Process for the preparation of azines using a cascade reactor

Abstract

The present invention is a process for continuously preparing azine, which comprises reacting ammonia, hydrogen peroxide and a ketone of the formula: R1R2CO (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) in the presence of an aqueous solution containing at least one activator to form azine. The reaction is carried out in at least two reactors arranged in cascade, the stirring in the first reactor being less than the stirring in each of the next reactor or the next plurality of reactors. The above reactants are injected into the first reactor. The above aqueous solution contains at least one activator and dissolved ammonia in a proportion of 50% to 100% of the saturation of ammonia in pure water at the temperature of the aqueous solution.

Description

Technical Field

[0001] The present invention relates to a process for the preparation of azine.

[0002] More specifically, the present invention relates to a process for the preparation of azine obtained by oxidizing ammonia in the presence of an activator using hydrogen peroxide in the presence of a ketone.

Background Art

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

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

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

[0006] In the Raschig process, ammonia is oxidized with hypochlorite to obtain a dilute solution of hydrazine hydrate, which then has to be distilled and concentrated. This process is no longer practically used because it is relatively non-selective, has low productivity, and is highly polluting.

[0007] 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

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

[0009] In the hydrogen peroxide method, in the presence of means for activating hydrogen peroxide, a mixture of ammonia and a ketone is oxidized with hydrogen peroxide to directly produce an azine, and then it 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 Patent Documents 1, 2 and 3.

[0010] These methods are also described in Non-Patent Document 1 and the references included therein.

[0011] In the hydrogen peroxide method, ammonia is oxidized with hydrogen peroxide in accordance with the following overall reaction in the presence of a ketone and means for activating hydrogen peroxide to form an azine:

Chemical formula

[0012] The activating means or activator can be a nitrile, amide, carboxylic acid, or a selenium, antimony or arsenic derivative. The azine is then hydrolyzed to hydrazine, and the ketone is regenerated in accordance with the following reaction:

Chemical formula

[0013] This hydrolysis is actually carried out in two steps to form an intermediate hydrazone:

Chemical formula

[0014] Even when an azine is produced by the hydrogen peroxide method or other methods, methyl ethyl ketone is preferably used because it is poorly soluble in an aqueous medium.

[0015] Specifically, in the hydrogen peroxide method, the azine of methyl ethyl ketone is relatively insoluble in the reaction medium, which is necessarily aqueous since it uses a commercially available aqueous hydrogen peroxide solution with a concentration of 30% to 70% by weight. Therefore, this azine can be easily recovered and separated by simple decantation. It is very stable especially in an alkaline medium, i.e., an ammoniacal reaction medium. In the current process, this azine is then purified, next hydrolyzed in a reactive distillation column, and finally methyl ethyl ketone is released at the top and recycled, and in particular, an aqueous solution of hydrazine hydrate is released at the bottom. This should contain as little carbonaceous products as possible as impurities and must be colorless.

[0016] Processes for efficiently preparing hydrazine hydrate are known from Patent Document 4.

[0017] However, improvements to this process are still sought. That is, an increase in the conversion degree of the reactants, an increase in the final yield, and a reduction in side reactions are always desired so that the production becomes as efficient as possible.

[0018] The reaction to form azine is relatively complex. This is because the reaction involves three phases: a gas phase containing ammonia, an organic phase containing ketone, and an aqueous phase containing an activator and hydrogen peroxide. However, for the reaction to proceed efficiently, the reactants need to contact each other. Therefore, the yield of this reaction is directly related to the exchange and contact between the phases of the reactants.

[0019] It is known from Non-Patent Document 2, which is a scientific paper, that stirring is a decisive improvement factor. It was observed that the higher the stirring speed, the higher the yield up to the threshold of 600 rpm. However, these experiments were conducted in a semi-batch reactor. Generally, industrial sites are equipped with continuous processes. Furthermore, applying stirring at 600 rpm to an industrial-scale reactor means significant energy consumption. Therefore, in a continuous industrial process, a solution is still sought to efficiently achieve these gas-liquid-liquid contacts, both in terms of yield and energy consumption.

[0020] Specifically, the inventors have found that by carrying out the mixing reaction in a plurality of reactors and adapting the stirring of each of the reactors, the formation of undesirable by-products of the reaction can be reduced. In particular, the method of the present invention has been found to be able to reduce the production of aminoperoxide, which is a by-product of the reaction. Aminoperoxide is described, for example, in Patent Document 5. This reduction is observed across all reactors.

Prior Art Documents

Patent Documents

[0021]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Patent Document 5

Non-Patent Documents

[0022]

Non-Patent Document 1

Non-Patent Document 2

[0023]

Figure 1

[0024]

Figure 2

[0025] Accordingly, the subject matter of the present invention is a process (method) for continuously preparing azine, comprising: a) reacting ammonia, hydrogen peroxide, and a ketone of the formula: R1R2CO (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) in the presence of an aqueous solution containing at least one activator to form azine, the reaction being carried out in at least two reactors arranged in cascade, the agitation in the first reactor being less than the agitation in the next reactor or each of the next plurality of reactors, An aqueous solution containing the hydrogen peroxide, the ketone, and at least one activator, and containing dissolved ammonia, preferably containing dissolved ammonium dissolved at a ratio of 50% to 100% relative to the saturation of ammonia in pure water at the temperature of the aqueous solution, is injected into the first reactor.

DETAILED DESCRIPTION OF THE INVENTION

[0026] Other features, aspects, subjects, and advantages of the present invention will become more apparent upon reading the following description.

[0027] It is specified that the expressions "from... to..." and "between... and..." used herein should be understood to include each of the recited limit values.

[0028] For the purposes of the present invention, "continuous" is understood to mean that the flow of reactants introduced into the reactor and products synthesized during the process is not interrupted.

[0029] The preparation of hydrazine hydrate is carried out according to the following steps: - Reacting ammonia, hydrogen peroxide, and an alkyl ketone of the formula: R1R2C=O in the presence of an aqueous solution containing at least one activator to form an azine; - Hydrolyzing the formed azine of the ketone to obtain hydrazine hydrate.

[0030] The present invention relates to the first step of this process. Reactant <Hydrogen peroxide>

[0031] Hydrogen peroxide can be used in a common commercially available form, such as an aqueous solution containing, for example, 30% to 90% by weight of oxygen peroxide.

[0032] Advantageously, it is possible to add one or more conventional stabilizers for the peroxide solution, such as phosphoric acid, pyrophosphoric acid, citric acid, nitrilotriacetic acid or ethylenediaminetetraacetic acid, or ammonium salts or alkali metal salts of these acids.

[0033] It is also known to add a sequestering agent that complexes metal ions to stabilize the hydrogen peroxide solution. This suppresses the redox reaction of hydrogen peroxide. Sequestering agents particularly used to stabilize aqueous hydrogen peroxide solutions are compounds in the form of acids or salts of the type containing phosphonic acid functional groups. The following commercial products can be used: - A product sold under the name DEQUEST® 2060 by Monsanto, a 50% aqueous solution of diethylenetriaminepenta(methylenephosphonic acid), - A product sold under the name DEQUEST® 2041, an aqueous solution of ethylenediaminetetra(methylenephosphonic acid), - Products sold under the names DEQUEST® 2010 and 2006, a 60% aqueous solution of 1-hydroxyethylidene-1,1-diphosphonic acid, a 29% aqueous solution of aminotris(methylenephosphonic acid), and a 40% pentasodium salt of this acid, respectively.

[0034] These acids can also be used in acid form or in fully or partially neutralized forms, such as in the form of sodium salts or ammonium salts.

[0035] The amount used is such that the solution containing all reactants and at least one activator at the inlet of the reactor is advantageously between 10 and 1000 ppm, preferably between 50 and 250 ppm. <Alkyl ketone>

[0036] The alkyl ketones of the formula: R1R2CO include 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. Accordingly, a preferred azine is the azine of methyl ethyl ketone called MEKazine. <Activator>

[0037] 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.

[0038] 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.

[0039] Examples include the following: (i) Amides of carboxylic acids of the formula: R5COOH, where R5 is hydrogen, a linear alkyl group having from 1 to 20 carbon atoms, or a branched or cyclic alkyl group having from 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 from 1 to 10 carbon atoms and n is an integer of 2 or more, and R6 may be a single bond, in which case n is 2.

[0040] 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.

[0041] Preferred amides are formamide, acetamide, monochloroacetamide and propionamide, and more preferably acetamide.

[0042] Among ammonium salts, salts of hydracids, salts of inorganic oxyacids, salts of arylsulfonic acids, acids of the formula: R5COOH or R6(COOH) n each salt of (wherein R5, R6 and n are as defined above), and salts of organic acids of arsenic are preferably used.

[0043] Preferred ammonium salts are formate, acetate, monochloroacetate, propionate, phenylarsonate and cacodylate.

[0044] Among nitriles, products of the formula R7(CN)n can preferably be mentioned, where n ranges from 1 to 5 according to 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 with a group that is not oxidized in the reactor of step (a), such as a halogen or carboxyl group, carboxylic acid ester group, nitro group, amine group, hydroxyl group or sulfonic acid group.

[0045] Preferred nitriles are acetonitrile and propionitrile.

[0046] 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. Preferably, the above-mentioned nitrile, ammonium salt or amide is used. Particularly preferably, a single activator which is acetamide is used.

[0047] 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.

[0048] These weak acid amides are derivatives of the corresponding carboxylic acids having a dissociation constant of less than 3×10 -3 i.e., carboxylic acids having a pKa greater than 3 in an aqueous solution at 25°C.

[0049] In the case of polycarboxylic acids, the acid in question is an acid whose first ionization constant is less than 3×10 -3 less than.

[0050] By way of example, carboxylic acids of the formula: R8COOH (wherein 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 polycarboxylic acids of the formula: R9(COOH)n (wherein R9 represents an alkylene radical having 1 to 10 carbon atoms, and n is a number of 2 or more; R9 may be a single bond, in which case n is 2) can be mentioned. The groups R8 and R9 may be substituted with halogen, or an OH, NO2 or methoxy group. Preferably, acetamide, propionamide, n-butylamide or isobutylamide are used.

[0051] The corresponding ammonium salt of acetamide is ammonium acetate.

[0052] Forming the ammonium salt in situ, i.e., using the corresponding carboxylic acid that gives the ammonium salt by reaction with ammonia, is not outside the scope of the present invention.

[0053] The ratio of the amide and 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. <Ammonia>

[0054] Ammonia is dissolved in an aqueous solution containing at least one activator.

[0055] The solubility of gaseous ammonia in pure water as a function of temperature is known from Lange's Handbook of Chemistry, author 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]

[0056] These values represent the maximum solubility of ammonia in pure water, i.e., the saturation of pure water with ammonia. In the context of the present invention, an aqueous solution preferably 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 aqueous solution, and contains at least one activator, and is introduced into the first reactor. This solubility of ammonia in the aqueous phase is expressed with respect to the amount of water contained in the aqueous phase containing at least one activator.

[0057] 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, 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.

[0058] Preferably, ammonia is dissolved in the aqueous solution containing an activator at a ratio between 50% and 85% of the saturation of ammonia in pure water at the temperature of the aqueous solution.

[0059] Preferably, the temperature of the aqueous solution is lower than the temperature of the reactor. More specifically, the temperature of the aqueous solution is 10°C or more lower than the temperature of the reactor, and more preferably 20°C or more lower than the temperature of the reactor.

[0060] The above 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, and 0.1 to 10 moles, preferably 1.5 to 4 moles of ammonia, per mole of hydrogen peroxide. 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 to azine. With the above ratios of reactants, it is possible to obtain a maximum conversion rate of hydrogen peroxide, typically higher than 90%, preferably higher than 95%, and the amount of azine produced can reach a maximum conversion rate of more than 75%, and in some cases 90%, of the hydrogen peroxide used. <a) Mixing reaction>

[0061] The above reaction can be carried out in a very wide temperature range, for example, between 0 °C and 100 °C, and the operation is advantageously between 30 °C and 70 °C. It is also possible to have a temperature gradient between various reactors. For example, the temperature of the first reactor can be about 45 °C, while the temperature of the last reactor can be about 60 °C. The operation can be carried out at any pressure, but it is simpler at atmospheric pressure, although 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>

[0062] The reaction is carried out in at least two reactors arranged in a cascade. Preferably, 3, 4 or 5 reactors in a cascade are used.

[0063] The agitation in the first reactor is less than that in the second reactor and subsequent reactors.

[0064] For the purposes of the present invention, agitation is understood to mean the velocity of the flow of the reaction medium within the reactor generated by the movement of a rotating element such as a blade, baffle, anchor or other rotating element, or by the Venturi effect. In the case of a medium agitated by a rotating element, the agitation of the reaction medium can be represented by the agitation speed of the rotating element itself.

[0065] If the process uses three or more reactors, the reactors located after the first reactor can be agitated at the same speed. It is also possible to agitate the reactors arranged after the first reactor at an increased speed, i.e., to agitate the third reactor at a speed greater than the agitation speed of the second reactor.

[0066] The reactor can have an internal diameter between 1 and 6 m, preferably between 2 and 5 m. The working height of the reactor can be between 1 and 10 m, preferably between 3 and 7 m. Thus, the reaction volume is 25 to 100 m 3 , preferably 40 to 70 m 3 and can be. The volumes of the reactors can be the same or different.

[0067] Preferably, the reactor may be provided with agitation means, such as blades.

[0068] Thus, the reactor may include a plurality of agitation stages, preferably two agitation stages. Each agitation stage may include a plurality of inclined blades. Preferably, the blades are located in the lower third and the upper third 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 30% to 70% of the diameter of the reactor.

[0069] The reactor of the present invention is not a microreactor.

[0070] The stirring of the reaction medium can be characterized by the Froude number. This parameter is known to those skilled in the art. In particular, it is defined in the publication: Le genie chimique a l'usage des chimistes [Chemical Engineering for Chemists] 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 (in meters) N = rotational speed of the stirrer (revolutions per second).

[0071] Preferably, the Froude number in the first reactor is strictly less than 0.018, and the Froude number in the next reactor(s) is 0.018 or more. More preferably, the Froude number in the first reactor is less than 0.010, and the Froude number in the next reactor(s) is greater than 0.018.

[0072] The above ketone may be introduced at the bottom of the first reactor, and the aqueous hydrogen peroxide solution may be introduced by a tube immersed in this first reactor. Ammonia is introduced into the first reactor in a form dissolved in an aqueous solution containing at least one activator.

[0073] In this way, the process according to the invention makes it possible to reduce the formation of aminoperoxide. In the first reactor, since the stirring is slow, the formation of aminoperoxide is low. In the next reactor, since the stirring speed is high, this aminoperoxide can be consumed more rapidly and converted into azine. Therefore, the amount of aminoperoxide decreases, while the amount of azine produced increases.

[0074] At the end of the reaction according to the present invention, the reaction mixture contains an azine of a ketone, some unreacted ketone, some activator, and some other by-products or impurities. Preparation of aqueous solution

[0075] The ammoniacal aqueous solution can be prepared using an absorption column.

[0076] An aqueous solution containing fresh ammonia and at least one activator can be supplied to the absorption column.

[0077] The purpose of the absorption column is to dissolve gaseous ammonia in an aqueous solution containing at least one activator. The function of the absorption column is to make the mixture of this gaseous ammonia and the aqueous solution containing the activator into a single phase.

[0078] At the outlet of the absorption column, 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 is obtained. Therefore, when the absorption column is used in the process, it is the temperature of the column that is relevant to the calculation of the ammonia saturation of the aqueous solution. <Dissolved ammonia>

[0079] According to this embodiment, the absorption column is intended 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. This solubility of ammonia in the aqueous phase is expressed with respect to the amount of water contained in the aqueous phase containing at least one activator.

[0080] 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.

[0081] The flow rate of fresh ammonia can be varied during the process in order to keep the solubility of ammonia in the aqueous solution constant. At the start of the process, the flow rate of ammonia will have to be sufficient to achieve the desired ammonia solubility. Thereafter, the flow rate can be decreased again to maintain the desired solubility. <Apparatus>

[0082] The temperature of the absorption column can be 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 can be between atmospheric pressure and about 10 bar absolute pressure. Preferably, the reaction is carried out at 1 - 5 bar absolute pressure.

[0083] The column can be a packed or plate distillation column. An aqueous solution containing ammonia and at least one activator is fed to the column.

[0084] It is also possible to completely or partially recover the ammonia stream produced by the process for preparing azine.

[0085] The aqueous solution containing at least one activator may be a recycled aqueous solution resulting from separation step b) which has undergone the regeneration and concentration steps completely or partially.

[0086] Preferably, the aqueous solution containing at least one activator is introduced at the top of the column, and fresh ammonia and / or recycled ammonia are preferably introduced at the bottom of the column in countercurrent. By bringing these streams into countercurrent contact, the mixing of the reactants is improved and the absorption of gaseous ammonia into the aqueous solution is improved.

[0087] Subsequently, the ammoniacal aqueous solution containing at least one activator is introduced into a first reactor, and the reaction for forming azine is carried out therein. <Circulation loop of ammonia-saturated aqueous solution>

[0088] According to one embodiment of the present invention, the absorption column can be supplied with the flow of the reaction medium from the first reactor in step a). This flow can be withdrawn using a pipe immersed in the reaction medium of the reactor. Then, it is introduced into the top of the absorption column. Once introduced into the absorption column, this flow derived from the reaction medium of step a) is mixed with an aqueous solution containing at least one activator, fresh ammonia, and optionally recycled ammonia. At the outlet of the column, an aqueous solution containing ammonia dissolved at a rate of 50% to 100% of the saturation of ammonia in pure water at the temperature of the column and containing at least one activator is sent to the first reactor. This circulation loop between the first reactor and the absorption column makes it possible to always maintain a high content of ammonia in the reaction medium of step a). In other words, it will be seen that the concentration of ammonia increases as the flow withdrawn from the reaction medium of step a) passes through the absorption column before being reinjected into the first reactor.

[0089] 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 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 extraction pipe is preferably arranged within the first third of the height of the liquid phase starting from the bottom of the reactor.

[0090] According to one embodiment, the reaction medium of each reactor can be withdrawn and introduced into the absorption column.

[0091] According to another embodiment, the reaction medium of a single reactor can be withdrawn and introduced into the absorption column, such as the first reactor or the last reactor for example.

[0092] According to yet another embodiment, instead of all reactors, the reaction media of some reactors can be withdrawn and introduced into the absorption column. <b) Separation reaction>

[0093] After the reaction to prepare the azine, the process according to the invention may include a step of separating the stream formed at the end of the previous step.

[0094] The aqueous phase containing the activator(s) is separated from the organic phase containing the alkyl ketone azine and the unreacted alkyl ketone by conventional means such as liquid-liquid extraction, distillation, decantation or any combination of these possibilities. Decantation is preferably used.

[0095] The resulting organic phase may contain the formed alkyl ketone azine, the unreacted alkyl ketone, the activator(s), and other impurities. <c) Regeneration reaction>

[0096] Following the separation step b), the aqueous phase can undergo a complete or partial regeneration and concentration step. This regenerated and concentrated aqueous phase can be recycled to the first reactor or, if there is an ammonia absorption column in the process, to it.

[0097] During the step of regenerating and concentrating the aqueous phase from the separation step b), the gaseous ammonia stream may be recycled to the ammonia absorption column if it is present in the process.

[0098] This regeneration step is described in European Patent No. 0399866 and European Patent No. 0518728.

[0099] Following the separation step b), the process may include the following steps: - a step of washing the organic phase from the separation step, - a step of hydrolyzing the stream obtained from the previous step to obtain hydrazine hydrate.

[0100] The reaction to form azine in the presence of a solution containing at least one activator of ammonia, hydrogen peroxide and alkyl ketone is carried out in four reactors provided in a cascade and designated as R1, R2, R3 and R4.

[0101] Ketone is supplied to reactor R1 via line 1. This may be a supply of fresh ketone or a supply that recycles the ketone generated from the process. Hydrogen peroxide is supplied to reactor R1 via line 2, and an aqueous ammonia solution containing at least one activator is supplied via line 3.

[0102] Lines 4, 5 and 6 carry the flows (A), (B) and (C) coming from reactors R1, R2, R3 to the next reactors, namely R2, R3 and R4, respectively. Line 7 transports the flow D formed in reactor R4 to decanter 8.

[0103] 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 line 9. The aqueous phase F is sent to unit 11 for regeneration and concentration of the aqueous phase. Line 12 is a line that bypasses unit 11 for regeneration and concentration. Depending on the quality of the aqueous phase, it is possible to direct the aqueous phase F to 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 that has undergone the regeneration and concentration step and / or the aqueous phase that has passed through the bypass line 12 is sent to reactor R1 via line 13. The regeneration and concentration unit 11 may include a purge 14 to remove excess water from the circuit.

[0104] The reaction for forming azine in the presence of a solution containing at least one activator of ammonia, hydrogen peroxide and alkyl ketone is carried out in four reactors designated as R41, R42, R43 and R44 provided in a cascade.

[0105] Reactor R41 is fed ketone via line 21, which may be a fresh ketone feed or a recycle feed of ketone from the process. Reactor R41 is fed oxygen peroxide via line 22 and an aqueous solution saturated with ammonia and containing at least one activating agent via line 23.

[0106] Lines 24, 25 and 26 carry the streams (A), (B) and (C) coming from reactors R41, R42, R43 to the next reactors, namely R42, R43 and R44, respectively. Line 27 transports stream D formed in reactor R44 to decanter 28.

[0107] The decanter 28 separates the organic phase E from the aqueous phase F. The organic phase E is sent via line 29 to the subsequent steps of the process. The aqueous phase F is sent to unit 31 for regeneration and concentration of the aqueous phase F. Line 32 is a line bypassing the regeneration and concentration unit 31. Depending on the quality of the aqueous phase, it is possible to either lead the aqueous phase F to unit 31 or to the bypass line 32. It is also possible to send only a part of the aqueous phase F to the regeneration and concentration unit 31. The aqueous phase that has undergone the regeneration and concentration step and / or the aqueous phase that has passed by the bypass line 32 is sent via line 34 to the top of the ammonia absorption column 33. During the regeneration and concentration steps, it is also possible to recover ammonia. This ammonia can be recycled via line 35 to the bottom of the ammonia absorption column 33. The regeneration and concentration unit 31 may contain a purge 36 to remove excess water from the circuit. The ammonia absorption column 33 can also be fed with fresh ammonia via line 37. Finally, the reaction phase of the reactor R41 is sent via line 38 to the top of the ammonia absorption column 33.

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

[0109] The following examples are illustrative of the present invention but are not intended to limit it in any way.

Example

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

[0111] The reaction steps are carried out according to the equipment in Figure 2. The process uses four cascaded reactors. Methyl ethyl ketone is used as the reactant.

[0112] The temperatures of the reactors are as follows: T R41 = 50 °C, T R42 = 51 °C, T R43 = 52.5 °C, T R44 = 55 °C. The reaction is carried out at atmospheric pressure.

[0113] The flow of aminoperoxide and the flow of amine generated in each reactor are evaluated.

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

[0115] The flow rate of the reactants arriving at reactor R41 is shown in Table 2 below:

Table 2

[0116] The stirring conditions of each process are shown in Tables 3 and 4 below. The reactor includes a stirrer with a diameter of 1.7 m. The formation of aminoperoxide and the generation of azine 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 indicate that the stirring system described in the claims is capable of reducing the production of aminoperoxide in each reactor. Therefore, the difference in stirring applied between reactor R41 and reactor R42 has a significant impact on the amount of aminoperoxide produced in these reactors, and this effect is still observed in reactors R43 and R44. Furthermore, an increase in yield is also obtained.

Claims

1. A process for the continuous preparation of azine, comprising: a) ammonia, hydrogen peroxide and formula: R 1 R 2 CO ketone (base R 1 and R 2 A process comprising a reaction step of reacting (which independently 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) in the presence of an aqueous solution containing at least one activator to form an azine, wherein The reaction is carried out in at least two reactors arranged in a cascade configuration. The stirring in the first reactor is less than the stirring in each of the subsequent reactors or multiple subsequent reactors. The aqueous solution containing the above-mentioned hydrogen peroxide, the above-mentioned ketone, and at least one activator, and dissolved in ammonia, preferably in a proportion of 50% to 100% of the saturation of ammonia in pure water at the temperature of the aqueous solution, is injected into the first reactor.

2. The process according to claim 1, characterized in that the aqueous solution containing at least one activator and dissolved ammonia is derived from an absorption column.

3. The process according to claim 1, characterized in that the stirring in the first reactor is characterized by a Froude number of exactly less than 0.018, and the stirring in the subsequent reactor(s) is characterized by a Froude number of 0.018 or greater.

4. The process according to claim 1, characterized in that the above reaction is carried out in three, four, or five reactors arranged in a cascade.

5. The process according to claim 1, characterized in that the ketone used in reaction step a) above is methyl ethyl ketone.

6. The process according to claim 1, characterized in that it includes a separation step b) after the reaction step a), which separates the flow formed at the end of the reaction step a).

7. The process according to claim 6, characterized by comprising step c) of regenerating and concentrating the aqueous phase from step b) above.

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

9. The process according to claim 7, characterized in that, during step c) of regenerating and concentrating the aqueous phase from step b) above, a gaseous ammonia stream is recycled to an ammonia absorption column.

10. A process according to any one of claims 6 to 9, characterized by comprising the following steps: - From the separation step b) above, a step of washing the organic phase, - A step in which the flow obtained from the previous step is hydrolyzed to obtain hydrazine hydrate.

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