FR2808016A1 - Aqueous composition for purification of, e.g., urban waste water, comprises a compound capable of releasing chlorine dioxide, an organic peracid, and a source of water - Google Patents

Abstract

An aqueous composition for treatment of an aqueous medium with chlorine dioxide comprises at least one compound capable of releasing chlorine dioxide, at least one organic peracid and a source of water, consisting totally or partially of the medium to be treated, within which the chlorine dioxide is generated and the medium so treated.

Description

The present invention relates to an aqueous composition based on chlorine dioxide, a method for preparing said composition and some of its applications.

There is an abundant literature on chlorine dioxide, its properties, its preparation processes and its uses. Thus, unlike chlorine, chlorine dioxide chlorine not organic products [obtaining chloromethanes (THM) or chloroacetic acids (HAA) for example], which is particularly important for one of the first uses of dioxide chlorine, that is to say the disinfection of water. Chlorine dioxide is also a weaker and more selective oxidant than chlorine, it acts at a lower dose, does not react with ammonia, ammonium compounds, or many organic compounds, and has biocidal properties in it. a wide pH range. Chloi dioxide, on the other hand, can not be compressed and transported in pressurized cylinders or tanks and a concentration of more than 10% in the air leads to violent self-decomposition. As a result, chlorine dioxide is generally prepared at the site of its use, thanks to more or less complex generators.

Chlorine dioxide is known for many applications taking advantage of its biocidal properties. Thus, it is used for the disinfection of drinking water, for the control of THM and HAA, for the bacteriological control of water cooling stationery water, for the disinfection of fruits and vegetables, for bacteriological control in beverage and brewery equipment the treatment of poultry carcasses, not to mention its effectiveness in odor control, for example by oxidation of hydrogen sulphides or organo-sulfur compounds, destruction by oxidation of phenols or mercaptans, bleaching.

Many techniques for obtaining chlorine dioxide have already been described. It has thus been proposed to generate chlorine dioxide from sodium chlorite, by acidification, by oxidation by means of chlorine or a persulfate, by action of acetic anhydride, by acidification of chlorite and hypochlorite, by oxidation. electrochemical chlorite. It has also been proposed to generate chlorine dioxide from sodium chlorate, for example by reduction by acidification in the presence of oxalic acid, by reduction with sulfur dioxide in the presence of sulfuric acid, if appropriate with addition. sodium chloride, by reduction with methanol or hydrogen peroxide. A major problem with chlorine dioxide is that it is toxic, delicate to handle, can not be stored and is explosive when concentrated in the air. As a result, the generation and use of chlorine dioxide has led to various technologies, summarized in US Pat. No. 5,885,543, namely: activating a solution of metallic chlorite by adding an acid or activating a powdery composition or another anhydrous composition by adding water or alternatively preparing an anhydrous activated composition capable of releasing the chlorine dioxide over time.

These techniques are described, for example, in US Pat. Nos. 5,437,381, 4,169, 5,567,405 and 5,573,743.

In general, these techniques have the disadvantage of either losing chlorine dioxide, or not generating enough of this product, or finally not being able to control the generation. In the present invention, it is proposed in US Pat. No. 5,853,689 to make a mixture of zeolite crystals impregnated with metallic chlorite and crystals of zeolites impregnated with ferric chloride or ferric sulphate and then to activate this mixture. by putting it in contact with a fluid containing water. the ferric salts becoming acidic in the presence of water and thus producing chlorine dioxide. In some embodiments, a mixture of zeolite crystals impregnated with sodium chlorate, sulfuric acid, hydrogen peroxide or peracetic acid and calcium chloride is used.

In US Pat. No. 5,885,543, it is proposed to activate by means of an acid a zeolite crystal impregnated with a metal chlorite and at least one impregnating agent chosen from the group constituted by chloride. calcium, magnesium sulfate, potassium chloride and potassium hydroxide. This patent US Pat. No. 5,885,543 thus proposes a stable, inactivated substance in liquid or dry form that does not release significant quantities of chlorine dioxide before its activation by an acid and, during activation, releases the carbon dioxide. chlorine at a useful and controllable rate.

According to WO 85/04107, the generation of chlorine dioxide from sodium chlorite and an acid is not effective, especially in terms of disinfection, except to increase the concentration of sodium chlorite. While US-A-4,084,747 proposes the use of lactic acid, WO 85/04107 proposes to use an organic acid other than lactic acid to lower the pH of the composition to less than 7. WO 94/00015 has proposed a biocidal composition containing little chlorine dioxide comprising water, a source of chlorite ions, a source of chloride ions and a source of chlorate ions in combination with one or more components selected from the group consisting of surfactants and viscosity modifiers, said components including a compound for adjusting the pH of said composition to a value greater than 7. These compositions are presented as an improvement in the compositions of the composition. US-A-4,880,638.

The invention provides novel compositions capable of generating chlorine dioxide.

The invention also provides compositions generating chlorine dioxide without using a generator, that is to say a more or less complex equipment located at the place of application.

The invention provides a composition which excludes any release or control of chlorine dioxide.

The invention also proposes a composition allowing a rigorous control of the amount of chlorine dioxide generated.

The invention also proposes a composition that does not use third bodies, both of which can be impregnated with compounds whose reaction can generate chlorine dioxide.

The invention further provides a composition for generating chlorine dioxide in both a highly diluted medium and a concentrated medium.

The invention also provides a composition capable of generating chlorine dioxide in a wide pH range, including greater than the invention still provides a composition with high biocidal activity. The invention also provides a composition for obtaining chlorine dioxide without risk of intoxication by possible emanation of this product or loss of said chlorine dioxide.

Other objects and advantages of the composition according to the invention will be apparent from the following.

The subject of the invention is therefore an aqueous composition that can be used for treating aqueous media using chlorine dioxide. said composition being actérisée in that it comprises a) at least one compound capable of releasing chlorine dioxide; b) at least one organic peracid c) a source of water consisting wholly or partially of the medium to be treated and in which the chlorine dioxide is generated.

The invention also relates to an aqueous composition consisting of a medium treated with chlorine dioxide, said composition resulting from contacting under conditions allowing the generation of said chlorine dioxide of a) at least one compound capable of releasing dioxide chlorine; b) at least one organic peracid; c) a source of water formed wholly or partially by said medium.

The invention also relates to a process for the preparation of an aqueous composition, which is carried out in that it consists in directly generating chlorine dioxide in an aqueous composition consisting of an aqueous medium to be oxidized or disinfected by placing in contact with conditions allowing this generation of at least one compound capable of releasing chlorine dioxide and at least one organic peracid.

Although all the compounds capable of generating chlorine dioxide are usable, preference is given to chlorites soluble in water and in particular to alkali or alkaline earth metal chlorites. Of these, sodium chlorite and potassium chlorite are preferred, with sodium chlorite being preferred. Chlorite can generally be used as a solution or as a powder.

Component b is chosen from organic peracids. Among these peracids, there may be mentioned peracetic acid, perpropionic acid, perbenzoic acid and polyperacids such as ethylene diamine tétraperacétique acid. and preference is given to aliphatic peracids.

Constituent c is constituted totally or partially by the medium to be treated. This medium may consist of water for agri-food use (washing, disinfection, deodorization for example). industrial water (cooling circuits, process water, paper mills for example), washing water of gaseous effluents, disinfecting water from production plants for the storage of products or, more generally, any aqueous medium in which the generation of chlorine dioxide desired.

Given the nature of the water to be treated, the pH of this water can vary within wide limits. In general, this pH can range from 2 to 10. Preferably, it is between 5 and 9.

In compositions according to the invention, the concentration of constituents or chlorine dioxide does not matter since these compositions are formed <i> in .situ. </ I> In fact, the generation of chlorine dioxide does not may not preexist the composition itself and, therefore, there can be no uncontrolled emissions or loss of chlorine dioxide, which is formed in the medium to be treated. In the same way, unlike aqueous compositions containing dissolved chlorine dioxide, at a concentration generally not exceeding that to be transported and stored, this restriction does not exist with the compositions according to the invention, formed at the same time than the chlorine dioxide they generate. On the other hand, it is advisable to have a minimum of concentration in each of the reactants to generate chlorine dioxide, this minimum being able to be as low as 0,01 nlg / I.

The compositions according to the invention may be formed at a temperature ranging from 0 to 120 ° C. and preferably from 15 ° to 40 ° C. under an absolute pressure ranging from a pressure of less than 1 bar to a pressure exceed 20 bars, this pressure preferably being between atmospheric pressure of 12 bars.

The molar ratio between the compound capable of releasing chlorine dioxide a and the organic peracid b can range from 1/10 to 2/1 and preferably from 1/3 to 1/1. As has been indicated, several components a and / or several constituents b can be used.

In general, organic peracids are used in the form of alcoholic or aqueous-alcoholic aqueous solutions, the weight concentration of which can range from 10 to 50% and preferably from 15 to 40%.

The compositions according to the invention, by the chlorine dioxide they generate, have high biocidal properties while using small amounts of organic peracid and a compound such as sodium chlorite. As the reaction between the chlorine dioxide is carried out in the medium to be treated itself, they dispense with the use of a generator or more or less porous substances capable of absorbing products leading to chlorine dioxide after contact. The compositions can be used in the applications mentioned above and more generally in all applications using chlorine dioxide.

The following example illustrates the invention. In this example, use is made of peracetic acid in 35% aqueous solution (APA 35) or 15% (APA 15) [by weight of acid by weight of solution] or of 15% perpropionic acid (APP 15) - Technical sodium chlorite powder 80%. <U> Example </ U> The medium to be treated consists of - bi-perinute water, buffered at pH 7.8 (EBP); water with a medium content of oxidizable matter, pH 7.7 (ES); - heavily loaded urban waste water, taken screaming out of treatment plant at pH 7.1 (ERU) a) Sodium chlorite and PAPA 35 are introduced into each of these waters at the rate of 1 g / l of each of the reagents and finds that the contents of C102 generated are 40 μg in 10 minutes, 120 μg in 30 minutes and 300 μg in one hour. In order to assess the biocidal power of the APA / chlorite mixture in ERU water, bacterial development is studied by a U.F.C. (Colony Forming Unit) as a function of the concentration of reagents, alone or as a mixture, at five concentrations 1) ERU water alone 2) APA 35 = 0.15 mg / 1 / chlorite = 0.05 mg / I 3) APA 35 = 0.3 mg / l / chlorite = 0.1 mg / 1 4) APA 35 = 1.5 mg / 1 / chlorite = 0.5 mg / 1 5) APA 35 = J mg / 1 I chlorite = 1 mg / 1 The results are shown in Figure 1.

In this figure, the bacterial count per ml (from 101 to 101) is plotted on the ordinate.

In the abscissa, the histogram A corresponds to the use of water ERU alone, columns B, C, D and E corresponding for the histogram bearing horizontal stripes, with chlorite alone, for the histogram with vertical stripes, to PAPA 35 alone and for the histogram cross-checked with the mixture chlorite + APA 35, column B corresponding to concentration 2 mentioned above, column C at concentration 3. column D at concentration 4 and column E at concentration 5.

This table clearly shows the biocidal efficacy of the APA 35 / chlorite mixture in ERU water. already at very low concentration of these reagents.

The rate of disappearance of the chlorite ions of a sodium chlorite / APA or APP perpropionic acid mixture 15 is measured in an urban wastewater (ERU).

The concentrations of the reagents are respectively 0.0074 mmol sodium chlorite and 0.0185 nlmol peracid per liter of ERU water.

The chlorite content (in g / l) is followed by ion chromatography of the initial time up to 72 hours.

The results are shown in Figure 2.

In this figure 2. the continuous line corresponds to the APP <B> 15. </ B> the dot line corresponding to PAPA 15.

Claims (5)

<U> CLAIMS </ U> 1. Aqueous composition usable for the treatment of aqueous media, using chlorine dioxide, characterized in that it comprises a) at least one compound capable of releasing chlorine dioxide b) at least one organic peracid C) a source of chlorine dioxide water, constituted totally or partially by the medium to be treated in which the chlorine dioxide is generated. 2. An aqueous composition consisting of a medium treated with chlorine dioxide, said composition resulting from contacting under conditions allowing the generation of chlorine dioxide of a) at least one compound capable of releasing at least one chlorine dioxide. an organic peracid c) a source of water constituted totally or partially by said medium 3. Composition according to claims 1 or 2, wherein the compound a is selected from chlorites soluble in water. 4. The composition of claim 3, wherein the chlorite is selected from alkali metal and alkaline earth chlorites. 5. Composition according to any one of claims 1 to 4 wherein the compound a is sodium chlorite. G. Composition according to one of claims 1 to 5. wherein the peroxide b is selected from peracetic acid, perpropionic. perbelloic or poly acids such as ethylene diamine tetraperacetic acid. 7. Composition according to one of claims 1 to 6, wherein the pH of the water component ç is between 2 and 10. 8. The composition of claim 7, wherein the pH of the water is between 5 9. Composition according to one of claims 1 to 8, wherein the molar ratio compound a / peracid b is between 1/10 and 2/1. 10. A process for preparing an aqueous composition according to one of 9 reverdi cations, characterized in that it consists in directly generating chlorine dioxide in an aqueous composition consisting of an aqueous medium to be oxidized or disinfected, by contacting under conditions allowing this generation of at least one compound capable of releasing chlorine dioxide and at least one ganic peracid. <B> 11 .- </ B> Composition according to one of claims 1 to 9, wherein the medium to be treated or the treated medium is constituted by industrial water. water for use @l; <->. gaseous effluent wash water or production facility disinfection water or product storage.