Method for preparing azine using cascade reactors

Abstract

The invention relates to a method for continuously preparing azine, which comprises a step of reacting ammonia, hydrogen peroxide and a ketone of formula R1R2CO, the groups R1 and R2 denoting, independently of each other, a methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl and octyl group, in the presence of an aqueous solution comprising at least one activator to form an azine, the reaction being carried out in at least two reactors arranged in cascade, the agitation of the first reactor being less than the agitation of the or each of the following reactors, the reactants being injected into the first reactor, the aqueous solution comprising at least one activator and comprising solubilised ammonia in a proportion of between 50% and 100% relative to the saturation of the ammonia in pure water at the temperature of the aqueous solution.

Description

PROCESS FOR PREPARING AZINE USING CASCADE REACTORS

[0001] The present invention relates to a process for preparing azine.

[0002] The present invention relates more specifically to a process for the preparation of azine obtained in the presence of a ketone by oxidation of ammonia with hydrogen peroxide and in the presence of an activator.

[0003] Hydrazine is used in various applications, mainly in the deoxygenation of boiler water (e.g. nuclear power plants) and is used in the preparation of pharmaceutical and agrochemical derivatives.

[0004] There is therefore an industrial need for the preparation of hydrazine hydrate, obtained from the hydrolysis of azine.

[0005] The industrial production of hydrazine hydrate is carried out according to the RASCH IG, BAYER processes or from hydrogen peroxide.

[0006] In the RASCH IG process, ammonia is oxidized with 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.

[0007] The BAYER process is an improvement of the RASCHIG process, which consists of 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.

[0008] The azine is then isolated and hydrolyzed to hydrazine hydrate. Yields are improved, but there is no improvement in environmental emissions.

[0009] The hydrogen peroxide process involves oxidizing a mixture of ammonia and a ketone with hydrogen peroxide in the presence of a hydrogen peroxide activator to directly produce the azine, which then only needs to be hydrolyzed to hydrazine hydrate. Yields are high and the process is less polluting. This hydrogen peroxide process is described in numerous patents, for example US 3,972,878, US 3,972,876 and US 4,093,656.

[0010] These processes are also described in ULLMANN'S ENCYCLOPEDIA OF INDUSTRIAL CHEMISTRY (1989), vol A 13, pages 180-183 and the references therein.

[0011] In hydrogen peroxide processes, ammonia is oxidized by hydrogen peroxide in the presence of a ketone and a hydrogen peroxide activator in the following overall reaction, forming an azine:

[0012] The activating agent or activator can be a nitrile, an amide, a carboxylic acid or a derivative of selenium, antimony or arsenic. Then the azine is hydrolyzed to hydrazine and the ketone is regenerated according to the following reaction

[0013] This hydrolysis is actually carried out in two stages, with the formation of an intermediate hydrazone: hydraz ne

[0014] Whether the azine is produced by an oxidized water process or another process, methyl ethyl ketone is advantageously used because it is sparingly soluble in an aqueous medium.

[0015] 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 with a concentration between 30 and 70% by weight are used. This azine is therefore easily recoverable and separable by simple decantation. It is very stable, especially in an alkaline medium, i.e. 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 especially an aqueous solution of hydrazine hydrate at the bottom. This must contain as few carbonaceous products as possible as impurities and must be colorless.

[0016] An efficient method for preparing hydrazine hydrate is known from WO 2020 / 229773.

[0017] However, improvements to this process are still being sought. In other words, an improvement in the conversion rate of reactants, an improvement in the final yield, a reduction in side reactions are constantly sought, so that production is as efficient as possible.

[0018] The azine formation reaction is relatively complex, as it involves three phases: a gas phase with ammonia, an organic phase with the ketone, and an aqueous phase with the activator and hydrogen peroxide. However, for the reaction to be efficient, it is necessary for the reactants to come into contact with each other. Thus, the efficiency of this reaction is directly linked to the exchanges and contacts between the phases of the reactants.

[0019] It is known from the scientific article Agitation effects in a gas-liquid-liquid reactor system: methyl ethyl ketazine production by R. Kaur and K.D.P.Nigam in the International Journal of Chemical Reactor Engineering!, January 2007, that agitation is a determining factor for improvement. It was observed that the higher the agitation speed, the more the yield increases up to a threshold value of 600 rpm. However, these experiments were conducted on a semi-batch reactor. However, industrial sites are generally equipped with continuous processes. Furthermore, agitation of 600 rpm applied to industrial volume reactors represents a significant energy consumption. Therefore, solutions are still being sought to make these gas-liquid-liquid contacts efficient, whether in terms of yield or energy consumption, within a continuous industrial process.

[0020] Indeed, the inventors discovered that by carrying out the mixing reaction in several reactors and by adapting the respective stirring of the reactors, they were able to reduce the formation of undesirable by-products of the reaction. In particular, it was found that the method according to the invention allows a reduction in the production of aminoperoxide, a by-product of the reaction. Aminoperoxide is for example described in application FR 2950887. This reduction is observed across all the reactors. Brief description of the figures

[0021] Figure 1 is a diagram of the device implementing the claimed method.

[0022] Figure 2 is a diagram of the device implementing the claimed method according to another embodiment. Brief description of the invention

[0023] Thus, the subject of the present invention is a process for the continuous preparation of azine, comprising a step a) of reacting ammonia, hydrogen peroxide and a ketone of formula R1R2CO, the groups R1 and R2 denoting independently of one another a methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl and octyl group, in the presence of an aqueous solution comprising at least one activator to form an azine, the reaction being carried out in at least 2 reactors arranged in cascade, the stirring of the first reactor being less than the stirring of the or each of the following reactors, the hydrogen peroxide, the ketone and an aqueous solution comprising at least one activator and comprising solubilized ammonia, preferably in a proportion of between 50% and 100% relative to the saturation of ammonia in pure water at the temperature of the aqueous solution, being injected into the first reactor. Detailed description of the invention

[0024] Other features, aspects, objects and advantages of the present invention will become even more apparent from the following description.

[0025] It is specified that the expressions “from ... to ...” and “between ... and ....” used in this description must be understood as including each of the limits mentioned.

[0026] “Continuous” means, for the purposes of the present invention, that the flow of reactants introduced into the reactor and of the products synthesized during the process is uninterrupted.

[0027] The preparation of hydrazine hydrate is carried out according to the following steps: - ammonia, hydrogen peroxide and an alkyl ketone of formula RIR2C=O are reacted in the presence of an aqueous solution comprising at least one activator to form an azine; - the azine of the ketone formed is hydrolyzed to obtain hydrazine hydrate.

[0028] The invention relates to the first step of this method. The reagents Hydrogen peroxide

[0029] Hydrogen peroxide may be used in its usual commercial form, for example in aqueous solution comprising between 30% and 90% by weight of oxygen peroxide.

[0030] Advantageously, one or more usual stabilizers of peroxide solutions may be added, for example phosphoric, pyrophosphoric, citric, nitrilotriacetic, ethylenediaminetetraacetic acid or the ammonium or alkali metal salts of these acids.

[0031] It is also known to stabilize hydrogen peroxide solutions by adding sequestering agents that will complex the metal ions. This inhibits the oxidation-reduction reaction of hydrogen peroxide.

[0007] Sequestering agents particularly used to stabilize hydrogen peroxide solutions are compounds of the type comprising phosphonic functions, in their acid form or in their salt form.

[0008] The following commercial products may be used: -the product sold under the name DEQUEST® 2060 by the company MONSANTO, which is a 50% aqueous solution of ethylene triamine penta(methylene phosphonic acid), -the product marketed under the name DEQUEST® 2041, which is an aqueous solution of ethylenediaminetetra(methylenephosphonic acid), -the products marketed under the name DEQUEST® 2010 and 2006, respectively a 60% aqueous solution of 2-hydroxyethylene-1,1-diphosphonic acid and a 29% aqueous solution of amino-tris-methylenephosphonic acid and 40% of pentasodium salt of this acid.

[0032] These acids can also be used in their acid form or completely or partially neutralized, for example in the form of sodium salt or ammonium salt.

[0033] 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. Alkyl ketone

[0034] The alkyl ketone of formula R1R2CO comprises groups R1 and R2 which independently denote a methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl and octyl group. Preferably, dimethyl ketone and methyl ethyl ketone are used. Particularly preferably, methyl ethyl ketone is used. Therefore, the preferred azine is methyl ethyl ketone azine, called MECazine. The activator

[0035] By "activator" is meant a compound that can activate hydrogen peroxide, i.e., a compound such that azine can be produced from ammonia, hydrogen peroxide and a ketone.

[0036] This activator can be chosen 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.

[0037] For example, we can cite: (i) carboxylic acid amides of formula R5COOH in which R5 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 atoms, or a phenyl radical which may be substituted, (ii) polycarboxylic acid amides of formula Rs(COOH)n in which Rs represents an alkylene radical having from 1 to 10 carbon atoms and n being an integer greater than or equal to 2, Rs can be a single bond, then n is 2.

[0038] The radicals Rs and Re can be substituted by halogens, OH, NO2 or methoxy groups. Also amides of organic arsenic acids can be mentioned. Organic arsenic acids are, for example, methylarsonic acid, phenylarsonic acid and cacodylic acid.

[0039] Preferred amides are formamide, acetamide, monochloroacetamide and propionamide, and more preferably acetamide.

[0040] Among the ammonium salts, the salts of hydracids, mineral oxyacids, arylsulfonic acids, acids of formulas RsCOOH or R6(COOH) are advantageously used. n , Rs, Re and n being defined previously, organic acids of arsenic.

[0041] Preferred ammonium salts are formate, acetate, monochloroacetate, propionate, phenylarsonate and cacodylate.

[0042] Among the nitriles, advantageously mentioned are the products of formula R?(CN)n, n being able to vary from 1 to 5 depending on the valence of R7, R7 is a cyclic or non-cyclic alkyl having from 1 to 12 carbon atoms or a benzyl or a pyridinyl group. R7 can be substituted by groups which do not oxidize in the reactor of step (a), for example halogens, carboxylic groups, carboxylic esters, nitro, amine, hydroxy or sulfonic acid.

[0043] The preferred nitriles are acetonitrile and propionitrile.

[0044] 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 preceding amides, ammonium salts or nitriles are used. Particularly preferably, a single activator, which is acetamide, is used.

[0045] This solution is aqueous. According to another embodiment, said solution is an aqueous solution of a weak acid amide and the ammonium salt corresponding to this acid as described in patent EP 0 487 160.

[0046] These weak acid amides are derived from the corresponding carboxylic acids which have a dissociation constant less than 3 x 10' 3 , that is, acids, which have a pKa greater than 3 in aqueous solution at 25°C.

[0047] For polycarboxylic acids, these are acids whose first ionization constant is less than 3 x 10' 3 .

[0048] Examples include carboxylic acids of formula RsCOOH in which Rs 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. carbon, or a phenyl radical which may be substituted, polycarboxylic acids of formula Rg(COOH) n in which R9 represents an alkylene radical having from 1 to 10 carbon atoms and n being a number greater than or equal to 2, R9 can be a single bond then n is 2. The radicals Rs and R9 can be substituted by halogens, OH, NO2 or methoxy groups. Acetamide, propionamide, n-butyramide or isobutyramide are preferably used.

[0049] The corresponding ammonium salt of acetamide is ammonium acetate.

[0050] It would not be outside 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.

[0051] The proportions of the amide and the corresponding ammonium salt can vary within wide limits. Usually 1 to 25 parts of the ammonium salt are used for 5 parts of amide and preferably 2 to 10. Ammonia

[0052] Ammonia is dissolved in the aqueous solution, which includes at least one activator.

[0053] 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, 12 eedition, 1979, on page 10.3. This solubility is expressed as the weight of gas dissolved in 100 grams of water at a pressure of 760 mm of mercury. The table disclosed on page 10.3 is reproduced below: Table 1

[0054] These values ​​express the maximum solubility of ammonia in pure water, i.e. the saturation of pure water by ammonia. In the context of the invention, an aqueous solution comprising solubilized ammonia, preferably in a proportion of between 50% and 100% relative to the saturation of ammonia in pure water at the temperature of the aqueous solution, and comprising at least one activator is introduced into the first reactor. This solubility of ammonia in the aqueous phase is expressed relative to the quantity of water contained in the aqueous phase comprising at least one activator.

[0055] In other words, starting from the values ​​disclosed in the aforementioned Lange's Handbook of Chemistry and reproduced in Table 1 above, at 20°C, a solubilization of ammonia of 26.45g to 52.9g of ammonia is targeted. At 70°C, a solubilization of 5.55g to 11.1g of ammonia is targeted.

[0056] Preferably, the ammonia is solubilized in the aqueous solution containing activator in a proportion of between 50% and 85% relative to the saturation of ammonia in pure water at the temperature of the aqueous solution.

[0057] Preferably, the temperature of the aqueous solution is lower than that of the reactor. More particularly, the temperature of the aqueous solution is more than 10°C lower than the temperature of the reactor, and even more preferably more than 20°C lower than the temperature of the reactor.

[0058] The reactants may be used in stoichiometric amounts. However, per mole of hydrogen peroxide from 0.2 to 5 moles and preferably from 1.5 to 4 moles of ketone; from 0.1 to 10 moles and preferably from 1.5 to 4 moles of ammonia may be used. The amount of solution comprising at least one activator may be between 0.1 and 2 kg per mole of hydrogen peroxide. This amount depends on its quality, i.e. its catalytic strength or its activity which allows the reactants to be converted into azine. The proportions of the reactants set above make it possible to obtain a maximum conversion, typically greater than 90%, preferably greater than 95% of hydrogen peroxide and an azine production corresponding to more than 75% of hydrogen peroxide involved and which may reach 90%. a) Mixing reaction

[0059] The reaction can take place over a very wide temperature range, for example between 0°C and 100°C, and it is advantageous to operate between 30°C and 70°C. It is possible for there to be a temperature gradient between the different reactors. For example, the temperature of the first reactor may be around 45°C, while that of the last reactor may be around 60°C. Although it is possible to operate at any pressure, it is simpler to operate at atmospheric pressure, but it is possible to go up to about 10 bar absolute. Preferably, the reaction is carried out between 1 and 5 bar absolute. The reactors

[0060] The reaction takes place in at least two reactors arranged in cascade. Preferably, 3, 4 or 5 cascade reactors are used.

[0061] The agitation at the first reactor is less than the agitation of the second reactor, and possibly of the following reactor(s).

[0062] For the purposes of the present invention, agitation means the speed of the flow of the reaction medium within the reactor generated by the movement of a moving part, such as a blade, a counter-blade, an anchor and any other moving part, or by a venturi effect. For a medium agitated by a moving part, the agitation of the reaction medium can be expressed by the agitation speed of the moving part itself.

[0063] When the process uses 3 or more reactors, the reactors positioned after the first reactor can be stirred at an identical speed. It is also possible for the reactors positioned after the first reactor to be stirred at an increasing speed, i.e., the third reactor is stirred at a speed higher than the stirring speed of the second reactor.

[0064] The reactors may have an internal diameter of between 1 and 6 m, preferably between 2 and 5 m. The useful height of the reactor may be between 1 and 10 m, preferably between 3 and 7 m. Thus, the reaction volume may be between 25 and 100 m 3 , preferably between 40 and 70 m 3 The reactors can be of the same volume or of different volumes.

[0065] Preferably, the reactors may be equipped with stirring means, for example blades.

[0066] Thus, the reactor may have several stirring stages, preferably two stirring stages. Each stirring stage may have several inclined blades. Preferably, the blades are positioned in the lower third of the reactor and in the upper third of the reactor. The diameter of the stirring rotors depends on the diameter of the reactor. Generally, the diameter of the rotor is between 30 and 70% of the diameter of the reactor.

[0067] The reactors according to the invention are not microreactors.

[0068] The agitation of the reaction medium can be characterized by the Froude number. This parameter is known to those skilled in the art. It is notably defined in the work: Chemical Engineering for the Use of Chemists by Joseph Lieto, Tec & Doc Lavoisier edition of 1998. The Froude number is calculated according to the following formula: Fr = N 2 D / g with g = acceleration of gravity, or 9.81 m / second 2 D = diameter of the agitator in meters, N = number of rotations of the agitator in revolutions per second

[0069] Preferably, the Froude number in the first reactor is strictly less than 0.018 and the Froude number in the following reactor(s) is greater than or equal to 0.018. More preferably, the Froude number in the first reactor is less than 0.010 and the Froude number in the following reactor(s) is greater than 0.018.

[0070] The introduction of the ketone can be done at the bottom of the first reactor and the introduction of the aqueous solution of hydrogen peroxide can be done by a rod dipping inside this first reactor. The ammonia is introduced into the first reactor in dissolved form in the aqueous solution containing at least one activator.

[0071] The process according to the invention thus makes it possible to reduce the formation of aminoperoxide. In the first reactor, the production of aminoperoxide is low, due to slow stirring. In the following reactors, the high stirring speed makes it possible to consume this aminoperoxide more quickly to transform it into azine. Thus, the quantity of aminoperoxide is less, while the quantity of azine produced is increased.

[0072] At the end of the reaction according to the invention, the reaction mixture comprises the ketone azine, optionally the unreacted ketone, optionally the activator(s), and optionally other by-products or impurities. Preparation of the aqueous solution

[0073] An aqueous ammonia solution can be prepared using an absorption column.

[0074] The absorption column can be fed with fresh ammonia and an aqueous solution containing at least one activator.

[0075] The absorption column aims to solubilize gaseous ammonia in the aqueous solution containing at least one activator. The absorption column has the function of making this mixture of gaseous ammonia and aqueous solution containing an activator monophasic.

[0076] At the outlet of the absorption column, an aqueous solution comprising solubilized ammonia in a proportion of between 50% and 100% relative to the saturation of ammonia in pure water at the column temperature and comprising at least one activator is obtained. Thus, when an absorption column is used within the process, then it is the column temperature which is relevant for calculating the ammonia saturation of the aqueous solution. Solubilized ammonia

[0077] According to this embodiment, the absorption column aims to solubilize the ammonia in the aqueous solution containing the activator at a percentage of between 50% and 100% relative to pure water saturated at the temperature of the column. This solubility of the ammonia in the aqueous phase is expressed relative to the quantity of water contained in the aqueous phase comprising at least one activator.

[0078] Preferably, the ammonia is solubilized in the aqueous solution containing activator in a proportion of between 50% and 85% relative to the saturation of ammonia in pure water at the column temperature.

[0079] The flow rate of fresh ammonia can be varied during the process to maintain a constant solubility of ammonia in the aqueous solution. At the start of the process, the ammonia flow rate should be sufficient to achieve the desired ammonia solubility. Subsequently, the flow rate can be reduced to maintain the desired solubility. The apparatus

[0080] The temperature of the absorption column may be between room temperature and 70°C, preferably between 20°C and 50°C, and most preferably between 25°C and 45°C. The pressure of the absorption column may be between atmospheric pressure and up to about 10 bar absolute. Preferably, the reaction is carried out between 1 and 5 bar absolute.

[0081] The column may be a packed or tray distillation column. It is fed with ammonia and an aqueous solution comprising at least one activator.

[0082] It is also possible to recover, totally or partially, the ammonia stream(s) generated by the azine preparation process.

[0083] The aqueous solution containing at least one activator may be a recycled aqueous solution, which comes from separation step b), which may have undergone, in whole or in part, a regeneration and concentration step.

[0084] Preferably, the aqueous solution comprising at least one activator is introduced at the top of the column and the fresh ammonia and / or the possibly recycled ammonia is introduced countercurrently, preferably at the bottom of the column. The meeting of these countercurrent flows allows better mixing of the reactants and better absorption of the gaseous ammonia into the aqueous solution.

[0085] The aqueous ammoniacal solution comprising at least one activator is then introduced into the first reactor, in which the azine formation reaction is carried out. Saturated aqueous ammonia solution circulation loop

[0086] According to one embodiment of the invention, the absorption column can be fed with a flow of the reaction medium from the first reactor of step a). This flow can be taken using a rod immersed in the reaction medium of the reactor. It is then introduced at the top of the absorption column. Once introduced into the absorption column, this flow from the reaction medium of step a) is mixed with the aqueous solution comprising at least one activator, and with fresh ammonia, and optionally with recycled ammonia. At the column outlet, the aqueous solution comprising ammonia solubilized in a proportion of between 50% and 100% relative to the saturation of ammonia in pure water at the temperature of the column and comprising at least one activator is sent to the first reactor. This circulation loop between the first reactor and the absorption column make it possible to constantly maintain a high ammonia content in the reaction medium of step a). In other words, the flow taken from the reaction medium of step a) will see its ammonia concentration increased by passing through the absorption column, before being reinjected into the first reactor.

[0087] When the agitation in the first reactor is low, i.e. when the agitation is not sufficient to homogenize the reaction medium, the aqueous phase then tends to be present in a greater concentration in the bottom of the reactor. It is then advantageous to sample the reaction medium rich in aqueous phase at this point to introduce it into the absorption column. The sampling rod is thus preferably positioned in the first third of the liquid phase height starting from the bottom of the reactor.

[0088] According to one embodiment, the reaction medium from each reactor can be taken and introduced into the absorption column.

[0089] According to another embodiment, the reaction medium from a single reactor can be taken and introduced into the absorption column, for example the first reactor or the last reactor.

[0090] According to yet another embodiment, the reaction media from several reactors, but not all of the reactors, can be taken and introduced into the absorption column. b) Separation reaction

[0091] The process according to the invention may comprise, after the azine preparation reaction, a step of separating the flow formed at the end of the previous step.

[0092] The aqueous phase comprising the activator(s) is separated from the organic phase comprising the azine of the alkyl ketone and optionally the unreacted alkyl ketone by conventional means such as liquid-liquid extraction, distillation, decantation or any combination of these possibilities. Preferably, decantation is used.

[0093] The resulting organic phase may include the alkyl ketone azine formed, unreacted alkyl ketone, activator(s), and possibly other impurities. c) Regeneration reaction

[0094] Following separation step b), the aqueous phase may undergo, in whole or in part, a regeneration and concentration step. This aqueous phase, thus regenerated and concentrated, may be recycled into the first reactor or into the ammonia absorption column, when it is present in the process.

[0095] During the regeneration and concentration step of the aqueous phase from separation step b), a stream of gaseous ammonia can be recycled in the ammonia absorption column, when present in the process.

[0096] This regeneration step is described in patents EP0399866 and EP0518728.

[0097] Following separation step b), the process may comprise: - a step of washing the organic phase, resulting from the separation step, - a step of hydrolysis of the stream obtained in the previous step to obtain hydrazine hydrate. Description of figures

[0098] Figure 1 represents an embodiment of the method according to the invention.

[0099] The reaction of ammonia, hydrogen peroxide and alkyl ketone in the presence of a solution comprising at least one activator to form an azine is carried out in 4 cascaded reactors denoted R1, R2, R3 and R4.

[0100] Reactor R1 is supplied with ketone via line 1. This may be a fresh ketone feed or a feed recycling a ketone from the process. Reactor R1 is supplied with oxygen peroxide via line 2 and with aqueous ammoniacal solution comprising at least one activator via line 3.

[0101] Lines 4, 5 and 6 carry respectively the flow (A), (B) and (C), which emanate from reactors R1, R2, R3 to the next reactor, i.e. R2, R3 and R4. Line 7 carries the flow D formed in reactor 4 to the decanter 8.

[0102] The decanter 8 separates the organic phase E and the aqueous phase F. The organic phase E is sent via the line 9 to the subsequent steps of the process. The aqueous phase 10 is sent to the unit 11 for regeneration and concentration of the aqueous phase F. The line 12 is a line, which bypasses the regeneration and concentration unit 11. Depending on the quality of the aqueous phase, it is possible to direct the aqueous phase F to the unit 11 or to the bypass line 12. It is also possible to send only a part of the aqueous phase F to the regeneration and concentration unit 11. The aqueous phase, which has undergone the regeneration and concentration step and / or the aqueous phase, which has passed via the bypass line 12 is brought to the reactor R1 via the line 13. The regeneration and concentration unit 11 may include a purge 14 in order to eliminate excess water from the circuit.

[0103] Figure 2 represents another embodiment of the method according to the invention.

[0104] The reaction of ammonia, hydrogen peroxide and alkyl ketone in the presence of a solution comprising at least one activator to form an azine is carried out in 4 cascaded reactors denoted R41, R42, R43 and R44.

[0105] Reactor R41 is supplied with ketone via line 21. This may be a fresh ketone feed or a feed recycling a ketone from the process. Reactor R41 is supplied with oxygen peroxide via line 22 and with a saturated aqueous ammonia solution comprising at least one activator via line 23.

[0106] Lines 24, 25 and 26 carry respectively the stream (A), (B) and (C), which emanate from reactors R41, R42, R43 to the next reactor, i.e. R42, R43 and R44. Line 27 carries the stream D formed in reactor 4 to the decanter 28.

[0107] The decanter 28 separates the organic phase E and the aqueous phase F. The organic phase E is sent via the line 29 to the subsequent stages of the process. The aqueous phase 30 is sent to the unit 31 for regeneration and concentration of the aqueous phase F. The line 32 is a line, which bypasses the regeneration and concentration unit 31. Depending on the quality of the aqueous phase, it is possible to direct the aqueous phase F to the unit 31 or to the bypass line 32. It is also possible to send only part of the aqueous phase F to the regeneration and concentration unit 31. The aqueous phase, which has undergone the regeneration and concentration step and / or the aqueous phase, which has passed via the short-circuit pipe 32 is brought to the top of the ammonia absorption column 33 via the pipe 34. During the regeneration and concentration step, it is also possible to recover ammonia.This ammonia can be recycled via line 35 at the bottom of the ammonia absorption column 33. The regeneration and concentration unit 31 can include a purge 36 in order to remove excess water from the circuit. The ammonia absorption column 33 can also be supplied with fresh ammonia via line 37. Finally, the reaction phase from reactor R41 is sent to the top of the ammonia absorption column 33, via line 38.

[0108] Line 38, absorption column 33, feed line 23 and reactor R41 form an ammonia recirculation loop.

[0109] The following examples illustrate the present invention, but are in no way limiting. Example

[0110] The example compares two processes for preparing azine, one according to the invention and the other comparative.

[0111] The reaction step is carried out according to the setup shown in Figure 2. The processes use 4 cascade reactors. Methyl ethyl ketone is used as a reactant.

[0112] The reactor temperatures are as follows: TR4I = 50°C; TR42 = 51°C; TR43 = 52.5°C; TR44 = 55°C. The reactions are carried out at atmospheric pressure.

[0113] The aminoperoxide and azine fluxes formed in each reactor are evaluated.

[0114] The circulation flow rate in line 38, i.e. from reactor R41 to the ammonia absorption column, is 24 t / h. Ammonia absorption is carried out at a temperature of 30°C.

[0115] The flow rates of the reactants arriving in reactor R41 are shown in Table 2 below: Table 2

[0116] The stirring conditions for each process are shown in Table 2 below. The reactors have a 1.7m diameter stirrer. The aminoperoxide formation and azine production are evaluated at the outlet of each reactor. The values ​​are shown in Tables 3 and 4 below. Table 3 Table 4

[0117] These results show that the stirring system as claimed makes it possible to reduce the production of aminoperoxide in each of the reactors. Thus, the difference in stirring applied between reactor 41 and reactor 42 has a significant effect on the quantity of aminoperoxide produced in these reactors, and this effect is still visible in reactors 43 and 44. Furthermore, an increase in efficiency is also obtained.

Claims

Demands

1. A process for the continuous preparation of azine, comprising a step a) of reacting ammonia, hydrogen peroxide and a ketone of formula R1R2CO, the groups Ri and R2 independently denoting a methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl and octyl group, in the presence of an aqueous solution comprising at least one activator to form an azine, the reaction being carried out in at least 2 reactors arranged in cascade, the stirring of the first reactor being less than the stirring of the or each of the subsequent reactors, the hydrogen peroxide, the ketone and an aqueous solution comprising at least one activator and comprising solubilized ammonia, preferably in a proportion of between 50% and 100% relative to the saturation of ammonia in pure water at the temperature of the aqueous solution, being injected into the first reactor.

2. A process according to claim 1, characterized in that the aqueous solution comprising at least one activator and solubilized ammonia is obtained from an absorption column.

3. A method according to any one of the preceding claims, characterized in that the agitation within the first reactor is characterized by a Froude number strictly less than 0.018 and the agitation of the subsequent reactor(s) is characterized by a Froude number greater than or equal to 0.

018.

4. A method according to any one of the preceding claims, characterized in that the reaction is carried out in 3, 4 or 5 reactors arranged in cascade.

5. A process according to any one of the preceding claims, characterized in that the ketone used in step a) is methylethyl ketone.

6. A method according to any one of the preceding claims, characterized in that it comprises, after the reaction step a), a separation step b) of the flow formed at the end of the reaction step a).

7. A process according to claim 6, characterized in that it comprises a step c) of regeneration and concentration of the aqueous phase from the separation step b).

8. A process according to claim 7, characterized in that during step c) of regeneration and concentration of the aqueous phase from the separation step b), the aqueous phase thus regenerated and concentrated is recycled into the ammonia absorption column.

9. A process according to claim 7 or 8, characterized in that during step c) of regeneration and concentration of the aqueous phase from the separation step b), a stream of gaseous ammonia is recycled into the ammonia absorption column.

10. A method according to any one of claims 6 to 9, characterized in that it comprises: -a washing step of the organic phase, resulting from the separation step b), -a hydrolysis step of the flux obtained in the previous step to obtain hydrazine hydrate.

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