EP0238735B1

EP0238735B1 - Destruction of carbonaceous material, and inert solid material formed by reaction of carbonaceous material with sulphur

Info

Publication number: EP0238735B1
Application number: EP86301671A
Authority: EP
Inventors: Harold W. Adams
Original assignee: Sultech Inc
Current assignee: Sultech Inc
Priority date: 1986-03-10
Filing date: 1986-03-10
Publication date: 1991-06-26
Anticipated expiration: 2006-03-10
Also published as: DE3679986D1; EP0238735A1

Description

The present invention relates to a method of destruction of carbonaceous materials, which may be toxic and/or hazardous chemicals, and the conversion of such materials to safe, inert and useful non-toxic products.
At present, the storage of hazardous and toxic chemicals (such as polychlorinated biphenyls, or PCBs) is very costly to industry. Failures to properly dispose of such toxic chemicals has resulted in long term devastating effects to both local and distant environments. PCBs are of substantial use in the electrical industry as insulating oils because of their high thermal stability. Unfortunately, there are difficult long term disposal problems associated with the use of PCBs, because they are very stable, non-inflammable and non-biodegradable, and at the same time, very toxic (in particular, they are highly carcinogenic). Because of their toxicity and dangerous effect on the environment when accidentally released, plans have been made to spend large amounts of money to phase out the use of PCBs in capacitors and transformers, but such planned replacement is, in effect, creating an even more severe short term problem in the safe disposal of discarded PCB. A long felt want in the chemical industry has been a safe and reliable process of conversion of such toxic chemicals to inert useful material which will itself have economic value.
Various methods of disposal or destruction or organic chemicals have been proposed, for example, in U.S. Patents 2175816, 3523812, 3622265, 3726808, 3736111, 3835183, 364223 and 3864305. Japanese specifications 74/127954 (Mitsubishi Monsanto) and 82/29373 (T.Ito) disclose methods of detoxification of PCBs by heating the latter with sulphur.
Japanese specification 74/127954 discloses detoxification of PCBs by reaction with sulphur for several hours; no further broad details of the method are given, although the examples suggest refluxing sulphur and a PCB in a flask at 285° to 315°C for three to five hours.
Japanese specification 82/29373 discloses a vapour phase reaction between sulphur vapour and vapourised PCB, in the absence of oxygen. The batch method described is said to result in instantaneous reaction between the PCB and the sulphur.
The present invention accordingly comprises a method of destruction of a carbonaceous material, which comprises feeding sulphur at a temperature in the range of 135 to 1500°c to a reaction vessel together with a flow of inert gas so as to maintain a substantially oxygen-free inert gas in the reaction vessel; separately feeding the carbonaceous material to the reaction vessel for reaction therein with the sulphur at a temperature between 500°C and 1500°C so as to form a substantially inert solid material comprising sulphur and carbon and containing unreacted residues of the carbonaceous material in an amount not exceeding a few parts per million; and separately removing vapour phase material and the solid material from the reaction vessel.
The resulting solid material is refractory, inert, non-inflammable and insoluble in organic solvents. The present invention further comprises a substantially inert solid material formed by reaction of sulphur with carbonaceous material at an elevated temperature in a substantially oxygen-free atmosphere, which solid material comprises carbon and sulphur in approximately equal proportions by weight, has no observable melting point, is substantially unaffected by aqua regia, is electrically conductive, and is substantially free of residue of the carbonaceous material.
The carbonaceous material to be destroyed according to the invention may be inorganic or organic chemicals; halogen-containing materials, such as polychlorinated biphenyls, are preferred in many embodiments of the present invention. when the method according to the invention is used for the destruction of PCBs, mass spectral analysis of the product indicates less than one part per million of unreacted PCB.
In the method according to the invention, the sulphur is fed to the reaction vessel at a temperature in the range of 135 to 1500°C; it is preferably supplied as a vapour at a temperature in the range 450 to 1500°C. When supplied as a vapour, the sulphur is fed into the reactor through a nozzle or spray nozzle.
The inert gas used in the method according to the invention is typically nitrogen, and the pressure in the reaction vessel is between one and two atmospheres.
The sulphur-containing gases are typically recycled to the sulphur which is fed to the reaction vessel and the reaction time is less than five minutes.
Reference will now be made to the accompanying drawing which is an exemplary embodiment of the operation of the method according to the invention.
Chemical waste (such as an inorganic or organic material, typically a halogen-containing compound such as a PCB), in liquid form, is fed, either via preheater 30 and heater 40, or directly, to a reactor 20. Sulphur (which may be fresh or recycled) is introduced into a heated melt tank 50, where the sulphur is melted, and then fed to a heater 60 (which may effect vapourisation) to be supplied into reactor 20 as a separate stream relative to the waste stream. Liquid sulphur 4 may be fed directly to heater 60.
An inert gas stream (such as nitrogen) is also fed to the reactor 20 so as to maintain an inert, substantially oxygen-free atmosphere in the reactor. Pressurised nitrogen gas may also be introduced into preheater 30, heater 40, melt tank 50 and heater 60, so as to pump or drive the liquid waste material and the sulphur into the reactor 20.
Reactor 20 is preferably a rotating screw-type oven, typically heated by electric induction heating coils to a temperature in the range of 500 to 1500°C inside the reactor. Within a matter of minutes at this temperature in less than five minutes) the waste organic material and the sulphur completely react together to produce a black solid reaction product, which generally contains less than one part per million of unreacted organic material.
Vapour products comprising unreacted sulphur and hydrogen sulphide, carbon disulphide and sulphur chloride gases are fed to a condenser 70, from which condensed sulphur is recycled to melt tank 50.
The remaining gases 9 from the condenser are then passed to a pollution recovery scrubber apparatus 80, from which a stream of clean effluent gas, and a stream of chemical intermediates is obtained.
The solid reaction product from reactor 20 is supplied to a post-reactor cooler unit, from which the solid may be transferred to appropriate grinding and mixing equipment.
The by-product gases 11 may include hydrogen sulphide, carbon disulphide, and sulphur chlorides, which may be recovered and removed from the effluent in a conventional manner. Sulphur vapours may also be recovered, condensed and recycled to the sulphur supply stream.
The sulphur may be fed to the reactor in molten form at a temperature of 135 to 450°C, or in vapour form at a temperature of 450 to 1500°C, again through a nozzle or spray nozzle.
The resulting black solid reaction product has a typical analysis as follows:
The black solid comprises substantially equal proportions by weight of sulphur and carbon; the exact molecular structure of the material is not known, but the following properties have been determined:

1. when ground to a powder, it resembles carbon black in appearance;
2. It has no observable melting point;
3. It is a complete absorber of ultra-violet and infra-red radiation;
4. It is insoluble in any solvent tested (including aqua regia);
5. It is an excellent electrical conductor.

The properties of this solid material mean that it is suitable for use as a filler for non-corrosive coatings, for solar energy absorber devices, for cements and asphalt, and for body implants; and as electronic resistors and conductors.
In particular, the combination of electrical conductive properties, absorption of infra-red, and chemical inertness mean that the material is particularly suitable for solar energy conversion devices, such as photovoltaic devices and thermo-electric conversion devices.
Current estimates of the efficiency and costs of the process according to the invention indicate that a plant could be constructed at a cost of $26,000,000.00 of a capacity to safely dispose of 24 tons per day of a PCB organic such as Westinghouse Company transformer oil "Inerteen 70-30@ (ASTM specification D-2283 Type D). The operating costs of such a plant, not including interest and amortization, nor credit for sale of by-product, would approximate $0.72 per 0,453kg (pound) of PCB destroyed Including interest and amortization, the total costs per pound of PCB destroyed are estimated at $1.50 per 0,453kg (pound), on the basis of a three year payout of investment.
It is thought that persons skilled in the art to which this invention relates will be able to obtain a clear understanding of the invention after considering the foregoing description in connection with the accompanying drawing. A more lengthy description is deemed unnecessary. It is understood that various changes in shape, size, and arrangement of the elements of this invention as claimed may be resorted to in actual practice, if desired. While the method according to the invention has been described primarily in terms of conversion from a hazardous chemical to a useful inert chemical, it is equally appropriate for conversion, to an inert material, of other organic chemicals and polymers, including other halogen-hydrocarbon materials.

Claims

A method of destruction of a carbonaceous material, which comprises feeding sulphur at a temperature in the range of 135 to 1500° C to a reaction vessel together with a flow of inert gas so as to maintain a substantially oxygen-free inert atmosphere in said reaction vessel; separately feeding said carbonaceous material to said reaction vessel for reaction therein with said sulphur at a temperature between 500°C and 1500°C so as to form a substantially inert solid material comprising sulphur and carbon and containing unreacted residues of said carbonaceous material in an amount not exceeding a few parts per million; and separately removing vapour phase material and said solid material from said reaction vessel.
A method according to claim 1, wherein said inert gas is nitrogen.
A method according to claim 1 or 2, wherein said sulphur is fed to said reaction vessel as a vapour at a temperature in the range 450 to 1500°C.
A method according to any of claims 1 to 3, wherein said reaction is carried out at a pressure between one and two atmospheres.
A method according to any of claims 1 to 4, wherein sulphur-containing gases are recycled to the sulphur fed to the reaction vessel.
A method according to any of claims 1 to 5, wherein the reaction time for reaction of said sulphur with said carbonaceous material is less than five minutes.
A method according to any of claims 1 to 6, wherein said carbonaceous material is pre-heated prior to being fed to said reaction vessel.
A method according to any of claims 1 to 7, wherein said carbonaceous material is an organic chemical.
A method according to any of claims 1 to 8, wherein said carbonaceous material contains halogen.
A method according to claim 9, wherein said carbonaceous material comprises a polychlorinated biphenyl.
A substantially inert solid material formed by reaction of sulphur with carbonaceous material at an elevated temperature in a substantially oxygen-free atmosphere, which solid material comprises carbon and sulphur in approximately equal proportions by weight, has no observable melting point, is substantially unaffected by aqua regia, is electrically conductive, and is substantially free of residue of said carbonaceous material.