Liquid purification or separation – Processes – Chemical treatment
Reexamination Certificate
1996-02-20
2001-06-12
Hruskoci, Peter A. (Department: 1724)
Liquid purification or separation
Processes
Chemical treatment
C210S903000, C210S909000
Reexamination Certificate
active
06245242
ABSTRACT:
The present invention relates to the ozone treatment of waste waters from the production of nitro-benzene from benzene and nitrating acid.
The literature discloses very many studies concerned with the degradation of organic compounds by ozone. These studies concentrate in the main on the kinetics and the decomposition products.
A large number of papers are further concerned with the pretreatment of tap and process water. The usual aim here is to kill off the pathogens, whether they are viruses, bacteria or other single-cell organisms.
Another extensive field concerns the treatment of industrially contaminated wastewater. A treatment with ozone is applied here in particular if there is insufficiently biodegradable or non-biodegradable matter in the water. This method of prior partial ozonolysis thus degrades organic compounds to a state where they are vulnerable to attack by bacteria (E. Gilbert, Water Res., 21 (10) 1273-8; D. R. Medley, J. Water Pollut. Control Fed., 55 (5) 489-94).
If, then, the wastewater contains nitrophenols, the combined application of various treatment methods such as coagulation, sedimentation, ozonation and adsorption on activated carbon is recommended (M. A. Shevchenko, Khim., Tekhnol. Vody, 8 (6), 7-10).
We have found, surprisingly, that waste waters from nitrobenzene production by nitration of benzene which contain various aromatic compounds but in the main 2,4-dinitrophenol can be cleaned up by the treatment with ozone alone at from 20 to 100° C., preferably at from 20 to 60° C., at from 1.5 to 10 bar absolute, preferably at from 1.5 to 5 bar absolute, and at a pH of from 3-12, essentially at pH 7-9, to such an extent that the levels of the original contaminants are reduced to below their limits of detection.
At the start of the oxidation the solution to be oxidized is in general at pH 12. In the course of the ozonation the pH decreases, but it should not drop below pH 4.5 as long as significant amounts of nondegraded dinitriphenol are still present, since otherwise the dinitrophenol is precipitated. The preferred pH range is from 7 to 9.
The reaction pressure is advantageously adjusted to 1.5-10, preferably 1.8-5, bar. This is because of the elevated reaction temperature at which ozone is only very slightly soluble, if at all. It is therefore advisable to aim at least for a certain increase in the solubility. Furthermore, the ozone yield of the ozone generators increases under superatmospheric pressure. It is therefore fore advisable also to maintain this pressure in the reactor. For reasons of apparatus construction, however, the pressure is usually limited to an upper value of 10 bar.
The ozone-containing gas must usefully be dispersed very finely and intensively in order to compensate for the low solubility of the ozone. The method used to obtain the very fine dispersion of the gas may make use of any desired aid, for example finely dispersing stirrers, ultrasonics, gas frits or customary injectors.
To carry out the process in a continuous manner, it is preferable to employ a cascade of reactors connected in countercurrent. This ensures that removal of ozone from the gas stream is so complete that it is usually possible to dispense with a residual ozone destruction stage.
The ozone content of the fresh gas should be as high as possible on account of the low solubility of ozone in water at elevated temperature. Levels of from 40 to 100 g of ozone per cubic meter of fresh gas have been found to be still easy to prepare on an industrial scale. By employing specific enrichment methods, for example an adsorption-desorption technique, it is also possible to obtain still higher ozone concentrations.
The process according to the present invention is used in particular for treating the wastewater from a nitrobenzene production plant. Since, however, nitrobenzene is also used for extracting residual amounts of aniline from the wastewater of the process for producing aniline from nitrobenzene, and the resulting waste waters can be subjected together to the ozone treatment, the water which is to be treated may also contain aniline, which is likewise degraded by ozone. Only inorganic compounds are produced according to the process of this invention.
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Chemical Abstracts(I) 102:172028 (1985).
Chemical Abstracts(II) 108:26755 (1988).
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Schuster Ludwig
Stechl Hanns-Helge
Wolff Dietrich
BASF - Aktiengesellschaft
Hruskoci Peter A.
Keil & Weinkauf
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