Process for cleaning up wastewaters from the hock process

Details Process for cleaning up wastewaters from the hock process Process for cleaning up wastewaters from the hock process

1999-08-19

2001-10-09

Hoey, Betsey Morrison (Department: 1724)

Liquid purification or separation

Processes

Chemical treatment

C210S761000, C210S909000, C210S919000

Reexamination Certificate

active

06299783

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a process for cleaning up wastewaters by wet oxidation, where the wastewaters are produced in the preparation of hydroxyl and carbonyl compounds by the Hock process. In particular, the invention relates to a process for cleaning up wastewaters by wet oxidation, which wastewaters are produced in the preparation of phenol and acetone by the Hock process.
2. Description of The Background
The simultaneous preparation of phenol and acetone by the Hock process is based on the oxidation of cumene to cumene hydroperoxide and the subsequent acid-catalyzed cleavage of the cumene hydroperoxide to form phenol and acetone. The catalyst in this reaction is preferably sulfuric acid. Depending on the process procedure, the production of phenol and acetone is accompanied by formation of a varying amount of byproduct. The different wastewater streams which are generally produced in the process, in particular due to various washing processes in the course of the workup of the cleavage product, are therefore generally contaminated with various organic and/or inorganic substances at varying concentrations. The same generally also applies to wastewaters from other Hock processes. These sometimes acidic, sometimes basic, wastewaters, generally require, either together or separately, a pretreatment to reduce the wastewater loading prior to introduction into a biological effluent treatment plant, in order not to overload the biological purification stage and to decrease the content of poorly biodegradable constituents. In particular, phenol-containing wastewaters, because of the toxicity of phenol, cannot be discharged into open bodies of water.
To clean up phenol-containing wastewaters from the Hock process, extractive processes using, e.g. cumene or acetophenone as extraction medium (e.g. DE 1 075 119 and DE 22 35 493), steam distillation processes and adsorption to surface-active substances, such as activated carbon or synthetic resin ion exchangers are known (cf. Ullmann's Encyclopedia G' Industrial Chemistry, 5th edition, Vol. A19, p. 308, VCH Verlagsgesellschaft, Weinheim, 1991). A residual phenol content is obtained which can be removed in a biological effluent treatment plant.
However, recently, still lower wastewater loadings than are achievable using these processes alone, which processes are orientated toward phenol, are increasingly being sought after. A wastewater loading as low as possible with respect to the entire spectrum of possible constituents is desired not least for environmental reasons. In addition, government regulations may impose increased costs for the treatment of wastewaters with high loading, which also stimulates the need for process which reduce wastewater loadings.
A generally known process of chemical wastewater treatment for improving the biodegradability of wastewater constituents and for reducing the wastewater loading is wet oxidation. Wet oxidation is a process in which, at elevated temperature and an elevated pressure to maintain the liquid phase, wastewater streams whose constituents are degraded too slowly in the course of the biological wastewater purification, or which can adversely affect this degradation, are worked up. The oxidizing agents used are preferably air or oxygen. In the ideal case, hydrocarbons for example, in the wet oxidation produce solely carbon dioxide and water. A gross differentiation is made between low-pressure (120° C., 6 bar) and high-pressure processes (320° C., 200 bar) (Römpp-Chemie-Lexikon [Römpp's Chemistry Lexicon], 9th edition, 1991). Although there is a general trend for higher temperatures to cause higher degradation rates in wet oxidation, the degradation rates achievable are always specific to a substance (see, for example, B. Perkow, Steiner. Vollmüller: Na&bgr;oxidation-Ein Beitrag zum Stand der Technik [Wet oxidation], Chem.-Ing.-Tech. 52 (1980), No. 12, p. 943 ff.). Therefore, various wet oxidation processes have been developed for specific applications, such as for wastewaters from the cyclic condensation of acetone (DE 44 28 413 A1) or for cyanide-containing wastewaters (e.g. DE 44 10 04 A1). The use of catalysts in wet oxidation to decrease the temperature required is also disclosed (e.g. DE 196 05 421 A1).
JP 1-310794 discloses a wet oxidation process preferably suitable for cleaning up wastewaters from the Hock process: the wastewaters containing organic substances are adjusted to a pH of from 1-3, preferably with sulfuric acid, nitric acid or hydrochloric acid, and then treated with an oxygen-containing gas at high temperatures and pressures in the liquid phase without a catalyst. Preferably, the treatment is carried out at from 175-200° C. and apparently superatmospheric pressures between approximately 3 and 6 bar, based on the vapor pressure, i.e. at pressures between approximately 12 and 22 bar absolute, for from 2-6 hours. The oxygen-containing gas can be pure oxygen or air for example.
However, the need remains for improved processes which overcome the disadvantages described above.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide an improved process for the wet oxidation of wastewaters which are produced in the preparation cf hydroxyl and carbonyl compounds from hydroperoxides via the Hock process.
It is another object of the invention to provide a process for reducing wastewater loading which may be practiced in a very simple manner on an industrial scale.
It is a particular object of the present invention to provide a process for reducing the loading of wastewaters that are by-products from the preparation of phenol and acetone by the Hock process.
The objects of the invention, and others, may be achieved with a process for cleaning up acidic or acidified wastewaters, which are produced in the preparation of hydroxyl and carbonyl compounds from hydroperoxides by the Hock process, by wet oxidation in the liquid phase using oxygen-containing gas, which comprises treating the wastewaters at pressures greater than 25 bar absolute and temperatures of from 150-250° C.
Various other objects, features and attendant advantages of the present invention will be more fully appreciated as the same becomes better understood from the following detailed description.
DETAILED DESCRIPTION OF THE INVENTION
Surprisingly, it has been found that, in comparison with the process described in JP 1-310794, simply by a moderate elevation of the pressure in the wet oxidation, a marked increase in the degradation rate, and thus reduction of the wastewater loading, can be achieved in the wastewaters treated according to the present invention. This is all the more surprising, since, usually, in particular a higher temperature, effects higher degradation rates and the pressure is only adjusted to maintain the liquid phase. In contrast to JP 1-310794, with the inventive process, acidification of the wastewaters to a pH of from 1-3 is not necessary for the wet oxidation. In fact, this pH range may even be undesirable, since the low pH makes the further wastewater treatment, i.e. downstream treatment, more complex. The moderate preferred reaction pressure between 30 and 50 bar absolute is, in contrast, very readily achievable technically and further requires, in contrast to the high-pressure wet oxidation, no corresponding high-pressure equipment.
The wastewaters to be treated according to the invention preferably originate from the Hock process for preparing phenol and acetone from cumene. Relatively large wastewater streams may be produced in this process, for example in the neutralization of the acidic cleavage product from the cumene hydroperoxide cleavage, which is generally catalyzed by sulfuric acid, usually with phenolate or alkali liquor and subsequent phase separation (cleavage product washing) or in the treatment of water from the decomposition of the phenolate liquor which originates from the cumene washing. On account of the byproduct formation during the process, the sometimes

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