CA2189289A1 - High purity chlorine dioxide production - Google Patents
High purity chlorine dioxide productionInfo
- Publication number
- CA2189289A1 CA2189289A1 CA 2189289 CA2189289A CA2189289A1 CA 2189289 A1 CA2189289 A1 CA 2189289A1 CA 2189289 CA2189289 CA 2189289 CA 2189289 A CA2189289 A CA 2189289A CA 2189289 A1 CA2189289 A1 CA 2189289A1
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- Prior art keywords
- chlorine dioxide
- aqueous solution
- chlorine
- sodium
- reaction zone
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Abstract
A chlorine dioxide generation operation wherein chlorine dioxide generated at high efficiency from sodium chlorate, hydrogen chloride, hydrogen peroxide and a suitable catalyst and such chlorine dioxide generation is integrated with a chlor-alkali cell or a chlorate cell to convert by-product sodium chloride from the chlorine dioxide generating process into useful chemicals.
Description
21 8928~
HIGH PURITY CHLORINE DIOXIDE PRODUCTION
The present invention relates to the production of chlorine dioxide, a chemical used in the bleaching of woodpulp.
Chlorine dioxide is produced commercially by the reduction of chlorate in an aqueous acid medium. Many such processes are effected at the boiling point of the reaction medium while a subatmospheric pressure is applied thereto.
The process may be depicted by the equation:
Cl03- + Cl- + 2H+ ~ ClO2 + ~Cl2 + H2O
The acid may be provided by a mineral acid, generally sulfuric acid. Hydrochloric acid also may be employed, which coincidentally provides the chloride ions.
The chloride ions may be added to the reaction medium in the form of the alkali metal chloride or may be produced in situ when the reducing agent is methanol, hydrogen peroxide or sulfur dioxide.
Other known chlorine dioxide generating processes include ones involving the reduction of chloric acid, such as by reaction with methanol or hydrogen peroxide, by electrochemical means or by catalytic decomposition.
The present invention provides an improved process of producing chlorine dioxide in which chlorine dioxide of high purity is produced. In the process of the present invention, sodium chlorate, hydrochloric acid or hydrogen chloride and hydrogen peroxide reactants are used to produce high purity chlorine dioxide and by-product sodium chloride. The sodium chloride by-product then is forwarded either to a chlor-alkali plant or a chlorate plant to form reactants for the process.
A chlor-alkali plant produces from the forwarded sodium chloride, aqueous sodium hydroxide by-product, chlorine and hydrogen, which then can be burned together to form HCl for the chlorine dioxide generating process.
In this embodiment of the invention, chlorine dioxide and sodium hydroxide products are formed from sodium chlorate and hydrogen peroxide.
A sodium chlorate plant produces sodium chlorate from the forwarded sodium chloride, which is circulated back to the chlorine dioxide generator to provide the sodium chlorate feed thereto. In this embodiment of the invention, chlorine dioxide and hydrogen are produced from feeds of HCl and hydrogen peroxide. The hydrogen may be burned to form water.
Accordingly, in one aspect of the present invention, there is provided a process for the preparation of an aqueous solution of chlorine dioxide of high purity, which comprises:
feeding sodium chlorate, hydrogen chloride and hydrogen peroxide to a reaction zone wherein chlorine dioxide is formed by reduction of chlorate ions in an aqueous acid reaction medium, the chlorine dioxide is formed into an aqueous solution thereof of high purity, chlorine potentially contaminating said aqueous solution of chlorine dioxide is at least partially reduced by said hydrogen peroxide and crystalline sodium chloride is formed, removing said aqueous solution of chlorine dioxide from said reaction zone, removing said crystalline sodium chloride from said reaction zone and forming an aqueous solution of said removed crystalline sodium chloride, subjecting the resulting aqueous solution of sodium chloride to an electrolysis process operation to form either:
(a) sodium hydroxide and hydrogen chloride, in which event, recycling the hydrogen chloride to said reaction zone to provide hydrogen chloride feed thereto and recovering the sodium hydroxide, or:
(b) sodium chlorate and hydrogen, in which event, recycling the sodium chlorate to said reaction zone to provide sodium chlorate feed thereto.
In one embodiment of the invention, the chlorine dioxide may be formed and the potentially contaminating chlorine may be reduced by the steps of feeding sodium chlorate, hydrogen chloride and hydrogen peroxide to an aqueous acid reaction medium to produce chlorine dioxide therefrom substantially uncontaminated by chlorine and dissolving the chlorine dioxide so formed in water to provide the aqueous solution of chlorine dioxide. The aqueous solution of chlorine dioxide may be further contacted with hydrogen peroxide to reduce any chlorine dissolved therein.
In this embodiment, the aqueous acid reaction medium may be contained in a reaction vessel in the reaction zone which reaction vessel is maintained at an atmospheric pressure, the chlorine dioxide is removed from the reaction vessel in admixture with an inert gas, and the crystalline sodium chloride is formed by evaporation of spent aqueous acid reaction zone in a second vessel in the reaction zone. However, as noted below, it is preferred to maintain the aqueous acid reaction medium at its boiling point while the reaction vessel is maintained under a subatmospheric pressure, so that the chlorine dioxide is removed from the reaction vessel in admixture with steam as the inert gas and the sodium chloride is crystallized in the reaction vessel, after saturation of the aqueous acid reaction medium following start up.
In another embodiment of the invention, the chlorine dioxide is formed and the potentially contaminating chlorine is reduced by the steps of feeding the sodium chlorate and hydrogen chloride to an aqueous acid reaction medium to produce a gaseous admixture of chlorine dioxide and chlorine therefrom, selectively 2 1 8928~
dissolving chlorine dioxide from the gaseous admixture to form an aqueous solution of the chlorine dioxide contained in the gaseous mixture contaminated by codissolved chlorine and residual chlorine gas, contacting the aqueous solution of chlorine dioxide contaminated with codissolved chlorine with hydrogen peroxide to reduce the codissolved chlorine, and reacting the residual chlorine gas with hydrogen to form hydrogen chloride, which is recycled to the aqueous acid reaction medium to provide hydrogen chloride feed thereto.
In order to obtain a high efficiency of chlorine dioxide production in the chlorine dioxide generation step and thereby ensure a high purity of chlorine dioxide, preferably greater than about 95% pure with the balance being essentially chlorine, the molar ratio of the concentration of chlorate ions to chloride ions in the reaction medium needs to be maintained as high as possible. This ratio, may be maximized by adding agents depressing the solubility of NaCl, for example, highly soluble, inert sodium salts, such as sodium nitrate or sodium perchlorate.
In one preferred embodiment of the present invention, there is provided a process for the production of chlorine dioxide, which comprises:
feeding sodium chlorate, hydrogen chloride and hydrogen peroxide to an aqueous and reaction medium in a reaction zone to produce chlorine dioxide from the reaction medium, maintaining the aqueous acid reaction medium at its boiling point while a subatmospheric pressure is applied to the reaction zone, removing chlorine dioxide from the reaction zone in admixture with steam while precipitating sodium chloride from the aqueous and reaction medium in the reaction zone, following saturation after start-up, and removing the precipitated sodium chloride from the reaction zone and forming the removed sodium chloride into an aqueous solution thereof.
In this preferred embodiment, the resulting aqueous solution of sodium chloride then is subjected to an electrolysis process. Such electrolysis process may convert such aqueous solution to sodium hydroxide, hydrogen or chlorine so produced, in which event, the hydrogen and chlorine so produced are reacted together to produce hydrogen chloride, the hydrogen chloride is recycled to the chlorine dioxide generating reaction zone to provide hydrogen chloride feed thereto and the sodium chloride is recovered. Alternatively, sodium chloride may be converted directly to hydrogen chloride and sodium hydroxide by employing an electrodialysis stack equipped with bipolar membranes.
Alternatively, the aqueous solution of sodium chloride may be electrolyzed to form sodium chlorate and hydrogen, in which event, the sodium chlorate is recycled to the chlorine dioxide generating reaction zone to provide sodium chlorate feed thereto. The by-product hydrogen may be burned to form water.
A catalyst can be used to further improve the purity of the product produced in this preferred embodiment of the invention. Such catalyst may comprise palladium compounds, for example, palladium (II) chloride, and complexes, particularly palladium coordinated with ligands, including a combination of palladium (II) with an amlno acid or an alkali metal salt thereof (as described in USP 4,154,810), palladium (II) with ~-diketone (as described in USP 4,051,229) or palladium (II) with chloride ion (as described in USP 4,178,356).
Generally, the molar ratio of HCl to H202 in the feed required to produce a given product purity is dependent on the reaction efficiency in generating chlorine dioxide. As illustrated graphically in Figure 1, the 21 8928~
lower the efficiency of chlorine dioxide production, the more H2O2 relative to HCl has to be fed in order to achieve the desired product purity. It is preferred to operate at high levels of efficiency of chlorine dioxide production to minimize the hydrogen peroxide requirement.
While the above-described invention is preferably carried out at subatmospheric pressure, it is possible to employ similar chemistry at atmospheric pressure.
In the following description, reference is made to the accompanying drawings, in which:
Figure 1 is a graphical representation of the relationship of chlorine dioxide generation efficiency to the molar ratio of HCl/H2O2 in the feed to the chlorine dioxide generating process for various chlorine dioxide product gas purities;
Figure 2 is a schematic flow sheet of a chlorine dioxide generating process provided in accordance with one embodiment pf the present invention;
Figure 3 is a schematic flow sheet of a chlorine dioxide generating process provided in accordance with another embodiment of the invention; and Figures 4 and 5 are schematic flow sheets of chlorine dioxide generating processes provided in accordance with additional embodiments of the invention, illustrating an alternative location of introduction of hydrogen peroxide to that illustrated in Figures 2 and 3 respectively.
Referring first to Figure 2, there is illustrated therein integration of chlorine dioxide generation into a caustic-chlorine cell. As seen therein, a chlorine dioxide generator 10 produces chlorine dioxide slightly contaminated with chlorine and crystalline sodium chloride, which.is removed by line 14. Chlorine dioxide is formed in gaseous admixture with oxygen and steam and is formed into an aqueous solution thereof. The chlorine dioxide is produced from an aqueous acid solution of sodium chlorate to which is fed hydrogen chloride, hydrogen peroxide and sodium chlorate by lines 15, 16 and 18 respectively. A premixing of hydrogen peroxide with at least one other feedstock prior to feed to the chlorine dioxide generator 10 is also possible. Steam is also added by line 20 to maintain the required reaction temperature. The aqueous acid reaction medium contained in the chlorine dioxide generator 10 is maintained at its boiling point under subatmospheric pressure.
Alternatively, the process may be effected at atmospheric pressure.
The reaction medium may be maintained at a temperature of about 40~ to about 80~C, preferably about 60~ to about 80~C, while a subatmospheric pressure of about 80 to about 300 mm Hg, preferably about 150 to about 240 mm Hg, is applied to the chlorine dioxide generator.
The reactants are fed by lines 15, 16 and 18 as required to maintain steady state conditions of production of chlorine dioxide in the chlorine dioxide generator 10 and a catalyst may be present in the reaction medium in the chlorine dioxide generator 10 to assist in achieving a high level of purity of chlorine dioxide product, preferably about 95% or greater, in line 12. The chlorine dioxide reaction generally is carried out to achieve a purity of chlorine dioxide in the product gas of at least about 95%. The purity of chlorine dioxide produced is determined by the efficiency of the chlorine dioxide producing reaction and by the molar ratio of HCl to H2O2 fed to the chlorine dioxide generator 10. As may be seen from Figure 1, the lower the efficiency of chlorine dioxide production, the more H2O2 relative to HCl is required to achieve a desired level of purity.
In general, the efficiency chlorine dioxide production is at least about 90%, preferably at least 21 8928~
about 95% and molar ratios of HCl:H202 of about 1:1 to about 3:1, preferably about 1.5:1 to about 2.5:1 may be employed. In general, the efficiency of generation of chlorine dioxide is higher for higher mole ratios of chlorate ions to chloride ions in the aqueous acid reaction medium in the chlorine dioxide generator. The efficiency of generation of chlorine dioxide from the reaction medium in the chlorine dioxide generator 10 may be further improved by the addition of a suitable catalyst, including palladium compounds and complexes.
When added, such catalyst may be present in the aqueous acid reaction medium in an amount of about 1 mg/L to about 40 mg/L, preferably about 5 mg/L to about 15 mg/L, based on Pd++ ions concentration.
The aqueous acid reaction medium in the chlorine dioxide generator 10 generally has a sodium chlorate concentration of about 1 to about 7 M, preferably about 5 to about 7 M, maintained by the feed of aqueous sodium chlorate in line 18, which may have a sodium chlorate concentration of about 4 to about 8 M, preferably about 5 to about 7 M.
The aqueous acid reaction medium in the chlorine dioxide generator 10 may have, in the absence of buffering ions, a total acid normality of about 0.01 to about 2 N, preferably about 0.05 to about 0.15 N, maintained by the feed of hydrogen chloride by line 14, which generally is in the form of hydrochloric acid having a total acid normality of about 5 to about 12 N, preferably about 9 to about 12 N.
As indicated above, higher molar ratios of chlorate ions to chloride ions in the aqueous acid reaction medium provide higher efficiencies of chlorine dioxide production, which assists in providing high levels of purity of chlorine dioxide produced by the process. In general, the molar ratio of C103-:Cl- may range from about 1:5 to about 7:1, preferably about 4:1 to about 7:1.
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The hydrogen peroxide is fed to the chlorine dioxide generator 10 generally as an aqueous solution thereof, generally having concentration of about 10 to about 75 wt%, preferably about 30 to about 50 wt%. Additional hydrogen peroxide may optionally be added to the product chlorine dioxide stream in line 12 through line 38 to improve the purity of the chlorine dioxide product, by reducing contaminating chlorine contained therein.
The presence of the sodium ions and chloride ions in the reaction medium causes the formation of sodium chloride as a by-product of the chlorine dioxide generating process. The sodium chloride saturates the aqueous acid reaction medium after initial start-up and crystallizes from the reaction medium. The crystalline sodium chloride is removed from the generator 10 by line 14 generally by filtration from the aqueous acid reaction medium.
The reactions occurring in the chlorine dioxide generator 10 may be depicted by the equations:
NaCl03 + 2HCl ~ Cl02 + ~Cl2 + NaCl + H20 Cl2 + H202 ~ 2HCl + ~2 The oxygen resulting from the in-situ reduction of chlorine is vented from the generator 10 with the chlorine dioxide stream in line 12. The chlorine dioxide in the product stream in line 12 generally is formed into an aqueous solution thereof for utilization in bleaching operations and thereby is separated from the oxygen contained therein.
The crystalline sodium chloride in line 14 is forwarded to chlor-alkali cell 22, generally after formation into an aqueous solution thereof of concentration about 2 to about 5 M, preferably about 4 to about 5 M. Some make up sodium chloride may be fed by line 24 to the sodium chloride feed to the chlor-alkali cell 22. The chlor-alkali cell 22 may be of conventional two-compartment cell configuration divided, for example, 21 ~d9289 by a cation exchange membrane or a diaphragm, in which the aqueous sodium chloride is fed to the anode compartment while an aqueous electrolyte, generally sodium hydroxide, is circulated through the cathode compartment. Water may be added to the cathode compartment.
The solutions are electrolyzed by the application of electrical power by line 26 to the anode and cathode of the chlor-alkali cell 22 resulting in the formation of an aqueous sodium hydroxide solution, which is removed by line 28, chlorine and hydrogen, which are removed by line 30 and 32 respectively. Generally, about 2200 kWhrs of power is used for the electrolysis to produce 1 tonne of sodium hydroxide (100% basis). Sodium hydroxide concentration in the product solution is generally about 5% to about 50%, preferably about 30% to about 35%. The electrolysis may be effected at a temperature of about 80~ to about 100~C, preferably about 85~ to about 95~C.
The reactions occurring in the chlor-alkali cell 22 can be depicted by the equation:
NaCl + H2O ~ NaOH + ~C12 + ~H2 The gaseous by-product chlorine and hydrogen may be forwarded by lines 30 and 32 to a hydrogen chloride burner 34 in which the hydrogen and chlorine are reacted to form hydrogen chloride, which then is recycled to the chlorine dioxide generator 10 by line 15. As an alternative to the addition of sodium chloride by line 24, an additional quantity of hydrogen chloride or hydrochloric acid may be fed by line 36.
By integrating the chlorine dioxide generator 10 with the chlor-alkali cell 22 and by balancing the various reactant feeds, high purity chlorine dioxide is produced, substantially uncontaminated with by-product chlorine, by reduction with a mixture of hydrogen chloride and hydrogen peroxide while by-product sodium chloride from the chlorine dioxide generating process is 21 892~9 used to form the hydrogen chloride utilized in the chlorine dioxide generating process and by-product sodium hydroxide, a chemical useful in the bleaching process of the pulp mill.
Turning now to consideration of Figure 3, this embodiment of the invention shows integration of the chlorine dioxide generator 10 with a chlorate cell 40.
The chlorine dioxide generator 10 operates in the manner and under the conditions generally described above with respect to Figure 2 and hence this description will not be repeated but rather is incorporated by reference thereto.
The crystalline sodium chloride in line 14 is made up into an aqueous solution of sodium chloride, which may have a concentration of about 2 to about 5 M, preferably about 4 to about 5 M. The sodium chlorate plant 40 may be any conventional sodium chlorate plant comprising a plurality of undivided cells in which sodium chlorate is formed electrolytically by the application of electrical power by line 42. Generally, 5000 kWhrs of power per tonne of NaClO3 is used for the electrolysis to form an aqueous solution of sodium chlorate concentration about 3 to about 6.5 M, preferably about 4.5 to about 6 M. The electrolysis may be effected at a temperature of about 60~ to about 100~C, preferably about 75~ to about 85~C.
The reaction occurring in the sodium chlorate plant 40 can be depicted by the equation:
NaCl + 3H2O ~ NaClO3 + 3H2 The hydrogen produced according to this equation is vented from the sodium chlorate plant 40 by line 44 and may be burned with air or oxygen to form water for the process.
The electrolysis in the chlorate plant 40 produces an aqueous solution of sodium chlorate and sodium chloride (cell liquor) which is passed by line 46 to a sodium chlorate crystallizer 48, wherein sodium chlorate is crystallized from the cell liquor by any convenient procedure. The mother liquor, from the crystallization, which may contain sodium chlorate in an amount of about 4 to about 7 M, preferably about 5 to about 6 M, and sodium chloride in an amount of about 1.5 to about 3 M, is recycled by line 50 to the sodium chlorate plant 40.
The sodium chlorate crystallized in the crystallizer 48 is recycled to the chlorine dioxide generator 10, after formation into an aqueous solution thereof of concentration as described above with respect to Figure 3.
By integrating the chlorine dioxide generator 10 with the sodium chlorate plant 40 and by balancing the various reactant feeds, high purity chlorine dioxide is produced, substantially uncontaminated with by-product chlorine, by reduction with a mixture of hydrogen chloride and hydrogen peroxide while by-product sodium chloride from the chlorine dioxide generating process is used to form sodium chlorate reactant for the chlorine dioxide generating process. Similarly, as in the case of Figure 2, hydrogen peroxide may optionally be added through line 52 to the product in order to improve the chlorine dioxide purity.
Figures 4 and 5 correspond to Figures 2 and 3 respectively but contain a modification related the addition point of H2O2. In these cases, hydrogen peroxide is added to the chlorine dioxide product rather than to the chlorine dioxide generator. In this modified process, chlorine is produced in significant quantities from the chlorine dioxide generating reaction medium and, upon selective dissolution of chlorine dioxide with water, an aqueous solution of chlorine dioxide with chlorine codissolved therein is formed in line 12.
Addition of hydrogen peroxide to the chlorine dioxide solution, following condensation of the steam and formation of the aqueous solution of chlorine dioxide, 21 8928~
results in reduction of the codissolved chlorine to provide high purity chlorine dioxide. This modified process leads to minimization of hydrogen peroxide consumption by the overall chlorine dioxide generating process while allowing a highly pure product to be obtained. A possible drawback of the modification shown in Figures 4 and 5 is the loss of the part of HCl values generated in the reaction between chlorine and hydrogen peroxide.
In the embodiment of Figure 4, the same reference numbers as are employed in Figure 2 are employed to designate the same elements. In this case, hydrogen peroxide is added by line 38 to the chlorine dioxide product stream in line 12 to remove chlorine contained therein by reduction. By-product chlorine, coproduced with chlorine dioxide in the chlorine generator 10, is forwarded by line 54 to the chlorine feed line 30 to the HCl burner 34.
Similarly, in the embodiment of Figure 5, the same reference numerals as are employed in Figure 3 are employed to designate the same elements. In this case, hydrogen peroxide is added by line 52 to the chlorine dioxide product stream in line 12 to remove chlorine contained therein by reduction. By-product chlorine, 2 5 coproduced with chlorine dioxide in the chlorine dioxide generator 10, is forwarded by line 56 to an HCl burner 58, for reaction therein with hydrogen produced by the sodium chlorate plant 40 and forwarded by line 60.
Reaction of hydrogen and chlorine in the HCl burner 58 produces HCl, which is recycled by line 62 to the HCl feed line 15. In this embodiment of the invention, the sodium chlorate crystallizer 48 is optional.
In summary of this disclosure, the present invention provides a novel procedure for the production of high purity chlorine dioxide using hydrogen peroxide and hydrogen chloride which produces only useful by-products.
Modifications are possible within the scope of the invention.
HIGH PURITY CHLORINE DIOXIDE PRODUCTION
The present invention relates to the production of chlorine dioxide, a chemical used in the bleaching of woodpulp.
Chlorine dioxide is produced commercially by the reduction of chlorate in an aqueous acid medium. Many such processes are effected at the boiling point of the reaction medium while a subatmospheric pressure is applied thereto.
The process may be depicted by the equation:
Cl03- + Cl- + 2H+ ~ ClO2 + ~Cl2 + H2O
The acid may be provided by a mineral acid, generally sulfuric acid. Hydrochloric acid also may be employed, which coincidentally provides the chloride ions.
The chloride ions may be added to the reaction medium in the form of the alkali metal chloride or may be produced in situ when the reducing agent is methanol, hydrogen peroxide or sulfur dioxide.
Other known chlorine dioxide generating processes include ones involving the reduction of chloric acid, such as by reaction with methanol or hydrogen peroxide, by electrochemical means or by catalytic decomposition.
The present invention provides an improved process of producing chlorine dioxide in which chlorine dioxide of high purity is produced. In the process of the present invention, sodium chlorate, hydrochloric acid or hydrogen chloride and hydrogen peroxide reactants are used to produce high purity chlorine dioxide and by-product sodium chloride. The sodium chloride by-product then is forwarded either to a chlor-alkali plant or a chlorate plant to form reactants for the process.
A chlor-alkali plant produces from the forwarded sodium chloride, aqueous sodium hydroxide by-product, chlorine and hydrogen, which then can be burned together to form HCl for the chlorine dioxide generating process.
In this embodiment of the invention, chlorine dioxide and sodium hydroxide products are formed from sodium chlorate and hydrogen peroxide.
A sodium chlorate plant produces sodium chlorate from the forwarded sodium chloride, which is circulated back to the chlorine dioxide generator to provide the sodium chlorate feed thereto. In this embodiment of the invention, chlorine dioxide and hydrogen are produced from feeds of HCl and hydrogen peroxide. The hydrogen may be burned to form water.
Accordingly, in one aspect of the present invention, there is provided a process for the preparation of an aqueous solution of chlorine dioxide of high purity, which comprises:
feeding sodium chlorate, hydrogen chloride and hydrogen peroxide to a reaction zone wherein chlorine dioxide is formed by reduction of chlorate ions in an aqueous acid reaction medium, the chlorine dioxide is formed into an aqueous solution thereof of high purity, chlorine potentially contaminating said aqueous solution of chlorine dioxide is at least partially reduced by said hydrogen peroxide and crystalline sodium chloride is formed, removing said aqueous solution of chlorine dioxide from said reaction zone, removing said crystalline sodium chloride from said reaction zone and forming an aqueous solution of said removed crystalline sodium chloride, subjecting the resulting aqueous solution of sodium chloride to an electrolysis process operation to form either:
(a) sodium hydroxide and hydrogen chloride, in which event, recycling the hydrogen chloride to said reaction zone to provide hydrogen chloride feed thereto and recovering the sodium hydroxide, or:
(b) sodium chlorate and hydrogen, in which event, recycling the sodium chlorate to said reaction zone to provide sodium chlorate feed thereto.
In one embodiment of the invention, the chlorine dioxide may be formed and the potentially contaminating chlorine may be reduced by the steps of feeding sodium chlorate, hydrogen chloride and hydrogen peroxide to an aqueous acid reaction medium to produce chlorine dioxide therefrom substantially uncontaminated by chlorine and dissolving the chlorine dioxide so formed in water to provide the aqueous solution of chlorine dioxide. The aqueous solution of chlorine dioxide may be further contacted with hydrogen peroxide to reduce any chlorine dissolved therein.
In this embodiment, the aqueous acid reaction medium may be contained in a reaction vessel in the reaction zone which reaction vessel is maintained at an atmospheric pressure, the chlorine dioxide is removed from the reaction vessel in admixture with an inert gas, and the crystalline sodium chloride is formed by evaporation of spent aqueous acid reaction zone in a second vessel in the reaction zone. However, as noted below, it is preferred to maintain the aqueous acid reaction medium at its boiling point while the reaction vessel is maintained under a subatmospheric pressure, so that the chlorine dioxide is removed from the reaction vessel in admixture with steam as the inert gas and the sodium chloride is crystallized in the reaction vessel, after saturation of the aqueous acid reaction medium following start up.
In another embodiment of the invention, the chlorine dioxide is formed and the potentially contaminating chlorine is reduced by the steps of feeding the sodium chlorate and hydrogen chloride to an aqueous acid reaction medium to produce a gaseous admixture of chlorine dioxide and chlorine therefrom, selectively 2 1 8928~
dissolving chlorine dioxide from the gaseous admixture to form an aqueous solution of the chlorine dioxide contained in the gaseous mixture contaminated by codissolved chlorine and residual chlorine gas, contacting the aqueous solution of chlorine dioxide contaminated with codissolved chlorine with hydrogen peroxide to reduce the codissolved chlorine, and reacting the residual chlorine gas with hydrogen to form hydrogen chloride, which is recycled to the aqueous acid reaction medium to provide hydrogen chloride feed thereto.
In order to obtain a high efficiency of chlorine dioxide production in the chlorine dioxide generation step and thereby ensure a high purity of chlorine dioxide, preferably greater than about 95% pure with the balance being essentially chlorine, the molar ratio of the concentration of chlorate ions to chloride ions in the reaction medium needs to be maintained as high as possible. This ratio, may be maximized by adding agents depressing the solubility of NaCl, for example, highly soluble, inert sodium salts, such as sodium nitrate or sodium perchlorate.
In one preferred embodiment of the present invention, there is provided a process for the production of chlorine dioxide, which comprises:
feeding sodium chlorate, hydrogen chloride and hydrogen peroxide to an aqueous and reaction medium in a reaction zone to produce chlorine dioxide from the reaction medium, maintaining the aqueous acid reaction medium at its boiling point while a subatmospheric pressure is applied to the reaction zone, removing chlorine dioxide from the reaction zone in admixture with steam while precipitating sodium chloride from the aqueous and reaction medium in the reaction zone, following saturation after start-up, and removing the precipitated sodium chloride from the reaction zone and forming the removed sodium chloride into an aqueous solution thereof.
In this preferred embodiment, the resulting aqueous solution of sodium chloride then is subjected to an electrolysis process. Such electrolysis process may convert such aqueous solution to sodium hydroxide, hydrogen or chlorine so produced, in which event, the hydrogen and chlorine so produced are reacted together to produce hydrogen chloride, the hydrogen chloride is recycled to the chlorine dioxide generating reaction zone to provide hydrogen chloride feed thereto and the sodium chloride is recovered. Alternatively, sodium chloride may be converted directly to hydrogen chloride and sodium hydroxide by employing an electrodialysis stack equipped with bipolar membranes.
Alternatively, the aqueous solution of sodium chloride may be electrolyzed to form sodium chlorate and hydrogen, in which event, the sodium chlorate is recycled to the chlorine dioxide generating reaction zone to provide sodium chlorate feed thereto. The by-product hydrogen may be burned to form water.
A catalyst can be used to further improve the purity of the product produced in this preferred embodiment of the invention. Such catalyst may comprise palladium compounds, for example, palladium (II) chloride, and complexes, particularly palladium coordinated with ligands, including a combination of palladium (II) with an amlno acid or an alkali metal salt thereof (as described in USP 4,154,810), palladium (II) with ~-diketone (as described in USP 4,051,229) or palladium (II) with chloride ion (as described in USP 4,178,356).
Generally, the molar ratio of HCl to H202 in the feed required to produce a given product purity is dependent on the reaction efficiency in generating chlorine dioxide. As illustrated graphically in Figure 1, the 21 8928~
lower the efficiency of chlorine dioxide production, the more H2O2 relative to HCl has to be fed in order to achieve the desired product purity. It is preferred to operate at high levels of efficiency of chlorine dioxide production to minimize the hydrogen peroxide requirement.
While the above-described invention is preferably carried out at subatmospheric pressure, it is possible to employ similar chemistry at atmospheric pressure.
In the following description, reference is made to the accompanying drawings, in which:
Figure 1 is a graphical representation of the relationship of chlorine dioxide generation efficiency to the molar ratio of HCl/H2O2 in the feed to the chlorine dioxide generating process for various chlorine dioxide product gas purities;
Figure 2 is a schematic flow sheet of a chlorine dioxide generating process provided in accordance with one embodiment pf the present invention;
Figure 3 is a schematic flow sheet of a chlorine dioxide generating process provided in accordance with another embodiment of the invention; and Figures 4 and 5 are schematic flow sheets of chlorine dioxide generating processes provided in accordance with additional embodiments of the invention, illustrating an alternative location of introduction of hydrogen peroxide to that illustrated in Figures 2 and 3 respectively.
Referring first to Figure 2, there is illustrated therein integration of chlorine dioxide generation into a caustic-chlorine cell. As seen therein, a chlorine dioxide generator 10 produces chlorine dioxide slightly contaminated with chlorine and crystalline sodium chloride, which.is removed by line 14. Chlorine dioxide is formed in gaseous admixture with oxygen and steam and is formed into an aqueous solution thereof. The chlorine dioxide is produced from an aqueous acid solution of sodium chlorate to which is fed hydrogen chloride, hydrogen peroxide and sodium chlorate by lines 15, 16 and 18 respectively. A premixing of hydrogen peroxide with at least one other feedstock prior to feed to the chlorine dioxide generator 10 is also possible. Steam is also added by line 20 to maintain the required reaction temperature. The aqueous acid reaction medium contained in the chlorine dioxide generator 10 is maintained at its boiling point under subatmospheric pressure.
Alternatively, the process may be effected at atmospheric pressure.
The reaction medium may be maintained at a temperature of about 40~ to about 80~C, preferably about 60~ to about 80~C, while a subatmospheric pressure of about 80 to about 300 mm Hg, preferably about 150 to about 240 mm Hg, is applied to the chlorine dioxide generator.
The reactants are fed by lines 15, 16 and 18 as required to maintain steady state conditions of production of chlorine dioxide in the chlorine dioxide generator 10 and a catalyst may be present in the reaction medium in the chlorine dioxide generator 10 to assist in achieving a high level of purity of chlorine dioxide product, preferably about 95% or greater, in line 12. The chlorine dioxide reaction generally is carried out to achieve a purity of chlorine dioxide in the product gas of at least about 95%. The purity of chlorine dioxide produced is determined by the efficiency of the chlorine dioxide producing reaction and by the molar ratio of HCl to H2O2 fed to the chlorine dioxide generator 10. As may be seen from Figure 1, the lower the efficiency of chlorine dioxide production, the more H2O2 relative to HCl is required to achieve a desired level of purity.
In general, the efficiency chlorine dioxide production is at least about 90%, preferably at least 21 8928~
about 95% and molar ratios of HCl:H202 of about 1:1 to about 3:1, preferably about 1.5:1 to about 2.5:1 may be employed. In general, the efficiency of generation of chlorine dioxide is higher for higher mole ratios of chlorate ions to chloride ions in the aqueous acid reaction medium in the chlorine dioxide generator. The efficiency of generation of chlorine dioxide from the reaction medium in the chlorine dioxide generator 10 may be further improved by the addition of a suitable catalyst, including palladium compounds and complexes.
When added, such catalyst may be present in the aqueous acid reaction medium in an amount of about 1 mg/L to about 40 mg/L, preferably about 5 mg/L to about 15 mg/L, based on Pd++ ions concentration.
The aqueous acid reaction medium in the chlorine dioxide generator 10 generally has a sodium chlorate concentration of about 1 to about 7 M, preferably about 5 to about 7 M, maintained by the feed of aqueous sodium chlorate in line 18, which may have a sodium chlorate concentration of about 4 to about 8 M, preferably about 5 to about 7 M.
The aqueous acid reaction medium in the chlorine dioxide generator 10 may have, in the absence of buffering ions, a total acid normality of about 0.01 to about 2 N, preferably about 0.05 to about 0.15 N, maintained by the feed of hydrogen chloride by line 14, which generally is in the form of hydrochloric acid having a total acid normality of about 5 to about 12 N, preferably about 9 to about 12 N.
As indicated above, higher molar ratios of chlorate ions to chloride ions in the aqueous acid reaction medium provide higher efficiencies of chlorine dioxide production, which assists in providing high levels of purity of chlorine dioxide produced by the process. In general, the molar ratio of C103-:Cl- may range from about 1:5 to about 7:1, preferably about 4:1 to about 7:1.
21 8~28~
The hydrogen peroxide is fed to the chlorine dioxide generator 10 generally as an aqueous solution thereof, generally having concentration of about 10 to about 75 wt%, preferably about 30 to about 50 wt%. Additional hydrogen peroxide may optionally be added to the product chlorine dioxide stream in line 12 through line 38 to improve the purity of the chlorine dioxide product, by reducing contaminating chlorine contained therein.
The presence of the sodium ions and chloride ions in the reaction medium causes the formation of sodium chloride as a by-product of the chlorine dioxide generating process. The sodium chloride saturates the aqueous acid reaction medium after initial start-up and crystallizes from the reaction medium. The crystalline sodium chloride is removed from the generator 10 by line 14 generally by filtration from the aqueous acid reaction medium.
The reactions occurring in the chlorine dioxide generator 10 may be depicted by the equations:
NaCl03 + 2HCl ~ Cl02 + ~Cl2 + NaCl + H20 Cl2 + H202 ~ 2HCl + ~2 The oxygen resulting from the in-situ reduction of chlorine is vented from the generator 10 with the chlorine dioxide stream in line 12. The chlorine dioxide in the product stream in line 12 generally is formed into an aqueous solution thereof for utilization in bleaching operations and thereby is separated from the oxygen contained therein.
The crystalline sodium chloride in line 14 is forwarded to chlor-alkali cell 22, generally after formation into an aqueous solution thereof of concentration about 2 to about 5 M, preferably about 4 to about 5 M. Some make up sodium chloride may be fed by line 24 to the sodium chloride feed to the chlor-alkali cell 22. The chlor-alkali cell 22 may be of conventional two-compartment cell configuration divided, for example, 21 ~d9289 by a cation exchange membrane or a diaphragm, in which the aqueous sodium chloride is fed to the anode compartment while an aqueous electrolyte, generally sodium hydroxide, is circulated through the cathode compartment. Water may be added to the cathode compartment.
The solutions are electrolyzed by the application of electrical power by line 26 to the anode and cathode of the chlor-alkali cell 22 resulting in the formation of an aqueous sodium hydroxide solution, which is removed by line 28, chlorine and hydrogen, which are removed by line 30 and 32 respectively. Generally, about 2200 kWhrs of power is used for the electrolysis to produce 1 tonne of sodium hydroxide (100% basis). Sodium hydroxide concentration in the product solution is generally about 5% to about 50%, preferably about 30% to about 35%. The electrolysis may be effected at a temperature of about 80~ to about 100~C, preferably about 85~ to about 95~C.
The reactions occurring in the chlor-alkali cell 22 can be depicted by the equation:
NaCl + H2O ~ NaOH + ~C12 + ~H2 The gaseous by-product chlorine and hydrogen may be forwarded by lines 30 and 32 to a hydrogen chloride burner 34 in which the hydrogen and chlorine are reacted to form hydrogen chloride, which then is recycled to the chlorine dioxide generator 10 by line 15. As an alternative to the addition of sodium chloride by line 24, an additional quantity of hydrogen chloride or hydrochloric acid may be fed by line 36.
By integrating the chlorine dioxide generator 10 with the chlor-alkali cell 22 and by balancing the various reactant feeds, high purity chlorine dioxide is produced, substantially uncontaminated with by-product chlorine, by reduction with a mixture of hydrogen chloride and hydrogen peroxide while by-product sodium chloride from the chlorine dioxide generating process is 21 892~9 used to form the hydrogen chloride utilized in the chlorine dioxide generating process and by-product sodium hydroxide, a chemical useful in the bleaching process of the pulp mill.
Turning now to consideration of Figure 3, this embodiment of the invention shows integration of the chlorine dioxide generator 10 with a chlorate cell 40.
The chlorine dioxide generator 10 operates in the manner and under the conditions generally described above with respect to Figure 2 and hence this description will not be repeated but rather is incorporated by reference thereto.
The crystalline sodium chloride in line 14 is made up into an aqueous solution of sodium chloride, which may have a concentration of about 2 to about 5 M, preferably about 4 to about 5 M. The sodium chlorate plant 40 may be any conventional sodium chlorate plant comprising a plurality of undivided cells in which sodium chlorate is formed electrolytically by the application of electrical power by line 42. Generally, 5000 kWhrs of power per tonne of NaClO3 is used for the electrolysis to form an aqueous solution of sodium chlorate concentration about 3 to about 6.5 M, preferably about 4.5 to about 6 M. The electrolysis may be effected at a temperature of about 60~ to about 100~C, preferably about 75~ to about 85~C.
The reaction occurring in the sodium chlorate plant 40 can be depicted by the equation:
NaCl + 3H2O ~ NaClO3 + 3H2 The hydrogen produced according to this equation is vented from the sodium chlorate plant 40 by line 44 and may be burned with air or oxygen to form water for the process.
The electrolysis in the chlorate plant 40 produces an aqueous solution of sodium chlorate and sodium chloride (cell liquor) which is passed by line 46 to a sodium chlorate crystallizer 48, wherein sodium chlorate is crystallized from the cell liquor by any convenient procedure. The mother liquor, from the crystallization, which may contain sodium chlorate in an amount of about 4 to about 7 M, preferably about 5 to about 6 M, and sodium chloride in an amount of about 1.5 to about 3 M, is recycled by line 50 to the sodium chlorate plant 40.
The sodium chlorate crystallized in the crystallizer 48 is recycled to the chlorine dioxide generator 10, after formation into an aqueous solution thereof of concentration as described above with respect to Figure 3.
By integrating the chlorine dioxide generator 10 with the sodium chlorate plant 40 and by balancing the various reactant feeds, high purity chlorine dioxide is produced, substantially uncontaminated with by-product chlorine, by reduction with a mixture of hydrogen chloride and hydrogen peroxide while by-product sodium chloride from the chlorine dioxide generating process is used to form sodium chlorate reactant for the chlorine dioxide generating process. Similarly, as in the case of Figure 2, hydrogen peroxide may optionally be added through line 52 to the product in order to improve the chlorine dioxide purity.
Figures 4 and 5 correspond to Figures 2 and 3 respectively but contain a modification related the addition point of H2O2. In these cases, hydrogen peroxide is added to the chlorine dioxide product rather than to the chlorine dioxide generator. In this modified process, chlorine is produced in significant quantities from the chlorine dioxide generating reaction medium and, upon selective dissolution of chlorine dioxide with water, an aqueous solution of chlorine dioxide with chlorine codissolved therein is formed in line 12.
Addition of hydrogen peroxide to the chlorine dioxide solution, following condensation of the steam and formation of the aqueous solution of chlorine dioxide, 21 8928~
results in reduction of the codissolved chlorine to provide high purity chlorine dioxide. This modified process leads to minimization of hydrogen peroxide consumption by the overall chlorine dioxide generating process while allowing a highly pure product to be obtained. A possible drawback of the modification shown in Figures 4 and 5 is the loss of the part of HCl values generated in the reaction between chlorine and hydrogen peroxide.
In the embodiment of Figure 4, the same reference numbers as are employed in Figure 2 are employed to designate the same elements. In this case, hydrogen peroxide is added by line 38 to the chlorine dioxide product stream in line 12 to remove chlorine contained therein by reduction. By-product chlorine, coproduced with chlorine dioxide in the chlorine generator 10, is forwarded by line 54 to the chlorine feed line 30 to the HCl burner 34.
Similarly, in the embodiment of Figure 5, the same reference numerals as are employed in Figure 3 are employed to designate the same elements. In this case, hydrogen peroxide is added by line 52 to the chlorine dioxide product stream in line 12 to remove chlorine contained therein by reduction. By-product chlorine, 2 5 coproduced with chlorine dioxide in the chlorine dioxide generator 10, is forwarded by line 56 to an HCl burner 58, for reaction therein with hydrogen produced by the sodium chlorate plant 40 and forwarded by line 60.
Reaction of hydrogen and chlorine in the HCl burner 58 produces HCl, which is recycled by line 62 to the HCl feed line 15. In this embodiment of the invention, the sodium chlorate crystallizer 48 is optional.
In summary of this disclosure, the present invention provides a novel procedure for the production of high purity chlorine dioxide using hydrogen peroxide and hydrogen chloride which produces only useful by-products.
Modifications are possible within the scope of the invention.
Claims (24)
1. A process for the preparation of an aqueous solution of chlorine dioxide of high purity, which comprises:
feeding sodium chlorate, hydrogen chloride and hydrogen peroxide to a reaction zone wherein chlorine dioxide is formed by reduction of chlorate ions in an aqueous acid reaction medium, the chlorine dioxide is formed into an aqueous solution thereof of high purity, chlorine potentially contaminating said aqueous solution of chlorine dioxide is at least partially reduced by said hydrogen peroxide and crystalline sodium chloride is formed, removing said aqueous solution of chlorine dioxide from said reaction zone, removing said crystalline sodium chloride from said reaction zone and forming an aqueous solution of said removed crystalline sodium chloride, subjecting the resulting aqueous solution of sodium chloride to an electrolysis process operation to form either:
(a) sodium hydroxide and hydrogen chloride, in which event, recycling the hydrogen chloride to said reaction zone to provide hydrogen chloride feed thereto and recovering the sodium hydroxide, or:
(b) sodium chlorate and hydrogen, in which event recycling the sodium chlorate to said reaction zone to provide sodium chlorate feed thereto.
feeding sodium chlorate, hydrogen chloride and hydrogen peroxide to a reaction zone wherein chlorine dioxide is formed by reduction of chlorate ions in an aqueous acid reaction medium, the chlorine dioxide is formed into an aqueous solution thereof of high purity, chlorine potentially contaminating said aqueous solution of chlorine dioxide is at least partially reduced by said hydrogen peroxide and crystalline sodium chloride is formed, removing said aqueous solution of chlorine dioxide from said reaction zone, removing said crystalline sodium chloride from said reaction zone and forming an aqueous solution of said removed crystalline sodium chloride, subjecting the resulting aqueous solution of sodium chloride to an electrolysis process operation to form either:
(a) sodium hydroxide and hydrogen chloride, in which event, recycling the hydrogen chloride to said reaction zone to provide hydrogen chloride feed thereto and recovering the sodium hydroxide, or:
(b) sodium chlorate and hydrogen, in which event recycling the sodium chlorate to said reaction zone to provide sodium chlorate feed thereto.
2. The process of claim 1 wherein said chlorine dioxide is formed and said potentially contaminating chlorine is reduced by:
feeding said sodium chlorate, hydrogen chloride and hydrogen peroxide to an aqueous acid reaction medium to produce chlorine dioxide therefrom substantially uncontaminated by chlorine and dissolving the chlorine dioxide so formed in water to provide said aqueous solution of chlorine dioxide.
feeding said sodium chlorate, hydrogen chloride and hydrogen peroxide to an aqueous acid reaction medium to produce chlorine dioxide therefrom substantially uncontaminated by chlorine and dissolving the chlorine dioxide so formed in water to provide said aqueous solution of chlorine dioxide.
3. The process of claim 2 wherein said aqueous solution of chlorine dioxide is contacted with hydrogen peroxide to reduce any chlorine dissolved therein.
4. The process of claim 2 or 3 wherein said aqueous acid reaction medium is contained in a reaction vessel in said reaction zone which reaction vessel is maintained at an atmospheric pressure, said chlorine dioxide is removed from said reaction vessel in admixture with an inert gas, and said crystalline sodium chloride is formed by evaporation of spent aqueous acid reaction medium in a second vessel in said reaction zone.
5. The process of claim 1 wherein said chlorine dioxide is formed and said potentially contaminating chlorine is reduced by:
feeding said sodium chlorate and hydrogen chloride to an aqueous acid reaction medium to produce a gaseous admixture of chlorine dioxide and chlorine therefrom, selectively dissolving chlorine dioxide from said gaseous admixture to form an aqueous solution of the chlorine dioxide contained in said gaseous admixture contaminated by codissolved chlorine and residual chlorine gas, contacting said aqueous solution of chlorine dioxide contaminated with codissolved chlorine with the hydrogen peroxide to reduce said codissolved chlorine, and reacting said residual chlorine gas with hydrogen to form hydrogen chloride which is recycled to said aqueous acid reaction medium to provide hydrogen chloride feed thereto.
feeding said sodium chlorate and hydrogen chloride to an aqueous acid reaction medium to produce a gaseous admixture of chlorine dioxide and chlorine therefrom, selectively dissolving chlorine dioxide from said gaseous admixture to form an aqueous solution of the chlorine dioxide contained in said gaseous admixture contaminated by codissolved chlorine and residual chlorine gas, contacting said aqueous solution of chlorine dioxide contaminated with codissolved chlorine with the hydrogen peroxide to reduce said codissolved chlorine, and reacting said residual chlorine gas with hydrogen to form hydrogen chloride which is recycled to said aqueous acid reaction medium to provide hydrogen chloride feed thereto.
6. A process for the production of chlorine dioxide, which comprises:
feeding sodium chlorate, hydrogen chloride and hydrogen peroxide to an aqueous acid reaction medium in a reaction zone to produce chlorine dioxide from said reaction medium, maintaining said aqueous acid reaction medium at its boiling point while a subatmospheric pressure is applied to said reaction zone, removing chlorine dioxide from said reaction zone in admixture with steam while precipitating sodium chloride from said aqueous acid reaction medium in said reaction zone, following saturation after start-up, removing said precipitated sodium chloride from said reaction zone and forming the removed sodium chloride into an aqueous solution thereof, and subjecting the resulting aqueous solution of sodium chloride to an electrolysis process to convert the aqueous solution of sodium chloride either:
(a) to sodium hydroxide, hydrogen and chlorine, in which event, reacting the chlorine and hydrogen together to form HCl, recycling the HCl to said reaction zone to provide hydrogen chloride feed thereto and recovering the sodium hydroxide, or:
(b) to sodium hydroxide and hydrogen chloride, in which event, recycling the hydrogen chloride to said reaction zone to provide hydrogen chloride feed thereto and recovering the sodium hydroxide; or (c) to sodium chlorate and hydrogen, in which event, recycling the sodium chlorate to said reaction zone to provide sodium chlorate feed thereto.
feeding sodium chlorate, hydrogen chloride and hydrogen peroxide to an aqueous acid reaction medium in a reaction zone to produce chlorine dioxide from said reaction medium, maintaining said aqueous acid reaction medium at its boiling point while a subatmospheric pressure is applied to said reaction zone, removing chlorine dioxide from said reaction zone in admixture with steam while precipitating sodium chloride from said aqueous acid reaction medium in said reaction zone, following saturation after start-up, removing said precipitated sodium chloride from said reaction zone and forming the removed sodium chloride into an aqueous solution thereof, and subjecting the resulting aqueous solution of sodium chloride to an electrolysis process to convert the aqueous solution of sodium chloride either:
(a) to sodium hydroxide, hydrogen and chlorine, in which event, reacting the chlorine and hydrogen together to form HCl, recycling the HCl to said reaction zone to provide hydrogen chloride feed thereto and recovering the sodium hydroxide, or:
(b) to sodium hydroxide and hydrogen chloride, in which event, recycling the hydrogen chloride to said reaction zone to provide hydrogen chloride feed thereto and recovering the sodium hydroxide; or (c) to sodium chlorate and hydrogen, in which event, recycling the sodium chlorate to said reaction zone to provide sodium chlorate feed thereto.
7. The process of claim 6 wherein said aqueous acid reaction medium is maintained at its boiling point at a temperature of about 40° to about 80°C while a subatmospheric pressure of about 80 to about 300 mm Hg is applied to said reaction zone.
8. The process of claim 7 wherein said temperature is about 60° to about 80°C and said atmospheric pressure is about 150 to about 240 mm Hg.
9. The process of claim 6, 7 or 8 wherein said reaction medium has a sodium chlorate concentration of about 1 to about 7 M and said hydrogen chloride provides an acid normality of about 0.01 to about 2N in said aqueous acid reaction medium.
10. The process of claim 9 wherein said sodium chlorate concentration is from about 5 to about 7 M and said acid normality is from about 0.05 to about 0.15 N.
11. The process of claim 6, 7 or 8 wherein said hydrogen peroxide is fed to said aqueous acid reaction medium in the form of an aqueous solution thereof having a concentration of about 10 to about 75 wt%.
12. The process of claim 11 wherein said hydrogen peroxide has a concentration of about 30 to about 50 wt%.
13. The process of claim 6, 7 or 8 wherein chlorine dioxide is produced having a purity of at least about 95%.
14. The process of claim 6, 7 or 8 wherein said hydrogen chloride and hydrogen peroxide are fed to said aqueous acid reaction medium at a molar ratio of about 1:1 to about 3:1.
15. The process of claim 14 wherein said molar ratio is about 1.5:1 to about 2:1.
16. The process of claim 6, 7 or 8 wherein a palladium catalyst is present in said aqueous acid reaction medium in an amount of about 1 to about 40 mg/L based on Pd++.
17. The process of claim 16 wherein the amount of catalyst present is about 5 to about 15 mg/L.
18. A continuous process for the production of chlorine dioxide having a purity of at least about 95%, which comprises:
feeding an aqueous solution of sodium chlorate, hydrochloric acid and an aqueous solution of hydrogen peroxide to a reaction zone in sufficient quantities to provide an aqueous acid reaction medium having, under steady state operating conditions, a sodium chlorate concentration of about 1 to about 7 M and an acid normality of about 0.01 to about 2N,
feeding an aqueous solution of sodium chlorate, hydrochloric acid and an aqueous solution of hydrogen peroxide to a reaction zone in sufficient quantities to provide an aqueous acid reaction medium having, under steady state operating conditions, a sodium chlorate concentration of about 1 to about 7 M and an acid normality of about 0.01 to about 2N,
19 maintaining said aqueous acid reaction medium at its boiling point at a temperature of about 40° to about 80°C
while a subatmospheric pressure of about 80 to about 300 mm Hg is applied to said reaction zone to effect production of chlorine dioxide from said aqueous acid reaction medium, removing a gaseous mixture of chlorine dioxide, oxygen and steam from said reaction zone while precipitating sodium chloride from the aqueous acid reaction medium in said reaction zone, following saturation after start up, forming an aqueous solution of chlorine dioxide from said gaseous mixture in which the chlorine dioxide is substantially contaminated with chlorine and has a purity of at least about 95%, removing said precipitated sodium chloride from said reaction zone and forming the removed sodium chloride into an aqueous solution thereof having a concentration of about 2 to about 5 M, subjecting the aqueous solution of sodium chloride to an electrolysis process to convert the aqueous solution of sodium chloride, either:
(a) to an aqueous solution of sodium hydroxide of concentration of about 5 to about 30 wt%, chlorine and hydrogen at a temperature of about 80° to about 100°C, in which event, reacting the chlorine and hydrogen to form HCl, forming hydrochloric acid of concentration of about 5 to about 2N from said HCl, recycling the hydrochloric acid to said reaction zone to provide hydrochloric acid to said reaction zone to provide hydrochloric acid feed thereto, and recovering said aqueous solution of sodium hydroxide, or:
(b) to an aqueous solution of sodium chlorate having a concentration of about 3 to about 0.5 M
also containing sodium chloride and hydrogen at a temperature of about 60° to about 100°C, in which event, crystallizing sodium chlorate from said aqueous solution of sodium chlorate, recycling mother liquor from said crystallization step having a sodium chlorate concentration of about 4 to about 7M and a sodium chloride concentration of about 1.5 to about 3 M to said electrolysis process, forming an aqueous solution of sodium chlorate having a concentration of about 4 to about 8M from crystalline sodium chlorate formed in said crystallization step, and recycling said aqueous solution of sodium chlorate to said reaction zone.
19. The process of claim 18 wherein said aqueous acid reaction medium has a sodium chlorate concentration of about 5 to about 7M, an acid normality of about 0.05 to about 0.15N and a temperature of about 60°C about 80°C, a subatmospheric pressure applied to said reaction zone is about 150 to about 240 mmHg, said hydrochloric acid and aqueous solution of hydrogen peroxide is fed to said reaction medium in a molar ratio of HCl: H2O2 of about 1.5:1 to about 2.5:1.
while a subatmospheric pressure of about 80 to about 300 mm Hg is applied to said reaction zone to effect production of chlorine dioxide from said aqueous acid reaction medium, removing a gaseous mixture of chlorine dioxide, oxygen and steam from said reaction zone while precipitating sodium chloride from the aqueous acid reaction medium in said reaction zone, following saturation after start up, forming an aqueous solution of chlorine dioxide from said gaseous mixture in which the chlorine dioxide is substantially contaminated with chlorine and has a purity of at least about 95%, removing said precipitated sodium chloride from said reaction zone and forming the removed sodium chloride into an aqueous solution thereof having a concentration of about 2 to about 5 M, subjecting the aqueous solution of sodium chloride to an electrolysis process to convert the aqueous solution of sodium chloride, either:
(a) to an aqueous solution of sodium hydroxide of concentration of about 5 to about 30 wt%, chlorine and hydrogen at a temperature of about 80° to about 100°C, in which event, reacting the chlorine and hydrogen to form HCl, forming hydrochloric acid of concentration of about 5 to about 2N from said HCl, recycling the hydrochloric acid to said reaction zone to provide hydrochloric acid to said reaction zone to provide hydrochloric acid feed thereto, and recovering said aqueous solution of sodium hydroxide, or:
(b) to an aqueous solution of sodium chlorate having a concentration of about 3 to about 0.5 M
also containing sodium chloride and hydrogen at a temperature of about 60° to about 100°C, in which event, crystallizing sodium chlorate from said aqueous solution of sodium chlorate, recycling mother liquor from said crystallization step having a sodium chlorate concentration of about 4 to about 7M and a sodium chloride concentration of about 1.5 to about 3 M to said electrolysis process, forming an aqueous solution of sodium chlorate having a concentration of about 4 to about 8M from crystalline sodium chlorate formed in said crystallization step, and recycling said aqueous solution of sodium chlorate to said reaction zone.
19. The process of claim 18 wherein said aqueous acid reaction medium has a sodium chlorate concentration of about 5 to about 7M, an acid normality of about 0.05 to about 0.15N and a temperature of about 60°C about 80°C, a subatmospheric pressure applied to said reaction zone is about 150 to about 240 mmHg, said hydrochloric acid and aqueous solution of hydrogen peroxide is fed to said reaction medium in a molar ratio of HCl: H2O2 of about 1.5:1 to about 2.5:1.
20. The process of claim 19 wherein said aqueous solution of sodium chlorate is fed to said reaction zone in a concentration of about 5 to about 7M, said hydrochloric acid is fed to said reaction zone at a concentration of about 9 to about 12 N and said aqueous solution of hydrogen peroxide is fed to said reaction zone at concentration of about 30 to about 50 wt%.
21. The process of claim 18, 19 or 20 wherein said aqueous solution of hydrogen peroxide is premixed with at least one of the other feeds to said reaction zone.
22. The process of claim 18, 19 or 20 wherein said aqueous acid reaction medium further contains a palladium catalyst in the form of a palladium (II) compound or complex in an amount of about 5 to about 15 mg/L, determined as Pd++.
23. The process of claim 18, 19 or 20 wherein said precipitated sodium chloride is made up into an aqueous solution of sodium chloride of about 4 to about 5 molar and said electrolysis process produces an aqueous solution of sodium hydroxide of concentration about 30 to about 35 wt% at a temperature of about 85° to about 95°C.
24. The process of claim 18, 19 or 20 wherein said precipitated sodium chloride is made up into an aqueous solution of sodium chloride of about 5 molar and said electrolysis process produces an aqueous solution of sodium chlorate of concentration about 4.5 to about 6 M
at a temperature of about 75° to about 85°C.
at a temperature of about 75° to about 85°C.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US55580595A | 1995-11-09 | 1995-11-09 | |
| US08/555,805 | 1995-11-09 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2189289A1 true CA2189289A1 (en) | 1997-05-10 |
Family
ID=24218692
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA 2189289 Abandoned CA2189289A1 (en) | 1995-11-09 | 1996-10-31 | High purity chlorine dioxide production |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA2189289A1 (en) |
Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US6251357B1 (en) | 1998-06-09 | 2001-06-26 | Sterling Canada, Inc. | High purity alkali metal chlorite and method of manufacture |
| CN1306068C (en) * | 2002-12-27 | 2007-03-21 | 北京化工机械厂 | External natural circulation multipole ionic film electrolytic device |
| CN109055966A (en) * | 2018-09-13 | 2018-12-21 | 北京化工大学 | A kind of chemical combined method for preparing chlorine dioxide of electrochemistry- |
-
1996
- 1996-10-31 CA CA 2189289 patent/CA2189289A1/en not_active Abandoned
Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US6251357B1 (en) | 1998-06-09 | 2001-06-26 | Sterling Canada, Inc. | High purity alkali metal chlorite and method of manufacture |
| CN1306068C (en) * | 2002-12-27 | 2007-03-21 | 北京化工机械厂 | External natural circulation multipole ionic film electrolytic device |
| CN109055966A (en) * | 2018-09-13 | 2018-12-21 | 北京化工大学 | A kind of chemical combined method for preparing chlorine dioxide of electrochemistry- |
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