CA2242685C - Nitric acid based chlorine dioxide generation process - Google Patents
Nitric acid based chlorine dioxide generation process Download PDFInfo
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- CA2242685C CA2242685C CA 2242685 CA2242685A CA2242685C CA 2242685 C CA2242685 C CA 2242685C CA 2242685 CA2242685 CA 2242685 CA 2242685 A CA2242685 A CA 2242685A CA 2242685 C CA2242685 C CA 2242685C
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- chlorate
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- alkali metal
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- OSVXSBDYLRYLIG-UHFFFAOYSA-N dioxidochlorine(.) Chemical compound O=Cl=O OSVXSBDYLRYLIG-UHFFFAOYSA-N 0.000 title claims abstract description 102
- 239000004155 Chlorine dioxide Substances 0.000 title claims abstract description 51
- 235000019398 chlorine dioxide Nutrition 0.000 title claims abstract description 51
- GRYLNZFGIOXLOG-UHFFFAOYSA-N Nitric acid Chemical compound O[N+]([O-])=O GRYLNZFGIOXLOG-UHFFFAOYSA-N 0.000 title claims abstract description 22
- 229910017604 nitric acid Inorganic materials 0.000 title claims abstract description 22
- 238000000034 method Methods 0.000 title claims description 70
- 230000008569 process Effects 0.000 title claims description 69
- XTEGARKTQYYJKE-UHFFFAOYSA-M Chlorate Chemical compound [O-]Cl(=O)=O XTEGARKTQYYJKE-UHFFFAOYSA-M 0.000 claims abstract description 50
- 239000012429 reaction media Substances 0.000 claims abstract description 25
- 238000004519 manufacturing process Methods 0.000 claims abstract description 16
- 239000002253 acid Substances 0.000 claims abstract description 14
- 239000011260 aqueous acid Substances 0.000 claims abstract description 14
- QAOWNCQODCNURD-UHFFFAOYSA-L Sulfate Chemical compound [O-]S([O-])(=O)=O QAOWNCQODCNURD-UHFFFAOYSA-L 0.000 claims abstract description 5
- OKKJLVBELUTLKV-UHFFFAOYSA-N Methanol Chemical compound OC OKKJLVBELUTLKV-UHFFFAOYSA-N 0.000 claims description 30
- -1 chlorate ions Chemical class 0.000 claims description 28
- 238000006243 chemical reaction Methods 0.000 claims description 24
- MHAJPDPJQMAIIY-UHFFFAOYSA-N Hydrogen peroxide Chemical compound OO MHAJPDPJQMAIIY-UHFFFAOYSA-N 0.000 claims description 22
- 239000003638 chemical reducing agent Substances 0.000 claims description 16
- 239000006227 byproduct Substances 0.000 claims description 11
- 230000020477 pH reduction Effects 0.000 claims description 11
- 229910001963 alkali metal nitrate Inorganic materials 0.000 claims description 9
- 229910052783 alkali metal Inorganic materials 0.000 claims description 8
- 229940005989 chlorate ion Drugs 0.000 claims description 8
- 239000012528 membrane Substances 0.000 claims description 8
- 238000005341 cation exchange Methods 0.000 claims description 7
- XTEGARKTQYYJKE-UHFFFAOYSA-N chloric acid Chemical compound OCl(=O)=O XTEGARKTQYYJKE-UHFFFAOYSA-N 0.000 claims description 7
- 229940005991 chloric acid Drugs 0.000 claims description 7
- 239000001257 hydrogen Substances 0.000 claims description 7
- 229910052739 hydrogen Inorganic materials 0.000 claims description 7
- 239000000243 solution Substances 0.000 claims description 7
- 229910001413 alkali metal ion Inorganic materials 0.000 claims description 5
- BZSXEZOLBIJVQK-UHFFFAOYSA-N 2-methylsulfonylbenzoic acid Chemical group CS(=O)(=O)C1=CC=CC=C1C(O)=O BZSXEZOLBIJVQK-UHFFFAOYSA-N 0.000 claims description 4
- VEXZGXHMUGYJMC-UHFFFAOYSA-M Chloride anion Chemical compound [Cl-] VEXZGXHMUGYJMC-UHFFFAOYSA-M 0.000 claims description 4
- 238000009835 boiling Methods 0.000 claims description 4
- 239000003054 catalyst Substances 0.000 claims description 4
- 230000000694 effects Effects 0.000 claims description 4
- 230000009467 reduction Effects 0.000 claims description 4
- 150000008044 alkali metal hydroxides Chemical class 0.000 claims description 3
- 239000007864 aqueous solution Substances 0.000 claims description 3
- 239000000203 mixture Substances 0.000 claims description 3
- 229910052750 molybdenum Inorganic materials 0.000 claims description 2
- 229910052763 palladium Inorganic materials 0.000 claims description 2
- 229910052697 platinum Inorganic materials 0.000 claims description 2
- 229910052720 vanadium Inorganic materials 0.000 claims description 2
- 238000010517 secondary reaction Methods 0.000 claims 3
- 239000012431 aqueous reaction media Substances 0.000 claims 2
- 235000019647 acidic taste Nutrition 0.000 description 24
- QAOWNCQODCNURD-UHFFFAOYSA-N Sulfuric acid Chemical compound OS(O)(=O)=O QAOWNCQODCNURD-UHFFFAOYSA-N 0.000 description 18
- VLTRZXGMWDSKGL-UHFFFAOYSA-N perchloric acid Chemical compound OCl(=O)(=O)=O VLTRZXGMWDSKGL-UHFFFAOYSA-N 0.000 description 8
- HEMHJVSKTPXQMS-UHFFFAOYSA-M Sodium hydroxide Chemical compound [OH-].[Na+] HEMHJVSKTPXQMS-UHFFFAOYSA-M 0.000 description 6
- 238000007792 addition Methods 0.000 description 5
- VEXZGXHMUGYJMC-UHFFFAOYSA-N Hydrochloric acid Chemical compound Cl VEXZGXHMUGYJMC-UHFFFAOYSA-N 0.000 description 4
- 239000000126 substance Substances 0.000 description 4
- PMZURENOXWZQFD-UHFFFAOYSA-L Sodium Sulfate Chemical compound [Na+].[Na+].[O-]S([O-])(=O)=O PMZURENOXWZQFD-UHFFFAOYSA-L 0.000 description 3
- 150000002823 nitrates Chemical class 0.000 description 3
- VWDWKYIASSYTQR-UHFFFAOYSA-N sodium nitrate Chemical compound [Na+].[O-][N+]([O-])=O VWDWKYIASSYTQR-UHFFFAOYSA-N 0.000 description 3
- NBIIXXVUZAFLBC-UHFFFAOYSA-N Phosphoric acid Chemical compound OP(O)(O)=O NBIIXXVUZAFLBC-UHFFFAOYSA-N 0.000 description 2
- RAHZWNYVWXNFOC-UHFFFAOYSA-N Sulphur dioxide Chemical compound O=S=O RAHZWNYVWXNFOC-UHFFFAOYSA-N 0.000 description 2
- 230000001419 dependent effect Effects 0.000 description 2
- 239000008246 gaseous mixture Substances 0.000 description 2
- 230000006872 improvement Effects 0.000 description 2
- 229910052500 inorganic mineral Inorganic materials 0.000 description 2
- BDAGIHXWWSANSR-UHFFFAOYSA-N methanoic acid Natural products OC=O BDAGIHXWWSANSR-UHFFFAOYSA-N 0.000 description 2
- 239000011707 mineral Substances 0.000 description 2
- 230000007935 neutral effect Effects 0.000 description 2
- 235000015097 nutrients Nutrition 0.000 description 2
- FGIUAXJPYTZDNR-UHFFFAOYSA-N potassium nitrate Chemical compound [K+].[O-][N+]([O-])=O FGIUAXJPYTZDNR-UHFFFAOYSA-N 0.000 description 2
- PAWQVTBBRAZDMG-UHFFFAOYSA-N 2-(3-bromo-2-fluorophenyl)acetic acid Chemical compound OC(=O)CC1=CC=CC(Br)=C1F PAWQVTBBRAZDMG-UHFFFAOYSA-N 0.000 description 1
- OSWFIVFLDKOXQC-UHFFFAOYSA-N 4-(3-methoxyphenyl)aniline Chemical compound COC1=CC=CC(C=2C=CC(N)=CC=2)=C1 OSWFIVFLDKOXQC-UHFFFAOYSA-N 0.000 description 1
- 101000637855 Homo sapiens Transmembrane protease serine 11E Proteins 0.000 description 1
- 229910002651 NO3 Inorganic materials 0.000 description 1
- NHNBFGGVMKEFGY-UHFFFAOYSA-N Nitrate Chemical compound [O-][N+]([O-])=O NHNBFGGVMKEFGY-UHFFFAOYSA-N 0.000 description 1
- 102100032001 Transmembrane protease serine 11E Human genes 0.000 description 1
- 230000002378 acidificating effect Effects 0.000 description 1
- 239000003513 alkali Substances 0.000 description 1
- 229910052936 alkali metal sulfate Inorganic materials 0.000 description 1
- 229910000147 aluminium phosphate Inorganic materials 0.000 description 1
- 238000005349 anion exchange Methods 0.000 description 1
- 150000001450 anions Chemical class 0.000 description 1
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 description 1
- 230000009286 beneficial effect Effects 0.000 description 1
- 239000007844 bleaching agent Substances 0.000 description 1
- 230000003197 catalytic effect Effects 0.000 description 1
- 150000001768 cations Chemical class 0.000 description 1
- 239000003153 chemical reaction reagent Substances 0.000 description 1
- 239000013078 crystal Substances 0.000 description 1
- 238000002425 crystallisation Methods 0.000 description 1
- 230000008025 crystallization Effects 0.000 description 1
- 230000007812 deficiency Effects 0.000 description 1
- IYGFDEZBVCNBRU-UHFFFAOYSA-L disodium sulfuric acid sulfate Chemical compound [H+].[H+].[H+].[H+].[Na+].[Na+].[O-]S([O-])(=O)=O.[O-]S([O-])(=O)=O.[O-]S([O-])(=O)=O IYGFDEZBVCNBRU-UHFFFAOYSA-L 0.000 description 1
- 239000003337 fertilizer Substances 0.000 description 1
- 235000019253 formic acid Nutrition 0.000 description 1
- 238000004868 gas analysis Methods 0.000 description 1
- 238000004817 gas chromatography Methods 0.000 description 1
- 230000010354 integration Effects 0.000 description 1
- 150000002500 ions Chemical class 0.000 description 1
- 239000007788 liquid Substances 0.000 description 1
- 238000005649 metathesis reaction Methods 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 230000003647 oxidation Effects 0.000 description 1
- 238000007254 oxidation reaction Methods 0.000 description 1
- 239000001301 oxygen Substances 0.000 description 1
- 229910052760 oxygen Inorganic materials 0.000 description 1
- 235000010333 potassium nitrate Nutrition 0.000 description 1
- 239000004323 potassium nitrate Substances 0.000 description 1
- 239000002244 precipitate Substances 0.000 description 1
- 239000000047 product Substances 0.000 description 1
- 239000000376 reactant Substances 0.000 description 1
- 239000011541 reaction mixture Substances 0.000 description 1
- 230000008929 regeneration Effects 0.000 description 1
- 238000011069 regeneration method Methods 0.000 description 1
- 150000003839 salts Chemical class 0.000 description 1
- 235000010344 sodium nitrate Nutrition 0.000 description 1
- 239000004317 sodium nitrate Substances 0.000 description 1
- 229910052938 sodium sulfate Inorganic materials 0.000 description 1
- 235000011152 sodium sulphate Nutrition 0.000 description 1
- 230000002459 sustained effect Effects 0.000 description 1
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 1
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- Organic Low-Molecular-Weight Compounds And Preparation Thereof (AREA)
- Inorganic Compounds Of Heavy Metals (AREA)
- Electrolytic Production Of Non-Metals, Compounds, Apparatuses Therefor (AREA)
Abstract
Chlorine dioxide is generated from a sulfate free aqueous acid reaction medium using nitric acid as the acid source. Highly efficient chlorine dioxide generation at high production rate is achieved in the low acidity range below about 2 N at low concentrations of chlorate below about 3 M, under crystallizing and non-crystallizing conditions.
Description
TITLE OF INVENTION
NITRIC ACID BA8ED CHLORINE DIOXIDE (3ENER.ATION PROCESS
FIELD OF THE INVENTION
The present invention is concerned with the production of chlorine dioxide from chlorate ions using hydrogen peroxide or methanol as the preferred reducing agents and, in particular, with the production of chlorine dioxide where the reaction medium is substantially free of sulfate ions and where the primary source of acidity is nitric acid.
BACKGROUND TO THE INVENTION
It is known to produce chlorine dioxide by reduction of an aqueous acid chlorate solution using various reducing agents, such as methanol, hydrogen peroxide and sulfur dioxide, wherein the acidity required for the chlorine dioxide generation reaction is supplied primarily by sulfuric acid. The process can be carried out either in the crystallizing mode, typically in a single vessel generator-evaporator-crystallizer at subatmospheric pressure with the sodium sulfate being precipitated from the reaction medium, or in a non-crystallizing mode where the conversion of chlorate takes place in at least one but typically two reaction vessels with the secondary vessel yielding a liquid acid effluent containing sulfuric acid and alkali metal sulfate along with unreacted chlorate and other by-products.
The single vessel sulfuric acid-based processes employing methanol as a reducing agent are described, for example, in US Patents 4,081,520 (Swindells et al), 4,473,540 (Fredette) and 4,770,868 (Norell), while the use of hydrogen peroxide as a reducing agent in chlorine dioxide generation is described, for example, in US Patents 5,091,166 (Engstrom et al), 5,091,167 (Engstrom et al) and 5,366,714 (Bigauskas).
One of the deficiencies of sulfuric acid based chlorine dioxide generators is a low production rate at low acidities. The lower limit of acidity below which the reaction rate becomes commercially unacceptable is somewhat dependent on the type of reducing agent used.
Typically an acidity of at least about 2 N sulfuric acid is required with the preferred acidity being at least about 4 N and at least about 5 N in the processes involving the use of hydrogen peroxide and methanol, respectively.
Another problem associated with the sulfuric acid based generators is the cost of disposal of excess saltcake by-product, especially in the case of non crystallizing generators. There is a need, therefore, to provide a chlorine dioxide generation process operating at a very low acidity, preferably below about 2 N, without a co-production of saltcake by-product.
While sulfate-free chlorine dioxide generators have been described in the prior art, none of them offers high efficiency and high production rate at low acidities (i.e., below about 2 N) without the necessity of a significant increase in the chlorate ion concentration.
US Patents 5,174,868 and 5,284,553 (Lipsztajn, et al) describe an operation involving the addition of chloric acid as a sole source of hydrogen ions whereby the high efficiency and production rate are achieved due to the presence of a dead load of sodium chlorate, resulting in the chlorate ion concentration in the reaction medium in the range of about 6 to about 9 M.
An analogous process disclosed in US Patent 5,486,344 (Winters et al) requires a preferred range of chlorate ion concentration of from about 2 M up to about 5 M.
US Patent 5,523,072 (Falgen et al) teaches a sulfate-free process in which the acidity is provided by phosphoric acid. The latter process requires an acidity of above about 2 N and a preferred range of chlorate ion concentration above about 2 M. The aforementioned US Patent 5,366,714 (Bigauskas) teaches both a sulfate-based and sulfate-free operation wherein the latter one involves the addition of a strong mineral acid, such as nitric acid, hydrochloric acid, perchloric acid or chloric acid. For a low acidity operation (below about 5 N), this patent suggests the use of a high concentration of chlorate ion, from about 2 M up to saturation, preferably about 3 to 4 M.
SUMMARY OF THE INVENTION
Surprisingly it has been found that by employing nitric acid as a source of acidity a sulfate-free chlorine dioxide generation process can be operated very efficiently and at a high production rate, even in the low acidity range (i.e. below about 2 N) and at low concentrations of chlorate (i.e. below about 3 M, preferably in the range of about 2 to 3 M). Chlorate concentrations higher than about 3 M may also be employed, especially in the process involving the use of methanol as a reducing agent. Such a combination of acidity and chlorate concentration has not been previously disclosed for a nitric acid based chlorine dioxide generation processes.
Accordingly, the present invention provides an improvement in a process for the production of chlorine dioxide by the reduction of chlorate ions in an aqueous acid reaction medium, the improvement being nitric acid providing the acidity to the reaction medium.
GENF,RAL DESC1~IPT~ON OF INVENTION
As noted above, the present invention provides a chlorine dioxide generating process which utilizes nitric acid as a source of acidity for the process.
Such a process has been found to be much less dependent on variations in acidity than other chlorine dioxide generating processes known in the art, thus enabling a very stable, continuous operation to be provided, which is less sensitive to the process upset conditions. In particular, the chlorine dioxide generating process may be operated at low acid normalities below about 2 N, preferably about 0.5 to about 2 N.
The nitric acid based chlorine dioxide generating process provided herein can be performed both in a crystallizing and non-crystallizing mode at both atmospheric and sub-atmospheric pressures. When operating under subatmospheric conditions, which is the preferred mode of operation, the aqueous acid reaction medium generating the chlorine dioxide is maintained at its boiling point at a temperature of about 50 to about 90°C, preferably about 70 to about 80°C, while a subatmospheric pressure is applied to the reaction zone of about 80 to about 400 mmHg (about 11 to about 53 kPa), preferably about 100 to about 250 mmHg (about 13 to about 33 kPa).
When operating in a crystallizing mode, a by-product nitrate corresponding to the cation of the chlorate reactant is crystallized from the aqueous acid reaction medium in the reaction zone and is continuously or periodically removed therefrom. In the non-crystallizing mode of operation, an aqueous stream is continuously or periodically removed from the reaction zone for processing to remove by-product nitrate salt.
A wide selection from the known reducing agents for reduction of chlorate ions to generate chlorine dioxide can be employed in the process of the invention, with hydrogen peroxide and methanol being the preferred ones. A combination of several reducing agents also may be employed, if desired.
Chlorate ions reduced by the reducing agent to chlorine dioxide in the process of the invention may be provided by an alkali metal chlorate, usually sodium chlorate, although chloric acid and mixtures of chloric acid and alkali metal chlorate may be used. However, in contrast to the prior art processes (see, for example, US Patent 5,296,108 (Kaczur et al)), the presence of chloric acid is not required in order to achieve high efficiencies at high production rates, when nitric acid is employed as a source of acidity, in accordance with the present invention. The 5 concentration of chlorate ions in the aqueous acid reaction medium depends to some extent on the reducing agent employed. For example, when hydrogen peroxide is the reducing agent, the chlorate ion concentration is generally below about 3 M, preferably about 2 to 3 M.
When methanol is employed as the reducing agents, higher chlorate concentration of up to about 4, preferably about 2 to about 3 M may be employed.
When operating the chlorine dioxide generating process in a single vessel generator-evaporator crystallizer at subatmospheric pressures, it is possible to modify the process conditions used in the process of the invention so that the concentrations in the reaction medium remain below the saturation level with respect to both alkali metal chlorate and alkali metal nitrate.
In such a case it is preferred to continuously or periodically withdraw the reaction medium from the single vessel and to subject the withdrawn reaction medium to electrochemical acidification in the anodic compartment of an electrochemical cell, which enables the regeneration of acidity values and at the same time the co-production of alkali metal hydroxide, preferably sodium hydroxide, in the cathodic compartment of the electrochemical cell. The acidified product withdrawn from the anodic compartment can be recycled back to the chlorine dioxide producing reaction vessel.
Such an operation enables there to be achieved the minimization of the quantity of the externally added nitric acid. If desired, all the acidity requirements can be sustained by the acid regenerated in the electrochemical cell from effluent from the chlorine dioxide generator.
NITRIC ACID BA8ED CHLORINE DIOXIDE (3ENER.ATION PROCESS
FIELD OF THE INVENTION
The present invention is concerned with the production of chlorine dioxide from chlorate ions using hydrogen peroxide or methanol as the preferred reducing agents and, in particular, with the production of chlorine dioxide where the reaction medium is substantially free of sulfate ions and where the primary source of acidity is nitric acid.
BACKGROUND TO THE INVENTION
It is known to produce chlorine dioxide by reduction of an aqueous acid chlorate solution using various reducing agents, such as methanol, hydrogen peroxide and sulfur dioxide, wherein the acidity required for the chlorine dioxide generation reaction is supplied primarily by sulfuric acid. The process can be carried out either in the crystallizing mode, typically in a single vessel generator-evaporator-crystallizer at subatmospheric pressure with the sodium sulfate being precipitated from the reaction medium, or in a non-crystallizing mode where the conversion of chlorate takes place in at least one but typically two reaction vessels with the secondary vessel yielding a liquid acid effluent containing sulfuric acid and alkali metal sulfate along with unreacted chlorate and other by-products.
The single vessel sulfuric acid-based processes employing methanol as a reducing agent are described, for example, in US Patents 4,081,520 (Swindells et al), 4,473,540 (Fredette) and 4,770,868 (Norell), while the use of hydrogen peroxide as a reducing agent in chlorine dioxide generation is described, for example, in US Patents 5,091,166 (Engstrom et al), 5,091,167 (Engstrom et al) and 5,366,714 (Bigauskas).
One of the deficiencies of sulfuric acid based chlorine dioxide generators is a low production rate at low acidities. The lower limit of acidity below which the reaction rate becomes commercially unacceptable is somewhat dependent on the type of reducing agent used.
Typically an acidity of at least about 2 N sulfuric acid is required with the preferred acidity being at least about 4 N and at least about 5 N in the processes involving the use of hydrogen peroxide and methanol, respectively.
Another problem associated with the sulfuric acid based generators is the cost of disposal of excess saltcake by-product, especially in the case of non crystallizing generators. There is a need, therefore, to provide a chlorine dioxide generation process operating at a very low acidity, preferably below about 2 N, without a co-production of saltcake by-product.
While sulfate-free chlorine dioxide generators have been described in the prior art, none of them offers high efficiency and high production rate at low acidities (i.e., below about 2 N) without the necessity of a significant increase in the chlorate ion concentration.
US Patents 5,174,868 and 5,284,553 (Lipsztajn, et al) describe an operation involving the addition of chloric acid as a sole source of hydrogen ions whereby the high efficiency and production rate are achieved due to the presence of a dead load of sodium chlorate, resulting in the chlorate ion concentration in the reaction medium in the range of about 6 to about 9 M.
An analogous process disclosed in US Patent 5,486,344 (Winters et al) requires a preferred range of chlorate ion concentration of from about 2 M up to about 5 M.
US Patent 5,523,072 (Falgen et al) teaches a sulfate-free process in which the acidity is provided by phosphoric acid. The latter process requires an acidity of above about 2 N and a preferred range of chlorate ion concentration above about 2 M. The aforementioned US Patent 5,366,714 (Bigauskas) teaches both a sulfate-based and sulfate-free operation wherein the latter one involves the addition of a strong mineral acid, such as nitric acid, hydrochloric acid, perchloric acid or chloric acid. For a low acidity operation (below about 5 N), this patent suggests the use of a high concentration of chlorate ion, from about 2 M up to saturation, preferably about 3 to 4 M.
SUMMARY OF THE INVENTION
Surprisingly it has been found that by employing nitric acid as a source of acidity a sulfate-free chlorine dioxide generation process can be operated very efficiently and at a high production rate, even in the low acidity range (i.e. below about 2 N) and at low concentrations of chlorate (i.e. below about 3 M, preferably in the range of about 2 to 3 M). Chlorate concentrations higher than about 3 M may also be employed, especially in the process involving the use of methanol as a reducing agent. Such a combination of acidity and chlorate concentration has not been previously disclosed for a nitric acid based chlorine dioxide generation processes.
Accordingly, the present invention provides an improvement in a process for the production of chlorine dioxide by the reduction of chlorate ions in an aqueous acid reaction medium, the improvement being nitric acid providing the acidity to the reaction medium.
GENF,RAL DESC1~IPT~ON OF INVENTION
As noted above, the present invention provides a chlorine dioxide generating process which utilizes nitric acid as a source of acidity for the process.
Such a process has been found to be much less dependent on variations in acidity than other chlorine dioxide generating processes known in the art, thus enabling a very stable, continuous operation to be provided, which is less sensitive to the process upset conditions. In particular, the chlorine dioxide generating process may be operated at low acid normalities below about 2 N, preferably about 0.5 to about 2 N.
The nitric acid based chlorine dioxide generating process provided herein can be performed both in a crystallizing and non-crystallizing mode at both atmospheric and sub-atmospheric pressures. When operating under subatmospheric conditions, which is the preferred mode of operation, the aqueous acid reaction medium generating the chlorine dioxide is maintained at its boiling point at a temperature of about 50 to about 90°C, preferably about 70 to about 80°C, while a subatmospheric pressure is applied to the reaction zone of about 80 to about 400 mmHg (about 11 to about 53 kPa), preferably about 100 to about 250 mmHg (about 13 to about 33 kPa).
When operating in a crystallizing mode, a by-product nitrate corresponding to the cation of the chlorate reactant is crystallized from the aqueous acid reaction medium in the reaction zone and is continuously or periodically removed therefrom. In the non-crystallizing mode of operation, an aqueous stream is continuously or periodically removed from the reaction zone for processing to remove by-product nitrate salt.
A wide selection from the known reducing agents for reduction of chlorate ions to generate chlorine dioxide can be employed in the process of the invention, with hydrogen peroxide and methanol being the preferred ones. A combination of several reducing agents also may be employed, if desired.
Chlorate ions reduced by the reducing agent to chlorine dioxide in the process of the invention may be provided by an alkali metal chlorate, usually sodium chlorate, although chloric acid and mixtures of chloric acid and alkali metal chlorate may be used. However, in contrast to the prior art processes (see, for example, US Patent 5,296,108 (Kaczur et al)), the presence of chloric acid is not required in order to achieve high efficiencies at high production rates, when nitric acid is employed as a source of acidity, in accordance with the present invention. The 5 concentration of chlorate ions in the aqueous acid reaction medium depends to some extent on the reducing agent employed. For example, when hydrogen peroxide is the reducing agent, the chlorate ion concentration is generally below about 3 M, preferably about 2 to 3 M.
When methanol is employed as the reducing agents, higher chlorate concentration of up to about 4, preferably about 2 to about 3 M may be employed.
When operating the chlorine dioxide generating process in a single vessel generator-evaporator crystallizer at subatmospheric pressures, it is possible to modify the process conditions used in the process of the invention so that the concentrations in the reaction medium remain below the saturation level with respect to both alkali metal chlorate and alkali metal nitrate.
In such a case it is preferred to continuously or periodically withdraw the reaction medium from the single vessel and to subject the withdrawn reaction medium to electrochemical acidification in the anodic compartment of an electrochemical cell, which enables the regeneration of acidity values and at the same time the co-production of alkali metal hydroxide, preferably sodium hydroxide, in the cathodic compartment of the electrochemical cell. The acidified product withdrawn from the anodic compartment can be recycled back to the chlorine dioxide producing reaction vessel.
Such an operation enables there to be achieved the minimization of the quantity of the externally added nitric acid. If desired, all the acidity requirements can be sustained by the acid regenerated in the electrochemical cell from effluent from the chlorine dioxide generator.
Any suitable electrochemical cell can be employed to effect such acidification, including a standard two-compartment cell equipped with a suitable separator, for example, a cation exchange membrane, or a three-s compartment cell equipped with two cation exchange membranes. In the latter case, it is preferred to direct the reaction mixture exiting the chlorine dioxide generator into the central compartment of the cell while circulating any suitable mineral acid, for example, nitric acid, sulfuric acid or perchloric acid, in the anode compartment as an anolyte. Hydrogen ions generated in the anode compartment of the three-compartment cell, are transferred through the cation exchange membrane into the central compartment while alkali metal ions are transferred through the second cation exchange membrane from the central compartment into the cathode compartment. By effecting such a three-compartment operation, there is prevented an oxidation of the various components of the reaction medium removed from the chlorine dioxide generator, for example, chlorate ions, chloride ions, hydrogen peroxide, methanol and formic acid, at the anode of the electrochemical cell.
Alternative cell configurations involve the use of both anion and cation exchange membranes, as well as bipolar membranes.
Due to the very high solubility of alkali metal nitrates and the low acidity requirements in the chlorine dioxide generation step, a very high current efficiency for the electrochemical acidification process can be achieved. It is believed that this phenomenon can be attributed to a low concentration ratio of hydrogen ions to alkali metal ions in the acidified stream. The ratio of hydrogen ions to alkali metal ions generally may vary from about 1:100 to about 5:1, preferably about 1:30 to about 2:1.
Alternative cell configurations involve the use of both anion and cation exchange membranes, as well as bipolar membranes.
Due to the very high solubility of alkali metal nitrates and the low acidity requirements in the chlorine dioxide generation step, a very high current efficiency for the electrochemical acidification process can be achieved. It is believed that this phenomenon can be attributed to a low concentration ratio of hydrogen ions to alkali metal ions in the acidified stream. The ratio of hydrogen ions to alkali metal ions generally may vary from about 1:100 to about 5:1, preferably about 1:30 to about 2:1.
When operating a subatmospheric type generator in a crystallizing mode for the generation of chlorine dioxide by the process of the invention, it is also possible to combine the chlorine dioxide generation process with the electrochemical acidification process.
In such a case, the alkali metal nitrate crystals which precipitate as a by-product of the process and which are continuously or periodically removed from the generator, can be dissolved, optionally with alkali metal chlorate, and the resulting solution can be subjected to an electrochemical acidification step, using one of the electrochemical processes described above, and the resulting acidified solution can be directed to the generator. Such electrochemical acidification may be effected in a manner to coproduce an alkali metal hydroxide, preferably sodium hydroxide, in the electrochemical cell as described above.
The alkali metal nitrate is a high value by product of the crystallizing mode of operation, which can be readily used, for example, as a nutrient for biological effluent treatment or as a fertilizer. When the alkali metal nitrate comprises sodium nitrate, a further conversion, for example, via metathesis, to other nitrates, for example, potassium nitrate or ammonium nitrate, is also possible.
When compared to the conventional sulfuric acid-based chlorine dioxide generating process, the nitric acid-based process of the present invention offers some additional advantages in terms of the composition of the crystalline by-product precipitated in the generator in the crystallizing mode of operation. While the conventional generators often co-produce an acidic sulfate, such as sodium sesquisulfate, having regard to the operating acid normality the process of the present invention always yields a neutral salt irrespective of the total acid normality of the reaction medium, thus minimizing the acid and alkali consumption. A neutral by-product stream is also easier to handle due to the lower corrosiveness when compared to conventional procedures.
A non-crystallizing, atmospheric type nitric acid-s based chlorine dioxide generation process can be operated in a single reaction vessel or in a multi vessel arrangement. In the latter case, the effluent from a primary reactor is directed to the secondary reactor enabling a further conversion of unreacted chlorate with an additional feed of the reducing agent.
The acidity level in the secondary reactor may be increased, if desired, to higher values, typically up to about 7 N, preferably about 5 to about 7 N, in order to ensure a substantially complete conversion of chlorate ions, thus minimizing losses of chlorate with the effluent. The effluent from the primary or secondary reactor may also be directed (cascaded) to a single vessel subatmospheric type process.
Alternatively, the effluent from the primary or secondary generator can be subjected to electrochemical acidification in the manner described in more detail above and recycled to the generator. It is possible, if desired, to effect hydrochloric acid addition to the secondary reactor in order to lower the residual chlorate ion concentration.
If desired, an effluent from the non-crystallizing chlorine dioxide generating process described above containing unreacted nitric acid and alkali metal nitrate may be used as a nutrient for biological effluent treatment or for pH control in the bleach plant of a pulp mill. Since essentially all nitrates are highly soluble, the use of nitric acid may be beneficial as compared to sulfuric acid due to the absence of scale forming deposits.
Both the crystallizing and non-crystallizing type nitric acid-based chlorine dioxide generation operations provided in accordance with the present invention, can operate in the substantial absence of added chloride ions. However, small additions of chloride can be made, if desired.
The chlorine dioxide generating process provided herein can operate with the optional addition of a catalyst selected from the group of catalysts known in the art, such as those described in US Patent 4,421,730 (Isa et al) or US Patent 4,770,868 (Norell). Examples of typical catalytic ions which may be employed include Ag, Mn, V, Mo, Pd and Pt. While the premixing of the reducing agent (for example, hydrogen peroxide or methanol) with the other feedstocks to the generator can be employed, it is generally not required.
The above-mentioned embodiments of the process of the present invention involve the generation at either atmospheric or subatmospheric pressures. However, it is also possible to operate the process at super atmospheric pressures, especially in water treatment applications.
In some applications of the process of the present invention, it is possible to replace at least part of the nitric acid with another strong acid, for example, perchloric acid. However, in general, it is preferred to operate the process with nitric acid alone as the source of acidity for the process.
In a case when the entire nitric acid feed is replaced by a perchloric acid feed, it is possible to effect an integration of the chlorine dioxide generator with the sodium chlorate manufacturing plant.
The invention is illustrated by the following Example.
EXAMPLE
A subatmospheric pressure pilot plant chlorine dioxide generator had a maximum volume capacity of 20 L. The chlorine dioxide generator was operated to generate chlorine dioxide under the following conditions:
Reducing agent . hydrogen peroxide Liquor Total [H'] : 1.0 to 2.0 N
Liquor [C103-] . 1.0 to 2.0 M
Temperature . about 70°C
5 Pressure . about 165 mmHg (about 22 kPa) Liquor (N03-] . 7.9 to 8.9 M (crystallization of NaN03 observed) .
Chemical feeds were made to the aqueous acid reaction medium (liquor) as the chlorine dioxide generator was 10 operated on a continuous basis at the boiling point of the liquor under the subatmospheric pressure. The chemical feeds were:
70~ w/w HN03 commercial, reagent grade solution 300 g/L HzOz solution prepared from industrial grade 50~ w/w H202.
6 M NaC103 solution prepared from crystallized, industrial grade NaC103 A gaseous mixture of chlorine dioxide, steam and oxygen was removed from the chlorine dioxide generator and an aqueous solution of chlorine dioxide formed from the gaseous mixture. The chemical efficiency of chlorine dioxide production based on gas analysis by gas chromatography, consumption of hydrogen peroxide and rates of chlorine dioxide generation were determined to be as follows:
Chemical efficiency . greater than 95~
H202 consumption . 0.25 to 0.3 t H20z/t C102 Rate of CLOZ generation . 1.4 g.min-1L-1 As may be seen from these results, highly efficient chlorine dioxide generation is achieved at commercially acceptable production rates.
SUMMARY OF DISCLOSURE
In summary of this disclosure, the present invention provides a process for the production of chlorine dioxide in which chlorate ions are reduced in the presence of nitric acid as at least the primary source of acidity for the process. Modifications are possible within the scope of this invention.
In such a case, the alkali metal nitrate crystals which precipitate as a by-product of the process and which are continuously or periodically removed from the generator, can be dissolved, optionally with alkali metal chlorate, and the resulting solution can be subjected to an electrochemical acidification step, using one of the electrochemical processes described above, and the resulting acidified solution can be directed to the generator. Such electrochemical acidification may be effected in a manner to coproduce an alkali metal hydroxide, preferably sodium hydroxide, in the electrochemical cell as described above.
The alkali metal nitrate is a high value by product of the crystallizing mode of operation, which can be readily used, for example, as a nutrient for biological effluent treatment or as a fertilizer. When the alkali metal nitrate comprises sodium nitrate, a further conversion, for example, via metathesis, to other nitrates, for example, potassium nitrate or ammonium nitrate, is also possible.
When compared to the conventional sulfuric acid-based chlorine dioxide generating process, the nitric acid-based process of the present invention offers some additional advantages in terms of the composition of the crystalline by-product precipitated in the generator in the crystallizing mode of operation. While the conventional generators often co-produce an acidic sulfate, such as sodium sesquisulfate, having regard to the operating acid normality the process of the present invention always yields a neutral salt irrespective of the total acid normality of the reaction medium, thus minimizing the acid and alkali consumption. A neutral by-product stream is also easier to handle due to the lower corrosiveness when compared to conventional procedures.
A non-crystallizing, atmospheric type nitric acid-s based chlorine dioxide generation process can be operated in a single reaction vessel or in a multi vessel arrangement. In the latter case, the effluent from a primary reactor is directed to the secondary reactor enabling a further conversion of unreacted chlorate with an additional feed of the reducing agent.
The acidity level in the secondary reactor may be increased, if desired, to higher values, typically up to about 7 N, preferably about 5 to about 7 N, in order to ensure a substantially complete conversion of chlorate ions, thus minimizing losses of chlorate with the effluent. The effluent from the primary or secondary reactor may also be directed (cascaded) to a single vessel subatmospheric type process.
Alternatively, the effluent from the primary or secondary generator can be subjected to electrochemical acidification in the manner described in more detail above and recycled to the generator. It is possible, if desired, to effect hydrochloric acid addition to the secondary reactor in order to lower the residual chlorate ion concentration.
If desired, an effluent from the non-crystallizing chlorine dioxide generating process described above containing unreacted nitric acid and alkali metal nitrate may be used as a nutrient for biological effluent treatment or for pH control in the bleach plant of a pulp mill. Since essentially all nitrates are highly soluble, the use of nitric acid may be beneficial as compared to sulfuric acid due to the absence of scale forming deposits.
Both the crystallizing and non-crystallizing type nitric acid-based chlorine dioxide generation operations provided in accordance with the present invention, can operate in the substantial absence of added chloride ions. However, small additions of chloride can be made, if desired.
The chlorine dioxide generating process provided herein can operate with the optional addition of a catalyst selected from the group of catalysts known in the art, such as those described in US Patent 4,421,730 (Isa et al) or US Patent 4,770,868 (Norell). Examples of typical catalytic ions which may be employed include Ag, Mn, V, Mo, Pd and Pt. While the premixing of the reducing agent (for example, hydrogen peroxide or methanol) with the other feedstocks to the generator can be employed, it is generally not required.
The above-mentioned embodiments of the process of the present invention involve the generation at either atmospheric or subatmospheric pressures. However, it is also possible to operate the process at super atmospheric pressures, especially in water treatment applications.
In some applications of the process of the present invention, it is possible to replace at least part of the nitric acid with another strong acid, for example, perchloric acid. However, in general, it is preferred to operate the process with nitric acid alone as the source of acidity for the process.
In a case when the entire nitric acid feed is replaced by a perchloric acid feed, it is possible to effect an integration of the chlorine dioxide generator with the sodium chlorate manufacturing plant.
The invention is illustrated by the following Example.
EXAMPLE
A subatmospheric pressure pilot plant chlorine dioxide generator had a maximum volume capacity of 20 L. The chlorine dioxide generator was operated to generate chlorine dioxide under the following conditions:
Reducing agent . hydrogen peroxide Liquor Total [H'] : 1.0 to 2.0 N
Liquor [C103-] . 1.0 to 2.0 M
Temperature . about 70°C
5 Pressure . about 165 mmHg (about 22 kPa) Liquor (N03-] . 7.9 to 8.9 M (crystallization of NaN03 observed) .
Chemical feeds were made to the aqueous acid reaction medium (liquor) as the chlorine dioxide generator was 10 operated on a continuous basis at the boiling point of the liquor under the subatmospheric pressure. The chemical feeds were:
70~ w/w HN03 commercial, reagent grade solution 300 g/L HzOz solution prepared from industrial grade 50~ w/w H202.
6 M NaC103 solution prepared from crystallized, industrial grade NaC103 A gaseous mixture of chlorine dioxide, steam and oxygen was removed from the chlorine dioxide generator and an aqueous solution of chlorine dioxide formed from the gaseous mixture. The chemical efficiency of chlorine dioxide production based on gas analysis by gas chromatography, consumption of hydrogen peroxide and rates of chlorine dioxide generation were determined to be as follows:
Chemical efficiency . greater than 95~
H202 consumption . 0.25 to 0.3 t H20z/t C102 Rate of CLOZ generation . 1.4 g.min-1L-1 As may be seen from these results, highly efficient chlorine dioxide generation is achieved at commercially acceptable production rates.
SUMMARY OF DISCLOSURE
In summary of this disclosure, the present invention provides a process for the production of chlorine dioxide in which chlorate ions are reduced in the presence of nitric acid as at least the primary source of acidity for the process. Modifications are possible within the scope of this invention.
Claims (21)
1. A process for the production of chlorine dioxide, which comprises reducing chlorate ions with hydrogen peroxide or methanol in an aqueous reaction medium, said aqueous reaction medium containing nitric acid, having a total acid normality of less than about 2 N and having a chlorate ion concentration of about 2 to about 3 M.
2. The process of claim 1 which is carried out in the substantial absence of sulfate ions.
3. The process of claim 1 or 2 wherein said aqueous acid reaction medium has a total acid normality of about 0.5 to about 2 N.
4. The process of any one of claims 1 to 3 wherein the chlorate ions in said aqueous acid reaction medium are selected from the group consisting of an alkali metal chlorate, chloric acid and a mixture of alkali metal chlorate and chloric acid.
5. The process of any one of claims 1 to 4 wherein said aqueous acid reaction medium is maintained at its boiling point in a reaction zone while a subatmospheric pressure is applied to the reaction zone.
6. The process of claim 5 wherein said reaction medium is maintained at a boiling point of about 50 to about 90°C while a subatmospheric pressure of about 80 to about 400 mmHg (about 11 to about 53 kPa) is applied to the reaction zone.
7. The process of claim 6 wherein said temperature is about 70 to about 80°C and said subatmospheric pressure is about 100 to about 250 mmHg (about 13 to about kPa).
8. The process of any one of claims 1 to 7 wherein said aqueous acid reaction medium is continuously or periodically removed from the reaction zone, subjected to electrochemical acidification in an anodic compartment of an electrochemical cell to at least partially regenerate acidity values consumed in the chlorine dioxide generating process with the cogeneration of alkali metal hydroxide in a cathodic compartment of the electrochemical cell, and the resulting acidified reaction medium is recycled back to the reaction zone.
9. The process of claim 8 wherein said electrochemical cell is a two-compartment cell wherein said anodic compartment and said cathodic compartment are separated by a cation-exchange membrane.
10. The process of claim 8 wherein said electrochemical cell is a three-compartment cell divided into an anode compartment, a central compartment and said cathodic compartment by two cation-exchange membranes, said removed aqueous acid reaction medium is fed to the central compartment and hydrogen ions generated in the anode compartment are transferred to the central compartment to effect said acidification.
11. The process of any one of claims 8 to 10 wherein the acidified reaction medium recycled to the reaction zone has a ratio of hydrogen ions to alkali metal ions of about 1:100 to about 5:1.
12. The process of claim 11 wherein the ratio of hydrogen ions to alkali metal ions is about 1:30 to about 2:1.
13. The process of any one of claims 1 to 7 wherein a by-product alkali metal nitrate is crystallized from the aqueous acid reaction medium in the reaction zone once saturation is reached after start up.
14. The process of claim 13 wherein said crystallized by-product alkali metal nitrate is continuously or periodically removed from the reaction zone, formed into an aqueous solution, subjected to electrochemical acidification in an anodic compartment of an electrochemical cell to at least partially regenerate acidity values consumed in the chloric dioxide generation process, and the resulting acid solution is recycled back to the reaction zone.
15. The process of claim 14 wherein alkali metal chlorate is added to said aqueous solution of alkali metal nitrate prior to said electrochemical acidification.
16. The process of any one of claims 1 to 7 which is carried out in a non-crystallizing mode of operation wherein aqueous effluent from a primary reaction zone is forwarded to a secondary reaction zone for a further reduction of chlorate unreacted in the primary reaction zone to chlorine dioxide with an additional feed of reducing agent to the secondary reaction zone.
17. The process of claim 16 wherein the aqueous acid reaction medium in the secondary reaction zone has a total acid normality of about 5 to about 7 N.
18. The process of any one of claims 1 to 17 wherein said alkali metal chlorate is sodium chlorate.
19. The process of any one of claims 1 to 18 which is carried out in the substantial absence of chloride ions.
20. The process of any one of claims 1 to 19 which is carried out in the presence of a catalyst for the chlorine dioxide generating reaction.
21. The process of claim 20 wherein said catalyst is selected from the group consisting of Ag, Mn, V, Mo, Pd and Pt.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US5455797P | 1997-08-01 | 1997-08-01 | |
| US60/054,557 | 1997-08-01 |
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| CA2242685A1 CA2242685A1 (en) | 1999-02-01 |
| CA2242685C true CA2242685C (en) | 2004-09-28 |
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| CA 2242685 Expired - Lifetime CA2242685C (en) | 1997-08-01 | 1998-07-09 | Nitric acid based chlorine dioxide generation process |
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| CA (1) | CA2242685C (en) |
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| CN105417497B (en) * | 2015-12-15 | 2017-12-08 | 刘学思 | A kind of process units and technique of high concentration of chlorine dioxide stable state liquid |
| CN105540548B (en) * | 2016-03-01 | 2017-08-11 | 四川清源环境工程有限公司 | A kind of method for preparing chlorine dioxide |
| CN110117794B (en) * | 2019-05-21 | 2021-05-18 | 盐城工学院 | Electro-reduction of CO2Three-chamber type electrolytic cell device for preparing formate and electrolytic method thereof |
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| Publication number | Priority date | Publication date | Assignee | Title |
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| GB663218A (en) * | 1948-03-17 | 1951-12-19 | Tennants Cons Ltd | Improvements in process for making chlorine dioxide |
| GB687099A (en) * | 1950-11-25 | 1953-02-04 | Tennants Cons Ltd | Improvements in or relating to the generation of high quality chlorine dioxide |
| CA1079931A (en) * | 1976-03-19 | 1980-06-24 | Richard Swindells | High efficiency production of chlorine dioxide by solvay process |
| JPS5953205B2 (en) * | 1981-05-19 | 1984-12-24 | 日本カ−リツト株式会社 | Method of producing high purity chlorine dioxide |
| SE500042C2 (en) * | 1990-08-31 | 1994-03-28 | Eka Nobel Ab | Process for continuous production of chlorine dioxide |
| US5487881A (en) * | 1993-02-26 | 1996-01-30 | Eka Nobel Inc. | Process of producing chlorine dioxide |
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| CN1126712C (en) | 2003-11-05 |
| CA2242685A1 (en) | 1999-02-01 |
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