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WO1993004979A1 - Regulation de l'acidite dans la fabrication de dioxyde de chlore - Google Patents

Regulation de l'acidite dans la fabrication de dioxyde de chlore Download PDF

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Publication number
WO1993004979A1
WO1993004979A1 PCT/SE1991/000605 SE9100605W WO9304979A1 WO 1993004979 A1 WO1993004979 A1 WO 1993004979A1 SE 9100605 W SE9100605 W SE 9100605W WO 9304979 A1 WO9304979 A1 WO 9304979A1
Authority
WO
WIPO (PCT)
Prior art keywords
acid
chlorine dioxide
sodium sulphate
solution
electrolysis
Prior art date
Application number
PCT/SE1991/000605
Other languages
English (en)
Inventor
Rolf Carl August BRÄNNLAND
Sture Erik Olof NORÉUS
Original Assignee
Eka Nobel Ab
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 Eka Nobel Ab filed Critical Eka Nobel Ab
Priority to CA002116427A priority Critical patent/CA2116427C/fr
Priority to US08/204,357 priority patent/US5423958A/en
Priority to PCT/SE1991/000605 priority patent/WO1993004979A1/fr
Priority claimed from CA002116427A external-priority patent/CA2116427C/fr
Publication of WO1993004979A1 publication Critical patent/WO1993004979A1/fr
Priority to FI941111A priority patent/FI112351B/fi

Links

Classifications

    • 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
    • C01B11/02—Oxides of chlorine
    • C01B11/022—Chlorine dioxide (ClO2)
    • C01B11/023—Preparation from chlorites or 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
    • C25B1/22—Inorganic acids

Definitions

  • the present invention relates to a method for technically producing chlorine dioxide intented for bleaching cellulose pulp produced, for instance, chemically, such as sulphate pulp or sulphite pulp, and involving a more effective use of the chemicals used by combining the manufacturing process with an electrolysis process for the purpose of controlling acidity in the generation of chlorine dioxide.
  • Chlorine dioxide is manufactured on a technical scale, by reacting sodium chlorate in aqueous solution with a suitable reductant.
  • a suitable reductant Conventional reductants are sulphur dioxide, sodium chloride, hydrogen chloride and methanol, although other inorganic substances are also mentioned in the litera ⁇ ture, such as nitrogen dioxide and sulphur, or organic sub ⁇ stances such as ethanol and oxalic acid.
  • Sulphuric acid or hydrochloric acid (hydrogen chloride) are the substances most commonly used to effect such acidifica ⁇ tion.
  • spent acid a strongly acid solution of sulphuric acid and sodium sulphate, or hydrochloric acid and sodium chloride
  • Sulphur containing spent acid has hitherto been used as a make-up chemical in the pulp mills, wherein the acid has been utilized to cleave or split tall oil soap for the production of tall oil, and the sodium sulphate is used to make up alkali losses and sulphur losses in the cooking chemical system of the pulp mills.
  • a modern variant of the chlorine dioxide process is based on reacting a mixture of sodium chloride and sodium chlorate in a solution which is acidified with sulphuric acid. The reaction takes place under vacuum conditions, 10-57 kPa, at a temperature of 45-85°C. A mixture of water vapour (steam), chlorine dioxide and chlorine departs during this reaction.
  • the reaction is represented by the formula:
  • NaC10 3 +NaCl+H 2 S0 4 C10 2 +l/2 Cl 2 +Na 2 S0 4 +H 2 0
  • NaCl0d+l/2S0 A C102.,+l/2Na2.-SO4 J ,
  • Sulphur dioxide can also be used to absorb in an aqueous solution chlorine gas which has not dissolved in the water washing tower used to produce chlorine dioxide water. This results in a mixed acid according to the formula:
  • This mixed acid can be returned to the chlorine dioxide reactor.
  • Flows of sodium chlorate, sodium chloride and sulphuric acid are delivered to the reactor.
  • the reaction products chlorine dioxide and chlorine are absorbed in a tower to which pure water is delivered and which produces a liquid which contains chlorine dioxide and chlorine.
  • the residual gas from the absorption tower is passed to a reac ⁇ tion vessel, to which sulphur dioxide and water are supplied.
  • the resultant mixed acid is passed back to the reactor.
  • Crystals of sodium sulphate (Na_SO.) formed in the chlorine dioxide reactor are pumped to a filter and ejected, whereas the mother liquor is returned to the reactor.
  • methanol is used as a reductant, which is supplied to the reactor along with sodium chlorate and sulphuric acid.
  • the chlorine dioxide gas formed is passed to a tower in which the gas is absorbed in water, and the resultant bleaching liquid is passed to the bleaching department.
  • Crystals of sodium sesquisulphate (Na 3 H[SO.] 2 ) formed in the chlorine dioxide reactor are pumped to a filter and ejected, whereas the mother liquor is returned to the reactor.
  • the following reaction formulas are representative of this embodiment:
  • the present invention solves these problems and relates to a method for generating chlorine dioxide, by reducing a chlorate solution in the presence of hydrogen ions at a pH- value below 7 with the use of one or more reductants and a sulphur-containing compound in the form of a reductant and/or an acid, characterized by maintaining the hydrogen ion con ⁇ centration (the acidity) in the chlorine dioxide generating process, completely or partially, with the aid of acid ob ⁇ tained by the electrolysis of a solution of sodium sulphate (Na 2 S0 4 or Na 3 H[S0 4 ] 2 ).
  • the crystals of sodium sulphate formed in the chlorine dioxide generating process are separated on a filter and re- dissolved and passed to the anode chamber and there subjected to electrolysis in, for instance, a membrane cell provided with a unipolar cation-selective membrane. Part of the sodium ions in the sodium sulphate solution is caused to pass the membrane and forms sodium hydroxide in the cathode chamber, this sodium hydroxide being removed from said chamber and used, preferably in the alkaline bleaching stage of the pulp mill.
  • the remaining acid sulphate/sulphuric acid solution is tapped off. Part of this acid solution is removed from the system and used, for instance, for the production of tall oil in the sulphate mill, and its corresponding sodium content is used, for instance, to make-up alkali losses in the cooking chemical system of the mill.
  • this acid solution is preferably sub ⁇ jected to evaporation, so as to maintain the water balance in the system.
  • the acid solution is re ⁇ turned to the chlorine dioxide generator and there used to control the acidity in the process.
  • the water in order to utilize the vapourized water, it is suitable to pass this water vapour to the crystal dissolving vessel, furthermore, the water can be vapourized at a pressure level such that the vapour formed can be used to heat the solution in the chlorine dioxide generator.
  • the mixed acid formed by reduction of chlorine gas with sulphur dioxide can be used to acidify the pulp prior to the first bleaching stage, in those instances when chlorine has been replaced to a great extent with chlorine dioxide and the initial acidity in the bleaching process is too low.
  • the mixed acid used for this purpose can be replaced in the chlorine dioxide generating process with chlorine-free acid generated in the electrolysis cell.
  • Part of the acid required to control acidity can be taken from an external source, in order to further increase flexi ⁇ bility.
  • Practical tests have been carried out with a simple mem ⁇ brane cell provided with an iron cathode, platinated titanium anode and a unipolar cation-selective membrane of perfluoro- sulphonic acid or perfluorocarboxyllc acid. i.e. the type that has long been used in the production of chlorine and alkali by electrolytic decomposition of sodium chloride. These tests have shown that the sodium sulphate obtained in crystal form in the chlorine dioxide generating process can be worked-up surprisingly easily.
  • the salt is dissolved in pure water, such as to obtain a concentration of about 400 g/1 Na 2 S0 4 . this solution being delivered continuous ⁇ ly to the electrolysis plant.
  • the electrolysis vessel is divided by means of a membrane into a chamber for the cathode and a chamber for the anode.
  • Sodium sulphate solution is supplied through a conduit and converted solution containing sulphuric acid, possibly with residual non-converted sodium sulphate, is removed through another conduit.
  • Oxygen gas is generated at the anode.
  • Sodium ions diffuse through the cation-selective membrane, where they form sodium hydroxide at the cathode and hydrogen gas is generated at the same time. Pure water is delivered through a conduit and the sodium hydroxide formed is removed through another conduit. It is also possible to use other types of electrolysis cells, although the effectiveness of these cells is somewhat lower.
  • the invention has enabled the consumption of acid and alkali in a pulp mill to be reduced considerably, by com- bining acid and alkali consuming processes with an electro ⁇ lytic process, wherein salts which are formed in the chlorine dioxide generating process are decomposed to their individual consituents and reused.
  • the biproducts oxygen gas and hydrogen gas are obtained, which can be utilized in the pulp manufacturing process for bleaching and for steam generation respectively.
  • the invention enables the quotient between acid requirements in the production of tall oil and the sulphate requirements for making-up losses in the cooking chemical cycle to be varied in accordance with the local con ⁇ ditions. Also of great value are the chemicals sodium hydroxide, oxygen gas and hydrogen gas formed in accordance with the invention and utilized within the pulp manufacturing process. This reuse of chemicals improves the economy of pulp manufacture and also reduces the load on the environment caused by the emission of non-consumed chemicals.
  • Figure 1 is a flow sheet pertaining to a preferred embodiment of the invention.
  • Figure 2 illustrates the con ⁇ struction of a suitable electrolysis cell in more detail.
  • the reactor 1 was operated under the following conditions:
  • the power consumed by the electrolysis process was 3460
  • sodium chloride was similarly used as the reductant for the chlorate in the reactor 1 and sulphur dioxide as the reductant in the absorption tower 3. although with the difference in relation to Example 1 that no solution was returned to the reactor 1 from the absorption tower 3.
  • the reactor 1 worked under the following conditions:
  • the generated mixture of chlorine dioxide and chlorine gas was transported to the absorption tower 2 with the aid of
  • the acid solution was pumped through the line 24 to the evaporation vessel 29, which was operated under vacuum condi ⁇ tions, 50 kPa and 82°C. 7071 kg/h water were evaporated and delivered to the dissolving tank 23.
  • the concentrated acid now had the composition:
  • methanol was used as the reductant for the sodium chlorate in the aforesaid reactor 1, which operated under the following conditions:
  • composition of the acid solution after electrolysis was:
  • This acid was supplied to the reactor 1 through the line 31.
  • This recirculation of acid enabled the acidity to be maintained in the chlorine dioxide generating process without supplying acid from an external source. Acid from an external source, however, can be supplied through the line 6 if con ⁇ sidered suitable.
  • the example has enabled the following savings to be made:
  • the invention is not limited to the cases described in Examples 1-3, but can also include chlorine dioxide generat ⁇ ing processes which are based on reductants other than those mentioned here, or on combinations of generating processes, for instance reduction with sulphur dioxide in a first stage followed by a second stage with chloride reduction, where- after sodium sulphate crystallizes out.
  • Figure 2 illustrates a preferred embodiment of the elec ⁇ trolysis cell 27, which is provided with an iron cathode 18, a platinated titanium electrode 19 and a unipolar cation selective membrane 20.
  • Hydrogen gas 21 is generated at the cathode and oxygen gas 22 is generated at the anode.
  • a solu ⁇ tion of sodium sulphate is delivered to the anode chamber through the line 23, and the acid formed is removed through the line 24. Pure water is supplied to the cathode chamber through the line 25, and the sodium hydroxide formed is re- moved through the line 26.
  • the chemical requirements of the sulphate mill can be covered by taking out flows from different points in the system, either separately or in com ⁇ bination.
  • a crystal mass of sodium sulphate can be taken out through the line 15 in order to cover the sodium and sulphur requirement of the pulp mill.
  • An acid, highly concentrated solution of sulphuric acid and sodium sulphate can be taken out through the line 30 for the production of tall oil.
  • a dilute solution of corresponding composition appropriate in those instances when the evaporation capacity is found avail ⁇ able in another location in the mill can be taken out through the line 32.

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  • Chemical & Material Sciences (AREA)
  • Inorganic Chemistry (AREA)
  • Organic Chemistry (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • General Life Sciences & Earth Sciences (AREA)
  • Geology (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)

Abstract

La production continue de dioxyde de chlore au moyen de la réduction de chlorate de sodium avec du dioxyde de soufre, de chlorure de sodium, du méthanol ou tout autre réducteur approprié nécessite des conditions de réaction acide. D'après l'invention, on maintient l'acidité, totalement ou partiellement, au moyen d'acide produit par l'électrolyse d'une solution de sulfate de sodium (Na2SO4 ou Na3H[SO4]2). On obtient ledit sulfate au moyen de la cristallisation et de la redissolution du sulfate de sodium produit par le processus de génération de dioxyde de chlore. L'électrolyse du sulfate de sodium est limitée pour des raisons d'efficacité, de façon qu'une partie seulement du sulfate est décomposée en acide, tandis que le résidu est recyclé avec l'acide vers le réacteur, où le dioxyde de chlore est produit. De l'hydroxyde de sodium, de l'oxygène gazeux et de l'hydrogène gazeux sont également constitués pendant le processus d'électrolyse et sont utilisés dans le processus de fabrication de pulpe.
PCT/SE1991/000605 1991-09-12 1991-09-12 Regulation de l'acidite dans la fabrication de dioxyde de chlore WO1993004979A1 (fr)

Priority Applications (4)

Application Number Priority Date Filing Date Title
CA002116427A CA2116427C (fr) 1991-09-12 1991-09-12 Regulation de l'acidite dans la fabrication du dioxyde de chlore
US08/204,357 US5423958A (en) 1991-09-12 1991-09-12 Acidity control in chlorine dioxide manufacture
PCT/SE1991/000605 WO1993004979A1 (fr) 1991-09-12 1991-09-12 Regulation de l'acidite dans la fabrication de dioxyde de chlore
FI941111A FI112351B (fi) 1991-09-12 1994-03-09 Happamuudensäätö klooridioksidin valmistuksessa

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
CA002116427A CA2116427C (fr) 1991-09-12 1991-09-12 Regulation de l'acidite dans la fabrication du dioxyde de chlore
PCT/SE1991/000605 WO1993004979A1 (fr) 1991-09-12 1991-09-12 Regulation de l'acidite dans la fabrication de dioxyde de chlore

Publications (1)

Publication Number Publication Date
WO1993004979A1 true WO1993004979A1 (fr) 1993-03-18

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Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO1995001466A1 (fr) * 1993-07-02 1995-01-12 Eka Nobel Ab Processus electrochimique
US5478446A (en) * 1993-07-02 1995-12-26 Eka Nobel Inc. Electrochemical process
CN109678116A (zh) * 2019-01-30 2019-04-26 广东至诚紫光新材料有限公司 用于污水处理的二氧化氯溶液及其制备方法、应用

Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4129484A (en) * 1976-05-11 1978-12-12 Kemanord Ab Process for regeneration of spent reaction solutions
US4678655A (en) * 1984-07-30 1987-07-07 Erco Industries Limited Acid recovery in clorine dioxide generation
EP0353367A1 (fr) * 1988-07-26 1990-02-07 Sterling Canada, Inc. Procédé et combiné de production de dioxyde de chlore et d'hydroxyde de sodium
WO1991018830A1 (fr) * 1990-06-07 1991-12-12 Sterling Canada, Inc. Production electrochimique de solutions acides de chlorate

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4129484A (en) * 1976-05-11 1978-12-12 Kemanord Ab Process for regeneration of spent reaction solutions
US4678655A (en) * 1984-07-30 1987-07-07 Erco Industries Limited Acid recovery in clorine dioxide generation
EP0353367A1 (fr) * 1988-07-26 1990-02-07 Sterling Canada, Inc. Procédé et combiné de production de dioxyde de chlore et d'hydroxyde de sodium
WO1991018830A1 (fr) * 1990-06-07 1991-12-12 Sterling Canada, Inc. Production electrochimique de solutions acides de chlorate

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO1995001466A1 (fr) * 1993-07-02 1995-01-12 Eka Nobel Ab Processus electrochimique
US5478446A (en) * 1993-07-02 1995-12-26 Eka Nobel Inc. Electrochemical process
CN109678116A (zh) * 2019-01-30 2019-04-26 广东至诚紫光新材料有限公司 用于污水处理的二氧化氯溶液及其制备方法、应用
CN109678116B (zh) * 2019-01-30 2022-05-27 广东至诚紫光新材料有限公司 用于污水处理的二氧化氯溶液及其制备方法、应用

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