Classifications

• • A—HUMAN NECESSITIES
  • A62—LIFE-SAVING; FIRE-FIGHTING
  • A62D—CHEMICAL MEANS FOR EXTINGUISHING FIRES OR FOR COMBATING OR PROTECTING AGAINST HARMFUL CHEMICAL AGENTS; CHEMICAL MATERIALS FOR USE IN BREATHING APPARATUS
  • A62D3/00—Processes for making harmful chemical substances harmless or less harmful, by effecting a chemical change in the substances
  • A62D3/30—Processes for making harmful chemical substances harmless or less harmful, by effecting a chemical change in the substances by reacting with chemical agents
  • A62D3/37—Processes for making harmful chemical substances harmless or less harmful, by effecting a chemical change in the substances by reacting with chemical agents by reduction, e.g. hydrogenation
• • A—HUMAN NECESSITIES
  • A62—LIFE-SAVING; FIRE-FIGHTING
  • A62D—CHEMICAL MEANS FOR EXTINGUISHING FIRES OR FOR COMBATING OR PROTECTING AGAINST HARMFUL CHEMICAL AGENTS; CHEMICAL MATERIALS FOR USE IN BREATHING APPARATUS
  • A62D2101/00—Harmful chemical substances made harmless, or less harmful, by effecting chemical change
  • A62D2101/20—Organic substances
  • A62D2101/22—Organic substances containing halogen

Definitions

• PCB's Polychlorinated biphenyls
• PCB's are non-conductors of electricity and have good resistance to high temperatures, so they are widely used as working fluids in heat exchangers and hydraulic systems and by the electrical industry in transformers and capacitors.
• PCB's are extremely toxic, but are difficult to destroy on account of their thermal stability and chemical inertness.
• the standard destruction method involves incineration at temperatures around 1500°C, but suffers from several disadvantages. Operation at these very high temperatures is expensive; and incomplete combustion can give rise to chlorinated dioxins or furans which are even more toxic than PCB's.
• the present invention provides a method for the destruction of PCB's and related compounds which involves reaction with metal rather than combustion, and operates at much lower temperatures.
• Shultz discloses as a non preferred embodiment, but does not claim, a process which involves contacting PCB's with a solid aluminium surface.
• his experiments involved heating transformer oils containing PCB's in the presence of aluminium foil at various temperatures, but did not result in complete destruction of the PCB's even over periods as long as 30 minutes.
• Japanese Kokai 51-25471 describes a method of decomposing PCB's by heating them to effect partial dissociation to HC1 or C1 2 , and passing the mixture over a suitable metal and recovering a chloride salt of the metal by sublimation from the decomposition system. There is no indication that air is excluded; and no evidence that complete decomposition of PCB's is achieved even after several hours reaction.
• This invention is based on the discovery that PCB's can be rapidly destroyed by heating in the presence of solid aluminium, but only provided certain critical parameters are observed.
• the invention thus provides a method of destroying halogen-containing organic compounds by reaction with a metal in the solid state at elevated temperature, characterized by contacting the compounds in gaseous form in the absence of oxygen with a metal selected from Al, Mg, Si, Ti and Be, and alloys thereof having a high specific surface area at a temperature of at least 450°C and a contact time of from 0.5 to 50 seconds.
• the compounds are preferably entrained in an inert carrier gas, for example argon or other gas in group 0 of the periodic table.
• an inert carrier gas for example argon or other gas in group 0 of the periodic table.
• High purity nitrogen may also be used, and is regarded for this purpose as an inert gas.
• nitrogen is known to form highly toxic compounds with PCB's but the concentrations so far observed of these are insignificant.
• concentration of the compounds in carrier gas is preferably from 10 ppm up to 10%.
• metals that can be used for reaction with the compounds are specified Al, Mg, Si, Ti and Be, and alloys of these metals with each other or with minor proportions of other metals.
• the five named metals have two characteristics in common: they form oxides having electrically insulating properties; and the oxides have high thermal and chemical stability.
• Berylium presents a toxicity problem in itself, and is on that account the least preferred.
• the most preferred metals are magnesium and, particularly, aluminium.
• the metals can be used in the natural state, i.e. without the need to remove any oxide film that may be present.
• Aluminium can be used having an anodic oxide film which may contain minor proportions of oxides of other metals such as Co, Ni, Sn, Cu etc., in the pores. It is not known with certainty whether any oxide film remains during operation of the method, or whether it is removed by reaction with halogen-containing organic compounds.
• the metal can be used in any physical form in which it has a high specific surface area. Suitable forms include a packed bed of spheres, chips or granules, a fluidized bed of powder, honeycomb, wire mesh or wire wool. Our presently preferred material is scrap aluminium and alloys thereof in granulated form, because this is cheap and readily obtainable. Sufficient metal surface area should be provided to ensure rapid and complete destruction of the halogen-containing organic compounds. This is generally 0.1 to 65 m 2 , preferably from 1 to 20 m 2 , of active metal surface (not necessarily bare metal surface, but surface not coated with e.g. inactivating carbonaceous deposits) per gram, of compound to be destroyed.
• reaction temperature needs to be at least 450°C.
• An upper limit on temperature is set by the melting point of the metal being used.
• One of the advantages of the method of this invention is the low temperatures required, and it is preferred not to use higher temperatures than are necessary in order to achieve reaction at the desired rate. Depending on other conditions, preferred reaction temperatures are likely to lie in the range 550°C to 650°C.
• reaction conditions absence of oxygen; state of the metal; temperature of the metal, are maintained as described above, destruction of halogen-containing organic compounds are achieved at short contact times.
• reaction time is related to the total surface area of metal per unit of halogen-containing organic compounds, and to the reaction temperature. Adjustment of gas flow to ensure complete destruction of the compounds is achieved by routine trial and error.
• Reaction products resulting from the method appear to be metal halide (e.g. aluminium chloride), low- boiling hydrocarbons, halogen, (e.g. chlorine) and carbon deposited on the metal substrate.
• metal halide e.g. aluminium chloride
• low- boiling hydrocarbons e.g. carbon
• halogen e.g. chlorine
• carbon deposited on the metal substrate e.g. carbon deposited on the metal substrate.
• the substrate gradually becomes inactive.
• the substrate can be regenerated.
• aluminium this can be achieved by subjecting the metal to sodium hydroxide solution, or less preferably, by heating the metal in air to burn off the carbon deposits.
• Other treatments for regenerating aluminium involve exposing the carbonised surface:-
• Hydrogen and chlorine may be diluted with flowing argon.
• treatment (a) is preferred. It seems possible that the regenerated surface is in some way "re-activated" by the chlorine. Using this treatment, a 79.7% recovery of usable surface was obtained.
• Treatment (b) is more preferred than (c).
• Other metal substrates can similarly be regenerated by removing the carbon deposits under conditions in which the substrate is not affected.
• the metal used was 1100 aluminium alloy chips (0.5 x 0.5 x 0.1 cm). A bed about 27 cm long of these chips was positioned in a vertical quartz tube 1.8 cm outside diameter, and maintained at a nominal temperature of 580°C. A vessel containing the reactant was positioned in the quartz tube below the bed, and was surrounded by a separate tube furnace whose temperature was raised from ambient to 600°C over a period of 60 minutes. The lower end of the quartz tube was closed except for an inlet port through which argon carrier gas was passed at a flow rate of 87.7 ml/min (NTP). As the reactant heated up it vapourized and became entrained in the carrier gas.
• NTP argon carrier gas
• the flow rate was such that the residence time of the gas in the bed of aluminium chips was about 15 seconds.
• the temperature profile of the bed of chips was measured as 366°C at 0 cm up from the bottom; 473 0 C at 5 cm; 563°C at 9 cm; 601°C at 16 cm and 600°C at 27 cm.
• the top end of the quartz tube was closed except for a gas outlet, and the reaction products were condensed. After the experiment, any remaining reactant, the material in the bed of aluminium chips and the reaction products were all analysed for halogen-containing organic compounds.
• the reactant was 0.0078 g of decachlorobiphenyl.
• the destruction efficiency was 99.9999%.
• the section from 14 to 24 cm (measured from the bottom) of the aluminium bed became black.
• the rate of heating of the reactant sample was varied so that the concentration of decachlorobiphenyl in carrier argon gas ranged from 166 ppm to 3048 ppm. In all cases, the destruction efficiency was at least 99.999%.

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• 1984
  • 1984-11-23 GB GB848429709A patent/GB8429709D0/en active Pending
• 1985
  • 1985-11-12 DE DE8585308218T patent/DE3568009D1/de not_active Expired
  • 1985-11-12 EP EP85308218A patent/EP0184342B1/de not_active Expired
  • 1985-11-12 AT AT85308218T patent/ATE40528T1/de not_active IP Right Cessation
  • 1985-11-21 CA CA000495858A patent/CA1258682A/en not_active Expired
  • 1985-11-22 IN IN984/DEL/85A patent/IN165170B/en unknown
  • 1985-11-22 ES ES549182A patent/ES8704867A1/es not_active Expired
  • 1985-11-22 AU AU50353/85A patent/AU586840B2/en not_active Ceased
  • 1985-11-22 NO NO854693A patent/NO163265C/no unknown
  • 1985-11-22 BR BR8505887A patent/BR8505887A/pt unknown
  • 1985-11-22 JP JP60263640A patent/JPS61137831A/ja active Pending

Patent Citations (6)

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