DE3517864A1 - METHOD FOR CONVERTING HALOGENIC TOXIC SUBSTANCES - Google Patents

Description

University of Southern California, University Park, Los Angeles, CA 90007, V.St.A.

b Process for converting toxic substances containing halogens

Substances

The invention relates generally to the field of organization Chemistry and especially the detoxification of harmful waste.

The disposal of waste from the chemical, agrochemical and other industries is currently a big problem. In particular, there are many chemical waste materials, such as halogenated hydrocarbons, which are not biodegradable and therefore either stored in safe, specialized areas or have to be rendered harmless in reactors specially built for this purpose.

For example, there are already plants for the degradation of halogenated hydrocarbons, in particular for the detoxification of Polychlorobiphenyl compounds (PCB) have been developed, but their establishment in the USA has not continued since 1976 because these compounds are too difficult to break down and cause ecological damage. Large quantities However, such compounds are stored and pose a considerable environmental hazard.

In one of the processes developed, organic waste is ^{evaporated at around 1000 °} C. and completely or partially oxidized. Incombustible ash is discharged directly from the reaction chamber while exhaust gases are passed through a secondary combustion chamber of about 1200 ⁰ C to the thermal degradation of the compound to be sawn

end up. However, this combustion system has the disadvantage that two combustion chambers are required and for each of these chambers a considerable use of energy is required and that also the presence of halogenated Hydrocarbons in the exhaust gas cannot be completely prevented. Obviously in this facility and other previously used plants in which halogenated hydrocarbons are in the presence of air are burned, free chlorine is formed in the combustion chamber, which is then halogenated hydrocarbons in the exhaust gas reformed. So if the initially present pollutant is actually broken down by these reactions every halogenated hydrocarbon is dangerous, and products such as chlorinated hydrocarbons, which form in the combustion chambers in the presence of free chlorine prevent generation harmless conversion products. But since the product formed is not clean, it has to be processed again and tested, and the "dirty" product must be encapsulated and stored until a better one Procedure is available.

The object of the invention is a method for elimination organic compounds containing halogen, such as carbon tetrachloride, chloroform, trichloroethane, tetrachlorethylene, Methylene chloride, the various freons, polychlorinated biphenyls, dioxins, etc., through conversion in compounds that do not pose a threat to the environment.

The invention is a process for the conversion of halogenated organic compounds into non-polluting substances, which consists in that the compound in a reducing atmosphere is pyrolyzed at a temperature in the range of about 825 ° C to 1125 ⁰ C. In particular, the reaction temperature is through

Burning methane with oxygen is produced, with the methane in stoichiometric excess over the reaction with the oxygen required amount is used, so that the reducing atmosphere is formed will.

The reducing atmosphere can be created by combining methane and the compound to be converted into one Reaction containers made of refractory material mixed together after the compound has been evaporated. The required temperature can be achieved by heating devices arranged on the reaction vessel or by burning of methane can be generated with limited amounts of oxygen within the reaction vessel. Included however, the methane must be in a stoichiometric excess over that for reaction with the oxygen according to the formula

CH ₄ + 2O ₂ > CO ₂ + 2H ₂ O

required amount be present. Under these conditions the halogen-carbon bonds are broken and all chlorine, for example, is converted to hydrogen chloride, and all organic compounds become mixtures of hydrogen, ethylene, acetylene and benzene reacted with small amounts of carbon and higher aromatics. Since there is no excess oxygen in the reaction vessel, dioxins and other chlorinated hydrocarbons are formed not created or reformed. The hydrogen chloride can be removed from the exhaust gas after a suitable heat exchange with water, alkali, lime or a generally basic wash, and the hydrocarbons and carbon can be used as fuel or for chemical purposes.

The reducing atmosphere can of course also be used with other reactants than methane, for example with hydrogen, be generated; however, methane is readily available and easier to use, so in the following detailed description is always called methane.

The drawing illustrates the method according to the invention schematically and as an example and shows a Device suitable for performing this method.

The compounds to be broken down are heated ^{to a temperature of at least 1000 °} C. for about 1 second in a reducing atmosphere. The reactor can be heated externally, for example by means of a methane heater or the like, or internally by burning methane or another fuel with oxygen using an excess of the fuel so that the added chlorine-containing compound is subjected to reducing pyrolysis . Alternatively, the reducing mixture (fuel in excess and organic halogen compound) can alternate with the oxidative heating, so that the exhaust gases from the alternating processes can be kept separate from one another.

In particular, a reactor 10 is provided with a gas-impermeable housing 12, which has an elongated Reactor chamber or zone 14 limited. Since the hydrogen chloride generated in zone 14 is corrosive, the housing must 12 an inner coating made of ceramic, such as aluminum oxide, silicon dioxide or the like or metal carbide, -moride or -nitride. The reactor 10 has at one end 15 a gas inlet line 16 for introduction of methane into a first inlet pipe 18 and a second

Gas inlet 20 for introducing oxygen into tube 18. The gas inlet lines 16 and 20 have flow measuring valves 22 and 24, respectively, for controlling the flow of methane and oxygen into the tube 18 and thereafter to a burner outlet 26 within the zone 14 so that the required oxidative heating can take place therein. With a flame temperature of about 1625 to 2100 ^° C., sufficient heat is generally generated. A socket 28 is passed through the reactor wall at the end 15 and is used to receive electrically conductive wires 30 and 32, which lead to a resistance wire 34 within the reaction zone 14 near the oxidative heating end 26. Alternatively, a spark spiral or another ignition

Ib facility can be used.

The reactor 10 also has an inlet 36 for the introduction of the halogen containing compounds or waste materials into a second inlet pipe 38 and inlet lines 40 and 42 for the introduction of methane and water vapor, respectively on. Inlets 35, 40 and 42 have valves 44, 46 and 48 for controlling the flow of the various gases through inlet tube 38 to an outlet end 50 in zone 14. The opposite end 52 of the reactor 10 is formed with an outlet 54 for discharging product gases from the zone 14 and has an outlet measuring valve 56 on. The reaction is preferably carried out in such a way that the product after the reaction required for the reaction Dwell time of generally 2 to 5 seconds is subtracted. The inlet valves 22, 24, 46, 48 and 68 and the outlet measuring valve 56 are therefore set so that that in zone 14 approximately atmospheric pressure is maintained. By adjusting these valves, however, the throughput be increased so that within the reactor 10 superatmospheric There is pressure.

Heat exchange means are used to control the temperature in zone 14 58 provided, in this case insulating means to maintain the desired temperature are in zone 14. Alternatively, the heat exchange means 58 can consist of methane heating devices (not shown) exist for heating the housing 12 and the zone 14 from the outside. Alternatively, the means 58 can also be made electrical heating coils or cooling coils of various types exist. To control the temperature in To support zone 14, water can also be drawn from the inlet 42 are measured into the tube 38 in order to dampen the oxidative heating in the zone 14.

The drawing also shows a washing and separation station 60 for fractionating the reaction products and lines 62 and 64 for the promotion of dehalogenated hydrocarbons and carbon waste or hydrogen chloride for storage or discharge. The station 60 also has a line 66 for returning any of the connections, which have not been dehalogenated, through a metering valve 68 to the inlet pipe 38 for re-reaction on.

Measured stoichiometric amounts are used during operation of methane and oxygen through the inlet lines 16 and 20 into inlet tube 18 wherein the gases mix and flow to end 26 and thence into reaction zone 14. Measured amounts of the dehaloge- ning compound are through the inlet pipe 36 into the pipe 38 along with a sufficient amount of Methane, which is introduced through line 40, passed so that the fuel is supplied in stoichiometric excess and a reducing atmosphere is thereby established in zone 14. Water can if necessary be fed through line 42 to reduce the temperature

to control the temperature in zone 14. After the introduction The conductive wires 30 and 32 are using the combustible amounts of methane and oxygen or air in the zone 14 Power is supplied so that the resistance wire 34 is made to glow so that it the gas mixture at the confluence ignites behind the outlet ends 26 and 50. Alternatively, an ignition spark or other ignition device can be used

be used.
10

Various methods and devices can be used to introduce the specified gases into zone 14 will. For example, a stoichiometric mixture of fuel and oxygen can pass through a first inlet and excess fuel or connection through second and third inlets directly into the Zone 14 will be introduced. Also can use fuel, oxygen and the connection is separated or introduced through a single inlet. The exhaust gas mixture is preferably or, if necessary, the connections are analyzed and homogenized before they are put into the device 10 will be introduced. This may be necessary to ensure that the amount of inorganic compounds is not too high. For example, certain non-toxic, water-soluble materials are expediently such as salt and lime, not imported in large quantities, as these materials are covered with the heat-resistant lining Formation of a vitreous coating which can reduce the thermal efficiency of the housing 12 can. The compound is also preferably in the gaseous state, generated by heating and / or the evaporation of runoff in liquid or solid Phase is present, introduced into the line 36.

In addition to hydrogen halides, the drain consists of the reaction zone 14 to a large extent from the de-

halogenated compound and small amounts of other compounds and elements. For example, can in the combustion process water vapor and carbon oxides are formed, and also oxides of sulfur are formed formed when sulfur is present in the compound or enters zone 14 in some other form. if When air is used as an oxygen source, the non-combustible components are oxidized, for example to oxides of nitrogen. All these oxides, which are soluble in water and react acidic in aqueous solution, can be removed from the drain along with the hydrogen chloride in wash / separation station 60.

In addition to the reaction products mentioned above, carbonaceous compounds can also be formed, either through the breakdown of the dehalogenated hydrocarbon or from accompanying impurities. For example, ethylene, acetylene and higher hydrocarbons, as well as some carbon, are produced in the form of soot. Carbon that forms inside the reactor can periodically be oxidized and removed by passing air through the reactor ^{at temperatures above 675 ° C.}

Using the above procedure, the reaction is very rapid and is generally within finished a few seconds. A residence time in the hot zone of the reactor of 2 to 10 is preferred Seconds.

The reaction products are separated and recovered at washing / separation station 60 as described. procedure and devices for separating hydrogen chloride and other water-soluble gases from hydrocarbons are known, for which reference is made, for example, to US Pat. No. 2,488,083, Gorin et al. For the

BATH ORIGINAL

separation of light gases from the reaction product Fractionators can also be used.

The reaction takes place by splitting carbon-halogen bonds in a reducing atmosphere and consequently with the generation of hydrogen halides and dehalogenated hydrocarbons. In the reactions described here, hydrogen chloride is broken down certain chlorinated hydrocarbons, carbon tetrachloride and chlorobenzene formed as these compounds as examples of the process described were chosen. Other halogenated hydrocarbons have or become weaker carbon-halogen bonds dehalogenated by a mechanism that requires lower activation energies than those mentioned above Links.

The methods for analyzing complex chain reactions, as described by Benson in Foundations of Chemical Kinetics, McGraw-Hill (1960), and those described in Kinetic Data on Gas Phase Unimolecular Reactions, by Benson et al in NSRD, NBS, 21, 1970, it can be seen that carbon tetrachloride is the chlorinated The hydrocarbon is the easiest to pyrolyze, while chlorobenzene is the hardest to get is pyrolyzing chlorinated hydrocarbon. Other chlorinated compounds, such as chloroform, trichloroethane, Tetrachlorethylene, methylene chloride, polychlorinated biphenyls and dioxins have carbon-halogen bond energies, which are between those of the compounds selected as examples and can therefore be used according to the Methods of the invention can be dehalogenated. Iodized and brominated hydrocarbons are also used degraded at lower temperatures and converted into non-halogenated hydrocarbons and hydrogen iodide and bromine

hydrogen converted at temperatures of about 200 ⁰ C or 100 ⁰ C below those which are given with reference to the chlorinated organic compounds.

The following examples illustrate the invention.

example 1

Using an apparatus as shown schematically in the drawing, carbon tetrachloride is pyrolyzed with methane in a reaction zone heated by burning methane in oxygen. The methane is present in stoichiometric excess over the oxygen so that a reducing atmosphere is created and the ratio of carbon tetrachloride to methane is maintained at about 3: 1; about 25% by weight is carbon tetrachloride. The reactor is kept at about 1025 ^° C. and the throughput is adjusted so that the residence time is about 3 seconds. The drain contains ethylene, acetylene, benzene, hydrogen and some higher molecular weight hydrocarbons, as well as some carbon in the form of soot. It contains all of the chlorine originally introduced as carbon tetrachloride in the form of hydrogen chloride, ie the gas mixture that escaped consisted of about 65 mol% of hydrogen chloride.

Example 2

This example was chosen as a typical example of an aromatic chlorine-containing compound chlorobenzene. In addition, chlorobenzene is known to be the organic compound containing chlorine that is the most difficult to pyrolyze. 2 moles (about 21% by weight) of methane were used per mole of chlorobenzene, and the gases were at a temperature of 1125 ^° C. with a residence time of

-14-

passed through a reaction zone for about 3 seconds. The drain mainly contained benzene and ethylene and that all chlorine as hydrogen chloride. Other products were Acetylene, hydrogen, heavier unsaturated hydrocarbons and carbon.

The invention consists in a method for breaking down halogen-containing compounds that is simple in its Implementation that is economical and efficient and in which all of the chlorine is converted into hydrogen chloride, which is easily is separable and neutralizable, is transferred.

Claims (11)

Patentanwälte European Patent Attorneys Hansmann & Vogeser Albert Roßhaupter Str. 6Sf D-8000 München 70 Tel. (089) 760 309t Attorney files: 20385 University of Southern California, University Park, Los Angeles, CA 90007, V.St.A. Process for converting toxic substances containing halogens Pat entansf. smells 1. A process for converting a halogen-containing organic compound, characterized in that the compound is ^{pyrolyzed in a reducing atmosphere at a temperature of at least 825 °} C., so that a hydrogen halide is formed as a component of the exhaust gas in the practical absence of halogenated hydrocarbons. 2. The method according to claim 1, characterized in that that the reducing atmosphere in a reaction chamber consists of a mixture of methane and oxygen is formed, the methane in the stoichiometric Excess over the amount required to implement according to the formula CH ₄ + 2O ₂ > CO ₂ + 2H ₂ O is required, is introduced. 3. The method according to claim 1 or 2, characterized in that the compound carbon tetrachloride, Chloroform, trichloroethane, tetrachlorethylene, methylene chloride, a polychlorinated biphenyl or dioxin and the exhaust gas contains hydrogen chloride in the absence of chlorinated hydrocarbons. 4. The method according to claim 1 or 2, characterized in that the temperature is kept at 1025 ⁰ C to 1125 ° C. 5. The method according to claim 2, characterized in that the compound carbon tetrachloride or chlorobenzene. 6. The method according to claim 3, characterized that the temperature is kept at 1025 to 1125 ° C. 7. Process for converting a halogen-containing organic Connection, characterized in that one introduces the compound in the gas phase into the first end of a single reaction chamber at a temperature of 825 to 1125 ^° C .; maintains a reducing atmosphere in this reaction chamber and the halogen of the compound in Hydrogen halide transferred; and the converted gases, which contain a hydrogen halide, but not containing halogenated hydrocarbons, from a second end of the reaction chamber withdraws. 8. The method according to claim 7, characterized in that one oxygen and a "™ j ** · introduces combustible gas into the reaction chamber and burns it in such quantities that the required temperature is adjusted, the amount of oxygen introduced being less than that stoichiometric for oxidation of the gases in the reaction chamber required so that the reducing atmosphere is formed. 9. The method according to claim 7 or 8, characterized in that the connection is a is a chlorinated organic compound and the exhaust gas is hydrogen chloride, but not chlorinated hydrocarbons, contains. 10. The method according to claim 9, characterized in that that the compound carbon tetrachloride, chloroform, trichloroethane, tetrachlorethylene, Methylene chloride, polychlorinated biphenyl or dioxin and the exhaust gas is hydrogen chloride, but none contains chlorinated hydrocarbons. 11. The method according to claim 9, characterized in that the compound is carbon tetrachloride or chlorobenzene.
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