Process for producing hydrazine hydrate in the presence of an antifoaming agent

Abstract

The present invention relates to a process for the preparation of hydrazine hydrate, which comprises the step of hydrolyzing an azine in a distillation column in the presence of at least one silicone of the polydialkylsiloxane, polydiarylsiloxane or polyalkyl-arylsiloxane type. The invention also relates to the use of at least one silicone of the polydialkylsiloxane type as an antifoaming agent in the process for the preparation of azine hydrates.

Description

[Technical field]

[0001] The present invention relates to a method for producing hydrazine hydrate.

[0002] The present invention more particularly relates to a method for preparing hydrazine hydrate from alkyl ketone azines obtained by oxidation of ammonia with hydrogen peroxide and an activator in the presence of a ketone. [Background technology]

[0003] Hydrazine is primarily used to deoxygenate boiler water (e.g. in nuclear power plants) and also in the manufacture of pharmaceutical and pesticide derivatives.

[0004] Therefore, there is an industrial need for the production of hydrazine hydrate.

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

[0006] The Raschig process requires the oxidation of ammonia with hypochlorite to obtain a dilute solution of hydrazine hydrate, which is then concentrated by distillation; however, this process is no longer in use due to its low selectivity, low productivity, and high pollution.

[0007] The Bayer process is a modification of the Raschig process, in which acetone is used to shift the chemical equilibrium by trapping the hydrazine formed in the form of an azine of the formula: [ka]

[0008] The azine is then isolated and hydrolyzed to give hydrazine hydrate, which improves yield but does not improve environmental emissions.

[0009] The hydrogen peroxide method involves the oxidation of a mixture of ammonia and ketones with hydrogen peroxide in the presence of a means for activating hydrogen peroxide to produce azines directly, which are then hydrolyzed to hydrazine hydrates. The yield is high and the method is less polluting. There are many patents that describe the hydrogen peroxide method, including, for example, US3972878, US3972876, US3948902, and US4093656.

[0010] These methods are also described in Ullmann's Encyclopedia of Industrial Chemistry (1989), vol. A13, pages 182-183 and the accompanying references.

[0011] In the hydrogen peroxide process, ammonia is oxidized by hydrogen peroxide in the presence of a ketone and a hydrogen peroxide activating means to form an azine according to the following overall reaction: [ka]

[0012] The activating means, i.e., activator, may be a nitrile, amide, carboxylic acid, or a selenium, antimony, or arsenic derivative. The azine is then hydrolyzed to the hydrazine and the ketone is regenerated according to the following reaction: [ka]

[0013] The hydrolysis actually occurs in two steps, with the formation of an intermediate hydrazone. [ka]

[0014] Whether the azines are produced by the hydrogen peroxide process or by some other process, methyl ethyl ketone is advantageously used since it is sparingly soluble in aqueous media.

[0015] In fact, in processes using hydrogen peroxide, the azine of methyl ethyl ketone is relatively insoluble in the reaction medium, which is necessarily aqueous, since a commercially available 30-70% by weight aqueous solution of hydrogen peroxide is used. This azine is therefore easy to recover and can be separated simply by decantation. It is very stable, especially in an alkaline environment, i.e. in the ammonia reaction mixture. In the current process, the azine is then purified and hydrolyzed in a reactive distillation column, and finally methyl ethyl ketone is released at the top for recycling, and, among other things, an aqueous solution of hydrazine hydrate is released at the bottom. This must contain as few carbon products as possible as impurities and be colorless.

[0016] The hydrolysis of azines is known. For example, EC Gilbert, in the Journal of the American Chemical Society vol. 51, pages 3397-3409 (1929), describes the equilibrium reactions of azine formation and azine hydrolysis and provides the thermodynamic parameters of the system in the case of water-soluble azines. For example, the hydrolysis of acetone azine is described in the document US 4724133 (Schirmann et al.). Complete hydrolysis can be achieved by carrying out the hydrolysis in a reaction column and continuously separating the ketone at the top and the hydrazine hydrate at the bottom of a distillation column. Of course, this system is suitable for continuous operation, as described in patents FR 1315348, GB 1211547, GB 1164460, US 4725421 (Schirmann et al.) or WO 00 / 37357.

[0017] An efficient process for the preparation of hydrazine hydrate is known from document WO2020 / 229773.

[0018] Typically, a distillation column is used for the hydrolysis step to carry out the synthesis process continuously. However, it has been reported that bubbles may occur in the distillation column during the hydrolysis step. The bubble tip causes simultaneous vapor and liquid flow, preventing efficient separation of the products.

[0019] The presence of bubbles in the column limits the productivity of the column and therefore of the manufacturing process: indeed, as soon as they appear, it is necessary to slow down the process to prevent a loss of selectivity.

[0020] In another context, document EP 0 761 595 discloses the use of non-ionic surfactants carrying polyoxyethylene groups and silica as anti-clogging agents for columns in the hydrolysis step.

[0021] However, it has been noted that these compounds are not effective in preventing foaming, nor are they heat resistant. In fact, these products tend to degrade, contaminating the manufacturing circuitry and causing impurities in the final product.

[0022] In the hydrazine synthesis process, the conditions for hydrolysis of azines or regeneration of the aqueous phase are very demanding, with temperatures in the boiler set in the range of 160-180 °C and wall temperatures even higher, so it is essential that the proposed antifoaming agent does not decompose under the influence of temperature.

[0023] Therefore, a first object of the present invention is to provide a method for producing hydrazine hydrate, which includes a hydrolysis step without generating bubbles in a distillation column, and a desirable object is to perform a stable hydrolysis reaction over time.

[0024] The manufacturing method according to the present invention meets the objectives set forth hereinabove.

[0025] The inventors have surprisingly found that the use of certain silicones can stabilize production rates by preventing foaming in the distillation column during the hydrolysis step.Furthermore, these antifoaming agents are resistant to high temperatures, so they are less susceptible to decomposition and do not or only little to pollute the distillation column and the production circuit.In fact, when all or part of the reagents in the system are recycled, the claimed silicones hardly remain as impurities in the production system.

[0026] The present invention therefore relates to a process for the preparation of hydrazine hydrate, which comprises the hydrolysis of an azine in a distillation column in the presence of at least one silicone of the polydialkylsiloxane, polydiarylsiloxane or polyalkylarylsiloxane type.

[0027] The present invention also relates to the use of one of the polydialkylsiloxane, polydiarylsiloxane or polyalkylarylsiloxane formulae as an antifoam agent in the process for producing azine hydrates. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0028] Other features, aspects, subjects and advantages of the present invention will become apparent from reading the following description.

[0029] It is expressly stated that the expressions "from to" and "between" as used herein are to be understood as including each of the limitations referenced.

[0030] The preparation of hydrazine hydrate is carried out according to the following steps: - Ammonia, hydrogen peroxide and a ketone of formula R1R2C=O are reacted in the presence of a solution containing at least one activator to form an azine in a working solution. - Hydrolysis of the azine of the formed ketone gives hydrazine hydrate.

[0031] The azine-containing organic phase from the previous step and water are injected into the reactive distillation column, and the hydrolysis step is carried out in a batch or continuous manner. The hydrolysis step is preferably carried out in a continuous manner.

[0032] The hydrolysis can be carried out in a packed or plate distillation column.

[0033] Preferably, the distillation is carried out under pressure, more particularly under a pressure of between 2 and 25 bar.

[0034] Advantageously, the distillation is carried out at a bottom temperature of between 150°C and 200°C, preferably between 175°C and 190°C.

[0035] According to a preferred embodiment, the hydrolysis can be carried out in a packed or plate distillation column, preferably operated under a pressure of from 2 to 25 bar and at a bottom temperature of from 150°C to 200°C.

[0036] Although conventional packed columns may be suitable, plate columns are commonly used. The number of plates may vary, depending on the residence time allowed on the plates and the pressure in the column, and hence the operating temperature. Typically, when operating at 175°C to 190°C at 8 to 10 bar pressure, the number of plates required ranges from 40 to 70.

[0037] The molar ratio of water to azine fed to this column is at least greater than the stoichiometric value, advantageously ranging from 5 to 30, preferably from 10 to 20.

[0038] The azines that undergo the hydrolysis step are the reaction products of the oxidation of ammonia in the presence of a ketone of formula R1R2CO. The R1 and R2 groups are each independently a linear or branched C1-C 10 It denotes an alkyl group. In particular, the R1 and R2 groups, independently of one another, denote methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl and octyl groups. Preferably, dimethyl ketone and methyl ethyl ketone are used. Particularly preferably, methyl ethyl ketone is used. Thus, a preferred azine is the azine of methyl ethyl ketone, called MEKazine.

[0039] For the purposes of the present invention, silicones comprise identical or different units of formula -(Si(-R3)(-R4)-O-), the R3 and R4 groups independently of each other denote alkyl or aryl groups.

[0040] In the process according to the invention, at least one polydialkylsiloxane, polydiarylsiloxane or polyalkyl-arylsiloxane silicone is added to the reaction medium, which silicone prevents the formation of bubbles in the column.

[0041] Preferably, the silicone according to the invention is non-volatile, in other words a silicone oil having a viscosity of more than 5 cSt at 25°C and in particular a vapour pressure of less than 13.3 Pa at 25°C.

[0042] In the present invention, polydialkylsiloxane refers to a linear, branched or cyclic C1-C 18 It is understood to mean siloxanes which contain alkyl groups, preferably methyl, ethyl, propyl, butyl, pentyl, hexyl, cyclohexyl, heptyl, octyl, and which may also carry fluorine atoms as substituents.

[0043] In the present invention, polydiarylsiloxane refers to a C6-C 10 It is understood to mean siloxanes containing aryl groups, preferably phenyl groups, and optionally carrying fluorine atoms.

[0044] In the present invention, polyalkyl-aryl siloxane refers to a C1-C 18 Alkyl groups and C6-C 10 It is understood to mean siloxanes containing aryl groups, preferably methyl and phenyl groups, and which may optionally carry fluorine atoms.

[0045] The silicones according to the invention are preferably non-volatile, have a viscosity of more than 5 cSt at 25° C. and can be chosen from polydimethylsiloxanes, polydiphenylsiloxanes, polymethylphenylsiloxanes and polyethylphenylsiloxanes. Advantageously, the silicones according to the invention are aliphatic polydialkylsiloxanes, preferably polydimethylsiloxanes, hereinafter referred to as PDMS.

[0046] According to a specific embodiment, the viscosity of the silicone used in the process of the present invention is from 5 to 1,000,000 cSt at 25° C., preferably from 50 cSt to 100,000 cSt, and more preferably from 80 to 10,000 cSt.

[0047] The international unit of kinematic viscosity is m 2 / s. Some silicone manufacturers express kinematic viscosity in centistokes or cSt. 1 cSt = 0.01 St = 1 mm 2 It should be noted that / s.

[0048] Other manufacturers also express viscosity in centipoise, cP, cPs or cs. It is important to note that 1 cP = 0.001 Pa s.

[0049] Advantageously, the silicone may be in the form of an aqueous emulsion, preferably in the form of an emulsion, the silicone being preferably present in said emulsion in a content ranging from 1 to 45% by weight, preferably from 4 to 30% by weight, relative to the total weight of the emulsion.

[0050] Preferably, the silicone can be mixed with silica, the latter being preferably present in a content ranging from 1 to 45% by weight, preferably from 4 to 30% by weight, relative to the total weight of the mixture of silicone and silica.

[0051] Examples include the following polydimethylsiloxanes: - AK ranges proposed by Wacker (5-60,000cSt at 25°C) (AK 100, AK 1000, AK 12500, etc.); - Xiameter PMX series proposed by Dow (Xiameter PMX 200 Silicone Fluid 100 cPs, Xiameter PMX 200 Silicone Fluid 350 cPs, Xiameter PMX 200 Silicone Fluid 1000 cPs, etc.); - The Bluesil series proposed by Elkem (Bluesil 47 V 100, Bluesil 47V 500, Bluesil 47 V 1000, etc.). The last number in the name gives information about the viscosity of the oil (mPas).

[0052] Elkem, for example, offers Silcolapse RG12, a polydimethylsiloxane formulated in an aqueous emulsion.

[0053] Elkem also proposes silica suspensions in polydimethylsiloxane, for example Silcolapse 411.

[0054] As silicones containing aryl groups according to the invention, polydiarylsiloxanes, in particular polydiphenylsiloxanes, and polyalkyl-arylsiloxanes can be used. Examples include the following commercially available products: - Methylphenylpolysiloxanes sold by Shin Etsu under the names KF 96-100 and KF 96-1000, with viscosities of 5 to 10,000 mm 2 We offer silicones in a viscosity range of 100 / s (centistokes). - methylphenylsiloxanes sold by Wacker in their AS series (especially AS 100PDMS), - Methylphenylpolysiloxanes sold by Shin Etsu under the names KF 500-100, KF 50-1000, and KF-54.

[0055] Among the fluorinated silicones, silicones containing the -(Si(-CH3)(-CH2-CH2-CF3)-O-) unit are preferred.

[0056] The commercially available FF160 and FF170 models sold by Momentive are suitable.

[0057] Dow's FS-1265 fluid products in 300 cSt, 1000 cSt and even 10,000 cSt may also be used.

[0058] According to one embodiment of the present invention, a mixture of silicones may be used.

[0059] For batch processing, the silicone can be added to the reaction medium prior to the hydrolysis step, either dissolved or dispersed in the medium, or added directly to the column.

[0060] Typically, in a continuous process, the water is preferably introduced at the top of the column, while the azine organic phase is preferably introduced between the middle and the top of the column.

[0061] The antifoam agent is preferably added to the system at the top of the column with the aqueous phase.

[0062] Preferably, the silicone is incorporated in a content ranging from 1 ppm to 5000 ppm by weight relative to the dialkyl ketone azine, preferably in a content ranging from 5 ppm to 4000 ppm by weight relative to the dialkyl ketone azine.

[0063] When in the form of silicone only, the silicone is introduced at a content ranging from 10 ppm to 4000 ppm by weight relative to the dialkyl ketone azine, preferably between 20 ppm and 1000 ppm by weight relative to the dialkyl ketone azine, and more particularly between 40 ppm and 500 ppm by weight relative to the dialkyl ketone azine.

[0064] When the silicone is in the form of an aqueous emulsion, the emulsion is introduced in a content ranging from 1 ppm to 500 ppm by weight relative to the azine of the dialkyl ketone, preferably in a content ranging from 1 ppm to 200 ppm relative to the azine of the dialkyl ketone.

[0065] After hydrolysis, the ketone is obtained overhead, in particular in the form of an azeotrope with water, and an aqueous solution of hydrazine hydrate is obtained at the bottom.

[0066] At the bottom of the column, a solution containing 30% or even up to 45% by weight of hydrazine hydrate is obtained.

[0067] Additionally, the antifoam agent may be used in other columns of the azine synthesis process.

[0068] Following the reaction step, the azine is separated from the aqueous phase. The aqueous phase is a working solution comprising water and activator, obtained after the formation of the azine. The separation is carried out, for example, by decantation. The working solution is then regenerated. A method for regenerating and recycling the working solution is known from document EP 399866, the contents of which are incorporated herein by reference. The working solution is maintained at at least 130° C. while removing the water provided by the reaction water and the hydrogen peroxide dilution water in the form of a stream comprising water, ammonia, ketones and CO2. The stream obtained in the previous step is introduced into a stripping column in the presence of at least one silicone as defined herein before as an antifoaming agent. An ammonia stripping column is known from document EP 0518728, the contents of which are incorporated herein by reference. The use of silicones at this stage of the process also allows the distillation in the column to be stabilized in a sustainable manner, without the generation of impurities in the circuit.

[0069] The present invention also relates to the use of at least one silicone of the polydialkylsiloxane, polydiarylsiloxane or polyalkylarylsiloxane formula as described hereinbefore as an antifoaming agent in the process for the preparation of azine hydrates.

[0070] According to one embodiment, silicone is introduced into the distillation column to allow for the hydrolysis of the azine.

[0071] According to another embodiment, the silicone is introduced into an ammonia stripping column fed with a flow from a step for regenerating a working solution recovered after a reaction step for the production of an azine with ammonia, hydrogen peroxide and a ketone.

[0072] The following examples are illustrative of the present invention but are not intended to be limiting thereof. EXAMPLES

[0073]

[0074] Comparative Example 1

[0075] The process disclosed in Example 1 of document WO2020 / 229773 was carried out for the synthesis of hydrazine hydrate from MEKazine. The hydrolysis column disclosed in this document was used without additives, with an input hydrazine flow rate of 6000 kg / h and a water flow rate of 12,000 kg.

[0076] After 5 days, column clogging and distillation instability were observed, necessitating a reduction in production rate to re-establish the correct temperature profile over the plate.

[0077] The temperature at the bottom of the column was 180° C. and the pressure in the column was 9 bar absolute.

[0078] Comparative Example 2

[0079] The process disclosed in Example 1 of document WO2020 / 229773 was carried out for the synthesis of hydrazine hydrate from MEKazine. The hydrolysis column described in this document was used and an ethoxylate derivative of palmitic acid was added.

[0080] Approximately 15 days after start-up, deposits were observed forming on the walls of the boiler and other parts of the hydrazine hydrate concentrate trains. Analysis determined the deposits to be palmitic acid hydrazide.

[0081] Example 3 according to the present invention

[0082] The process disclosed in Example 1 of the document WO2020 / 229773 was carried out for the synthesis of hydrazine hydrate from MEKazine. The hydrolysis column described in this document was used with the addition of PMDS 100 cPs silicone under the trade name Xiameter PMX 200 Silicone Fluid 100 cPs at a flow rate of 1-2 kg / h for an input of 6000 kg / h of hydrazine and 12,000 kg of water. The column operated stably under these conditions for more than two months.

[0083] The results of these three examples are summarized in Table 1 below. [Table 1]

[0084] These results show that the silicones of the invention make it possible to stabilize distillation in a sustainable manner without contaminating the process circuit with degradation products.

[0085]

[0086] The antifoaming effect of the additive was tested in the laboratory.

[0087] 10 g of methyl ethyl ketone azine taken from the distillation azine purification process were introduced into 90 mL of water and refluxed at 95° C. under a nitrogen flow rate of 300 mL / min. Bubbles appeared from the reaction medium. It was necessary to wait a few minutes until the bubble height stabilized. The bubbles stabilized at a height of 4-5 cm above the liquid level in the reactor.

[0088] The antifoam was added to the reaction medium using a peristaltic pump at a flow rate of 0.1 g / min (pre-adjusted for each antifoam compound evaluated) through a thin tube that allowed the introduction of approximately one drop of antifoam every 10-15 seconds.

[0089] The change in the decrease in foam height (H) during the introduction of the antifoam agent was recorded as (Hinitial-H(t)) / Hinitial.

[0090] The results of these examples are summarized below in Table 2. Examples 4-8 are in accordance with the invention, while Examples 9 and 10 are comparative examples. [Table 2]

[0091] 1 The defoamer used is PDMS 100 cPs silicone, sold by Dow under the trade name Xiameter PMX 200 Silicone Fluid 100 cPs.

[0092] 2 The defoamer used is a PDMS 500 cPs silicone containing 10% silica by weight, sold under the trade name Silcolapse 411 by Elkem.

[0093] 3 The antifoam agent used was PDMS 1000 cPs silicone, sold by Sigma-Aldrich under the trade name "silicone oil" and has a viscosity of 1000 cPs.

[0094] 4 The antifoam agent used was PMDS 10000 cPs silicone, sold by Sigma-Aldrich under the trade name "Silicone Oil" and has a viscosity of 10000 cPs.

[0095] 5 The antifoam agent used is an aqueous emulsion containing 10% by weight silicone and 10% by weight silica, sold by Elkem under the trade name Silcolapse RG12.

[0096] 6 The antifoam agent used is an EO / PO polyether with a mass of 2000 g / mol, 10% EO units and a viscosity of 350 cPs, sold under the trade name Pluronic PE 6100 by BASF.

[0097] 7 The antifoam agent used is an EO / PO polyether with a mass of 3500 g / mol, 10% EO units and a viscosity of 800 cPs, sold under the trade name Pluronic PE 10100 by BASF.

[0098] For Examples 9 and 10, the addition of antifoaming agent results in foaming properties that increase the foam height by up to 55% in the case of Example 9 as soon as the first drop is added to the medium.

[0099] Furthermore, in Comparative Examples 8 and 9, it is observed that the foam level is not stable, the foam level decreases and then increases.

[0100] In the examples of the present invention, a dramatic reduction in foam is observed.

[0101] As a result, the silicones of the present invention prevent foam formation as soon as they are introduced into the distillation column. The effect is immediate.

Claims

1. A method for producing hydrazine hydrate, comprising the steps of: A process for the preparation of hydrazine hydrate comprising the step of hydrolyzing an azine in a distillation column in the presence of at least one silicone of the polydialkylsiloxane, polydiarylsiloxane or polyalkylarylsiloxane type.

2. 2. The method for producing hydrazine hydrate according to claim 1, wherein the silicone is selected from the group consisting of polydimethylsiloxane, polydiphenylsiloxane, polymethylphenylsiloxane and polyethylphenylsiloxane.

3. A process for the preparation of hydrazine hydrate according to claim 1 or 2, characterized in that the viscosity of the silicone is from 5 to 1,000,000 cSt, preferably from 50 to 100,000 cSt, more particularly from 80 to 10,000 cSt at 25°C.

4. A method for the preparation of hydrazine hydrate according to any one of the preceding claims, characterized in that the silicone is polydimethylsiloxane.

5. 2. A process for the preparation of hydrazine hydrate according to any one of the preceding claims, characterized in that the silicone is in the form of an aqueous emulsion.

6. 2. A process for the preparation of hydrazine hydrate according to any one of the preceding claims, characterized in that the silicone is introduced at the top of the distillation column and water is introduced into the column for hydrolysis.

7. 10. A process for the preparation of hydrazine hydrate according to any one of the preceding claims, characterized in that the silicone is introduced in a content ranging from 1 ppm to 5000 ppm by weight relative to the azine, preferably in a content ranging from 5 ppm to 4000 ppm by weight relative to the azine.

8. A process for the preparation of hydrazine hydrate according to any one of the preceding claims, characterized in that the azine is methyl ethyl ketone azine or dimethyl ketone azine, preferably the azine is methyl ethyl ketone azine.

9. A process for the preparation of hydrazine hydrate according to any one of the preceding claims, characterized in that it comprises the following steps: - reacting ammonia, hydrogen peroxide and a ketone in the presence of a solution containing at least one activator to form an azine in a working solution prior to said hydrolyzing step.

10. A method for producing hydrazine hydrate according to claim 9, comprising the steps of: - separating the azine from the working solution; - Water, ammonia, ketones and CO ２ regenerating the working solution to at least 130° C. while removing water provided by the reaction water and the hydrogen peroxide dilution water in the form of a stream comprising - passing the stream obtained in said step through a stripping column in the presence of at least one silicone as defined in any one of claims 1 to 5 as an antifoaming agent.

11. Use of at least one silicone according to any one of claims 1 to 5 as an antifoaming agent in an azine hydrate production process.

12. 12. Use according to claim 11, characterized in that the silicone is introduced into a distillation column for the hydrolysis of azines.

13. 13. Use according to claim 11 or 12, characterized in that the silicone is introduced into an ammonia stripping column which is fed with a stream from a step for regenerating a working solution recovered after the step of reaction of ammonia, hydrogen peroxide and a ketone to form an azine.

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