NO762638L - PROCEDURES FOR DECOMPOSITION OF HALOGENATED ORGANIC COMPOUNDS. - Google Patents

Description

Procedure for splitting halogenated organic compounds.

The present invention relates to a method for splitting halogenated organic compounds, which method involves (a) that the halogenated organic compound is preheated to a temperature above ea. 300°C, and (b) that the preheated organic compound is brought into contact with a catalytic amount of pea noble metal catalyst in the presence of an oxidizing agent at a temperature of at least 350°C. Suitable noble metal catalysts are ruthenium, platinum or a combination of ruthenium and platinum.

The present invention thus relates to the cleavage of halogenated organic compounds. The invention relates in particular to the removal of vinyl halides (e.g. by splitting them) from gas streams.

Polyvinyl chloride, produced by polymerization of vinyl chloride, is one of the most valuable of the modern commercial plastics. Unfortunately, it is now considered to be well established that vinyl chloride in sufficient concentration is harmful. In light of this, extensive research is now being carried out into methods for splitting or removing vinyl chloride. The present invention relates to a method for splitting a vinyl halide, such as vinyl chloride. The invention relates in particular to a method for splitting vinyl halide, such as vinyl chloride, in the presence of an oxygen-containing gas stream such as air.

While the cleavage of vinyl chloride is an important application of the present process, it is obvious that the process is also useful for cleaving other halogenated organic compounds which will be defined below.

The standard of the technique as it emerges from the following may possibly be relevant.

Ruthenium is known as a catalyst for the decomposing oxidation of organic compounds such as sucrose, glycine and eicosane (1).

Catalytic cleavage of ethyl chloride with platinum metal is described in two publications (2,3).

However, it is generally recognized that halogen-containing compounds are toxic to oxidation catalysts of noble metals (4,5,6).

(1) Doc. Acad. Nank SSSR 200 (5), 1105-b (1971)

ABOUT. 76.: 14867 u

(.2)Chemist Ztz 88 (1)', 15-16 (964) CA. 60: 7503b (3) Z. Electrochem. 58, 762-6 (1954) CA. 49: 6708e

(4) "Industrial Pollution Control Handbook", edited by

H.F. Lund, McGraw-Hill, 1971, Chapter 5

(5) ibid (4) - chapter 7

(6) ibid (4) - chapter 14

US patent 3,453,073 states that the halogen content in chlorinated hydrocarbons is extracted by passing a gaseous mixture of the chlorinated hydrocarbon, water and oxygen through a layer of a catalyst to form hydrogen chloride which is then extracted. Although this patent describes a large number of catalysts, ruthenium is not disclosed.

US patent 3,845-191 describes a method for oxidizing perhalogen hydrocarbons, including chlorofluorohydrocarbons, which method involves bringing the perhalogen hydrocarbon into contact with oxygen and an oxide of calcium, aluminium, barium,

magnesium, iron, nickel or mixtures thereof at 750 - 1100°C

US patent no. 3,933-980 describes a method for reducing the amount of ethylenically unsaturated, chlorinated hydrocarbons in gaseous mixtures. In short, the method involves bringing a gas stream containing the ethylenically unsaturated, chlorinated hydrocarbons into contact with ozone. No catalyst is used in the process.

British patent no. 1,046,313 specifies a method for the production of chlorine, bromine or iodine from compounds of these halogens with hydrogen. In short, the method involves oxidation of the hydrogen halide in the gas phase using ruthenium compounds as a catalyst. Since different catalysts are usually used in the oxidation of hydrogen halides and organic halides, they are considered by those skilled in the art to be completely non-analogous reactions.

A paper by Bond and Sadeghi [J. Appl. Chem., Biotechnol, 25, 241 (1975)] describes the catalytic destruction of chlorinated hydrocarbons using a platinum-alumina catalyst. The article states that a hydrocarbon fuel is required for those molecules that contain more chlorine atoms than hydrogen atoms. All the examples in the article, however, use a hydrocarbon fuel. The article also does not contain the teaching about preheating the starting material before it is passed through the reactor.

In summary, it can thus be said that the state of the art does not teach or realize the advantages that are achieved by preheating the raw material as is apparent from the present invention. Nor does the prior art teach ruthenium as a catalyst for the decomposition of vinyl halides. It also does not teach a ruthenium-platinum catalyst for the cleavage of vinyl halides.

The present invention generally relates to a method for splitting halogenated organic compounds', which method involves: (a) that the halogenated organic compound is heated to

a temperature above approx. 300°C,

(b) contacting the heated organic compound with a catalytic amount of a noble metal catalyst in the presence of an oxidizing agent at a temperature of at least about 350°C.

In one embodiment, the present invention relates to a method for splitting halogenated organic compounds, which embodiment involves: (a) that a gas stream containing the halogenated organic compounds and an oxidizing gas is heated to a temperature above approx. 300°C, (b) that the heated gas stream from step (a) is caused to pass through a heated zone in which it is brought into contact with one noble metal catalyst at a temperature of at least approx. 350°C.

Suitable noble metal catalysts are ruthenium, platinum and

a combination of ruthenium and platinum.

In a preferred embodiment, the halogenated organic compound is vinyl chloride, the oxidizing gas is air or a mixture of nitrogen and oxygen, and the noble metal catalyst is supported on a non-oxidizable support.

Suitable halogenated organic compounds for use in the present process are those which contain 1-4 carbon atoms and which contain at least as many hydrogen atoms as halogen atoms. Also suitable are mixtures of halogenated organic compounds which contain 1-4 carbon atoms and in which the total number of hydrogen atoms in the mixture is at least as many as the total number of halogen atoms. Particularly suitable halogenated organic compounds are unsaturated organic compounds; such as vinyl halides and mixtures of halogenated compounds with one carbon atom and halogenated compounds with 2 carbon atoms containing vinyl halides, in these mixtures the total number of hydrogen atoms is at least equal to the total number of halogen atoms. The preferred halogenated organic compounds are those in which the halogen is chlorine. Using chlorine as a typical halogen, examples of suitable halogenated organic compounds are those having the formulas CHgCl, CH2C12, CH3CHC12, CH2C1-CH2C1, CH2=CHC1, CH_CH=CHC1, CH0CH_CH=CHC1.

3 5 <Z

From the above, it is clear that the halogenated organic compounds contain only carbon, hydrogen and halogen.

One of the catalysts used in the present method is ruthenium; Ruthenium can be in the form of finely divided metallic ruthenium or in the form of ruthenium coated on or impregnated in a non-oxidizing carrier as a support. Suitable supports include Al 2 O 2 , SiO 2 sic>Fe 2° 3° 9 diatomaceous earth, or more generally any of the non-oxidizing supports normally used with noble metal catalysts (eg platinum). These catalytic forms of ruthenium are widely commercially available and are well known.

When ruthenium is used in a form placed on a support, the catalyst will generally contain 0.01 - 1% by weight of ruthenium. This is not a critical feature of the present invention, then

any amount of ruthenium is effective to some extent in the present process. The preferred form of the catalyst is ruthenium impregnated on aluminum oxide.

Another catalyst used in the present process is platinum. Platinum can be in the form of finely divided metallic platinum or in the form of platinum coated or impregnated on a non-oxidizing carrier as a substrate. In general, any of the non-oxidizing supports commonly used for noble metal catalysts can be used. are used. Examples of suitable supports include those indicated in the description of the ruthenium catalyst. Platinum impregnated on an aluminum oxide support is the preferred catalyst form..

These catalyst forms for platinum are readily available commercially and are well known. In particular, catalysts are placed

on carriers conventionally used in petroleum reforming processes. These catalysts contain 0.1 - 1.0% by weight platinum, usually 0.4 - 0.6% by weight. They also usually contain a small amount (eg 0.1 - 0.3%) of halogen, such as chlorine.

The following US patents state methods for preparing suitable platinum catalysts: 2,898-289, 2,909-481 and 2,940,924.

A typical example of a suitable platinum catalyst is the "Houdry 3K" catalyst available from Air Products and Chemicals. This catalyst has the following properties:

Another catalyst used in the present process is a combination of ruthenium and platinum. The catalyst may be in the form of finely divided metallic ruthenium and finely divided metallic platinum, or each of the metals individually supported on a non-oxidizing support which may be the same or different, or both metals supported on the same non-oxidizing support (usually referred to as bimetallic catalyst). When the metals are placed on a carrier, they can be coated or impregnated and will usually contain approx. 0.01 - 1% by weight of the metal, although larger and smaller amounts can be used. The non-oxidizing supports may be any of those known, as indicated under the description of the ruthenium catalyst. '

Catalysts in this form are commercially readily available and well known.

It is clear that one metal catalyst can be used as a finely divided metal, and the other placed on a support, or both metals can be used in finely divided form or placed on supports, or a bimetallic catalyst can be used alone. If the metals are either in finely divided metallic form or individually placed on supports, they can also be deposited in the reaction zone in a mixture or in successive layers. Some unique effects can be achieved with the latter coating technique, in that if the halogenated organic compounds successively come into contact first with platinum and then with ruthenium, the decomposition products in the waste gas will contain a considerable amount of elemental halogen, while the opposite sequence will lead to a considerable amount of hydrogen halide and less elemental halogen. This is discussed in more detail below.

Catalysts in which the metal is impregnated on aluminum oxide are preferred and are available from Engelhard Industries, Newark, New Jersey.

With regard to the relative amounts of the platinum catalyst and the ruthenium catalyst, a suitable amount is in the range of 1 - 20 parts of platinum catalyst per part ruthenium catalyst. A more suitable amount is 1 - 10 parts platinum catalyst per part ruthenium catalyst. Preferably, the amount of platinum catalyst is in the range of 2-5 parts per part ruthenium catalyst. All the specified intervals are based on the amount of active substance,

i.e. platinum or ruthenium.

It is interesting to note that in the present method, ruthenium has been found to be approx. 50 times as efficient as platinum, when platinum is coated on a support (e.g. aluminum oxide coated with platinum), although the same degree of increased efficiency does not appear with platinum-impregnated catalysts. It has also been shown that palladium, ferric oxide and manganese oxide are not effective in the present method.

It is further of interest that the use of a platinum catalyst leads to the transfer of substantially all of the halogen content present to hydrogen halides, while the use of a ruthenium catalyst leads to a product mixture containing a considerable amount of halogen gases in addition to hydrogen halides.

Suitable oxidizing agents include air, oxygen and mixtures of nitrogen and oxygen.

An important feature of the present invention is the heating of the halogenated organic compound before it is brought into the reaction zone where it is brought into contact with the catalyst. The oxidation of the halogenated organic compound in the presence of catalyst is exothermic, but does not proceed simultaneously. In order for the reaction to take place when the halogenated organic compound comes into contact with the catalyst, it is necessary that it has a certain elevated minimum temperature before it comes into contact with the catalyst. (This is often called "preheating"). This particular heating step should be carried out using a temperature above about 300°C, more suitably above 320°C, and preferably above 340°C. The maximum temperature for this heating step is approx. 600°C, preferably approx. 500°C.

It has been shown that this preheating improves the lifetime of the catalyst and provides more efficient cleavage of the halogenated organic compound. It has also been shown that attempts to carry out the method by simple heating of the reactants to the required temperatures in the reaction zone without preheating lead to the catalyst being quickly rendered ineffective due to the deposition of coal and carbonaceous compounds. This is particularly the case when vinyl chloride is the halogenated organic compound that is decomposed.'

The heated halogenated organic compound is then fed to a reaction zone containing the catalyst. As the reaction is exothermic, the temperature in the reaction zone varies, with the highest suitable temperature being in the range from approx. 350° to approx. 600°C, preferably in the range from approx. 400° to approx. 500°C.

(The highest temperature in the reaction zone is often referred to as the "hot-spot" temperature).

When using a combination catalyst of ruthenium and platinum, the order in which the catalyst is placed in the reactor affects the type of fission products. In the following, the terms "first" and "second" ("then") refer to the order in which the catalysts come into contact with the halogenated organic compound and the oxidizing agent. If the platinum catalyst is placed first and the ruthenium catalyst next, this results in to a product with. a very low concentration of vinyl chloride but a significant amount of chlorine. If the ruthenium catalyst is placed first and then the platinum catalyst, this results in a product with a low concentration of vinyl chloride and a significantly lower concentration of chlorine than when the catalyst is.

placed in reverse order.

The present method is particularly suitable for use with air (or a mixture of nitrogen and oxygen) containing the halogenated organic compound, e.g. vinyl chloride, as the halogenated organic compound may be present within a wide range. To state a more specific doctrine, the GHSV (volume rate of gas per hour) for the gas including the halogenated organic compound of the catalyst may be in the range of 100 - 100.OOO l/h.

Although it is assumed to be apparent from the foregoing, it may be good to state that the present invention is also applicable to methods where liquid halogenated organic compounds are vaporized and injected into the oxidizing gas.

The pressure is not critical, but performing the method in the liquid phase requires that it be under pressure.

A particularly outstanding feature of the present invention is that the catalyst has a long lifetime which still provides an outlet containing only a small amount of vinyl chloride. In laboratory experiments, e.g. the catalyst has been effective for at least 360 hours of continuous operation.

The waste gas from the present method can optionally be made to pass through a gas scrubber to absorb the cleavage products.

To further illustrate the invention, the following examples are given.

Examples

I - Ruthenium as a catalyst.

In the following examples, the reactor, which was a stainless steel tube with a length of 11 cm and a diameter of 1.3 cm, was placed in a Lindburg furnace. A preheater, a stainless steel tube with a length of 20 cm and a diameter of 1.3 cm, was placed in front of the reactor.

The catalyst was a commercial catalyst obtained from Engelhard. It consisted of 2 mm Al 2 O 3 spheres as supports, containing 0.5% Ru. 5 g of catalyst were packed in the reactor.

Example 1

Air containing 5500 ppm vinyl chloride was passed through the apparatus at a preheater temperature of 340°C and a maximum reactor temperature of 376°C. The velocity of the air containing vinyl chloride passing through the apparatus was 1200 ml/min. The vinyl chloride concentration in the outlet air was 2 ppm. Catalyst activity remained constant during 360 hours of continuous operation. Analysis of the waste gas showed that the vinyl chloride had been transferred to C02'H20'HC109Cl2*^7% of the chlorine in the vinyl chloride had been transferred to Cl2, the remainder having been transferred to HC1.

Example 2

Example 1 was repeated except that the maximum reactor temperature was 450°C. Similar results were obtained.

Example 3 - 5

Example 1 was repeated except that the catalyst was as follows:

Example 3 - palladium

Example 4 - ferric oxide

Example 5 - manganese oxide.

These catalysts were not effective in reducing the vinyl chloride content.

II - Platinum as a catalyst.

In the following examples, the reactor, which was a stainless steel tube of length 11 cm and diameter 1.3 cm with a 3.2 mm thermocouple axially placed, was placed in a Lindburg dvn. A preheater, a stainless steel tube with a length of 20 cm and a diameter of 1.3 cm, was placed in front of the reactor. 5 cm of "Houdry 3K" reforming catalyst was placed in the reactor and occupied 7 cm of the reactor length. This catalyst was 1.6 mm extrudate and contained 0.6% Pt and 0.2% Cl impregnated on aluminum oxide.

The composition of the gas feed was as follows in volume%:<N>2- 86.8; 02 - 11,<2>; c 2 H 5 ci -1.7; C 2 H Cl -0.13;

clc 2 H 4 ci - 0.079; CHCl 3 - 0.033; CC14- 0.018.

The composition of the off-gas was analyzed chromatographically using a flame ionization detector.

In all cases, the indicated value for the reactor temperature is the highest temperature in the reaction zone.

Example 6

This example shows the results of a series of experiments in which the preheater temperature was 322°C and the volume rate and reactor temperature varied. The results were as follows:

In the outlet gas, COCl2 was less than 1 ppmv, and the percentage of chloride that ended up as Cl2? was less than 0.2%.

Example 7

In a series of experiments the preheater temperature was 300°C or lower. The reactor temperature was 357°C, and the volume rate was 2400 h. The concentration of RC1 in the outlet gas was above 10 ppmv in all experiments, which showed that the catalyst was losing its effectiveness.

Example 8

This experiment was carried out under the following conditions:

The total concentration of RC1 was below 0.2 ppmv.

Example 9

This example illustrates the effect of preheater temperature on catalyst lifetime.

At a volume rate of 2400 h"1 and a preheater temperature of 343 C, the total concentration of RCl was 0.2 ppmv after 240 hours of operation under different conditions under which the catalyst underwent deactivation several times by either keeping the preheater below 300°C or using less than the stoichiometric amount of air.. The reactor temperature was between 357° and 437° C. during this experiment.

In the following examples, larger equipment was used.

The reactor was a stainless steel tube with a length of 33 cm and a diameter of 33 cm. 2.7 cm, which tube contained a 3.2 mm thermocouple along the . the pipe's centerline. The preheater consisted of a coil of 1.3 cm pipe placed in an electrically heated oven.

Electric heating wires were placed around the line from the preheater to the reactor and the reactor itself to regulate their temperatures.

The reactor contained 170 cm ■a•"Houdry 3KM reforming catalyst,

0j6% Pt and 0.2% Cl impregnated on aluminum oxide.

The feed gas had the following composition in volume%:

The composition of the outlet gas from the reactor was determined using chromatographic analysis with a flame ionization detector.

The chlorine determination was carried out in a conventional manner.

Example 10

A series of experiments was carried out in which volume velocity, preheater temperature and reactor temperature were varied. The results appear in the following table:

Example 11

This example shows the effect of using a reactor temperature lower than 400°C in a reactor of this size.

The volume rate was 5000 h-1.

The preheater temperature, reactor temperature and vinyl chloride content for five trials are shown in the following:

Example• 12

This example shows the effect of the preheater temperature.

The volume velocity was 5000 h"<1>in both experiments. :

Experiment A - Using a preheater temperature of 300°C, the reactor temperature only reached 310°C, showing that no reaction took place. The concentration of vinyl chloride in the outlet gas was 2000 ppmv, which was approximately the same as in the inlet gas. This also shows that no reaction occurred.

Experiment B - Using a preheater temperature of 330°C, the temperature in the reactor reached 465°C. The concentration of vinyl chloride in the outlet gas was 0.3 - 1.4 ppmv.

This example clearly shows the improvement of the present invention. It shows that without added hydrogen fuel, the reaction requires a preheater temperature above 300°C.

Example 13

This example shows that the catalyst has a long life

by the present method.

The preheater temperature was in the range 391 - 413°C.

The reactor temperature was in the range 425 - 458°C.

After 224 hours of operation at volume velocities of 4000 - 6000 h"1, the concentration of vinyl chloride in the outlet gas was less than 1 ppmv.

III - Combination of ruthenium and platinum as a catalyst.

In the following examples, the reactor, which was a stainless steel tube with a length of 11 cm and a diameter of 1.3 cm, was placed in a Lindburg furnace. A preheater, a stainless steel tube with a length of 20 cm and a diameter of 1.3 cm, was placed in front of the reactor.

The catalysts were commercial catalysts obtained from Engelhard. The platinum catalyst included 3 mm Al 2 _0 3 spheres containing 0.5 wt% platinum (coating). The ruthenium catalyst included 1.6 mm A 2 O 2 spheres containing 0.5 wt% ruthenium.

The composition of the feed gas was in all examples the following (% by volume): N2 - 86.8} 02. - 11.2; C₂Cl - 1.7; C2HCl - 0.13} C1C2H4C1"°>079>cl2- °»°79; chci3-0.033; cci^ -0/018.

The composition of the outlet gas was analyzed chromatographically with a flame ionization detector.

Example 14

This example shows the results obtained by applying

5 g of platinum-coated aluminum oxide catalyst alone in the reactor.

Four experiments were carried out using different preheater

and reactor temperatures. The GHSV in all experiments was 2400 h"<1>. The results are given in Table I:

Example 15

This example shows the results obtained when gases come into contact with platinum-coated catalyst before coming into contact with ruthenium-coated catalyst. 49 platinum-coated catalyst followed by 1 g of ruthenium-coated catalyst was placed in the reactor. Four trials were conducted at GHSV of 2400 h"<1> and four trials were conducted at GHSV of 4800 h"<1>. The results are shown in Table II.

Example 16

This example shows the results obtained when the gases come into contact with the ruthenium-coated catalyst before they come into contact with the platinum-coated catalyst. 1 g of ruthenium-coated catalyst followed by 4 g of platinum-coated catalyst was placed in the reactor. Four trials were conducted at GHSV 2400 h"<1>, and four trials were conducted at GHSV 4800 h-1. The results are shown in Table III.

Claims (1)

1. Procedure for splitting halogenated organic compounds containing. 1-4 carbon atoms and at least as many hydrogen atoms as halogen atoms, characterized by that (a) the halogenated organic compounds are heated to a o temperature above approx. 300 C, and (b) the heated organic compounds are brought into contact with a catalytic amount of a noble metal catalyst in the presence of an oxidizing agent at a temperature of at least about 350°C, the noble metal catalyst being ruthenium, platinum or a combination of ruthenium and platinum. 2. Method according to claim 1, characterized in that air or a mixture of nitrogen and oxygen is used as the oxidizing agent. 3. Process according to claim 1 or 2, characterized in that the halogenated organic compounds consist of vinyl halides or mixtures of halogenated compounds with 1 carbon atom and halogenated compounds with 2 carbon atoms containing vinyl halides, the total number of hydrogen atoms in the mixture being at least equal to the total number of halogen atoms . Procedure according to requirements 1-3» characterized in that the halogenated organic compound is vinyl chloride. 5. Method according to claims 1-4, characterized in that ruthenium is used as a catalyst. 6. Method according to claim 5, characterized in that the ruthenium is placed on a non-oxidizing support and that the catalyst contains 0.01 - 1% by weight of ruthenium. 7. Method according to claims 2-6, characterized by: (a) a gas stream including the halogenated organic compound and the oxidizing agent is heated to a temperature above about 300°C, and (b) the heated gas stream from step (a) is passed through a heated zone at a temperature of at least approx. 350°C, in which zone it comes into contact with the catalyst. 8. Process according to claims 1 - 4i, characterized in that the catalyst is finely divided platinum, platinum coated on a non-oxidizing carrier or platinum impregnated on a non-oxidizing carrier. 9. Method according to claim 8, characterized in that the halogenated organic compounds and the oxidizing agent are the only reactive materials. 10. Method according to claims 1-4 or 8, characterized in that: (a) a gas stream including the halogenated organic compound and the oxidizing agent is heated to a temperature above about 300°C, and (b) the heated gas flow from step (a) is passed through a heated zone with a temperature of at least approx. 350°C, in which zone it comes into contact with the catalyst. 11. Method according to claim 10, characterized in that the halogenated organic compounds and the oxidizing agent are the only reactive materials. 12. Method according to claim 1, characterized by - that the oxidizing agent is air, oxygen or a mixture of nitrogen and air, and that the catalyst is a combination of ruthenium and platinum, the catalysts being present in an amount of 1 - 20 parts platinum: per part ruthenium. 13- Method according to claim 12, characterized in that the oxidizing agent is air or a mixture of nitrogen and oxygen. 14. Method according to claim 12 or 13, characterized in that the dehalogenated organic compounds consist of vinyl halides or mixtures of halogenated compounds m^H in halogenated acids with 1 carbon atom and halogenated compounds ices with 2 carbon atoms, containing vinyl halides, the total number of hydrogen atoms in the mixture being at least equal to the total number of halogen atoms. 15. Method according to claims 12-14, characterized in that the halogenated organic compound is vinyl chloride. 16. Process according to claims 12-15, characterized in that the ruthenium-platinum catalyst comprises ruthenium placed on a non-oxidizing carrier and platinum placed on a non-oxidizing carrier. 17. Method according to claims 12-15, characterized in that the ruthenium-platinum catalyst includes ruthenium impregnated on aluminum oxide or diatomaceous earth and platinum impregnated on aluminum oxide or diatomaceous earth. 18o Method according to claims 12 - 15, characterized in that the ruthenium pQatina catalyst is a bimetallic catalyst, in which both ruthenium and platinum is placed on a single non-oxidizing support. 19. Method according to claims 12-15, characterized in that the ruthenium-platinum catalyst is finely divided metallic ruthenium and finely divided metallic platinum. 20. Method according to claim 17, characterized in that the heated organic compound is first contacted with the ruthenium catalyst and then with the platinum catalyst. 21. Method according to claim 17, characterized in that the heated organic compound is first brought into contact with the platinum catalyst and then with the ruthenium catalyst. 22. Method according to claim 18, characterized in that the heated organic compound is first brought into contact with the ruthenium catalyst and then with the platinum catalyst. 23. Method according to claim 18, characterized in that the heated organic compound is first brought into contact with the platinum catalyst and then with the ruthenium catalyst. 24. Method according to claim 19, characterized in that the heated organic compound is first brought into contact with the ruthenium catalyst and then with the platinum catalyst. 25. Method according to claim 19, characterized in that the heated organic compound is first brought into contact with the platinum catalyst and then with the ruthenium catalyst. 26. Method according to claims 12-25, characterized in that: (a) a gas stream comprising the halogenated organic compound and the oxidizing agent is heated to a temperature above about 300°C, and (b) the heated gas stream from step (a) is passed through a heated zone at a temperature of at least approx. 350°C, in which zone it comes into contact with the catalyst.