NO770055L - CATALYTIC OXIDIZATION OF C2-C4 HALOGENATED HYDROCARBONS. - Google Patents

Description

Catalytic oxidation of C2~C4 halogenated hydrocarbons.

C^-C^ halogenated, e.g. chlorinated or brominated hydrocarbons, are used commercially for many purposes. E.g. vinyl chloride and vinylidene chloride are used to produce valuable

. polymers and copolymers. Other chlorinated C 2 hydrocarbons such as methyl chloroform (1,1,1-trichloroethane) and trichloroethylene can be used

as solvents and are used e.g. when degreasing metals. : Ethylene dichloride and ethylene dibromide are used in gasoline as part of anti-knock agents.

Recently, vinyl chloride has been indicated as a possible carcinogen. and very strict requirements have been set with regard to contamination by this substance in places where people travel or work. In places where vinyl chloride is produced or used, e.g. polymerized, gas streams can be produced which contain relatively small, but still unacceptable amounts of vinyl chloride which cannot be recovered economically. Such process streams can include vented light gases from the process equipment itself, e.g. from distillation columns, coolers and dryers, storage vessels and from areas where vinyl chloride is processed in one way or another. There is thus a need* for a method which can destroy or substantially reduce the content of vinyl chloride in such gas streams. In a similar way, there is a need to be able to process gas streams that. contains other C^* C_ and C . chlorinated and brominated hydrocarbons.

It has been indicated that certain chlorinated hydrocarbons such as methylchloroform, vinylidene chloride, trichloroethane, tetrachloroethene and chloroform are to varying degrees sensitive to a Hopcalit-catalyzed decomposition with moist air (approx. 50% relative humidity) at temperatures above 300°C, e.g. e.g. 305°-.415°C. See e.g. the articles “Catalytic Cbmbustion of Atmospherlc

Contaminants. Over Hopcalite" by J.G. Christian et al, Int. J. Air Wat. Poll. Pergamon Press 1965, Vol. 9, pages 1-10 and "Catalytic Decomposition of Halogenated Hydrocarbons over Hopcalite Catalyst" by J.K. Musick et al, Ind. Eng .Chem., Prod< Res. Develop., Vol. 13, No. 3, 1974, pages 175-179.

It has now been discovered that ^ 2~ CA halogenated, e.g. chlorinated and brominated, hydrocarbon, e.g. C2"chlorinated and brominated hydrocarbons, which are found, for example, in gas streams, can be substantially reduced by contacting such halogenated hydrocarbons with oxygen-containing gas in the presence of

, cobalt oxide catalyst at temperatures from 20 to 500°c, e.g.

80-10d°C. It has been found that temperatures in the lower part of

the area, e.g. from room temperature, i.e. from 20-23°C and up to 80°C, are effective for short periods of time. Temperatures of more than 100°C, e.g. 100-300°C are particularly useful. More particularly, it has been found that C1-chlorinated hydrocarbons such as vinyl chloride, vinylidene chloride, methyl chloride and trichlorethylene can be removed from gas streams, e.g. air, containing such chlorinated hydrocarbons, at relatively mild temperatures in the presence of a hydrated cobalt oxide catalyst and at conditions involving relatively low relative humidity, e.g. less than 5%

(measured at 23°C). The exact mechanism by which the aforementioned C^-C^ halogenates is not known. hydrocarbons are removed from the gas stream, but it is assumed that the principal mechanism is an oxidative decomposition. However, other mechanisms and processes such as dehydrochlorination can also partly help to remove such halogenated hydrocarbons from gas streams.

The temperature at which the present method can be carried out varies within the range from 20-500°C, and will be regulated within this range depending on the relative humidity of the gas streams which are in contact with the catalyst, i.e. the relative humidity in the reaction zone, dlv.s.^ in the destruction zone to achieve a significant catalytic activity. When you have low relative humidity, you should use temperatures in the lower part of the mentioned range, e.g. from 20-110°C. By e.g. a relative humidity of less than 2% by weight, the vinyl chloride content in a synthetic gas stream can be significantly reduced*i.e. from approx. a level of 50 ppm to an undetectable level (0.5 ppm);, at temperatures from 100-110°C, e.g. 104°C, using a hydrohydrated cobalt oxide catalyst and a gas amount of said synthetic gas of approx. 9 1 per hour. over the catalyst. When the relative humidity of the gas stream is higher than 5% by weight, temperatures above 110°C should be used

to maintain corresponding catalytic activity.

C2~C4 halogenated hydrocarbons that can be destroyed using the present method are both chlorinated

and brominated hydrocarbons containing from two to four carbon atoms and from 1 to 4, preferably 1 to 3, more preferably no more than 2, halogen atoms per molecule. Examples of such halogenated hydrocarbons include: vinyl, chloride, vinylidene chloride, methyl chloroform (1,1,1-trichloroethane)-1,1,2-trichloroethane,

trichlorethylene, perchlorethylene, vinyl bromide, vinylidene bromide, dichloroethane, ethylene dichloride, ethylene dibromide, propyl chloride, propyl bromide, isopropyl chloride, 1-2- and 3-chloro-propene, 1,2- and 2,3-dichloro-propane, allyl chloride, epichlorohydrin, chloroprene , butylene dichloride, etc. The ratio of hydrogen to halogen atoms in the halogenated hydrocarbons should preferably be at least one. Preferred are unsaturated C2-halogenated hydrocarbons, e.g. vinyl compounds and incompletely halogenated derivatives of ethylene. The present method is particularly applicable to C2-chlorinated hydrocarbons such as vinyl chloride, vinylidene chloride, methyl chloroform and trichloroethylene. As the present cobalt oxide, different types of cobalt oxides can be used. Examples of such oxides include cobalt (II) oxide (GoO, cobalt (III) oxide (COjO^) and cobalt (II, III) oxide (Co-jO^). Preferably, cobalt oxide is used in the highest oxidation state, i.e. cobalt (III9 oxide or mixed oxidation state,

i.e. a mixture of cobalt (II, III) oxide. The term "cobalt oxide" as used here means any of the aforementioned oxides or combinations of such oxides. The cobalt oxide content in the active part of the catalyst is usually from 70 to 75% by weight, disregarding the support layer for the catalyst, at least 80, i.e.

preferably at least 85% by weight. The rest of the catalyst can be smaller amounts of other metal compounds, e.g. impure

names of metal oxides which do not significantly affect

the catalyst's catalytic function, as well as water of hydration.

The metal oxide moiety may have entered during the preparation of the catalyst or may be present in the reactants used to prepare the catalyst.

It is believed that some water of hydration associated with the cobalt oxide catalyst is beneficial to the catalytic activity. For example, it could be observed that a cobalt catalyst that had little or no water of hydration was catalytically less active than the cobalt catalyst

which contained significant amounts of water of hydration. The presence or absence of water of hydration is related to the temperature of the surface of the cobalt oxide catalyst during its preparation or use. If e.g. the cobalt oxide is produced by thermal decomposition of a cobalt salt at temperatures of more than 500°C, e.g. 530°C, then this will contain little water of hydration in the resulting cobalt oxide, and will consequently have little catalytic activity at the lower temperatures that could be used in the present process.

The total amount of water associated with the cobalt oxide as hydration water will depend on the particular mixture or the particular cobalt oxide used, as well as the method for producing the oxide. Especially will dry-~. the conditions with respect to the cobalt oxide could vary greatly, and this would have a large influence on the water of hydration of the catalyst. It has been found that a cobalt oxide catalyst which has an amount of water of hydration which is at least as high as that which can be obtained by drying an aqueous filter cake of precipitated cobalt oxide or one cobalt oxide mixture at 200°C for a sufficiently long period of time to achieve equilibrium, is a satisfactory quenching hydrated cobalt oxide catalyst. Such a temperature is sufficient to remove essentially all that water

which is present in the filter cake without excessive loss of water of hydration. Higher drying temperatures can be used, but care should be taken at such temperatures in order not to lose too much hydration water and thereby a significant amount of the present beneficial effect.

The effect of the water of hydration in the cobalt oxide catalyst can best be determined by using cobalt oxide as a destruction catalyst, i.e. a yinyl chloride destruction catalyst and observe the catalyst's activity by a reduction in the content of halogenated hydrocarbons in the gas stream being treated, which is relatively simple in industry with known analytical equipment. Particularly useful hydrated cobalt oxide catalysts are those capable of removing at least 70, as much as 80% by weight of the vinyl chloride present in an air stream containing approx. 50 ppm vinyl chloride under conditions

which includes less than one percent relative humidity (measured at 23°C), a reactor temperature of 14°C and a gas flow rate over the catalyst of 9 l per hour, and a ratio between the catalyst layer's depth and diameter of at least two, and an average residence time in contact with the catalyst of 10 seconds. The average residence time is the time obtained by dividing the catalyst volume by the volumetric flow through the catalyst. Preferably at least 90% and most preferably in lalt. substantially all detectable amounts of the vinyl chloride in the gas stream are removed from the air stream under such conditions.

The cobalt oxide catalyst can be used in unsupported form or can be supported on an inert substrate. By "inert" it is understood that the substrate is chemically inert to the cobalt oxide catalyst that is deposited on the supporting layer, and is chemically resistant to the components of the gas stream containing the halogenated carbon, e.g. a gas containing vinyl chloride,

as well as the oxidation products that occur during the process. Examples of such inert materials include asbestos, pumice, activated charcoal, silica gel, colloidal silica gel, fused silica, activated alumina, and clay. The activity of the supported cobalt oxide catalyst will vary

depending on the method of manufacture. E.g. a mechanical mixture of cobalt oxide and the substrate will be more active than a substrate impregnated with catalyst. Heating the supported catalyst to high temperatures can deactivate it by sintering the cobalt oxide, : siJjxtEgr the substrate so that. one forms a mass transfer barrier or causes a reaction between the catalyst and the substrate. If you e.g. heats cobalt oxide supported on aluminum oxide to 850°C, it is stated that this

will result in the formation of a catalytically inactive cobalt aluminate (CoAl 0^) . See e.g. "The Oxidation of Hydrocarbons and CO over Metal. III Co304" by Young-Fang Yu Yao, Journal of

Catalysis, 33, pages 108-122 (1974). When the catalyst is used in a supported form, the amount of catalyst on the substrate must be

sufficient to obtain a catalyzed destruction of the aforementioned C^~ C^ halogenated hydrocarbons, i.e. one must use a catalytic amount. The catalytic amount of the catalyst and whether a substrate is inert or not can easily be determined in industry with known analytical equipment.

The cobalt oxide catalyst can be prepared in a number of well-known ways. E.g. the cobalt catalyst can be prepared by precipitating the hydroxide from a solution of cobalt salt. The precipitate is then dried to remove the water phase and partially dehydrate the hydroxide and form the oxide. Typically, drying can be carried out at temperatures from 100-200°C. When using a substrate for a catalyst, the cobalt hydroxide can be deposited directly on the substrate. In addition, cobalt oxide catalysts can be prepared by thermal decomposition of other suitable oxygen-containing anion salts of cobalt, e.g. nitrates, carbonates and oxalates. The thermal decomposition should preferably not be carried out at temperatures which completely dehydrate the cobalt oxide. The surface area of the cobalt oxide catalyst produced may vary, in most cases it is preferred to have a relatively high surface area.

If the cobalt oxide catalyst becomes deactivated in use (not permanently poisoned), it is possible to regenerate the catalyst by passing a dried oxygen-containing gas, i.e. a gas containing less than 5, preferably less than approx. 2, advantageously less than 1% relative humidity, i.e. that you can use air, oxygen or oxygen-enriched air, in intimate contact with the catalyst at elevated temperatures, e.g. from 150 to 200°C, in the absence of polluting gases, e.g. hydrogen halide (hydrogen chloride), C^-C^ halogenated hydrocarbons (vinyl chloride) as well as large amounts of water vapour. The catalyst is contacted with oxygen for a sufficiently long period of time to regenerate the catalyst, i.e. from 0.5 to 10 hours. The length of the contact time will depend on the amount of catalyst, its activity level, and the temperature during treatment and the rate of flow through the catalyst bed. A totally regenerated catalyst appears to be as effective as freshly prepared catalyst.

The present method results in the removal of C2~C4 halogenated hydrocarbons, e.g. C2-chlorinated hydrocarbons from a gas stream containing such hydrocarbons. The effectiveness of the removal will depend on the actual treatment conditions and the particular halogenated compounds to be removed. It seems that the removal is achieved in principle by an oxidative decomposition or destruction. Adsorption can make up a certain part of the removal at temperatures that are significantly below the boiling point of the halogenated hydrocarbon. Dehydrochlorination can also be a mechanism that can occur in the reaction zone. It is not currently known to what extent the latter two mechanisms participate in the removal. By the term "destruction" as used here, oxidative decomposition is understood alone or in combination with one or both of the other two aforementioned mechanisms.

In accordance with the present method, C2~C^ halogenated hydrocarbons, e.g. chlorinated hydrocarbons such as vinyl chloride, catalytically oxidized at temperatures between 20 and 500°C, e.g. from 20 to 300°C. Suitable temperatures are less than 300°C, e.g. from 50 to 250°C. At lower temperatures, e.g., from 20 to 50°C, the catalytic activity will decrease rapidly with time, but for certain purposes, e.g. in gas masks, even a few moments of activity will be important. Economically desirable temperatures are between 80 or 100°C and up to 250°C, e.g. between 100 and 150°C or 200°C. The use of such moderate temperatures, e.g. at 100-115°C,

in order to thereby be able to achieve a destruction of the aforementioned halogenated hydrocarbons, is surprising because one often uses significantly higher temperatures to destroy such compounds by non-catalytic processes. The use of moderate destruction temperatures is consequently a significant economic advantage because a great deal of heat energy can be obtained. Furthermore, a destruction process which is operated at approx. 100°C use waste steam with relatively low pressure, which is usually easy to

common in chemical processing plants, whereby the present method can again provide significant economic benefits. Temperatures in the range from 100 to 150°C or 200°C are preferred,

for such temperatures facilitates the removal of the oxidation products, e.g. hydrogen chloride, carbon dioxide and water, from the surface of the catalyst.

The aforementioned temperatures are reactor temperatures as described in the following examples, i.e. the temperature of the gas flow over the catalyst bed. The temperature on the catalyst surface is assumed to be somewhat higher than the reactor temperature, which is due to the heat produced by the destruction by the oxidative decomposition of the halogenated hydrocarbons on the catalyst surface.

The particular destruction or combustion temperature that is chosen will depend on the relative humidity of the gas flow that is fed into the reactor. Although there is evidence that cobalt oxide is relatively resistant to inhibition by water, water vapour, i.e. moisture in the gas streams that contact the catalyst tend to lower the activity of the cobalt oxide catalyst. This lowering of activity is more pronounced at low temperatures, i.e. in the range from 20 to 110°C. Higher temperatures are therefore necessary to achieve a particular level with regard to catalyst activity when using a moist gas stream than when using a substantially dry gas, i.e. a gas stream with relatively low relative humidity.

The relative humidity of a gas stream as used here is the value obtained when the relative humidity is measured at room temperature (23°C) and normal pressure (745 millimeters of mercury). Low relative humidity means less than approx. 5, preferably less than 2% by weight.

The activity of the cobalt catalyst used

in the present method can be expressed as its efficiency at the prevailing destruction conditions, i.e. percent C2~C4 halogenated hydrocarbon that is removed from the gas stream

after the conditions have become constant. The catalyst's effect can be determined by the equation:

where is the initial concentration of halogenated hydrocarbon in the gas stream and C f the final concentration. The higher the efficiency of the catalyst, the higher its activity will be.

As mentioned earlier, the degree of inhibition of the activity on the catalyst due to water vapor will be temperature-dependent. The lower the destruction temperature, the more pronounced the lowering of the activity will be. Consequently, for any desired level with regard to catalyst activity, it will be possible either to regulate the relative humidity of the gas stream to be treated, or the treatment temperature itself. Thus, the reactor temperature should be kept at a level within the aforementioned range to prevent reduction or loss of activity due to moisture in the gas stream that is contacted with the catalyst. The catalyst's activity level will depend on the halogenated hydrocarbon to be removed from the stream,

the initial concentration of this hydrocarbon and the final concentration in the treated stream, which again depends on how the gas is to be used, determination with regard to emission concentrations etc. It is therefore impossible to set a minimum acceptable level with regard to activity, as such a level will be determined by the wishes and needs of the individual facility. In practice, however, it will be easy to find the operating conditions necessary to achieve a desired catalyst activity.

In general, the higher the destruction temperature and the lower the relative humidity of the supplied gas flow, the higher the activity of the catalyst. When, therefore, the amount of hot energy available for the destruction or the materials in the apparatus itself limits the combustion temperature or the destruction temperature to a special range, then the relative humidity of the combined gas streams that are contacted with the catalyst must be kept at a level within the aforementioned range of variation that will maintain the catalyst activity at the desired level. If, on the other hand, the available heat energy and the materials used in the apparatus do not limit the destruction temperature, then this can be adjusted (usually upwards), to avoid disadvantages of the moisture on the catalyst activity. Within a temperature range from 20-500°C, for example from 50-300°C, then either the temperature during the destruction or the relative humidity of the treated gas stream or both will be regulated so that the desired catalyst activity is achieved. When e.g. the destruction temperature is lower than 110°C, then the relative humidity should be kept below 5%, e.g. 2%, preferably less than 1%.

The above-described effect of the water vapor on the catalyst's activity can be described as a reversible poisoning or inhibition, to distinguish this effect from what is obtained in a so-called irreversible poisoning, e.g. the effect of sulfur compounds on noble metal catalysts, reactions on the catalyst's surface, etc. In the latter cases, the catalyst's activity cannot usually be reversed without reworking it. As shown in the following examples, the catalyst's reduced effect in the present method will be due to an increase in the water vapor level in the gas stream being treated, and it can be reversed by lowering the relative humidity of the gas stream to its previous level level.

In one embodiment of the present method, the gas stream is dried to a desired moisture level and then destroyed at temperatures in the aforementioned range. Said halogenated hydrocarbon-containing gas stream can optionally be dried by passing it through a drying column containing a desiccant. Either solid or liquid desiccants can be used to remove water vapor from the gas stream. Examples of such desiccants include silica gel, activated alumina, fused anhydrous calcium sulfate, lime, magnesium perchlorate, calcium chloride, potassium hydroxide, sulfuric acid, lithium chloride solutions, and ethylene glycol. Drying of gases is well known in many chemical processes. Thus, the use of solid desiccants in gas masks is well known to absorb water vapour. The methods used to dry the gas are not critical in the present method.

The amount of oxygen used during oxidation of the aforementioned C^-C^ halogenated hydrocarbons in the present method should be sufficient to destroy

(oxidized) the amount of said halogenated hydrocarbons that are present in the gas stream, i.e. a destructive or oxidizing amount necessary to reduce the halogenated hydrocarbons to a desired level. The amount of oxygen should at least be stoichiometrically sufficient to oxidize all the carbon in the halogenated hydrocarbons to carbon dioxide and preferably sufficient to oxidize both the carbon present and the hydrogen present in the halogenated hydrocarbons to carbon dioxide and water respectively. With regard to vinyl chloride, the stoichiometric amount of oxygen will appear from the following equation:

The calculated heat of reaction for the above reaction is approx. 270 kilocalories per moles of vinyl chloride.

Generally, an amount of oxygen used will far exceed the stoichiometric amount necessary to

essentially ensure a complete oxidative decomposition of the halogenated hydrocarbons. The amount of oxygen is not critical, provided that you have sufficient amounts to achieve the aforementioned degree of oxidation. The oxygen can be provided by using air, oxygen or oxygen-enriched air. The oxygen-containing stream, if this is separate from said stream containing C^-C^ halogenated hydrocarbons can also be dried in the aforementioned manner to a low relative humidity before mixing with said stream containing halogenated hydrocarbons.

In a preferred embodiment of the present process, the stream containing C₁-C₁ halogenated hydrocarbons is dried, if necessary, and then mixed with dried oxygen-containing gas and fed into a preheating chamber. In the event that the stream containing C1-2 halogenated hydrocarbons is sufficiently dry or already contains sufficient amounts of oxygen, no further drying or mixing with an oxygen-containing stream is necessary. This is often the case in places where the aforementioned C2~C4 halogenated hydrocarbon is present in a well-ventilated state. The dried oxygen-containing process stream, which also contains C2~C4 halogenated hydrocarbon, is then preheated, if this is necessary, and then fed into a catalytic reactor where the cobalt oxide catalyst has been placed, either as a solid or fluidized bed. The preheating should take place close to the reactor temperature. Although preheating can be carried out before drying, this is usually not economically desirable.

According to known technology, the diameter of the catalyst bed in a fixed bed in a flow-type catalytic reactor should be at least six times and the bed depth should be at least 30 times the effective diameter of the catalyst particles, in order to thereby keep the edge of the bed and the final effect relatively small. The preheated gas stream is kept in contact with the cobalt catalyst for a sufficiently long time to cause destruction or oxidation. The contact time is from 2 to 10 seconds at 100°C under conditions of relatively low humidity. The gas stream leaving the catalytic reactor has a greatly reduced content of C2~C4 halogenated hydrocarbons. The gas stream coming out of the reactor should preferably contain less than 10 ppm, preferably less than 5 ppm, and most desirably less than 1 ppm of C2~C4 halogenated hydrocarbons, and is then cooled for further processing. It is e.g. advantageously passing the reactor stream through a scrubber containing caustic soda to remove hydrogen halide, e.g. halogen chloride or halogen bromide which is the oxidation or dehydrohalogenation product before treating other harmless gas products. Although only one catalyst layer has been described, several can of course be used. E.g. several separate layers can be used in sequence, and such layers can be in one unit, e.g. in stacked layers or separate units.

Apparatus in contact with said C2~C4 halogenated hydrocarbon stream and their oxidation products are usually made of acid-resistant construction materials to thereby have minimal corrosion problems. Examples of metallic construction metals are monel, nickel and stainless steel. Acid-resistant plastics such as Teflon (a trademark of E.I. duPont DeNemours and Company for polytetrafluoroethylene) and Ryton (a trademark of Phillips Petroleum Company for polyphenylene sulfide resins) can also be used in the apparatus itself due to the low temperatures used herein. oxidase ion process..

The following examples illustrate the invention.

Example 1.

A solution of 70/5 g of cobalt (II) sulfate heptahydrate dissolved in 200 g of distilled water was slowly added to a solution of 35 g of anhydrous sodium hydroxide dissolved in 70 g of distilled water with vigorous stirring. After adding approx. 25 g of distilled water to reduce the viscosity of the paste-like precipitated reactant mass, 10.9 g of a 35% by weight aqueous solution of hydrogen peroxide was added in approx. portions of 0.5 ml to the somewhat viscous cobalt oxide suspension with vigorous stirring. After the hydrogen peroxide solution had been added, the mixture was stirred for approx. 15 minutes. The precipitate was then washed with distilled water, using a centrifuge, and then isolated by filtration. The wet filter cake was pressed between felt mats using a hydraulic press. The pressed filter cake was then dried at a temperature of approx. 50°C for two to three days. The partially dried filter cake was broken up with a mortar to minus 4 mesh particle size and then dried at approx. 200°C for 7 hours. The dried product was then sieved to remove minus 20 mesh finer particles and the minus 4 plus 20 mesh particle size fraction was then dried at approx. 200°c for 6 hours. The cobalt content was determined to be 83.3% as cobalt (II) oxide by elemental X-ray analysis. X-ray diffraction analysis of the oxide indicated that a crystalline phase was present which was identified as hydrated cobalt (III) oxide. A thermogravimetric analysis of an oxide sample at 400°C indicated a total weight loss of 9.0% by weight. This is due to a loss of hydration water so that cobalt (II, III) oxide was formed.

Example II.

Nitrogen containing approx. 52 parts per million of vinyl chloride and approx. 4.5 parts per million of vinylidene chloride was mixed with oxygen so that a stream was obtained which had the approximate composition of air, i.e. about. 80% by volume/20% by volume nitrogen/oxygen. This synthetic airflow had a dew point of less than -25°C (relative humidity of less than 2%). The small amount of vinyl and vinylidene (hereafter collectively referred to as vinyl chloride) in the nitrogen was disregarded in the calculation of said 80/20 volume % mixture of nitrogen and oxygen. The humidification of the synthetic air stream was accomplished by passing a portion of the stream through a simple water bubbler. The degree of wetting was regulated by adjusting the relative amount of the gas flow that was passed through the bubble apparatus.

Said vinyl chloride-containing synthetic air stream was then introduced into a pre-heating chamber which was a tightly bound spiral with a diameter of approx. 6 cm and approx. 6 cm in height and was made from a stainless steel tube with a diameter of 6 mm. The spiral was placed in a 700 watt oven and heated to the desired temperature of the gas stream at intake into the reactor. The preheated synthetic gas stream was fed into the bottom of a vertical catalytic reactor constructed of 316 stainless steel with a diameter of approx. 1.8 cm and which had a length of approx. 20 cm. The catalyst was supported by a 35 mesh stainless steel mesh that was placed approx. 3.75 cm above the intake opening for said synthetic air. Another screen or sieve was placed on top of the catalyst bed to prevent a ejection of catalyst particles. Two thermo-domes were placed in the reactor approx. 1.25 cm above and below the catalyst bed to measure the temperature of the synthetic air stream. These thermocouples were placed so that the connection point was located in the center of the reactor. The reactor was insulated with asbestos to prevent heat loss and heated using a heating coil. The thermodome which was placed approx. 1.25 cm above the catalyst bed was used as a reference for the temperature of the catalyst bed.

The reactor gas that came out was cooled to room temperature using an approx. 1 m long U-shaped tube of stainless steel with a diameter of 6.2 mm. The cooled reactor gas was then released into a laboratory fume hood. At various times during the experiment, samples were taken from the gas in the preheater and from the reactor gas coming out of the cooler, to determine the vinyl chloride concentration in the gas stream before and after it had passed through the catalyst bed. The vinyl chloride concentration in said gas streams was measured by a gas-liquid chromatographic method where a flame ionization detector was used. The total gas flow in the reactor was calculated from the intake and the outlet temperature of the reactor.

About. 10.3 g of the cobalt oxide catalyst described in example I was added to the reactor as a catalyst bed and tested as a destruction catalyst for vinyl chloride and vinylidene chloride. The temperature of the reactor was maintained at 104°C.

The data obtained are set out in Table I.

Data from Table I show that the cobalt oxide catalyst prepared as described in Example I has high catalytic activity as a destruction catalyst for vinyl chloride and vinylidene chloride at relatively low relative humidity, i.e. less than 5%, e.g. 1.5%. More importantly, the catalytic activity of this cobalt oxide catalyst has a certain resistance to inhibition by water vapour, see e.g. samples 3-7. Thus, there was only a review of approx. 2% of the vinyl chloride after 69 minutes of operation with an atmosphere containing 53% relative humidity (see sample no. 6. ). Furthermore, the activity of the cobalt oxide catalyst was regenerated by passing a low relative humidity gas stream through the catalyst. Thus, only 9 minutes were obtained after lowering the relative humidity of the gas flow from 53% to approx. 1% a significant increase in activity (compare sample no. 7 with sample no. 8). Data show that when the relative humidity was again increased to approx. 25%, then the short regeneration that had previously been used (approx. 25 minutes) was not sufficient to completely bring the catalytic activity back to its original level.

Example III.

The cobalt oxide catalyst used in the example

II was dried overnight in the reactor at 104°C by passing continuously a synthetic gas stream of the type mentioned above (not containing any vinyl or vinylidene chloride)

with a relative humidity of approx. 0.5% through the catalyst layer in a total amount of approx. 44 liters per hour.

The experiment from example II was repeated except that the nitrogen tank used to form the synthetic air mixture therein contained from 10 to 50 parts per million of vinyl chloride,. vinylidene chloride, methyl chloroform, 1,1,2-trichloroethylene and perchlorethylene. The reactor temperature was kept at 104°C and the total gas flow through the reactor of said mixture was 44 liters per hour. The small amount of chlorinated hydrocarbons in the nitrogen was taken out of consideration when calculating said synthetic air flow. The data obtained are listed in Table II.

Data from Table II show that the cobalt oxide catalyst from Example I has high catalytic activity under destruction conditions at relatively low relative humidity and at 104°C with regard to vinyl chloride, vinylidene chloride and methyl chloroform. Although the catalyst had high activity with regard to the destruction of trichlorethylene, this activity decreased after approx. 1-2/3

hours of operation. The initial partial activity with respect to perchlorethylene destruction rapidly decreased.

Example IV.

A solution of 141 g of cobalt (II) sulfate heptahydrate

in 450 g of distilled water, a solution of 70 g of anhydrous sodium hydroxide dissolved in 140 g of distilled water was slowly added with vigorous stirring. 22 g of a 35% by weight aqueous solution of hydrogen peroxide was then slowly added for approx. portions of 0.5 ml within 25 minutes. After the addition was complete, the reactant mixture was stirred for 15 minutes. The precipitate was washed with distilled water, using a centrifuge, and then isolated by filtration. The wet filter cake was pressed between felt mats and the pressed filter cake dried at approx. 50°C for 5 hours. The partially dried filter cake was ground with a mortar and the -8, +30 mesh particle size fraction of this product was dried at approx. 200°C for approx. 5.1/2 hours. About 670 mm Hg was used during the last hour of the dry period.

The cobalt content in the product was 81.2% by weight as cobalt (II) oxide (CoO), by elementary X-ray spectroscopic analysis. X-ray diffraction analysis indicated a crystalline phase, and this was identified as hydrated cobalt (III) oxide (CoOOH).

A thermogravimetric analysis to 400°C indicated that it was

a total weight loss of approximately 11.8% by weight.

About 11 g of this catalyst was tested as a destruction catalyst for vinyl chloride and vinylidene chloride at a temperature of 104°C as described in example II. The test was carried out for a total of 3 hours and 3/4 quarters and during this period a maximum relative humidity of approx. 27% (approx. 1.85 hours). The results of this experiment corresponded to those obtained for the catalyst of Example I. Example V.

5.1 g of the cobalt catalyst from Examples II and III

was mixed with 5.2 g of the cobalt catalyst from Example IV. The catalyst mixture was dried at 185°C for approx. 1 hour under a vacuum of approx. 670 mm Hg. The dried cobalt oxide mixture was then added to the reactor described in example II as a catalyst bed and tested as a destruction catalyst for vinyl chloride and vinylidene chloride as described in example II. The results are shown in Table III.

a Temperature of the gas flow at the inlet and outlet from the catalyst layer in °C.

b-f See Table I.

g Sample obtained 13 minutes after increasing the reactor temperature. h Sample obtained 11 minutes after increasing the reactor temperature. i Sample after the catalyst had been heated to approx. 104°C in the reactor for approx. 4 and 3/4 days.

Data from Table III indicate that the catalyst mixture has relatively high catalytic activity at a low relative humidity in the temperature range from 23 to 104°C. Although the catalytic activity at 23°C decreased approx. 50% within 2 hours, so the level of activity was still significant after this time. The activity with regard to the destruction of vinylidene chloride was of the same type as for vinyl chloride.

Example VI.

A solution of 100 g of cobalt (II) sulfate heptahydrate dissolved in 320 g of distilled water was slowly stirred under vigorous stirring. added a solution of 50 g of anhydrous sodium hydroxide dissolved in 100 g of distilled water. After the cobalt sulphate solution had been added, the reactant mass was stirred for about 10 minutes. The precipitated product was washed with distilled water by decanting using a centrifuge. The precipitate was washed a total of 4 times. After washing, the product was isolated by filtration. The filter cake was dried at approx. 50°C for 20 hours. It was then granulated using a mortar to a minus 8

mesh particle product. The minus 8, plus 30 mesh particle size fraction of this product was then dried at approx. 200°C for 5.5 hours. During the last hour of drying, a vacuum of 670 mm of mercury was used. The cobalt content in the oxide was approx. 94.8% by weight as cobalt (II, III) oxide, as determined by elemental X-ray spectroscopic analysis. X-ray diffraction analysis indicated the presence of a crystalline phase, and this phase was cobalt (II,III) oxide (Co_O ). Thermal gravimetric analysis at 400 oC indicated a total weight loss of approx. 3.1%.

Using the apparatus and method from example II, 12.5 g of this cobalt oxide catalyst was added to the reactor as a catalyst bed, and tested as a destruction catalyst for vinyl chloride and vinylidene chloride. The results obtained are indicated in Table IV.

Data from Table IV show that the cobalt oxide catalyst had high catalytic activity with regard to the destruction of vinyl chloride and vinylidene chloride at 104°C and at both high and low relative humidity. The oxide sample had excellent resistance to inhibition of catalytic activity due to water vapor. Even after an operating time of 1-1/2 hours at approx. 60% relative humidity, less than 0.5 parts per million of vinyl chloride in the effluent gas from the reactor and no vinylidene chloride was detectable. As with the cobalt oxide catalyst from example I, the loss of activity after prolonged contact with a relatively moist atmosphere could be reversed by passing relatively dry air through the heated catalyst layer. Example VII.

About. 20 cm 3 of a commercial cobalt oxide on aluminum oxide catalyst was dried in a vacuum oven at approx. 200°C and a vacuum of approx. 670 mercury for approx. 2-1/2 hours. The cobalt content in this catalyst was approx. 18% by weight as cobalt (II) oxide

2

(CoO), and had a B.E.T. surface area of 45 m per gram. 19.3 grams of the dried catalyst was added to the reactor as indicated in Example II and tested as a destruction catalyst for vinyl chloride. The catalyst was added to the reactor, which had a temperature of approx. 104°C, and an 80/20 nitrogen/oxygen gas flow was passed through the reactor. This gas stream was preheated to approx. 108°C during charging.

The catalyst showed no activity with respect to the destruction of vinyl chloride or vinylidene chloride at a gas flow of 44 liters per hour, an inlet temperature of 180°C and a relative humidity of approx. 1.5%. An X-ray spectroscopic analysis of the commercial catalyst indicated that the cobalt was present as highly crystalline cobalt (II,III) oxide and differed from the cobalt oxide samples prepared in Examples 1, IV and VI.

Example VIII

Using the method of Example VI, cobalt oxide was prepared by using 93 grams of cobalt (II) sulfate heptahydrate dissolved in 300 grams of distilled water, and 47 grams of anhydrous sodium hydroxide dissolved in 94 grams of distilled water. The final drying of the product was carried out at approx. 200°C for approx. 7 hours. A vacuum of approx. 670 mm Hg during final drying, i.e. the last two hours. The cobalt content in the oxide was 93.7% by weight as cobalt (II,III) oxide determined by elementary X-ray spectroscopic analysis. X-ray diffraction analysis indicated a crystalline phase and this was identified as cobalt (II,III) oxide (CO^O^). Thermal gravimetric analysis indicated a total weight loss of approx. 3.6% by weight at approx. 400°C.

By using the apparatus and the method from example II, approx. 7 grams of this cobalt oxide catalyst was added to the reactor as a catalyst layer and tested as a destruction catalyst for vinyl chloride-vinylidene chloride at temperatures from 23 to 104°C. The results are shown in Table V.

Data from Table V show that the cobalt oxide catalyst had a significant level of catalytic activity with respect to the destruction of vinyl chloride and vinylidene chloride at temperatures from 23 to 104°C at low relative humidity.

Example IX.

The cobalt oxide that was used as a catalyst layer in example VIII was heated in the reactor to approx. 104°C for 1 day and 18 hours. The cobalt oxide was then tested as a destruction catalyst for a mixture of C2-chlorinated hydrocarbons, using the same method as in example III. The total gas flow of C2~chlorinated hydrocarbons and synthetic air through the reactor was 44 liters per hour. The data obtained are set out in Table VI.

They obtained data. as indicated in Table VI shows that the cobalt oxide catalyst from Example VIII has high catalytic activity at low relative humidity in temperatures from 104-190°C with respect to vinyl chloride, vinylidene chloride, methyl chloroform and trichloroethylene. Although initially there was high catalytic activity with respect to perchlorethylene at both 150 and 190°C, the activity decreased rapidly at both temperatures.

Example X.

7.5 grams of cobalt oxide prepared as in example VIII was in approx. two hours in a muffle furnace heated to about 500°C. After heating, the cobalt content was determined and 96.2% by weight was found as cobalt (II,III) oxide by elementary X-ray spectroscopic analysis. X-ray diffraction analysis indicated that a strongly crystalline phase was present, and this phase was identified as cobalt (II,III) oxide. Thermogravimetric analysis indicated a total weight loss of 0.5% by weight at a temperature of 400°C.

Apparatus and the procedure as in example II were used, and approx. 6.7 grams of this heat-treated oxide catalyst to the reactor as the reactor bed, and tried it as a destruct ion catalyst for vinyl chloride and vinylidene chloride.

The results obtained are indicated in Table VII.

Data from Table VII show that the heat-treated cobalt oxide has significantly greater sensitivity with regard to inhibition of the catalytic activity with increasing relative humidity than corresponding oxide samples not heated strongly, see e.g. example VI. Comparison between the analysis results of the strongly heated cobalt oxide and the cobalt oxide from example VIII indicates that heating the oxide to about 500°c significantly reduces the amount of hydration water in the catalyst.

Example XI.

A commercial sample of cobalt oxide was processed into pellets with a diameter of approx. 6 mm and a length of approx. 6 mm, using a manual press. Said pellets were dried at approx. 200°C for 20 hours. During the last approx. 3.1/2 hours of the drying period a vacuum of approx. 670 mm Hg. A conventional X-ray spectroscopic analysis indicated that the cobalt content in the oxide was 92.9% by weight as Co^O^. An X-ray diffraction analysis indicated that a crystalline phase was present, and that this phase was cobalt (II, III) oxide, Co-^O^. A heat gravimetric analysis indicated a total weight loss of approx. 0.3% by weight at approx. 400°C.

One used the apparatus and the method as in example II and approx. 14.5 grams of the oxide as a catalyst layer, and tested the catalyst as a destruction catalyst for vinyl chloride and vinylidene chloride at a reactor temperature of 104°C. The results are given in Table VIII.

Comparing the data from Table VIII with the data from previous examples shows that this commercial cobalt oxide sample had a lower but experimentally significant level of catalytic activity with respect to the destruction of vinyl chloride and vinylidene chloride. The results also show that this cobalt oxide catalyst had a high sensitivity to the inhibition of water vapor in relation to the cobalt oxides from examples I-VI. Both cobalt oxide from this example and example X contained relatively low amounts of hydration water, which is evident from the results of the thermal gravimetric analysis.

Example XII.

A commercial sample of cobalt oxide which had been added approx. 2.5% by weight of distilled water as a binder was worked up into pellets as indicated in Example XI. Said pellets were dried at approx. 200°C for 8 hours. During the last approx. A vacuum of 670 mm Hg was used for 3 hours of drying. An elemental analysis showed that the cobalt content in the oxide was 95.5% by weight as cobalt (II) oxide. An X-ray diffraction analysis indicated that the oxide was essentially crystalline cobalt (II) oxide. A thermal gravimetric analysis indicated a weight loss of less than 0.2% by weight at 350°C.

This oxide was used in the apparatus and progress

the method from example II as a catalyst layer, and tested for the destruction of vinyl chloride and vinylidene chloride. The results are given in Table IX.

Data from Table IX show that this commercial cobalt oxide sample had a low, yet experimentally significant level of catalytic activity for the destruction of vinyl chloride and vinylidene chloride.

Example XIII

A commercial sample of cobalt oxide with 5% by weight of distilled water added as a binder was processed into pellets as described in Example XI. These were dried at approx. 200°C for about 7 hours. During the last approx. A vacuum of 670 mm Hg was used for 3 hours of drying. An elemental analysis showed that the oxide contained approx. 95.3% by weight cobalt as cobalt (II,III) oxide (Co^O^). X-ray diffraction analysis showed that the oxide was mainly crystalline cobalt (II,III) oxide. Thermal gravimetric analysis indicated a total weight loss of approx. 0.1% by weight at 400°C.

Using the apparatus and method from Example

II, 17.6 grams of this oxide was added to the reactor as a catalyst layer and tested at 104°C. The results are given in Table X.

The results from Table X show that this commercial cobalt oxide had a significant level of activity with respect to

destruction of vinyl chloride and vinylidene chloride. Data show that this sample, which contained little water of hydration, also has a rapidly decreasing activity with time.

Example XIV.

A cobalt oxide was prepared as indicated in Example I. The amount of each reactant was 141 grams of cobalt (II) sulfate heptahydrate dissolved in 450 grams of distilled water, 70 grams of anhydrous sodium hydroxide dissolved in 140 grams of distilled water and 22 grams of a 35% by weight aqueous solution of hydrogen peroxide. After drying at approx. 50°C for approx. After 5 hours, the filter cake was granulated with a mortar. The minus 30 mesh particle size fraction of this cobalt oxide sample was pelleted as described in Example XI, then dried at approx. 200°C for approx. 3 hours under a vacuum of 670 mm Hg.

The apparatus and method from example II was used and approx. 3.6 grams of this oxide as catalyst at a temperature of 104°C. The synthesized air mixture contained 37.5 ppm vinyl chloride and 3 ppm vinylidene chloride and an inlet temperature of the reactor of 108°c. The flow rate was approx.

9 liters per hour and the relative humidity approx. -2.5%. By these

conditions, only 0.5 ppm vinyl chloride and no vinylidene chloride were found in the off-gas from the reactor. At a total flow rate of approx. 44 liters per hour and a relative humidity of 1.2%, 9.5 ppm vinyl chloride and 0.5 ppm vinylidene chloride were found in the gas from the reactor. These results obtained using a relatively small amount of oxide show that the low activity of the commercial oxide samples from Examples XI-XIII

was not due to the fact that the catalyst was prepared in pelletized form.

Example XV.

Using the method from Example VI, a cobalt oxide was produced. The reactants used were 93 grams of cobalt (II) sulfate heptahydrate dissolved in 300 grams of distilled water and 47 grams of anhydrous sodium hydroxide dissolved in 94 grams of distilled water. After washing, approx. 1/4 of the wet centrifuged cake stirred in twice its own volume of commercial fused silica in distilled water. After filtration, the filter cake was dried at 50°C for 2 days and 18 hours. It was then granulated in a mortar to a minus 8 mesh particle product. The minus 8, plus 30 mesh particle size fraction of this product was then dried at approx. 200°c for 7 hours. During the last 4.1/2 hours of drying, a vacuum of 670 mm Hg was used. The cobalt content in the oxide was 57.9% by weight as cobalt (II,III) oxide (Co-jO^) determined by elemental X-ray spectroscopic analysis. The X-ray diffraction analysis indicated that a crystalline phase was present and this was cobalt (II, III) oxide. Thermal gravimetric analysis indicated a total weight loss of

3.8% by weight at 400°C.

The apparatus and method from example II was used and approx. 7.8 grams of this oxide as a catalyst. The tests were carried out at a reactor temperature of 104°C. The results obtained are indicated in Table XI.

The results from Table XI show that the cobalt oxide-fused silica samples had high catalytic activity with regard to the removal of both vinyl chloride and vinylidene chloride at both high and low relative humidity. As with the previous cobalt oxide samples (see examples II and VI), the small loss of activity after prolonged contact with a gas stream with high humidity could be compensated by passing air with relatively low humidity through the heated catalyst layer. Example XVI.

After washing with distilled water and drying overnight at approx. 70°C and a vacuum of 670 mm Hg, 20 grams of a commercial 8-14 mesh activated alumina was impregnated under vacuum with a solution of 20 grams of cobalt(II) sulfate heptahydrate dissolved in 20 grams of distilled water. After pouring off the excess cobalt(II) sulfate solution, the alumina particles were dried at 70°C for approx. 2 hours at 27 0 mm Hg. The dried particles were reacted with a solution of 5 grams of anhydrous sodium hydroxide dissolved in 20 grams of distilled water for approx. 1 hour at approx. 70°C. After pouring off the excess of the sodium hydroxide solution, the alumina particles were washed with distilled water. They were then dried at 70°C for 2 hours and then at approx. 200°C for 18 hours. During the last 2.1/2 hours of the latter drying period, a vacuum of 670 mm Hg was used. The cobalt content was determined as 7.9% by weight cobalt (II,III) oxide (Co 3 O 4 ) by conventional elemental X-ray spectroscopic analysis.

By using the apparatus and the method from example II, approx. 17 grams of this cobalt oxide on activated alumina was added to the reactor as a catalyst layer and tested at a temperature of 104°C. The results are given in Table XII.

The results from table XII show that this cobalt oxide on an activated alumina sample had a significant level of activity with regard to the destruction of vinyl chloride and vinylidene chloride at low relative humidity.

Example XVII.

About. 20 grams of a commercially available cobalt(II) hydroxide was stirred in 150 grams of distilled water. The suspension was filtered, and the filter cake dried at approx. 70°C

for two days. The dried filter cake was pulverized in a mortar. The minus 8 plus 30 mesh particle size fraction was then dried at 200°C for 5 hours and a quarter. During the last 3 hours there was a vacuum of 670 mm Hg. The cobalt content was determined to be 93.6 wt% cobalt (II, III) oxide as Co 3 O . X-ray diffraction analysis indicated a crystalline phase which was identified as cobalt (II, III) oxide. The surface area of the cobalt oxide product was 115 m 2 /gram.

About. 10 grams of this cobalt oxide was added to the reactor as indicated in example II as a catalyst layer and then tested as a destruction catalyst for vinyl chloride. The catalyst layer occupied a volume of approx. 13 cm 3. The procedure from example II was followed except that the vinyl chloride was added to the system by means of a standard nitrogen gas cylinder containing analytically measured 2.5% by weight of vinyl chloride. The amount of vinyl chloride supplied to the reactor was regulated by the amount of nitrogen containing vinyl chloride that was added to the system.

The synthetic air stream was introduced into the reactor in a quantity of 44 liters per minute. The actual conditions and results are set out in Table XIII.

Data from Table XIII show that at a reactor temperature of 104°C, the catalyst activity appears to drop rapidly and then stabilise. When the reactor temperature is raised again, there is a significant increase in activity.

Further testing with the catalyst from example XVII showed that when the apparent capacity of the catalyst for

to destroy vinyl chloride was exceeded, then other C2~chlorinated hydrocarbons could be observed in the product gas from the reactor. When e.g. a synthetic air flow that contained 20% relative humidity and approx. 2960 ppm vinyl chloride was passed through the catalyst's filter in a quantity of 9 liters per hour (residence time approx. 5 seconds) and a temperature of 188°C, then approx. 680 ppm vinyl chloride, 23 ppm vinylidene chloride, 190 ppm 1,2-dichloroethylene and approx. 11 ppm trichlorethylene and 280 ppm trichloroethane. These results show that when there are too long residence times

and too much vinyl chloride beyond the catalyst's capacity, then side reactions occur. When the relative humidity of the gas stream was lowered to approx. 0.9%, then there was a significant reduction in the concentration of the by-products. Thus, the relative concentrations of the by-products will depend on the operating conditions, such as the vinyl chloride concentration in the output gas, relative humidity of the supplied gases, reactor temperature, residence time, catalyst activity etc.

After prolonged testing at 188°C in the presence of vinyl chloride concentrations of up to 3300 ppm, the surface area of the cobalt catalyst was found to be 42 m 2 /gram. This reduction of the surface area is directly proportional to the initial lowering of the activity as could be observed in Table XIII.

The above-mentioned examples show that the hydrated cobalt oxide has high catalytic activity at temperatures from approx. 20°C, e.g. 23°C, to approx. 190°C, e.g. 188°C, both at low and high relative humidity with regard to the destruction of C₁-halogenated hydrocarbons, e.g. vinyl chloride, vinylidene chloride, methyl chloroform and trichloroethylene, especially vinyl and vinylidene chloride. The above-mentioned examples also show that cobalt oxide catalysts which do not have a significant content of water of hydration, i.e. more than 1, preferably more than 2 or 3% by weight (as determined by thermal gravimetric analysis at 400°C)/can be used under conditions of low relative humidity. Hydrated cobalt catalysts are preferred. Furthermore, the examples show that the content of C 1 -halogenated hydrocarbons in the gas stream can be reduced to low levels, preferably less than 10 ppm, e.g. less than 0.5 ppm (when the initial concentration is higher than the preferred reduced levels.).

The above-described catalysts are particularly useful for reducing the content of C1-chlorinated hydrocarbons, e.g. vinyl chloride and vinylidene chloride, in air. The catalysts can thus be used when processing air that is vented from production sites for polyvinyl chloride, storage tanks for vinyl chloride, etc.

The concentration of C^-C^ halogenated hydrocarbons in the gas streams can vary greatly. Usually, the concentration in air streams will be below or above the explosion range. For example the concentration of vinyl chloride in air will usually be kept below 4% by weight. It is therefore assumed that the present method will find application to air streams that contain less than 4, e.g. less than 1% by weight of vinyl chloride. Furthermore, the present method can be used for the destruction of vinyl chloride at even very low concentration levels, e.g. less than 0.05% by weight (500 ppm), or even less than 0.01% by weight (100 ppm). As shown in the examples, destruction of vinyl chloride and vinylidene chloride occurs even at concentrations of less than 100 ppm, e.g. 50 ppm and 10 ppm. Thus, the concentration range for vinyl chloride can vary from approx. 5 ppm to 4% by weight, e.g. from 10 ppm to 0.1% by weight, more commonly from 0.001 to 0.05% by weight. With good ventilation, a vinyl chloride content in the gas stream of 0.001 to 0.01 (100 ppm) can be achieved. The aforementioned concentrations also apply

other C^~C^ halogenated hydrocarbons described herein or combinations of such halogenated hydrocarbons in gas streams.

For an application of the present method, it is indicated that the gas streams containing C^-C^ halogenated, e.g. chlorinated hydrocarbons such as vinyl chloride, e.g. vinyl chloride-containing air, will be dried to low relative humidity, i.e. less than 5%, preferably less than 2%, by absorption, adsorption, compression, cooling or compression and cooling. A simple and effective way to dry such a gas stream is to pass the gas stream through a drying column which contains a solid or liquid desiccant, e.g. of the type described earlier. The dried gas stream can then preheated to approx. 100-200°C using low-pressure steam and then fed into a catalyst bed, whether this is solid or fluidized, which contains the cobalt oxide catalyst together with the oxides and amounts of oxygen. The bed can also be heated using waste steam with low pressure. The outflowing gas from the reactor can be washed in a commonly known manner to remove the hydrogen chloride gas which is a by-product, for example in a scrubber with alkali, and the harmless outflowing gases from the washing device can be discharged on

an acceptable way.

Said cobalt oxides according to the present invention can also be used in protective breathing devices for individuals, e.g. in a gas mask. The activity of the "present cobalt oxide at room temperature, at least i

short periods of time, can provide the time necessary for a worker to be able to leave a contaminated area and reach a safe place, e.g. an uncontaminated area. It is believed that a normal gas mask can be modified so that it can include an additional layer of cobalt oxide according to the present invention,

or such oxide can replace the catalytic material already present in the gas mask.

Typically, a gas mask will consist of a container (cylindrical or rectangular) which has side walls, a lower and an upper lid at opposite ends which are closed by means of O-rings or in another suitable way. The lids contain air inlet and outlet devices. Inside the container there are a number of parallel perforated sieves where adsorbing materials or catalysts are placed to remove harmful vapors from the air that is passed through the container. Typically, the first layer will be activated charcoal followed by at least one layer of desiccant, e.g. caustic soda melted on pumice stone, ■ melted calcium chloride, etc. Then one can place the cobalt oxide according to the present invention for catalytic oxidation of C2-C4 nalo9enated hydrocarbons followed by a protective layer of desiccant to protect the oxide from moisture. Typically, the individual layers of adsorbents and catalysts will be separated by parallel nets which often contain filters, e.g. of cotton. The air inlet usually contains a valve which allows the air to pass in one direction only, i.e. inward, and a filter to remove suspended solids that had to be found in the air. The air outlet is connected to a nozzle by means of a wire. The mouthpiece can also be fitted with a one-way valve to remove air from the person wearing the mask.

Although the present method has been described with reference to specific details in certain embodiments, it is understood that such details are not to be regarded as limitations of the invention as such.

Claims (24)

1. Process for treating a gas stream containing C^-C^ halogenated hydrocarbons, and where said halogenated hydrocarbons are selected from the group consisting of chlorinated and brominated hydrocarbons, characterized in that the halogenated hydrocarbon is contacted with an oxidizing amount of an oxygen-containing gas in the presence of cobalt oxide catalyst at temperatures from 20 to 500°C for a sufficiently long time to reduce the content of halogenated hydrocarbon in the gas stream, and where said temperature is such that it inhibits a water-induced loss of catalyst activity. 2. Method according to claim 1, characterized in that said halogenated hydrocarbon is vinyl chloride, vinylidene chloride, ethylene dichloride, 1,1,1-trichloroethane, 1,1,2-trichloroethane, trichlorethylene, perchloroethylene or mixtures of such halogenated hydrocarbons. 3. Method according to claim 1, characterized in that the gas flow is an air flow. 4. Method according to claim 3, characterized in that the gas stream contains from 0.0005 to 4% by weight of halogenated hydrocarbon. 5. Method according to claim 1, characterized in that the temperature varies from 50 to 300°C. 6. Method according to claim 1, characterized in that the cobalt oxide is hydrated cobalt oxide and is selected from the group consisting of cobalt (II) oxide, cobalt (III) oxide and cobalt (II,III) oxide. 7. Method according to claim 1, characterized in that the relative humidity of the combined gas streams which are contacted with the catalyst is less than 5%. 8. Method according to claim 7, characterized in that the relative humidity is less than 2%. 9. Method according to claim 6, characterized in that the hydrated cobalt oxide contains hydration water in an amount that is at least as high as that obtained by drying an aqueous filter cake of the precipitated cobalt oxide at 200°C. 10. Method for treating an air stream containing a C 2 -chlorinated hydrocarbon, characterized in that the chlorinated hydrocarbon is contacted with an oxidizing amount of oxygen at a temperature from 20 to 500°C in the presence of cobalt oxide catalyst for a sufficiently long time to reduce the content of said C^-chlorinated hydrocarbon in the air stream, and where said temperature is chosen so that it inhibits any water-induced loss of catalyst activity. 11. Method according to claim 10, characterized in that the chlorinated hydrocarbon is vinyl chloride, vinylidene chloride, ethylene dichloride, 1,1,1-trichloroethane, 1,1,2-trichloroethane, trichlorethylene, perchloroethylene or mixtures of such chlorinated hydrocarbons. 12. Method according to claim 10, characterized in that the chlorinated hydrocarbon contains from two to three chlorine atoms. 13. Method according to claim 11, characterized in that the cobalt oxide is hydrated cobalt oxide. 14. Method according to claim 13, characterized in that the relative humidity of the combined gas streams that are contacted with the catalyst is less than 5%. 15. Method according to claim 14, characterized in that the temperature is in the range from 20 to 300°C. 16. Method according to claim 14, characterized in that the hydrated cobalt oxide catalyst is cobalt (II) oxide, cobalt (III) or cobalt (II,III) oxide. 17. Process for reducing the content of vinyl chloride in a vinyl chloride-containing gas stream, characterized by contacting vinyl chloride in the gas stream with an oxidizing amount of an oxygen-containing gas in the presence of a cobalt oxide catalyst selected from the group consisting of cobalt (II) oxide , cobalt (III) oxide and cobalt (II,III) oxide at. temperatures from 20° to 300°C for a sufficiently long period of time to reduce the vinyl chloride content in the gas stream, and where said temperature is such that it inhibits any water-induced loss of catalyst activity. 18. Method according to claim 17, characterized in that the cobalt oxide is hydrated cobalt oxide. 19. Method according to claim 18, characterized in that the relative humidity of the combined gas streams which are contacted with the catalyst is less than 5%. 20. Method according to claim 17, characterized in that the vinyl chloride-containing gas stream is an air stream, and that this has a relative humidity of less than 5% before it is contacted with the cobalt oxide catalyst. 21. Method according to claim 20, characterized in that the relative humidity of the air flow is less than 2% and that the cobalt oxide catalyst is hydrated cobalt oxide. 22. Method according to claim 21, characterized in that the temperatures lie in the range from 80 to 250°C. ' 23. Method according to claim 17, characterized in that the total amount of the oxygen-containing gas is at least the amount necessary to oxidize carbon and the hydrogen content in the vinyl chloride to carbon dioxide and water. 24. Method according to claim 17, characterized in that the vinyl chloride content in the gas stream varies from 0.001 to 0.1% by weight.