Method for preparing azine by using cascade reactor

Abstract

The invention relates to a process for the continuous preparation of azine, comprising the step of reacting ammonia, hydrogen peroxide and a ketone of formula R1R2CO in the presence of an aqueous solution comprising at least one activator to produce azine, the groups R1 and R2 independently of each other representing methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl and octyl; the reaction is carried out in at least two reactors which are arranged in a cascading manner; the stirring of the first reactor is less than that of the subsequent reactor or each subsequent reactor; the reactants are injected into the first reactor, the aqueous solution comprising at least one activator and comprising dissolved ammonia in a proportion of between 50% and 100% relative to the saturation of ammonia in pure water at the temperature of the aqueous solution.

Description

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

[0002] The invention relates more particularly to a process for preparing an azine obtained by oxidizing ammonia with hydrogen peroxide in the presence of a ketone and in the presence of an activator.

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

[0004] Therefore, there is an industrial need to prepare hydrazine hydrate, which is obtained by hydrolysis of azine.

[0005] Hydrazine hydrate is produced industrially by the Raschig or Bayer process or from hydrogen peroxide.

[0006] In the Raschig process, ammonia is oxidized with hypochlorite to give a dilute solution of hydrazine hydrate, which must then be concentrated by distillation. This process is relatively non-selective, relatively inefficient and highly polluting and is no longer used in practice.

[0007] The Bayer process is a modification of the Raschig process which involves altering the chemical equilibrium by trapping the hydrazine formed in the azine form of the formula:

[0008] .

[0009] The azine is then separated and hydrolyzed to hydrazine hydrate. The yield is improved, but the environmental emissions are not improved.

[0010] The hydrogen peroxide method involves oxidizing a mixture of ammonia and ketone with hydrogen peroxide in the presence of a means for activating hydrogen peroxide to directly prepare an azine, which then only needs to be hydrolyzed to hydrazine hydrate. The yield is high and the pollution is low. This hydrogen peroxide method is described in many patents, such as US3972878, US3972876 and US4093656.

[0011] These methods are described in Ullmann, Encyclopedia of Industrial Chemistry (1989), Vol. A13, pp. 180-183, and references included therein.

[0012] In the hydrogen peroxide process, ammonia is oxidized by hydrogen peroxide in the presence of a ketone and a means for activating hydrogen peroxide to form an azine according to the following overall reaction:

[0013] .

[0014] The activation tool or activator can be a nitrile, an amide, a carboxylic acid or a selenium, antimony or arsenic derivative. The azine is then hydrolyzed to a hydrazine and the ketone is regenerated according to the following reaction:

[0015] .

[0016] This hydrolysis actually occurs in two stages, with the formation of an intermediate hydrazone:

[0017] .

[0018] Whether the azine is produced by the hydrogen peroxide process or some other method, the use of methyl ethyl ketone is advantageous because of its low solubility in aqueous media.

[0019] Specifically, in the hydrogen peroxide process, the azine of methyl ethyl ketone is relatively insoluble in the reaction medium, which is necessarily aqueous due to the use of commercial aqueous hydrogen peroxide solutions in concentrations between 30% and 70% by weight. This azine can therefore be easily recovered and separated by simple decantation. It is highly stable, in particular in alkaline media, i.e. in ammoniacal reaction media. In the current process, this azine is subsequently purified and then hydrolyzed in a reactive distillation column, ultimately releasing methyl ethyl ketone at the top to be recovered and, most importantly, an aqueous solution of hydrazine hydrate at the bottom. This solution must contain as little carbon product impurities as possible and must be colorless.

[0020] A method for efficiently preparing hydrazine hydrate is known from document WO2020 / 229773.

[0021] However, people are still seeking to improve this process. In other words, people are constantly looking to increase the degree of conversion of the reactants, increase the final yield and reduce side reactions, so that the production is as efficient as possible.

[0022] 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 the activator and hydrogen peroxide. However, in order for the reaction to be efficient, the reactants must be in contact with each other. Therefore, the yield of the reaction is directly related to the exchange and contact between the phases of the reactants.

[0023] From the scientific article Agitation Effects in a Gas-Liquid-Liquid Reactor System: Methyl Ethyl Keta-zine Production published by R. Kaur and KDP Nigam in the International Journal of Chemical Reactor Engineering in January 2007, it can be seen that agitation is a decisive improvement factor. It was observed that the higher the agitation speed, the greater the yield increase, up to a threshold of 600 rpm. However, these experiments were conducted in semi-batch reactors. However, in general, industrial sites are equipped with continuous processes. Moreover, applying agitation of 600 rpm to industrial-scale reactors represents a huge energy consumption. Therefore, solutions are still being sought to make these gas-liquid-liquid contacts efficient in continuous industrial processes, both in terms of yield and energy consumption.

[0024] Specifically, the inventors have found that by carrying out a mixed reaction in a plurality of reactors and adjusting the corresponding stirring of the reactors, they can reduce the formation of unwanted by-products in the reaction. In particular, it has been found that the generation of the by-product aminoperoxide can be reduced according to the method of the present invention. For example, aminoperoxide has been described in the application FR2950887. This reduction has been observed in all reactors. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 is a schematic diagram of an apparatus for implementing the claimed method.

[0026] Figure 2 is a schematic diagram of an apparatus for implementing the claimed method according to another embodiment. Summary of the invention

[0027] The subject of the present invention is therefore a process for the continuous preparation of an azine comprising the steps a) reacting ammonia, hydrogen peroxide and a ketone of the formula R1R2CO in the presence of an aqueous solution comprising at least one activating agent to form the azine, the radicals R1 and R2 independently of one another representing methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl and octyl;

[0028] The reaction is carried out in at least two reactors arranged in cascade;

[0029] The agitation of the first reactor is less than the agitation of the next reactor or each next reactor;

[0030] The hydrogen peroxide, the ketone and an aqueous solution containing at least one activating agent and containing dissolved ammonia are injected into the first reactor, preferably the proportion of the dissolved ammonia is between 50% and 100% relative to the saturation of ammonia in pure water at the temperature of the aqueous solution. DETAILED DESCRIPTION

[0031] Other features, aspects, subjects and advantages of the present invention will become more apparent from reading the following description.

[0032] It is expressly noted that “from… to…” and “between… and…” used in this specification should be understood to include every limit mentioned.

[0033] For the purposes of the present invention, "continuous" is understood to mean that the flow of reactants introduced into the reactor and products synthesized in the process is uninterrupted.

[0034] The preparation of hydrazine hydrate is carried out according to the following steps:

[0035] - ammonia, hydrogen peroxide and an alkyl ketone of formula R1R2C=0 react in the presence of an aqueous solution comprising at least one activating agent to form an azine;

[0036] - Hydrolysis of the azine of the ketone formed to give hydrazine hydrate.

[0037] The present invention relates to the first step of the method.

[0038] Reactants

[0039] Hydrogen Peroxide

[0040] Hydrogen peroxide may be used in its common commercial form, for example an aqueous solution containing 30 to 90% by weight of oxygen peroxide.

[0041] Advantageously, one or more special stabilizers for peroxide solutions may be added, for example phosphoric acid, pyrophosphoric acid, citric acid, nitrilotriacetic acid or ethylenediaminetetraacetic acid, or the ammonium or alkali metal salts of these acids.

[0042] It is also known to stabilize hydrogen peroxide solutions by adding chelating agents to the hydrogen peroxide solution, which complex the metal ions. This inhibits the redox reaction of hydrogen peroxide. Chelating agents particularly useful for stabilizing hydrogen peroxide solutions are compounds containing phosphonic acid functional groups in acid form or in salt form. The following commercial products can be used:

[0043] - the product sold under the name DEQUEST® 2060 by the company Monsanto, which is a 50% aqueous solution of diethylenetriamine penta(methylenephosphonic acid),

[0044] - the product sold under the name DEQUEST® 2041, which is an aqueous solution of ethylenediaminetetrakis(methylenephosphonic acid),

[0045] - Products sold under the names DEQUEST® 2010 and 2006, respectively, which are 60% aqueous solutions of 1-hydroxyethylidene-1,1-diphosphonic acid and 29% aqueous solutions of aminotri(methylenephosphonic acid) and 40% aqueous solutions of the pentasodium salt of the acid.

[0046] These acids can also be used in acid form or in fully or partially neutralized form, for example in the form of sodium or ammonium salts.

[0047] The amount of all reactants and of the solution comprising at least one activator at the reactor inlet is advantageously between 10 ppm and 1000 ppm, preferably between 50 ppm and 250 ppm.

[0048] Alkyl Ketone

[0049] The alkyl ketone of formula R1R2CO comprises the radicals R1 and R2, which independently represent methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl and octyl. Preferably, dimethyl ketone and methyl ethyl ketone are used. Particularly preferably, methyl ethyl ketone is used. Therefore, the preferred azine is the azine of methyl ethyl ketone, referred to as MEK azine.

[0050] Activator

[0051] "Activator" is understood to mean a compound which is capable of activating hydrogen peroxide, ie a compound which is capable of producing an azine from ammonia, hydrogen peroxide and a ketone.

[0052] The activator may 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.

[0053] As examples, one can mention:

[0054] (i) amides of carboxylic acids of the formula R5COOH, wherein R5 is hydrogen, 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) a carboxylic acid of the formula R6(COOH) n Amides of polycarboxylic acids of, wherein R6 represents an alkylene group having 1 to 10 carbon atoms and n is an integer greater than or equal to 2; R6 may be a single bond, in which case n is 2.

[0055] The radicals R5 and R6 may be substituted by halogen or OH, NO2 or methoxy. Amides of organic acids of arsenic may also be mentioned. Organic acids of arsenic are, for example, methylarsenic acid, phenylarsenic acid and dimethylarsenic acid.

[0056] Preferred amides are formamide, acetamide, monochloroacetamide and propionamide, more preferably acetamide.

[0057] Among the ammonium salts, hydrochloric acid, inorganic oxygen-containing acid, arylsulfonic acid, a compound of the formula R5COOH or R6(COOH) is advantageously used. n The invention also includes salts of arsenic acids (wherein R5, R6 and n are as defined above) and salts of organic acids of arsenic.

[0058] Preferred ammonium salts are formates, acetates, monochloroacetates, propionates, phenylarsenates and cacodylate.

[0059] Among the nitriles, mention may advantageously be made of the formula R7(CN) n wherein n may range from 1 to 5 depending on the valence of R7, R7 being a cyclic or acyclic alkyl group having 1 to 12 carbon atoms, or a benzyl group or a pyridyl group. R7 may be substituted with groups that are not oxidized in the reactor of step (a), such as halogen or carboxyl, carboxylate, nitro, amine, hydroxyl or sulfonic acid groups.

[0060] Preferred nitriles are acetonitrile and propionitrile.

[0061] The solution containing at least one activator is formed by dissolving one or more products selected from organic or inorganic oxyacids, their ammonium salts and derivatives thereof: anhydrides, esters, amides, nitriles, acyl peroxides or mixtures thereof as defined above. Advantageously, the above-mentioned nitriles, ammonium salts or amides are used. Particularly preferably, a single activator is used, namely acetamide.

[0062] The solution is an aqueous solution. According to another embodiment, the solution is an aqueous solution of an amide of a weak acid and an ammonium salt corresponding to the acid as described in patent EP0487160.

[0063] These weak acid amides are derivatives of the corresponding carboxylic acids with dissociation constants less than 3x10 -3 , in other words, an acid with a pKa greater than 3 in aqueous solution at 25°C.

[0064] For polycarboxylic acids, the acid in question is one whose first dissociation constant is less than 3x10 -3 of acid.

[0065] For example, mention may be made of carboxylic acids of formula R8COOH, in which R8 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; and carboxylic acids of formula R9(COOH) nA polycarboxylic acid of 1, 2 or 3 wherein R9 represents an alkylene radical having 1 to 10 carbon atoms and n is a number greater than or equal to 2; R9 may be a single bond, in which case n is 2. The radicals R8 and R9 may be substituted by halogen or OH, NO2 or methoxy. Preferably, acetamide, propionamide, n-butyramide or isobutyramide is used.

[0066] The corresponding ammonium salt of acetamide is ammonium acetate.

[0067] It does not depart from the scope of the present invention to form the ammonium salt in situ, ie using the corresponding carboxylic acid, which is obtained by reaction with ammonia.

[0068] The ratio of amide to the corresponding ammonium salt can be varied within wide limits. Per 5 parts of amide, 1 to 25 parts of ammonium salt are generally used, preferably 2 to 10 parts.

[0069] ammonia

[0070] Ammonia is dissolved in an aqueous solution comprising at least one activating agent.

[0071] The solubility of gaseous ammonia in pure water as a function of temperature is known from Lange's Handbook of Chemistry, edited by John A. Dean, 12th edition, 1979, page 10.3. The solubility expresses the weight of the gas dissolved in 100 grams of water at a pressure of 760 mm Hg. The table disclosed on page 10.3 is reproduced below:

[0072]

[0073] Table 1

[0074] These values ​​represent the maximum solubility of ammonia in pure water, i.e. the saturation of ammonia with respect to pure water. In the context of the present invention, an aqueous solution comprising dissolved ammonia and comprising at least one activating agent is introduced into the first reactor, preferably in a proportion of dissolved ammonia between 50% and 100% relative to the saturation of ammonia in pure water at the temperature of the aqueous solution. This solubility of ammonia in the aqueous phase is expressed relative to the amount of water contained in the aqueous phase comprising at least one activating agent.

[0075] In other words, starting from the values ​​disclosed in the above-mentioned Langer's Handbook of Chemistry and reproduced in the above Table 1, at 20°C, the target amount of ammonia dissolved is 26.45 g to 52.9 g of ammonia. At 70°C, the target amount of ammonia dissolved is 5.55 g to 11.1 g of ammonia.

[0076] Preferably, ammonia is dissolved in the aqueous solution containing the activator in a ratio of 50% to 85% relative to the saturation of ammonia in pure water at the temperature of the aqueous solution.

[0077] Preferably, the temperature of the aqueous solution is lower than the temperature of the reactor. More specifically, the temperature of the aqueous solution is more than 10°C lower than the temperature of the reactor, and more preferably more than 20°C lower than the temperature of the reactor.

[0078] The reactants can be used in stoichiometric amounts. However, 0.2 to 5, preferably 1.5 to 4, ketones can be used per mole of hydrogen peroxide, and 0.1 to 10, preferably 1.5 to 4, ammonia. The amount of solution containing at least one activator can be between 0.1 kg and 2 kg per mole of hydrogen peroxide. This amount depends on its mass, i.e. on its catalytic strength or activity in converting the reactants into azine. The above-mentioned specified proportions of the reactants make it possible to obtain a maximum conversion of hydrogen peroxide (usually greater than 90%, preferably greater than 95%) and an azine yield of greater than 75%, possibly up to 90%, corresponding to the hydrogen peroxide used.

[0079] a) Mixed reactions

[0080] The reaction can be carried out in a very wide temperature range, for example between 0°C and 100°C, advantageously between 30°C and 70°C. There may be a temperature gradient between the reactors. For example, the temperature of the first reactor may be around 45°C, while the temperature of the last reactor may be around 60°C. Although it can be operated at any pressure, it is simpler to operate at atmospheric pressure, although it can be increased to an absolute pressure of about 10 bar. Preferably, the reaction is carried out at an absolute pressure of 1 bar to 5 bar.

[0081] Reactor

[0082] The reaction takes place in at least two reactors arranged in cascade. Preferably, 3, 4 or 5 reactors in cascade are used.

[0083] Agitation in the first reactor is less than that in the second and any subsequent reactors.

[0084] For the purposes of the present invention, agitation is understood to be the velocity of the flow of the reaction medium within the reactor, which is generated by the movement of rotating elements such as blades, baffles, anchors or any other rotating element, or by the Venturi effect. For a medium agitated by a rotating element, the agitation of the reaction medium can be expressed by the agitation velocity of the rotating element itself.

[0085] When the method uses 3 or more reactors, the reactors located after the first reactor can be stirred at the same speed. The reactors located after the first reactor can also be stirred at an increased speed, that is, the third reactor is stirred at a stirring speed greater than that of the second reactor.

[0086] The inner diameter of the reactor can be between 1 meter and 6 meters, preferably between 2 meters and 5 meters. The working height of the reactor can be between 1 meter and 10 meters, preferably between 3 meters and 7 meters. Therefore, the reaction volume can be between 25 cubic meters and 100 cubic meters, preferably between 40 cubic meters and 70 cubic meters. The reactors can have the same volume or different volumes.

[0087] Preferably, the reactor may be equipped with stirring means, such as blades.

[0088] Therefore, the reactor can include multiple stirring stages, preferably two stirring stages. Each stirring stage can include several inclined blades. Preferably, the blades are located at the lower third and the upper third of the reactor. The diameter of the stirring rotating element depends on the diameter of the reactor. Typically, the diameter of the rotating element is between 30% and 70% of the reactor diameter.

[0089] The reactor according to the invention is not a microreactor.

[0090] 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 clearly defined in the publication by Joseph Lieto, "Le génie chimique à l'usage des chimistes [Chemical Engineering for Chemists]", published by Tec & Doc Lavoisier in 1998. The Froude number is calculated according to the following formula: Fr = N 2 D / g, where

[0091] g = acceleration due to gravity, or 9.81 m / s 2

[0092] D = agitator diameter, in m

[0093] N = the number of revolutions of the agitator, in revolutions per second.

[0094] Preferably, the Froude number in the first reactor is strictly less than 0.018 and the Froude number in the following reactor 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 is greater than 0.018.

[0095] The ketone may be introduced at the bottom of the first reactor and the aqueous hydrogen peroxide solution may be introduced through a pipe immersed in the first reactor. Ammonia is introduced into the first reactor in the form of a solution dissolved in an aqueous solution containing at least one activator.

[0096] Therefore, the process according to the invention can reduce the formation of aminoperoxides. In the first reactor, the production of aminoperoxides is low due to slow stirring. In the next reactor, the high stirring speed can consume this aminoperoxide faster and convert it into azine. Therefore, the amount of aminoperoxides is reduced, while the amount of azine produced is increased.

[0097] At the end of the reaction according to the invention, the reaction mixture comprises the ketonic azine, any unreacted ketone, any activating agent and any other by-products or impurities.

[0098] Preparation of aqueous solution

[0099] An absorption tower may be used to prepare an ammoniacal aqueous solution.

[0100] The absorption column is fed with fresh ammonia and an aqueous solution comprising at least one activating agent.

[0101] The absorption tower is intended to dissolve gaseous ammonia in an aqueous solution containing at least one activator. The function of the absorption tower is to make the mixture of gaseous ammonia and aqueous solution containing activator into a single phase.

[0102] At the outlet of the absorption tower, an aqueous solution is obtained which contains dissolved ammonia in a proportion between 50% and 100% of the saturation of ammonia in pure water at the tower temperature and contains at least one activator. Therefore, when an absorption tower is used in the process, the temperature of the tower is relevant for the calculation of the ammonia saturation of the aqueous solution.

[0103] Dissolved Ammonia

[0104] According to this embodiment, the purpose of the absorption tower is to dissolve ammonia in the aqueous solution containing the activator at a percentage of 50% to 100% relative to saturated pure water at the temperature of the tower. This solubility of ammonia in the aqueous phase is expressed relative to the amount of water contained in the aqueous phase containing at least one activator.

[0105] Preferably, ammonia is dissolved in the aqueous solution containing the activator at a ratio of 50% to 85% relative to the saturation of ammonia in pure water at the tower temperature.

[0106] During the process, the flow rate of fresh ammonia may be varied to keep the solubility of ammonia in the aqueous solution constant. At the beginning of the process, the flow rate of ammonia will have to be sufficient to achieve the desired ammonia solubility. Subsequently, the flow rate will be able to be reduced to maintain the desired solubility.

[0107] Device

[0108] The temperature of the absorption tower can be between ambient temperature and 70° C., preferably between 20° C. and 50° C., preferably between 25° C. and 45° C. The pressure of the absorption tower can be between atmospheric pressure and up to about 10 bar absolute pressure. Preferably, the reaction is carried out at 1 bar to 5 bar absolute pressure.

[0109] The column may be a packed distillation column or a plate distillation column. Ammonia and an aqueous solution comprising at least one activating agent are fed thereto.

[0110] It is also possible to fully or partially recover the ammonia stream resulting from the process for preparing azine.

[0111] The aqueous solution comprising at least one activating agent may be a recycled aqueous solution from separation step b), which may have been subjected in whole or in part to a regeneration and concentration step.

[0112] Preferably, the aqueous solution comprising at least one activating agent is introduced at the top of the column, and fresh ammonia and / or any recycled ammonia is introduced countercurrently, preferably at the bottom of the column. The meeting of these flows in countercurrent form allows for better mixing of the reactants and better absorption of the gaseous ammonia into the aqueous solution.

[0113] Then, an aqueous ammoniacal solution comprising at least one activating agent is introduced into the first reactor, wherein the azine-forming reaction is carried out.

[0114] Circulation loop of aqueous solution saturated with ammonia

[0115] According to one embodiment of the present invention, the reaction medium of the first reactor of step a) can be used to feed the absorption tower. The stream can be extracted using a pipeline of the reaction medium immersed in the reactor. It is then introduced at the top of the absorption tower. Once introduced into the absorption tower, the stream of the reaction medium from step a) is mixed with an aqueous solution containing at least one activator, fresh ammonia and optionally recovered ammonia. At the outlet of the tower, an aqueous solution containing dissolved ammonia and at least one activator is fed into the first reactor, and the proportion of dissolved ammonia is between 50% and 100% relative to the saturation of ammonia in pure water at the tower temperature. This circulation loop between the first reactor and the absorption tower makes it possible to continuously maintain a high ammonia content in the reaction medium of step a). In other words, the ammonia concentration of the stream extracted from the reaction medium of step a) increases when it flows through the absorption tower before being re-injected into the first reactor.

[0116] When the stirring in the first reactor is low, i.e. when the stirring is insufficient to homogenize the reaction medium, the aqueous phase tends to be present at a higher concentration at the bottom of the reactor. It is therefore advantageous to withdraw the reaction medium rich in the aqueous phase from this location in order to introduce it into the absorption column. Therefore, the withdrawal conduit is preferably located in the first third of the liquid phase height starting from the bottom of the reactor.

[0117] According to one embodiment, the reaction medium of each reactor may be withdrawn and introduced into an absorption column.

[0118] According to another embodiment, the reaction medium of a single reactor can be withdrawn and introduced into an absorption column, for example the first reactor or the last reactor.

[0119] According to yet another embodiment, the reaction medium of a plurality of reactors, but not all of the reactors, may be withdrawn and introduced into the absorption column.

[0120] b) Separation reaction

[0121] After the reaction for preparing the azine, the process according to the invention may comprise a step of separating the stream formed at the end of the previous step.

[0122] The aqueous phase comprising the activator is separated from the organic phase comprising the azine of the alkyl ketone and any unreacted alkyl ketone by conventional separation means such as liquid-liquid extraction, distillation, decanting or any combination of these possibilities. Preferably decanting is used.

[0123] The obtained organic phase may contain the azine of the formed alkyl ketone, unreacted alkyl ketone, activating agent and any other impurities.

[0124] c) Regeneration reaction

[0125] After separation step b), the aqueous phase can be subjected completely or partially to a regeneration and concentration step. The regenerated and concentrated aqueous phase can thus be recycled to the first reactor or, when it is present in the process, to the ammonia absorber.

[0126] In the step of regenerating and concentrating the aqueous phase coming from separation step b), when a gaseous ammonia stream is present in the process, it can be recycled to the ammonia absorber.

[0127] This regeneration step is described in patents EP0399866 and EP0518728.

[0128] After separation step b), the method may comprise:

[0129] - a step of washing the organic phase coming from the separation step,

[0130] - a step of hydrolyzing the stream obtained from the previous step to obtain hydrazine hydrate.

[0131] Illustration

[0132] Figure 1 One embodiment of the method according to the invention is shown.

[0133] The reaction of ammonia, hydrogen peroxide and an alkyl ketone in the presence of a solution comprising at least one activating agent to form an azine is carried out in four reactors installed in cascade (denoted R1, R2, R3 and R4).

[0134] Reactor R1 is fed with ketone via line 1. This can be a feed containing fresh ketone or a feed of ketone recovered from the process. Reactor R1 is fed with hydrogen peroxide via line 2 and with an aqueous ammoniacal solution comprising at least one activating agent via line 3.

[0135] Lines 4, 5 and 6 carry the streams (A), (B) and (C) from reactors R1, R2 and R3 respectively to the following reactors, namely R2, R3 and R4. Line 7 conveys the stream D formed in reactor R4 to a decanter 8.

[0136] The decanter 8 separates the organic phase E and the aqueous phase F. The organic phase E is sent to the subsequent steps of the process via the pipeline 9. The aqueous phase F is sent to the regeneration and concentration unit 11 of the aqueous phase F. The pipeline 12 is a pipeline that bypasses the regeneration and concentration unit 11. Depending on the quality of the aqueous phase, the aqueous phase F can be directed to the unit 11 or to the bypass line 12. It is also possible to send only a portion of the aqueous phase F to the regeneration and concentration unit 11. The aqueous phase that has passed through the regeneration and concentration steps and / or the aqueous phase that has passed through the bypass line 12 is sent to the reactor R1 via the pipeline 13. The regeneration and concentration unit 11 may include a purge 14 to remove excess water in the circuit.

[0137] Figure 2 A further embodiment of the method according to the invention is shown.

[0138] The reaction of ammonia, hydrogen peroxide and an alkyl ketone in the presence of a solution comprising at least one activating agent to form an azine is carried out in four reactors installed in cascade (denoted R41, R42, R43 and R44).

[0139] Reactor R41 is fed with ketone via line 21. This can be a feed containing fresh ketone or a feed of ketone recovered from the process. Reactor R41 is fed with hydrogen peroxide via line 22 and with an aqueous solution saturated with ammonia containing at least one activating agent via line 23.

[0140] Lines 24, 25 and 26 carry streams (A), (B) and (C) from reactors R41, R42 and R43 to the following reactors, namely R42, R43 and R44, respectively. Line 27 conveys stream D formed in reactor R44 to decanter 28.

[0141] The decanter 28 separates the organic phase E and the aqueous phase F. The organic phase E is sent to the subsequent steps of the process via the pipeline 29. The aqueous phase F is sent to the regeneration and concentration unit 31 of the aqueous phase F. The pipeline 32 is a pipeline that bypasses the regeneration and concentration unit 31. Depending on the quality of the aqueous phase, the aqueous phase F can be directed to the unit 31 or to the bypass pipeline 32. It is also possible to send only a portion of the aqueous phase F to the regeneration and concentration unit 31. The aqueous phase that has passed the regeneration and concentration step and / or the aqueous phase that has passed through the bypass pipeline 32 is sent to the top of the ammonia absorber 33 via the pipeline 34. In the regeneration and concentration step, ammonia can also be recovered. The ammonia can be recovered to the bottom of the ammonia absorber 33 via the pipeline 35. The regeneration and concentration unit 31 may include a purge 36 to remove excess water in the line. The ammonia absorber 33 may also be fed with fresh ammonia via the pipeline 37. Finally, the reaction phase of the reactor R41 is sent to the top of the ammonia absorber 33 via the pipeline 38.

[0142] Line 38, absorber 33, feed line 23 and reactor R41 form an ammonia recycle loop.

[0143] The following examples illustrate the invention but are not intended to limit it in any way.

[0144] Example

[0145] This example compares two methods of preparing azine, one according to the invention and the other a comparative method.

[0146] The reaction steps are as follows Figure 2 The process is carried out in a device. The process uses 4 reactors in cascade. Methyl ethyl ketone is used as a reactant.

[0147] The temperature of the reactor is as follows: T R41 =50°C; T R42 =51°C; T R43 =52.5°C; T R44 = 55°C. The reaction was carried out under atmospheric pressure.

[0148] The flows of aminoperoxide and ammonia formed in each reactor were evaluated.

[0149] The circulation flow rate in the pipeline 38, that is, the circulation flow rate from the reactor R41 to the ammonia absorber is 24 t / h. The absorption of ammonia is carried out at a temperature of 30°C.

[0150] The flow rates of reactants reaching reactor R41 are shown in Table 2 below:

[0151]

[0152] Table 2

[0153] The stirring conditions for each process are shown in Tables 3 and 4 below. The reactor included a stirrer with a diameter of 1.7 m. The formation of aminoperoxides and the generation of azine were evaluated at the outlet of each reactor. The values ​​are shown in Tables 3 and 4 below.

[0154]

[0155] Table 3

[0156]

[0157] Table 4

[0158] These results show that the stirring system claimed can reduce the generation of aminoperoxide in each reactor. Therefore, the stirring difference applied between reactor R41 and reactor R42 has a significant impact on the amount of aminoperoxide produced in these reactors, and this impact is still visible in reactors R43 and R44. In addition, an increase in yield is also obtained.

Claims

1. A process for the continuous preparation of an azine, comprising a step a) of reacting ammonia, hydrogen peroxide and a ketone of formula R1R2CO in the presence of an aqueous solution containing at least one activating agent to form an azine, wherein the radicals R1 and R2 independently represent methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl and octyl; The reaction is carried out in at least two reactors arranged in cascade; The agitation of the first reactor is less than the agitation of the next reactor or each next reactor; The hydrogen peroxide, the ketone and an aqueous solution comprising at least one activating agent and containing dissolved ammonia are injected into the first reactor, preferably the proportion of the dissolved ammonia is between 50% and 100% relative to the saturation of ammonia in pure water at the temperature of the aqueous solution.

2. The method according to claim 1, characterized in that The aqueous solution comprising at least one activating agent and dissolved ammonia originates from an absorption tower.

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

018.

4. The 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. The method according to any one of the preceding claims, characterized in that The ketone used in step a) is methyl ethyl ketone.

6. The method according to any one of the preceding claims, characterized in that The method comprises, after step a) of reacting, a step b) of separating the stream formed at the end of step a) of reacting.

7. The method according to claim 6, characterized in that The process comprises a step c) of regenerating and concentrating the aqueous phase coming from separation step b).

8. The method according to claim 7, characterized in that In the step c) of regenerating and concentrating the aqueous phase from the separation step b), the aqueous phase thus regenerated and concentrated is recycled to the ammonia absorption tower.

9. The method according to claim 7 or 8, characterized in that: In step c) of regenerating and concentrating the aqueous phase coming from separation step b), the gaseous ammonia stream is recycled to the ammonia absorber.

10. The method according to any one of claims 6 to 9, characterized in that The method comprises: - a step of washing the organic phase coming from separation step b), - a step of hydrolyzing the stream obtained from the previous step to obtain hydrazine hydrate.

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