DEGRADATION OF ORGANOCHLORINES

Abstract: Organochlorine compounds, particularly intractable waste material such as polychlorobenzenes and polychlorobiphenyls, are degraded by oxidation by a Ru or Os catalyst in the form of the tetroxide in the presence of a base. The tetroxide may be generated by an oxidising agent, such as sodium hypochlorite, or generated electrochemically. The organochlorine compound may be subjected to a preliminary dehalogenation step by treatment with strong base and alkanol under mild conditions.

Description: DEGRADATION OF QRGANOCH QRINES Technical Field The present invention relates to the degradation of organochlorine compounds, particularly the destruction of organochlorine-containing waste products from industry. Alternatively, the compounds may be only partially degraded and transformed into useful products. Prior Art It is known that organochlorine compounds, particularly chlorine polysubstituted aromatic rings are particularly difficult to oxidise or otherwise degrade. Industrial waste containing organochlorine compounds are referred to as intractable wastes, and their safe disposal constitutes a persistent problem. One approach has been to destroy the wastes in high temperature incinerator. However, such high temperature combustion has the potential to yield lethal dioxins as a by-product. There is understandable resistance to the siting of such high temperature incinerators anywhere near residential areas. The oxidation of certain polychlorinated dioxins using ruthenium catalysts has been described by D.C. Ayres in Nature, 290, 323 (1981) and Platinum Metals Review, 25_, 160 (1981). However, this work concerns oxygen-containing chlorophenols which may be easier to degrade than non-oxygen containing compounds. The alkaline dehalogenation of polychlorobiphenyls has been described in Hutzinger, et. al., "The Chemistry of PCB's" page 115 under severe high temperature-high pressure conditions. Brunelle, et. al, describe the use of milder conditions in Environment Science and Technology, ljL, 740 (1985) It is an object of the present invention to provide a chemical technique for the dehalogenation and oxidation in solution of such organochlorine-containing wastes. The term "dehalogenation" is used herein to mean the removal of halogen from a molecule without implying any particular structure in the dehalogenated product. Summary of the Invention A first aspect of the invention provides a process of . oxidation of an organochlorine compound, the organochlorine compound including a ring structure substituted by at leas one chlorine atom, and wherein the ring structure is not substituted by hydroxy; which comprises oxidising a solution of the organochlorine compound in the presence of a base, a actalytic amount of a Ru or Os metal compound, and an oxidising means sufficiently strong to allow formation of the catalytic metal tetroxide; the catalytic metal tetroxide being operative to effect said oxidation. The organochlorine compound before treatment is generally soluble only in organic solvents, such as acetonitrile, carbon tetrachloride etc. The base may be provided by the use of a basic oxidising agent, such as sodium hypochlorite, or may be provided separately (such as in the form of caustic soda). The nature of the Ru or Os compound is largely immaterial provided that it can be converted in-situ. to the catalytically active tetroxide, and not otherwise interfere in the process. Suitable ruthenium compounds include chlororuthenates, ruthenium(IV) oxide, tetroxoruthenates, tetroxoruthenium(Vlll) and trisoxalatoruthenate(III) . The corresponding osmium compounds may also be used. The oxidising agent must be sufficiently strong to maintain a catalytic concentration of the tetroxide and is generally used in aqueous basic solution. Suitable oxidising agents include alkali metal hypochlorite, potassium persulphate, hexacyanoferrate(III) , and potassium tetraoxomanganate(VII) . The alkali metal hypochlorite. may be generated in situ using hypochlorous acid and a base, or industrially by the use of gaseous/liquid chlorine and a base; the base being caustic soda, soda ash or limestone. The oxidising agent need not generate the tetroxide directly. For example the oxidant need only be strong enough to form perruthenate, Ru(VII), which disproportionates in base to form the tetroxide and ruthenate(VI). The latter is re-oxidised to perruthenate to continue the cycle. Alternatively, the oxidising means may be an electrochemical process of oxidation carried out in known manner. If necessary, the oxidation may be carried out at elevated temperature, but normally room temperature is sufficient. The organochlorine compound may be a monochlorinated or polychlorinated benzene, aryl, bicycloaryl, polycycloaryl, cycloalkyl, bicycloalkyl or polycycloalkyl; or a compound containing such chlorinated moiety. Further chlorine atoms may be present on aliphatic side-chains. Suitable compounds include chlorobenzenes, chloronapthalenes, chlorobiphenyls, chlorohexanes, and compounds such as DDT and chlordane. With the more inert of these organochlorine compounds, such as hexachlorobenzene and hexachlorocyclohexane, it has been found that oxidation is more readily achieved if the organochlorine compound is first subjected to a dehalogenation process. Thus, a second aspect of the invention provides a process of dehalogenation of an organochlorine compound a process of dehalogenation of an organochlorine compound which comprises treating a solution of the organochlorine compound in an organic solvent with a strong base in the presence of an alkanol at atmospheric pressure, so as to dehalogenate the organochlorine compound. The solvent is, for example, isobutyl-methyl ketone, diglyme, or can be an alkanol. The strong base is usually sodium or potassium hydroxide, which may be introduced in solid pellet form. The alkanol is usually a C,-C 8 alkanol, preferably methanol. The process is generally carried out at elevated temperature, for example 50 to 150 C, at the reflux temperature of the solvent used. It is advantageous that the process can be carried out at atmospheric pressure, thus removing the need for high pressures used in previous processes and the attendant dangers. The process results in partial or complete dehalogenation of the organochlorine compound. The organic phase contains an organic residue comprising a variety o undefined dehalogenated and partially dehalogenated compounds and other by-products (including insoluble sodium :■ chloride). The dehalogenation process of the second aspect of the invention is generally carried out as a preliminary pre-treatment before oxidation according to the first aspect of the invention. Alternatively, the dehalogenation process can be used as a pretreatment for a different process; such as a non-catalytic oxidation process, or the transformation of the fully or partially dehalogenated product into a useful non-degraded product. Thus, the two processes may be carried out quite independently of one another and the present invention covers these processes independently. Description of Preferred Embodiments The embodiments of the present invention will now be described by way of example only:- Example 1 - Dehalogenation of organochlorine substrates A suspension of hexachlorobenzene (1.0 g) and sodium hydroxide (5 g) in isobutyl-methylketone (10 mL) and methanol (10 mL) is stirred magnetically and refluxed at 90 C for 1 h. Hexachlorobenzene dissolves in the colourless solvent system which turns yellow/brown, but some pellets of sodium hydroxide remain suspended in the solvent. Water (40 mL) is added to the reaction mixture at 25 C. The mixture becomes clear with two layers and is, then, acidified (5 M Nitric acid, 25 mL) . The organic layer is extracted with 1 M nitric acid (2 x 5 mL) . The combined aqueous solutions are titrated, in the presence of 2 ml of 5% potassium dichromate as the indicator, against 0.1 M silver nitrate. The end-point reveals that about 70 mL of silver nitrate is used, which indicates that the hexachlorobenzene has been about one third dehalogenated. The organic layer is dried (MgS0 4 ) and rotary-evaporated, giving a red/brown oil. This is examined using an HP 5890A Gas Chromatograph with an HP 3393A Integrator and a BP-20 capillary column under a program of temperatures from 150° to 230° at a rate of 15°C min ~ . An authentic sample of hexachlorobenzene is eluted at 6.9 min. However, the GLC (gas-liquid chromatography) confirms that hexachlorobenzene is absent from the reaction mixture. The organic residue is oxidised as described below. Example 2 - Ruthenium Catalvsed-Oxidation of various organochlorine substrates A mixture of hydrated ruthenium (III) chloride (0.3g) in acetonitrile (10 mL)and carbon tetrachloride (15 mL) is stirred magneticallly in a conical flask. Sodium hypochlorite aqueous solution (40 mL) is added slowly to the mixture. Additional base may be added. The mixture turns from black to yellow, which characterizes RuO.. At this stage, the organic substrate (or the residue from the dehalogenation step) (0.1-1 g; see Tables I and II) is added to the catalyst. If the reaction occurs rapidly, a black shade appears in the mixture. In the presence of hypochlorite RuO. is regenerated. The reaction occurs from a few seconds to 2 days, depending on the reactivity of the substrate. The RuO 4„ in the reaction mixture is destroyed by addition of 2-propanol. The mixture is treated starting with acidification and the organic layer is examined by GLC (gas-liquid chromatography) , as described above. According to the GLC evidence, the substrates are oxidised to undetectable products, which are presumably carbon dioxide and water. Gas evolution was observed on acidification and carbonate was detected by precipitation as calcium carbonate. The final organic extract reveals the mass of the starting organochlorines is reduced to negligible levels. The results are set out in Tables 1 and 2. Substrates (b), (c) and (d) fall outside the scope of the present invention. Table 1. Substrates oxidised without prior dehalogenation Substrates % Degraded (a) *l-Chlorobenzene 90 (b) 4-Chlorophenol 99 (c) 2,4,6-Trichlorophenol 99 (d) 2,4-Dichloro-l-naphthol 99 (e) 4-Chloro-2'-hydroxybiphenyl 59 (f) l,l,l-Trichloro-2,2-bis (4'chlorophenyl)ethane (DDT) 78 * The chlorobenzene is oxidised by RuO. regenerated chemically, whereas for other compounds the oxidation is carried out by u0 4 regenerated electrochemically. Table 2. Substrates oxidised indirectly after dehalogenation with NaQH/methanol/iso-butγl methyl ketone Substrates % Degraded (h) *Hexachlorobenzene (1 g) 99 (i) gamma-Hexachlorocyclohexane (1 g) 99 * Hexachlorobenzene is dehalogenated at 90°C; gamma-hexachlorocyclohexane is degraded at 25°C. Example 3 - Hexachlorobenzene (HCB) A suspension of hexachlorobenzene (Fluka product) (l.Og) and potassium hydroxide (5.0 g) in diglyme (10.0 mL) and methanol (10.0 mL) is stirred magnetically and refluxed at 90°C for 2 h. Diglyme and methanol are distilled off under reduced pressure (at water pump pressure) . The residue is dissolved in a solvent system of CC1./H 2 0 (20:20 mL) . The two-phase mixture is added to ruthenium trichloride (0.3 g) and potassium persulphate (11.0 g) in 1 M NaOH (240 mL) . The mixture is magnetically stirred at room temperature for 5 h. The CC1 4 layer is separated from the alkaline solution. The ruthenium catalyst is precipitated by addition of 2-propanol (2 mL) . The black Ru0 2 (aq) is removed by filtration. To determine the extent of the reaction, the filtrate is acidified (5 M HNO_). Apparently, C0 2 is evolved during acidification. The acidic solution is extracted with CH 2 C1 2 (3 x 25 mL) . the acidic filtrate is analysed for total chloride ions with a Cl ~ ion selective electrode. The Cl- release is determined to be 100% of the original HCB. The combined organic extracts are dried (MgSO.) and the solvents are rotary-evaporated. The residue (< 0.001 g), dissolved in CH_C1 ? , is examined using an HP 5890A Gas Chromatograph with an HP 3393A Integrator, a flame ionisation detector and a BP-20 capillary column (25 m x 0.33 mm). At oven temperature of 140°C and He rate flow of 9 9..00 mmLL mmiinn- ,, aann aauutthheennttiicc ssaammppllee ooff hheexxaacchhlloorroobbeennzzeennee iiss eluted at 23.6 min. T The method has a reasonable sensitivity ffoorr HHCCBB ooff 22 gg IT 1 . The results confirmed that 99.97 of HCB is oxidised. Example 4 - Polvchlorobiphenyls (PCB's) A sample of commercial PCB's was reduced in volume by distilling off solvent at 100°C and 20 mm of Hg. The PCB (1.0 g) is dissolved in hot 1-butanol (20 mL) , Potassium hydroxide (5.0 g) is added to the solution and the mixture is stirred magnetically and refluxed at 110°C for 5 h. During the progress of the reaction, the mixture turns from colourless to dark brown. The 1-butanol solvent is distilled off at reduced pressure and a black -residue is obtained. The residue is cooled and dissolved in a two-phase solvent system of CCl./H^O (20:20 mL) . The Cl ~ released in the aqueous layer was found to be 49.0% of the starting PCB's. The two-phase mixture is added dropwise to RuO. generated from RuCl 3 (0.3 g) and NaCIO (50 mL) . The mixture is magnetically stirred and refluxed at 80 β C for 20 h. In the presence of excess NaOCl the mixture is yellow due to RuO.. However, if the oxidant is depleted the mixture turns black/green with precipitates of black Ru0 2 (aq). During the progress of the reaction the mixture is brown/green/black. Thus, sodium hypochlorite is added periodically giving the total volume of 220 ml used. The reaction mixture is cooled and the layer of CC1. is separated from that of the base. The RuO. in each layer is reduced by 2-propanol (2 mL) . To determine the extent of the reaction, the aqueous layer is acidified and extracted with CH 2 C1_ (3 x 25 mL) . Apparently, C0 2 is evolved during acidification. The combined organic extracts are dried (MgS0 4 ) and the solvents are rotary evaporated. The residue (*0.001 g) from the organic extracts is dissolved in CH_C1 7 and analysed by gas chromatography (gc) . The gc of the residue was performed as described in Example 1, except that a BP-1 capillary column (25 m x 0.33 mm) was used at the rate of He flow of 70 mL min " and under two programs of temperatures: (i) The first program starts from 40 to 180°C at a rate of 15°C min " . (ii) The second program starts from 180 to 280°C at a rate of 8°C min- . The solvents of the authentic sample of the commercial PCB's elute at retention times between 8 and 10 min, whereas the PCB's elute in the region 17-27 min. The gc results confirmed that over 99.9% of the starting PCB's is oxidized. Example 5 - Chlordane Chlordane was a commercial sample obtained from Chemspray Pty. Ltd. at Smithfield in Sydney. It contains 800 g L of chlordane and related compounds in a hydrocarbon solvent. Sodium hypochlorite (120 mL) is added to RuCl_ (0.3 g) dissolved in water (5 mL) . A solution of chlordane (1.94 g) in CC1 4 (10 mL) is added to the freshly generated Ru0 4 and the mixture is stirred magnetically at 80°C for 20 h. During this time more NaCIO is added making a total volume of 700 mL. The CC1 4 layer is separated from the aqueous layer. The Ru0 4 is reduced by 2-propanol (2 mL) and Ru0 2 (aq) is removed by filtration. To determine the extent of the reaction, the aqueous layer is acidified (C0 2 released) and extracted with CH 2 C1_ (3 x 25 mL) . The organic extracts are dried (MgS0 4 ) and the solvents are rotary evaporated. The residue is dissolved in CH 2 C1 2 and analysed by gc under conditions similar to those used for the analysis of PCB's. The mass of the total residue (0.12 g) indicates that 94.0% of the original chlordane sample is oxidised. The gc evidence confirmed that 94.0% of the starting material is oxidised. Example 6 - The RuQ -catalvsed Electrochemical Oxidation of Hexachlorobenzene (HCB) A mixture of hexachlorobenzene (0.25 g) and potassium hydroxide (1.25 g) in methanol (6 ml) and diglyme (6 ml) was -stirred magnetically under reflux for 3 h at 100°C. The solvents were removed at a reduced pressure to produce a residue. The electroxidation was carried out with a three-electrode system consisting of the following: (i) a reticulated carbon electrode block as the working electrode (ii) a reticulated carbon block as the auxilliary electrode and (iii) a Ag/AgCl (saturated KC1) electrode with a KN0 3 salt bridge and a vycor glass frit as the reference electrode. The reactions were carried out in a single-compartment cell. Oxygen was passed into 1 M sodium hydroxide (150 ml) in the electrochemical cell. Ruthenium trichloride (0.1 g) was dissolved in water (5 ml) and added to the base. The mixture was stirred magnetically and maintained at a voltage of 1.4 V vs. Ag/AgCl (Saturated KC1) for 15 min. The ruthenium catalyst turned from black to yellow/brown, characteristic of Ru0 4 . The residue was dissolved in a two-phase system of water/CCl 4 (20:20 ml) and added dropwise to the catalyst solution. A sample of the aqueous solution (1 ml) was withdrawn 1 h after the progress of the reaction. The Cl- ion content in the base was determined to be over 99.9% of that expected from the hexachlorobenzene starting material. With the voltage maintained at 1.4 V. a current of 0.2 A was recorded. The current of the alkaline solution increased to 0.6 A with the addition of the ruthenium catalyst. As result of the addition of the hexachlorobenzene substrates to the catalyst solution, the current increased further to a maximum of 0.9 A. During the progress of the reaction, some R 0 2 (aq) was deposited on the cathodic electrode. Consequently, the current decreased. The deposits were redissolved and the current "recovered" to 0.9 A by changing the current direction every 2 h. The electrolysis was continued for 6 h. During this time, the biphase mixture changed from black to yellow. The excess Ru0 4 was destroyed by addition of 2-propanol (2 ml) . The ruthenium precipitates were removed by filtration. To verify the extent of the reaction, the reaction mixture was acidified and extracted with dichloromethane (3 x 25 ml) . Apparently, carbon dioxide is evolved during acidification. The combined extracts including CC1 4 , were dried (MgS0 4 ) and rotary-evaporated. The residue was less than 0.001 g. The original hexachlorobenzene was oxidised to over 99%.

Claims: CLAIMS 1. A process of oxidation of an organochlorine compound, the organochlorine compound including a ring structure substituted by at least one chlorine atom, and wherein the ring structure is not substituted by hydroxy; which comprises oxidising a solution of the organochlorine-- compound in the presence of a base, a catalytic amount of a Ru or Os metal compound, and an oxidising means sufficiently strong to allow formation of the catalytic metal tetroxide; the catalytic metal tetroxide being operative to effect said oxidation. 2. A process according to claim 1, wherein the organochlorine compound is dissolved in an organic solvent selected from acetonitrile and carbon tetrachloride. 3. A process according to claim 1, wherein the base and. the oxidising means are jointly provided in the form of an alkali metal hypochlorite. 4. A process according to claim 1 wherein the oxidising agent is an alkali metal hypochlorite, persulphate, hexacyanoferrate (III) or tetraoxomanganate (VII) . 5. A process according to claim 1 wherein oxidation is carried out electrochemically. 6. A process according to claim 1 wherein the organochlorine compound is a polychlorinated benzene, aryl, bicycloaryl, polycycloaryl, cycloalkyl, bicycloalkyl, polycycloalkyl, or a compound containing said polychlorinated moiety. 7. A process according to claim 1 wherein prior to oxidation the organochlorine compound is subjected to a dehalogenation step which comprises treating a solution of the organochlorine compound in an organic solvent with a strong base in the presence of an alkanol, so as to dehalogenate the organochlorine compound. 8. A process according to claim 7 wherein the organic solvent is an alkylketone, an alkanol or diglyme. 10 9. A process according to claim 7 wherein the dehalogenation step is carried out under reflux. 10. A process of dehalogenation of an organochlorine 15 compound which comprises treating a solution of the organochlorine compound in an organic solvent with a strong base in the presence of an alkanol at atmospheric pressure, so as to dehalogenate the organochlorine compound 20 25 30 35 5634S/MS

Inventors: BEATTIE JAMES, KAZIRO ROBERT, LAY PETER, BEATTIE, JAMES, KAZIRO, ROBERT, LAY, PETER
Applicants: UNIV SYDNEY, THE UNIVERSITY OF SYDNEY
Application year: 1988
Main classification: A62D3
IPC codes: A62D3, A62D101, B09B3