CA1112845A - Destruction of sodium hypochlorite in solutions from a chlorate electrolytic cell - Google Patents
Destruction of sodium hypochlorite in solutions from a chlorate electrolytic cellInfo
- Publication number
- CA1112845A CA1112845A CA331,845A CA331845A CA1112845A CA 1112845 A CA1112845 A CA 1112845A CA 331845 A CA331845 A CA 331845A CA 1112845 A CA1112845 A CA 1112845A
- Authority
- CA
- Canada
- Prior art keywords
- chlorate
- solution
- ammonia
- hypochlorite
- sodium hypochlorite
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
- XTEGARKTQYYJKE-UHFFFAOYSA-M Chlorate Chemical compound [O-]Cl(=O)=O XTEGARKTQYYJKE-UHFFFAOYSA-M 0.000 title claims abstract description 89
- SUKJFIGYRHOWBL-UHFFFAOYSA-N sodium hypochlorite Chemical compound [Na+].Cl[O-] SUKJFIGYRHOWBL-UHFFFAOYSA-N 0.000 title claims abstract description 33
- 239000005708 Sodium hypochlorite Substances 0.000 title claims abstract description 26
- 230000006378 damage Effects 0.000 title claims description 14
- QGZKDVFQNNGYKY-UHFFFAOYSA-N Ammonia Chemical compound N QGZKDVFQNNGYKY-UHFFFAOYSA-N 0.000 claims abstract description 82
- WQYVRQLZKVEZGA-UHFFFAOYSA-N hypochlorite Chemical compound Cl[O-] WQYVRQLZKVEZGA-UHFFFAOYSA-N 0.000 claims abstract description 57
- 229910021529 ammonia Inorganic materials 0.000 claims abstract description 34
- 150000003863 ammonium salts Chemical class 0.000 claims abstract description 16
- 239000003795 chemical substances by application Substances 0.000 claims abstract description 9
- NLXLAEXVIDQMFP-UHFFFAOYSA-N Ammonia chloride Chemical group [NH4+].[Cl-] NLXLAEXVIDQMFP-UHFFFAOYSA-N 0.000 claims description 16
- 238000000034 method Methods 0.000 claims description 14
- 235000019270 ammonium chloride Nutrition 0.000 claims description 8
- 230000014759 maintenance of location Effects 0.000 claims description 7
- 239000012429 reaction media Substances 0.000 claims description 3
- 238000003756 stirring Methods 0.000 claims description 3
- 238000006243 chemical reaction Methods 0.000 abstract description 32
- BFNBIHQBYMNNAN-UHFFFAOYSA-N ammonium sulfate Chemical compound N.N.OS(O)(=O)=O BFNBIHQBYMNNAN-UHFFFAOYSA-N 0.000 abstract description 2
- 229910052921 ammonium sulfate Inorganic materials 0.000 abstract description 2
- 239000001166 ammonium sulphate Substances 0.000 abstract description 2
- 235000011130 ammonium sulphate Nutrition 0.000 abstract description 2
- YUUVAZCKXDQEIS-UHFFFAOYSA-N azanium;chlorite Chemical compound [NH4+].[O-]Cl=O YUUVAZCKXDQEIS-UHFFFAOYSA-N 0.000 abstract 1
- 150000001875 compounds Chemical class 0.000 abstract 1
- 239000000243 solution Substances 0.000 description 40
- QDHHCQZDFGDHMP-UHFFFAOYSA-N Chloramine Chemical class ClN QDHHCQZDFGDHMP-UHFFFAOYSA-N 0.000 description 16
- ZAMOUSCENKQFHK-UHFFFAOYSA-N Chlorine atom Chemical compound [Cl] ZAMOUSCENKQFHK-UHFFFAOYSA-N 0.000 description 8
- FAPWRFPIFSIZLT-UHFFFAOYSA-M Sodium chloride Chemical compound [Na+].[Cl-] FAPWRFPIFSIZLT-UHFFFAOYSA-M 0.000 description 8
- 239000000460 chlorine Substances 0.000 description 8
- 229910052801 chlorine Inorganic materials 0.000 description 8
- 229910000069 nitrogen hydride Inorganic materials 0.000 description 8
- VHUUQVKOLVNVRT-UHFFFAOYSA-N Ammonium hydroxide Chemical compound [NH4+].[OH-] VHUUQVKOLVNVRT-UHFFFAOYSA-N 0.000 description 7
- 235000011114 ammonium hydroxide Nutrition 0.000 description 7
- BZSXEZOLBIJVQK-UHFFFAOYSA-N 2-methylsulfonylbenzoic acid Chemical compound CS(=O)(=O)C1=CC=CC=C1C(O)=O BZSXEZOLBIJVQK-UHFFFAOYSA-N 0.000 description 6
- 229910019093 NaOCl Inorganic materials 0.000 description 6
- 239000000908 ammonium hydroxide Substances 0.000 description 6
- 238000004519 manufacturing process Methods 0.000 description 6
- VEXZGXHMUGYJMC-UHFFFAOYSA-N Hydrochloric acid Chemical compound Cl VEXZGXHMUGYJMC-UHFFFAOYSA-N 0.000 description 5
- 239000011780 sodium chloride Substances 0.000 description 4
- HEMHJVSKTPXQMS-UHFFFAOYSA-M Sodium hydroxide Chemical compound [OH-].[Na+] HEMHJVSKTPXQMS-UHFFFAOYSA-M 0.000 description 3
- XTEGARKTQYYJKE-UHFFFAOYSA-N chloric acid Chemical compound OCl(=O)=O XTEGARKTQYYJKE-UHFFFAOYSA-N 0.000 description 3
- 230000007797 corrosion Effects 0.000 description 3
- 238000005260 corrosion Methods 0.000 description 3
- 230000000694 effects Effects 0.000 description 3
- 239000007800 oxidant agent Substances 0.000 description 3
- JHWIEAWILPSRMU-UHFFFAOYSA-N 2-methyl-3-pyrimidin-4-ylpropanoic acid Chemical compound OC(=O)C(C)CC1=CC=NC=N1 JHWIEAWILPSRMU-UHFFFAOYSA-N 0.000 description 2
- MHAJPDPJQMAIIY-UHFFFAOYSA-N Hydrogen peroxide Chemical compound OO MHAJPDPJQMAIIY-UHFFFAOYSA-N 0.000 description 2
- 230000015572 biosynthetic process Effects 0.000 description 2
- 239000006227 byproduct Substances 0.000 description 2
- 150000001805 chlorine compounds Chemical class 0.000 description 2
- 238000002425 crystallisation Methods 0.000 description 2
- 230000008025 crystallization Effects 0.000 description 2
- 238000000354 decomposition reaction Methods 0.000 description 2
- 230000001066 destructive effect Effects 0.000 description 2
- 238000005868 electrolysis reaction Methods 0.000 description 2
- 229960000443 hydrochloric acid Drugs 0.000 description 2
- 235000011167 hydrochloric acid Nutrition 0.000 description 2
- 230000001590 oxidative effect Effects 0.000 description 2
- 230000000717 retained effect Effects 0.000 description 2
- GEHJYWRUCIMESM-UHFFFAOYSA-L sodium sulfite Chemical compound [Na+].[Na+].[O-]S([O-])=O GEHJYWRUCIMESM-UHFFFAOYSA-L 0.000 description 2
- GETQZCLCWQTVFV-UHFFFAOYSA-N trimethylamine Chemical compound CN(C)C GETQZCLCWQTVFV-UHFFFAOYSA-N 0.000 description 2
- QGZKDVFQNNGYKY-UHFFFAOYSA-O Ammonium Chemical compound [NH4+] QGZKDVFQNNGYKY-UHFFFAOYSA-O 0.000 description 1
- VEXZGXHMUGYJMC-UHFFFAOYSA-M Chloride anion Chemical compound [Cl-] VEXZGXHMUGYJMC-UHFFFAOYSA-M 0.000 description 1
- WQDWFCGISCUJEK-UHFFFAOYSA-N [Cl].ClN Chemical compound [Cl].ClN WQDWFCGISCUJEK-UHFFFAOYSA-N 0.000 description 1
- 229940077464 ammonium ion Drugs 0.000 description 1
- AQLMHYSWFMLWBS-UHFFFAOYSA-N arsenite(1-) Chemical compound O[As](O)[O-] AQLMHYSWFMLWBS-UHFFFAOYSA-N 0.000 description 1
- 239000003153 chemical reaction reagent Substances 0.000 description 1
- 230000007423 decrease Effects 0.000 description 1
- 230000001419 dependent effect Effects 0.000 description 1
- 238000002474 experimental method Methods 0.000 description 1
- 239000000203 mixture Substances 0.000 description 1
- VIKNJXKGJWUCNN-XGXHKTLJSA-N norethisterone Chemical compound O=C1CC[C@@H]2[C@H]3CC[C@](C)([C@](CC4)(O)C#C)[C@@H]4[C@@H]3CCC2=C1 VIKNJXKGJWUCNN-XGXHKTLJSA-N 0.000 description 1
- 238000002360 preparation method Methods 0.000 description 1
- 235000010265 sodium sulphite Nutrition 0.000 description 1
- 238000004448 titration Methods 0.000 description 1
Classifications
-
- C—CHEMISTRY; METALLURGY
- C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
- C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
- C25B1/00—Electrolytic production of inorganic compounds or non-metals
- C25B1/01—Products
- C25B1/24—Halogens or compounds thereof
- C25B1/26—Chlorine; Compounds thereof
- C25B1/265—Chlorates
-
- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
- C01B11/00—Oxides or oxyacids of halogens; Salts thereof
- C01B11/12—Chloric acid
- C01B11/14—Chlorates
- C01B11/145—Separation; Crystallisation; Purification, After-treatment; Stabilisation by additives
Landscapes
- Chemical & Material Sciences (AREA)
- Organic Chemistry (AREA)
- Inorganic Chemistry (AREA)
- Engineering & Computer Science (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Electrochemistry (AREA)
- Materials Engineering (AREA)
- Metallurgy (AREA)
- Electrolytic Production Of Non-Metals, Compounds, Apparatuses Therefor (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE
Sodium hypochlorite present in a chlorate solution from a chlorate electrolytic cell is destroyed by adding to the solution a solution compound selected from ammonia and ammonium salts such as ammonium chlorite and ammonium sul-phate. The destroying agent is added to the solution up-stream of the chlorate crystallizer in such an amount as to provide a molar ratio of hypochlorite to ammonia of less than 1.5. During reaction the pH is maintained at 6.0 to 6.5.
Sodium hypochlorite present in a chlorate solution from a chlorate electrolytic cell is destroyed by adding to the solution a solution compound selected from ammonia and ammonium salts such as ammonium chlorite and ammonium sul-phate. The destroying agent is added to the solution up-stream of the chlorate crystallizer in such an amount as to provide a molar ratio of hypochlorite to ammonia of less than 1.5. During reaction the pH is maintained at 6.0 to 6.5.
Description
B9~5 The present invention relates to the manufacture of sodium chlorate by electrolysis of aqueous sodium chloride and, more particularly, to a process for destroying sodium hypochlorite present in the chlorate solution resulting from the electrolysis ~efore ;t is ~ed to a chlorate crystallizer.
As is well ~nown, a level of sodium hypochlorite is present in the solution leaving the reactor vessels in the chlorate production circuit. In the last stage of said pro-duction circuit, the chlorate solution is fed to a crystalliza-tion tank (crystallizer) generally made of stainless steelwhere the chlorate is allowed to crystallize. As, however, sodium hypochlorite is an active oxidant, it is responsible for extensive corrosion of the crystallizer. Hence, the high desirability of eliminating the hypochlorite from the chlorate solution before the latter is fed to the crystallizer.
The concentration of sodium hypochlorite in the chlorate solution at exit from the reactors is generally in the range of 2000 to 6000 mg.p.l. From the reactors, the solution at pH 6.0 to 6.8 is fed to a retention tank where it is retained for 1 to 8 hours during which the hypochlorite concentration is reduced to the range of 200 to 1000 mg.p.l.
by conversion to chlorate. If the solution was retained for a sufficiently long time at optimum temperature and pH level for hypochlorite conversion to chlorate, then the hypochlorite would substantially completely disappear. However, the time necessary for this conversion is so long as to be impractical (e.g. 36 hours are necessary to reduce hypochlorite concen-tration from 3500 mg.p.l. to 0.7 mg.p.l. at a pH suitable for maximum conversion rate~. Thus~ various techniques have been proposed for the destruction of hypochlorite still present in B4~
the chlorate solution at exit from the retention tank. Two such techniques which involve the reaction of hypochlorite with hydrogen peroxide and sodium sulphite, respectively, have never been adopted because they are both costly and, further-more, the latter one results in highly undesirable by-products.
A third technique which consists in the addition of ammonia or ammonium salts to the chlorate solution, has been adopted and practised by several _hlorate plants. As these plants, however, have continued to experience extensive corrosion of the crystal-lizers and ensuing equipment, this third technique has not metwith full success due apparently to uncontrolled factors in the destruction reactions.
The reaction between ammonia or ammonium salts and sodium hypochlorite is known to proceed rapidly and to result in the complete destruction of the latter. The said reaction, however, results in the production of chloramines which, like the hypochlorite, are active oxidants. Thus, the net result of the reaction is that, whereas sodium hypochlorite is destroyed, --another oxidant (the chloramines) is produced which, like the -hypochlorite, leads to extensive corrosion of the chlorate crystallizer.
It has now been found that the amount of chloramines produced in the reaction ~etween ammonia or ammonium salts and sodium hypochlorite can be maintained at a very low level if the reaction is carried under certain very specific conditions to be defined hereinafter.
It is therefore a principal object of the invention to provide a process to destroy sodium hypochlorite present in chlorate solutions from electrolytic chlorate cells.
It is another object of this invention to provide a process for destroying sodium hypochlorite present in chlorate solutions by addition of ammonia or an ammonium salt to said solutions.
It is still another object of this invention to provide a process for destroying sodium hypochlorite present in chlorate solutions by means of ammonia or ammonium salts while maintaining production of by-product chloramines at a very low level.
The foregoing and additional objects will become apparent from the following description, taken in conjunction with the accompanying drawings and attached claims.
The process according to the present invention com-prises the destruction of sodium hypochlorite present in a chlorate solution from a chlorate electrolytic cell by the addition of ammonia or an ammonium salt to the solution before it is fed to a chlorate crystallizer and is especially charac-terized in that the ammonia or ammonium salt is added to the solution in such an amount as to provide a molar ratio of sodium hypochlorite to ammonia of less than 1.5 and that the pH of the solution after addition of ammonia or ammonium salt is maintained within the range 6.0 to 6.5.
The invention will now be described in detail having reference to the accompanying drawings in which:
Figure 1 is a graph illustrating the theoretical amount of hypochlorite destroyed and chloramine produced through reaction with varying amounts of ammonia; and Figure 2 is a graph showing the effect of pH on the decomposition rate of residual chlorine (chloramine) at 60C
and with constant stirring.
In essence, the present invention is based on the 4~
discovery that the reaction between sodium hypochlorite present in a chlorate solution and ammonia or an ammonium salt results in very little residual chlorine in the form of chloramine in the solution if ammonia or an ammonium salt is added to the sol-ution in such an amount as to provide a NaOCl/NH3 molar ratio of l.S or less and if the pH of the reaction medium is kept within the range of about 6.0 to 6.5. ~s the addition of ammonia or ammonium salt has the effect of raising the pH, the chlorate solution prior to said addition should suitably be at a pH of about 4.5 to 5.5.
For simplicity, the detailed des¢ription of the invention will now be made using-ammonia as the reagent for hypochlorite. It should be understood however that the description equally applies to ammonium salts such as for instance ammonium chloride and ammonium sulphate.
When ammonia is added to a chlorate solution contain-ing sodium hypochlorite, the reaction mechanism whereby the hypochlorite is destroyed with concomittant formation of a chloramine can be illustrated as follows:
2NH3 ~ 2NaOCl -~ 2NH2Cl + 2NaOH (1) This reaction appears to be rapid and to be the first step in any hypochlorite destruction mechanism involving ammo-nium ion. ~his reaction can be followed by the reaction:
2NH2Cl + NaOC1 -~ N2 + NaCl + H2O + 2HCl (2) Clearly, if there is insufficient ammonia to form chloramine by reaction (1), then after reaction (2) hypochlorite remains in excess. The percentage destruction of a given quantity of hypochlorite by ammonia has been calculated for a range of NaOCl/NH3 molar ratios. The results are plotted in Figure 1 and are particularly shown in Region A of this figure.
In this region the residual chlorine compound is obviously hypochlorite. As the NaOCl/NH3 molar ratio decreases below 1.5, the situation arises where there is insufficient hypo-chlorite left for the complete descruction by reaction (2) of the chloramine formed in reaction ~1). In this event a residual chloramine content exists in solution which can rise theoreti-cally to a maximum of 100% conversion of hypochlorite to chloramine at NaOC1/NH3 molar ratio of 1Ø At ratios between 1.0 and 1.5, the residual chlorine compound is chloramine as shown in Region B of Figure 1. Comparison of the above theore-tically derived regions with experimentally derived data shows excellent agreement for Region A but poor agreement for Region B with experimental values for residual chlorine always being below theory. This discrepancy between experiment and theory in Region B is explained by the closeness of the relative rates of formation of chloramine (reaction 1) and destruction thereof by hypochlorite (reaction 2).
When the molar ratio of NaOCl/NH3 becomes less than 1.0 as shown in Region C of Figure 1, a new situation arises where ammonia is present in sufficient amount to allow the following decomposition reaction to take place:
3NH2Cl + NH3 --3 N2 + HCl + 2NH4Cl (3) It has been found experimentally, and this is clearly illustrated in Figure 2, that this reaction is pH dependent in that its rate increases with acidity between pH 10 and pH 6.
Thus where sufficient ammonia is used to obtain a NaOCl/NH3 molar ratio of less than 1.0, reaction (3) is sufficiently rapid at pH 6.0 to 6.5 that ultimate levels of chloramine of 0.1 m Mole/l (milli mole litre) are attained with a total residence 30 time after ammonia addition, of approximately 90 minutes.
~2a4~;
On the basis of the above, it has been determined that the addition of ammonia to a chlorate solution containing an undesirable amount of sodium hypochlorite results in the substantially complete destruction of the hypochlorite and very little residual chlorine in the form of chloramine, if the ammonia is added to the solution in such amount as to pro-vide a molar ratio NaOCl/NH3 of less than 1.5 and the pH of the total reaction medium after addition of ammonia is main-tained in the range 6.0 to 6.5. In order to obtain the above pH range, the chlorate solution before ammonia is added thereto must be in the range 4.5 to 5.5. However, when an ammonium salt is used instead of ammonia as the destructive agent for hypochlorite, the chlorate solution prior to addition of the ammonium salt should already be at pH of about 7 to 8.5.
In practice, the destruction of sodium hypochlorite by the process of this invention, may be effected at any stage in the chlorate production circuit, between the chlorate cell reactors and the chlorate crystallizer. It is much preferred, however, that hypochlorite destruction be effected after the stage known as the retention stage in which the chlorate solu-tion is allowed to stand for a period of 1 to 8 hours. During this retention period, the sodium hypochlorite concentration in the chlorate solution is reduced from 2000-6000 mg.p.l.
(concentxation at exit from chlorate cell reactors) to 200-1000 mg.p.l. by conversion of the hypochlorite to chlorate.
In addition, the pH of the chlorate solution after the reten-tion stage is in the range of 4.5 to 6Ø Thus the advantages of adding ammonia or ammonium chloride to the sodium chlorate solution after the retention stage are readily apparent from the above. When it is necessary to adjust the pH of the g5 solution prior to ammonia or am~o~ium chloride addition, this may suitably be done by adding sodium hydroxide or hydro-chloric acid as the case may be.
In certain circumstances, it may be necessary to proceed to the destruction of the hypochlorite only after the chlorate solution has been made strongly alkaline (pH 10 to 11) in preparation for the crystallization stage~ In such a case the pH of the solution must be brought down to the suitable range by means of hydrochloric acid before any addition of ammonia or ammonium chloride.
For best results, the chlorate solution during reaction between hypochlorite and ammonia or ammonium chloride should be kept under constant stirring and should be at an elevated temperature, preferably about 40C.
; If desired, any residual chloramine left in the chlorate solution after the above described treatment may be efficiently and quickly destroyed by the addition of a stoichiometric amount of trimethylamine.
The following examples are illustrative of the practice 20 of the invention. -Example 1 Eleven aliquots of a sodium chlorate solution contain-ing 600 g/l of sodium chlorate, 110 g/l of sodium chloride, 3 g/l of sodium dichromate and 0.8 g/l of sodium hypochlorite ; at a pH of 5.5 and a temperature of 60C were subjected to treatment with ammonium hydroxide. To each aliquot ammonium hydroxide was added in such an amount that from aliquot (1) to aliquot (11) the molar ratio of sodium hypochlorite to ammonium hydroxide varied from 0.75 to 3.85. For each aliquot, the reaction was allowed to proceed for 30 minutes whereafter the a~
final pH was determined and the residual active chlorine was determined by arsenite titration. The results obtained with the eleven aliquots are recorded in Table I. It can be clearly seen from Table I that the residual active chlorine increases sharply when the molar ratio of sodium hypochlorite to ammonium hydroxide exceeds 1.55.
Table I
Aliquot ReactantsResidual Final Number ~NaClO~Chlorine pH
~NH4OH] mg/l 1 0.75 373
As is well ~nown, a level of sodium hypochlorite is present in the solution leaving the reactor vessels in the chlorate production circuit. In the last stage of said pro-duction circuit, the chlorate solution is fed to a crystalliza-tion tank (crystallizer) generally made of stainless steelwhere the chlorate is allowed to crystallize. As, however, sodium hypochlorite is an active oxidant, it is responsible for extensive corrosion of the crystallizer. Hence, the high desirability of eliminating the hypochlorite from the chlorate solution before the latter is fed to the crystallizer.
The concentration of sodium hypochlorite in the chlorate solution at exit from the reactors is generally in the range of 2000 to 6000 mg.p.l. From the reactors, the solution at pH 6.0 to 6.8 is fed to a retention tank where it is retained for 1 to 8 hours during which the hypochlorite concentration is reduced to the range of 200 to 1000 mg.p.l.
by conversion to chlorate. If the solution was retained for a sufficiently long time at optimum temperature and pH level for hypochlorite conversion to chlorate, then the hypochlorite would substantially completely disappear. However, the time necessary for this conversion is so long as to be impractical (e.g. 36 hours are necessary to reduce hypochlorite concen-tration from 3500 mg.p.l. to 0.7 mg.p.l. at a pH suitable for maximum conversion rate~. Thus~ various techniques have been proposed for the destruction of hypochlorite still present in B4~
the chlorate solution at exit from the retention tank. Two such techniques which involve the reaction of hypochlorite with hydrogen peroxide and sodium sulphite, respectively, have never been adopted because they are both costly and, further-more, the latter one results in highly undesirable by-products.
A third technique which consists in the addition of ammonia or ammonium salts to the chlorate solution, has been adopted and practised by several _hlorate plants. As these plants, however, have continued to experience extensive corrosion of the crystal-lizers and ensuing equipment, this third technique has not metwith full success due apparently to uncontrolled factors in the destruction reactions.
The reaction between ammonia or ammonium salts and sodium hypochlorite is known to proceed rapidly and to result in the complete destruction of the latter. The said reaction, however, results in the production of chloramines which, like the hypochlorite, are active oxidants. Thus, the net result of the reaction is that, whereas sodium hypochlorite is destroyed, --another oxidant (the chloramines) is produced which, like the -hypochlorite, leads to extensive corrosion of the chlorate crystallizer.
It has now been found that the amount of chloramines produced in the reaction ~etween ammonia or ammonium salts and sodium hypochlorite can be maintained at a very low level if the reaction is carried under certain very specific conditions to be defined hereinafter.
It is therefore a principal object of the invention to provide a process to destroy sodium hypochlorite present in chlorate solutions from electrolytic chlorate cells.
It is another object of this invention to provide a process for destroying sodium hypochlorite present in chlorate solutions by addition of ammonia or an ammonium salt to said solutions.
It is still another object of this invention to provide a process for destroying sodium hypochlorite present in chlorate solutions by means of ammonia or ammonium salts while maintaining production of by-product chloramines at a very low level.
The foregoing and additional objects will become apparent from the following description, taken in conjunction with the accompanying drawings and attached claims.
The process according to the present invention com-prises the destruction of sodium hypochlorite present in a chlorate solution from a chlorate electrolytic cell by the addition of ammonia or an ammonium salt to the solution before it is fed to a chlorate crystallizer and is especially charac-terized in that the ammonia or ammonium salt is added to the solution in such an amount as to provide a molar ratio of sodium hypochlorite to ammonia of less than 1.5 and that the pH of the solution after addition of ammonia or ammonium salt is maintained within the range 6.0 to 6.5.
The invention will now be described in detail having reference to the accompanying drawings in which:
Figure 1 is a graph illustrating the theoretical amount of hypochlorite destroyed and chloramine produced through reaction with varying amounts of ammonia; and Figure 2 is a graph showing the effect of pH on the decomposition rate of residual chlorine (chloramine) at 60C
and with constant stirring.
In essence, the present invention is based on the 4~
discovery that the reaction between sodium hypochlorite present in a chlorate solution and ammonia or an ammonium salt results in very little residual chlorine in the form of chloramine in the solution if ammonia or an ammonium salt is added to the sol-ution in such an amount as to provide a NaOCl/NH3 molar ratio of l.S or less and if the pH of the reaction medium is kept within the range of about 6.0 to 6.5. ~s the addition of ammonia or ammonium salt has the effect of raising the pH, the chlorate solution prior to said addition should suitably be at a pH of about 4.5 to 5.5.
For simplicity, the detailed des¢ription of the invention will now be made using-ammonia as the reagent for hypochlorite. It should be understood however that the description equally applies to ammonium salts such as for instance ammonium chloride and ammonium sulphate.
When ammonia is added to a chlorate solution contain-ing sodium hypochlorite, the reaction mechanism whereby the hypochlorite is destroyed with concomittant formation of a chloramine can be illustrated as follows:
2NH3 ~ 2NaOCl -~ 2NH2Cl + 2NaOH (1) This reaction appears to be rapid and to be the first step in any hypochlorite destruction mechanism involving ammo-nium ion. ~his reaction can be followed by the reaction:
2NH2Cl + NaOC1 -~ N2 + NaCl + H2O + 2HCl (2) Clearly, if there is insufficient ammonia to form chloramine by reaction (1), then after reaction (2) hypochlorite remains in excess. The percentage destruction of a given quantity of hypochlorite by ammonia has been calculated for a range of NaOCl/NH3 molar ratios. The results are plotted in Figure 1 and are particularly shown in Region A of this figure.
In this region the residual chlorine compound is obviously hypochlorite. As the NaOCl/NH3 molar ratio decreases below 1.5, the situation arises where there is insufficient hypo-chlorite left for the complete descruction by reaction (2) of the chloramine formed in reaction ~1). In this event a residual chloramine content exists in solution which can rise theoreti-cally to a maximum of 100% conversion of hypochlorite to chloramine at NaOC1/NH3 molar ratio of 1Ø At ratios between 1.0 and 1.5, the residual chlorine compound is chloramine as shown in Region B of Figure 1. Comparison of the above theore-tically derived regions with experimentally derived data shows excellent agreement for Region A but poor agreement for Region B with experimental values for residual chlorine always being below theory. This discrepancy between experiment and theory in Region B is explained by the closeness of the relative rates of formation of chloramine (reaction 1) and destruction thereof by hypochlorite (reaction 2).
When the molar ratio of NaOCl/NH3 becomes less than 1.0 as shown in Region C of Figure 1, a new situation arises where ammonia is present in sufficient amount to allow the following decomposition reaction to take place:
3NH2Cl + NH3 --3 N2 + HCl + 2NH4Cl (3) It has been found experimentally, and this is clearly illustrated in Figure 2, that this reaction is pH dependent in that its rate increases with acidity between pH 10 and pH 6.
Thus where sufficient ammonia is used to obtain a NaOCl/NH3 molar ratio of less than 1.0, reaction (3) is sufficiently rapid at pH 6.0 to 6.5 that ultimate levels of chloramine of 0.1 m Mole/l (milli mole litre) are attained with a total residence 30 time after ammonia addition, of approximately 90 minutes.
~2a4~;
On the basis of the above, it has been determined that the addition of ammonia to a chlorate solution containing an undesirable amount of sodium hypochlorite results in the substantially complete destruction of the hypochlorite and very little residual chlorine in the form of chloramine, if the ammonia is added to the solution in such amount as to pro-vide a molar ratio NaOCl/NH3 of less than 1.5 and the pH of the total reaction medium after addition of ammonia is main-tained in the range 6.0 to 6.5. In order to obtain the above pH range, the chlorate solution before ammonia is added thereto must be in the range 4.5 to 5.5. However, when an ammonium salt is used instead of ammonia as the destructive agent for hypochlorite, the chlorate solution prior to addition of the ammonium salt should already be at pH of about 7 to 8.5.
In practice, the destruction of sodium hypochlorite by the process of this invention, may be effected at any stage in the chlorate production circuit, between the chlorate cell reactors and the chlorate crystallizer. It is much preferred, however, that hypochlorite destruction be effected after the stage known as the retention stage in which the chlorate solu-tion is allowed to stand for a period of 1 to 8 hours. During this retention period, the sodium hypochlorite concentration in the chlorate solution is reduced from 2000-6000 mg.p.l.
(concentxation at exit from chlorate cell reactors) to 200-1000 mg.p.l. by conversion of the hypochlorite to chlorate.
In addition, the pH of the chlorate solution after the reten-tion stage is in the range of 4.5 to 6Ø Thus the advantages of adding ammonia or ammonium chloride to the sodium chlorate solution after the retention stage are readily apparent from the above. When it is necessary to adjust the pH of the g5 solution prior to ammonia or am~o~ium chloride addition, this may suitably be done by adding sodium hydroxide or hydro-chloric acid as the case may be.
In certain circumstances, it may be necessary to proceed to the destruction of the hypochlorite only after the chlorate solution has been made strongly alkaline (pH 10 to 11) in preparation for the crystallization stage~ In such a case the pH of the solution must be brought down to the suitable range by means of hydrochloric acid before any addition of ammonia or ammonium chloride.
For best results, the chlorate solution during reaction between hypochlorite and ammonia or ammonium chloride should be kept under constant stirring and should be at an elevated temperature, preferably about 40C.
; If desired, any residual chloramine left in the chlorate solution after the above described treatment may be efficiently and quickly destroyed by the addition of a stoichiometric amount of trimethylamine.
The following examples are illustrative of the practice 20 of the invention. -Example 1 Eleven aliquots of a sodium chlorate solution contain-ing 600 g/l of sodium chlorate, 110 g/l of sodium chloride, 3 g/l of sodium dichromate and 0.8 g/l of sodium hypochlorite ; at a pH of 5.5 and a temperature of 60C were subjected to treatment with ammonium hydroxide. To each aliquot ammonium hydroxide was added in such an amount that from aliquot (1) to aliquot (11) the molar ratio of sodium hypochlorite to ammonium hydroxide varied from 0.75 to 3.85. For each aliquot, the reaction was allowed to proceed for 30 minutes whereafter the a~
final pH was determined and the residual active chlorine was determined by arsenite titration. The results obtained with the eleven aliquots are recorded in Table I. It can be clearly seen from Table I that the residual active chlorine increases sharply when the molar ratio of sodium hypochlorite to ammonium hydroxide exceeds 1.55.
Table I
Aliquot ReactantsResidual Final Number ~NaClO~Chlorine pH
~NH4OH] mg/l 1 0.75 373
2 0.85 332 8.90
3 1.05 298 8.10
4 1.15 179 6.50 1.25 74 7.20 6 1.30 41 6.40 7 1.40 19 6.10 8 1.55 22 5.95 9 1.60 26 5.85 2.20 250 6.25 20 11 3.85 503 6.75 Example ?
In order to determine the effect of pH on hypochlorite destruction, tests were made with three aliquots of a sodium chlorate solution having the same composition and same tempera-ture as in Example 1 except that the pH's of the three aliquots were controlled at 10.5, 8.1 and 6.1 respectively. In all aliquots, ammonium hydroxide was added to obtain a molar ratio of ammonium hydroxide to sodium hypochlorite equal to 1.50. The residual active chlorine in each aliquot was analysed at 10 minutesintervals over a period of 120 minutes. The results are a~s recorded in Table II.
Table II
Time in Residual Active Chlorine .
Minutes Aliquot 1 Aliquot 2 Aliquot 3 , pH 10.5 pH 8.1 pH 6.1 0 800 80~ 800 298 141 N.D.*
283 134 N.D.
268 119 N.D.
100 258 112 N.D.
110 246 104 N.D.
120 231 97 N.D.
*N.D. = Not Detectable Example 3 As indicated in the foregoing description, it has been found that when ammonium chloride is used as the hypo-chlorite destructive agent, the initial pH of the chlorate solution must be adjusted to a sufficiently high level so that it will fall in the suitable range of 5.5 to 6.5 at the end of the reaction. In order to determine how high this initial pH
should be, tests were made with six samples prepared from the following solution:
sodium chlorate 500 g/l sodium chloride 120 g/l _ g _ 12~145 sodium dichromate 3 g/1 sodium hypochlorite 0~8 g~l Temperature 60C
The initial pH values of the six samples were adjusted to 5.0, 6.0, 7.0, 8.0, 9.0 and 10.0 respectively. To each sample ammonium chloride was added to achieve a molar ratio of sodium hypochlorite to ammonium chloride equal to 1.5. Final pH for each sample was determined after 10 minutes of reaction.
The results are as follows:
Sample Initial pH Final pH
1 5.0 1.78 2 6.0 5.23 3 7.0 5.96 4 8.0 6.32 9.0 7.20 6 10.0 8.90
In order to determine the effect of pH on hypochlorite destruction, tests were made with three aliquots of a sodium chlorate solution having the same composition and same tempera-ture as in Example 1 except that the pH's of the three aliquots were controlled at 10.5, 8.1 and 6.1 respectively. In all aliquots, ammonium hydroxide was added to obtain a molar ratio of ammonium hydroxide to sodium hypochlorite equal to 1.50. The residual active chlorine in each aliquot was analysed at 10 minutesintervals over a period of 120 minutes. The results are a~s recorded in Table II.
Table II
Time in Residual Active Chlorine .
Minutes Aliquot 1 Aliquot 2 Aliquot 3 , pH 10.5 pH 8.1 pH 6.1 0 800 80~ 800 298 141 N.D.*
283 134 N.D.
268 119 N.D.
100 258 112 N.D.
110 246 104 N.D.
120 231 97 N.D.
*N.D. = Not Detectable Example 3 As indicated in the foregoing description, it has been found that when ammonium chloride is used as the hypo-chlorite destructive agent, the initial pH of the chlorate solution must be adjusted to a sufficiently high level so that it will fall in the suitable range of 5.5 to 6.5 at the end of the reaction. In order to determine how high this initial pH
should be, tests were made with six samples prepared from the following solution:
sodium chlorate 500 g/l sodium chloride 120 g/l _ g _ 12~145 sodium dichromate 3 g/1 sodium hypochlorite 0~8 g~l Temperature 60C
The initial pH values of the six samples were adjusted to 5.0, 6.0, 7.0, 8.0, 9.0 and 10.0 respectively. To each sample ammonium chloride was added to achieve a molar ratio of sodium hypochlorite to ammonium chloride equal to 1.5. Final pH for each sample was determined after 10 minutes of reaction.
The results are as follows:
Sample Initial pH Final pH
1 5.0 1.78 2 6.0 5.23 3 7.0 5.96 4 8.0 6.32 9.0 7.20 6 10.0 8.90
Claims (4)
1. A process for the destruction of sodium hypochlorite present in a chlorate solution from a chlorate electrolytic cell comprising the addition of a destroying agent selected from ammonia and ammonium salts to the solution before the latter is fed to a chlorate crystallizer, character-ized in that the destroying agent is added to the solution in such an amount as to provide a molar ratio of hypochlorite to ammonia of less than 1.5 and that the pH of the solution after addition of the destroying agent is maintained within the range 6.0 to 6.5.
2. A process as claimed in Claim 1 wherein the chlorate solution is one that has been allowed to stand for 1 to 8 hours in a retention tank and is at a pH of 4.5 to 5.5 and wherein the destroying agent is ammonia.
3. A process as claimed in Claim 1 wherein the pH
of the chlorate solution is adjusted to between 7.0 and 8.5 prior to addition of the destroying agent and wherein said destroying agent is ammonium chloride.
of the chlorate solution is adjusted to between 7.0 and 8.5 prior to addition of the destroying agent and wherein said destroying agent is ammonium chloride.
4. A process as claimed in Claim 1, 2 or 3 wherein the temperature is maintained above 40°C and the reaction medium is kept under constant stirring.
Priority Applications (6)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA331,845A CA1112845A (en) | 1979-07-16 | 1979-07-16 | Destruction of sodium hypochlorite in solutions from a chlorate electrolytic cell |
| DE19803026275 DE3026275A1 (en) | 1979-07-16 | 1980-07-11 | Decomposition of sodium hypochlorite in chlorate solns. - by adding ammonia under controlled conditions which also cause decomposition of chloramine(s) |
| BR8004313A BR8004313A (en) | 1979-07-16 | 1980-07-11 | PROCESS FOR THE DESTRUCTION OF SODIUM HYPOCLORITE |
| SE8005149A SE8005149L (en) | 1979-07-16 | 1980-07-14 | PROCEDURE FOR ENLARGING SODIUM HYPOCHLORITE IN A CHLORATE SOLUTION |
| FI802235A FI802235A7 (en) | 1979-07-16 | 1980-07-14 | Decomposition of sodium hypochlorite in solutions from chlorate electrolysis cells. |
| JP9577180A JPS5617904A (en) | 1979-07-16 | 1980-07-15 | Method of decomposing sodium hypochlorite in solution of chlorate |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA331,845A CA1112845A (en) | 1979-07-16 | 1979-07-16 | Destruction of sodium hypochlorite in solutions from a chlorate electrolytic cell |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1112845A true CA1112845A (en) | 1981-11-24 |
Family
ID=4114684
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA331,845A Expired CA1112845A (en) | 1979-07-16 | 1979-07-16 | Destruction of sodium hypochlorite in solutions from a chlorate electrolytic cell |
Country Status (6)
| Country | Link |
|---|---|
| JP (1) | JPS5617904A (en) |
| BR (1) | BR8004313A (en) |
| CA (1) | CA1112845A (en) |
| DE (1) | DE3026275A1 (en) |
| FI (1) | FI802235A7 (en) |
| SE (1) | SE8005149L (en) |
Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| AU611465B2 (en) * | 1987-09-14 | 1991-06-13 | Chemetics International Company Limited | Stripping and recovery of dichromate in electrolytic chromate systems |
| AU626035B2 (en) * | 1989-02-22 | 1992-07-23 | Atochem | Process for destroying hypochlorite in a solution of perchlorate |
| AU634519B2 (en) * | 1989-02-22 | 1993-02-25 | Atochem | Process for destroying hypochlorite in a solution of chlorate |
Families Citing this family (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4773975A (en) * | 1986-10-29 | 1988-09-27 | Tenneco Canada Inc. | Electrochemical removal of hypochlorites from chlorate cell liquors |
-
1979
- 1979-07-16 CA CA331,845A patent/CA1112845A/en not_active Expired
-
1980
- 1980-07-11 BR BR8004313A patent/BR8004313A/en unknown
- 1980-07-11 DE DE19803026275 patent/DE3026275A1/en not_active Withdrawn
- 1980-07-14 FI FI802235A patent/FI802235A7/en not_active Application Discontinuation
- 1980-07-14 SE SE8005149A patent/SE8005149L/en unknown
- 1980-07-15 JP JP9577180A patent/JPS5617904A/en active Pending
Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| AU611465B2 (en) * | 1987-09-14 | 1991-06-13 | Chemetics International Company Limited | Stripping and recovery of dichromate in electrolytic chromate systems |
| AU626035B2 (en) * | 1989-02-22 | 1992-07-23 | Atochem | Process for destroying hypochlorite in a solution of perchlorate |
| AU634519B2 (en) * | 1989-02-22 | 1993-02-25 | Atochem | Process for destroying hypochlorite in a solution of chlorate |
Also Published As
| Publication number | Publication date |
|---|---|
| BR8004313A (en) | 1981-01-27 |
| FI802235A7 (en) | 1981-01-01 |
| SE8005149L (en) | 1981-01-17 |
| DE3026275A1 (en) | 1981-02-12 |
| JPS5617904A (en) | 1981-02-20 |
Similar Documents
| Publication | Publication Date | Title |
|---|---|---|
| US4405465A (en) | Process for the removal of chlorate and hypochlorite from spent alkali metal chloride brines | |
| CA2225650C (en) | Process for the production of aqueous chlorine dioxide solutions | |
| US4137166A (en) | Process for the purification of waste water containing ammonia and ammonium salts | |
| EP1501758B1 (en) | Process for the preparation of concentrated solutions of stabilized hypobromites | |
| US4627969A (en) | Production of chlorine dioxide | |
| CA1112845A (en) | Destruction of sodium hypochlorite in solutions from a chlorate electrolytic cell | |
| CA1254366A (en) | Sulfate removal from alkali metal chlorate solutions | |
| EP3997061B1 (en) | Process for producing a solution of ammonium carbamate | |
| CA1238764A (en) | Production of chlorine dioxide | |
| CA1090091A (en) | Production of chlorine dioxide from buffered reaction media | |
| US5062966A (en) | Process for decomposing solutions of hydroxylammonium salts | |
| CA1105877A (en) | Process for producing chlorine dioxide | |
| US5082567A (en) | Regeneration of cationic exchange resins | |
| Medir et al. | Stability of chlorine dioxide in aqueous solution | |
| US5154910A (en) | Process for the production of chlorine dioxide | |
| US6921521B2 (en) | Method of producing chlorine dioxide employs alkaline chlorate in a mineral acid medium and urea as a reducing agent | |
| JP2673518B2 (en) | How to remove chlorate in salt water | |
| JPH06170380A (en) | Method for fixing fluorine in waste liquid containing fluorophosphate ion | |
| JPH07165401A (en) | Chlorine dioxide continuous production method | |
| EP0535113B1 (en) | Methanol-based chlorine dioxide process | |
| US4931268A (en) | Production of chlorine dioxide | |
| US5009754A (en) | Consumption of hypochlorite values contained in perchlorate solutions of electrolysis | |
| US5124009A (en) | Consumption of hypochlorite values contained in chlorate solutions of electrolysis | |
| PL107863B1 (en) | HOW TO MAKE CHLORINE DIOXIDE METHOD OF PRODUCING CHLORINE DIOXIDE | |
| JP3301754B2 (en) | Method for removing chlorate from aqueous alkali chloride solution |
Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MKEX | Expiry |