EP1339636A1

EP1339636A1 - Method for generating chlorine dioxide

Info

Publication number: EP1339636A1
Application number: EP01980620A
Authority: EP
Inventors: Hervé Suty; Pierre Mekarbane
Original assignee: Atofina SA
Current assignee: Arkema SA
Priority date: 2000-12-04
Filing date: 2001-10-22
Publication date: 2003-09-03
Also published as: US20040033190A1; JP2004515435A; FR2817545B1; FR2817545A1; CA2430633A1; WO2002046095A1

Abstract

The invention concerns a method for generating chlorine dioxide by reacting a chlorite with an acid, which consists in using a C1-C12 alkanesulphonic acid and, more particularly, methane-sulphonic acid.

Description

PROCESS FOR GENERATING CHLORINE DIOXIDE

The invention relates to chlorine dioxide and more particularly relates to its preparation from chlorites with a view to its use in all applications of disinfection, cleaning and oxidation of pollutants.

Due to its oxidizing and biocidal properties, chlorine dioxide is widely used for the treatment of drinking water, water from cooling circuits and water from equipment in contact with foodstuffs. It is also used for the washing treatment of gaseous effluents (elimination of odors and VOCs), for the disinfection of storage and transport facilities for drinking water, as well as for the elimination of pollutants (dyes , sulfides, mercaptans, etc.) in industrial waters or, in the petroleum sector, for desulfurization.

Since chlorine dioxide is a toxic gas, difficult to handle, non-storable at high concentration and explosive in mixture with air, it is generally prepared at the time of its use in dilute solution.

Among the various known methods of generating chlorine dioxide, the most used consists of reacting an acid with a chlorite, in particular sodium chlorite. The most commonly used acid is hydrochloric acid because it leads to a very high chlorine dioxide yield. Indeed, for an HCl / NaCIO ₂ molar ratio of 2.2, the yield of chlorine dioxide following the reaction:

5 NaCIO ₂ + 4 HCI → 4 CIO ₂ + 5 NaCI + 2 H ₂ O (1)

exceeds 90%.

Unfortunately, as indicated in the reaction equation above, hydrochloric acid provides a considerable amount of chlorides which cause corrosion of the installations (cooling circuits, pipes, exchangers, etc.).

Other acids have been used to generate chlorine dioxide from chlorites (US Patents 4,084,747, EP 287,074, EP 423,816, US 5,407,656 and WO 89/10747). As such there may be mentioned sulfamic acid and organic acids such as citric acid, lactic acid and salicylic acid. However, with these acids, the chlorine dioxide yield is low and does not reach 50% for an acid / NaCIO ₂ molar ratio of 2.2. In addition, sulfamic acid is poorly soluble in water. It has now been found that hydrochloric acid can be advantageously replaced by methanesulfonic acid (AMS). Indeed, as shown by the comparison of equation (1) and the following equation:

5 NaCIO ₂ + 4 CH ₃ SO ₃ H → 4 CIO ₂ + 4 CH ₃ SO ₃ Na + NaCI + 2 H ₂ O (2)

AMS considerably reduces the amount of chlorides present in the chlorine dioxide solution compared to hydrochloric acid.

On the other hand, AMS which, like hydrochloric acid, is a strong acid (pKa = -1.92) leads to a yield of chlorine dioxide comparable to that obtained with hydrochloric acid and much higher than the yields obtained with the acids already proposed to replace hydrochloric acid. There is therefore no need to use a high AMS / sodium chlorite molar ratio; the result is a saving in reagent and a lower residual acid content in the prepared chlorine dioxide solution.

The use of AMS has other advantages, including the following:

1. AMS can be directly substituted for hydrochloric acid without changing the generator. Indeed, AMS is available in a 70% aqueous solution and is easier to handle (non-volatile, odorless, stable).

2. AMS is easily biodegradable (100% in 28 days), non-viscous and does not evaporate.

3. Under French law, the AMS is approved for cleaning equipment in contact with foodstuffs. 4. Unlike chlorite and hydrochloric acid, there is no possible confusion between AMS and sodium chlorite because the names of the products are very different. This is important from a security point of view.

The subject of the invention is therefore a process for generating chlorine dioxide by reaction of a chlorite with an acid, characterized in that the acid used is an alkanesulfonic acid, linear or branched, containing from 1 to 12 carbon atoms , or a mixture of such acids.

Besides the particularly preferred AMS, non-limiting examples of alkanesulfonic acids can be mentioned, ethanesulfonic, propanesulfonic, butanesulfonic and octranesulfonic acids. The chlorite used to generate the chlorine dioxide is preferably sodium chlorite, but it would not be departing from the scope of the present invention to use any chlorite provided that the counterion of the chlorite is not an activator decomposition of chlorine dioxide. By way of nonlimiting examples of such chlorites include ammonium chlorite, potassium chlorite and calcium chlorite.

As in the known methods, the reaction for generating chlorine dioxide is generally carried out in an aqueous medium at chlorine dioxide concentrations of 0.001 to 10%, preferably between 0.1 and 3%.

The acid / chlorite molar ratio can range from 0.1 to 50, but is preferably between 1 and 10.

The temperature and the reaction pressure are not critical parameters and can vary within wide limits. The temperature is generally between 3 and 120 ° C, preferably between 15 and 40 ° C. The pressure can range from 1 to 20 bars, but it is preferable to work at atmospheric pressure or at a pressure of up to 7 bars.

Depending on the value of the other parameters, the reaction time can range from 1 minute to 8 hours. It is preferably between 10 and 50 minutes. Although the invention aims to completely replace hydrochloric acid, it would not be departing from the scope of the present invention to use a mixture of alkanesulfonic acid with up to 10% hydrochloric acid or another acid.

In the following examples which illustrate the invention without limiting it, the determination of chlorine dioxide was carried out by UV at 360 nm on a Perkin Elmer double beam spectrophotometer and that of chlorides by ion chromatography.

EXAMPLE 1

In a reactor with a contact time of 31 minutes, an aqueous solution of sodium chlorite at 1 15 g / l and an aqueous solution of AMS at 264 g / l were introduced simultaneously and continuously. solution being 85 ml / h which corresponds to an AMS / NaCIO ₂ molar ratio of 2.2.

At the outlet of the reactor, the mixture was diluted with moderately mineralized city water (pH 7.7) at a flow rate of 10 l / h.

Taking into account the dilution, the amount of NaCIO ₂ used was 962 mg / l and, based on equation (2), should lead to a theoretical production of CIO ₂ equal to 573 mg / l.

The concentration of CIO ₂ in the solution obtained after dilution with tap water being 495 mg / l, the generator yield was 86%.

EXAMPLE 2

Example 1 was repeated, but replacing the aqueous AMS solution at 264 g / l with an aqueous HCl solution at 102 g / l or by an aqueous AMS solution at 537 g / l. The contact time in the reactor being 15 minutes and the flow rate of each reagent being 174 ml / h, a total flow rate of 19.46 l / h was obtained after dilution with city water.

The results of these tests are summarized in the following table.

The town water used for the dilution of the solution at the outlet of the generator having an average content of chloride ions of 25 mg / l, the addition of chlorides is mainly due to the reaction acid + chlorite ions. On examining the results above, it turns out that, for an identical generator yield, the amount of residual chlorides is approximately 10 times greater by the HCI route than by the AMS route.

In order to evaluate the stability of the chlorine dioxide generated by the AMS and HCI routes, the CIO ₂ solutions generated in this example were stored in transparent glass vials, placed in daylight. The concentration of CIO ₂ was monitored over 15 days in order to evaluate the decomposition of the solution.

It appears from the results of the table above that the CIO ₂ generated by the AMS route and at least as stable as that generated by the HCI route.

EXAMPLE 3

The procedure was as in Examples 1 and 2 with different acids and under the following conditions:

- [NaCIO ₂ ] 115 g / l - [acid] see table

- flow rate of each reagent 152 ml / h

- contact time in the reactor 18 minutes - total flow 19.89 l / h

- [CIO ₂ ] theoretical 525 mg / l

Except in the case of sulfamic acid, the solubility limit of which controls the concentration of the acid solution, the acid concentration of the other solutions was chosen so as to have an acid / NaClO ₂ molar ratio equal to 2.2.

The following table collates the results of these tests.

EXAMPLE 4

Example 1 was reproduced, but by varying the flow rate of the reactants and therefore the residence time in the reactor.

The results collated in the following table show that the optimal reaction time for the AMS + sodium chlorite mixture is between 25 and 35 minutes, the maximum yield being of the order of 85%.

EXAMPLE 5

Biocidal tests on highly polluted water were carried out using waste water (ERU) sampled at the outlet of the Colombes treatment plant (pH = 7.5-8). The chemical demand for CIO ₂ in this water was 1.7 mg / l (concentration limit from which we begin to observe a residual CIO ₂ after a contact time of 15 minutes).

In a first series of tests, the bacterial count was carried out using Bacti-Count T samplers which are representative of total germs and allow a count between 10 ³ and 10 ⁷ bacteria per milliliter. A blank was previously made to know the concentration of bacteria in the water leaving the treatment plant.

Two treatments at 1 mg / l of CIO ₂ , generated by the HCI route and by the AMS route, were then carried out on this water. Once the biocide has been injected, wait 15 minutes in the dark and then immerse the Bacti-Count tablets in the sample. They are drained and incubated at about 30 ° C.

The results collated in the following table show that, in both cases, the inactivation of total germs is greater than 99% (equivalent to an inactivation of 1 log). These biocidal tests do not reveal any difference between the inactivation of total germs by chlorine dioxide via the HCI route and the AMS route.

A second series of biocidal tests was carried out on Petrifilm 3M (total flora); these are squared tabs containing agar on the upper film. The samples are now treated with 0.2, 0.4 and 0.8 mg / l of IOC ₂ . The manipulations are identical to the previous ones (Bacti-Count), except that several dilutions are made.

From the results gathered in the previous table, we can conclude that the biocidal efficiency of chlorine dioxide is identical (within a margin of 10%) whatever its generation mode: AMS or HCI. EXAMPLE 6

The inactivation of Escherichia Coli bacteria (1.5-5 * 10 ⁸ CFU / ml) was tested (5 minutes at 25 ° C) according to standard NF EN 1276. According to this standard, a product is said to be active if inactivation (R) is greater than or equal to 5 log.

Examination of the results of these tests (see table below) shows that the biocidal activity is identical, whether the chlorine dioxide is produced from HCl or from AMS.

EXAMPLE 7

Chlorine dioxide solutions were prepared in situ by directly mixing aqueous solutions of AMS and sodium chlorite.

With an AMS / NaCIO ₂ molar ratio set at 3, the formation of non-negligible amounts of chlorine dioxide is observed.

EXAMPLE 8

Tests have been carried out in order to study the static corrosivity by weight loss due to acid solutions on different metals. The production of chlorine dioxide depends on the acid / chlorite molar ratio, it is therefore necessary to reason in number of moles of acid rather than in weight of commercial product.

8.1 AMS omβar .Â HCI

The tests were carried out with 33 cm ² plates of unalloyed aluminum (family 10,000, A5, purity> 99.5%).

Before the test, the platelets were subjected to the following treatments:

- pickling in a 50 g / l sodium hydroxide solution brought to 50 ° C,

- rinsing with demineralized water, - neutralization at 25 ° C in a 50% nitric acid solution,

- drying and immediate weighing.

The plates were then immersed for 24 hours, at 60 ° C. and with stirring by magnetic bar, in one liter of a solution of 0.103 mol / 1 of acid in demineralized water, this solution being placed in a reactor topped a refrigerant.

After the test, the platelets were subjected to the following treatments:

- pickling of the corrosion layer at 80 ° C in a solution of chromic oxide (20 g) and orthophosphoric acid at 85% (50 ml) in one liter of demineralized water,

- rinsing and brushing with a nylon brush,

- new rinsing, drying and weighing.

The following table indicates the weight loss (Δm) observed and the corresponding corrosion rate (V).

From these results, it can be concluded that AMS is much less corrosive than hydrochloric acid on aluminum. 8.2 ^ S cρ /? 7j „aré.à. 'ac de. ^ The tests were carried out with 12 cm ² aluminum plates

AG5 (cast alloy, 5% Mg, family 50000) or carbon steel XC18, and using Contrexéville water (typical composition: SO ₄ ^{2 "} = 1, 192 g / l; Ca ²⁺ = 0.476 g / l ; Mg ²⁺ = 0.084 g / l; HCO ₃ ^" = 0.377 g / l; CI ^" = 0.007 g / l; Na ⁺ = 0.007 g / l; K ⁺ = 0.003 g / l). The platelets were immersed for 144 hours at 40 ° C. in a closed reactor in 100 ml of an aqueous acid solution at 0.103 mol / l.

Before and after testing, the aluminum wafers were treated as described in 8.1.

Before testing, the XC18 steel plates were treated as follows: degreasing with trichlorethylene, polishing with 400 and 600 paper, rinsing and drying with compressed air. After testing, the XC18 steel plates were immersed in a 10% HCl solution with a few drops of corrosion inhibitor (Norust CM 150 from CECA), then rubbed with a rubberized tip to remove rust, rinsed with water and dried with compressed air.

Examination of the results collected in the following table shows that AMS has advantages over sulfamic acid with regard to corrosion on carbon steel and aluminum.

Claims

1. A process for generating chlorine dioxide by reaction of a chlorite with an acid, characterized in that the acid used is an alkanesulfonic acid, linear or branched, containing from 1 to 12 carbon atoms, or a mixture of such acids.

2. The method of claim 1 wherein methane sulfonic acid is used.

3. Method according to claim 1 or 2 wherein sodium chlorite is used.

4. Method according to one of claims 1 to 3 wherein the acid / chlorite molar ratio ranges from 0.1 to 50 and is preferably between 1 and 10.

5. Method according to one of claims 1 to 4 wherein the reaction is carried out at a temperature between 3 and 120 ° C, preferably between 15 and 40 ° C.

6. Method according to one of claims 1 to 5 wherein one operates at a pressure ranging from 1 to 20 bars, preferably 1 to 7 bars.

7. Method according to one of claims 1 to 6 wherein the reaction time ranges from 1 minute to 8 hours and is preferably between 10 and

50 minutes.