JPH0638862B2 - Method for converting halogen-containing compounds - Google Patents

Description

Description: FIELD OF THE INVENTION This invention relates generally to the field of organic chemistry and particularly to the detoxification of hazardous wastes.

[Prior art and its problems]

The treatment of waste from chemical, agricultural and other industries is now a major issue. In particular, many wastes of various chemicals such as halogenated hydrocarbons are known, which must be stored in a specific safe place or ashed in a specially designed reactor. I won't.

For example, ashing processes have been envisioned to allow the decomposition of halogenated hydrocarbons, especially the detoxification of polychlorinated biphenyl (PCB) compounds, but the production of polychlorinated biphenyl compounds has been It has been discontinued in the United States since 1976 due to adverse ecological effects.
However, such compounds remain in large storage and are considered very dangerous.

There is a special method of evaporating the organic waste and completely or partially oxidizing it at about 1000 ° C. According to this method, non-combustible ash is directly discarded from the reaction vessel, and the generated gas is passed through the second combustion chamber at about 1200 ° C. to completely combust and decompose it.

However, this ashing method requires two combustion vessels and each vessel must be supplied with considerable energy. Moreover, it is often not possible to completely remove the halogenated hydrocarbons present in the effluent vapor. Such a conventional ashing method, which ditches the necessary means for the combustion of halogenated hydrocarbons in air, liberates chlorine gas in the combustion vessel, which in turn It becomes halogenated hydrocarbons again in the exhaust stream.
Any halogenated hydrocarbon is dangerous, even if the original dangerous compounds are decomposed by such reactions. And products such as chlorinated hydrocarbons generated in the combustion vessel due to the presence of free chlorine gas impede the safe processing of ash products. Therefore, unless the resulting ash is safe, it must be reprocessed and retested. And this so-called messy ash must be properly encapsulated or stored until a safe disposal method is established.

[Means for solving problems]

The present invention provides a method for treating an organic compound containing halogen such as carbon tetrachloride, chloroform, trichloroethane, tetrachloroethane, methylene chloride, freons, polychlorinated biphenyls, etc. by converting it into a compound which is harmless to the environment. To do.

In particular, the present invention provides a method for treating a halogen-containing organic compound by thermally decomposing it in a reducing atmosphere in the temperature range of about 825 ° C to 1125 ° C. Furthermore, the reaction temperature is obtained by combustion of methane and oxygen, which is stoichiometrically in excess of the amount required for the reaction with oxygen. A reducing atmosphere is thus achieved.

The reducing atmosphere is formed by mixing methane with the compound to be converted in a reaction vessel made of a suitable refractory material, which compound has been vaporized by known methods. The required temperature may be obtained from a heater provided outside the reaction vessel, or may be obtained by combustion of a fixed amount of oxygen and methane in the reaction vessel. However, it should be noted that methane needs to be added in a stoichiometric excess in excess of the reaction CH ₄ + 2O ₂ → CO ₂ + 2H ₂ O sufficient to react with oxygen. Under such conditions, the bond between the halogen and carbon will be cleaved. For example, all chlorine will react to give hydrogen chloride and all organic compounds will be converted to a mixture of hydrogen, ethylene, acetylene, and benzene with reduced carbon number and higher aromatics. Since there is no excess oxygen in the reaction vessel, dioxane and other chlorinated hydrocarbons are neither newly synthesized nor regenerated.
Hydrogen chloride can be removed from the gas stream after convenient heat exchange with water, alkalis, lime or common basic detergents. Hydrocarbons and carbon may also be used for fuel or chemical purposes.

The reducing atmosphere can be obtained by using a reaction substance other than methane, for example, hydrogen, but methane is widely used and is easy to handle. Therefore, in the detailed description given below, the description will be focused on methane.

Hereinafter, the present invention will be described along with specific embodiments, but the specific embodiments merely exemplify the present invention which can take forms different from the specific embodiments disclosed. Therefore, the detailed description of specific structures and functions is not limiting.

The process proceeds by heating the compound so that it decomposes in a reducing atmosphere at a temperature of at least 1000 ° C. for about 1 second. The reactor can be externally heated to maintain this temperature, such as with a methane heater. Also, the reaction vessel is internally heated by burning excess methane or other fuel with oxygen in the presence of excess fuel to reductively pyrolyze the added chlorinated compound to obtain the required reaction temperature. You can also Further, the reducing mixture (excess fuel and organic halide) may be alternately heated and oxidized to keep the effluent streams from the other process separate.

In more detail with reference to the accompanying drawings,
The reaction vessel 10 has an elongated reaction chamber or zone 1 therein.
4 is provided with a casing 12 through which gas cannot pass. Since the hydrogen chloride produced in the zone 14 is corrosive, the casing 12 is made of ceramics such as aluminum oxide and silica, or metal carbide, molybdenum (molybdenum).
ride) or nitride must be applied to the inner surface. At one end 15 of the reaction vessel 10 is attached a gas inflow conduit 16 for introducing methane into a first inflow pipe 18 and a second gas inflow conduit 20 for introducing oxygen in the pipe 18. ing. The gas inflow conduit 16
And 20 are equipped with flow metering valves 22 and 24, respectively, which further into the tube 18 to accommodate the required oxidative heating in the zone 14.
The amount of methane and oxygen flowing into the inner crater tip 26 is adjusted. Generally, a flame at a temperature of about 1625 ° C to 2100 ° C will provide sufficient heat. A sleeve 28 is pierced into the wall of the reactor at one end 15 from which conductive wires 30 and 32 connect to a resistance wire 34 in the reaction zone 14. The resistance wire 34 is adjacent to the oxidative heating tip 26. Alternatively, a spark coil or other ignition device may be employed.

An inlet conduit 36 is also attached to the reactor 10. It is a secondary halide containing various compounds or waste.
It is for introducing into the inflow pipe 38 of. Similarly, inlet conduits 40 and 42 are also installed to introduce methane and steam, respectively. The inflow conduits 36, 42 and 42 are respectively associated with flow measuring valves 44, 46 and 48 through the inflow pipe 38 to the zone 14.
The flow rate of each gas emitted from the tip 50 inside is adjusted. The other end 52 of the reaction vessel 10 is provided with an exhaust device 54 for withdrawing the produced gas from the zone 14, and is accompanied by an exhaust valve 56 for flow rate measurement. The reaction is preferably allowed to proceed while withdrawing the product so that the residence time required for conversion (generally about 2 to 5 seconds) is constant. Therefore, the inflow valves 22, 2
4, 46, 68 and the exhaust valve 56 are adjusted so that the pressure in zone 14 is approximately equal to atmospheric pressure. However, the amount of raw material processed within a certain period of time depends on the reaction vessel 1
It may be increased by appropriately adjusting the valve so that a pressure higher than atmospheric pressure is applied in zero.

A heat exchange device 58 is provided to regulate the temperature in zone 14, but in this case is an insulating means to maintain the desired temperature in zone 14. Heat exchanger 58 may also comprise a methane heater (not shown) for externally heating casing 12 and zone 14. In addition, a quantity of water may be introduced into the tube 38 from the inflow conduit 42 to help control the temperature in the zone 14. Thereby, the heat at the time of oxidation in the zone 14 can be cooled.

A wash and separation device 60 is also provided to fractionate the reaction products, as shown. It is likewise fitted with conduits 62 and 64, respectively, through which the dehalogenated hydrocarbons and carbon wastes and hydrogen chloride are discharged for storage or treatment. The device 60 includes
A conduit 66 is attached to recirculate the non-dehalogenated compound to the inlet pipe 38 via a flow metering valve 68 for reprocessing.

In operation, methane and oxygen stoichiometry are metered and metered methane and oxygen are introduced into the inlet pipe 18 via the inlet conduits 16 and 20. There, the gases are mixed and flow into the chip 26 and further into the reaction zone 14.
A quantity of the compound to be dehalogenated is fed into the tube 38 via the inlet conduit 36 and admixed with a sufficient amount of methane gas via the conduit 40 to supply a stoichiometric excess of fuel, so that A reducing atmosphere is formed in the zone 14. If desired, water may be added via conduit 42 to regulate the temperature in zone 14. A combustible amount of methane gas and oxygen or air is introduced into zone 14 and then current is applied to conductive wires 30 and 32 in order to fully glow discharge resistance wire 34, tip 26 and tip 5
The gas mixture is ignited at the inlet confluence from zero. Apart from
Spark discharge or other ignition means may be used.

It should be noted that various methods and devices can be utilized to introduce the gases described herein to zone 14. For example, a constant mixture of fuel and oxygen may be introduced through the first inlet, or excess fuel and compound may be introduced directly into zone 14 through the second and third inlets, respectively. Also, fuel, oxygen and compounds separately or 1
It may be introduced through one inflow port. Prior to introduction into the apparatus 10, it is preferable to appropriately analyze and homogenize the waste mixture or compound, if necessary. In processing,
It may be necessary to make sure that the levels of inorganic compounds are not too high. For example, do not introduce large amounts of certain non-toxic water-soluble substances such as salt and lime. Because such materials react with the refractory lining to form a glassy coating which can reduce the thermal efficiency of the casing 12. If liquid or solid waste is to be treated by heating and / or evaporation, it may also be desirable to introduce the compound in the vapor phase into conduit 36.

In addition to hydrogen halide, the major components exiting reaction zone 14 include dehalogenated compounds introduced therein. There is also a small amount of compounds and elements ignited. For example, water vapor and oxides of carbon may be formed as a result of the combustion process. In addition, sulfur may be contained in the compound, or due to some reason, zone 14
If incorporated into the, sulfur oxides will be formed. If air is used as the oxygen source, non-flammable compounds will be oxidized, for example to nitrogen oxides. All of these oxides are soluble in water and inherently acidic in water so that they can be removed from the effluent by the wash separator 60 described above. Hydrogen chloride is also removed at the same time.

In addition to the above reaction products, carbon compounds may be formed from the decomposition of dehalogenated carbon compounds or from contaminating impurities. For example, ethylene, acetylene and higher molecular weight hydrocarbons containing soot-like carbon are produced. Any carbon that accumulates in the reaction vessel can be periodically oxidized and removed by passing air through the reaction vessel at temperatures above 675 ° C.

According to the method described above, the reaction is very fast and is generally complete in a few seconds. The residence time in the high temperature zone in the reaction vessel is 2
It is preferably from 10 to 10 seconds.

As described above, the reaction products are separated and collected by the washing separation device 60. Methods and devices for separating hydrogen chloride and other water-soluble gases from hydrocarbons are known. See, for example, US Pat. No. 2,488,083 (Gorin et al.). A fractionator may be used to remove light gases from the reaction product.

The reaction proceeds by cleaving the carbon-halogen bond in a reducing atmosphere, resulting in hydrogen halide and dehalogenated hydrocarbon. In the reaction described here, hydrogen chloride is produced by decomposition of specific chlorinated hydrocarbons, carbon tetrachloride and chlorobenzene. These compounds have been chosen as suitable examples for the above process, because the carbon-halogen bonds of other halogenated hydrocarbons are weaker than the compounds specifically mentioned here and are therefore necessary for their dehalogenation. The activation energy is lower than that required for the compounds discussed here.

Benson's "Introduction to Chemical Kinetics" (Maglow Hill: 19
60) based on the method for diffracting a complex chain reaction and the kinetic data summarized in Benson et al., "Kinetics data for gas phase single molecule reactions" (NSRD, NBS, 21, 1970). Thus, carbon tetrachloride is the compound that is most susceptible to thermal decomposition, and chlorobenzene is the most difficult compound to thermally decompose. The carbon-halogen bond energies of other chlorinated compounds such as chloroform, trichloroethane, tetrachloroethane, methylene chloride, polychlorinated biphenyls and dioxins fall between those of the above two compounds. Therefore, these compounds also belong to the same range as the above example. Still further, iodinated hydrocarbons and brominated hydrocarbons are decomposed at lower temperatures, at temperatures of about 200 ° C. and 100 ° C., respectively, which are lower than those mentioned for chlorinated organic compounds, respectively, and non-halogenated hydrocarbons and iodinated hydrocarbons. Converted to hydrogen and non-halogenated hydrocarbons and hydrogen bromide.

The invention is further described by the following examples.

[Example I]

Using the apparatus shown schematically in the accompanying drawings, carbon tetrachloride was pyrolyzed with methane in a reaction zone heated by the combustion of methane and oxygen. Methane and oxygen were added stoichiometrically in excess of methane, and the carbon tetrachloride to methane ratio was maintained at about 3: 1. Carbon tetrachloride was about 25 weight percent. Reaction container is about 1
The feed, kept at 025 ° C. and treated for a period of time, was maintained so that the residence time was about 3 seconds. The effluent stream contained ethylene, acetylene, benzene, hydrogen and higher molecular weight hydrocarbons. Similarly, it also contained some soot-like carbon. The effluent, in the form of hydrogen chloride, contained all the chlorine initially introduced as carbon tetrachloride. That is, the total amount of chlorine gas was about 60 mole percent of the exhaust gas.

Example 2 In this example, chlorobenzene was chosen as a typical example of a compound containing aromatic chlorine. However, the compound is known to be the most resistant to thermal decomposition among all organic compounds containing chlorine. Two moles of methane (about 21 weight percent) were used for each mole of chlorobenzene. The gases were then passed through the reaction zone at a temperature of 1125 ° C. The residence time was about 3 seconds. The effluent stream contained exclusively benzene and ethylene as well as chlorine converted to hydrogen chloride. By-products included acetylene, hydrogen, higher molecular weight unsaturated hydrocarbons and carbon.

As described above, the decomposition method of the halogen-containing compound of the present invention is simple in operation, economical, and efficient. Also, in the process of this invention, all chlorine was readily separated and converted to neutralized hydrogen chloride.

[Brief description of drawings]

The accompanying drawings are schematic illustrations of apparatus suitable for carrying out the method of the present invention. 10: reaction vessel, 12: casing, 16, 20, 3
6,40,42: conduit, 22,24,44,46,4
8, 68: Flow rate measuring valve, 34: Resistance wire, 58: Heat exchange device, 60: Washing / separating device.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Maia A. Bisman, California, United States 90004, Los Angeles, Building 3-209, S. Giuanita Avenyu 204 (56) References Japanese Patent Publication No. 56-39290 (JP, B2) International publication 822001 (WO, A) International publication 834244 (WO, A)

Claims (9)

[Claims] 1. An organic compound containing at least 8 halogen.
When thermally decomposing in a reducing atmosphere at a temperature of 25 ° C. to produce hydrogen halide substantially free of halogenated hydrocarbon as an effluent, the reducing atmosphere contains methane and oxygen in a single reaction vessel. Halogen-containing methane, wherein the methane is present in a stoichiometric excess over that required for reaction with oxygen according to the reaction formula CH ₄ + 2O ₂ → CO ₂ + 2H _2. Methods of converting compounds. 2. The compound is selected from the group consisting of carbon tetrachloride, chloroform, trichloroethane, tetrachloroethane, methylene chloride, polychlorinated biphenyls, and dioxins, and the effluent formed is a substance of chlorinated hydrocarbons. The method of claim 1 including hydrogen chloride that is absent in nature. 3. The temperature is about 1025 ° C. to 1125 ° C.
The method of claim 1 wherein: 4. The method of claim 1 wherein said compound is selected from the group consisting of carbon tetrachloride and chlorobenzene. 5. The temperature is about 1025 ° C. to 1125 ° C.
The method of claim 2 wherein: 6. An organic compound containing halogen in a gas phase is introduced into one end of a single reaction vessel having a temperature of about 825 ° C. to 1125 ° C., and oxygen and combustible gas are added in an amount sufficient to reach the temperature. While introducing into the reaction vessel and burning, the amount of oxygen is made smaller than the amount required for stoichiometric oxidation of the gas in the reaction vessel to maintain a reducing atmosphere, Converting halogen to hydrogen halide, and discharging the converted gas from the other end of the reaction vessel, wherein the converted gas contains hydrogen halide substantially free of halogenated hydrocarbons. The method according to claim 1. 7. The method according to claim 6, wherein the compound is a chlorinated organic compound, and the derived gas contains hydrogen chloride substantially free of chlorinated hydrocarbons. 8. The compound is selected from the group consisting of carbon tetrachloride, chloroform, trichloroethane, tetrachloroethane, methylene chloride, polychlorinated biphenyls, and dioxins, and the derived substance formed is a substance of chlorinated hydrocarbon. The method of claim 7 including hydrogen chloride that is absent in nature. 9. The method according to claim 7, wherein the compound is carbon tetrachloride or chlorobenzene.