Chemistry of inorganic compounds – Nitrogen or compound thereof – Binary compound
Reexamination Certificate
2001-04-05
2003-04-22
Langel, Wayne A. (Department: 1754)
Chemistry of inorganic compounds
Nitrogen or compound thereof
Binary compound
C564S249000
Reexamination Certificate
active
06551568
ABSTRACT:
The subject-matter of the present invention is a process for the preparation of azine and a process for the preparation of hydrazine employing it.
The synthesis of hydrazine from ammonia and hydrogen peroxide is described in Ullmann's Encyclopedia of Industrial Chemistry (1989), Vol. A 13, pages 182-183.
In a first stage, ammonia, hydrogen peroxide and a reactant carrying a carbonyl group are reacted in a reactor in order to form an azine, according to the reaction (I):
In this scheme, R
1
and R
2
, which are identical or different, represent a hydrogen atom or a C
1
-C
4
alkyl radical, provided that at least one of R
1
and R
2
is other than a hydrogen atom, or else R
1
and R
2
form, together with the carbon atom to which they are bonded, a C
3
-C
6
cycloalkyl radical.
This reaction is necessarily carried out in the presence of a catalyst (or activator) or of a mixture of catalysts included within a composition denoted as working solution. At the end of the reaction, the azine is separated from the working solution. The latter is then regenerated and then recycled in the reactor of Stage (I).
In a second stage, the azine is hydrolysed to hydrazine, according to the reaction (II):
the reactant carrying a carbonyl group is recovered and recycled in the reactor of Stage (I).
This process was disclosed in particular in U.S. Pat. Nos. 3,972,878 and 3,972,876.
The term “working solution” is therefore understood to mean any aqueous solution or suspension comprising a catalyst or a mixture of catalysts which is capable of converting a mixture of ammonia, of hydrogen peroxide and of a reactant carrying a carbonyl group to an azine.
This working solution is disclosed in Patents EP 399,866, EP 487,160 and EP 70,155. It is composed, for example, of an aqueous solution of acetamide and of ammonium acetate. The ammonium acetate is formed in the reactor, in particular by reaction of acetic acid with ammonia. The working solution can also be composed of an aqueous solution of cacodylic acid and of ammonium cacodylate.
Application EP 0,518,728 discloses a process for the synthesis of azine in which the working solution and more generally any stream entering the reactor for the synthesis of the azine are devoid of CO
2
. According to this application, the presence of CO
2
in the synthesis process generally results from undesirable reactions of the hydrogen peroxide with various organic impurities which are produced in certain stages of the process. The CO
2
thus formed reacts in its turn with the hydrogen peroxide, which results in an excessive consumption of H
2
O
2
and a fall in the yield of azine intermediate and thus of hydrazine.
To overcome this disadvantage, Application EP 0,518,728 discloses a process for the preparation of intermediate azine, in which
a) ammonia, hydrogen peroxide and a reactant carrying a carbonyl group are brought into contact in a reactor with a working solution, then
b) the azine thus formed is separated from the working solution, then
c) the working solution is regenerated by bringing it to a temperature of at least 130° C., so that the CO
2
and most of the water (formed during the reaction of Stage a) or contributed by the water of dilution of the hydrogen peroxide) are removed in the form of an aqueous stream, denoted C
1
in the continuation of the present text, which therefore comprises, in the dissolved state, in addition to the CO
2
(essentially present in the carbonate form), a certain amount of the ammonia and of the reactant carrying a carbonyl group employed in Stage a), then
d) the working solution, regenerated according to Stage c), is recycled in the reactor of Stage a).
The stream C
1
comprises a certain amount of ammonia and of reactant carrying a carbonyl group. However, it cannot be directly recycled in the reactor for the synthesis of the azine, specifically because of the presence of a significant amount of CO
2
. In order to economize on the significant amounts of reactants which can be used in the process, Application EP 0,518,728 therefore recommends complementing Stage d) of the said process by treating this stream C
1
so as to remove the CO
2
therefrom, in order to be able thus to recycle the ammonia and the reactant carrying a carbonyl group which it comprises in the reactor for the synthesis of azine. FIG.
1
/
3
represents a device suited to the implementation of this process. It is described in a detailed way later in the present text, in the appropriate part.
A process for the treatment of the stream C
1
appropriate for the removal of CO
2
, such as the removal mentioned in Stage d), is also disclosed by Application EP 0,518,728.
According to this process, the stream C
1
is first of all treated in a stripping column, the top stream of which is cooled in a condenser. The NH
3
is collected in the gaseous state, and the liquid phase obtained is separated, in a settling tank, into the organic phase, rich in reactant carrying a carbonyl group, and the aqueous phase.
The NH
3
and the organic phase thus obtained are recycled to the reactor for the synthesis of the azine.
The aqueous phase, which comprises all the CO
2
present in the stream C
1
, is fed to a 2nd distillation column, so as to collect:
at the column top, an aqueous stream devoid of CO
2
and comprising a certain amount of ammonia and of reactant carrying a carbonyl group, which is therefore recycled to the reactor for the synthesis of the azine,
at the column bottom, an aqueous stream, denoted C
2
in the continuation of the present text, which comprises virtually all the CO
2
present in C
1
and also small amounts of ammonia and of reactant carrying a carbonyl group.
FIG.
2
/
3
represents, as a reminder, the device taught by EP 518, 728 for the treatment of the stream C
1
.
Under the practical conditions of implementation of the process, the Stream C
2
generally comprises from 0.1 to 20% by weight of CO
2
(present in the form of carbonate in the dissolved state), from 1 to 15% of NH
3
and from 0.1 to 10% of reactant carrying a carbonyl group.
In the present text, except when otherwise indicated, the percentages shown for the components are percentages expressed by weight.
Application EP 0,518,728 gives no teaching relating to the treatment to be given to the Stream C
2
. According to this application, it cannot be recycled to the reactor for the synthesis of the azine, since it comprises CO
2
.
The removal of such a Stream C
2
might be envisaged by means of known techniques, such as incineration. However, this removal would necessarily be accompanied by releases to the atmosphere of a mixture of compounds of the NO or NO
2
type, resulting from the combustion of NH
3
. In point of fact, it is desirable to limit as far as possible the discharge to the atmosphere of such compounds. Furthermore, this removal would also involve the loss of small amounts of reactants which can be used in the process, namely ammonia and reactant carrying a carbonyl group, which loss is harmful to the economics of the process.
Application EP 0,518,728 suggests removing the CO
2
by washing with sodium hydroxide solution, in order to retain the CO
2
in the form of an aqueous sodium carbonate solution and to leave the ammonia, the reactant carrying a carbonyl group and water vapour in gaseous form.
A novel process for the preparation of the azine has now surprisingly been found which, in contrast to the teaching of Patent EP 0,518,728, involves an acid in the treatment of the Stream C
2
.
One aim of the invention is therefore to provide a process for the preparation of azine in which the discharges of effluents to the environment are reduced.
Another aim of the invention is to provide a process for the preparation of azine in which the losses of reactants of use in the reaction are reduced.
These aims can be achieved, in all or in part, by the process for the preparation of azine which is the subject-matter of the invention, which process is described hereinbelow.
The subject-matter of the invention is therefore, firstly, a process for the preparation of azine compri
Brenguer Georges
Jullin Rémi
Ricard Jean-Philippe
Atofina
Langel Wayne A.
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