Chemistry of inorganic compounds – Nitrogen or compound thereof – Binary compound
Reexamination Certificate
2000-10-31
2003-02-11
Langel, Wayne A. (Department: 1754)
Chemistry of inorganic compounds
Nitrogen or compound thereof
Binary compound
C568S383000
Reexamination Certificate
active
06517798
ABSTRACT:
The present invention relates to a process for the preparation of hydrazine hydrate. The present invention relates more specifically to an improved process for the manufacture of hydrazine hydrate from methyl ethyl ketone azine.
The industrial production of hydrazine hydrate is carried out according to the Raschig, Bayer or hydrogen peroxide processes.
In the Raschig process, ammonia is oxidized with a hypochlorite in order to obtain a dilute hydrazine hydrate solution, which subsequently has to be concentrated by distillation. This process is not very selective, has a low yield and is highly polluting, and is virtually no longer used.
The Bayer process is an alternative form of the Raschig process which consists in shifting a chemical equilibrium by trapping, using a ketone, the hydrazine formed in the azine form. The azine is subsequently isolated and then hydrolysed to hydrazine hydrate. The yields are improved but there is no improvement with respect to the discharges to the environment.
The hydrogen peroxide process consists in oxidizing a mixture of ammonia and a ketone with hydrogen peroxide in the presence of a means for activating the hydrogen peroxide in order to directly form the azine, which it is sufficient subsequently to hydrolyse to hydrazine hydrate. The yields are high and the process is not polluting. The hydrogen peroxide process is used by the Applicant Company and is disclosed in numerous patents, for example U.S. Pat. No. 3,972,878, U.S. Pat. No. 3,972,876, U.S. Pat. No. 3,948,902 and U.S. Pat. No. 4,093,656.
The hydrolysis of an azine to hydrazine hydrate is disclosed in Patents U.S. Pat. No. 4,724,133 (Schirmann et al.), U.S. Pat. No. 4,725,421 (Schirmann et al.) and GB 1,164,460. This hydrolysis is carried out in a distillation column which is fed with water and azine. The ketone is recovered at the top and the hydrazine hydrate at the bottom.
EP 70,155 also discloses another hydrogen peroxide process.
These processes are also described in Ullmann's Encyclopaedia of Industrial Chemistry (1989), Vol. A 13, pages 182-183 and the references included.
In hydrogen peroxide processes, ammonia is oxidized with hydrogen peroxide in the presence of a ketone and of a means for activating the hydrogen peroxide according to the following overall reaction, an azine being formed:
The activation means can be a nitrile, an amide, a carboxylic acid or a selenium, antimony or arsenic derivative. The azine is then hydrolysed to hydrazine and the regenerated ketone is recycled according to the following reaction:
This hydrolysis is carried out in a distillation column. The ketone is recovered at the top and the hydrazine hydrate at the bottom.
Whether the azine originates from a hydrogen peroxide process or another method of preparation, this azine has to be hydrolysed in order to obtain the hydrazine hydrate. The present invention relates to the hydrolysis of methyl ethyl ketone azine (also known as mekazine in the continuation of the text), whatever its source, in order to convert it into hydrazine hydrate. The Applicant Company has discovered that heterocycles of the pyrazoline family were formed during hydrolysis and that, if the products are not bled off, the hydrazine hydrate is coloured.
The present invention relates to a process for the preparation of hydrazine hydrate in which methyl ethyl ketone azine is hydrolysed in order to obtain hydrazine hydrate and methyl ethyl ketone, characterized in that heterocycles of the pyrazoline family are bled off in an amount sufficient to prevent coloration of the hydrazine hydrate.
Whether the azine is produced by a hydrogen peroxide process or another process, methyl ethyl ketone is advantageously used because it has little solubility in the aqueous medium.
In the hydrogen peroxide process, methyl ethyl ketone azine was chosen industrially because it is relatively insoluble in the reaction mixture, which reaction mixture is necessarily aqueous since use is made of commercial aqueous hydrogen peroxide solutions assaying between 30 and 70% by weight. This azine is therefore easy to recover and to separate by simple settling. It is very stable, in particular in alkaline medium, that is to say in the ammoniacal reaction mixture. In all modern processes, this azine is subsequently purified and then hydrolysed in a reactive distillation column in order to release “at the end” methyl ethyl ketone at the top, to be recycled to the manufacturing reaction, and in particular an aqueous hydrazine hydrate solution at the bottom, which should comprise as few carbonaceous products as possible as impurities and should be colourless.
Although conventional packed columns can be suitable, use is generally made of plate columns. The number of plates can vary enormously according to the residence time allowed on the plates and the pressure, and therefore the temperatures at which the operation is carried out. In practice, when the operation is carried out under a pressure of 8 to 10 bar, the number of plates needed is of the order of 40 to 50.
This column is operated continuously and the reactants, that is to say mekazine and water, are injected into the top part of the column.
In point of fact, the Applicant Company has discovered that, when mekazine is hydrolysed according to the following equilibrium reactions:
this end is clearly achieved, as indicated in
FIG. 1
, which represents the variations in
groups and in N—N groups along the entire length of the column. The amount of the groups is expressed in molar equivalent per 100 g of the sample under consideration. The carbonyl groups
are quantitatively determined by oximation, whereas the N—N groups are quantitatively determined by conventional iodometry after hydrolysis with sulphuric acid according to techniques known to a person skilled in the art. Plate 1 is at the bottom of the column and plate 40 is at the top. It is clearly observed that hydrolysis is complete, since the content of
groups in the bottom is zero, just as the content of N—N groups at the top is also zero.
However, the Applicant Company has also observed that, if care is not taken, although hydrolysis of the mekazine is complete, a hydrazine hydrate solution is obtained at the bottom which is not colourless but coloured and sometimes highly coloured, this being due to a content, sometimes a very high content, of carbonaceous products. In contrast to what might have been thought, these carbonaceous products are neither methyl ethyl ketone azine nor hydrazone but heterocycles derived from mekazine: 3,4,5-trimethyl-5-ethylpyrazoline
and 3,5-diethyl-5-methylpyrazoline
These compounds, which are isomers of mekazine, are formed in the hydrolysis column and are responsible for the yellow, indeed even brown or red, colorations which can be observed.
This hydrolysis is carried out, for example, in a plate or packed column of the distillation column type which is fed with the azine and water. The following are obtained: (i) at the top, methyl ethyl ketone with water, since an azeotrope with water is formed, and (ii) at the bottom, an aqueous hydrazine hydrate solution.
The hydrolysis of azines is known. For example, E. C. Gilbert, in an article in the Journal of the American Chemical Society, Vol. 51, pages 3397-3409 (1929), describes equilibrium reactions for the formation of azines and the hydrolysis reactions of the latter. The hydrolysis has to be carried out in a reactive column, such that, by continuously separating the methyl ethyl ketone at the distillation column top and the hydrazine hydrate at the column bottom, complete hydrolysis can be achieved. Of course, this system works best when the operation is carried out continuously, as disclosed in French Patent 1,315,348, British Patent 1,211,547 or U.S. Pat. No. 4,725,421.
In all these patents, the reaction is carried out in a packed distillation column or better still a plate distillation column operating under a pressure of 2 to 25 bar with a bottom temperature of 150° C. to 200° C.
In this column, the azine is hydrolysed and the hydrazine hydrate is separa
Atofino
Langel Wayne A.
Pennie & Edmonds LLP
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