Organic compounds -- part of the class 532-570 series – Organic compounds – Oxygen containing
Reexamination Certificate
2002-02-07
2003-01-14
Parsa, Jafar (Department: 1621)
Organic compounds -- part of the class 532-570 series
Organic compounds
Oxygen containing
C568S927000, C568S939000, C568S940000
Reexamination Certificate
active
06506948
ABSTRACT:
BACKGROUND OF THE INVENTION
Nitroaromatic compositions have been widely used as intermediates in the chemical industry and are well suited for producing a variety of industrial chemicals such as aromatic amines. Nitration of aromatic hydrocarbons is effected commercially by the mixed acid method wherein the aromatic compound is contacted with a concentrated mixture of sulfuric acid and nitric acid. Subsequent to nitration an organic layer containing the desired nitration product and an aqueous spent acid layer is formed. These layers are separated and the nitroaromatic product recovered.
A major problem in the industry associated with the production of dinitrotoluene (DNT) is that of wastewater and wash water treatment. Prior to discharge these wastewater and wash water streams generated from multiple water and aqueous acid wash steps and from water of reaction require removal of the byproducts, such as, picric acid, nitrocresols, nitrophenols, as well as acids and so forth. The removal problem is significantly more severe with dinitration processes than with mononitration processes.
Representative patents which pertain to the nitration of aromatic compounds, including the nitration of toluene and the treatment of wash water streams generated in these processes are as follows:
U.S. Pat. No. 4,642,396 discloses a process for recovering nitric acid from the nitration medium which contains unreacted aromatic compound, nitroaromatic dissolved in nitric acid and water. The process involves treating the spent acid containing nitric acid with nitric oxide under conditions for generating nitrogen dioxide and water. The nitrogen dioxide is removed from the reaction medium as a gas. It is subsequently oxidized to nitric acid. The nitroaromatic compound is forced into the organic layer because of the reduced concentration of nitric acid and recovered therefrom.
U.S. Pat. No. 4,241,229 discloses a process for the recovery of nitroaromatic compounds from wastewater and wash waters in a mixed acid nitration process. In the nitration of benzene, it had been common practice to strip the wash liquors with steam. Steam stripping was deemed costly in terms of equipment and energy. The patentees suggested contacting the wash liquor with the aromatic compound being nitrated and recycling the resulting solution to the nitration reaction.
U.S. Pat. No. 4,257,986 discloses a process for the manufacture of dinitrotoluene by the mixed acid technique. The improvement in the process resides in contacting the spent acid with feed aromatic compound to remove contaminant organics and residual nitric acid. There is also disclosed an extraction process wherein denitrated acid is contacted with crude dinitrotoluene to remove substantially all of the residual nitric acid dissolved in the dinitrotoluene. Residual toluene is removed by air sparging or solvent extraction with butane.
BRIEF SUMMARY OF THE INVENTION
This invention relates to a multi-step process for the removal of nitrotoluenes from the wastewaters and wash waters generated in the mixed acid dinitration of toluene. In the basic process for the production of dinitrotoluene, toluene is contacted with a mixture of nitric and sulfuric acid under conditions for effecting dinitration. Generally, three wastewater and wash water streams contaminated with residual levels of mononitrotoluene, dinitrotoluene and organic byproducts are generated. One wastewater stream is generated from the steam stripping of nitric acid and organics from spent acid, the distillate, and, herein, referred to as “weak acid wastewater”; another stream is generated from washing the dinitrotoluene reaction product, herein referred to as “acid wash water”; and one stream results from alkaline washing of the dinitrotoluene reaction product, herein referred to as “alkaline wash water”. The improvement for effecting recovery of dinitrotoluene from the wastewater and wash water streams and effecting a purification of the wash water streams for subsequent disposal comprises the steps:
(a) initially extracting the residual levels of mononitrotoluene, dinitrotoluene and organic byproducts from at least one of the weak acid wastewater stream and acid wash water streams by contacting at least one stream with toluene and thereby generating an organic phase and an aqueous phase;
(b) separating the thus formed organic phase from the aqueous phase;
(c) extracting residual levels of mononitrotoluene, dinitrotoluene and organic byproducts from the alkaline wash water stream by contacting said stream with the organic phase generated in step (a) and thereby generating a toluene/dinitrotoluene organic layer and an extracted alkaline wash water fraction; and,
(d) separating the toluene/dinitrotoluene organic layer from the extracted alkaline wash water fraction.
There are advantages that may be obtained by the process depending upon which embodiments are employed; they include:
an ability to extract 99+% of the dinitrotoluene and mononitrotoluene in two or three extraction stages and isolate most of the impurities in a single stream so that they can be efficiently destroyed chemically, physically or biologically without the complicating factor of having large amounts of dinitrotoluene interfere with the destruction process; and,
an ability to recover virtually all of the dinitrotoluene that was formerly wasted or destroyed.
REFERENCES:
patent: 4241229 (1980-12-01), Alexanderson
patent: 4257986 (1981-03-01), Milligan et al.
patent: 4597875 (1986-07-01), Carr et al.
patent: 4642396 (1987-02-01), Carr et al.
patent: 4650912 (1987-03-01), Pohl et al.
Air Products and Chemicals Inc.
Bongiorno Mary E.
Parsa Jafar
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