DE69311493T2 - Process for the disposal of chlorinated organic products by oxidation - Google Patents

Description

The present invention relates to a process for disposing of chlorinated organic products. In particular, the present invention relates to a process for disposing of chlorinated organic products by an oxidation treatment with hydrogen peroxide (H₂O₂) in the presence of Fe(II) ions, optionally with inclusion of other transition metal ions, and a phase transfer reagent.

Chlorinated organic products are a class of substances that are widely used in various technical fields. The most common of these are compounds with an alkyl structure, an aromatic or alkylaromatic structure, such as polychlorinated biphenyls (PCBs), 1,1,1-trichloro-2,2-bis(p-chlorophenyl)ethane (DDT), tetrachloroethane, dichlorobenzenes, chlorophenols, hexachlorocyclohexane, or olefinic structure such as trichloroethylene.

In general, they are toxic and highly polluting products, the disposal of which after use presents many problems. In practice, it is necessary to use a disposal process that can be used on a large scale and that is as effective, economical and free of risks to the environment as possible. It is particularly difficult to achieve this optimal objective because chlorinated organic products are very stable and, when treated with chemical and/or physical means, they form highly polluting by-products.

For example, polychlorinated biphenyls (PCBs) are highly toxic and carcinogenic aromatic chlorine compounds which, until recently, were widely used as oils for electrical equipment and in particular for capacitors due to their dielectric properties. Due to their high toxicity, current regulations require the removal of PCBs and their replacement with hydrocarbon mineral oils. This makes it necessary to remove large quantities of PCBs which are usually either dissolved in organic solvents (e.g. hexachlorobenzene) or impregnated in insulating and/or support materials such as paper, cardboard, wood, etc. It is also often necessary to remove PCBs from mineral oils which may be contaminated as a result of improper cleaning of electrical equipment before replacement.

The most commonly used treatment for the disposal of chlorinated organic products is incineration, which is carried out in suitably equipped plants to prevent the formation of highly toxic chlorinated organic compounds such as parachlorodibenzodioxins, parachlorodibenzofurans and the like. In addition to the fact that this involves the disposal not only of the chlorinated compounds but also of the materials contaminated with them, this is in any case an expensive process which is not free of risks for the environment.

In US-A-5 004 551, chlorinated phenols are treated using an oxidizing agent in the presence of a catalytic amount of a protoporphyrin complex with Fe³⁺ to convert the hazardous chlorophenols to degradation, with the hazardous products being degraded by microorganisms.

The Applicant has now discovered a process for the disposal of chlorinated organic products, which comprises oxidizing such products with H₂O₂ in the presence of suitable catalysts and phase transfer reagents, with a formation of non-toxic substances and a possibility of recycling the contaminated materials, with clear economic and environmental advantages compared with the processes used up to now.

It is therefore an object of the present invention to provide a process for the disposal of chlorinated organic products which comprises treating these products with an aqueous H₂O₂ solution in the presence of Fe(II) ions, which may optionally be associated with one or more transition metal ions, selected from Cu(II), Ti(IV), Mn(II), Co(II), Ni(II), W(IV) and Mo(IV), and in the presence of a phase transfer reagent.

Among the chlorinated products to which the process of the present invention can be applied, we can mention by way of example those which have:

(a) an aromatic structure, such as polychlorobiphenyls (PCBs), chlorobenzenes (for example ortho- and meta- dichlorobenzene), chlorophenols (for example para-, tri- and pentachlorophenol), etc.;

(b) an alkyl aromatic structure such as 1,1,1-trichloro-2-2-bis(p-chlorophenyl)ethane (DDT) and others;

(c) an olefinic structure such as trichloroethylene, perchlorobutadiene, etc.;

(d) an aliphatic or cycloaliphatic structure such as tetrachloroethane, hexachlorocyclohexane, hydrogenated chloral, hexachloroethane, perchloroacetone, etc.

The reaction involved in the process of the present invention is a heterogeneous phase oxidation reaction since the chlorinated organic products are not soluble in the aqueous phase containing the H2O2/Fe2+ oxidation system. Therefore, the presence of a phase transfer reagent is necessary, i.e. a product which acts as a "bridge" between the molecules of the chlorinated organic product and the oxidation system. For an exhaustive discussion of such products see C. Starks, C. Liotta, "Phase transfer catalysts", Academic Press (1978).

Among the products known in the art as phase transfer reagents, those which can be advantageously used in the process of the present invention are the ammonium, phosphonium or arsonium salts of the general formula:

where:

Q is selected from N, P and As;

R₁, R₂, R₃ and R₄ are the same or different from one another and are selected from hydrogen, C₁-C₃₅, preferably C₁-C₁₂ alkyl groups, C₆-C₁₀ aryl groups, C₇-C₃₀, preferably C₇-C₁₂ arylalkyl or alkylaryl groups, provided that at least one of R₁, R₂, R₃ and R₄ is other than hydrogen; X⁻ is selected from OH⁻, Cl⁻, Br⁻, I⁻ and BH⁻⁻.

Another class of phase transfer reagents useful in the process of the present invention is represented by the pyridinium salts of the formula:

where R is a C₁-C₂₀ alkyl group, while X⁻ is as defined above.

Another class of products which can be used as phase transfer reagents in the process of the present invention are those of ephedrine salts, having the general formula:

where: R₅ are the same or different C₁-C₆ alkyl groups; X⁻ is as defined above. Such products are described by Gani V., Tapinte C., Viout P. in "Tetrahedron Letters", page 4435, 1983, and by Bunton C., Robinson L., Stam M. in "Tetrahedron Letters", page 121, 1971.

It is also possible to use mixtures of different phase transfer reagents in order to best combine the characteristics of each type of transfer reagent in order to obtain a good mineralization of the chlorine atoms as well as a complete elimination of the chlorinated organic products.

Examples of phase transfer reagents which can be used in the process of the present invention are the following:

(C4 H9 )4 N+ X⁻; (C10 H21 )3 N+ C3 H7 X⁻; (C18 H37 )3 N+CH3 X⁻;

(C18 H37 )2 N+ (CH 3 ) 2 X - ; (C4 H9 )3 P+ C16 H33 X⁻;

(C7 H15 )3 N+CH3 X⁻; (C6 H5 )3 As+CH3 X⁻; (C6 H5 CH2 )N+ (CH3 )3 X⁻;

For the embodiment of the present invention, the tetraalkylammonium salts are particularly preferred in which the alkyls, identical or different, have 1 to 35 carbon atoms, preferably 1 to 12 carbon atoms.

The chlorinated organic products to be removed are usually present in amounts of 100 to 5000 ppm, while the phase transfer reagent is used in concentrations ranging from 20 to 500 ppm, preferably from 100 to 300 ppm, based on the aqueous phase.

In addition to the phase transfer reagents, the process of the present invention comprises the use of Fe(II) ions as catalysts, optionally associated with one or more transition metal ions selected from Cu(II), Ti(IV), Mn(II), Co(II), Ni(II), W(IV) and Mo(IV). Among these, Cu(II) ions are preferred. Metal ions are added in amounts usually ranging from 50 to 1000 ppm for the Fe(II) ions and from 0 to 400 ppm for the other transition metal ions specified above. In a preferred embodiment, mixtures of Fe(II) ions and Cu(II), Ti(IV), Mn(II), Co(II), Ni(II), W(IV) or Mo(IV) ions are used in equimolar amounts, each of whose concentrations ranges from 50 to 400 ppm, preferably from 150 to 250 ppm.

The metal ions mentioned above are added in the form of soluble salts. In particular, with Fe(II) ions it is possible to use, for example, iron(II) sulfate, iron(II) chloride, iron(II) nitrate, ammonium iron(II) sulfate, etc. From a work-related and economic point of view

Iron(II) sulfate heptahydrate FeSO₄ 7H₂O is particularly preferred. Among the copper sulfates, for example, copper sulfate pentahydrate CuSO₄ 5H₂O can be used.

With regard to hydrogen peroxide, it is used in the form of an aqueous solution, in such quantities that the molar ratio of H₂O₂ added to chlorinated product initially present generally ranges from 0.2 to 100, preferably from 0.2 to 30. The concentration of the aqueous hydrogen peroxide solution is not a limiting parameter; to simplify the working conditions, hydrogen peroxide solutions of 30 to 50% by volume are generally used. The hydrogen peroxide solution is preferably added gradually and continuously to the reaction mixture in order to more easily control the reaction conditions, in particular the temperature and the pH. The rate of addition generally ranges from 0.2 to 3 ml/min, but it can be varied over a wide range depending on the specific reaction conditions.

The reaction temperature can be varied over a wide range, generally from 40 to 200°C, preferably from 70 to 120°C. The pH generally ranges from about 2 to 7, preferably from about 3 to 4, and is maintained in such ranges during the reaction by the addition of small amounts of an aqueous solution of an acid (H₂SO₄) or a base (e.g. NaOH).

The process of the present invention leads to a quantitative conversion of the chlorinated organic products to non-toxic products, accompanied by a good degree of mineralization of the chlorine atoms, i.e. conversion of the organic chlorine to chlorine ions.

In the case where the chlorinated product to be disposed of is dissolved in an organic solvent or in a mineral oil of the hydrocarbon type, the reaction mixture is heated to a preset reaction temperature and then stirred intensively to bring the two phases into intimate contact with each other, thereby obtaining a water/oil macroemulsion (the predominant phase is the organic phase).

The present invention will be illustrated in more detail by the following examples which are given merely for illustration and not to limit the scope of the invention.

In each example, the course of the reaction was reproduced by taking small amounts of the reaction mixture after a programmed addition of hydrogen peroxide and determining the following parameters.

(a) Concentration of chlorinated organic product

It is determined by gas chromatographic analysis (2-meter-long column packed with Tenax solid phase; carrier gas: nitrogen; temperature program: isothermal at 100ºC for 2 minutes; gradient at 10ºC/min up to 180ºC; isothermal at 180ºC for 25 minutes). Each injection (0.6 µl) is carried out with a sample diluted with CH₂Cl₂ in a 1:1 ratio to which CH₃OH has been added as an internal standard.

With regard to PCBs, all calculations were based on the three main PCB isomers, for which the following compositions were determined:

C12 H7 Cl3 : 21.21%

C12 H5 Cl5 : 0.95%

C12 H6 Cl4 : 77.83%

On the basis of such a composition, an average molecular weight of 280.5 was determined, with the average number of chlorine atoms being 3.74.

(b) Chlorine ion concentration

The chlorine ions are recovered by extraction with H₂O acidified with 0.1% HNO₃ and analyzed by voltammetric titration in an acidic medium with AgNO₃.

(c) COD (chemical oxygen demand)

It is determined by oxidation with potassium bichromate in an acidic medium and by titration with iron(II) sulfate according to the method described by N.W. Hanson in "Official, Standardized and Recommended Methods of Analysis" (page 383, The Society for Analytical Chemistry, 1973).

EXAMPLES 1 TO 3

In a reaction flask equipped with a condenser, dropping funnels, a pH meter and a magnetic stirrer, 455 ml of a mineral oil contaminated with PCBs (3431 ppm) was added. Then an aqueous solution was added consisting of 45 ml of H₂O in which the following were dissolved: FeSO₄ 7H₂O and CuSO4 5H₂O in such amounts as to obtain a concentration of 200 ppm for both the Fe²⁺ ions and the Cu²⁺ ions; tetrabutylammonium hydroxide (ITBA) in the following amounts:

- 150 ppm (Example 1);

- 300 ppm (Example 2);

- 0 ppm (Example 3, comparison).

The resulting mixture was heated to 95°C in an oil bath and the pH was adjusted by small additions of a 10% aqueous NaOH solution or a 15% aqueous H2SO4 solution until a value of approximately 3.0 was obtained. The mixture was stirred vigorously to form a water-in-oil macroemulsion. Then an aqueous H2O2 solution (45% by volume) was added stepwise at a rate of approximately 0.6 ml/min. After the programmed addition of hydrogen peroxide (as indicated in Table I), samples of the reaction mixture (5 ml each) were taken for analysis. For each sample, the concentration of residual PCB ([PCB]) and the concentration of chlorine ions ([Cl-]) were determined according to the procedures described above. The results are listed in Table I, which also gives the percentage of mineralization (%[Cl⊃min;]), expressed as the ratio between the actual Cl⊃min; ion concentration obtained and the maximum Cl⊃min; ion concentration obtainable.

During the reaction, the pH was maintained at approximately 3.0 by small additions (0.1 - 0.3 ml) of the NaOH or H₂SO₄ solutions, while the temperature was kept constant at 94°C.

The reaction with 150 ppm of ITBA (Example 1) and without ITBA (Example 3) lasted 60 minutes, while the reaction with 300 ppm of ITBA (Example 2) lasted 95 minutes.

From a comparison of the data obtained, it can be concluded first of all that without the contribution of the phase transfer reagent, no PCB oxidation takes place. With the addition of the phase transfer reagent, an almost complete PCB elimination is obtained, with a satisfactory degree of mineralization, especially in the case of the reaction with a low ITBA concentration (Example 1).

EXAMPLES 4 TO 6

Following the same procedures as described in Examples 1 to 3, the effectiveness of another phase transfer reagent, tetrabutylammonium bromide (TBAB), was checked by comparing the following reactions:

- with 150 ppm of TBAB (Example 4);

- with 472 ppm of TBAB (Example 5);

- without TBAB (Example 6, comparison).

The data obtained are shown in Table II. As in Examples 1 to 3, it is possible to observe that without phase transfer reagent the reaction does not take place and that the best results in terms of PCB oxidation as well as PCB mineralization are obtained with low concentrations of phase transfer reagent (Example 4).

EXAMPLES 7 TO 9

Following the same procedures as described in Examples 1 to 3, the effectiveness of another phase transfer reagent, tetrabutylammonium iodide (TBAI), was checked by comparing the following reactions:

- with 166 ppm of TBAI (Example 7);

- with 460 ppm of TBAI (Example 8);

- without TBAB (Example 9, comparison).

The obtained data are shown in Table III.

EXAMPLES 10 TO 11

Following the same procedures as described in Examples 1 to 3, the effectiveness of a phase transfer reagent mixture (ITBA + TBAB) was checked by comparing the following reactions:

- with 100 ppm of ITBA + 100 ppm of TBAB (Example 10);

- without phase transfer reagents (Example 11, Comparison).

The obtained data are shown in Table IV.

From a comparison of the results of Examples 10 with those obtained in Examples 1, 4 and 7, it is obvious that the coupling of the two phase transfer reagents of Example 10 makes it possible to combine most suitably the essentially quantitative PCB oxidation with a good degree of PCB mineralization.

EXAMPLE 12

The same reactor used for the previous examples was filled with 500 ml of H₂O in which the following products were dissolved: FeSO₄ 7H₂O and CuSO₄ 5H₂O in amounts such that a 200 ppm concentration is obtained for both Fe³⁺ and Cu²⁺ ions; tetrabutylammonium hydroxide (ITBA) in an amount equal to 150 ppm.

Then, 20 g of a paper contaminated with PCBs, previously cut into small pieces, were added to the reactor. The PCB concentration in the paper was equal to 1060 ppm. It was determined using a small paper sample (1 g) extracted at room temperature for 14 hours with 20 ml of CH₂Cl₂; the PCB-containing solvent was then evaporated using methanol. as an internal standard using gas chromatography.

Keeping the solution under intensive stirring, a 45% aqueous hydrogen peroxide solution was gradually added until a total H₂O₂ concentration equal to 127.5 g/l was obtained. At the end of the reaction, the chloride ion concentration in the aqueous phase was determined by voltammetric titration in an acidic medium with AgNO₃. The residual PCB concentration in both the aqueous phase and in the pulp was determined by gas chromatography after extraction with CH₂Cl₂ as previously described. The data obtained are shown in Table V.

EXAMPLE 13 (Oxidation of hexachlorocyclohexane)

In a round-bottomed reaction flask with a volume of 250 ml, equipped with dropping funnels, a pH meter and a magnetic stirrer, 0.5 g of hexachlorocyclohexane (ECE) was added. Then an aqueous solution was added consisting of 100 ml of H₂O in which the following were dissolved: FeSO₄ 7H₂O and CuSO₄ 5H₂O in such amounts as to obtain a concentration equal to 200 ppm for both Fe²⁺ and Cu²⁺ ions; tetrabutylammonium hydroxide (ITBA) in amounts equal to 500 ppm.

The resulting mixture was heated in an oil bath at 95°C; the pH was adjusted to approximately 3.4 to 3.5 by small additions of a 15% aqueous H₂SO₄ solution or a 10% aqueous NaOH solution. The mixture was stirred vigorously to dissolve all of the ECE. Then an aqueous H₂O₂ solution (56 vol%) was added gradually at a rate of approximately 0.4 ml/min. After the programmed additions of H₂O₂ (as indicated in Table VI), samples of the reaction mixture were (5 ml each) were taken for analysis. In Table VI, the amounts of H₂O₂ added are expressed as numbers of stoichometric equivalents, where stoichometric equivalent is the theoretical amount of H₂O₂ (100%) necessary for the complete oxidation of the organic substance to CO₂ and H₂O.

For each sample, the residual ECE concentration ([ECE]), the COD and the chlorine ion concentration ([Cl⊃min;]) were determined according to the procedures described above. The results are presented in Table VI, which also gives the percentage of mineralization (%[Cl⊃min;]), expressed as a ratio between the Cl⊃min; ion concentration actually obtained and the maximum Cl⊃min; concentration obtainable.

During the reaction, the pH was maintained at approximately 3.4 by small additions (0.1-0.2 ml) of the NaOH or H₂SO₄ solutions, while the temperature was kept constant at 97°C.

EXAMPLE 14 (Oxidation of meta-chlorobenzene)

In a 500 ml round bottom reaction flask equipped with dropping funnels, a pH meter and a magnetic stirrer, 1 g (0.766 ml) of meta-dichlorobenzene (MDB) was added. Then an aqueous solution was added consisting of 200 ml of H₂O in which the following were dissolved: FeSO₄ 7H₂O and CuSO₄ 5H₂O in such amounts as to obtain a concentration equal to 200 ppm of both Fe²⁺ and Cu²⁺ ions; tetrabutylammonium hydroxide (ITBA) in amounts equal to 500 ppm.

The resulting mixture was heated to 95°C in an oil bath; the pH was adjusted by small additions of a 15% aqueous H₂SO₄ solution or a 10% aqueous NaOH solution was adjusted to a value of approximately 3.5. The mixture was stirred vigorously to dissolve all the MDB. An aqueous H2O2 solution (60 vol%) was then added gradually at a rate of approximately 0.44 ml/min. After the programmed additions of H2O2 (as indicated in Table VI), samples of the reaction mixture (20 ml each) were taken for analysis. For each sample, the residual MDB concentration ([MDB]) and the chlorine ion concentration ([Cl⁻]) were determined according to the procedures described above. The results are listed in Table VI, which also gives the percentage of mineralization (%[Cl⁻]), expressed as a ratio between the Cl⁻ ion concentration actually obtained and the maximum Cl⁻ ion concentration obtainable.

During the reaction, the pH was maintained at approximately 3.5 by small additions (0.1-0.2 ml) of the NaOH or H₂SO₄ solutions, while the temperature was kept constant at 97°C.

EXAMPLES 15 - 17 (Oxidation of chlorophenols)

In a 500 ml round bottom reaction flask equipped with dropping funnels, a pH meter and a magnetic stirrer, 6.25 g of para-chlorophenol (PCF) (Example 15) or 0.25 g of trichlorophenol (TCF) (Example 16) or 0.25 g of pentachlorophenol (PECF) (Example 17) were added. Then an aqueous solution was added consisting of 250 ml of H₂O in which the following were dissolved: FeSO₄ 7H₂O and CuSO₄ 5H₂O in such amounts as to obtain a concentration equal to 200 ppm for both Fe²⁺ and Cu²⁺ ions; tetrabutylammonium hydroxide (ITBA) in amounts equal to 500 ppm.

The resulting mixture was heated to 95ºC in an oil bath; the pH was adjusted by small additions of a 15% aqueous H₂SO₄ solution or a 10% aqueous NaOH solution to approximately 3.0. The mixture was stirred vigorously to dissolve all of the PCF, TCF or PECF. An aqueous H₂O₂ solution (50 vol. %) was then added gradually at a rate of approximately 0.2 ml/min. After the programmed additions of H₂O₂ (as indicated in Table VII), samples of the reaction mixture (5 ml each) were taken for analysis. For each sample, the residual concentration of PCF, TCF or PECF ([PCF], [TCF], [PECF]), COD and chlorine ion concentration ([Cl⁻]) were determined according to the procedures described above. The results are presented in Table VII, which also gives the percentage of mineralization (%[Cl⊃min;]), expressed as a ratio between the actual Cl⊃min; ion concentration obtained and the maximum Cl⊃min; ion concentration obtainable.

During the reaction, the pH was maintained at approximately 3.0 by small additions (0.1-0.2 ml) of the NaOH or H₂SO₄ solutions while the temperature was kept constant at 97 °C. Table I

* maximum achievable concentration of Cl⊃min; ions Table II

* maximum achievable concentration of Cl⊃min; ions Table III

* maximum achievable concentration of Cl⊃min; ions Table IV

* maximum achievable concentration of Cl⊃min; ions Table V

* maximum achievable concentration of Cl⊃min; ions Table VI

maximum achievable concentration of Cl⊃min; ions Table VII

maximum achievable concentration of Cl⊃min; ions

Claims (12)

1. A process for the disposal of chlorinated organic products, which comprises treating the products with an aqueous H₂O₂ solution in the presence of Fe(II) ions, optionally in association with one or more transition metal ions selected from Cu(II), Ti(IV), Mn(II), Co(II), Ni(II), W(IV) and Mo(IV), and in the presence of a phase transfer agent selected from ammonium, phosphonium or arsonium salts, pyridinium salts or ephedrine salts. The ammonium, phosphonium or arsonium salts have the general formula: where: Q is selected from N, P and As; R₁, R₂, R₃ and R₄ are the same or different from one another and are selected from hydrogen, C₁-C₃₅ alkyl groups, C₆-C₁₀ aryl groups, C₁-C₁₀ arylalkyl or alkylaryl groups, provided that at least one of R₁, R₂, R₃ and R₄ is other than hydrogen; X⊃min; is selected from OH⊃min;, Cl⊃min;, Br⊃min;, I⊃min; and BH₄⊃min;. The pyridinium salts have a general formula: where R represents a C₁-C₂₀ alkyl group, while X⊃min; is as defined above. The ephedrine salts have the general formula: where: R₅ is the same or different and represents C₁-C₆ alkyl groups; X⁻ is as defined above. 2. Process according to claim 1, wherein the chlorinated organic products have an aromatic, alkylaromatic, olefinic, aliphatic or cycloaliphatic structure. 3. Process according to claim 2, wherein the chlorinated organic products are selected from: polychlorinated biphenyls (PCBs), chlorobenzenes, chlorophenols, 1,1,1-trichloro-2,2-bis(p-chlorophenyl)ethane (DDT), trichloroethylene, perchlorobutadiene, tetrachloroethane, hexachlorocyclohexane, hydrated chloral, hexachloroethane, perchloroacetone. 4. A process according to any one of the preceding claims, wherein the phase transfer agent is selected from ammonium, phosphonium or arsonium salts, pyridinium salts or ephedrine salts of the general formula: where: Q is selected from N, P and As; R₁, R₂, R₃ and R₄ are the same or different from one another and are selected from hydrogen, C₁-C₃₅ alkyl groups, C₆-C₁₀ aryl groups, C₁-C₁₀ arylalkyl or alkylaryl groups, provided that at least one of R₁, R₂, R₃ and R₄ is other than hydrogen; X⊃min; is selected from OH⊃min;, Cl⊃min;, Br⊃min;, I⊃min; and BH₄⊃min;. 5. The process according to claim 4, wherein the phase transfer agent is selected from tetraalkylammonium salts in which the alkyls are the same or different and contain 1 to 35 carbon atoms. 6. Process according to one of the preceding claims, wherein the phase transfer agent is used in a concentration in the range of 20 to 500 ppm based on the aqueous phase. 7. A process according to claim 6, wherein the chain transfer agent is used in a concentration in the range of 100 to 300 ppm based on the aqueous phase. 8. Process according to one of the preceding claims, wherein the Fe(II) ions are used in a concentration in the range of 50 to 1000 ppm, based on the aqueous phase. 9. Process according to one of the preceding claims, wherein the Cu(II), Ti(IV), Mn(II), Co(II), Ni(II), W(IV) or Mo(IV) ions are used in a concentration in the range of 0 to 400 ppm, based on the aqueous phase. 10. A process according to any one of the preceding claims, wherein the Fe(II) ions and one or more transition metal ions selected from Cu(II), Ti(IV), Mn(II), Co(II), Ni(II), W(IV) and Mo(IV) are used in equimolar amounts, each in a concentration ranging from 50 to 400 ppm. 11. A process according to any preceding claim, wherein the aqueous H₂O₂ solution is used in such amounts that the molar ratio of added H₂O₂ to chlorinated organic products initially present is in the range of 0.2 to 100. 12. The process of claim 11, wherein the molar ratio of added H₂O₂ to chlorinated organic products initially present is in the range of 0.2 to 30.