Liquid purification or separation – Processes – Chemical treatment
Reexamination Certificate
2000-06-02
2001-12-04
Hoey, Betsey Morrison (Department: 1724)
Liquid purification or separation
Processes
Chemical treatment
C210S763000
Reexamination Certificate
active
06325946
ABSTRACT:
INTRODUCTION AND BACKGROUND OF THE INVENTION
The present invention relates to a process for treating waste water.
A wide variety of processes and combinations of processes are used for treating waste water such as, for example, chemico-physical methods such as precipitation and flocculation, or adsorptive processes, for example using active carbon, or the removal of harmful substances by biodegradation or oxidation of harmful substances by different methods.
The oxidative treatment of waste water with oxygen-containing gases, using titanium, silicon or zirconium-containing mixed catalysts at high temperatures and under pressure is known (EP 0 257 983 A).
In order to be able to perform waste water treatment under ambient conditions, compounds which form hydroxyl radicals, for example hydrogen peroxide, are used in many cases for the oxidation of harmful substances. Frequently, however, hydrogen peroxide alone is not reactive enough. It has to be activated in an appropriate manner.
UV light may be used, for example, for activation purposes. UV light causes amplified production of hydroxyl radicals from hydrogen peroxide. This hydroxyl radical production is also catalyzed by dissolved iron salts. The combination of hydrogen peroxide and dissolved iron(II) salts is called Fenton's reagent (O. Specht, I. Wurdack, D. Wabner “Mehrstufige Pilotanlage zur oxidativen Abwasserbehandlung nach dem Fenton-Verfahren (H
2
O
2
/Fe-Katalysator), Chemie Ingenieur Technik 9/1995).
However, the use of Fenton's reagent has serious disadvantages (I. Wurdack, C. Höfl, G. Sigl, O. Specht, D. Wabner “Oxidativer Abbau von AOX und CSB in realen Abwässern: Vergleich verschiedener “Advanced Oxidation Processes”, 3rd GVC conference “Verfahrenstechnik der Abwasser- und Schlammbehandlung”, VDI-Verlag 1996): The reaction proceeds only at a very acid pH values between 2 and 3. Thus, the waste water has to be initially acidified, and then neutralized again after oxidation with Fenton's reagent, before it can be passed into a sewage treatment plant or receiving waters. This results in considerable salting out of the waste water and the production of considerable amounts of a sparingly soluble iron hydroxide precipitate which has to be removed. In addition, there is a high, non-specific, consumption of H
2
O
2
during this reaction.
It is accordingly an object of the invention was to get round the disadvantages of Fenton's reagent mentioned above. Salting out of the waste water should be avoided and the non-specific consumption of H
2
O
2
should be restricted as far as possible.
SUMMARY OF THE INVENTION
The above and other objects of the invention can be achieved by a process for treating waste water which is characterized in that the waste water is treated with hydroxyl radical producers, such as for example hydrogen peroxide, in the presence of titanium-containing silicates as catalyst.
In one embodiment of the invention, metal silicates are used as catalyst.
Furthermore, a titanium-containing metal silicate selected from the group consisting of titanium silicalite TS1, titanium silicalite TS2, titanium-containing ZSM5, titanium-containing DAY, titanium-containing beta-zeolite and mixtures thereof may be used as catalyst.
Crystalline metal silicates with regular micropores or mesopores are sometimes very effective catalysts for the synthesis of various products. In particular, microporous products with the general composition represented by the formula (SiO
2
)1−x(TiO
2
)x, in which titanium atoms replace some of the silicon atoms in the crystal lattice, have gained industrial importance as oxidation catalysts. Here, titanium silicalite-1 (U.S. Pat. No. 4,410,501 incorporated herein by reference) and titanium silicalite-2 (J.S. Reddy, S. Sivasanker, P. Ratnasamy, J. Mol. Catal. 71 (1992) 373) may be mentioned in particular. Thus, for example, the reaction of olefins with hydrogen peroxide to give epoxides (EP 100 119), the reaction of aromatic compounds with hydrogen peroxide to give hydroxyaromatic compounds (DE 31 35 559), the reaction of aliphatic hydrocarbons with hydrogen peroxide to give alcohols and ketones (EP 376 453) and the reaction of cyclohexanone with hydrogen peroxide and ammonia to give cyclohexanone oxime (EP 208 311) are known.
According to the invention, microporous or mesoporous, titanium-containing metal silicates, in particular titanium silicalite-1, may be used as a catalyst in the presence of hydroxyl radical producers, e.g. hydrogen peroxide, for the oxidation of constituents of waste waters under mild reaction conditions, e.g. at neutral pH and room temperature.
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Abbau von Schadstoffen in Problem-wässern durch katalytische Oxidation, Jörg Hofmann, Heiko Tauchnitz und Heike Vanselow, pp. 399-401.
Heterogene Katalyse fü die Vorbehandlung von Abwassern, Nikolaus Gschwind.
Versuche zur hemmenden Wirkung der mikrobiellen Nitrifikation durch Test-substanzen un Testsubstanzgemische, Regina Walter, Ines Rensch, Markus Wegewitz, pp. 43 and 124.
Abwasser, Oxidativer Abbau von AOX und CSB in realen Abwässern: Vergleich verschiedener, “Advanced Oxidation Processes”, pp. 85-85.
Mehrstufige Pilotanlage zur oxidativen Abwasserbehandlung nach dem Fenton-Verfahren (H2O2/Fe-Katalysator), Chemie Ingenieur Technik 9195, pp. 1089-1090.
Finkeldei Caspar-Heinrich
Hasenzahl Steffen
Preuss Andrea
Woyciechowski Matthias
Degussa - AG
Hoey Betsey Morrison
Smith , Gambrell & Russell, LLP
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