The present invention relates to a process for the preparation of hydrazine hydrate. The present invention relates more specifically to an improved process for preparing hydrazine hydrate from methyl ethyl ketone azine obtained in the presence of methyl ethyl ketone by oxidation of ammonia with hydrogen peroxide and a activator.

Hydrazine is used in various applications, mainly in the deoxygenation of boiler waters (eg nuclear power stations) and is used in the preparation of pharmaceutical and agrochemical derivatives.

There is therefore an industrial need for the preparation of hydrazine hydrate.

The industrial production of hydrazine hydrate is done according to the RASCHIG, BAYER or hydrogen peroxide processes.

In the RASCHIG process, ammonia is oxidized with a hypochlorite to obtain a dilute solution of hydrazine hydrate which must then be concentrated by distillation. This process, which is not very selective, not very productive and very polluting, is almost no longer used.

The BAYER process is a variant of the RASCHIG process which consists in shifting a chemical equilibrium by trapping, using acetone, the hydrazine formed in the form of azine of the following formula: (CH3)2C = NN = C-( CH3)2.

The azine is then isolated and then hydrolyzed to hydrazine hydrate. Yields are improved, but there is no improvement in terms of releases into the environment.

The hydrogen peroxide process consists of oxidizing a mixture of ammonia and a ketone with hydrogen peroxide in the presence of a means of activating the hydrogen peroxide to directly produce the azine which then suffices to hydrolyse to hydrazine hydrate. Yields are high and the process is non-polluting. This hydrogen peroxide process is described in numerous patents, for example US 3,972,878, US 3,972,876, US 3,948,902 and US 4,093,656.

The hydrolysis of an azine to hydrazine hydrate is described in US patents 4,724,133 SCHIRMANN et al., US 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. At the top, the ketone is recovered and at the bottom, a concentrated solution of hydrazine hydrate.

These methods are also described in ULLMANN'S ENCYCLOPEDIA OF INDUSTRIAL CHEMISTRY (1989), vol A 13, pages 182-183 and the references therein.

In hydrogen peroxide processes, ammonia is oxidized by hydrogen peroxide in the presence of a ketone and a means of activating the hydrogen peroxide according to the following overall reaction, making an azine:

The activation means or activator can be a nitrile, an amide, a carboxylic acid or else a derivative of selenium, antimony or arsenic. Then the azine is hydrolyzed into hydrazine and the ketone is regenerated according to the following reaction:

This hydrolysis is actually carried out in two stages, with the formation of an intermediate hydrazone:

Whether the azine is produced by a hydrogen peroxide process or another process, methyl ethyl ketone is advantageously used because it is poorly soluble in an aqueous medium.

Indeed, in the hydrogen peroxide process, the azine of methyl ethyl ketone is relatively insoluble in the reaction medium which is necessarily aqueous since commercial aqueous solutions of hydrogen peroxide containing between 30 and 70 are used. % in weight. This azine is therefore easily recoverable and separable by simple decantation. It is very stable especially in alkaline medium, that is to say in the ammoniacal reaction medium. In current processes, this azine is then purified, then hydrolyzed in a reactive distillation column to ultimately release methyl ethyl ketone at the top to be recycled, and above all an aqueous solution of hydrazine hydrate at the bottom, which must contain as few carbonaceous products as possible as impurities and should be colorless.

However, in these processes using hydrogen peroxide and using methyl ethyl ketone (also called MEK), small amounts of a by-product, methyl ethyl ketone oxime (or MEK oxime) are formed. whose presence disrupts the proper functioning of the process.

The MEK oxime has the following formula:

The MEK oxime is formed mainly upstream of the hydrolysis step during the azine synthesis steps and the possible treatment of the aqueous phase at the outlet of the synthesis step. This by-product can accumulate on the hydrolysis column trays and cause column operation problems, as well as hydrazine decompositions due to its accumulation above a certain concentration. Preferably, the oxime content of the methyl ethyl ketone is less than or equal to 20% by weight, more preferably between 5% and 13% by weight, relative to the total weight of the liquid phase on the plates of the column or in the parts of the column where its concentration is at its maximum.

Unfortunately, the oxime of the MEK is difficult to separate by distillation from the azine which is the majority product, so that, in industrial processes, they are sent simultaneously to the equipment which makes it possible to hydrolyze the azine in hydrate of hydrazine. When this hydrolysis is carried out in a distillation column, for example a reactive plate column, the oxime is concentrated at certain places in the column (for example on certain plates). An abnormal decomposition of the hydrazine hydrate is also observed, leading to significant reductions in yield.

There is therefore a need for an industrial process for the preparation of hydrazine hydrate improved as regards the treatment of by-products such as oximes, in particular the oxime of MEK.

Document WO 99/58446 describes the purging of the oxime from the methyl ethyl ketone during the step of hydrolysis of the azine into hydrazine hydrate. It is mentioned that the azine obtained after separation from the aqueous phase is accompanied by unreacted methyl ethyl ketone and various by-products including the oxime of MEK.

However, this document gives no indication as to a possible treatment of this purge.

There is therefore a need for an improved process for the preparation of hydrazine hydrate in which the by-products are treated more economically and more respectfully of the environment.

Surprisingly, the present inventor has discovered that when recycling the oxime purge from the MEK upstream of the hydrolysis step, an equilibrium regime is established and the oxime content stabilizes in the process, which makes it possible to operate the hydrolysis column satisfactorily.

Indeed, it was discovered that part of the recycled oxime is consumed under the conditions of the hydrolysis, which makes it possible to achieve a stabilization of the concentration of oxime in the process and not an increase contrary to what could be expected.

The recycling of the oxime purge according to the invention has numerous advantages. This avoids discharging an effluent containing azine and hydrazone which represent intermediate products leading to hydrazine, while eliminating the oxime by-product from the process, without adding operations or additional cost to the process.

If the effluent containing the oxime were discharged, it would be necessary to implement an additional treatment, such as for example an incineration or an oxidation treatment before its discharge into the environment.

The process as according to the invention also makes it possible not to lose the hydrazone and azine compounds which may be contained in the oxime purge because the hydrazone and the azine lead by hydrolysis to the hydrazine hydrate. It also makes it possible to eliminate the oxime formed without adding a complex unit operation to the process. It is understood in particular by azine, the azine of methyl ethyl ketone also called mecazine.

Thus, the present invention relates to a process for the preparation of hydrazine hydrate comprising the following steps:

ammonia, hydrogen peroxide and methyl ethyl ketone are reacted in the presence of a solution comprising at least one activator to form an azine (and optionally the oxime of methyl ethyl ketone);

the azine of the methyl ethyl ketone formed is hydrolyzed to obtain hydrazine hydrate while purging the oxime of the methyl ethyl ketone during said hydrolysis step;

said method being characterized in that said purge of oxime from the methyl ethyl ketone is recycled upstream of the hydrolysis step.

It is understood that during the formation of azine, the oxime by-product of methyl ethyl ketone is also formed.

More particularly, the present invention relates to a process for the preparation of hydrazine hydrate comprising the following steps:

(a) reacting ammonia, hydrogen peroxide and methyl ethyl ketone in the presence of a solution comprising at least one activator to form an azine;

(b) separating from the reaction mixture resulting from step (a):

- the aqueous phase comprising said at least one activator; and

- the organic phase comprising the azine and the oxime of the methyl ethyl ketone formed and optionally the unreacted methyl ethyl ketone;

(c) optionally, the aqueous phase is recycled to step (a) after optional treatment;

(d) washing, preferably against the current, the organic phase;

(e) optionally, the washed organic phase is distilled so as to recover the azine;

(f) the azine is hydrolyzed to obtain hydrazine hydrate and regenerate the methyl ethyl ketone, while purging the oxime from the methyl ethyl ketone;

(g) optionally, the methyl ethyl ketone obtained in step (f) is recycled to step (a);

(h) the purge of the oxime of the methyl ethyl ketone obtained in stage (f) is recycled to at least one of stages (a), (b), (c), (d) or (g ).

According to the invention, the recycling of the purging of the oxime of the MEK is carried out upstream of the hydrolysis stage (f). The oxime purge includes MEK oxime, but can also include azine, hydrazone, and water. Said purge is in particular in aqueous form.

Preferably, all of the steps of the method are carried out continuously.

Step (a): Formation of azine from methyl ethyl ketone

In step (a), ammonia, hydrogen peroxide and methyl ethyl ketone are reacted in the presence of a solution comprising at least one activator to form an azine, that is to say the azine of methyl ethyl ketone.

Ammonia can be anhydrous or in aqueous solution.

Hydrogen peroxide can be used in its usual commercial form, for example in aqueous solution between 30% and 90% by weight of H2C>2. Advantageously, it is possible to add one or more usual stabilizers for peroxidic solutions, for example phosphoric, pyrophosphoric, citric, nitrilo-triacetic acid, ethylenediaminetetraacetic acid or the ammonium or alkali metal salts of these acids. The quantity to be used is advantageously between 10 and 1000 ppm and, preferably, between 50 and 250 ppm of all the reagents and of the solution comprising at least one activator at the inlet of the reactor.

By "activator" is meant a compound which makes it possible to activate hydrogen peroxide, that is to say a compound such that azine can be produced from ammonia, hydrogen peroxide and methyl ethyl ketone.

This activator can be chosen from organic or inorganic oxyacids, their ammonium salts and their derivatives: anhydrides, esters, amides, nitriles, acyl peroxides, or their mixtures. Advantageously, amides, ammonium salts and nitriles are used.

By way of example, we can cite:

(i} amides of carboxylic acids of formula R 5 COOH in which R 5 is hydrogen, a linear alkyl radical having from 1 to 20 carbon atoms, or a branched or cyclic alkyl radical having from 3 to 12 carbon, or a phenyl radical which may be substituted,

(ii} polycarboxylic acid amides of formula R 6 (COOH) n in which R 6 represents an alkylene radical having from 1 to 10 carbon atoms and n being an integer greater than or equal to 2, R 6 may be a single bond, then n is 2.

Les radicaux R5 et R6 peuvent être substitués par des halogènes, des groupements OH, NO2 ou méthoxy. On peut citer aussi les amides des acides organiques de l'arsenic. Les acides organiques de l'arsenic sont, par exemple, l'acide méthylarsonic, l'acide phénylarsonic et l'acide cacodylique.

Les amides préférés sont le formamide, l'acétamide, le monochloracétamide et le propionamide, et plus préférentiellement l’acétamide.

Parmi les sels d'ammonium, on utilise avantageusement les sels d'hydracides, d'oxyacides minéraux, d'acides arylsulfoniques, d'acides de formules R5COOH ou R6(COOH)n, R5 , R6 et n étant définis précédemment, des acides organiques de l'arsenic. Les sels d'ammonium préférés sont le formiate, l'acétate, le monochloracétate, le propionate, le phénylarsonate et le cacodylate.

Parmi les nitriles, on peut citer avantageusement les produits de formule R7(CN)n, n pouvant varier de 1 à 5 selon la valence de R7, R7 est un alkyle cyclique ou non cyclique ayant de 1 à 12 atomes de carbone ou un benzyle ou un groupement pyridinyl. R7 peut être substitué par des groupements qui ne s'oxydent pas dans le réacteur de l'étape (a), par exemple des halogènes, des groupes carboxyliques, esters carboxyliques, nitro, amine, hydroxy ou acide sulfonique.

Les nitriles préférés sont l'acétonitrile et le propionitrile.

The solution comprising at least one activator is formed by dissolving one or more products chosen from organic or inorganic oxyacids, their ammonium salts and their derivatives: anhydrides, esters, amides, nitriles, acyl peroxides, or their mixtures as defined above. Advantageously, the above amides, ammonium salts or nitriles are used. Particularly preferably, a single activator is used, which is acetamide.

This solution can be aqueous or based on an alcohol or on a mixture of alcohol and water. Among the alcohols, saturated aliphatic alcohols having

1 to 6 carbon atoms and preferably 1 to 2 carbon atoms.

Advantageously, diols and more particularly diols having

2 to 5 carbon atoms. Mention may be made, for example, of glycol, propylene glycol, 1,3 propanediol, 1,3 and 1,4 butanediol and 1,5 pentanediol.

According to one embodiment, said solution is an alcoholic solution of an organic acid of arsenic and is described in patent EP 0 070 155.

According to another embodiment, said solution is an aqueous solution of a weak acid amide and of the ammonium salt corresponding to this acid as described in patent EP 0 487 160.

These weak acid amides are derived from the corresponding carboxylic acids which have a dissociation constant less than 3 x 10 3 , ie acids which have a pK greater than 3 in aqueous solution at 25°C.

For the polycarboxylic acids, these are the acids whose first ionization constant is less than 3×10 3 .

By way of example, mention may be made of the carboxylic acids of formula RsCOOH in which Re is a linear alkyl radical having from 1 to 20 carbon atoms, or a branched or cyclic alkyl radical having from 3 to 12 carbon atoms, or a radical phenyl which may be substituted, polycarboxylic acids of formula R9(COOH) n in which Rg represents an alkylene radical having from 1 to 10 carbon atoms and n being a number greater than or equal to 2, Rg may be a single bond then n is equal to 2. The Rs and Rg radicals can be substituted by halogens, OH, NO2 or methoxy groups. Preferably, acetamide, propionamide, n-butyramide or isobutyramide are used.

The corresponding ammonium salt of acetamide is ammonium acetate.

It would not be departing from the scope of the invention to form the ammonium salt in situ, that is to say by using the corresponding carboxylic acid which gives the ammonium salt by reaction with ammonia.

The proportions of the amide and of the corresponding ammonium salt can vary within wide limits. Usually 1 to 25 parts of the ammonium salt are used per 5 parts of amide and preferably 2 to 10.

The reactants can be used in stoichiometric amounts. However, 0.2 to 5 moles and preferably 1.5 to 4 moles of methyl ethyl ketone can be used per mole of hydrogen peroxide; from 0.1 to 10 moles and preferably from 1.5 to 4 moles of ammonia. The amount of solution comprising at least one activator can be between 0.1 and 2 kg per mole of hydrogen peroxide. This quantity depends on its quality, that is to say on its catalytic force or its activity which makes it possible to convert the reagents into azine. The proportions of the reagents fixed above make it possible to obtain a total conversion of the hydrogen peroxide and a production of azine corresponding to more than 50% of the hydrogen peroxide engaged and possibly reaching 90%.

The contacting of hydrogen peroxide, ammonia, methyl ethyl ketone with the solution comprising at least one activator can be carried out in any way.

It is possible to operate in a homogeneous medium or in a medium which ensures at least sufficient solubilization of the reactants to be able to obtain azine. The reaction can take place in a very wide temperature range, for example between 0°C and 100°C, and it is advantageously carried out between 30°C and 70°C. Although one can operate at any pressure, it is easier to be at atmospheric pressure, but one can go up to about 10 bars if necessary to preferably maintain the reaction of step (a) in phase liquid.

The reagents can be introduced simultaneously or separately and in any order into the solution comprising at least one activator.

It is possible to use all sorts of reactors, agitated or not agitated, or even simple capacitors which can be arranged in parallel, in series, in co-current or in counter-current, or any combination of these possibilities.

There is thus obtained, following the reaction of step (a), a reaction mixture comprising the azine and the oxime of the methyl ethyl ketone formed, optionally the methyl ethyl ketone which has not reacted, optionally the activator(s), and possibly other by-products or impurities.

Step (b): Phase separation

On sépare la phase aqueuse comprenant le ou les activateur(s) de la phase organique comprenant l’azine et l’oxime de méthyl éthyl cétone formées et éventuellement la méthyl éthyl cétone n'ayant pas réagi par des moyens classiques tels que l'extraction liquide-liquide, la distillation, la décantation ou toute combinaison de ces possibilités. De préférence, on utilise la décantation.

La phase organique obtenue peut comprendre l’azine et l’oxime de la méthyl éthyl cétone formées, de la méthyl éthyl cétone n'ayant pas réagi, de(s) l’activateur(s), et éventuellement d’autres impuretés.

Etape (c) : Recyclage de la phase aqueuse

Dans l'étape (c), la phase aqueuse peut être traitée avant recyclage à l’étape (a), classiquement par exemple par régénération thermique puis éventuellement concentration.

Les étapes (a), (b) et (c) sont décrites par exemple dans les brevets EP 399 866 et EP 518 728.

Etape (d) : Lavage de la phase organique

L’étape de lavage de la phase organique obtenue à l’étape (b) est une étape pouvant être réalisée selon des techniques connues de l’homme du métier, comme indiqué par exemple dans le document WO 2018/065997 (p.13, « Organic layer Processing section », second paragraphe). L’étape de lavage permet notamment de récupérer le(s) activateur(s), par exemple l’acétamide, qui serai(en)t encore présent(s) dans la phase organique.

Le lavage peut être effectué dans une colonne de lavage à contre-courant.

Preferably, the washing is carried out in countercurrent by the oxime purge carried out in stage (f) of hydrolysis, optionally after addition of water. Washing can be done by all or part of the oxime purge. Even more preferably, the purge is sufficient to carry out the washing, without adding water, which in particular makes it possible to save additional water entering the process.

For example, the oxime purge as defined above is added at the top of the column and the organic phase to be washed is added at the bottom of the column. The activator(s) which may still be contained in the organic phase thus pass(s) into the aqueous washing phase (ie the oxime purge).

According to one embodiment, after passing through the washing column, the resulting aqueous phase is either recycled to step (a) with the aqueous phase recovered in step (b), or else can be returned directly to the column of hydrolysis.

Step (e): Distillation of the organic phase

The step of distillation of the washed organic phase is a step that can be carried out according to techniques known to those skilled in the art, as indicated for example in document WO 2018/065997 (p.13, Organic layer Processing section), in particular in a distillation column.

The distillation step serves in particular to separate the azine from the heavy, high-boiling impurities. The latter are recovered at the bottom of the column, for example. The distillation step also serves to separate the azine formed in step (a) from the unreacted methyl ethyl ketone, which can be recovered at the top of the column. It is possible to recycle the methyl ethyl ketone thus recovered in stage (a) of synthesis of the azine. Thus, at the end of the washing and distillation steps, a purified organic phase is obtained, comprising the azine and the oxime of methyl ethyl ketone.

Step (f): Hydrolysis of the azine, regeneration of the MEK and purging of the oxime

Azine hydrolysis and methyl ethyl ketone regeneration

The hydrolysis step is preferably carried out continuously, under pressure, in a reactive distillation column into which are injected the water and the organic phase comprising the azine and the oxime coming from steps (d) or ( e).

The hydrolysis can be carried out in a packed or plate distillation column, preferably operating under a pressure of 2 to 25 bars and with a bottom temperature of between 150°C and 200°C.

Although conventional packed columns may be suitable, tray columns are generally used. Depending on the residence time allowed on the plates and the pressure, therefore the temperatures at which one operates, the number of plates can vary enormously. In practice, when operating under a pressure of 8 to 10 bars, the number of plates required is around 40 to 50.

Following hydrolysis, we obtain:

at the top, methyl ethyl ketone in particular in the form of an azeotrope with water, and

at the bottom, an aqueous solution of hydrazine hydrate.

The hydrolysis of azines is known. For example, EC GILBERT, in an article in the Journal of American Chemical Society vol.51, pages 3397-3409 (1929), describes the balanced reactions of formation of azine and the reactions of hydrolysis thereof and provides the thermodynamic parameters of the system in the case of water-soluble azines. For example, the hydrolysis of azine from acetone is described in US 4,724,133. With regard to azines insoluble in aqueous solutions (for example azine from methyl ethyl ketone) the hydrolysis must be carried out in a reactive column, so that by continuously separating the methyl ethyl ketone at the top of the distillation column and the hydrazine hydrate at the bottom of the column, total hydrolysis can be achieved.

In all these patents, the reaction is carried out in a packed or better still plate distillation column operating under a pressure of 2 to 25 bars and with a bottom temperature of 150° C. to 200° C.

When working with pure azine, that is to say obtained for example from hydrazine hydrate and methyl ethyl ketone, it is actually found by working according to these patents, that one obtains with good yield of dilute solutions of hydrazine hydrate.

In this column, the hydrolysis of the azine and the separation of the hydrazine hydrate from the methyl ethyl ketone take place. These conditions are known. A person skilled in the art easily determines the number of trays or the packing height, as well as the azine and water supply points. Solutions at 30% or even up to 45% by weight of hydrazine hydrate are obtained at the bottom. For example, the water/azine molar ratio in the feed for this column is at least greater than the stoichiometry and advantageously between 5 and 30, preferably between 10 and 20. The temperature of the bottom of the column can be between 150° C and 200°C, preferably between 175°C and 190°C. The pressure is a function of the boiling temperature of azine, water and ketone.

La réaction de l'étape (a) peut produire une phase organique contenant jusqu'à 5% en poids d'oxime, par rapport au poids total de la phase organique. De préférence, la phase organique produite à l’issue de l’étape a) ou b) comprend entre 0,1 % et 5%, par exemple entre 1 ,5 et 2,5% en poids d’oxime de la méthyl éthyl cétone.

Par exemple, lorsqu'on opère avec l'azine de la méthyl éthyl cétone provenant d'une opération d'oxydation avec l'eau oxygénée selon le brevet EP 70 155 ou encore selon les brevets EP 399 866, EP 518 728 ou EP 487 160, on observe que cette azine n'est pas pure, mais qu'elle contient une quantité d'oxime pouvant varier entre 0,1 % et 1 % d'oxime de la méthyl éthyl cétone dont le point d'ébullition est de 151 °C à pression atmosphérique à comparer à 161 °C pour l'azine de la méthyl éthyl cétone.

Purge de l’oxime

On effectue selon l’invention la purge de l’oxime de la MEK lors de l’étape (f) d’hydrolyse.

Selon le nombre de plateaux ou la hauteur de garnissage, la position de l'alimentation en azine et la position de l'alimentation en eau, le reflux, la nature de l'azine etc ..., l'homme du métier peut déterminerfacilement dans quelle partie de la colonne on obtient la concentration maximum en oxime. Il est en effet plus simple de purger l'oxime par un soutirage à l'endroit où sa concentration est maximum. On peut faire un soutirage en continu, ou en discontinu, de préférence en continu.

La quantité à soutirer peut se déterminer facilement par analyse par chromatographie en phase gazeuse de la concentration en oxime.

According to document WO 99/58446, the azine comprising the oxime can be introduced into the hydrolysis column. This oxime, because of its azeotropic behavior with water, is classified in the column at an intermediate level between hydrazine hydrate and methyl ethyl ketone and, for this reason, it can be separated quite easily by lateral withdrawal.

Preferably, the purging of the oxime from the methyl ethyl ketone is therefore carried out by withdrawal, preferably by continuous lateral withdrawal.

Step (g): Recycling of the regenerated methyl ethyl ketone

The methyl ethyl ketone obtained in step (f) can be recycled to step (a).

Step (h): recycling of the oxime purge

Preferably step (h) of recycling is carried out continuously. The oxime purge of the methyl ethyl ketone obtained in step (f) can be recycled to at least one of steps (a),

(b), (c), (d) or (g) of the process according to the invention, preferably in at least one of the steps

(c), (d) or (g). Preferably, the oxime purge of the methyl ethyl ketone obtained in step (f) is recycled to step (d) of washing the organic phase.

Thus, the oxime purge can be recycled:

either in the aqueous phase resulting from separation step (b) which is recycled to step (a);

either with the methyl ethyl ketone recovered at the top of the hydrolysis column and which is recycled to stage (a);

either in the washing step (d).

Description of Figures

Figure 1: Process for the preparation of hydrazine hydrate according to the invention

Figure 1 represents an example of industrial implementation of the process according to the invention.

A represents step (a) of synthesis of mecazine, flow 1 comprises ammonia, hydrogen peroxide as well as the necessary supplements in acetic acid, ammonium acetate or acetamide or even in methyl ethyl ketone as well as the various additives useful during the synthesis step, such as peroxide stabilizers, for example. Stream 13 corresponds to the recycling of the aqueous phase according to step (c), after its thermal regeneration and concentration to eliminate excess water. Stream 8 corresponds to the recycling of the methyl ethyl ketone regenerated during the hydrolysis step and recovered at the outlet of the hydrolysis column E according to step (g).

B represents a settling tank at the outlet of step (a) of synthesis of the azine which receives the reaction mixture 2. It makes it possible to separate the organic phase containing the crude mecazine corresponding to stream 3 and the aqueous phase containing the activator, for example acetamide, and corresponding to flow 4 according to step (b).

C represents a backwash column according to step (d). The organic phase, stream 3 is introduced at the bottom of column C and is backwashed by stream 10 corresponding to the methyl ethyl ketone oxime purge extracted from the trays of the azine hydrolysis column, E according to step (h). Stream 12, corresponding to the aqueous phase at the outlet of washing column C, is then returned to section G corresponding to the step of thermal regeneration and concentration of the aqueous phase with stream 4.

The washed organic phase, flow 5, is sent for purification to a distillation column D according to step (e). This column makes it possible to recover a little methyl ethyl ketone recycled at A at the top and makes it possible to eliminate the heavy impurities present in the azine (not shown) at the bottom.

The organic phase comprising the distilled azine, stream 6, is then sent to the hydrolysis column E. The hydrolysis column E is a distillation column operating under pressure. The distilled azine, 6, is introduced into column E as well as water, flow 7, necessary for the hydrolysis.

After the hydrolysis step (f), at the top, after condensation of the vapors and settling at F, stream 8 is obtained, mainly comprising methyl ethyl ketone, water and a little azine. This phase is recycled to the azine A synthesis step.

The decanted aqueous phase, stream 9, is returned to the hydrolysis column at the top. Stream 11 corresponds to the hydrazine hydrate solution obtained and recovered at the bottom of the column.

The examples are given purely by way of illustration and do not limit the invention.

EXAMPLES

Example 1: Preparation process according to the invention

The method as described for Figure 1 is implemented.

Column E operates under the conditions described below:

Bottom temperature 178-190°C

Head condenser temperature 160°C

Head pressure 7.5 to 9.7 bar absolute

Reboiling Temperature 200°C, Pressure 16 bar

Distilled azine feed 6,5000 kg/hour

Water supply 7 10000 kg/hour

Withdrawal of hydrazine at the bottom 12 t/h of an aqueous solution at 22.2% expressed as hydrazine hydrate (or 14.2% expressed as hydrazine N 2 H 4 )

After the hydrolysis step (f), at the top, after condensation of the vapors and settling, approximately 6,500 kg/hour of organic phase, stream 8, comprising mainly methyl ethyl ketone, water and a little of azine. This phase is recycled to the azine A synthesis step.

The decanted aqueous phase, stream 9, is returned to the hydrolysis column at the top.

A purge, stream 10, is performed on the trays of the hydrolysis column at a rate of 1477 kg/h, where the methyl ethyl ketone oxime accumulates. This purge is returned to washing column C to wash the organic phase from separator B.

The statement of the flow rates and analyzes carried out around the washing column C are reported in Table 1:

It can be seen that 150 kg/h of azine are thus recovered in the organic phase (stream 5) during the washing of stream 3 by purging with oxime 10. Apart from the uncertainties of analysis, this corresponds to the recovery of 37 and 88 kg of azine and hydrazone contained in this purge 10. The oxime contained in the purge 10 is also transferred almost quantitatively into the azine stream 5 at the outlet of the washing column.

The balance is also carried out around the hydrolysis column E and is reported in Table 2:

It can be seen that the oxime is mainly consumed during the hydrolysis of the azine in column E when the process according to the invention is carried out by recycling the purge 10.

Flow 3 (Table 1) represents 154 kg/h of oxime produced upstream of the hydrolysis by the step of synthesis of azine A and thermal regeneration of the aqueous phase G. This production is well compensated by the loss of oxime observed between the washing stage C and the hydrolysis E, therefore between flow 5 (318 kg/h of oxime) and flow 10 recycling the oxime at 171 kg/h, i.e. a consumption of 318- 171.147 kg/h of oxime.

It is observed that the oxime does not increase in the process and remains at a concentration of 11% on the trays of the hydrolysis column E.

CLAIMS

1. Process for the preparation of hydrazine hydrate comprising the following steps:

- Ammonia, hydrogen peroxide and methyl ethyl ketone are reacted in the presence of a solution comprising at least one activator to form an azine;

- The azine of the methyl ethyl ketone formed is hydrolyzed to obtain hydrazine hydrate while purging the oxime of the methyl ethyl ketone during said hydrolysis step;

said method being characterized in that said purge of oxime from the methyl ethyl ketone is recycled upstream of the hydrolysis step.

2. Process for the preparation of hydrazine hydrate according to claim 1, comprising the following steps:

(a) reacting ammonia, hydrogen peroxide and methyl ethyl ketone in the presence of a solution comprising at least one activator to form an azine;

(b) separating from the reaction mixture resulting from step (a):

- the aqueous phase comprising the activator(s); and

- the organic phase comprising the azine and the oxime of the methyl ethyl ketone formed and optionally the unreacted methyl ethyl ketone;

(c) optionally, the aqueous phase is recycled to step (a) after optional treatment;

(d) washing, preferably against the current, the organic phase;

(e) optionally, the washed organic phase is distilled so as to recover the azine;

(f) the azine is hydrolyzed to obtain hydrazine hydrate and regenerate the methyl ethyl ketone, while purging the oxime from the methyl ethyl ketone;

(g) optionally, the methyl ethyl ketone obtained in step (f) is recycled to step (a);

(h) the purge of the oxime of the methyl ethyl ketone obtained in stage (f) is recycled to at least one of stages (a), (b), (c), (d) or (g ).

3. Process according to claim 2, in which the oxime purge of the methyl ethyl ketone obtained in stage (f) is recycled to at least one of stages (c), (d) or (g).

4. Process according to claim 2, in which the oxime purge of the methyl ethyl ketone obtained in stage (f) is recycled to stage (d) of washing the organic phase.

5. A process according to claim 4, wherein the oxime purge of the methyl ethyl ketone is sufficient to effect said washing of the organic phase, without addition of water.

6. Process according to any one of the preceding claims, in which the purging of the oxime of the methyl ethyl ketone is carried out by drawing off, preferably by continuous side drawing.

7. Method according to any one of the preceding claims, in which step (h) of recycling is carried out continuously.

8. Process according to any one of the preceding claims, in which the step (f) of hydrolyzing the azine and regenerating the methyl ethyl ketone is carried out in a packed or plate distillation column, preferably operating under a pressure of 2 to 25 bars and with a base temperature of 150°C to 200°C.

9. Process according to claim 8, in which the oxime content of the methyl ethyl ketone is less than or equal to 20% by weight, preferably between 5% and 13% by weight relative to the total weight of the liquid phase present on the plates or in the parts of the column where its concentration is at its maximum.

10. A method according to any preceding claim, wherein said activator is acetamide.