Organic compounds -- part of the class 532-570 series – Organic compounds – Amino nitrogen containing
Reexamination Certificate
2000-02-23
2001-06-05
Vollano, Jean F. (Department: 1621)
Organic compounds -- part of the class 532-570 series
Organic compounds
Amino nitrogen containing
C564S439000
Reexamination Certificate
active
06242650
ABSTRACT:
The subject of the present invention is a process for the decoloration of aqueous effluents more particularly comprising aromatic amines.
Aromatic amines or polyamines are conventionally synthesized from the corresponding mononitro or polynitro aromatic derivatives by the use of a hydrogenation reaction. Such a type of process is commonly employed to prepare, among other compounds, aniline from mononitrobenzene the various isomers of toluidine from the isomers of mononitrotoluene or alternatively the various isomers of toluenediamine from the isomers of dinitrotoluene.
The hydrogenation reaction is accompanied by the production of large amounts of water, which it is necessary to separate from the amines synthesized before the latter are employed in subsequent conversion reactions. Such a scenario is found, for example, in the synthesis of toluene diisocyanates from toluenediamine.
The separation of water and the amines prepared takes place according to known methods, such as distillation, mainly
The water recovered is coloured, or alternatively becomes coloured, because it contains more or less high amounts of amines. This is because aromatic amines, under the effect mainly of light and/or of atmospheric oxygen, oxidize to give conjugated polyaromatic compounds comprising, inter alia, azo functional groups. In some cases, there may even be the appearance of a precipitate in the water.
It is clear that such effluents cannot be discharged directly and must consequently form the subject of a pretreatment targeted at removing the amines and this coloration which they induce.
Various solutions have been provided, mainly with the aim of decolouring this water. Thus, mention may be made of processes in which amines present in aqueous effluents are oxidized. For example, treatments based on bleach, aqueous hydrogen peroxide solution or ozone, or those involving a concentrated sulfuric acid
itric acid mixture or alternatively persulfate, are known. Processes are also known which employ physicochemical techniques, such as, for example, adsorption on resins, biological techniques, such as the use of enzymes, alone or in combination with chemical compounds, such as aqueous hydrogen peroxide solution, or which alternatively involve chemical treatments, such as the blocking of amines with aldehyde functional groups. Finally, it is possible to use methods of purification by an electrochemical route. These techniques, while their advantage is not questioned here, however exhibit various disadvantages. This is because some of the techniques provided are difficult to employ on an industrial scale and sometimes require the commitment and continuation of relatively large investments. This is the case, for example, when enzymes are used as treatment agent. The known means can also employ compounds which are rather unfavourable to the environment, as such or as a result of the products of which they are the source; compounds or products which have to be removed subsequently, for this reason requiring an additional stage.
Finally, these products are not always desired for reasons of industrial hygiene and safety.
The first objective of the present invention is thus to provide a method for decolouring aqueous effluents comprising aromatic amines which is simple to employ and inexpensive.
Another objective of the invention is to make available a very efficient process which would make it possible both to decolour water comprising aromatic amines and also to block the mechanism of coloration of this water.
These aims and others are achieved by the present invention, the subject of which is a process for the decoloration of an aqueous effluent comprising aromatic amines and/or their derivatives in which the said aqueous effluent is brought into contact with an agent chosen from alkali metal or alkaline earth metal sulfite, alkali metal or alkaline earth metal hydrogensulfite, or their mixtures.
As may be observed, the process according to the invention is very simple to employ. This is because the operation of bringing the agent into contact with the effluents to be treated is efficient and does not require restrictive conditions of employment, in particular as regards safety.
Moreover, the process according to the invention does not require the commitment of very large investments because it is sufficient to have available a vessel in which the abovementioned agent can be brought into contact with water.
In addition, it is pointed out that neither the sulfite nor the hydrogensulfite are the source of products which are harmful to the environment. On the one hand, the amounts employed are not very high and, on the other hand, the resulting products are essentially sulfates, which are not regarded as priority pollutants.
Moreover, and this constitutes a: additional advantage, the water treated according to the process of the present invention does not experience a substantial increase in its COD (Chemical Oxygen Demand). For this reason, it is not necessary, a priori, to combine the process according to the invention with an additional stage in which the COD of the effluents would be decreased.
However, other characteristics and advantages of the present invention will become more clearly apparent on reading the description and examples which will follow.
As was indicated previously, the present invention is intended to treat aqueous effluents comprising aromatic amines and/or their derivatives.
Aromatic mines is understood to mean aromatic mono- or polyamines comprising at least one C
6
-C
14
aromatic unit. The aromatic nucleus is preferably C
6
-C
10
. The said aromatic nucleus may or may not be substituted by one or more saturated or unsaturated, linear, cyclic or branched, C
1
-C
10
hydrocarbon radicals.
More specifically, the abovementioned hydrocarbon radicals optionally substituting the said aromatic units can be chosen from C
1
-C
10
, preferably C
1
-C
6
, alkyl, aryl, alkylaryl and arylalkyl radicals.
According to a preferred embodiment of the invention, the said amines are primary amines.
Mention may be made, as suitable mono- or polyfunctional amines, of those comprising a benzene or naphthalene nucleus substituted or not by one or more methyl, ethyl, propyl, butyl, pentyl or hexyl radicals and/or their isomers.
The process according to the invention can preferably be employed to treat aqueous effluents comprising at least one of the following amines: aniline, one or more of the isomers of toluidine, one or more of the isomers of toluenediamine, one or more of the isomers of xylylenediamine or one or more of the isomers of phenylenediamine.
It should be noted that the water treated according to the process of the invention is advantageously that recovered from the synthesis of the amines mentioned above.
However, of course, the present invention is not limited to this type of effluent. Thus, it can likewise be applied in the treatment of aqueous effluents comprising such amines, independently of their preparation.
Derivatives of aromatic amines is understood to denote the oxidation products of the aromatic amines defined previously. Thus, the treated effluents can comprise, optionally as a mixture with the abovementioned amines, oligomers obtained by oxidation of the latter. In this case, the derivatives can comprise primary, secondary or tertiary amine functional groups, alone or as a mixture. Moreover, the said derivatives can comprise other functional groups of the azo, imine or azoxy type, without, however, being limited to these examples.
The amount of amines present in the aqueous effluents to be treated depends on the source of the effluents, in other words on the conditions under which they were obtained. Thus, the amine content can be a function in particular of the operating conditions of the process or of the duration of storage of these effluents.
The process according to the invention can also be particularly appropriate for the treatment of discharge peaks, that is to say for the treatment of effluents comprising, in an unusual way, high amounts of amines. This is in particu
Coudret Jean-Luc
Marion Philippe
Rhodia Chimie
Seugnet Jean-Louis
Vollano Jean F.
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