WO1995033524A1

WO1995033524A1 - Treatment of materials to remove contaminants

Info

Publication number: WO1995033524A1
Application number: PCT/GB1995/001282
Authority: WO
Inventors: Malcolm Strapp
Original assignee: Grosvenor Power Services Limited
Priority date: 1994-06-03
Filing date: 1995-06-02
Publication date: 1995-12-14
Also published as: AU2624295A; GB9411118D0

Abstract

A process for decontaminating materials containing organic halides, such as polychlorobiphenyls comprises treatment of the material over a catalyst comprising one or more active metal compounds at an elevated temperature.

Description

TITLE: Treatment of materials to remove contaminants

DESCRIPTION

This invention concerns treatment of materials to remove contaminants, such as organic halides. Organic halides are found as contaminants of various liquids and solids. Example of such organic halides are polychlorobiphenyls which have been found to be undesirable contaminants of liquids as they are non- biodegradable. The most effective treatment of PCB contaminated liquids, such as electrical oils, is incineration. However, in order to conserve such oils, their re-use is allowable when PCB contamination is below 10 ppm. Thus, methods have been devised for removing PCB's from oils. One method is to use sodium metal which is both dangerous and expensive. Because sodium is highly reactive special plant is required for this method. Another method is catalysed treatment with hydrogen at high pressure. Again special plant is required to cope with the high pressure and hence this method is also expensive.

An object of this invention is to provide a method of removing contaminants, such as organic halides, from liquids or finely-divided, preferably free flowing, solids eg powdered solids. According to this invention there is provided a process for removal of contaminants from a material , such as a liquid or a finely-divided preferably free flowing , solid dispersed in a liquid comprising dispersing a catalyst into the material to be treated at an elevated temperature.

The process of the invention may be operated as a batch process or as a continuous process. In the batch process the catalyst is dispersed into the material to be treated in suitable proportions in a chamber, preferably with agitation of the mixture. After a suitable period of treatment, the catalyst may be separated from the treated material by any suitable means, such as by filtration or by use of a settling tank. The separated out catalyst may then be reused after any necessary further treatment.

In a continuous process the material to be treated and the catalyst are fed into a treatment chamber continuously in suitable proportions and passed through the chamber at a suitable speed preferably with agitation to achieve the desired treatment, whereafter the catalyst and treated material may be separated, if desired, for example, by means of filtration or settlement. Catalyst separated out may be reused after any necessary further treatment.

Typically the process of the invention will be used for removing organic halides, such as PCB's from oils and synthetic liquids. Examples of oils include electrical oils, heat transfer oils, hydraulic oils, fuel oils and process oils. Examples of synthetic liquids include esters and various polymers, such as electrical, hydraulic and heat transfer liquids.

The process of the invention may also be used for treating any liquid or free flowing or finely-divided solid, such as a powder, containing organic halides when dispersed in a liquid, such as an oil.

The catalyst preferably comprises one or more active metal compounds. Preferred metal compounds include oxides, hydroxides and sulphides. Preferred metals include nickel, iron, copper, molybdenum, tungsten and chromium. Preferably a nickel compound will always be present either alone or in combination with one or more other metal compounds.

The catalyst may be supported on a carrier. Suitable carriers for the active metal compounds are those having a relatively high surface area. Carriers that may be re-used as fuels are one type that may be suitable for use in the invention, such as carbon based carriers, for example charcoal and coke. Other suitable carriers may be of a type that can be regenerated by burning off collected residues. Examples of that type of carrier include clays, alumina, silica and bauxite. Thus, exhausted supported catalytic mass may be regenerated in the case of non-carbon based carriers by controlled burning off of deactivating residues. Carbon based catalytic mass may be disposed of as solid fuel. In both cases process liquid is preferably monitored to prevent contamination surviving the process and contaminating the carrier mass. Prior to regeneration or disposal by burning, the catalytic mass may be purged with non-contaminated liquid to prevent halogenated material being present during combustion conditions.

Exhausted unsupported catalyst may be regenerated by burning off, or by solution in acid and precipitation by addition of alkali. In some situations such catalyst may be reactivated by solvent washing or acid scouring to remove surface contamination.

The supported catalyst may be prepared in any convenient way. A preferred way is to precipitate metal as hydroxide or carbonate onto carrier material from an aqueous solution of metal salt by the addition of alkali. Unsupported catalyst may be produced by precipitation of metal hydroxide or carbonate direct from aqueous solutions of the relevant salt.

The temperature of the treatment process of the invention may be as high as is desirable but not so high that significant degradation of the material under treatment is likely. Typically temperatures in the range of 250 to 375°C, especially in the range of 275 to 325°C, may be used for the process of the invention. The amount of unsupported metal catalyst used in the process of the invention is preferably above 0% upto 100% by weight of the material under treatment. The amount of metal catalyst present when used on a carrier may be anything above 0% upto about 100% by weight of the carrier. Preferably metal catalyst is present in amount of from 0.5 to 100% by weight of the carrier. The amount of metal catalyst used may depend on one or more of various factors. Higher amounts of catalyst may give longer catalytic life and enhanced ability to process highly contaminated materials. On the other hand lower levels of catalyst may facilitate disposal of exhausted catalytic mass.

For some materials the process of the invention may be used to decontaminate materials so that they are suitable for standard reclamation procedures before re¬ use for their original purposes. On the other hand highly contaminated materials may require such severe treatment that the resultant decontaminated material is not suitable for re-use.

It is believed that the mechanism for the catalytic treatment of materials by the process of the invention may involve activation of chlorine atoms in the organic halides, which react with hydrogen from the organic compounds, such as hydrocarbons to produce HC1. Thus, there may be a small amount of cracking of hydrocarbon in the process.

This invention will now be further described by means of the following Examples.

Example 1

In order to remove PCB's from transformer oil containing 50 ppm of PCB's, 1% by weight of powdered nickel oxide to the total weight of the oil was dispersed into the oil in a chamber heated to temperature in the range of 275 to 325°C.

After a period of 15 minutes the oil and catalyst were separated and the oil was found to have a PCB level well below an acceptable level of 10 ppm. Example 2

In order to remove PCB's from transformer oil containing 50 ppm of PCB's, a metered flow of powdered nickel oxide was dispersed into a flow of the oil passing through a reaction chamber. The amount of nickel oxide used was 1% by weight of the oil. The oil was passed through the reaction chamber at such a rate to give a minimum of 15 minutes residence time of oil in the reactor. The reactor was maintained at a temperature in the range 275 to 325°C. Upon leaving the reactor the catalyst was separated out and the oil was found to have a PCB content well below an acceptable level of 10 ppm.

Claims

1. A process for removal of contaminants from a material, such as a liquid or a finely-divided solid dispersed in a liquid, comprising dispersing a catalyst into the material to be treated at an elevated temperature.

2. A process as claimed in claim 1 operated as a batch process, in which the catalyst is dispersed into the material to be treated in a suitable proportion in a chamber.

3. A process, as claimed in claim 2, wherein the dispersion of material to be treated and catalyst is agitated.

4. A process as claimed in claim 2 or 3, wherein, after a suitable treatment period, the catalyst is separated from the treated material.

5. A process as claimed in claim 4, wherein separation of the catalyst is by filtration.

6. A process as claimed in claim 4, wherein separation of the catalyst is achieved by means of a settling tank.

7. A process as claimed in claims 4, 5 or 6, wherein the catalyst used has been recycled from a previous batch operation.

8. A process as claimed in claim 1 operated as a continuous process, in which the catalyst and material to be treated are fed into a treatment chamber continuously in suitable proportions and passed through the chamber at a suitable speed.

9. A process as claimed in claim 8, wherein the mixture of material to be treated and catalyst is agitated.

10. A process as claimed in claim 8 or 9, wherein the catalyst is separated from the treated material.

11. A process as claimed in claim 10, wherein the catalyst is separated out by filtration.

12. A process as claimed in claim 11, wherein the catalyst is separated out by means of a settling tank.

13. A process as claimed in claim 10, 11 or 12, wherein the catalyst used has been recycled after separation from the treated material.

14. A process as claimed in any one of claims 1 to 13, wherein the material to be treated is selected from oils and synthetic liquids containing organic halides.

15. A process as claimed in claim 14, wherein the oil is selected from electrical oils, heat transfer oils, hydraulic oils, fuel oils and process oils.

16. A process as claimed in claim 14, wherein the synthetic liquid is selected from esters and polymers used as electrical, hydraulic and heat transfer liquids.

17. A process as claimed in any one of the claims 1 to 13, wherein the material to be treated is selected from free-flowing and finely divided solids containing organic halides when dispersed in a liquid.

18. A process as claimed in claim 17, wherein the liquid is an oil.

19. A process as claimed in any one of claims 14 to

18, wherein the organic halides are polychlorobiphenyls.

20. A process as claimed in any one of claims 1 to

19, wherein the catalyst comprises one or more active metal compounds.

21. A process as claimed in claim 20, wherein the metal compounds are selected from oxides, hydroxides and sulphides.

22. A process as claimed in claim 20 or 21, wherein the metal compounds are selected from compounds of nickel, iron, copper, molybdenum, tungsten and chromium.

23. A process as claimed in claim 20, 21 or 22, wherein the catalyst is selected from a nickel compound alone and a nickel compound with one or more other metal compounds.

24. A process as claimed in any one of claims 1 to 23, wherein the catalyst is supported on a carrier.

25. A process as claimed in claim 24, wherein the carrier has a high surface area.

26. A process as claimed in claim 24 or 25, wherein the carrier is re-usable as a fuel.

27. A process as claimed in claim 26, wherein the carrier is selected from charcoal and coke.

28. A process as claimed in claim 24 or 25, wherein the carrier can be regenerated by burning off collected residues.

29. A process as claimed in claim 28, wherein the carrier is selected from clays, alumina, silica and bauxite.

30. A process as claimed in any one of claims 24 to

29, wherein, prior to regeneration or disposal by burning of the carrier, the catalytic mass is purged with non-contaminated liquid.

31. A process as claimed in any one of claims 1 to 23, wherein exhausted unsupported catalyst is regenerated by burning off or by dissolving in acid and precipitation by addition of alkali.

32. A process as claimed in any one of claims 1 to 23, wherein exhausted unsupported catalyst is reactivated by solvent washing or acid scouring.

33. A process as claimed in any one of claims 24 to

30, wherein the supported catalyst is prepared by precipitation of metal as hydroxide or carbonate onto carrier material from an aqueous solution of metal salt by addition of alkali.

34. A process as claimed in any one of claims 20 to 23, wherein unsupported catalyst is produced by precipitation of metal hydroxide or carbonate direct from an aqueous solution of metal salt.

35. A process as claimed in any one of claims 1 to 34, wherein the elevated temperature is in the range of

250 to 375°C.

36. A process as claimed in claim 35, wherein the elevated temperature is in the range of 275 to 325°C.

37. A process as claimed in any one of claims 20 to 23 and 34 to 36, wherein the catalyst is unsupported and is present in an amount above 0% up to 100% by weight of the material under treatment.

38. A process as claimed in any one of claims 20 to 30, 35 and 36, wherein the amount of metal catalyst present when used on a carrier is above 0% up to 100% by weight of the carrier.

39. A process as claimed in claim 38, wherein the metal catalyst is present in an amount of from 0.5 to 100% by weight of the carrier.

40. A process as claimed in claim 1 and substantially as hereinbefore described with reference to Example 1 or Example 2.