Process for preparing hydrazine hydrate using an absorption column

Abstract

The present invention relates to a process for preparing hydrazine hydrate, comprising the following consecutive steps: a) preparing by means of an absorption column of an aqueous solution containing dissolved ammonia and at least one activator, and introducing into said absorption column an aqueous solution containing at least one activator and fresh ammonia; then b) reacting the aqueous ammonia solution containing at least one activator obtained in the previous step with hydrogen peroxide and a ketone in at least one reactor; then c) separating the organic phase containing azine from the aqueous phase from the stream formed at the end of the previous step; then d) hydrolyzing the organic phase obtained in the previous step to obtain hydrazine hydrate.

Description

Technical Field

[0001] The present invention relates to a process for preparing hydrazine hydrate from an alkyl ketone azine obtained by the oxidation of ammonia with hydrogen peroxide in the presence of an activator in the presence of a ketone.

Background Art

[0002] Hydrazine is used mainly in the deoxygenation of boiler water (e.g., in nuclear power plants) and in various different applications such as in the preparation of pharmaceutical and pesticide derivatives.

[0003] Therefore, there is an industrial demand for the preparation of hydrazine hydrate.

[0004] Hydrazine hydrate is industrially produced from hydrogen peroxide by the Raschig process or the Bayer process.

[0005] In the Raschig process, ammonia is oxidized with hypochlorite to obtain a dilute solution of hydrazine hydrate, which then has to be concentrated by distillation. This process is practically no longer used because it is relatively non-selective, relatively unproductive, and highly polluting.

[0006] The Bayer process is an improvement of the Raschig process, using acetone to shift the chemical equilibrium and capture the hydrazine formed in the form of the azine of the following formula: (CH3)2C=N-N=C-(CH3)2

[0007] The azine is then isolated and then hydrolyzed to hydrazine hydrate. The yield is improved, but there is no improvement in environmental emissions.

[0008] The hydrogen peroxide method only needs to oxidize a mixture of ammonia and a ketone with hydrogen peroxide in the presence of a means for activating hydrogen peroxide to directly synthesize an azine, and then hydrolyze this to hydrazine hydrate. The yield is high and the method has little pollution. This hydrogen peroxide method is described in many patents, such as Patent Document 1, Patent Document 2, Patent Document 3, etc.

[0009] These methods are also described in Non-Patent Document 1 and the references included therein.

[0010] In the hydrogen peroxide method, ammonia is oxidized in the presence of a ketone and a means for activating hydrogen peroxide according to the following overall reaction to form an azine:

Chemical formula

[0011] The activating means or activator can be a nitrile, amide, carboxylic acid, or a selenium, antimony, or arsenic derivative. Then, the azine is hydrolyzed to hydrazine, and the ketone is regenerated according to the following reaction:

Chemical formula

[0012] This hydrolysis is actually carried out in two steps to form an intermediate hydrazone:

Chemical formula

[0013] The reaction to form azine is relatively complex because it involves three phases: a gas phase containing ammonia, an organic phase containing ketone, and an aqueous phase containing an activator and hydrogen peroxide. Methyl ethyl ketone is preferably used because its azine dissolves in the organic phase and is insoluble in the aqueous medium. Therefore, it can be easily recovered at the end of the reaction and separated by simple decantation. This azine also has the advantage of being very stable, especially in an alkaline medium, i.e., an ammoniacal reaction medium.

[0014] In the current method, this azine is then purified and next hydrolyzed in a reactive distillation column, finally releasing methyl ethyl ketone at the top, which can be recycled, and most importantly, releasing an aqueous solution of hydrazine hydrate at the bottom. This should contain as little carbon product as possible as an impurity and must be colorless.

[0015] A process for efficiently preparing hydrazine hydrate is known from Patent Document 4.

[0016] From the paper in Non-Patent Document 2, it is known that stirring is a decisive improvement factor. Specifically, for the reaction to proceed efficiently, the reactants need to contact each other. That is, ammonia in the gas phase, hydrogen peroxide and the activator in the aqueous phase, and ketone in the organic phase need to contact each other. The yield of this reaction is directly related to the exchange and contact between various phases. The aforementioned publication has studied the yield of the reaction as a function of the stirring speed of the reaction medium and as a function of the number of phases present in the reactor.

[0017] It is observed that the higher the stirring speed, the yield increases up to a threshold of 600 rpm. However, these experiments were carried out in a semi-batch reactor. Currently, it is difficult to transfer this process to an industrial device, i.e., a much larger-capacity device. Stirring at 600 rpm applied to an industrial reactor indicates significant energy consumption. This level of stirring is difficult to achieve when applying this process to industrial quantities.

Prior Art Documents

Patent Documents

[0018]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Non-Patent Documents

[0019]

Non-Patent Document 1

Non-Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0020] As a result, in industrial processes, solutions for efficiently performing such gas-liquid-liquid contact with satisfactory yields, reasonable energy consumption, and simple installation are still being sought.

Means for Solving the Problems

[0021] This technical problem is solved by a process (method) of mixing various phases in two steps. First, gaseous ammonia is dissolved in the aqueous phase using an absorption column, and then this ammoniacal aqueous phase is mixed with the organic phase in a conventional stirred reactor.

Advantages of the Invention

[0022] By this method, it becomes possible to use a standard liquid-liquid biphasic reactor at its own standard stirring level. It has been observed that very good yields can be obtained even at very low stirring levels.

Brief Description of the Drawings

[0023]

Figure 1

Embodiments for Carrying Out the Invention

[0024] Accordingly, the subject of the present invention is a process for preparing hydrazine hydrate, comprising the following consecutive steps: a) preparing, by means of an absorption column for an aqueous solution containing ammonia dissolved at a ratio of 50% to 100% with respect to the saturation of ammonia in pure water at the temperature of the absorption column, and containing at least one activator, and introducing into the absorption column an aqueous solution containing at least one activator and fresh ammonia; then b) reacting the aqueous ammonia solution containing at least one activator obtained in the previous step in at least one reactor with hydrogen peroxide and a ketone of the formula: R1R2CO, wherein the groups R1 and R2 independently of one another represent a methyl group, an ethyl group, a propyl group, a butyl group, a pentyl group, a hexyl group, a heptyl group and an octyl group; then c) separating an organic phase containing azine from the aqueous phase from the stream formed at the end of the previous step; then d) hydrolyzing the organic phase obtained in the previous step to obtain hydrazine hydrate.

[0025] Other features, aspects, subjects and advantages of the present invention will become clearer by reading the following description.

[0026] It is specified that the expressions "from... to..." and "between... and..." used herein should be understood as including each of the recited limits. Preparation of aqueous solution

[0027] The aqueous ammonia solution is prepared using an absorption column.

[0028] The absorption column is supplied with fresh ammonia and an aqueous solution containing at least one activator.

[0029] The absorption column is intended to dissolve gaseous ammonia in an aqueous solution containing at least one activator. The function of the absorption column is to make this mixture of gaseous ammonia and the aqueous solution containing the activator into a single phase.

[0030] At the outlet of the absorption column, an aqueous solution is obtained that contains ammonia dissolved at a ratio of 50% to 100% with respect to the saturation of ammonia in pure water at the temperature of the column, and contains at least one activator. <Dissolved ammonia>

[0031] The solubility of gaseous ammonia in pure water as a function of temperature is known from Lange's Handbook of Chemistry, editor John A. Dean, 12th edition, 1979, page 10.3. This solubility is expressed as the weight of the gas dissolved in 100 g of water at a mercury pressure of 760 mm. The table disclosed on page 10.3 is reproduced below:

Table 1

[0032] These values represent the maximum solubility of ammonia in pure water, i.e., the saturation of pure water by ammonia. In the context of the present invention, the absorption column aims to dissolve ammonia in an aqueous solution containing an activator at a ratio of 50% to 100% with respect to saturated pure water at the temperature of the column. The solubility of ammonia in this aqueous phase is represented by a relative value with respect to the amount of water contained in the aqueous phase containing at least one activator.

[0033] In other words, starting from the values disclosed in the aforementioned Lange's Chemical Handbook and reproduced in Table 1 above, at 20 °C, the dissolution of 26.45 g to 52.9 g of ammonia is targeted. At 70 °C, the dissolution of 5.55 g to 11.1 g of ammonia is targeted.

[0034] Preferably, ammonia is dissolved in an aqueous solution containing an activator at a ratio of 50% to 85% with respect to the saturation of ammonia in pure water at the temperature of the column.

[0035] The flow rate of fresh ammonia can be varied during the process to keep the solubility of ammonia in the aqueous solution constant. At the start of the process, the flow rate of ammonia must be sufficient to achieve the desired ammonia solubility. Thereafter, the flow rate can be reduced to maintain the desired solubility. <Activator>

[0036] The "activator" is understood to mean a compound that enables the activation of hydrogen peroxide, i.e., a compound that enables the production of azine from ammonia, hydrogen peroxide, and ketone.

[0037] This activator can be selected from organic or inorganic oxyacids, their ammonium salts, and their derivatives: anhydrides, esters, amides, nitriles, acyl peroxides, or mixtures thereof. Advantageously, amides, ammonium salts, and nitriles are used.

[0038] Examples include the following: (i) Amides of carboxylic acids of the formula: R5COOH, where R5 is a linear alkyl group having 1 to 20 carbon atoms, or a branched or cyclic alkyl group having 3 to 12 carbon atoms, or an unsubstituted or substituted phenyl group. (ii) Amides of polycarboxylic acids of the formula: R6(COOH)n, where R6 represents an alkylene group having 1 to 10 carbon atoms, n is an integer of 2 or more, and R6 may be a single bond, in which case n is 2.

[0039] The groups R5 and R6 may be substituted by halogen, or an OH, NO2 or methoxy group. Mention may also be made of amides of organic acids of arsenic. Organic acids of arsenic are, for example, methylarsonic acid, phenylarsonic acid and cacodylic acid.

[0040] Preferred amides are formamide, acetamide, monochloroacetamide and propionamide, more preferably acetamide.

[0041] Among ammonium salts, salts of hydroacids, salts of oxyacids anhydrides, salts of arylsulfonic acids, salts of acids of the formula R5COOH or R6(COOH)n (wherein R5, R6 and n are as defined above), and salts of organic acids of arsenic are preferably used.

[0042] Preferred ammonium salts are formate, acetate, monochloroacetate, propionate, phenylarsonate and cacodylate.

[0043] Among nitriles, products of the formula R7(CN)n can preferably be mentioned, where n ranges from 1 to 5 depending on the valence of R7, and R7 is a cyclic or acyclic alkyl having 1 to 12 carbon atoms, or a benzyl or pyridinyl group. R7 may be substituted by a group that is not oxidized in the reactor of step (b), such as halogen or a carboxyl group, carboxylic acid ester group, nitro group, amine group, hydroxyl group or sulfonic acid group.

[0044] Preferred nitriles are acetonitrile and propionitrile.

[0045] A solution containing at least one activator is formed by dissolving one or more products selected from organic or inorganic oxyacids, their ammonium salts, and their derivatives: anhydrides, esters, amides, nitriles, acyl peroxides, or mixtures thereof as defined above. Advantageously, the above-mentioned nitrile, ammonium salt or amide is used. Particularly preferably, a single activator which is acetamide is used.

[0046] This solution is aqueous. According to another embodiment, the solution is an aqueous solution of an amide of a weak acid and the ammonium salt corresponding to this acid, as described in European Patent No. 0 487 160.

[0047] These weak acid amides are derivatives of the corresponding carboxylic acids having a dissociation constant of less than 3×10 -3 , in other words, acids having a pKa greater than 3 in an aqueous solution at 25°C.

[0048] In the case of polycarboxylic acids, the acid in question has a first ionization constant of less than 3×10 -3 .

[0049] By way of example, carboxylic acids of the formula R8COOH where R8 is a linear alkyl radical having 1 to 20 carbon atoms, or a branched or cyclic alkyl radical having 3 to 12 carbon atoms, or an unsubstituted or substituted phenyl radical, and polycarboxylic acids of the formula R9(COOH) n where R9 represents an alkylene radical having 1 to 10 carbon atoms and n is a number of 2 or more can be mentioned; R9 may be a single bond, in which case n is 2. The radicals R8 and R9 may be substituted by halogen, or an OH, NO2 or methoxy group. Preferably, acetamide, propionamide, n-butylamide or isobutylamide is used.

[0050] The corresponding ammonium salt of acetamide is ammonium acetate.

[0051] The in-situ formation of the ammonium salt, i.e., the use of the corresponding carboxylic acid that gives the ammonium salt by reaction with ammonia, is not outside the scope of the present invention.

[0052] The ratio of the amide to the corresponding ammonium salt may vary within a wide range. Generally, 1 to 25 parts, preferably 2 to 10 parts of the ammonium salt are used per 5 parts of the amide. <Apparatus>

[0053] The temperature of the absorption column is between ambient temperature and 70 °C, preferably between 20 °C and 50 °C, more preferably between 25 °C and 45 °C. The pressure of the absorption column may be between atmospheric pressure and a maximum of about 10 bar absolute pressure. Preferably, the reaction is carried out between 1 and 5 bar absolute pressure.

[0054] The column may be a packed distillation column or a plate distillation column.

[0055] It is also possible to completely or partially recover the ammonia stream generated by the process for preparing azine.

[0056] The aqueous solution containing at least one activator may be a recirculated aqueous solution that has completely or partially undergone the regeneration and concentration steps and is derived from separation step c).

[0057] Preferably, the aqueous solution containing at least one activator is introduced at the top of the column, and fresh ammonia and / or recirculated ammonia are preferably introduced countercurrently at the bottom of the column. By combining these streams countercurrently, the mixing of the reactants is improved and the absorption of gaseous ammonia into the aqueous solution is improved.

[0058] Subsequently, the ammoniacal aqueous solution containing at least one activator is introduced into the reactor, and the reaction for forming azine is carried out therein. <b) Mixing reaction>

[0059] The mixing reaction is carried out in at least one reactor. An aqueous solution containing ammonia dissolved at a ratio of 50% to 100% with respect to the saturation of ammonia in pure water at the temperature of the column, and containing at least one activator obtained in the previous step, hydrogen peroxide and a ketone of the formula R1R2CO (groups R1 and R2 independently of each other represent a methyl group, an ethyl group, a propyl group, a butyl group, a pentyl group, a hexyl group, a heptyl group and an octyl group) are introduced into the reactor. <Hydrogen peroxide>

[0060] Hydrogen peroxide can be used in a common commercially available form, for example, an aqueous solution containing 30% to 90% by weight of hydrogen peroxide. Advantageously, it is possible to add one or more conventional stabilizers for peroxide solutions, such as phosphoric acid, pyrophosphoric acid, citric acid, nitrilotriacetic acid or ethylenediaminetetraacetic acid or ammonium salts or alkali metal salts of these acids.

[0061] It is also a known practice to add a sequestering agent that will complex metal ions to stabilize the hydrogen peroxide solution. This suppresses the redox reaction of hydrogen peroxide.

[0062] Sequestering agents particularly used to stabilize hydrogen peroxide solutions are compounds of the type containing a phosphonic acid functional group, in acid form or salt form.

[0063] The following commercial products can be used: - A product sold under the name DEQUEST® 2060 by Monsanto, an aqueous solution of 50% diethylenetriaminepenta(methylenephosphonic acid), - A product sold under the name DEQUEST® 2041, an aqueous solution of ethylenediaminetetra(methylenephosphonic acid), - Aqueous solutions of 1-hydroxyethylidene-1,1-diphosphonic acid at 60% and aminotris(methylenephosphonic acid) and the 40% pentasodium salt of this acid at 29%, respectively, sold under the names DEQUEST (registered trademark) 2010 and 2006.

[0064] These acids can also be used in acid form or in fully or partially neutralized form, for example in the form of sodium salts or ammonium salts.

[0065] The amount used is preferably between 10 and 1000 ppm, preferably between 50 and 250 ppm, of a solution containing at least one activator at the inlet of all reactants and reactors. <Alkyl ketone>

[0066] The alkyl ketone of the formula R1R2CO contains groups R1 and R2 which, independently of one another, represent a methyl group, an ethyl group, a propyl group, a butyl group, a pentyl group, a hexyl group, a heptyl group and an octyl group. Preferably, dimethyl ketone and methyl ethyl ketone are used. Particularly preferably, methyl ethyl ketone is used. Thus, a preferred azine is the azine of methyl ethyl ketone called MEKazine.

[0067] The reactants can be used in stoichiometric amounts. However, it is possible to use 0.2 to 5 moles, preferably 1.5 to 4 moles, of ketone per mole of hydrogen peroxide, and 0.1 to 10 moles, preferably 1.5 to 4 moles, of ammonia. The amount of the solution containing at least one activator can be 0.1 to 2 kg per mole of hydrogen peroxide. This amount depends on its quality, i.e. its catalytic strength or the activity enabling the conversion of the reactants into azine. With the above ratios of reactants, it is possible to obtain a maximum conversion rate of hydrogen peroxide, typically over 90%, preferably over 95%, and a production amount of azine reaching over 75%, in some cases 90%, of the hydrogen peroxide used. <Mixing conditions>

[0068] The reaction can be carried out over a very wide temperature range, for example between 0 °C and 100 °C, and the operation is advantageously between 30 °C and 70 °C. The operation can be carried out at any pressure, but it is simpler to be at atmospheric pressure, and an increase up to approximately 10 bar absolute pressure is possible. Preferably, the reaction is carried out at an absolute pressure of 1 to 5 bar. <Reactor>

[0069] The reactor can have an inner diameter of 1 to 6 m, preferably 2 to 5 m. The working height of the reactor can be 1 to 10 m, preferably 3 to 7 m. Thus, the reaction volume can be 25 to 100 m 3 , preferably 40 to 70 m 3 ³.

[0070] The reactor may be provided with means enabling agitation, such as blades for example.

[0071] Thus, the reactor can include a plurality of agitation stages, preferably two agitation stages. Each agitation stage can include a plurality of inclined blades. Preferably, the blades are arranged at one-third from the bottom and one-third from the top of the reactor. The diameter of the agitation rotating element depends on the diameter of the reactor. Generally, the diameter of the rotating element is between 30% and 70% of the diameter of the reactor.

[0072] The reactor according to the present invention is not a microreactor.

[0073] It is also possible to use a plurality of reactors arranged in cascade. According to this embodiment, the reaction can be carried out in at least two reactors arranged in cascade. Preferably, 3, 4 or 5 reactors in cascade are used. The reactors may have the same volume or different volumes.

[0074] Preferably, the agitation in the first reactor is less than the agitation in the second reactor and subsequent reactors.

[0075] For the purposes of the present invention, stirring is understood to mean the velocity of the flow of the reaction medium in the reactor, which is generated by the movement of a rotating element such as a blade, an anchor or other rotating element, and in some cases in the presence of baffles, or by the Venturi effect. In the case of a medium stirred by a rotating element, the stirring of the reaction medium can be represented by the stirring speed of the rotating element itself.

[0076] According to a particular embodiment of the present invention, if the process uses two, three or more reactors, the reactors arranged after the first reactor can be stirred at the same speed. It is also possible to stir the reactors arranged after the first reactor at an increased speed, i.e., it is also possible to stir the third reactor at a speed greater than the stirring speed of the second reactor.

[0077] The stirring of the reaction medium can be characterized by the Froude number. This parameter is known to those skilled in the art. It is defined in particular in the publication: Chemical Engineering for Chemists (Le genie chimique a l'usage des chimistes) by Joseph Lieto, published by Tec & Doc Lavoisier, 1998). The Froude number is calculated by the following formula: Fr = N 2 D / g where g = acceleration due to gravity, or 9.81 m / s 2 D = diameter of the stirrer (meters) N = rotational speed of the stirrer (revolutions / second).

[0078] When the process according to the present invention includes two or more reactors, the fluid number of the first reactor may be less than 0.018, and the fluid number of the next reactor may be greater than 0.018. Preferably, the fluid number in the first reactor is strictly less than 0.018, and the fluid number in the next reactor is 0.018 or more. More preferably, the fluid number in the first reactor is strictly less than 0.010, and the fluid number in the next reactor is strictly greater than 0.018.

[0079] The ketone can be introduced at the bottom of the reactor, and the aqueous hydrogen peroxide solution can be introduced by a tube immersed in the reactor.

[0080] This mixing step forms an azine.

[0081] At the end of the reaction according to the present invention, the reaction mixture contains an azine, some unreacted ketone, some activator, and some other by-products or impurities. <Circulation loop of an aqueous solution saturated with ammonia>

[0082] According to one embodiment of the present invention, the absorption column of step a) can supply the flow of the reaction medium of the reactor of step b). This flow can be withdrawn using a pipe immersed in the reaction medium of the reactor. Next, this flow is introduced into the top of the absorption column. Once introduced into the absorption column, this flow derived from the reaction medium of step b) is mixed with an aqueous solution containing at least one activator, fresh ammonia, and optionally recycled ammonia. At the outlet of the column, the dissolved ammonia is included in a proportion of 50% to 100% with respect to the ammonia saturation in pure water at the temperature of the column, and the aqueous solution containing at least one activator is sent to the reactor. This circulation loop between the reactor and the absorption column makes it possible to always maintain a high ammonia content in the reaction medium of step b). In other words, the flow withdrawn from the reaction medium of step b) will have an increased ammonia concentration when passing through the absorption column before being reinjected into the reactor.

[0083] When the agitation in the reactor is low, i.e., when the agitation is not sufficient to homogenize the reaction medium, the aqueous phase tends to be present at a high concentration at the bottom of the reactor. Therefore, it is advantageous to withdraw the reaction medium rich in the aqueous phase from this position and introduce it into the absorption column. Accordingly, the withdrawal pipe is preferably arranged starting from the bottom of the reactor and at 1 / 3 of the height of the liquid phase.

[0084] According to one embodiment, when the process uses a plurality of reactors, the reaction medium of each reactor can be withdrawn and introduced into the absorption column.

[0085] According to another embodiment, when the process uses a plurality of reactors, the reaction medium of a single reactor can be withdrawn and introduced into the absorption column of, for example, the first reactor or the last reactor.

[0086] According to yet another embodiment, when the process uses a plurality of reactors, the reaction medium of some but not all of the reactors can be withdrawn and introduced into the absorption column. <c) Separation>

[0087] After the reaction for preparing the azine, the process according to the invention includes a step of separating the stream formed at the end of step b).

[0088] The aqueous phase containing the activator is separated from the organic phase containing the azine and the unreacted alkyl ketone by conventional separation means, such as liquid - liquid extraction, distillation, decantation, or any combination of these possible means. Preferably, decantation is used.

[0089] The obtained organic phase may contain azine, unreacted alkyl ketone, activator(s), and other impurities. <Any recirculation of the aqueous phase>

[0090] Following the separation step c), the aqueous phase can undergo a complete or partial regeneration and concentration step. The aqueous phase thus regenerated and concentrated can be recycled to the absorption column.

[0091] During the step of regenerating and concentrating the aqueous phase from the separation step, a gaseous ammonia stream can be separated and recycled to the absorption column. <Optional washing of the organic phase>

[0092] The process may include a step of washing the organic phase isolated in step c). The step of washing the organic phase obtained in step c) can be carried out by techniques known to those skilled in the art, as shown, for example, in the document WO 2018 / 065997 (page 13, "Organic layer treatment section", second paragraph). This washing step makes it possible, in particular, to recover the activator that may still be present in the organic phase, such as acetamide.

[0093] The above washing can be carried out in a countercurrent washing column.

[0094] The activator that may still be present in the organic phase thus migrates to the aqueous washing phase.

[0095] According to one embodiment, after passing through the washing column, the resulting aqueous phase can be recycled to step a) together with the aqueous phase recovered in step c). <Optional distillation of the organic phase>

[0096] The process may include a step of distilling the organic phase isolated in step c) and optionally washed. The step of distilling the optionally washed organic phase can be carried out by techniques known to those skilled in the art, in particular within a distillation column, as shown, for example, in the document WO 2018 / 065997 (page 13, "Organic layer treatment section").

[0097] The above distillation step is used in particular to separate the azine from high-boiling heavy impurities. These impurities are recovered, for example, at the bottom of the column. The distillation step is also used to separate the azine produced in step b) from the unreacted alkyl ketone, which can be recovered at the top of the column. The alkyl ketone thus recovered can be recycled to the azine synthesis step b). Thus, at the end of the washing and distillation steps, a purified organic phase containing azine is obtained. <d) Hydrolysis>

[0098] The process according to the invention comprises a step of hydrolyzing the (purified or unpurified) organic phase obtained in the previous step in order to obtain hydrazine hydrate.

[0099] The hydrolysis step is carried out under pressure in a reactive distillation column (distillation tower) into which water and the (purified or unpurified) organic phase containing the azine resulting from step c) are injected.

[0100] The hydrolysis can be carried out in a packed or plate distillation column, preferably operating at a bottom temperature of 150 °C to 200 °C under a pressure of 2 to 25 bar absolute pressure.

[0101] Conventional packed columns may be suitable, but generally plate columns are used. Depending on the residence time and pressure allowed on the plates, and thus the operating temperature, the number of plates can vary widely. In practice, when operating under a pressure of 8 to 10 bar absolute pressure, the number of plates required is of the order of 40 to 70.

[0102] What is obtained after hydrolysis is as follows: - at the top, in particular the alkyl ketone in the form of an azeotrope with water, and - at the bottom, an aqueous solution of hydrazine hydrate.

[0103] The hydrolysis of azines is known. For example, E.C. Gilbert described the equilibrium reactions of azine formation and azine hydrolysis in a paper in the Journal of the American Chemical Society, Vol. 51, pages 3397 - 3409 (1929), and provided the thermodynamic parameters of the system in the case of water - soluble azines. For example, the hydrolysis of the azine of acetone is described in U.S. Patent No. 4,724,133. In the case of azines insoluble in aqueous solutions, such as the azine of methyl ethyl ketone, hydrolysis needs to be carried out in a reactive column, and by continuously separating methyl ethyl ketone at the top of the column and hydrazine hydrate at the bottom of the column, complete hydrolysis can be achieved.

[0104] When carried out using pure azine, that is, pure azine obtained from, for example, hydrazine hydrate and methyl ethyl ketone, and working according to these patents, it has actually been found that a dilute solution of hydrazine hydrate can be obtained in good yield.

[0105] In this column, the hydrolysis of azine and the separation of hydrazine hydrate and methyl ethyl ketone are carried out. These conditions are known. A person skilled in the art will be able to easily determine the number of plates, the height of the packing, and the supply points of water and azine. A solution with hydrazine hydrate added up to 20 wt% or 45 wt% is obtained at the bottom. For example, the molar ratio of water / azine during the supply to this column is at least greater than stoichiometry, preferably between 5 and 30, and more preferably between 10 and 20. The temperature at the bottom of the column is between 150 °C and 200 °C, preferably between 175 °C and 190 °C. The pressure depends on the boiling points of azine, water, and ketone. Such hydrolysis is also described in U.S. Patent No. 4,725,421 and International Publication No. 00 / 37357.

[0106] The process according to the present invention can be carried out continuously or batch - wise. Preferably, it is carried out batch - wise. (Description of the Drawings)

[0107] Figure 1 shows an embodiment of the process according to the present invention.

[0108] The preparation of the aqueous ammonia solution is carried out in the absorption column 1. Fresh ammonia is supplied to the absorption column 1 via line 2, and an aqueous solution containing at least one activator is supplied via line 3.

[0109] The aqueous ammonia solution containing at least one activator is supplied to the reactor R via the supply line 4.

[0110] Line 5, the absorption column 1, the supply line 4 and the reactor R form a loop for recirculating the aqueous solution containing dissolved ammonia and activator.

[0111] The reaction of ammonia, hydrogen peroxide and an alkyl ketone in the presence of a solution containing at least one activator is carried out in the reactor R.

[0112] Hydrogen peroxide is supplied to the reactor R via line 6. A ketone is supplied to the reactor R via line 7. This can be a fresh supply of ketone or a supply that recycles the ketone generated from the process.

[0113] Line 8 transports the stream A formed in the reactor R to the decanter 9.

[0114] The decanter 9 separates the organic phase B and the aqueous phase C. The organic phase B is sent to the hydrolysis column 16 via line 10. Water is supplied via line 17. Hydrazine hydrate is recovered via line 18. The ketone stream and the water stream obtained at the top of the column following the hydrolysis of the azine in the hydrolysis column 16 exit through line 19.

[0115] The aqueous phase C is sent via line 11 to the unit 12 for regeneration and concentration of the aqueous phase C.

[0116] Line 13 is a line that bypasses the regeneration and concentration unit 12. Depending on the quality of the aqueous phase, it is possible to direct the aqueous phase C either to the regeneration and concentration unit 12 or to the bypass line 13. It is also possible to send only a part of the aqueous phase C to the regeneration and concentration unit 12. The aqueous phase that has undergone the regeneration and concentration step and / or the aqueous phase that has passed through the bypass line 13 is sent to the top of the absorption column 1 via line 3. During the regeneration and concentration steps, it is also possible to recover ammonia. This ammonia can be recycled to the bottom of the absorption column 1 via line 14. The regeneration and concentration unit 12 may include a purge 15 to remove excess water from the circuit.

[0117] The following examples illustrate the present invention but do not limit it in any way.

Example

[0118] Example 1: Measurement of solubility of ammonia gas in aqueous phase

[0119] Several aqueous phases containing water, ammonium acetate, acetamide, and MEK (methyl ethyl ketone) with different contents were prepared. These aqueous phases were saturated with ammonia at the indicated temperature by flowing ammonia gas at atmospheric pressure in a reactor equipped with a condenser while stirring until the mixture was saturated, i.e., until ammonia gas was no longer absorbed and exited the reactor. Then, while reducing the ammonia flow rate, it was further flowed for another 30 minutes. The ammonia content of the aqueous phase was analyzed by titrating with 1N sulfuric acid (1 ml of the sample).

[0120] One experiment was conducted at 50°C. The results are shown in Table 2 below:

Table 2

[0121] The second experiment was carried out at 60°C. The results are shown in Table 3.

Table 3

[0122] When the ammonia content at saturation in the aqueous phase is related to the amount of water in these aqueous phases, it is found to be close to the solubility value of ammonia in pure water. That is, as shown in Lange's Handbook of Chemistry, it is 23.5 g / 100 g at 50 °C and 16.8 g / 100 g at 60 °C.

[0123] Example 2: Process according to the present invention

[0124] Description of the reaction assembly: Steps a) and b)

[0125] The 1000 ml reactor is equipped with a double jacket that can be heated to maintain the reaction temperature at the desired temperature. It is stirred by a rotating element consisting of three straight glass blades with a diameter of 4 cm. A condenser maintained at 5 °C by the circulation of glycol water is attached to the reactor. The condenser is connected to a bubbler device filled with silicone oil, which monitors the gas evolution and enables the reaction to be maintained at atmospheric pressure.

[0126] The absorption column is a glass column with an inner diameter of about 2 cm, filled with glass beads with a diameter of about 2 mm up to a height of about 10 cm. The double wall is maintained at a temperature of 25 °C to 30 °C by the circulation of water through a thermostatically controlled bath. The gas phase pressure equilibrium is carried out between the headspace of the reactor and the top of the absorption column.

[0127] Ammonia gas is injected into the bottom of the absorption column by an adjustable mass flow meter. The ammonia flow rate is reduced when it is observed that the gas evolution at the bubbler becomes intense.

[0128] The recirculation of the aqueous phase from the reactor to the absorption column is carried out by a peristaltic pump, and the aqueous phase drawn from the reactor is injected into the top of the absorption column. The withdrawal of the recirculated aqueous phase from the reactor is carried out at a height approximately one-third of the height of the liquid phase from the bottom of the reactor.

[0129] The ammoniacal aqueous phase is introduced through the top of the reactor, above the liquid phase of the reactor. Hydrogen peroxide is also introduced through the top of the reactor, above the liquid phase of the reactor.

[0130] Procedure

[0131] Introduce the components of the aqueous phase, namely MEK, water, acetamide, and ammonium acetate, into the reactor. Start stirring and bring the temperature of the medium to the desired reaction temperature. Also start the pump for recirculating the aqueous phase.

[0132] Introduce the reactants at the ratios shown in Table 4 below: [Table 4]

[0133] Hydrogen peroxide is a commercially available 70% aqueous solution.

[0134] Set the stirring of the reaction medium to 100 rpm.

[0135] When the reaction temperature in the reactor reaches 50 °C, start the introduction of fresh ammonia and the introduction of H2O2 simultaneously. Inject 48.6 g of a 70% H2O2 solution over 1 hour, i.e., inject H2O2 at a flow rate of 1 mol / h.

[0136] Set the flow rate of ammonia to 31.8 g / h, i.e., 1.87 mol / h, at t = 0; then adjust during the reaction so that there is no excess ammonia at the outlet of the bubbler device.

[0137] The ammonia content at the outlet of the column and in the aqueous phase was analyzed by titration with 1N sulfuric acid (1 ml of sample).

[0138] The dissolution ratio of ammonia in the aqueous solution at the outlet of the above column is calculated as the relative value to the value of ammonia in pure water at 30 °C, that is, the value of 41.0 g, according to the values in the table on page 10.3 of Lange's Handbook of Chemistry, edited by John A. Dean, 12th edition, 1979.

[0139] The flow velocity of the flow in the recirculation loop is 370 g / h.

[0140] Samples are taken to measure the content of MEKazine in the reactor.

[0141] The yield of MEKazine is calculated according to the following formula: the number of moles of azine produced / the number of moles of theoretical azine (that is, 1 mole per mole of H2O2).

[0142] The data of the reaction are shown in Table 5 below:

Table 5

[0143] Description of the reaction assembly: Step c)

[0144] After the decantation step, MEKazine is recovered.

[0145] Description of the reaction assembly: Step d)

[0146] The apparatus consists of a distillation column with a height of 2.5 m and a diameter of 20 mm, filled with Raschig rings (diameter 5 mm), and temperature sensors are installed at several locations along the column. At the top of the column, there is a condenser and a device capable of setting the flow rates of the condensate returned to the top of the column and the withdrawn condensate. The reflux ratio is set by a timer device (the mass ratio of the reflux flow rate to the withdrawn flow rate).

[0147] The boiler at the bottom of the distillation column has a volume of 160 ml and is equipped with a device for visualizing the liquid level. By manually withdrawing from the boiler, the produced hydrazine hydrate solution can be taken out, and the liquid level in the boiler can be kept substantially constant.

[0148] Water and MEKazine are introduced by a pump starting from the top of the distillation column and in the first one-third.

[0149] All assemblies are designed to operate at the desired operating pressure (absolute pressure 8 bar) and are equipped with a rupture seal of 12 bar as a safety measure.

[0150] Tower adjustment

[0151] Introduce a hydrazine hydrate solution containing 25% hydrazine hydrate (N2H4.H2O) into the boiler and gradually increase the bottom temperature until steam reaches the top of the column. The pressure is set to 8 bar in absolute pressure.

[0152] Hydrolysis of azine

[0153] Next, start introducing water simultaneously at a flow rate of 36 g / h (2 mol / h) and methyl ethyl ketone azine at a flow rate of 28 g / h (0.2 mol / h). When the column reaches equilibrium, set the reflux ratio at the top of the column to 0.5 and continuously withdraw hydrazine hydrate at the bottom to keep the level in the boiler constant.

[0154] The operation is carried out for about 8 hours. The bottom temperature is 178 - 177 °C and the top temperature is 150 - 151 °C.

[0155] During operation, an aqueous solution of 31 g / h of hydrazine hydrate with a concentration of 31% (expressed as N2H4.H2O) is thus withdrawn at the bottom of the column. 32 g / h of methyl ethyl ketone containing 12% water is taken out at the top.

[0156] Example 3: Process according to the present invention

[0157] The process of Example 3 is the same as that of Example 2, but the flow rate of the recirculation loop is changed: that is, it is doubled.

[0158] The reaction data are shown in Table 6 below:

Table 6

[0159] These results show that a very good yield can be obtained at the optimal ammonia consumption.

Claims

1. The process for preparing hydrazine hydrate includes the following sequential steps: a) Prepare an absorption column by introducing an aqueous solution containing ammonia dissolved in pure water at a ratio of 50% to 100% relative to the saturation of ammonia at the absorption column temperature, and containing at least one activator, into the absorption column; then b) An aqueous ammonia solution containing at least one activator obtained in the previous step is heated in at least one reactor with hydrogen peroxide and formula: R 1 R 2 CO ketone (wherein the formula, the group R 1 and R 2 These react independently with a methyl group, ethyl group, propyl group, butyl group, pentyl group, hexyl group, heptyl group, and octyl group; then c) Separate the organic phase containing azine from the aqueous phase from the flow formed at the end of the previous step; then d) The organic phase obtained in the previous step is hydrolyzed to obtain hydrazine hydrate.

2. The process according to claim 1, wherein in step a) above, an aqueous solution containing at least one activator is introduced at the top of the absorption column, and fresh ammonia is introduced in a countercurrent, preferably at the bottom of the absorption column.

3. The process according to claim 1, wherein the flow of the reaction medium in the reactor in step b) above is supplied to the absorption column in step a), and this flow is injected at the top of the absorption column.

4. The process according to claim 1, wherein the aqueous solution isolated in step c) above is recycled back into the absorption column in step a) above.

5. The process according to claim 1, wherein one or more streams of ammonia recycled in the process are supplied to the absorption column in step a) above.

6. The process according to claim 1, wherein the ketone used in step b) above is methyl ethyl ketone.

7. The process according to claim 1, characterized by comprising the step of regenerating and concentrating the aqueous phase from step c) above.

8. The process according to claim 1, characterized by comprising the step of washing the organic phase from step c) above.

9. The process according to any one of claims 1 to 8, characterized in that the above process is carried out in a batch manner.

10. The process according to any one of claims 1 to 8, characterized in that the above process is carried out continuously.

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