the catholyte solution and by the step of admixing gaseous SO2 with water to form a solution of sulfurous acid which is oxidized in the anode compartment to sulfuric acid at a concentration of approximately 1 molar.
  • admixing SO2 with NaOH formed a catholyte solution of 0.50 M NaHSO3. Quite obviously, different designs can change the concentration of NAHSO3.
  • the preferred anode for this electrolysis has a low overpotential for oxygen evolution under acidic conditions.
  • other electrode materials such as noble metals like platinum, for example, can be used at the expense of increased oxygen evolution overpotential.
  • Materials of this type are known [See German Offen. 2,331,959 (C.A. Vol 80, 1974, p. 522) and German Offen. 2,331,949 (C.A. Vol. 82, 1975, p. 486)].
  • the preferred anode is the DSA-O2® (pH below 2) of the Electrosynthesis Company, Inc., P.O. Box 16, E. Amherst, N.Y. 14051, which is made of ruthenium oxide on titanium.
  • the cathode which is preferably utilized is conventional and can be at least one noble metal such as gold, silver, platinum, palladium, or rhodium or a non-noble metal such as copper and nickel, or carbon, such as graphite and reticulated vitreous carbon (RVC).
  • the preferred cathode is graphite.
  • the dimensionally stable and cation-permselective membrane used in the cell includes fluorinated polymers. These and other materials are disclosed in U.S. 3,920,551 and 3,905,879 which are hereby incorporated by reference.
  • Perfluorosulfonic acid products sold by the Du Pont Plastic Products and Resins Department under the trademark Nafion, are the preferred membrane material.
  • the membranes are available with reinforcement of fabric of Teflon® TFE fluorocarbon resin which provides a mechanically durable, all-fluorocarbon product with outstanding chemical and temperature resistance.
  • These Nafion® products are copolymers of tetrafluoroethylene and monomers such as perfluoro-3, 6-dioxa-4-methyl-7-octensulfonic acid.
  • the redox reaction process of this invention offers several surprising advantages over the conventional reduction of aqueous sulfur dioxide and oxidation of sodium hydroxide. These advantages include (1) no net gain or loss of protons and, ideally, constant pH, and (2) feeding sodium bisulfite solutions, instead of strongly acidic aqueous sulfur dioxide solutions, to the cathode compartment, thereby helping the pH of the catholyte recycle to be maintained at a relatively constant value of slightly acidic to neutral pH throughout the electrolysis.
  • Suitable process conditions were found to be: an optimum catholyte temperature range of 20-25°C, an optimum catholyte pH range of 4.6-5.8, a preferred pH value of 5.16, and an optimum range for reduction potential of -1.25 V to 1.50 V versus Ag°/AgCl, the preferred reduction potential being -1.37V.
  • the anode/cathode redox reaction system of this invention is operationally most practicable on a large scale when using gaseous SO2 for reacting with a dilute NaOH solution to provide an NaHSO3 catholyte solution and for dissolving in water to provide a dilute acid anolyte solution.
  • gaseous SO2 for reacting with a dilute NaOH solution to provide an NaHSO3 catholyte solution and for dissolving in water to provide a dilute acid anolyte solution.
  • Na2S2O5 was a more convenient source of NaHSO3 solution
  • H2SO4 was a more convenient source of acid anolyte solution.
  • FIG. 1 An electrolysis unit is shown in Figure 1 which also includes a process flow diagram.
  • the unit comprised a two-compartment electrolysis cell 10, anolyte supply system 20, catholyte supply system 30, anolyte product take-off and recirculation system 40, catholyte take-off and recirculation system 50, and instrumentation 61-79.
  • Electrolysis cell 10 was a monopolar, plate-and-frame type ElectroCell MP-Cell from ElectroCell AB (Akersberga, Sweden). Cell 10 was equipped with a 0.02 m2 graphite cathode 13, a 0.01 m2 DSA-O2® (pH below 2) anode 11, and a Nafion 324 cation-exchange membrane 15 to form an anolyte half cell 17 and a catholyte half cell 19. Electrolysis cell 10 was powered from a Sorensen Nobatron DC power supply, Model DCR20-125.
  • the entire electrolysis unit was constructed from non-metallic components. All plumbing was constructed from PVC pipe, connectors, and valves.
  • the anolyte and catholyte were respectively fed from tanks 21, 31 through lines 22, 24 and 32, 34 with electronic metering pumps 23, 33, made by Liquid Metronics, Inc., Model A121-95T.
  • Concentrated sodium hydroxide was fed from tank 36 through lines 37, 39 into the catholyte recycle with an electronic metering pump 38, made by Liquid Metronics, Inc. Model A751-95T.
  • the anolyte and catholyte were respectively recycled through lines 41, 44, 46, 48, 49 and 51, 54, 56, 58, 59 with seal-less, magnetic drive, centrifugal, chemical pumps 47, 57, having polypropylene bodies and impellers and with polypropylene encased magnets from March Manufacturing, Inc., Model TE-5.5C-MD.
  • Recycle flow rates were monitored with non-metallic rotameters 45, 55, having polysufone bodies, CPVC end connections, and PVC internals from Electrosynthesis Co., Inc., Model M200-C-2-HT-V. Recycle flow rates were controlled by flow control valves 63, 73.
  • the anolyte and catholyte recycles were cooled through all-glass heat exchangers 61, 71 from Corning Process Systems, Model HE 1.5.
  • the anolyte and catholyte recycle temperatures was monitored with FEP coated, type J thermocouples 62, 72 from Omega Engineering, Inc., part number ICSS-18G-12-FEP.
  • Catholyte pH was monitored with a double-junction, combination electrode 75 for high sodium ion solutions from Cole-Parmer Instrument Co., part number J-5994-23, connected to an Orion Model 211 digital pH meter.
  • Oxygen was removed from the anolyte through line 76, and hydrogen was removed from the catholyte, as a minor byproduct, through line 77.
  • Nitrogen was selectively fed to the respective half cells through lines 78, 79.
  • Catholyte samples were selectively removed through samples valve 74.
  • the laboratory-scale pilot electrolysis unit was monitored and controlled by an Apple IIe computer system with an ISAAC Model 91A data acquisition and control system.
  • Control electronics were designed and constructed, and a computer program was developed to allow unattended, independent control of the anolyte recycle temperature, the catholyte recycle temperature, and the catholyte pH.
  • the control program also included data logging features which would record the following operating parameters: cell potential; current; catholyte pH; catholyte temperature; and anolyte temperature.
  • the progress of the electrolysis reaction was monitored at periodic time intervals by determining the molar concentration of dithionite, bisulfite, and thiosulfate in the catholyte recycle. Standard iodimetric titrations were adapted to perform these analyses.
  • the reduction potential and catholyte pH were found to have the greatest effect on the bisulfite-to-dithionite conversion.
  • Catholyte recycle temperature was found to have a moderate effect on the conversion.
  • Batch electrolyses were run to optimize these three operating parameters. The batch electrolyses were performed under the following conditions: the initial concentration of the catholyte solution was 0.50M NaHSO3; the anolyte solution was 1M H2SO4; the catholyte recycle volume was 2.7-4.3 liters; the anolyte recycle volume was 5.0-10.4 liters; and the anolyte and catholyte recycle rates were 3.8-41. gal/min.
  • the reduction potential was varied over a potential range of -1.25 to -1.75V versus Ag°/AgCl.
  • the catholyte pH was varied from 4.25 to 5.25.
  • the electrolyses were run for five hours at the following temperature ranges: 11-13°C, 24-28°C; and 41-46°C.
  • the bisulfite-to-dithionite conversion, the bisulfite-to-thiosulfate conversion, bisulfite reacted, and the current efficiency were calculated by the following equations:
  • Equation 17 has a correlation coefficient of 0.997.
  • the bisulfite-to-dithionite conversion reached a maximum at -1.37 to -1.50 V versus Ag°/AgCl and pH 5.00-5.25.
  • Equation 18 has a correlation coefficient of 0.995 and shows, when plotted as a calculated three-dimensional response surface, that more thiosulfate is formed as the catholyte pH decreases and as the reduction potential becomes more cathodic. This result indicates that thiosulfate is formed by an electrolytic pathway in addition to the dithionite solution decomposition pathway.
  • Equation 19 has a correlation coefficient of 0.999.
  • % Current Eff. 179.4 - 107.4(pH) - 254.2(V) + 11.1(pH)2 -109.8(V)2 - 3.5(pH)(V) (19) Equation 19 has a correlation coefficient of 0.999.
  • Catholyte pH did not appear to have a large effect on the current efficiency.
  • the current efficiency did decrease rather quickly, however, as the reduction potential became more cathodic. This phenomenon can be attributed to over-reduction of Na2S and reduction of water.
  • the optimum reduction potential for current efficiency was found to be -1.25 to -1.37V versus Ag°/AgCl.
  • the overall equation which describes the net effect of maximizing the bisulfite-to-dithionite conversion, minimizing the bisulfite-to-thiosulfate conversion, and maximizing the current efficiency, can be calculated by summing equation 17, equation 19, and the negative of equation 18.
  • the calculated net effect can be plotted on the Z axis of a three-dimensional response surface where the X axis is the catholyte pH from 4.0 to 5.5 and the Y axis is the reduction potential from -2.0V to -1.0V versus Ag°/AgCl.
  • equation 20 was differentiated with respect to catholyte pH and to reduction potential.

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  • Chemical & Material Sciences (AREA)
  • Inorganic Chemistry (AREA)
  • Engineering & Computer Science (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Electrochemistry (AREA)
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  • Electrolytic Production Of Non-Metals, Compounds, Apparatuses Therefor (AREA)
EP89302255A 1988-03-08 1989-03-07 Elektrolytische Darstellung von Natriumhydrosulfit Withdrawn EP0332394A1 (de)

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US164874 2002-06-07

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Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
RU2146221C1 (ru) * 1998-10-14 2000-03-10 Дагестанский государственный университет Способ получения дитионита натрия

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR819947A (fr) * 1936-04-04 1937-10-28 Ig Farbenindustrie Ag Procédé pour la production d'hyposulfites
US3748238A (en) * 1972-05-08 1973-07-24 Sybron Corp Electrolytic process for the preparation of sodium hydrosulfite
SU652238A1 (ru) * 1976-01-06 1979-03-15 Новочеркасский ордена Трудового Красного Знамени политехнический институт им. Серго Орджоникидзе Способ получени серной кислоты

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR819947A (fr) * 1936-04-04 1937-10-28 Ig Farbenindustrie Ag Procédé pour la production d'hyposulfites
US3748238A (en) * 1972-05-08 1973-07-24 Sybron Corp Electrolytic process for the preparation of sodium hydrosulfite
SU652238A1 (ru) * 1976-01-06 1979-03-15 Новочеркасский ордена Трудового Красного Знамени политехнический институт им. Серго Орджоникидзе Способ получени серной кислоты

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
RU2146221C1 (ru) * 1998-10-14 2000-03-10 Дагестанский государственный университет Способ получения дитионита натрия

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