Method for preparing hydrazine hydrate by using absorption tower

Abstract

The invention relates to a method for producing hydrazine hydrate, comprising the following consecutive steps: a) producing an aqueous solution comprising dissolved ammonia and comprising at least one activator by introducing an aqueous solution comprising at least one activator and fresh ammonia into an absorption column; the aqueous ammonia solution comprising at least one activator obtained in the previous step is then reacted with hydrogen peroxide and a ketone in at least one reactor, then c) the organic phase comprising azine is separated from the aqueous phase in the stream formed at the end of the previous step, and then d) the organic phase obtained in the previous step is hydrolyzed to obtain hydrazine hydrate.

Description

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

[0002] 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.

[0003] Therefore, there is an industrial need to prepare hydrazine hydrate.

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

[0005] 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.

[0006] The Bayer process is a modification of the Raschig process which involves altering the chemical equilibrium by trapping the hydrazine in the azine form with acetone:

[0007] .

[0008] The azine is then separated and hydrolyzed to hydrazine hydrate. The yield is improved, but the environmental emissions are not improved.

[0009] The hydrogen peroxide method involves oxidizing a mixture of ammonia and ketone with hydrogen peroxide in the presence of a tool for activating hydrogen peroxide to directly synthesize 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.

[0010] These methods are described in Ullmann, Encyclopedia of Industrial Chemistry (1989), Vol. A13, pp. 180-183, and references included therein.

[0011] 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:

[0012] .

[0013] 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:

[0014] .

[0015] This hydrolysis actually occurs in two stages, with the formation of an intermediate hydrazone:

[0016] .

[0017] The reaction to form the azine is relatively complex, since it involves three phases: a gas phase containing ammonia, an organic phase containing the ketone, and an aqueous phase containing the activator and hydrogen peroxide. The use of methyl ethyl ketone is advantageous, since the azine of methyl ethyl ketone is soluble in the organic phase and has a very low solubility in aqueous media. It can therefore be easily recovered at the end of the reaction and separated by simple decantation. This azine also has the advantage of being very stable, particularly in alkaline media, i.e. in ammoniacal reaction media.

[0018] 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, which can 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.

[0019] A method for efficiently preparing hydrazine hydrate is known from document WO2020 / 229773.

[0020] 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. Specifically, in order for the reaction to be effective, the reactants must be in contact with each other, namely ammonia in the gas phase, hydrogen peroxide and activator in the aqueous phase, and ketone in the organic phase. The yield of the reaction is directly related to the exchange and contact between the phases. The above publication studies the reaction yield as a function of the agitation speed of the reaction medium and as a function of the number of phases present in the reactor.

[0021] It was observed that the higher the stirring speed, the more the yield increased, up to a threshold of 600 rpm. However, these experiments were performed in a semi-batch reactor. Now, this method is difficult to transfer to an industrial unit, i.e. to a larger capacity. Applying 600 rpm of stirring to an industrial-scale reactor represents a huge energy consumption. It is difficult to achieve this level of stirring when the method is applied to industrial quantities.

[0022] Therefore, solutions are still being sought to make these gas-liquid-liquid contacts efficient in industrial processes with satisfactory yields, reasonable energy consumption and simple installation.

[0023] This technical problem has been solved by mixing the different phases in two steps: first, the gaseous ammonia is dissolved in the aqueous phase using an absorption tower, and then this ammoniacal aqueous phase is mixed with the organic phase in a conventional stirred reactor.

[0024] This solution can use a standard liquid-liquid two-phase reactor, and the stirring level is also standard. It has been observed that very good yields can be obtained even at very low stirring levels. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0026] The subject of the present invention is therefore a process for preparing hydrazine hydrate comprising the following successive steps:

[0027] a) preparing an aqueous solution containing dissolved ammonia in a proportion of saturation of ammonia in pure water of between 50% and 100% relative to the tower temperature and containing at least one activator by introducing the aqueous solution containing at least one activator and fresh ammonia into the absorption tower; then

[0028] b) reacting, in at least one reactor, the aqueous ammonia solution obtained in the previous step and comprising at least one activating agent with hydrogen peroxide and a ketone of formula R1R2CO, the radicals R1 and R2 independently of one another representing methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl and octyl; then

[0029] c) separating the organic phase containing the azine from the aqueous phase from the stream formed at the end of the previous step; then

[0030] d) hydrolyzing the organic phase obtained in the previous step to obtain hydrazine hydrate. 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 pointed out that the expressions “from… to…” and “between… and…” used in this description should be understood to include every limit value mentioned.

[0033] Preparation of aqueous solution

[0034] An ammoniacal aqueous solution is prepared using an absorption tower.

[0035] The absorption column is fed with fresh ammonia and an aqueous solution comprising at least one activating agent.

[0036] 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.

[0037] At the outlet of the absorption column, an aqueous solution is obtained which contains dissolved ammonia in a proportion of between 50% and 100% of the saturation of ammonia in pure water at the column temperature and contains at least one activator.

[0038] Dissolved Ammonia

[0039] The solubility of gaseous ammonia in pure water as a function of temperature is known from the book Lange's Handbook of Chemistry, edited by John A. Dean, 12th edition, 1979, page 10.3. The solubility expresses the weight of gas dissolved in 100 g of water at a pressure of 760 mm Hg. The table disclosed on page 10.3 is reproduced below:

[0040]

[0041] Table 1

[0042] 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, 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. The 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.

[0043] 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.

[0044] 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 tower temperature.

[0045] 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 must be sufficient to achieve the desired ammonia solubility. Subsequently, the flow rate will be able to be reduced to maintain the desired solubility.

[0046] Activator

[0047] An "activator" is understood to be a compound which is able to activate hydrogen peroxide, ie a compound which is able to produce an azine from ammonia, hydrogen peroxide and a ketone.

[0048] 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.

[0049] As examples, one can mention:

[0050] (i) amides of carboxylic acids of the formula R5COOH, wherein R5 is hydrogen, a straight-chain 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,

[0051] (ii) 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.

[0052] 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.

[0053] Preferred amides are formamide, acetamide, monochloroacetamide and propionamide, more preferably acetamide.

[0054] 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 acids of the type described herein (wherein R5, R6 and n are as defined above) and salts of organic acids of arsenic.

[0055] Preferred ammonium salts are formates, acetates, monochloroacetates, propionates, phenylarsenates and cacodylate.

[0056] Among the nitriles, mention may advantageously be made of the formula R7(CN) nwherein 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 a group that is not oxidized in the reactor of step (b), such as a halogen or a carboxyl group, a carboxylate group, a nitro group, an amine group, a hydroxyl group or a sulfonic acid group.

[0057] Preferred nitriles are acetonitrile and propionitrile.

[0058] 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.

[0059] 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.

[0060] 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.

[0061] For polycarboxylic acids, the acid in question is one whose first dissociation constant is less than 3x10 -3 of acid.

[0062] 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) n A 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.

[0063] The corresponding ammonium salt of acetamide is ammonium acetate.

[0064] 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.

[0065] 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.

[0066] Device

[0067] 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.

[0068] The column may be a packed distillation column or a plate distillation column.

[0069] It is also possible to fully or partially recover the ammonia stream resulting from the process for preparing azine.

[0070] The aqueous solution comprising at least one activating agent may be a recycled aqueous solution from separation step c), which may have been subjected in whole or in part to regeneration and concentration steps.

[0071] 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.

[0072] Then, an aqueous ammoniacal solution containing at least one activating agent is introduced into the reactor, wherein the azine-forming reaction is carried out.

[0073] b) Mixed reactions

[0074] The mixed reaction is carried out in at least one reactor. An aqueous solution is introduced into the reactor, which contains dissolved ammonia in a proportion of between 50% and 100% of the saturation of ammonia in pure water at the tower temperature, and contains at least one activator (obtained in the previous step), hydrogen peroxide and a ketone of formula R1R2CO, the radicals R1 and R2 independently of one another representing methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl and octyl.

[0075] Hydrogen Peroxide

[0076] Hydrogen peroxide can be used in its common commercial form, for example an aqueous solution containing 30 to 90% by weight of oxygen peroxide. 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 ammonium or alkali metal salts of these acids.

[0077] 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.

[0078] Chelating agents particularly useful for stabilizing hydrogen peroxide solutions are compounds comprising a phosphonic acid function in acid form or in salt form.

[0079] The following commercial products are available:

[0080] - the product sold under the name DEQUEST® 2060 by the company Monsanto, which is a 50% aqueous solution of diethylenetriamine penta(methylenephosphonic acid),

[0081] - the product sold under the name DEQUEST® 2041, which is an aqueous solution of ethylenediaminetetrakis(methylenephosphonic acid),

[0082] - 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.

[0083] 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.

[0084] 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.

[0085] Alkyl Ketone

[0086] 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.

[0087] The reactants can be used in stoichiometric amounts. However, 0.2 to 5, preferably 1.5 to 4, ketones and 0.1 to 10, preferably 1.5-4, ammonia can be used per mole of hydrogen peroxide. 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-specified proportions of the reactants make it possible to obtain a maximum conversion of hydrogen peroxide (generally greater than 90%, preferably greater than 95%) and an azine yield of greater than 75%, possibly up to 90%, of the hydrogen peroxide used.

[0088] Mixing conditions

[0089] The reaction can be carried out over a very wide temperature range, for example between 0°C and 100°C, advantageously between 30°C and 70°C. Although it can be carried out at any pressure, it is simpler to operate at atmospheric pressure, although it can be increased to about 10 bar absolute. Preferably, the reaction is carried out at a pressure of 1 bar to 5 bar absolute.

[0090] Reactor

[0091] The inner diameter of the reactor may be between 1 meter and 6 meters, preferably between 2 meters and 5 meters. The working height of the reactor may be between 1 meter and 10 meters, preferably between 3 meters and 7 meters. Therefore, the reaction volume may be between 25 cubic meters and 100 cubic meters, preferably between 40 cubic meters and 70 cubic meters.

[0092] The reactor may be equipped with stirring means, such as blades.

[0093] 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.

[0094] The reactor according to the invention is not a microreactor.

[0095] It is also possible to use multiple reactors arranged in cascade. According to this embodiment, the reaction can occur in at least two reactors arranged in cascade. Preferably, 3, 4 or 5 reactors in cascade are used. The reactors can have the same volume or different volumes.

[0096] Preferably, the agitation in the first reactor is less than that in the second and any subsequent reactors.

[0097] 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 a rotating element such as a blade, an anchor or any other rotating element, optionally in the presence of baffles, 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.

[0098] According to a particular embodiment of the invention, when the process uses 2, 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.

[0099] 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

[0100] g = acceleration due to gravity, or 9.81 m / s 2

[0101] D = agitator diameter, in m

[0102] N = the number of revolutions of the agitator, in revolutions per second.

[0103] When the process according to the invention comprises 2 or more reactors, the Froude number in the first reactor may be less than 0.018 and the Froude number in the following reactor may be greater than 0.018. 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 strictly less than 0.010 and the Froude number in the following reactor is strictly greater than 0.018.

[0104] The ketone may be introduced at the bottom of the reactor and the aqueous hydrogen peroxide solution may be introduced through a tube immersed in the reactor.

[0105] This mixing step results in the formation of azine.

[0106] At the end of the reaction according to the invention, the reaction mixture comprises the azine, any unreacted ketone, any activating agent and any other by-products or impurities.

[0107] Circulation loop of aqueous solution saturated with ammonia

[0108] According to one embodiment of the present invention, the absorption tower of step a) can be fed with the flow of the reaction medium of the reactor of step b). The flow can be extracted using a pipe immersed in the reaction medium of the reactor. It is then introduced at the top of the absorption tower. Once introduced into the absorption tower, the flow of the reaction medium from step b) 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 containing at least one activator is fed into the 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 reactor and the absorption tower makes it possible to continuously maintain a high ammonia content in the reaction medium of step b). In other words, the ammonia concentration of the flow extracted from the reaction medium of step b) increases when it flows through the absorption tower before being re-injected into the reactor.

[0109] When the stirring in the 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.

[0110] According to one embodiment, when the method uses multiple reactors, the reaction medium of each reactor may be withdrawn and introduced into an absorption column.

[0111] According to another embodiment, when the process uses multiple reactors, the reaction medium of a single reactor can be withdrawn and introduced into an absorption column, such as the first reactor or the last reactor.

[0112] According to yet another embodiment, when the process uses multiple reactors, the reaction medium of several reactors, but not all reactors, may be withdrawn and introduced into an absorption column.

[0113] c) Separation

[0114] After the reaction to prepare the azine, the process according to the invention comprises a step of separating the stream formed at the end of step b).

[0115] The aqueous phase comprising the activator is separated from the organic phase comprising the azine 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.

[0116] The obtained organic phase may contain the azine, unreacted alkyl ketone, activating agent and any other impurities.

[0117] Optional water phase recycle

[0118] After separation step c), the aqueous phase can be subjected completely or partially to a regeneration and concentration step. The aqueous phase thus regenerated and concentrated can be recycled to the absorption column.

[0119] In the step of regenerating and concentrating the aqueous phase from the separation step, a gaseous ammonia stream can be separated and recycled to the absorption column.

[0120] Optional organic phase wash

[0121] The method may comprise a step of washing the organic phase separated in step c). The step of washing the organic phase obtained in step c) is a step that can be carried out by techniques known to a person skilled in the art, as indicated, for example, in document WO 2018 / 065997 (page 13, "Organic layer processing section", second paragraph). The washing step makes it possible in particular to recover the activating agent (e.g. acetamide) that may still be present in the organic phase.

[0122] Washing can be carried out in a countercurrent scrubber.

[0123] Thus, any activating agent still present in the organic phase passes into the aqueous wash phase.

[0124] According to one embodiment, after passing through the washing column, the obtained aqueous phase can be recycled to step a), wherein the aqueous phase is recovered in step c).

[0125] Optional distillation of the organic phase

[0126] The process may comprise a step of distilling the organic phase separated and optionally washed in step c). The step of distilling the (optionally washed) organic phase is a step that can be carried out by techniques known to those skilled in the art, such as indicated in document WO 2018 / 065997 (page 13, "Organic layer treatment section"), in particular in a distillation column.

[0127] The distillation step is particularly useful for separating the azine from heavy impurities having a high boiling point. These impurities are recovered, for example, at the bottom of the column. The distillation step is also useful for separating the azine formed in step (b) from the unreacted alkyl ketone, which can be recovered at the top of the column. The alkyl ketone thus recovered can be recycled to the azine synthesis step (b). Thus, at the end of the washing and distillation steps, a purified organic phase comprising the azine is obtained.

[0128] d) Hydrolysis

[0129] The process according to the invention comprises a step of hydrolyzing the (purified or not) organic phase obtained in the previous step to obtain hydrazine hydrate.

[0130] The hydrolysis step is carried out under pressure in a reactive distillation column into which water and the (purified or non-purified) organic phase comprising the azine from step c) are injected.

[0131] The hydrolysis can be carried out in a packed distillation column or a plate distillation column, preferably operated at a pressure of 2 to 25 bar absolute and a bottom temperature of between 150°C and 200°C.

[0132] Although conventional packed columns may be suitable, tray columns are usually used. The number of trays may vary greatly depending on the residence time and pressure allowed on the trays, and therefore on the operating temperature. In practice, when operating at 8 to 10 bar absolute pressure, the number of trays required is about 40 to 70.

[0133] After hydrolysis, we get:

[0134] - alkyl ketones present overhead, in particular in the form of azeotropes with water, and

[0135] - At the bottom, an aqueous solution of hydrazine hydrate.

[0136] The hydrolysis of azine is known. For example, EC Gilbert in an article in the Journal of the American Chemical Society, Vol. 51, pp. 3397-3409 (1929) describes the equilibrium reactions of azine formation and azine hydrolysis reactions and provides the thermodynamic parameters of the system in the case of water-soluble azines. For example, the hydrolysis of azine in acetone is described in US Pat. No. 4,724,133. For azines that are insoluble in aqueous solution, such as azine in methyl ethyl ketone, the hydrolysis must be carried out in a reaction column so that complete hydrolysis can be achieved by continuously separating methyl ethyl ketone at the top of the distillation column and continuously separating hydrazine hydrate at the bottom of the column.

[0137] When pure azine is used, ie obtained, for example, from hydrazine hydrate and methyl ethyl ketone, it has in fact been found that dilute solutions of hydrazine hydrate can be obtained in good yields when working according to these patents.

[0138] What is carried out in this tower is the hydrolysis of azine and the separation of hydrazine hydrate and methyl ethyl ketone. These conditions are known. Those skilled in the art will easily determine the number of plates or packing heights, as well as the feed points of water and azine. A solution of 20% or even up to 45% by weight of hydrazine hydrate is obtained at the bottom. For example, the water / azine molar ratio in the tower feed is at least greater than the stoichiometric ratio, advantageously between 5 and 30, preferably between 10 and 20. The temperature at the bottom of the tower can be between 150°C and 200°C, preferably between 175°C and 190°C. The pressure depends on the boiling points of azine, water and ketone. This hydrolysis is also described in US4725421 and WO00 / 37357.

[0139] The method according to the present invention can be carried out continuously or batchwise. Preferably, it is carried out batchwise.

[0140] Illustration

[0141] Figure 1 An embodiment of the method according to the invention is shown.

[0142] The preparation of the ammoniacal aqueous solution is carried out in an absorption column 1. The column 1 is fed with fresh ammonia via line 2 and with an aqueous solution comprising at least one activating agent via line 3.

[0143] An ammoniacal aqueous solution comprising at least one activating agent is fed to the reactor R via line 4 .

[0144] The line 5, the absorption column 1, the feed line 4 and the reactor R form a loop for recycling the aqueous solution comprising dissolved ammonia and the activator.

[0145] The reaction of ammonia, hydrogen peroxide and alkyl ketone in the presence of a solution comprising at least one activating agent is carried out in a reactor marked R.

[0146] Reactor R is fed with hydrogen peroxide via line 6. Ketone is fed via line 7. This can be a feed containing fresh ketone or a feed recycling ketone originating from the process.

[0147] The line 8 conveys the stream A formed in the reactor R to a decanter 9 .

[0148] Decanter 9 separates organic phase B and aqueous phase C. Organic phase B is fed to hydrolysis column 16 via pipeline 10. Water is supplied via pipeline 17. Hydrazine hydrate is recovered via pipeline 18. After the hydrolysis of the azine in hydrolysis column 16, a stream of ketone and water obtained at the top of the column leaves via pipeline 19.

[0149] The aqueous phase C is sent via line 11 to a regeneration and concentration unit 12 for the aqueous phase C.

[0150] Line 13 is a line that bypasses the regeneration and concentration unit 12. Depending on the quality of the aqueous phase, the aqueous phase C can be directed to the unit 12 or to the bypass line 13. It is also possible to send only a portion of the aqueous phase C to the regeneration and concentration unit 12. The aqueous phase that has passed the regeneration and concentration steps and / or the aqueous phase that has passed through the bypass line 13 is sent to the top of the absorption tower 1 through the line 3. During the regeneration and concentration steps, ammonia can also be recovered. The ammonia can be recycled to the bottom of the absorption tower 1 through the pipeline 14. The regeneration and concentration unit 12 may include a purge 15 to remove excess water in the line.

[0151] The following examples illustrate the invention but are not intended to limit it in any way.

[0152] Example

[0153] Example 1: Determination of the solubility of ammonia in aqueous phase

[0154] Several aqueous phases containing different contents of water, ammonium acetate, acetamide and MEK (methyl ethyl ketone) were prepared. These aqueous phases were saturated with ammonia in a reactor equipped with a condenser, by stirring, at atmospheric pressure at the temperature indicated by the ammonia flush, until the mixture was saturated, i.e. until ammonia was no longer absorbed and left the reactor. The flushing was then continued for 30 minutes while reducing the ammonia flow. The aqueous phase was analyzed for ammonia content by titration with 1 N sulfuric acid (1 ml sample).

[0155] An experiment was conducted at 50°C. The results are shown in Table 2 below:

[0156]

[0157] Table 2

[0158] A second experiment was conducted at 60°C. The results are shown in Table 3 below:

[0159]

[0160] Table 3

[0161] It can be seen that if the amount of ammonia is related to the amount of water contained in these aqueous phases, the ammonia content of the aqueous phase at saturation is close to the solubility value of ammonia in pure water, namely 23.5 g / 100 g at 50°C and 16.8 g / 100 g at 60°C, as indicated in Lange's Handbook of Chemistry.

[0162] Example 2: Method according to the present invention

[0163] Description of the react component: steps a) and b)

[0164] The 1000 ml reactor was equipped with a double jacket, which could be heated to keep the reaction temperature at the desired temperature. It was stirred by a rotating element consisting of three straight glass blades with a diameter of 4 cm. The reactor was equipped with a condenser maintained at 5 ° C by a glycol water circulation. The condenser was connected to a bubbler filled with silicone oil, which made it possible to monitor the gas release and keep the reaction at atmospheric pressure.

[0165] The absorption tower is a glass tower with an internal diameter of about 2 cm and filled with glass beads of about 2 mm in diameter to a height of about 10 cm. The double wall is maintained at a temperature of 25° C. to 30° C. by circulation of water from a thermostatically controlled bath. Gas phase pressure equalization is performed between the head space of the reactor and the top of the absorption tower.

[0166] Ammonia is injected at the bottom of the absorber via an adjustable mass flow meter. If increased gas evolution is observed at the bubbler, the ammonia flow rate is reduced.

[0167] The aqueous phase of the reactor is recycled to the absorption tower by a peristaltic pump; the aqueous phase drawn from the reactor is injected at the top of the absorption tower. The aqueous phase drawn from the reactor for recycling is carried out approximately at the first third of the liquid phase height starting from the bottom of the reactor.

[0168] The ammoniacal aqueous phase is introduced through the top of the reactor, above the liquid phase of the reactor. Hydrogen peroxide is also introduced through the top of the reactor, above the liquid phase of the reactor.

[0169] step:

[0170] The components of the aqueous phase, namely MEK, water, acetamide and ammonium acetate, were introduced into the reactor. Agitation was started and the temperature of the medium was adjusted to the desired reaction temperature. The pump for recycling the aqueous phase was also started.

[0171] The reactants were introduced in the ratio shown in Table 4 below:

[0172]

[0173] Table 4

[0174] Hydrogen peroxide is commercially available as a 70% aqueous solution.

[0175] The stirring of the reaction medium was set to 100 rpm.

[0176] When the reaction temperature in the reactor reached 50°C, the introduction of fresh ammonia and H2O2 started simultaneously. 48.6 g of 70% H2O2 solution was poured in one hour, i.e., the flow rate of H2O2 was 1 mol / h.

[0177] The ammonia flow rate was set at 31.8 g / h, ie 1.87 mol / h, at t=0 and was then adjusted during the reaction so that there was not any excess ammonia at the outlet of the bubbler.

[0178] The ammonia content at the column outlet and in the aqueous phase was analyzed by titration with 1 N sulfuric acid (1 ml sample).

[0179] The percentage of ammonia dissolved in the aqueous solution at the tower outlet was calculated based on the values ​​in the table of Langer's Handbook of Chemistry (ed. John A. Dean, 12th edition, 1979, page 10.3) relative to the value of ammonia in pure water at 30°C, i.e. relative to the value of 41.0 g.

[0180] The flow rate of the stream in the recirculation loop was 370 g / h.

[0181] Samples were taken to determine the MEK azine content in the reactor.

[0182] The yield of MEK azine was calculated according to the following formula: number of moles of azine formed / theoretical number of moles of azine (ie, 1 mole per mole of H2O2).

[0183] The reaction data are shown in Table 5 below:

[0184]

[0185] Table 5

[0186] Description of the React component: Step c)

[0187] The MEK azine is recovered after the decantation step.

[0188] Description of the React component: step d).

[0189] The device consists of a distillation column with a height of 2.5m and a diameter of 20mm, which is equipped with Raschigring (diameter 5mm) and temperature sensors at several positions along the column. The top of the column is equipped with a condenser and a device that can set the flow rate of condensate returning to the top of the column and the condensate withdrawn. The reflux ratio is set by a timing device (mass ratio of reflux flow to withdrawal flow).

[0190] The boiler at the bottom of the tower has a volume of 160 ml and is equipped with a device that allows visualization of the liquid level. Manual pumping at the boiler allows the generated hydrazine hydrate solution to be pumped out and the liquid level in the boiler to be kept essentially constant.

[0191] Water and MEK azine were introduced via pumps in the first third of the column from the top.

[0192] All components are designed to operate at the required operating pressure (8 bar absolute) and are equipped with 12 bar burst seals as a safety measure.

[0193] Tower Adjustment

[0194] A hydrazine hydrate solution containing 25% hydrazine hydrate (N2H4.H2O) is introduced into the boiler and the bottom temperature is gradually increased until water vapor reaches the top of the tower. The pressure is set to 8 bar absolute pressure.

[0195] Hydrolysis of azine

[0196] Then, water was introduced at a rate of 36 g / h (2 mol / h) and methyl ethyl ketazine was introduced at a rate of 28 g / h (0.2 mol / h) simultaneously. When the tower reached equilibrium, the reflux ratio at the top of the tower was set to 0.5, and hydrazine hydrate was continuously withdrawn at the bottom to keep the liquid level in the boiler constant.

[0197] This operation was carried out for about 8 hours. The bottom temperature was 178-177°C and the top temperature was 150-151°C.

[0198] During operation, 31 g / h of 31% aqueous hydrazine hydrate (expressed as N2H4.H2O) was extracted from the bottom of the tower, and 32 g / h of methyl ethyl ketone containing 12% water was extracted from the top.

[0199] Example 3: Method according to the present invention

[0200] The method of Example 3 follows the same method as Example 2, except that the flow rate of the stream in the recirculation loop is changed: it is doubled.

[0201] The reaction data are shown in Table 6 below:

[0202]

[0203] Table 6

[0204] These results show that very good yields were obtained with optimal ammonia consumption.

Claims

1. A method for preparing hydrazine hydrate, comprising the following consecutive steps: a) preparing an aqueous solution containing dissolved ammonia in a proportion of between 50% and 100% relative to the saturation of ammonia in pure water at the tower temperature and containing at least one activator by introducing the aqueous solution containing at least one activator and fresh ammonia into an absorption tower; then b) reacting, in at least one reactor, the aqueous ammonia solution obtained in the previous step and comprising at least one activating agent with hydrogen peroxide and a ketone of formula R1R2CO, the radicals R1 and R2 independently of one another representing methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl and octyl; then c) separating the organic phase containing the azine from the aqueous phase from the stream formed at the end of the previous step; then d) hydrolyzing the organic phase obtained in the previous step to obtain hydrazine hydrate.

2. The method according to claim 1, characterized in that In step a), the aqueous solution comprising at least one activating agent is introduced at the top of the absorption tower and the fresh ammonia is introduced countercurrently, preferably at the bottom of the absorption tower.

3. The method according to claim 1 or 2, characterized in that: The flow of the reaction medium of the reactor of step b) is fed to the absorption tower of step a), said flow being injected at the top of said tower.

4. The method according to any one of the preceding claims, characterized in that The aqueous solution separated in step c) is circulated to the absorption tower in step a).

5. The method according to any one of the preceding claims, characterized in that The absorption column of step a) is fed with one or more ammonia streams circulating in the process.

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

7. The method according to any one of the preceding claims, characterized in that The process comprises the steps of regenerating and concentrating the aqueous phase coming from separation step c).

8. The method according to any one of the preceding claims, characterized in that The process comprises a step of washing the organic phase coming from separation step c).

9. The method according to any one of the preceding claims, characterized in that The method is carried out batchwise.

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

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