Liquid purification or separation – Processes – Chemical treatment
Patent
1994-11-28
1997-07-01
Cintins, Ivars
Liquid purification or separation
Processes
Chemical treatment
210909, B01D 5700
Patent
active
056434669
DESCRIPTION:
BRIEF SUMMARY
DESCRIPTION
This invention concerns treatment of liquids such as, for example, oils, in order to remove contaminants such as, for example, polychlorobiphenyls (PCB's).
PCB's, 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 pressures and hence this method is also expensive.
An object of this invention is to provide a method of removing PCB's from liquids without the need for hydrogen under pressure.
According to this invention there is provided a process for removal of contaminants from a liquid comprising passing the liquid through a catalytic bed at an elevated temperature.
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 used as electrical, hydraulic and heat transfer liquids.
The catalytic bed preferably comprises a carrier and 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.
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 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.
The catalytic bed may be prepared in any convenient way. A preferred way is to precipitate metal as hydroxide or carbonate onto the carrier material from an aqueous solution of metal salt by the addition of alkali.
The temperature of the catalytic bed may be as high as is desirable but not so high that significant degradation of the liquid under treatment is likely. Typically temperatures in the range of 275.degree. to 375.degree. C., especially in the range of 275.degree. to 325.degree. C., may be used for the process of the invention. The temperature of the catalytic bed may also be increased to compensate for decreased catalytic activity or in order to process liquids with higher levels of contamination. The amount of metal catalyst present in the catalytic bed 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 15% 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 liquids. On the other hand lower levels of catalyst may facilitate disposal of exhausted catalytic mass.
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Database WPIL, Derwent Publications Ltd., AN 85-046957 & JP 600 004 589 (Mitsubushi Heavy Ind.) 11 Jan. 1985.
Cintins Ivars
Gosvenor Power Services Limited
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