EP0002783A2 - Electrolyse de solutions salines aqueuses - Google Patents

Electrolyse de solutions salines aqueuses Download PDF

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Publication number
EP0002783A2
EP0002783A2 EP78101763A EP78101763A EP0002783A2 EP 0002783 A2 EP0002783 A2 EP 0002783A2 EP 78101763 A EP78101763 A EP 78101763A EP 78101763 A EP78101763 A EP 78101763A EP 0002783 A2 EP0002783 A2 EP 0002783A2
Authority
EP
European Patent Office
Prior art keywords
electrolyte
compartment
gas
catholyte
cell
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Ceased
Application number
EP78101763A
Other languages
German (de)
English (en)
Other versions
EP0002783A3 (fr
Inventor
Bruce E. Kurtz
Robert H. Fitch
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Allied Corp
Original Assignee
Allied Corp
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Allied Corp filed Critical Allied Corp
Publication of EP0002783A2 publication Critical patent/EP0002783A2/fr
Publication of EP0002783A3 publication Critical patent/EP0002783A3/fr
Ceased legal-status Critical Current

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    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
    • C25B15/00—Operating or servicing cells
    • C25B15/08—Supplying or removing reactants or electrolytes; Regeneration of electrolytes

Definitions

  • an improved process for the electrolysis of an aqueous salt solution in a bank of a plurality of electrolytic cells wherein each cell has an anode electrolyte compartment and a cathode electrolyte compartment, the compartments being separated by a permselective membrane, and at least one electrolyte is transferred serially from one of the compartments of one or more cells to a corresponding electrolyte compartment of a succeeding cell.
  • the improvement comprises effecting the transfer by means of a gas-lift in which gas present in the electrolyte compartment rises through the electrolyte solution in a confined space which is dimensioned such that liquid electrolyte is lifted by the gas up to a disengaging point at which the gas separates and is removed from the compartment, and the liquid is allowed to fall freely through a confined void space to a predetermined point at which it is collected and fed by gravity into the corresponding electrolyte compartment of a succeeding cell at approximately the same elevation as the preceding cell.
  • an improved process for operating a bank of a plurality of electrolytic cells wherein each cell has an anode compartment and cathode compartment, the compartments being separated by a cationic permselective membrane, and sodium hydroxide catholyte is transferred serially from the cathode compartment of one or more cells to the cathode compartment of at least one succeeding cell in the bank.
  • the improvement comprises effecting the transfer by means of gas-lift in which hydrogen, produced in the cathode compartment rises through the sodium hydroxide catholyte solution in a confined space dimensioned to cause the hydrogen to lift the catholyte solution to a disengaging point at which the hydrogen is separated and catholyte solution is allowed to fall freely through a confined void space to a predetermined point wherein it is collected and fed by gravity to the cathode compartment of a succeeding cell at approximately the same elevation as the preceding cell.
  • the drawing is a schematic flow diagram illustrating a bank of two permselective membrane cells employing series electrolyte flow in accordance with this invention.
  • the invention comprises a method for accomplishing series electrolyte flow in a multi-compartment bipolar permselective membrane electrolyzer which utilizes the gas evolved in the electrode compartment for an autogenous gas-lift in order to transport the electrolyte from the electrolyte compartment of one cell to the electrolyte compartment of the next cell, and to establish a high electrical resistance in the stream of electrolyte between the exit of the preceding cell and the entrance of the succeeding cell so as to electrically isolate the electrolyte of the preceding cell from the electrolyte of the succeeding cell.
  • series electrolyte flow can be advantageously applied to any electrolytic or any electrodialytic process in which it is desired to minimize the adverse effects of a high concentration of a particular ionic species generated in one or both of the electrolyte streams.
  • a high concentration of a particular ionic species generated in one or both of the electrolyte streams For example, in the electrolysis of metal halide brines, high concentrations of hydroxyl ions in the catholyte tend to reduce current efficiency by back-migration through the membrane into the anode compartment.
  • series catholyte flow can be advantageously applied to electrolysis of sodium chloride brine, and also to the electrolysis of potassium chloride brine and other metal halide brines in which hydroxyl ions are generated in a catholyte according to the equation
  • series electrolyte flow can also be accomplished, for those processes which do not involve evolution of a gas, by the introduction of a gas from an external source into the bottom of the electrolyte compartment.
  • the gas may be unreactive to the various components of the electrolyte or, if so desired, the gas may serve a dual purpose by being chosen as a reactant.
  • An example of a process in which a gas could be introduced to serve as motivating medium for the gas-lift and as a reactant would be the oxygen depolarization of a chlorine/caustic soda permselective membrane electrolyzer.
  • the cathodes in such an electrolyzer would possess an electro-catalytic coating to promote the reaction
  • the oxygen gas would also serve as the motivating gas to accomplish series catholyte flow according to this invention.
  • the present invention accomplishes series catholyte flow in an electrolyzer unit comprising a bank of a plurality of electrolytic permselective membrane cells in a manner which avoids the use of auxiliary equipment and also serves to electrically isolate the cells from each other.
  • the invention utilizes the hydrogen gas generated within the cathode compartment to raise the catholyte caustic soda liquid through a riser pipe from the top of a preceding cathode compartment to a disengaging device wherein the hydrogen is separated from the catholyte, the catholyte then falls freely downward through a void confined space in a downcomer, to a level from which it flows, by gravity, into the bottom of a succeeding cathode compartment.
  • the height of the void space is dictated by the difference in the bulk density of the two phase system (catholyte liquid and hydrogen gas) in the preceding cathode compartment and the bulk density of the single phase (catholyte liquid) in the downcomer leading to the bottom of the succeeding cell.
  • each cell has a cathode compartment 104 and 204, and an anode compartment 110 and 210 separated by permselective membranes 108 and 208, respectively.
  • Each cathode compartment has a cathode 106 and 206.
  • Lines 112 and 212 feed into the cathode compartments containing catholyte 102 and 202, respectively.
  • the upper portion of each catholyte compartment is equipped with risers 114 and 214 through which the catholyte flows by means of a gas-lift generated by gas bubbles 116 and 216.
  • water from an external source, or catholyte from a preceding cell is fed via line 112 into cathode compartment 104. Regardless of the feed, water is electrolyzed at cathode 106 to produce hydroxyl ions and hydrogen gas which forms bubbles 116.
  • Sodium ions from anode compartment 110 migrate through permselective membrane 108 into the catholyte compartment to form aqueous caustic soda.
  • the hydrogen gas bubbles and the aqueous caustic soda catholyte form a two-phase system which flows from the cathode compartment 102 through riser 114 up to separation point 118.
  • the hydrogen gas passes into header 120 while the liquid caustic soda catholyte is allowed to fall freely through confined void space 220 to collection point 218.
  • the dimensions of riser 114 and void confined space 220 are selected such that at separation point 118, the flowing liquid will occupy only a small portion of the available cross section, thus preventing the entrainment of hydrogen gas in the liquid catholyte as it falls to . collection point 218 and also to allow the liquid catholyte to fall freely, thus preventing electrical current from passing from cell 100 to cell 200.
  • the liquid catholyte flows from collection point 218, via gravity, through feed 212 into catholyte compartment 204 of the succeeding cell 200 wherein the water in the catholyte compartment is electrolyzed at cathode 206 resulting in a repeat of the process occurring in cell 100.
  • the difference between the height of the separation point 118 and the collection point 218 is designated in the drawing as Ah and is approximately proportional to the difference between the effective density of the two phase system in riser 114 (liquid catholyte and hydrogen gas) and the single phase system in feed 212 (catholyte liquid).
  • Ah will, of course, be a maximum for a no-flow condition and will be reduced to some extent by resistance to flow in 114 and 212. However, proper design of these lines will make the resistance to flow negligible at usual flow rates.
  • the extent of the difference in effective density between the catholyte-hydrogen mixture and the catholyte falling through void space 220 to collection point 218 determines the effective gas-lift and it depends on the relative volumes of catholyte and hydrogen present in the cathode compartment. This, in turn, depends on the physical properties of the catholyte and hydrogen, the size of the bubbles formed and the horizontal cross-sectional area of the cathode compartment. It is only this latter factor which can be controlled by the design of the electrolyzer and it will be evident that the cross-sectional area should be established within certain limits in order to assure proper operation.
  • the hydrogen bubbles will occupy only a small fraction of the total cathode compartment volume and there will accordingly be little difference in density between the contents of the cathode compartment and the liquid catholyte alone resulting in too small a gas-lift effect and too small a ⁇ h to accomplish adequate electrical isolation between the cathode compartments.
  • the hydrogen bubbles will occupy a large fraction of the total cathode compartment volume, hence, Ah will be more than large enough to accomplish adequate electrical isolation.
  • the hydrogen will occupy such a large fraction of the cathode compartment volume, the resistance to the flow of electrical current through the catholyte will be increased causing the cell to operate at too high a voltage.
  • the horizontal cross-sectional area of the cathode compartment should be confined within certain limits.
  • the cathode compartment horizontal cross-sectional area required for satisfactory gas-lift effect will depend on the volumetric rate of hydrogen evolution. More specifically, it will be proportional to the product of the cathode area and the current density according to the equation wherein
  • the proportionality constant K should be in the range of 0.01 to 2.0, preferably, 0.05 to 1.0. At K values less than about 0.01 the cell will operate at an undesirably high voltage due to the large fraction of the catholyte compartment occupied by the hydrogen. At K values more than about 2.0, the rate of hydrogen evolution will be insufficient to create the necessary gas-lift effect.
  • the anodes employed were constructed of titanium coated with rare earth metal oxides and available under the trade name "DSA".
  • the cathode was mild steel.
  • the membrane was a cationic permselective membrane supplied under the trade name "Nafion”.
  • the current density employed was 0.25 amps/cm 2 .
  • the pressure within the anode compartment was maintained at about 7 inches of water, that within the cathode compartment at about 1 inch of water.
  • Example 1 comprises the average result of two runs at approximately the same final caustic concentration
  • Example 2 is the average of 3 runs at approximately the same final caustic concentration
  • Example 3 is the average of 2 runs at approximately the same final caustic concentration. The duration of each run was approximately 1 hour. The results are shown in the Table.
  • the voltage was satisfactorily low.
  • the difference in level between the separation point and the collection point was, in all cases, in the range of 3 to 6 cm, quite satisfactory for electrical isolation between adjacent cathode compartments.
  • For periods of operation at current densities less than 0.25 amps/cm 2 it was observed that the difference in catholyte levels between adjacent cathode compartments was diminished, but was still adequate (2-3 cm), at current densities in the range of 0.12 amps/cm 2 , corresponding to a K value of about 1.0.
  • the autogenous gas-lift method of this invention avoids increased complexity and cost, and decreased reliability of the electrolyzer. It also utilizes the energy generated by the buoyancy of the hydrogen bubbles which would otherwise be wasted. As compared to the alternative of gravity flow for transporting the catholyte, the gas-lift method avoids the need for having adjacent cathode compartments at successively lower positions which would seriously complicate the design and increase the cost of the electrolyzer.
  • the gas-lift method of this invention accomplishes this by creating a discontinuity in the catholyte stream where the stream falls freely through a confined void space created by the difference in head.

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Electrochemistry (AREA)
  • Materials Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Electrolytic Production Of Non-Metals, Compounds, Apparatuses Therefor (AREA)
EP78101763A 1977-12-30 1978-12-19 Electrolyse de solutions salines aqueuses Ceased EP0002783A3 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
US86612077A 1977-12-30 1977-12-30
US866120 1977-12-30

Publications (2)

Publication Number Publication Date
EP0002783A2 true EP0002783A2 (fr) 1979-07-11
EP0002783A3 EP0002783A3 (fr) 1979-07-25

Family

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Family Applications (1)

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EP78101763A Ceased EP0002783A3 (fr) 1977-12-30 1978-12-19 Electrolyse de solutions salines aqueuses

Country Status (2)

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EP (1) EP0002783A3 (fr)
JP (1) JPS5496498A (fr)

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0046603A1 (fr) * 1980-08-27 1982-03-03 Fernand Louis Oscar Joseph Chauvier Dispositif pour la production de chlore par électrolyse
EP0121585A1 (fr) * 1983-04-12 1984-10-17 The Dow Chemical Company Cellule d'électrolyse de chlore du type à circulation d'électrolyte en série

Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US1441408A (en) * 1915-08-12 1923-01-09 Dow Chemical Co Method of and apparatus for electrolyzing liquid
US3855091A (en) * 1972-01-19 1974-12-17 Ppg Industries Inc Method of separating chlorine from chlorine-anolyte liquor froth of an electrolytic cell
US3928165A (en) * 1973-07-02 1975-12-23 Ppg Industries Inc Electrolytic cell including means for separating chlorine from the chlorine-electrolyte froth formed in the cell
US4059495A (en) * 1975-04-24 1977-11-22 Oronzio De Nora Impianti Elettrochimici S.P.A. Method of electrolyte feeding and recirculation in an electrolysis cell

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US1441408A (en) * 1915-08-12 1923-01-09 Dow Chemical Co Method of and apparatus for electrolyzing liquid
US3855091A (en) * 1972-01-19 1974-12-17 Ppg Industries Inc Method of separating chlorine from chlorine-anolyte liquor froth of an electrolytic cell
US3928165A (en) * 1973-07-02 1975-12-23 Ppg Industries Inc Electrolytic cell including means for separating chlorine from the chlorine-electrolyte froth formed in the cell
US4059495A (en) * 1975-04-24 1977-11-22 Oronzio De Nora Impianti Elettrochimici S.P.A. Method of electrolyte feeding and recirculation in an electrolysis cell

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0046603A1 (fr) * 1980-08-27 1982-03-03 Fernand Louis Oscar Joseph Chauvier Dispositif pour la production de chlore par électrolyse
EP0121585A1 (fr) * 1983-04-12 1984-10-17 The Dow Chemical Company Cellule d'électrolyse de chlore du type à circulation d'électrolyte en série

Also Published As

Publication number Publication date
JPS6128753B2 (fr) 1986-07-02
JPS5496498A (en) 1979-07-30
EP0002783A3 (fr) 1979-07-25

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Inventor name: KURTZ, BRUCE E.

Inventor name: FITCH, ROBERT H.