Liquid purification or separation – Processes – Chemical treatment
Patent
1996-12-23
1998-06-30
Woo, Jay H.
Liquid purification or separation
Processes
Chemical treatment
210758, 210763, C02F 176
Patent
active
057728976
DESCRIPTION:
BRIEF SUMMARY
This invention relates to a catalytic oxidation process.
For environmental reasons it is often desirous to treat aqueous effluents in order to decompose contaminants such as organic compounds therein before discharge of the effluent, for example into rivers, estuaries, or the sea. In the present invention this decomposition is effected by oxidation.
U.S. Pat. No. 3,944,487 describes a discontinuous process for the treatment of waste water by digesting the waste water with sodium hypochlorite and then passing the so treated waste water through a catalytic filter bed of granular catalyst particles such as a mixture of nickel and cobalt oxides on a porous activated alumina support; the catalytic filter bed is then regenerated by incineration of pollutant particles trapped on the filter bed by passing air through the bed at high temperature.
A continuous process for the catalytic decomposition of an solution containing an oxidising agent, such as hypochlorite or hydrogen peroxide, has been proposed in EP-A-0 211 530. In the process of this reference, the solution is continuously passed through a fixed bed of catalyst comprising pieces of a non-porous inert material, such as alpha-alumina, supporting an intimate mixture of nickel oxide, and optionally cobalt oxide, and a minor amount of an oxide of a Group IlI element. The Group III oxide, e.g. alumina, in intimate mixture with the nickel oxide, promotes the activity of the nickel oxide for the decomposition of the oxidising agent. A similar process is disclosed in EP-A-0 276 044 where the catalyst is pieces of a non-porous inert material supporting an intimate mixture of nickel and Group IIA oxides. Those references also disclose that this procedure may be employed for the continuous decomposition of oxidisable materials such as organic pollutants in effluents by adding an aqueous solution of the oxidising agent to the effluent and then passing the mixture through the catalyst bed. The nickel oxide catalyses the decomposition of the oxidising agent, releasing oxygen which oxidises the oxidisable material.
We have found that where the catalysed decomposition of an oxidising agent using a fixed catalyst bed is employed to effect oxidation of oxidisable materials in aqueous media, a significant proportion of the available oxygen resulting from the decomposition of the oxidising agent is in fact released from the aqueous effluent as oxygen gas and so has not been utilised for oxidation of the oxidisable material. This represents a waste of oxidising agent. Furthermore, although the data quoted in the aforesaid EP-A-0 211 530 shows that a large proportion of the oxidisable material was removed from the aqueous medium, we have found that, where the oxidisable material is relatively volatile, it is probable t at a significant proportion of the oxidisable material is merely stripped from the aqueous medium by the evolved oxygen. Discharge of such evolved gas containing oxidisable materials is likewise undesirable. Hence it is desirable to minimise the amount of gas evolved, both from consideration of the economic aspects of wasting oxidising agent and from environmental considerations.
A convenient measure of the selectivity of the oxidation is the ratio of the amount of oxidising agent used for oxidation of the oxidisable material to the total amount of oxidising agent decomposed. In some cases the selectivity can be determined from measurement of the amount of oxidising agent decomposed and the amount of oxygen evolved from the aqueous medium. By analysis of the evolved gas, it is also possible to determine whether the oxidisable materials have simply been stripped from the aqueous medium into the gas phase. However, with catalysts of poor activity or of good selectivity, the rate of gas evolution may be too small to enable an accurate measurement to be obtained.
As mentioned above, the catalysts specified in the aforesaid EP-A-211 530 and EP-A-276 044 comprised an intimate mixture of nickel oxide (optionally plus cobalt oxide) and a minor amount of an oxide of a Gr
REFERENCES:
patent: 3944487 (1976-03-01), Davis et al.
patent: 4297333 (1981-10-01), Crawford et al.
patent: 4764286 (1988-08-01), Bon et al.
Imperial Chemical Industries plc
Morrison Betsey J.
Woo Jay H.
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