FR2819312A1 - Monitoring the composition of aqueous chlorine dioxide solutions, e.g. for water treatment, comprises determination of oxychlorine species by spectrophotometry - Google Patents

Abstract

Monitoring the composition of aqueous chlorine dioxide (ClO2) solutions, comprises determination of oxychlorine species by spectrophotometry.

Description

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PROCESS FOR CONTROLLING THE COMPOSITION OF CHLORINE DIOXIDE SOLUTIONS
The subject of the invention is a method for controlling! composition of aqueous chlorine dioxide solutions in oxychlorinated species.

 Chlorine dioxide is a biocidal reagent widely used in the treatment of drinking, industrial, industrial or urban waste water as well as in the treatment of swimming pool water, or in the food industry (disinfecting agent).

 Due to its instability, this excellent biocidal reagent, effective even at concentrations of the order of 0.1 ppm, is generally produced on the site of use using generators, by reaction of sodium chlorite and d hydrochloric acid or sodium chlorite and chlorine water.

 Other acids than hydrochloric acid can be used such as nitric acid, sulfuric acid, or even organic acids. Chlorine water can be prepared from chlorine gas and water or from a mixture of a hypochlorite salt and an acid such as hydrochloric acid.

transformation du dioxyde de chlore généré en chlorate et de produire un dioxyde de chlore exempt de chlore tout en minimisant les consommations des matières premières. On peut rappeler que le dioxyde de chlore est particulièrement intéressant car il ne génère pas de dérivés organo-chlorés en quantité significative mais que cette propriété n'est bien entendue vérifiée que si le dioxyde de chlore contient une quantité minimale de chlore. The quality of the chlorine dioxide solution produced as well as the conversion efficiency of chlorite are essential for using chlorine dioxide under optimal technical and economic conditions. So, it is important to avoid the

transforming the chlorine dioxide generated into chlorate and producing a chlorine dioxide free of chlorine while minimizing the consumption of raw materials. It may be recalled that chlorine dioxide is particularly interesting because it does not generate organochlorine derivatives in significant quantity but that this property is of course verified only if the chlorine dioxide contains a minimum quantity of chlorine.

 To ensure the proper functioning of a generator, it is necessary to carry out a balance of reaction products making it possible to control the contents of chlorine dioxide, free chlorine, chlorite and chlorate.

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Today there is a titrimetric method with potassium iodide to carry out these analyzes, but this method is not very reliable.

 I! There is therefore a real need for a reliable and easy-to-implement method for correctly operating chlorine dioxide generators.

 The present invention describes a process for controlling or dosing the composition of aqueous chlorine dioxide solutions, in particular compositions from on-site generators. The advantage of the method is that it uses measurement principles based solely on spectrophotometric characterizations which can be carried out without problem using spectrophotometers conventionally used by operators.

 More specifically, the subject of the invention is a process for controlling the composition of aqueous solutions of chlorine dioxide, characterized in that it consists in independently determining each of the oxychlorinated species present in these solutions by spectrophotometry.

 Unlike laboratory methods which use techniques such as ion chromatography, capillary electrophoresis or spectrocolorimetry, spectrophotometry used in the process according to the invention is a simple and reliable method which can be implemented. works on the generator site.

 In the process according to the invention, the control of the composition of the chlorine dioxide solutions generally comprises the following operations: I) determination of the chlorine dioxide concentration by spectrophotometry at 360 nm; 2) determination of the hypochlorite concentration, either directly by spectrophotometry, or indirectly by assay by spectrophotometry of the compound resulting from the reaction of the hypochlorite with syringaldazine; 3) determination of the chlorite concentration, either directly by spectrophotometry, or indirectly from a solution of indigo carmine; 4) determination of the chlorate concentration by spectrophotometry from an indigo carmine solution.

 More precisely, the chlorine dioxide concentration is determined directly by spectrophotometry at 360 nm, which corresponds to the maximum absorption of the product in question. Given the concentrations encountered at the generator outlet (between 0.5 and 3 g / l), a dilution should be carried out to obtain an absorbance between 0.05 and 1.

 FIG. 1 represents the spectrum of a solution of C102 at approximately 5. 10-4 mollI.

The spectrum shows no change depending on the pH (between 5.5 and 9.5).

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The determination of the other oxychlorinated species is advantageously carried out after elimination of the predominant species from the solutions, namely chlorine dioxide itself. This elimination can be carried out by simple degassing of the solutions, either with air or with nitrogen.

 The sodium hypochlorite has, in borate buffer, an absorption band at 292 nm and, for high concentrations (more than 2% of the total chlorine dioxide content), it can be measured directly by UV spectrophotometry at 292 nm. For lower concentrations, it is preferred to assay at 530 nm the compound resulting from the reaction of the hypochlorite in phosphate buffer with syringaldazine.

 Figure 2 shows the spectrum of a hypochlorite solution (3.10-4 mol / 1) in borate buffer.

 FIG. 3 shows the evolution of the absorbance at 530 nm of the compound formed between the syringaldazine (2.2. 10-5 mol / 1) and different concentrations of hypochlorite as a function of time.

 Since the chlorite ions absorb in the ultraviolet, it is possible, for high contents, to dose them directly by spectrophotometry at 260 and at 292 nm. The hypochlorite also absorbing at 292 nm, when the two species are present, account should be taken of the molar extinction coefficients of these species and the absorbances measured at the two wavelengths make it possible to calculate the concentration in each of the species.

 FIG. 4 represents the absorption spectrum of a solution containing 3.10-4 mol of chlorite (borate buffer).

 For concentrations lower than ppm (relative to the total chlorine dioxide content), the determination of the chlorite concentration is advantageously carried out by spectrophotometry at 610 nm of the product resulting from the oxidation of indigo carmine. This operation is preferably carried out at pH = 2, after elimination of the chlorine dioxide by degassing, as indicated above and of the hypochlorite which should be blocked, for example by addition of ammonia; it is possible to establish a relationship between the absorbance of indigo and the chlorite concentration (Figure 5).

 The chlorate concentration is determined by spectrophotometry at 610 nm of the product resulting from the oxidation of indigo carmine, at pH = O. In the absence of other species (CI02-, CIO ', Cul02), there is a relationship between the absorbance of indigo and the chlorate concentration (Figure 6).

 The presence of C102 has no influence on the chlorates.

 ClO-or Cl2 reacting on indigo at pH = O when the sample contains hypochlorite, it is advisable to subtract from the initial absorbance the part attributable to the chlorine initially present in the sample.

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In the presence of chlorite and chlorates, the measurement of the absorbances at pH = 2 and pH = 0 makes it possible to determine the concentration in each of these ions.

 It thus appears that spectrophotometry can be validly used in the determination of the oxychlorinated species present in the chlorine dioxide solutions coming from the generators. Since chlorine dioxide is the majority species, a simple measurement at 360 nm after appropriate dilution will make it possible to determine the content of this oxidizing agent. Depending on their concentration in the solution, the other oxychlorinated species can be assayed either by direct spectrophotometry, or by spectrophotometry of products resulting from the reaction of the species with syringaldazine (hypochlorite) or with indigo carmine (chlorite, chlorate).

 This process for controlling the composition of chlorine dioxide solutions, using only a spectrophotometer, can easily be implemented on the production site itself.

dans l'exemple qui suit et qui est donné à titre purement illustratif. The implementation of the method according to the invention from a chlorine dioxide solution containing oxychlorinated species can be carried out as described

in the example which follows and which is given purely by way of illustration.

In a 100 ml flask, the following are introduced at ... oC: [CIO-] = 5. 10-5 mollI.

 [C102-] = 5. 10-5 mollI.

 ICI03-1 = 5. 10-5 mollI.

[C102] = 10-3 mol / I. a) Determination of chlorine dioxide:
After dilution ten times, direct analysis by spectrophotometry at 360 nm (5 cm cell)
Results: Absorbance (A) = 0.62, hence a concentration C in mg C102 / 1 equal to 67; this concentration is
A x 67450 obtained by applying the relation C = ------
1250 x L in which C = concentration of the standard solution in mg C102 / 1,
A = absorbance of the solution,
L = length of the tank in cm,
1250 = e = molar extinction coefficient of ClO2 at
360 nm in mol-1 cm-1,
67450 = molecular weight of ClO2 in mg / mol and taking into account the dilution.

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b) Après dégazage à l'air, la solution est analysée directement par spectrophotométrie afin d'obtenir une estimation de la teneur en ions hypochlorite et chlorite.

b) After degassing in air, the solution is analyzed directly by spectrophotometry in order to obtain an estimate of the content of hypochlorite and chlorite ions.

The absorbances at 292 (A 292) and 260 nm (A 260) [5 cm cell] are noted and the concentrations of the chlorite and hypochlorite ions are calculated from equations (1) and (2).

[C102 j measured [CIO-] measured 5, 3. 10'4, 4. 10-5 5, 5. 10-5 4, 8. 10-5

c) Dosage de CIO- : Protocole expérimental : 397 al de syringaldazine à 0, 1 % sont ajoutés à l'échantillon (fiole de 50 ml) contenant 5 ml de solution dégazée et 5 ml de tampon phosphate 0, 5 mol/1 et complétée avec de l'eau désionisée. La lecture est effectuée à 530 nm après 2 minutes d'attente en cuve de 1 cm.

c) Determination of CIO-: Experimental protocol: 397 al of syringaldazine at 0.1% are added to the sample (50 ml flask) containing 5 ml of degassed solution and 5 ml of phosphate buffer 0.5 mol / l and supplemented with deionized water. The reading is carried out at 530 nm after 2 minutes of waiting in a 1 cm cell.

Essai 1 2 3 [CIO-] mollI 4, 54. 10'" 4, 47. 10 4, 48. 10-6 Results: The absorbance values read make it possible to calculate the concentrations of hypochlorite ions. Three tests were carried out and the results obtained are as follows:

Trial 1 2 3 [CIO-] mollI 4, 54. 10 '"4, 47. 10 4, 48. 10-6

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On obtient dans cette solution diluée une valeur moyenne en hypochlorite égale à 4, 5. 10'6 mollI, ce qui correspond à une concentration de 4, 5. 10-5 mollI dans la solution mère. d) Dosage de CI02' :
Protocole expérimental : 2,5 ml d'une solution aqueuse d'indigo (3,4.104 mol/l) sont ajoutés à une solution contenant 5 ml de solution dégazée, 500 ul de fer (II),

10-4 mol/1, 500 ul de NH3, 1, 315 mol/1.

In this diluted solution, an average hypochlorite value equal to 4.5 × 10'6 mollI is obtained, which corresponds to a concentration of 4.5 × 10-5 mollI in the mother solution. d) Determination of CI02 ':
Experimental protocol: 2.5 ml of an aqueous solution of indigo (3.4.104 mol / l) are added to a solution containing 5 ml of degassed solution, 500 μl of iron (II),

10-4 mol / 1.500 μl NH3, 1.315 mol / 1.

The solution is heated to 45 / 55OC for 5 minutes and cooled for approximately 10 minutes.

 The reading is carried out at 610 nm in a 5 cm cell.

dessous :

Méthode 1 2 [CIO-] mollI 5, 4. 10-" 5, 7. 10-6 4, 9. 10' 5, 6. 10-6

La valeur moyenne obtenue est de 5, 4 10-6 mollI correspondant à une solution mère contenant 5, 4 10-5 mollI de chlorite. e) Dosage de CI03- :
Protocole expérimental : 2,5 mL de solution d'indigo (3,4.10-4 mol/l) sont ajoutés à une solution contenant 1 ml de solution dégazée (fiole de 50 ml). L'échan-

tillon est complété par de l'acide chlorhydrique 10 mol/1, il est chauffé à 44/55OC pendant 10 minutes et refroidi pendant environ 10 minutes. La lecture s'effectue à 610 nm en cuve de 5 cm. Results:
Two series of measurements are carried out, with or without the addition of ammonia, carried out before degassing (methods 1 and 2). The results are reported below

below:

Method 1 2 [CIO-] mollI 5, 4. 10- "5, 7. 10-6 4, 9. 10 '5, 6. 10-6

The average value obtained is 5.4 4 10-6 mollI corresponding to a stock solution containing 5.4 10-5 mollI of chlorite. e) Determination of CI03-:
Experimental protocol: 2.5 ml of indigo solution (3.4.10-4 mol / l) are added to a solution containing 1 ml of degassed solution (50 ml flask). The exchanged

tillon is supplemented with hydrochloric acid 10 mol / 1, it is heated to 44 / 55OC for 10 minutes and cooled for about 10 minutes. The reading is carried out at 610 nm in a 5 cm cell.

Results:
The two series of measurements give 5.8 respectively. 10-5 and 5.6. 10-5 mol / 1 of chlorate.

Claims (11)

 1. A method of controlling the composition of aqueous chlorine dioxide solutions in oxychlorinated species, characterized in that it consists in carrying out these determinations by spectrophotometry.  2. Method according to claim 1, characterized in that the chlorine dioxide solutions comprise, in addition to this product, at least one of the following species: hypochlorite, chlorite, chlorate.  3. Method according to one of claims 1 or 2, characterized in that it consists in determining the concentration of chlorine dioxide by spectrophotometry at approximately 360 nm.  4. Method according to any one of claims 1 to 3, characterized in that it consists in determining the hypochlorite concentration by direct spectrophotometry at 292 nm.  5. Method according to any one of claims 1 to 3, characterized in that it consists in determining the hypochlorite concentration by spectrophotometry at 530 nm of the compound resulting from the reaction of the hypochlorite with syringaldazine.  6. Method according to any one of claims 1 to 5, characterized in that it consists in determining the chlorite concentration by direct spectrophotometry at 260 and 292 nm.  7. Method according to claims 1 to 5, characterized in that the chlorite concentration is measured at 610 nm on the product resulting from the action of chlorite on indigo carmine at pH = 2.  8. Method according to any one of claims 1 to 7, characterized in that the chlorate concentration is carried out by spectrophotometry at 610 nm of the product resulting from the oxidation by chlorate of indigo carmine at pH = 0.  9. Method according to any one of claims 1 to 8, characterized in that all of the dosing operations are carried out by a single active spectrophotometer on the U. V. and the visible. <Desc / Clms Page number 8>  10. Method according to any one of claims 2 to 9, characterized in that each species is assayed in the absence of the other species.  11. Method according to any one of claims 1 to 9, characterized in that each species is assayed in the presence of at least one of the other oxychlorinated species.