Liquid purification or separation – Processes – Chemical treatment
Patent
1994-12-19
1996-04-16
Hruskoci, Peter A.
Liquid purification or separation
Processes
Chemical treatment
210903, 423628, 502 8, 502325, 502331, 502339, C02F 170
Patent
active
055079563
DESCRIPTION:
BRIEF SUMMARY
The invention relates to an abrasion-resistant carrier catalyst for removing nitrite and/or nitrate from correspondingly polluted water and to its use for removing the oxygen, nitrite or nitrate content in water.
In recent years, the nitrite and/or nitrate contents found in the ground water and the surface water in the Federal Republic of Germany have risen considerably. They fluctuate considerably according to the location and may partially exceed the tolerable maximum limits. In the newest guidelines of the European Community, a permissible limit value of 50 mg nitrate per liter is recommended for drinking water and a limit value of 0.1 mg/l is recommended as a limit value for nitrite. The rising nitrite and nitrate contents in many ground and surface waters increasingly require methods for the removal of nitrite and nitrate within the scope of the treatment of drinking water.
In order to remove nitrite and nitrate from drinking water, biological methods and physical/chemical measures from the realm of desalinization of water may be used. Known disadvantages of these methods are the possible contamination by bacteria or their metabolic products or the mere shifting of the problem.
The removal of oxygen from water (which may also be free of nitrite or nitrate) is desirable in many cases. Thus, it is known that oxygen in water promotes the corrosion of metallic components, such as cooling systems. In food production, for example, in the production of beverages, such as fruit juices or alcoholic beverages, a low-oxygen or oxygen-rich water is preferably used.
European Patent Document EP-A-0 359 074 (U.S. Pat. No. 4,990,266) describes a catalytically operating method for removing nitrite and/or nitrate from nitrite- and/or nitrate-laden water while selectively forming nitrogen. A carrier catalyst is used which is formed of a porous carrier impregnated by a metal component composed of palladium and/or rhodium or of palladium and a metal of the copper group. This carrier has a bimodal pore radius distribution with an at least 30% proportion, relative to the total pore volume, of macropores having a minimum radius of 200 nm (2,000) .ANG. and/or an inhomogeneous distribution of the metal component with a concentration in the surface region, or it is present as a powder.
It is an object of the present invention to provide a particularly abrasion-resistant carrier catalyst which permits the selective conversion of nitrite and/or nitrate to nitrogen. This object is achieved by means of the carrier catalyst recited in the claims.
It is another object of the present invention to provide an improved catalytically operating process for removing oxygen, nitrite and/or nitrate from water. In particular, it is an object of the invention to develop an improved catalytic process which can be carried out under the conditions which normally exist during the treatment of water and in which the oxygen, nitrite and/or nitrate content is removed while harmless products are formed, particularly water and nitrogen, without in the process polluting the water with undesirable amounts of ammonium.
The carrier catalyst according to the invention which is suitable for the removal of the nitrite and/or nitrate content of nitrite- and/or nitrate-laden water while selectively forming nitrogen comprises a porous inorganic carrier material impregnated with a metal component and is characterized in that the carrier is composed of aluminum oxide of the "theta" and "kappa" modifications, the "alpha" modification being present in a proportion of less than 10% by weight, relative to the weight of the carrier, and the carrier being free of aluminum oxide of the "gamma" and "delta" modifications and has either one maximum (monomodal pore distribution) of the pore diameter in the range of from 70 to 150 nm (700 to 1,500 .ANG.) or two maxima (bimodal pore distribution) of a pore diameter in the range of from 10 to 150 nm (100 to 1,500 .ANG.), the median pore diameter being between 30 and 50 nm (300 and 500 .ANG.).
The specific surface calculated acco
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Bischoff Michael
Bonse Dirk
Bretz Karl-Heinz
Derleth Helmut
Sell Michael
Hruskoci Peter A.
Solvay Unweltchemie GmbH
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