US3464901A - Production of chlorates - Google Patents

Production of chlorates Download PDF

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Publication number
US3464901A
US3464901A US510592A US3464901DA US3464901A US 3464901 A US3464901 A US 3464901A US 510592 A US510592 A US 510592A US 3464901D A US3464901D A US 3464901DA US 3464901 A US3464901 A US 3464901A
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cell
chlorate
alkali metal
alkali
per liter
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Morris P Grotheer
Edward H Cook Jr
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Occidental Chemical Corp
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Hooker Chemical Corp
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Assigned to OCCIDENTAL CHEMICAL CORPORATION reassignment OCCIDENTAL CHEMICAL CORPORATION CHANGE OF NAME (SEE DOCUMENT FOR DETAILS). EFFECTIVE APRIL 1, 1982. Assignors: HOOKER CHEMICALS & PLASTICS CORP.
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    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B11/00—Oxides or oxyacids of halogens; Salts thereof
    • C01B11/12—Chloric acid
    • C01B11/14—Chlorates
    • 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
    • C25B1/24—Halogens or compounds thereof
    • C25B1/26—Chlorine; Compounds thereof
    • C25B1/265—Chlorates
    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
    • C25B13/00—Diaphragms; Spacing elements
    • C25B13/04—Diaphragms; Spacing elements characterised by the material
    • C25B13/05—Diaphragms; Spacing elements characterised by the material based on inorganic materials
    • C25B13/06—Diaphragms; Spacing elements characterised by the material based on inorganic materials based on asbestos

Definitions

  • An alkali metal chlorate may be produced by the electrochemical decomposition of an alkali metal chloride in a diaphragm type chlor-alkali cell to produce chlorine and caustic which products are inter-reacted chemically at a pH of about 6 to 8 to produce hypochlorite and subsequently chlorate. A portion of the chlorate containing reaction mixture is made up with alkali metal chloride, acidified and fed to the anode compartment of the cell to afford an anolyte pH of about 1 to 5.
  • This invention relates to the production of chlorates and more particularly to a method of producing alkali metal chlorates by means of a chlor-alkali cell.
  • Chlorates particularly sodium chlorate
  • chlorate cells have been produced by the electrolysis of aqueous solutions of alkali metal chlorides such as sodium chloride in electrolytic cells referred to as chlorate cells.
  • Such cells produce chlorates in the cell by reacting chlorine produced at the anode with hydroxide ions produced at the cathode.
  • the anode and cathode are not separated by a diaphragm and, therefore, the chlorine and caustic react with each other almost as soon as they are formed.
  • a method for the production of an alkali metal chlorate by the electrochemical decomposition of an alkali metal chloride in a chlor-alkali cell comprising subjecting an aqueous solution of an alkali metal chloride to a decomposition voltage to produce chlorine and an alkali metal hydroxide, removing said chlorine and alkali metal hydroxide from said cell, mixing and reacting said chlorine and alkali metal hydroxide at a pH of about 6 to 8 to form a reaction mixture containing hypochlorite and subsequently alkali metal chlorate, acidifying at least a portion of said reaction mixture and returning said acidified portion to the anolyte compartment of said cell, said acidification being in an amount to produce an anolyte pH of about
  • the present invention advantageously utilizes both electrochemical and chemical processes for forming chlorates in a manner such that electrical power is not needlessly utilized to effect the chemical reaction of hypochlorite to alkali metal chlorate. Using the present method, current efficiencies are improved over
  • the high efliciencies obtained by the present invention are realized by controlling the electrolyte temperature, pH and salt concentrations within the cell and by controlled reaction conditions for reacting chlorine and alkali metal hydroxide. Without such controls, especially pH conditions, the efficiency of the process greatly diminishes.
  • alkali metal chlorates such as lithium chlorate, potassium chlorate, sodium chlorate, cesium chlorate, and the like
  • other alkali metal chlorates are also applicable and are to be included.
  • a chlor-alkali diaphragm cell 10 is operated under conditions favoring the present invention to thereby produce chlorine 12 and an alkali metal hydroxide 14 in an alkali metal chlorate-chloride solution.
  • the chlorine 12 is evolved from the cell as a gas from the anolyte compartment where it is produced.
  • Alkali metal hydroxide 14 is produced in the catholyte compartment of the chlor-alkali cell in admixture with unreacted alkali metal chloride and recycled alkali metal chlorate.
  • the chlorine 12 and alkali metal hydroxide solution 14 are passed to reactor 16 wherein they are mixed and reacted.
  • pH control 18 a pH of 6 to 8, and more preferably a pH of about 6.5 to 7.5, is maintained in the re actor.
  • the chlorine reacts with the alkali metal hydroxide to produce alkali metal hypochlorite which rapidly converts to alkali metal chlorate.
  • the hypochlorite content remains very 'low, even under continuous operating conditions.
  • the alkali metal hypochlorite content in reactor 16 is readily maintained below about 5 grams per liter.
  • the pH is controlled within the desired range by addition of caustic and/or acid, such as HCl.
  • the caustic can be supplied as cell liquor over and above that produced in the chlor-alkali cell and the acid can be supplied as chlorine, as well as HCl, over and above that produced in the cell.
  • HCl When HCl is used it can be obtained by burning hydrogen and chlorine gases evolved from a chlor-alkali cell.
  • caustic When caustic is added, it is added in an amount commensurate with the HCl or chlorine added to the anolyte feed solution and can be supplied as cell liquor.
  • the chlorine and caustic are completely mixed in the reactor using conventional techniques such as countercurrent flow of gas to caustic, using finely dispersed gaseous chlorine and/or rapid agitation.
  • the reaction is rapid and exothermic in nature.
  • reaction mixture which now contains an increased amount of alkali metal chlorate over that fed to the diaphragm cell 10, in addition to about 0.1 to 5 grams per liter of hypochlorite and alkali metal chloride, is passed to retention tank 17 for a holding period of about five minutes to two hours to reduce the hyprochlorite concentration to preferably below about 0.5 gram per liter.
  • Retention tank 17 can be operated in a manner whereby the solution therein is recycled through reactor 16 thereby increasing the chlorate concentration in the liquor.
  • a portion or all of the chlorate can be removed with the mother liquor which contains sodium chloride and residual chlorate preferably being returned to the cell for further reaction.
  • Several methods can be used to crystallize the chlorate from the reaction mixture. A lowering of the temperature of the solution will change the solubility of the chlorate without greatly affecting the solubility of the sodium chloride.
  • Other methods are also known for removing the chlorate from the alkali metal chloride solution and such other methods can be used if desired.
  • the chlorate content of the reaction mixture is kept at a level where at least 100 grams per liter and preferably 130 to 300 grams per liter of alkali metal chloride can be retained in the anolyte feed solution when the alkali metal chloride is sodium chloride. Slightly different amounts of other alkali metal chlorides can be used depending on their particular solubilities.
  • the effect of chlorates being present in the feed solution can be overcome by controlling the cell operating conditions. Independent of the method used, it is preferred to remove a portion of alkali metal chlorate 22 continuously or periodically to maintain the desired chlorate and chloride concentration in the anolyte feed solution.
  • Recycle liquor from anolyte recirculation 32, retention tank 17 and crystallization process 20 is resaturated with additional amounts of NaCl 26 and/or water 28 as brine or solid salt in saturator 24 so as to provide a feed solution for the diaphragm cell containing at least 100 grams per liter of NaCl and up to about 750 grams per liter of sodium chlorate.
  • this feed solution contains 50 to about 600 grams per liter of sodium chlorate and 130 to 300 grams per liter of sodium chloride,
  • satur-ator 24 replenishes the anolyte feed liquor with additional amounts of alkali metal chloride 26 and additional amounts of water 28 are as needed in the process to provide an anolyte feed solution containing at least 100 grams per liter of alkali metal chloride.
  • the resaturated liquor is then acidified 30 preferably with chlorine gas or HCl prior to being returned to the anolyte compartment of the diaphragm cell. 10.
  • the amount of acid or chlorine added is sufficient to produce a pH in the anolyte compartment of the chlor-alkali cell of about 1 to 5, and more preferably about 2 to 4.
  • the anolyte recirculation method can also be used wherein anolyte liquor 32 is withdrawn from the anolyte compartment of the chlor-alkali cell and replenished with alkali metal chloride, acidified, prefer-aby with HCl or chlorine, and returned to the anolyte compartment of the chlor-alkali cell 10.
  • the feed to the chlor-alkali cell is at a rate greater than that at which cell liquor, alkali metal hydroxide 14, is withdrawn from the cell. This excess feed rate is about 1.5 to 10 times the rate of withdrawal from the catholyte compartment. The excess feed liquor is removed as anolyte liquor 32 for recirculation.
  • the chlor-alkali cell 10 used in the present invention can be any of the numerous types of chloro-alkali diaphragm cells wherein gaseous chlorine and aqueous alkali metal hydroxide cell liquor are produced.
  • a typical chloralkali cell is described by Stuart in US. 1,862,244.
  • Such cells normally have graphite anodes and metal cathodes such as steel. .Asbestos or synthetic fibers are used as the diaphragm material.
  • a group of 50 to 100 or more cells are operated as described herein with the chlorine and caustic produced thereby being reacted as described herein.
  • the feed solution to the chlor-alkali cell of the present invention includes an alkali metal chlorate in addition to alkali metal chloride and particularly, in that the alkali metal chlorate is often in a concentration in excess of the alkali metal chloride, somewhat different operating conditions are preferred from those normally used in chlor-alkali cells.
  • the cell operating temperature is preferably controlled in the range of about degrees centigrade to 100 degrees centrigrade, and more preferably in the range of degrees centrigrade to degrees centrigrade. These preferred ranges are somewhat lower than those preferred in normal chlor-alkali cell operation.
  • the amount of inhibitor used is that sufi'icient to inhibit the oxidation of the metal during temporary shutdown and start-upperiods.
  • sodium dichromate is used as the inhibitor, about 0.01 to about one percent by Weight of the feed solution is used.
  • a stainless steel or chromium-containing steel can be used as the cathode material to thereby eliminate the desirability of using a reagent to prevent chlorate reduction.
  • the diaphragm used in the present cell can be any porous material resistant to the conditions within the cell.
  • the most preferred materials are asbestos, Teflon, after chlorinated polyvinyl chloride, polyvinylidene chloride, and the like materials.
  • the most preferred diaphragm materials are the more porous and acid resistant asbestos such as anthophyllite and asbestos mixtures containing anthophyllite.
  • the diaphragm used in the cell is preferably more porous than that conventionally used for normal chlorine and caustic production. When deposited asbestos is used, the diaphragm weight is preferably 25 to 100 percent of that used for normal chlor-alkali production.
  • Example 1 The process of the present invention was operated in accordance with the drawing using a Hooker Type S-l chlor-alkali cell operated continuously at a current of 6,000 amperes.
  • the chlor-alkali cell used had a 30 pound asbestos diaphragm deposited on a mild steel 6 strand per inch woven wire mesh cathode.
  • the cell was operated by continuously feeding to the anolyte compartment of the cell an acidic solution of about 150 grams per liter of sodium chloride, 500 grams per liter of sodium chlorate, two grams per liter of sodium dichromate and about one-half gram per liter of sodium hydrochlorite at a rate of 11 to 12 liters per minute.
  • the feed solution was acidified with HCl to a pH of about three.
  • the flow from the anolyte compartment through the diaphragm into the catholyte compartment was about 2.5 liters per minute.
  • the excess feed solution was withdrawn from the anolyte compartment at a rate of about 8% to 9 /2 liters per minute and passed to a resa-turator for replenishment of sodium chloride.
  • the solution in the reactor was passed to a retention tank which provided an average retention time of about one to one and one-half hours prior to being returned through the sodium chloride saturator to the cell for further electrolysis or being withdrawn for chlorate crystallization.
  • the hydrochlorite concentration in the retention tank was in the range of about 0.5 to 2.0. grams per liter.
  • the temperature in the retention tank was maintained at about 80 degrees centigrade to promote the reaction of hypochlorite to chlorate.
  • a circulating stream was maintained between the retention tank and the reactor.
  • a second stream of liquor was withdrawn from the retention tank and passed to the saturator for ultimate recycle to the cell.
  • a third stream of liquor is withdrawn from the retention tank for crystallization of sodium chlorate.
  • Sodium chlorate is crystallized from the retention tank solution at a rate of about 8.5 pounds per hour by reducing the temperature of the solution to crystallize a crop of sodium chlorate crystals.
  • the mother liquor from the chlorate crystallization process is passed to the saturator wherein it is mixed with the withdrawn anolyte solution, the retention tank effluent and replenishing amounts of sodium chloride and water to form the anolyte feed solution.
  • This solution is acidified With HCl and returned to the anolyte compartment of the cell thereby providing a feed concentration of about 150 grams per liter of sodium chloride, 500 grams per liter of sodium chlorate, two grams per liter of sodium dichromate, about one-half gram per liter of sodium hypochlorite, at a pH of about 3.
  • the cell efliciency under the controlled cell pH conditions and chlorine-caustic reaction conditions and pH was higher than that attainable in conventional sodium chlorate cells.
  • Examples 2-5 The process of the present invention is again eifected using a chlor-alkali diaphragm cell having a graphite anode and a steel mesh cathode using a deposited anthophyllite asbestos diaphragm.
  • the pH of the electrolyte in the anolyte compartment of the chlor-alkali cell was varied under controlled conditions to determine the effect on the anode current efficiency.
  • Example 2 The process of operating the chlor-alkali cell to produce chlorates was effected in the same manner as Example 1 with the exception that a current density of one ampere per square inch was used at a cell temperature of 60 degrees centigrade.
  • the anolyte feed solution was maintained fairly constant at about 500 grams per liter of sodium chlorate and 150 grams per liter of sodium chloride. Varying amounts of hydrochoric acid were added to the feed solution to provide the anolyte pH shown for each by Examples 2 through 5.
  • the current efliciency was determined by Orsat gas analysis. Table I shows the results obtained.
  • Examples 6-10 The method of the present invention was operated in accordance with the drawing and in the manner of Example 1. The process was operated using different cell temperatures and anolyte pHs to determine the optimum pH and temperatures at an anolyte feed concentration of about 150 grams per liter of sodium chloride, 500 grams per liter of sodium chlorate and about two grams per liter of sodium dichromate.
  • the chlor-alkali cell used is a Hooker Type S4 cell having a graphite anode and a mild steel mesh cathode on which is deposited a 120 pound asbestos diaphragm. The cell is operated at 55,000 amperes using an anolyte feed rate of about 75 liters per minute.
  • the reaction of the sodium hydroxide produced in the catholyte compartment of the cell and the chlorine produced in the anode compartment was eliected at a temperature of about degrees centigrade and a pH of 6.8 to 7.2. Under these conditions of pH and temperature, substantially all of the chlorine is absorbed and reacted with the cell liquor using a co-current mixing action in the reactor. A hypochlorite level of about 2 grams per liter is obtained under continuous reaction conditions in the reactor. The reaction proceeded to completion in the formation of sodium chlorate.
  • Table 11 illustrates the total cell efliciency at various electrolyte pHs in the anode compartment of the cell and at various operating temperatures.
  • the total cell efficiency is based on the current efficiency, the graphite consumption, the acid and caustic requirements for pH b adjustments and power cost.
  • the optimum conditions produced a cost factor of 100.0 with the less than optimum cost conditions being indicated in relation to the optimum which for the given chlor-alkali cell is at a cell temperature of 80 degrees centigrade and an anolyte pH of 3.0.
  • Example 11 Using the information obtained in Examples 6 through 10, experiments were run using the chlor-alkali cell and process of Example 1 wherein the concentration of sodium chloride in the anolyte feed solution was varied from 50 grams per liter to 300 grams per liter and the sodium chlorate concentration was varied from about 50 grams per liter to about 750 grams per liter, the sodium chloride being near the saturation point at the given sodium chlorate concentrations.
  • the solution in the anolyte compartment had a pH of about 3 to 4
  • good cell efficiencies were obtained in the temperature range of 60 to 95 degrees centigrade at sodium chloride concentrations above grams per liter.
  • a method for the production of an alkali metal chlorate by the electrochemical decomposition of an alkali metal chloride in a chlor-alkali diaphragm cell comprising subjecting an aqueous solution of an alkali metal chloride to a decomposition voltage to produce chlorine and an alkali metal hydroxide, removing said chlorine and alkali metal hydroxide from said cell, mixing and reacting said chlorine and alkali metal hydroxide at a pH of about 6 to 8 to form a reaction mixture containing hypochlorite and subsequently alkali metal chlorate, acidifying at least a portion of said reaction mixture and returning said portion to the anolyte compartment of said cell, said acidification being in an amount to produce an anolyte pH of about 1 to 5.
  • diaphragm material in the chlor-alkali cell contains anthophyllite asbestos.
  • alkali metal chloride and alkali metal chlorate are sodium chloride and sodium chlorate, respectively.
  • reaction mixture is acidified with a compound selected from the group consisting of chlorine, hydrochloric acid and mixtures thereof.
  • chlor-alkali cell is operated by feeding anolyte solution to said cell at a rate in excess of that flowing through the diaphragm with the excess brine being withdrawn from the anolyte compartment, resaturated with sodium chloride, acidified and returned to the anolyte compartment for further electrolysis.

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  • Chemical & Material Sciences (AREA)
  • Organic Chemistry (AREA)
  • Inorganic Chemistry (AREA)
  • Engineering & Computer Science (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Electrochemistry (AREA)
  • Materials Engineering (AREA)
  • Metallurgy (AREA)
  • Electrolytic Production Of Non-Metals, Compounds, Apparatuses Therefor (AREA)
US510592A 1965-11-30 1965-11-30 Production of chlorates Expired - Lifetime US3464901A (en)

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BE (1) BE690501A (pt)
DE (1) DE1567587A1 (pt)
FR (1) FR1502455A (pt)
GB (1) GB1161677A (pt)
NL (2) NL6616837A (pt)

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4159929A (en) * 1978-05-17 1979-07-03 Hooker Chemicals & Plastics Corp. Chemical and electro-chemical process for production of alkali metal chlorates

Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2511516A (en) * 1945-10-31 1950-06-13 Western Electrochemical Compan Process for making sodium chlorate
US2628935A (en) * 1946-06-05 1953-02-17 Pennsylvania Salt Mfg Co Electrolytic production of chlorates
US2954333A (en) * 1957-07-11 1960-09-27 Columbia Southern Chem Corp Method of electrolyzing brine
US3043757A (en) * 1959-07-08 1962-07-10 Olin Mathieson Electrolytic production of sodium chlorate
US3055821A (en) * 1960-03-07 1962-09-25 Olin Mathieson Diaphragmless monopolar elecrolytic cell
US3219563A (en) * 1960-06-22 1965-11-23 Ici Ltd Multi-electrolytic cell comprising a plurality of diaphragm-free unit cells and the use of same for preparing alkali metal chlorates

Patent Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2511516A (en) * 1945-10-31 1950-06-13 Western Electrochemical Compan Process for making sodium chlorate
US2628935A (en) * 1946-06-05 1953-02-17 Pennsylvania Salt Mfg Co Electrolytic production of chlorates
US2954333A (en) * 1957-07-11 1960-09-27 Columbia Southern Chem Corp Method of electrolyzing brine
US3043757A (en) * 1959-07-08 1962-07-10 Olin Mathieson Electrolytic production of sodium chlorate
US3055821A (en) * 1960-03-07 1962-09-25 Olin Mathieson Diaphragmless monopolar elecrolytic cell
US3219563A (en) * 1960-06-22 1965-11-23 Ici Ltd Multi-electrolytic cell comprising a plurality of diaphragm-free unit cells and the use of same for preparing alkali metal chlorates

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4159929A (en) * 1978-05-17 1979-07-03 Hooker Chemicals & Plastics Corp. Chemical and electro-chemical process for production of alkali metal chlorates

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NL6616837A (pt) 1967-05-31
FR1502455A (fr) 1967-11-18
DE1567587A1 (de) 1970-07-16
BE690501A (pt) 1967-05-30
GB1161677A (en) 1969-08-20
NL136039C (pt)

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