FR2564324A1 - PROCESS FOR THE CONVERSION OF HALOGENATED TOXIC SUBSTANCES - Google Patents

Abstract

ACCORDING TO THE INVENTION, A PROCESS FOR THE CONVERSION OF CHLORINATED ORGANIC COMPOUNDS BY GAS PHASE PYROLYSIS IN A REDUCING ATMOSPHERE TO PRODUCE HYDROGEN CHLORIDE IN THE ESSENTIAL ABSENCE OF HALOGENATED HYDROCARBONS.

Description

The invention relates generally to the field

  orgariwui chemistry and most likely detoxified

cation of da: gezaux residues.

  The disposal of residues from the chemical, agricultural and other industries is a serious contemporary problem. 1there are in particular many chemical residues such as halogenated hydrocarbons, which are not biodegradable and must therefore be stored in safe, specialized areas, or incinerated in reactors

specially designed.

  For example, incineration systems have been designed for the destruction of halogenated hydrocarbons it in

  particular for the detoxification of biphenic compounds

  polychlorinated nylon (PCB), the manufacture of which has been inter-

  broken in the United States since 1976 because of their persistence and their ecological nuisance. However, there are still large amounts of these compounds in

  storage costs, which therefore creates a real danger.

  In a particular process, the organic residues are vaporized and totally or partially oxidized around 1000oC. The incombustible ash is discharged directly from the reaction chamber, while the residual gases pass through a second combustion chamber around 1 2000C

  to complete the thermal decomposition of the compound.

  However, not only does this incineration system require two combustion chambers, each of which requires a substantial supply of energy, but very often it does not

  not completely eliminate the presence of hydrocarbon-

  halogenated fumes in the tributary stream. It seems that this incineration system and others that involve the combustion of halogenated hydrocarbons in the presence of air, form free chlorine gas in the

  combustion chamber, which then re-forms hydro-

  halogenated carbides in the discharge stream. Even if the initial dangerous compound may have been degraded by these reactions, any halogenated hydrocarbon is dangerous and products such as chlorinated hydrocarbons which form in the combustion chambers as a result of the -2 - presence of free chlorine gas constitute another disadvantage for the safe disposal of incineration products. Thus, if the ash formed is not "clean", it must be reprocessed and re-analyzed, and the "dirty" ash must be suitably coated and stored until it is available. '' a safe evacuation process. The invention provides a process for the removal of organic compounds containing a halogen, such as

  carbon tetrachloride, chloroform, trichloro-

  ethane, tetrachloro & thylene, methylene chloride, various freons, polychlorinated biphenyls, laes dioxineas and others, by conversion to compounds which do not exhibit

no danger to the environment.

  Specifically, a method is provided for the evacuation of

  tion of organic compounds containing a halogen, which

  consists in pyrolyzing the compound in a reduced atmosphere

  temperature at around 825 to 1,125 C.

  in particular, the indicated reaction temperature may

  come from the combustion of methane and oxygen, the methane being in a stoachiometric excess compared to that necessary to react with oxygen, thus producing

the reducing atmosphere.

  The reducing atmosphere may come from a mixture of metbane and the compound to be converted, said compound having been vaporized according to known methods, in a reactor

  made of a suitable refractory material. The temperature

  The required amount may% tra supplied by external heating elements around the reactor, or may come from the combustion of mithane with limited quantities of oxygen in the reactor. However, it should be noted that the methane must be in a stoichiometric excess relative to the amount required to react with oxygen according to the formula

CH4 + 2 02 - C2 + 2 H20

  Under these conditions, the halogen-carbon bonds are broken, for example all of the chlorine reacts to form hydroxogen chloride and all of the organic compounds are then converted into mixtures of hydrogen, ethylene, acetylene and benzene with lower

  quantities of carbon and higher aromatic hydrocarbons

  laughing. Since there is no excess oxygen in the reactor, there is neither production nor reformation of various chlorinated hydrocarbons and dioxins. Hydrogen acid can be

  separated from the gas stream after an appropriate heat exchange

  prayed with water, alkali, lime or giant ash

  usually basic, and hydrocarbons and carbon can

  can be used as fuel or for applica-

chemical tions.

  It is obvious that the reducing atmosphere can

  be supplied using reagents other than metha-

  does, for example hydrogen, but since methane is wide-

  available and easier to use, the description

  detailed below is given in relation to methane.

  The invention therefore relates to a method for

  conversion of an organic compound containing a halogen, ca-

  characterized in that the compound is pyrolyzed in an atmosphere

  reducing sphere at a temperature of at least 8250C for

  sea, as effluent, a hydrogen halide in the absence

  essential halogenated hydrocarbons.

  According to other characteristics: - the temperature is between approximately 825

at 1125 "C;

  - the halogenated compound is chosen from tetra-

  carbon chloride and chlorobenzene; - the temperature is between approximately 1025 and 1125 ° C;

  - the process for the conversion of a compound or-

  halogen-containing ganics consists of: introducing the compound in the gas phase into a first end of a simple reaction chamber having a temperature between approximately 825 and 1125C; to maintain a reducing atmosphere in the

  reaction chamber and to convert the halogen into the compound

  dried into a hydrogen halide; then

  to extract the converted gases a second ex-

  end of the reaction chamber, the gases comprising a ha-

  hydrogen logene in the essential absence of haloenated hydrocarbons; the process consists in introducing and burning oxygen and a combustible gas into the reaction chamber in sufficient quantities to produce said temperature, the quantity of oxygen being less than that required for

  the stoichiometric oxidation of the gases in the reaction chamber

  tion, so as to produce a reducing atmosphere; - the ciosé is a chlorinated organic compound and the gases extracted contain hydrogen dcloride in the absene essentlelle of chlorinated hydrocarbons The Figure of the single appended drawing is a diagram of the process of the invention and represents, by way of example , a

  equipment for carrying out the process according to the invention.

  As required, a detailed embodiment of the invention is described here. However, it is evident that this

  embodiment is given only as an example of the

  vention which can take different forms from the mode of reaction

  specified reading, described here. Consequently, the specific details of structure and operation do not limit

the invention.

  The process is carried out by heating the compounds to be degraded in a reducing atmosphere at temperatures of at least 1,000 ° C for about 1 second. The reactor can be heated from the outside to maintain this temperature, such as by methane or similar heating elements,

  or can be heated from the inside by burning metal

  thane or other fuels a v e c d 1 'o x y -

  gene to provide the required reaction temperatures,

  in the presence of an excess of fuel which produces a pyro-

  reducing lysis of the added chlorine compound. We can also

  alternating the reducing mixture (excess fuel and organic halide) with the oxidative heating by keeping the discharge streams separated according to the alternating processes, More specifically and referring to the figure of the appended drawing, a reactor 10 is provided. comprising a gas impermeable jacket 12 which defines an internal elongated reaction chamber or reaction zone 14. Since the hydrochloric acid produced in zone 14 is corrosive, the jacket 12 must be revisited internally with a ceramic material such as aluminum oxide,

  silica or the like, or with carbides, bo-

  metal rures or nitrides. The reactor 10 has at one end 15 a gas inlet conduit 16 for the introduction of methane into a first inlet tube 18 and a second gas inlet 20 for the introduction of oxygen into the tube 18. The gas inlet pipes 16 and 20 are equipped with positive displacement valves 22 and 24, respectively, to regulate the methane and oxygen flow rate in the tube 18, then towards the end of the burner 26 in zone 14, in proportions that provide in

  this area the oxidative heat required. Generally

  However, a flame temperature of approximately 1,625 to 2,100 C provides sufficient heat. A sleeve 28 passes through the wall of the reactor at the end 15, for the passage of electrical conductor wires 30 and 32 connected to a resistance wire 34 in the reaction zone 14, which is arranged near the oxidizing heating end 26. You can also use an ignition coil or any other

ignition device.

  The reactor 10 also includes an inlet 36 for the introduction of the oa compounds from the residual materials containing a halide into a second inlet tube 38,

  as well as intake ducts 40 and 42 for the intro-

  6 -t D O2564324 reduction of methane and water vapor, respectively. The

  admissions 36, 40 and 42 are fitted with volumetric valves-

  triques 44, 46 and 48, respectively, to adjust the flow rate of the respective gases in the intake tube 38 towards one end 50 in the zone 14. An opposite end 52 of the reactor 10 comprises an evacuation device 54 for withdrawing production gas outside zone 14, on

  which is fitted with a volumetric discharge valve 56.

  The reaction is preferably carried out by withdrawing the product so as to maintain the required residence time.

  for conversion, usually about 2 to 5 seconds.

  Consequently, the inlet valves 22, 24, 46, 48 and 68 and the volumetric discharge valve 56 are adjusted to maintain in the zone 14 a pressure close to the

  atmospheric pressure. However, it is possible to increase

  ment the capacity by an appropriate adjustment of these valves to provide a pressure higher than the pressure

  atmospheric in reactor 10.

  Heat exchangers 58 are provided for regulating the temperature in zone 14 and in this case include insulating devices for maintaining the temperature

  desired in zone 14. Or, the heat exchangers

  their 58 may include methane heating elements, not shown, for externally heating the jacket 12 and the zone 14. The exchangers 58 could also include heating or heating coils

  electrical cooling of various types, if necessary.

  To further facilitate the temperature setting in zone 14, it is possible to establish a water circulation

  determ & néeadana the tube 38 by the admission 42 for inter-

  partially break the oxidative heating in zone 14.

  There is also shown in the figure a washing and separation station 60 for the fractionation of the reaction products, as well as conduits 62 * t 64 for the transfer of dehalogenated hydrocarbons and carbon residues, and hydrochloric acid, respectively, to places of storage or disposal. Extension 60

7 2564324

  includes a conduit 66 for the recycling of any compound

  which would not have been dehalogenated by a volume valve

  stick 68 towards the intake tube 38 for a new treatment. In activity, determined stoichiometric quantities of methane and oxygen are introduced into the intake tube 18 through the intake conduits 16 and 20, in which the gases mix and flow to

  the end of the burner 26, then in the reaction zone 14.

  Measured quantities of the compound to be dehalogenated are sent via the inlet pipe 36 into the tube 38, together with sufficient quantities of methane gas via the pipe 40 to provide a stoichiometric excess of fuel, and therefore a reducing atmosphere, in The area

  14. If necessary, water can be added by the

  duit 42 to adjust the temperature in zone 14. After the introduction of combustible quantities of methane and oxygen, or air, in zone 14, a current is applied to the conducting wires 30 and 32 so as to cause a sufficient incandescence of the resistance 34 to ignite the gas mixture at the confluence of the currents

  gaseous coming from the ends 26 and 50. One can also

  for this purpose use an ignition coil or any

other ignition device.

  It is obvious that various methods can be used and

  equipment for introducing the gases described in zone 14.

  For example, stoichiometric mixtures can be introduced.

  fuel and oxygen by a first intake, then an excess of fuel and the compound respectively by a second and a third intake, directly in the zone 14. It is also possible to introduce the fuel, the oxygen and the compound separately, or by means of a single admission. It is preferable that the mixture or the residual compounds are suitably

  analyzed and homogenized, if necessary, before the introduction

  duction in the apparatus 10. The treatment can be%

  necessary to ensure that the level of inorganic compounds

8 2564324

  ganiques is not excessive. For example, some materials

  non-toxic water-soluble rials such as salt and lime, must not be introduced in large quantities,

  because these materials can react with refractive

  shut up forming a vitrified layer capable of reducing the thermal efficiency of the jacket 12. It is also preferable to introduce the compound into the conduit 36

  in the gaseous state, resulting from heating and / or vapo-

  of residues which are liquid or solid.

  In addition to halogenated hydracids, a major constituent of the tributary from reaction zone 14 includes the entrained dehalogenated compound, as well as small amounts of other compounds and elements. By

  exempsle, water vapor and low carbon oxides

  They may be formed as a result of the combustion process, and if sulfur is present in the compound or introduced in some other way into zone 14, sulfur oxides may form. If air is used as the oxygen source, the non-combustible components will be oxidized, for example, nitrogen oxides. All these water-soluble and essentially acidic oxides in aqueous solution can be extracted from the effluent stream by the station.

  washing-separation 60, at the same time as chlorine acid

  water. In addition to the reaction products mentioned above, carbon compounds may form due to the degradation of the dehalogenated hydrocarbon or any other impurities present. For example, there is production of ethylene, acetylene and higher hydrocarbons, including that of a little carbon in the form of soot. Any carbon that accumulates in the reactor can be oxidized and periodically removed by passing a stream of air through the reactor at higher temperatures b

6750C.

  By applying the above procedure, the temple

  reaction time is very short, usually around-

  a few seconds. It is best to maintain one. residence time in the hot zone of the reactor from 2 to 10 seconds As described, the reaction products are separated and recovered at the washing-separation station 60. Methods and equipment for separating hydrochloric acid and other gases water-soluble hydrocarbons are well known. For example, reference may be made to US Patent 2,488,083 to Gorin et al. You can also use fractionation qppweils for gas removal

slight reaction product.

  The reaction takes place by breaking the carbon-halogen bonds in a reducing atmosphere, with

  subsequent production of halogenated hydracids and hydro-

  dehalogenated carbides. In the specific reactions described here, the production of hydrochloric acid is due to the degradation of specific chlorinated hydrocarbons, carbon tetrachloride and chlorobenzene, these compounds

  having been chosen as examples of the process described.

  Other halogenated hydrocarbons have carbon-

  halogen weaker or are dehalogenated by

  nisms that allow more activation energies

  weak than the compounds chosen specifically here.

  According to the methods of analysis of complex chain reactions, described by Benson in Foundations of Chemical Kinetics, McGraw-Hill (1960) and the speed indications

  data in Kinetic Data on Gas Phase Unimolecular Reac-

  tions, Beneon et al, NSRD, NBS, 21, 1970, carbon tetrachloride appears to be the most chlorinated hydrocarbon

  easy to pyrolyze and chlorobenzene is the most diffi-

  eyelash. Other chlorinated compounds such as chloroform, trichloroethane, tetrachlorethylene, methylene chloride, polychlorinated biphenyls and dioxins, have carbon-halogen binding energies on the order of those of the compounds chosen by way of example and enter

  therefore in the context of the examples described. In addition, hydro-

  iodinated and brominated carbides are degraded at temperatures

  and are converted to non-hydrocarbons

  halogenated and in hydroiodic acid and hydrobromic acid at temperatures, respectively of about 200 and 1000C

  lower than those described for organic compounds

chlorinated nicks.

  The following examples are given by way of illustration.

tration of the invention.

Example 1

  Using the equipment shown schematically

  in the figure of the appended drawing, pyrolysis of the tetrachlo-

  carbon rure with methane in a reaction zone heated by the combustion of methane and oxygen. The

  methane is present in a stoichiometric excess amount

  swaps with oxygen to produce a reducing atmosphere, and the ratio of carbon tetrachloride to methane is maintained in a proportion of about 3 to 1, about 25% by weight of carbon tetrachloride. The reactor is maintained at a temperature in the region of 1050 ° C. and the capacity adjusted to obtain a residence time of approximately 3 seconds. The exhaust stream contains ethylene, acetylene, benzene, hydrogen and

  a little higher hydrocarbons as well as a low pro-

  portion of carbon in the form of soot. The evacuation current

  tion contains all of the chlorine initially introduced

  as carbon tetrachloride, as chlorine acid

  water, i.e. the amount of hydrochloric acid

  that gaseous reaches about 65 mole% of the exhaust gases.

Example 2

  In this example, chlorobenzene is chosen as the typical representative of an aromatic compound containing chlorine. In addition, this compound is known to be the most difficult to pyrolyze among all the organic compounds containing chlorine. Two moles (approximately 21% by weight) of methane are used per mole of chlorobenzene and the gases pass through a reaction zone at a temperature of 1125 ° C., with a residence time of approximately 3 seconds. The exhaust stream mainly contains benzene and ethylene with all of the chlorine in the form of hydrochloric acid. As secondary products are acetylene, hydrogen, unsaturated hydrocarbons

and carbon.

  In summary, it can be seen that the process for the degradation of halogen-containing compounds, thus provided, is simple to carry out, economical and effective and allows the conversion of all of the chlorine into hydrochloric acid.

easily separated and neutralized.

Claims (11)

  1. Process for the conversion of an organic compound containing a halogen, characterized in that the compound is pyrolysed in a reducing atmosphere at a temperature of at least 8250C to form, as an effluent, a hydrogen haloenide   in the essential absence of halogenated hydrocarbons.   2. Method according to claim 1, wherein the reducing atmosphere is formed in a single chamber   reaction by mixing methane and oxygen,   thane being in a stoachiometric excess of cebiei required   to react with oxygen depending on the reaction - CH4 + 2 02. Co2 + 2 H20   3. Process according to one of claims 1 and 2,   in which the compound is chosen from tetrachloride   carbon, chloroform, trichloroethane, tetrachloro-   ethylene, methylene chloride, poly- biphenyls   chlorine and dioxins, and the effluent formed includes   hydrochloric acid in the essential absence of hydro- chlorinated carbides.   4. Method according to one of claims 1 and 2,   in which the temperature is between approximately 1025 and 1125 C.   5. Method according to claim 2, in which the compound is chosen from carbon tetrachloride and chlorobenzene.   6. Process according to claim 3, in which the   temperature is between about 1025 and 1125 C.   7. A process for the conversion of an organic compound containing a halogen, which consists in: introducing the compound in gaseous phase into a first end of a simple reaction chamber having a temperature between approximately 825 and 1125 C; maintaining a reducing atmosphere in the reaction chamber and converting the halogen in the compound to a hydrogen halide; then extracting the converted gases from a second end of the reaction chamber, the gases comprising a haloide 13 2564324   of hydrogen in the essential absence of halo hydrocarbons   Genoa. 8. The process as claimed in claim 7, which consists in introducing and burning oxygen and a combustible gas into the reaction chamber in quantities sufficient to produce said temperature, the quantity of oxygen.   being less than that required for stoichiometric oxidation   metric of the gases in the reaction chamber, so that   produce a reducing atmosphere.   9. Method according to one of claims 7 and 8,   in which the compound is a chlorinated organic compound and the gases extracted contain hydrogen chloride in   the essential absence of chlorinated hydrocarbons.   10. The method of claim 9, wherein the compound is selected from carbon tetrachloride, chloroform, trichloroethane, tetrachlorethylene, methylene chloride, polychlorinated biphenyls and dioxins and the tributary formed contains acid hydrochloric in the essential absence of hydrocarbons chlorinated.   11. The method of claim 9, wherein the   compound is carbon tetrachloride or chlorobenzene.