RU2806028C2 - Improved method for producing hydrazine hydrate with pyrazoline recycling - Google Patents

Abstract

FIELD: chemical industry.

SUBSTANCE: method for producing hydrazine hydrate includes the step of reacting ammonia, hydrogen peroxide and methyl ethyl ketone in the presence of a solution containing at least one activator to produce azine. Then the stages of separation from the resulting reaction mixture of the aqueous phase containing the activator and the organic phase containing azine are carried out. The organic phase is washed. The washed organic phase is distilled to recover the azine. Hydrolysis of azine is carried out to obtain hydrazine hydrate and regenerate methyl ethyl ketone. In this case, by-products (heterocyclic compounds of the pyrazoline family) are purged. The resulting purge stream of heterocyclic compounds of the pyrazoline family is recycled to at least one of the preceding reaction steps, separation of the aqueous and organic phase, or washing of the organic phase. A variant of the method for producing hydrazine hydrate is proposed.

EFFECT: group of inventions makes it possible to eliminate the coloring of hydrazine hydrate by stabilizing the concentration of heterocyclic compounds of the pyrazoline family in the hydrolysis column during stable hydrolysis in a continuous mode.

11 cl, 1 dwg, 2 tbl, 1 ex

Description

The present invention relates to a method for producing hydrazine hydrate. More specifically, the present invention relates 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 using an activator.

Hydrazine is used for a variety of purposes, mainly to remove oxygen from boiler water (for example, in nuclear power plants) and to produce pharmaceutical and agrochemical derivatives.

Therefore, there is an industrial demand for hydrazine hydrate.

Industrial production of hydrazine hydrate is carried out using the RASCHIG, BAYER methods or using hydrogen peroxide.

In the RASCHIG method, ammonia is oxidized with hypochlorite to produce a dilute solution of hydrazine hydrate, which is then concentrated by distillation. This method, characterized by low selectivity, low productivity and high levels of environmental pollution, is almost never used.

The BAYER method is a variant of the RASCHIG method and consists of shifting the chemical equilibrium by trapping hydrazine with acetone, which is formed in the azine form of the following formula: (CH ₃ ) ₂ C=NN=C-(CH ₃ ) ₂ . The azine is then isolated and hydrolyzed to produce hydrazine hydrate. The yield increases, but emissions into the environment remain the same.

The hydrogen peroxide method consists of oxidizing a mixture of ammonia and a ketone with hydrogen peroxide in the presence of a hydrogen peroxide activator to directly produce an azine, which then only needs to be hydrolyzed to hydrazine hydrate. The yield increases, there are no emissions into the environment. The method using hydrogen peroxide is described in many patents, for example, US 3972878, US 3972876, US 3948902 and US 4093656.

Hydrolysis of azine to hydrazine hydrate is described in US Pat. No. 4,724,133 to SCHIRMANN et al., US Pat. No. 4,725,421 to SCHIRMANN et al., and GB 1164460. This hydrolysis is carried out in a distillation column fed with water and azine. The ketone is removed from the upper part, and a concentrated solution of hydrazine hydrate is removed from the lower part.

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

In the hydrogen peroxide method, ammonia is oxidized with hydrogen peroxide in the presence of a ketone and a hydrogen peroxide activator according to the following general reaction equation to produce an azine:

The activator may be a nitrile, amide, carboxylic acid or derivative of selenium, antimony or arsenic. The azine is then hydrolyzed to hydrazine and the ketone is regenerated according to the following reaction equation:

In fact, hydrolysis is carried out in two stages with the formation of the intermediate hydrazone:

Whether the azine is prepared using hydrogen peroxide or another method, methyl ethyl ketone is preferably used as the ketone, since it is poorly soluble in an aqueous medium.

Indeed, in the method using hydrogen peroxide, the methyl ethyl ketone azine is almost insoluble in the reaction medium, which is inevitably aqueous due to the use of commercially available aqueous solutions of hydrogen peroxide with a concentration of 30 to 70 wt%. Therefore, azine can be easily extracted and separated by simple decantation. It is stable, especially in an alkaline environment, that is, in an ammonia reaction environment. In the described methods, the azine is purified, then hydrolyzed in a reactive distillation column to ultimately produce methyl ethyl ketone at the top, which is recycled, and at the bottom, an aqueous solution of hydrazine hydrate, which should contain as little carbon-containing impurity products as possible , and should be colorless.

However, in processes using hydrogen peroxide and methyl ethyl ketone (also called MEK), a small amount of by-products, namely heterocyclic compounds of the pyrazoline family, are formed. Specifically, these by-products are 3,4,5-trimethyl-5-ethylpyrazoline and 3,5-diethyl-5-methylpyrazoline, having the following formulas:

These compounds are isomers of methyl ethyl ketone azine. They are formed mainly in the hydrolysis column and cause yellow and even brown or red coloration of hydrazine. Thus, in the lower part of the column, not a colorless solution of hydrazine hydrate can be obtained, but a colored one, and sometimes strongly, depending on the content of heterocyclic compounds of the pyrazoline family.

These by-products can accumulate on the trays of the hydrolysis column and cause the coloring problems described above and malfunction if they exceed a certain concentration. Preferably, the content of heterocyclic compounds of the pyrazoline family is less than or equal to 5 wt.%, more preferably, is from 1% to 3 wt.%. relative to the total weight of the liquid phase on the column trays or in those parts of the hydrolysis column where the specified content is maximum. These values are sufficient to exclude coloration of the resulting hydrazine hydrate.

Therefore, there is a need for a process for the preparation of hydrazine hydrate that is improved in terms of processing by-products such as heterocyclic compounds of the pyrazoline family, in particular 3,4,5-trimethyl-5-ethylpyrazoline and 3,5-diethyl-5-methylpyrazoline.

WO 99/58445 describes the batch purge of heterocyclic compounds of the pyrazoline family during the hydrolysis of azine to hydrazine hydrate. It is mentioned that these compounds are formed in the hydrolysis column. However, this document does not say anything about possible treatment of the purge stream.

Therefore, there is a need for an improved process for producing hydrazine hydrate in which the by-products are processed in a more cost-effective manner with less damage to the environment.

Surprisingly, it has been discovered that when the purge stream of heterocyclic compounds of the pyrazoline family is recycled upstream of the hydrolysis step, these by-products are solubilized in the azine at the inlet of distillation step (e) and are removed in that distillation step. Surprisingly, it is possible to remove heterocyclic compounds of the pyrazoline family during the distillation step. Moreover, hydrazine precursors (azine and hydrazone) that may be present in the purge stream can be returned to the azine stream and re-entered into the hydrolysis column. The recirculation according to the invention allows the concentration of heterocyclic compounds of the pyrazoline family in the hydrolysis column to be stabilized at a level low enough to obtain a colorless solution of hydrazine hydrate at the bottom of the hydrolysis column while the hydrolysis is carried out in a stable, continuous manner.

There are many advantages to recirculating the purge stream of heterocyclic compounds of the pyrazoline family in accordance with the invention. This eliminates the discharge of effluent containing azine and hydrazone, which are intermediate products in the production of hydrazine, while eliminating by-products from the process, not to mention technological advantages and additional costs. If an effluent containing these heterocyclic compounds were to be discharged, additional treatment would be necessary, such as, for example, incineration or oxidation prior to release to the environment.

The process according to the invention also prevents the loss of hydrazone and azine that may be present in the purge stream, since the hydrazone and azine are converted to hydrazine hydrate upon hydrolysis.

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

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

(b) separated from the reaction mixture obtained in step (a):

- aqueous phase containing activator(s); And

- an organic phase containing the formed azine and, possibly, unreacted methyl ethyl ketone;

(c) optionally recycled to step (a) the aqueous phase after possible treatment;

(d) washing, preferably in countercurrent, the organic phase;

(f) distilling the washed organic phase to recover the azine;

(f) hydrolyze the azine to obtain hydrazine hydrate and regenerate methyl ethyl ketone, while purging heterocyclic compounds of the pyrazoline family;

(g) optionally recycling the methyl ethyl ketone obtained in step (f) to step (a);

(h) recycling the purge stream of heterocyclic pyrazoline family compounds obtained in step (f) to one of steps (a), (b), (c), (d) or (g).

The purge stream of heterocyclic compounds of the pyrazoline family contains these heterocyclic compounds, but may also contain azine, hydrazone and water. Said purge stream is aqueous.

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

By “heterocyclic compounds of the pyrazoline family” is meant a pyrazoline ring substituted at at least one carbon atom, in particular a pyrazoline ring of the following formula (I):

in which Ra, Rb, Rc, Rd and Re independently of each other can be selected from H and (C ₁ -C ₂₀ )alkyl; wherein at least one of the radicals Ra, Rb, Rc, Rd and Re is (C ₁ -C ₂₀ )alkyl.

The term "(C ₁ -C ₂₀ )alkyl" means aliphatic saturated hydrocarbons, which may be linear or branched and contain from 1 to 20 carbon atoms. Preferably, alkyls have 1 to 4 carbon atoms, even 1 to 2 carbon atoms. Examples include methyl and ethyl. By "branched" it is meant that the alkyl group is substituted on the alkyl backbone.

Azine refers to methyl ethyl ketone azine, also called MEKazine.

Step (a): Formation of methyl ethyl ketone azine

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

Ammonia may be an anhydride or an aqueous solution.

Hydrogen peroxide can be used in a conventional, commercially available form, for example, in an aqueous solution with a concentration of from 30% to 90% by weight H ₂ O ₂ . Advantageously, one or more conventional stabilizers for peroxide solutions can be added, for example phosphoric, pyrophosphoric, citric, nitrilotriacetic, ethylenediaminetetraacetic acids or ammonium or alkali metal salts of these acids. The amount used is advantageously from 10 to 1000 ppm, preferably from 50 to 250 ppm, based on all reactants and the solution containing at least one activator at the reactor inlet.

By “activator” is meant a compound that allows the activation of hydrogen peroxide, that is, a compound that allows the production of azine from ammonia, hydrogen peroxide and methyl ethyl ketone.

The activator can be selected from organic or inorganic hydroxy acids, their ammonium salts or their derivatives: anhydrides, esters, amides, nitriles, acyl peroxides or mixtures thereof. Preferably, amides, ammonium salts and nitriles are used.

Examples include:

(i) amides of carboxylic acids of the formula R ₅ COOH, in which R ₅ is hydrogen, a linear alkyl radical of 1 to 20 carbon atoms, or a branched or cyclic alkyl radical of 3 to 12 carbon atoms, or a phenyl radical, optionally , substituted,

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

The radicals R ₅ and R ₆ can be replaced by halogens, OH groups, NO ₂ or a methoxy group. Amides of arsenic organic acids may also be mentioned. Examples of arsenic organic acids are methylarsonic acid, phenylarsonic acid and cacodylic acid.

Preferred amides are formamide, acetamide, monochloroacetamide and propionamide, acetamide being more preferred.

Of the ammonium salts, mainly hydrogen acids, mineral hydroxy acids, arylsulfonic acids, acids of the formula R ₅ COOH or R ₆ (COOH) _n are used, where R ₅ , R ₆ and n correspond to those defined above, arsenic organic acids. Preferred ammonium salts are formate, acetate, monochloroacetate, propinate, phenylarsonate and cacodylate.

Among the nitriles, mention may be made, preferably, of the formula R ₇ (CN) _n , where n can vary from 1 to 5 depending on the valency of R ₇ , R ₇ is alkyl, cyclic or non-cyclic, containing from 1 to 12 carbon atoms, or benzyl or pyridinyl group. R ₇ may be replaced by groups that are not oxidized in the reactor of step (a), for example, halogens, carboxyl groups, carboxylic acid esters, nitro, amino, hydroxy groups or sulfonic acids. Preferred nitriles are acetonitrile and propionitrile.

A solution containing at least an activator is prepared by dissolving one or more products selected from organic or inorganic hydroxy acids, their ammonium salts and their derivatives: anhydrides, esters, amides, nitriles, acyl peroxides or mixtures thereof similar to those defined above. Preferably, amides, ammonium salts or the aforementioned nitriles are used. Particularly preferably, a single activator is used which is acetamide.

This solution may be aqueous or alcohol-based or a mixture of alcohol and water. Of the alcohols, aliphatic saturated alcohols containing from 1 to 6 carbon atoms, preferably from 1 to 2 carbon atoms, are preferably used.

Also preferably, diols are used, more preferably diols containing from 2 to 5 carbon atoms. For example, glycol, propylene glycol, 1,3-propanediol, 1,3- and 1,4-butanediol and 1,5-pentanediol may be mentioned.

According to one embodiment, said solution is an alcoholic solution of arsenic organic acid and is described in patent EP 0070155. According to another embodiment, said solution is an aqueous solution of a weak acid amide and an ammonium salt corresponding to this acid, such as described in the EP patent 0487160.

Amides of weak acids are derivatives of the corresponding carboxylic acids characterized by a dissociation constant of less than 3x10 ^-3 , that is, acids characterized by a pK of more than 3 in an aqueous solution at 25°C. In the case of polycarboxylic acids, these are acids whose first ionization constant is less than 3x10 ^-3 . For example, mention may be made of carboxylic acids of the formula R ₈ COOH, in which R ₈ is a linear alkyl radical of 1 to 20 carbon atoms, or a branched or cyclic alkyl radical of 3 to 12 carbon atoms, or an optionally substituted phenyl radical , polycarboxylic acids of the formula R ₉ (COOH) _n , in which R ₉ is an alkylene radical containing from 1 to 10 carbon atoms, and n is a number greater than or equal to 2, R ₉ may be a single bond, in which case n is 2. Radicals R ₈ and R ₉ may be substituted with halogens, OH, NO ₂ or methoxy groups. Preferably, acetamide, propionamide, n-butyramide or isobutyramide are used.

The corresponding ammonium salt of acetamide is ammonium acetate. Without departing from the scope of the invention, the ammonium salt can be prepared in situ, that is, using the appropriate carboxylic acid, which reacts with ammonia to form the ammonium salt.

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

The reagents may be used in stoichiometric quantities. However, per mole of hydrogen peroxide, from 0.2 to 5 moles, preferably from 1.5 to 4 moles, of methyl ethyl ketone can be used; from 0.1 to 10 moles, preferably from 1.5 to 4 moles of ammonia. The amount of solution containing at least the activator may be from 0.1 to 2 kg per mole of hydrogen peroxide. This quantity depends on its quality, that is, on its catalytic activity, which allows the conversion of reagents into azine. The above ratios of reagents make it possible to achieve a total degree of hydrogen peroxide conversion and azine production corresponding to more than 50% of the hydrogen peroxide consumed, perhaps 90%.

Bringing hydrogen peroxide, ammonia, methyl ethyl ketone into contact with a solution containing at least one activator can be done by any method. It can be carried out in a homogeneous environment or in an environment that provides at least solubilization of the reagents sufficient to obtain azine. The reaction can take place over a wide temperature range, for example from 0°C to 100°C, preferably it is carried out in the range from 30°C to 70°C. Although it is possible to operate at any pressure, it is easier to operate at atmospheric pressure, however, the pressure can be increased to about 10 bar if it is desired to preferably maintain the reaction of step (a) in the liquid phase.

The reagents can be introduced into a solution containing at least one activator, simultaneously or separately, and in any order. It is possible to use any type of reactor, with or without stirrer, or simple vessels that can be arranged in parallel, in series, co-current or counter-current, or in any combination of these possibilities.

Thus, after step (a) a reaction mixture is obtained containing the formed azine, optionally unreacted methyl ethyl ketone, optionally activator(s) and possibly other by-products or impurities.

Step (b): phase separation

An aqueous phase containing one or more activators is separated from an organic phase containing the formed azine and possibly unreacted methyl ethyl ketone by classical methods such as liquid-liquid extraction, distillation, decantation, or any combination of these possibilities. Preferably, decanting is used.

The resulting organic phase may contain the formed azine and unreacted methyl ethyl ketone, activator(s) and possibly other impurities.

Step (c): recirculation of the aqueous phase

In step (c), the aqueous phase can be treated before recycling to step (a), for example classical, by thermal regeneration with possible subsequent concentration.

Steps (a), (b) and (c) are described, for example, in patents EP 399866 and EP 518728.

Step (d): washing of the organic phase

The step of washing the organic phase obtained in step (b) is a step that can be carried out by methods known to those skilled in the art and described, for example, in the document WO 2018/065997 (page 13, section “Treatment of the organic layer”, second paragraph). The washing step in particular makes it possible to recover the activator(s), for example acetamide, which may still be present in the organic phase.

Washing can be carried out in a countercurrent wash column. Preferably, the washing is carried out in countercurrent with a purge stream of heterocyclic compounds of the pyrazoline family obtained in hydrolysis step (f), possibly after addition of water. The flushing may be carried out with all or part of the purge stream. More preferably, the purge flow is sufficient to carry out washing without adding water, which in particular allows the introduction of additional water into the process to be reduced. For example, the purge stream of heterocyclic compounds of the pyrazoline family, as defined above, is introduced at the top of the column, the organic phase to be washed is introduced at the bottom of the column. The activator(s), possibly still contained in the organic phase, are transferred to the aqueous wash phase (ie, the purge stream of heterocyclic compounds of the pyrazoline family).

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

Step (e): distillation of the organic phase

The distillation step of the washed organic phase is a step that can be carried out in any way known to those skilled in the art, for example as described in WO 2018/065997 (page 13, section "Treatment of the organic layer"), namely in a distillation column .

The distillation step is particularly designed to separate the azine from the heterocyclic compounds of the pyrazoline family defined above and other heavy high boiling point impurities. These by-products are withdrawn, for example, from the bottom of the column. The distillation step is also designed to separate the azine formed in step (a) from unreacted methyl ethyl ketone, which can be withdrawn from the top of the column. The methyl ethyl ketone thus obtained can be recycled to step (a) of the azine synthesis.

So, at the output of the washing and distillation stages, a purified organic phase containing azine is obtained.

Step (f): azine hydrolysis, MEK regeneration and purge of heterocyclic compounds of the pyrazoline family

Azine hydrolysis and methyl ethyl ketone regeneration

The hydrolysis step is preferably carried out continuously, under pressure, in a reactive distillation column into which water and the azine-containing organic phase obtained in steps (d) or (e) are supplied.

The hydrolysis can be carried out in a packed or tray distillation column, preferably operating at a pressure of 2 to 25 bar and a bottom temperature of 150°C to 200°C.

Although classical packed columns are suitable, tray columns are generally used. According to the accepted residence time on the trays and pressure, and therefore operating temperatures, the number of trays can vary within wide limits. In practice, when the operating pressure is between 8 and 10 bar, the required number of trays may be on the order of 40 to 50.

After hydrolysis one gets:

- at the top of the column: methyl ethyl ketone, namely in the form of an azeotropic mixture with water and

- at the bottom of the column: an aqueous solution of hydrazine hydrate.

The hydrolysis process of azines is known. For example, E.C. GILBERT, in an article published in the Journal of American Chemical Society vol.51, pages 3397-3409 (1929), describes the equilibrium reactions of azine formation and its hydrolysis reactions and gives the thermodynamic parameters of the system for the case of azines soluble in water. For example, the hydrolysis of acetone azine is described in US 4 724 133. In the case of azines that are insoluble in aqueous solutions (for example, methyl ethyl ketone azine), the hydrolysis must be carried out in the reaction column in such a way that methyl ethyl ketone and hydrazine hydrate are continuously withdrawn from the top of the distillation column - from the bottom of the column, complete hydrolysis could be achieved. Of course, this system works best in continuous mode, as described in FR 1315348 or GB 1211547 or US 4725421.

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

When working with pure azine, that is, obtained, for example, from hydrazine hydrate and methyl ethyl ketone, indeed, according to these patents, dilute solutions of hydrazine hydrate can be obtained in high yield.

In this column, azine is hydrolyzed and hydrazine hydrate is separated from methyl ethyl ketone. The conditions there are known. It will not be difficult for those skilled in the art to determine the number of plates and the height of the nozzle, as well as the azine and water supply points. In the lower part, solutions of hydrazine hydrate are obtained with a concentration of 30% or even up to 45% by weight. For example, the molar ratio of water/azine fed to the column is at least greater than stoichiometric and is advantageously between 5 and 30, preferably between 10 and 20. The bottom temperature of the column may be in the range of 150° C. to 200° C. , preferably from 175°C to 190°C. The pressure is a function of the equilibrium temperature of the azine, water and ketone. Such hydrolysis is also described in US 4725421 and WO 00/37357.

Purge of heterocyclic compounds of the pyrazoline family

According to the invention, the purging of heterocyclic compounds of the pyrazoline family is carried out in stage (f) of hydrolysis.

Depending on the number of trays or packing height, azine feed point and water feed point, reflux return, nature of azine, etc., specialists can easily determine in which part of the column the maximum concentration of heterocyclic compounds of the pyrazoline family can be obtained. Indeed, the easiest way to purge heterocyclic compounds of the pyrazoline family is by sampling from the point where their concentration is maximum, for example, on one or more plates. Selection can be carried out continuously or periodically, preferably continuously.

The amount taken can be easily determined by chromatographic analysis of the concentration of heterocyclic compounds in the gas phase.

Preferably, the purging of heterocyclic compounds of the pyrazoline family is carried out by selection, preferably by continuous side selection.

Step (g): recycling of recovered methyl ethyl ketone

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

Step (h): Recirculation of the purge stream of heterocyclic compounds of the pyrazoline family

Recirculation step (h) is preferably carried out continuously. The purge stream of heterocyclic pyrazoline family compounds obtained in step (f) may be recycled to at least one of the following process steps of the invention: (a), (b), (c), (d) or (g ), preferably at least one of steps (c), (d) or (g). More preferably, the purge stream of heterocyclic pyrazoline family compounds obtained in step (f) is recycled to the organic phase washing step (d).

Thus, the purge stream of heterocyclic compounds of the pyrazoline family can be recycled:

- either in the aqueous phase obtained in separation step (b), which is recycled to step (a);

- either with methyl ethyl ketone withdrawn from the top of the hydrolysis column, which is recycled to stage (a);

- or to stage (d) of washing.

DESCRIPTION OF DRAWINGS

Fig. 1: Method for producing hydrazine hydrate according to the invention

In fig. 1 shows an example of industrial implementation of the method according to the invention.

A means stage (a) of the synthesis of mecasin, stream 1 contains ammonia, hydrogen peroxide, as well as the necessary additives of acetic acid, ammonium acetate, acetamide or methyl ethyl ketone, as well as various additives used in the synthesis stage, for example, stabilizers of peroxide solutions. Stream 13 corresponds to the recirculation of the aqueous phase according to step (c) after its thermal regeneration and concentration to remove excess water. Stream 8 corresponds to the recirculation of methyl ethyl ketone regenerated in the hydrolysis step and discharged at the outlet of the hydrolysis column E according to step (g).

B means the decanter at the outlet of step (a) of the azine synthesis, into which reaction mixture 2 is fed. It allows the organic phase containing the crude mecasine (stream 3) to be separated from the aqueous phase containing the activator, for example acetamide, corresponding to stream 4, according to step (b).

C corresponds to the countercurrent washing column according to step (d). The organic phase, stream 3, is fed to the bottom of column C and washed in countercurrent with stream 10, corresponding to the purge stream of heterocyclic compounds of the pyrazoline family taken from the trays of azine hydrolysis column E according to step (h). Stream 12, corresponding to the aqueous phase at the outlet of washing column C, is then fed to section G, corresponding to the stage of thermal regeneration and concentration of the aqueous phase together with stream 4.

The washed organic phase, stream 5, is fed to distillation column D for purification according to step (e). From this column a small amount of methyl ethyl ketone is withdrawn from the top, which is recycled to A, and heterocyclic compounds of the pyrazoline family present in the azine are withdrawn from the bottom (not shown).

The organic phase containing distilled azine, stream 6, is then fed to hydrolysis column E. The hydrolysis column E is a distillation column operating under pressure. Distilled azine, stream 6, is introduced into column E along with water, stream 7, required for hydrolysis.

After step (f) hydrolysis at the top, after condensation of the vapors and decantation in F, stream 8 is obtained containing mainly methyl ethyl ketone, water and a small amount of azine. This phase is recycled to step A of the azine synthesis. The decanted aqueous phase, stream 9, is fed to the top of the hydrolysis column. Stream 11 corresponds to the hydrazine hydrate solution obtained and discharged at the bottom of the column.

The examples are provided for illustration purposes only and do not limit the invention.

EXAMPLES

Example 1: production method according to the invention

The method described with reference to FIG. 1. Column E operated under the following conditions:

Bottom temperature 178-190°С Upper condenser temperature 160°C Pressure at the top of the column from 7.5 to 9.7 bar abs. Re-boiling temperature 200°C, pressure 16 bar Supply of distilled azine 6 5000 kg/h Water supply 7 10000 kg/h Selection of azine from below 12 t/h of an aqueous solution of 22.2% in terms of hydrazine hydrate (or 14.2% in terms of hydrazine N ₂ H ₄ )

After hydrolysis step (f), about 6500 kg/h of organic phase, stream 8, containing mainly methyl ethyl ketone, water and a small amount of azine, was removed from the upper part, after condensation of the vapors and decantation. This phase was recycled to step A of the azine synthesis. The decanted aqueous phase, stream 9, was returned to the top of the hydrolysis column.

Purge stream 10 was collected from the trays of the hydrolysis column with a flow rate of 1477 kg/h in the place where heterocyclic compounds of the pyrazoline family accumulated. This purge stream was sent to wash column C to wash the organic phase produced in separator B.

An overview of the flow rates and analytical results performed on Wash Column C is presented in Table 1:

Table 1 Column C for washing crude azine Organic phase Aqueous phase entrance exit growth entrance exit growth Stream No. 3 5 5-3 10 12 12-10 kg/h kg/h kg/h kg/h kg/h kg/h MEK 315 370 0.3 18 MEK-azine 5416 5565 150 75 38 -37 MEK-hydrazone 0 0 89 2 -88 Pyrazolines 5 37 32 28 0 -28 Acetamide 46 0 0 49 Water 49 318 1137 777 General flow 7006 7401 1477 892

It can be seen that when azine stream 3 was washed with pyrazoline family heterocyclic compounds purge stream 10, the heterocyclic pyrazoline family compounds contained in purge stream 10 were transferred substantially quantitatively to azine stream 5 at the outlet of the washing column.

It can be seen that 150 kg/h of azine was removed in the organic phase (stream 5) when stream 3 was washed with a purge stream of 10 heterocyclic compounds of the pyrazoline family. Within the analytical error, this corresponds to the removal of 37 to 88 kg of azine and hydrazone contained in purge stream 10.

Pyrazolines are removed during azine purification by distillation of stream 5 to form distilled azine 6 from the bottom of the distillation column along with heavy residues.

The hydrazine hydrate solution (titer 22.2% hydrazine hydrate or 14.2% in terms of hydrazine N ₂ H ₄ ) obtained at the bottom of the column (stream 11) contains only a small amount of pyrazoline, which does not create problems with coloring the final hydrate solution hydrazine obtained by this method after concentration.

A balance was also compiled for hydrolysis column E, shown in Table 2:

table 2 Column E hydrolysis Washed azine Washed and distilled. azine Purging pyrazoline MEK recycling Water Hydrazine hydrate Stream No. 5 6 10 8 7 eleven kg/h kg/h kg/h kg/h kg/h kg/h MEK 370 21 0.3 5206 0 MEK-azine 5565 5523 75 404 0 MEK-hydrazone 0 0 89 0 6 Pyrazolines 37 3 28 0 0 2 Acetamide 0 0 0 0 0 Water 318 21 1137 849 11000 7768 N ₂ H ₄ hydrazine 0 0 0 0 0 1305 Diff. impurities 792 136 0 330 0 104 General flow 7401 5987 1477 6789 11000 9186

Claims (29)

1. A method for producing hydrazine hydrate, including the following stages, in which (a) reacting ammonia, hydrogen peroxide and methyl ethyl ketone in the presence of a solution containing at least one activator to obtain an azine; (b) separated from the reaction mixture obtained in step (a), - aqueous phase containing activator(s); And - organic phase containing the formed azine; (d) washing the organic phase; (f) distilling the washed organic phase to recover the azine; (f) hydrolyzing the azine to obtain hydrazine hydrate and regenerating methyl ethyl ketone, while purging heterocyclic compounds of the pyrazoline family; (h) recycling the purge stream of heterocyclic compounds of the pyrazoline family obtained in step (f) to at least one of steps (a), (b) or (d). 2. A method for producing hydrazine hydrate, including the following stages, in which (a) reacting ammonia, hydrogen peroxide and methyl ethyl ketone in the presence of a solution containing at least one activator to obtain an azine; (b) separated from the reaction mixture obtained in step (a), - aqueous phase containing activator(s); And - organic phase containing the formed azine; (c) recirculate to step (a) the aqueous phase; (d) washing the organic phase; (f) distilling the washed organic phase to recover the azine; (f) hydrolyzing the azine to obtain hydrazine hydrate and regenerating methyl ethyl ketone, while purging heterocyclic compounds of the pyrazoline family; (g) recycling to step (a) the methyl ethyl ketone obtained in step (f); (h) recycling the purge stream of heterocyclic pyrazoline family compounds obtained in step (f) to at least one of steps (a), (b), (c), (d) or (g). 3. The method of claim 2, wherein the purge stream of heterocyclic compounds of the pyrazoline family obtained in step (f) is recycled to at least one of steps (c), (d) or (g). 4. The method according to claim 1 or 2, in which the purge stream of heterocyclic compounds of the pyrazoline family obtained in step (f) is recycled to step (d) of washing the organic phase. 5. The method of claim 4, wherein the purge stream of heterocyclic compounds of the pyrazoline family is sufficient to carry out said washing of the organic phase without adding water. 6. The method according to one of the preceding paragraphs, in which the purging of heterocyclic compounds of the pyrazoline family is carried out by selection. 7. The method according to one of the preceding claims, in which stage (h) of recirculation is carried out continuously. 8. The method according to one of the preceding claims, in which the heterocyclic compounds of the pyrazoline family are 3,4,5-trimethyl-5-ethylpyrazoline and 3,5-diethyl-5-methylpyrazoline. 9. The process according to one of the preceding claims, wherein step (f) of azine hydrolysis and methyl ethyl ketone regeneration is carried out in a packed or tray distillation column. 10. The method according to claim 9, in which the content of heterocyclic compounds of the pyrazoline family is less than or equal to 5 wt.%, more preferably is from 1 to 3 wt.%. relative to the total weight of the liquid phase on the column trays or in those parts of the hydrolysis column where the specified content is maximum. 11. The method according to one of the preceding claims, in which the specified activator is acetamide.