Organic compounds -- part of the class 532-570 series – Organic compounds – Oxygen containing
Reexamination Certificate
2002-02-19
2003-07-01
Parsa, J. (Department: 1621)
Organic compounds -- part of the class 532-570 series
Organic compounds
Oxygen containing
C568S936000
Reexamination Certificate
active
06586645
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a continuous adiabatic process for preparing nitrochlorobenzene, in which the waste sulfuric acid produced during the practice of the process is reconcentrated and recycled into the nitration reaction.
Nitrochlorobenzenes are important intermediates in the preparation of dyes, pharmaceutics, and pesticides. There is a particularly high demand for ortho-nitrochlorobenzene, which is obtained in the nitration of chlorobenzene to about 35%. Para-nitrochlorobenzene, too, has a number of industrial uses. Substantially undesired is the production of meta-nitrochlorobenzene, which has only very limited industrial applications.
Industrially, nitrochlorobenzenes are prepared by nitration of chlorobenzene. For nitration, it is customary to use a mixture of sulfuric acid, nitric acid, and water. During the reaction, a significant amount of waste sulfuric acid contaminated with organic compounds is produced, requiring complicated and expensive work-up. To avoid the production of waste acid, processes comprising reconcentration of the sulfuric acid, in which most of the water and the organic compounds are removed from the sulfuric acid, which is then recirculated into the nitration reaction, have been developed. The reconcentration of the waste sulfuric acid succeeds in a particularly elegant manner when the nitration reaction is carried out under adiabatic conditions, since in this case there is no heat exchange with the environment and the energy released during the process can be used to reconcentrate the waste sulfuric acid. Moreover, in contrast to an isothermal process with dissipation of heat, it is possible to use materials of a better quality, which, under the reaction conditions, show considerably few signs of corrosion.
U.S. Pat. No. 4,453,027 claims an adiabatic nitration process for the preparation of mononitrohalogenobenzenes. The nitrating acid used contains 11.1% by weight of nitric acid, 68.5% by weight of sulfuric acid, and 20.4% of water. The temperature of the resulting waste sulfuric acid after the reaction is stated to be from 100 to 110° C. If the reaction is carried out adiabatically, at the nitric acid concentration mentioned above, the temperature increase during the reaction is about 100° C., so that the reaction must be started at from 0 to 10° C. and the reactants to be fed in must be available at this temperature. If 60% strength nitric acid is used, the resulting waste sulfuric acid is reconcentrated to 84.1%; if 98% strength nitric acid is used, this value is still 77.3% by weight. If the heat of the reaction is used for the reconcentration, the waste sulfuric acid cools to about 0° C. From a technical and an economical point of view, such a process no longer makes sense, since it requires the use of refrigerating brines and special apparatus.
U.S. Pat. No. 4,021,498 describes the adiabatic mononitration of aromatic compounds. It is emphasized that the reaction must be carried out with vigorous stirring to achieve complete conversion. Even in a tube reactor, a stirrer is required. However, it is not stated how vigorous the stirring must be to achieve complete conversion. This patent focuses on the adiabatic mononitration of benzene, since all examples refer to this reaction. Details of the adiabatic mononitration of halogenated aromatic compounds in general and chlorobenzene in particular are not given.
EP 779,270 A describes a process for preparing mononitroaromatic compounds using reactors having a large number of special internals that are arranged in such a manner that adjacent internals are located virtually perpendicular to each other. This process has the disadvantage that it requires the use of reactors designed especially for this process, the purchase of these reactors being a costly investment.
EP 675,104 A describes an adiabatic process for nitrating halogenobenzenes in which the reactants are mixed while applying a certain mixing energy, mixing being carried out in a temperature range of from 60 to 160° C. Using the temperatures mentioned, it is possible to obtain the high reaction rate required for adiabatic operation. However, this process has the disadvantage that relatively high amounts of undesirable meta-nitrochlorobenzene are obtained, the removal of which is complicated and costly.
Accordingly, there was a need for a process for the continuous preparation of nitrochlorobenzene, which process is carried out under adiabatic conditions and at the same time affords relatively low amounts of meta-nitrochlorobenzene.
SUMMARY OF THE INVENTION
Surprisingly, we have found a process for the continuous preparation of nitrochlorobenzene comprising reacting chlorobenzene with sulfuric acid, nitric acid, and water, wherein
(a) the feedstocks chlorobenzene, sulfuric acid, nitric acid, and water are introduced simultaneously or successively into a reactor equipped with mixing elements and are mixed at an average mixing power density of 1.5 to 40 watt/liter and at a reaction mixture temperature during initial mixing of 10 to 50° C.,
(b) the content of sulfuric acid in the reaction mixture during mixing, based on the sum of sulfuric acid, nitric acid, and water, is 70 to 80% by weight,
(c) the reaction proceeds under adiabatic conditions,
(d) at the reactor outlet, the crude nitrochlorobenzene is separated from the waste sulfuric acid, and
(e) the waste sulfuric acid is reconcentrated to the original content of sulfuric acid and recycled into the nitration reaction.
DETAILED DESCRIPTION OF THE INVENTION
The feedstocks used in the process according to the invention are chlorobenzene, sulfuric acid, nitric acid and water, where the chlorobenzene may contain nitrochlorobenzene. The amount of nitrochlorobenzene is generally 0 to 20% by weight. Here, water can be used as such or else introduced into the reaction as dilution water of the nitric acid and/or the sulfuric acid. Preferably, water is introduced into the reaction as dilution water of the nitric acid and/or the sulfuric acid.
In the process according to the invention, the feedstocks chloro-benzene, sulfuric acid, nitric acid, and water are introduced individually or as mixtures into a reactor equipped with mixing elements. The feedstocks can be introduced into the reactor simultaneously or successively. Introduction into the reactor can be carried out, for example, by adding chlorobenzene and nitric acid and, if appropriate, water as separate strains simultaneously or successively to the reconcentrated recycled sulfuric acid, it being possible for the nitric acid to be diluted by water and/or sulfuric acid. It is also possible to pre-mix chlorobenzene with water and sulfuric acid and to introduce the resulting mixture as a separate stream into the reactor. In the reactor, mixing with nitric acid, which may be mixed with sulfuric acid and/or water, takes place. It is furthermore possible to introduce chlorobenzene and a nitrating acid prepared by mixing sulfuric acid, nitric acid, and water in separate streams into the reactor. In a preferred embodiment of the process according to the invention, nitric acid and reconcentrated recycled sulfuric acid are mixed to give a nitrating acid, and nitrating acid and chlorobenzene are introduced into the reactor in separate streams. For the reaction to succeed, it is of minor importance in which order and composition the reactants are introduced into the reactor, as long as the reaction mixture obtained once all reactants have been mixed has the composition according to the invention and mixing takes place at the intensity according to the invention and at the temperature according to the invention.
At the time of mixing, the content of sulfuric acid in the reaction mixture, based on the sum of sulfuric acid, nitric acid, and water, is 56.5 to 84.5% by weight, preferably 67.1 to 80.9% by weight, particularly preferably 69.5 to 78.6% by weight.
The content of nitric acid at the time of mixing, based on the sum of nitric acid, sulfuric acid, and water, is 3 to 10% by weight, preferably 4 to 8% by weight,
Demuth Ralf
König Bernd-Michael
Leiberich Ricarda
Linn Thomas
Raatz Hans-Joachim
Akorli Godfried R.
Bayer Aktiengesellschaft
Eyl Diderico van
Parsa J.
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