Liquid purification or separation – Processes – Chemical treatment
Patent
1997-03-07
1998-07-14
Hruskoci, Peter A.
Liquid purification or separation
Processes
Chemical treatment
210763, C02F 170
Patent
active
057799156
DESCRIPTION:
BRIEF SUMMARY
DESCRIPTION
The invention relates to a method for removing substances from water, especially compounds and by-products of oxidative treatment of water.
The known methods of water treatment are often multi-step processes wherein, for example, thermal-alkaline, oxidative, biological or adsorptive treatments can be combined in various ways.
It is known that surface waters can be used for obtaining potable water, for example by bank filtration. For hygienic reasons, and to satisfy the limits specified in the Potable Water Ordinance, the microorganisms and organic substances must be removed in particular.
Likewise, physical processes, such as membrane separation methods or filtering methods are known and are being employed.
In oxidative water treatment, e.g., by disinfection with chlorine, hypochlorite, chlorine dioxide and ozone, in the presence of oxidizable substances, by-products are also formed, e.g., halogen-oxygen compounds such as chlorine-oxygen compounds, or bromates, or halogenated hydrocarbons such as trihalogen methane, which have to be removed, so that the water can be used to supply potable water, or can be discharged as treated water, for example into a main ditch, or supplied as potable water into the production process.
In oxidative treatment, with ozone for example, a halide such as chloride or bromide, is oxidized by the following mechanism:
This reaction is dependent upon pH, upon the amount of oxidant, and also upon time.
Since bromate ions have a provable carcinogenic activity, they have to be removed from the water. The World Health Organization (WHO) requires that the bromate content in potable water not exceed 25 .mu.g/l, and a limit of 3 .mu.g/l is anticipated for the future.
Since chlorate ions are undesirable in drinking water, they have to be removed from the water. Even in the case of disinfection with chlorine dioxide undesirable by-products are formed, which are proven to cause hemolytic anemias and thus should not be contained in potable water.
But even from waters which are not to be used as drinking water, these substances have to be removed since their oxidation potential can be undesirable in many cases.
The object of the invention is to provide a method for water treatment wherein halogen-oxygen compounds can be removed economically or their residual concentrations can be minimized. Halogen-oxygen compounds in the sense of the invention are chlorate and bromate compounds.
According to the invention these compounds are reduced with hydrogen on a supported precious metal catalyst.
The reductive decomposition of bromate takes place according to the following equation: ##STR1##
The reductive decomposition of chlorate takes place according to the following equation: ##STR2##
Precious metal catalysts which contain as an active metal substance, metals of the eighth subgroup of the periodic table of the elements, e.g., platinum, palladium, iridium, rhodium, preferably palladium or a combination of palladium with a metal of the copper group, preferably copper or silver, especially copper, are used as catalysts.
In a preferred embodiment of the invention, supported palladium/copper or palladium catalysts are used.
Inorganic oxides, e.g., Al.sub.2 O.sub.3, preferably .gamma.-Al.sub.2 O.sub.3, SiO.sub.2, ZrO.sub.2, MgO or TiO.sub.2, are used as support materials. Combinations of these or other support materials, such as alumosilicates, magnesium alumosilicates or active carbon, are also suitable. Preferably inorganic materials are used which are resistant to water and abrasion.
According to the invention, hydrogen gas is charged into the water to be treated, and the water charged with hydrogen is contacted with the catalyst.
In a preferred variant, a catalyst is used which contains as metal component preferably palladium and/or rhodium or palladium and a metal of the copper group, especially copper. The catalyst support material is impregnated with the metal component in a known manner.
For example, an impregnated support can be used which has an inhomogenous distribution of the meta
REFERENCES:
patent: 4397720 (1983-08-01), Moore et al.
patent: 4990266 (1991-02-01), Vorlop et al.
patent: 5279717 (1994-01-01), Okajima et al.
patent: 5392428 (1995-02-01), Dilla et a l.
Becker Arne
Koch Veronika
Neuenfeldt Gerhard
Schindler Hubert
Sell Michael
Hruskoci Peter A.
Solvay Umweltchemie GmbH
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