Title of Invention

A PROCESS FOR THE PREPARATION OF AZINE

Abstract

ABSTRACT A Process For The Preparation Of Azine IN/PCT/2001/00523/CHE. The present invention provides a process for the preparation of azine and of hydrazine by bringing ammonia, hydrogen peroxide and a reactant carrying a carbonyl group into contact with a working solution comprising: the treatment of an aqueous stream resulting from the circuit for the regeneration of the said working solution with an amount of acid such that the pH of the said stream is brought to a value of less than 6.4, then the recycling of the said stream in the reactor for the synthesis of the azine.

Full Text

The subject-matter of the present invention is a process for the preparation of azine and a process for the preparation of hydrazine employing it. The synthesis of hydrazine from ammonia and hydrogen peroxide is described in Ullmann's Encyclopedia of Industrial Chemistry (1989), Vol. A 13, pages 182-183. In this scheme, R1 and R2, which are identical or different, represent a hydrogen atom or a C1-C4 alkyl radical, provided that at least one of R1 and Rz is other than a hydrogen atom, or else R1 and R2 form, together with the carbon atom to which they are bonded, a C3-C6 cycloalkyl radical. This reaction is necessarily carried out in the presence of a catalyst (or activator) or of a mixture of catalysts included within a composition denoted as working solution- At the end of the reaction, the azine is separated from the working solution. The latter is then regenerated and then recycled in the reactor of Stage (I). the reactant carrying a carbonyl group is recovered and recycled in the reactor of Stage (I). This process was disclosed in particular in Patents US 3,972,878 and US 3,972,876. The term "working solution" is therefore understood to mean any aqueous solution or suspension comprising a catalyst or a mixture of catalysts which is capable of converting a mixture of ammonia, of hydrogen peroxide and of a reactant carrying a carbonyl group to an azine. This working solution is disclosed in Patents EP 399,866, EP 487,160 and EP_70,155.. It is composed, for example, of an aqueous solution of acetamide and of ammonium acetate. The ammonium acetate is formed in the reactor, in particular by reaction of acetic acid with ammonia. The working solution can also be composed of an aqueous solution of cacodylic acid and of ammonium cacodylate. Application EP 0,518,728 discloses a process for the synthesis of azine in which the working solution and more generally any stream entering the reactor for the synthesis of the azine are devoid of C02. According to this application, the presence of C02 in the synthesis process generally results from undesirable reactions of the hydrogen peroxide with various organic impurities which are produced in certain stages of the process. The C02 thus formed reacts in its turn with the hydrogen peroxide, which results in an excessive consumption of H202 and a fall in the yield of azine intermediate and thus of hydrazine. To overcome this disadvantage, Application EP 0,518,728 discloses a process for the preparation of intermediate azine, in which: a) ammonia, hydrogen peroxide and a reactant carrying a carbonyl group are brought into contact in a reactor with a working solution, then b) the azine thus formed is separated from the working solution, then c) the working solution is regenerated by bringing it to a temperature of at least 130°C, so that the C02 and most of the water (formed during the reaction of Stage a) or contributed by the water of dilution of the hydrogen peroxide) are removed in the form of an aqueous stream, denoted CI in the continuation of the present text, which therefore comprises, in the dissolved state, in addition to the C02 (essentially present in the carbonate form), a certain amount of the ammonia and of the reactant carrying a carbonyl group employed in Stage a), then d) the working solution, regenerated according to Stage c) , is recycled in the reactor of Stage a). The stream Cl comprises a certain amount of ammonia and of reactant carrying a carbonyl group. However, it cannot be directly recycled in the reactor for the synthesis of the azine, specifically because of the presence of a significant amount of C02. In order to economize on the significant amounts of reactants which can be used in the process, Application EP 0,518,728. therefore recommends complementing Stage d) of the said process by treating this stream Cl so as to remove the C02 therefrom, in order to be able thus to recycle the ammonia and the reactant carrying a carbonyl group which it comprises in the reactor for the synthesis of azine. Figure 1/3 represents a device suited to the implementation of this process. It is described in a detailed way later in the present text, in the appropriate part. A process for the treatment of the stream Cl appropriate for the removal of C02, such as the removal mentioned in Stage d), is also disclosed by Application EP 0,518,728. According to this process, the stream Cl is first of all treated in a stripping column, the top stream of which is cooled in a condenser. The NH3 is collected in the gaseous state, and the liquid phase obtained is separated, in a settling tank, into the organic phase, rich in reactant carrying a carbonyl group, and the agueous phase. The NH3 and the organic phase thus obtained are recycled to the reactor for the synthesis of the azine. The aqueous phase, which comprises all the C02 present in the stream CI, is fed to a 2nd distillation column, so as to collect: - at the column top, an aqueous stream devoid of C02 and comprising a certain amount of ammonia and of reactant carrying a carbonyl group, which is therefore recycled to the reactor for the synthesis of the azine, - at the column bottom, an aqueous stream, denoted C2 in the continuation of the present text, which comprises virtually all the C02 present in CI and also small amounts of ammonia and of reactant carrying a carbonyl group. Figure 2/3 represents, as a reminder, the device taught by EP 518, 728 for the treatment of the stream CI. Under the practical conditions of Implementation of the process, the Stream C2 generally comprises from 0.1 to 20% by weight of CO2 (present in :he form of carbonate in the dissolved state) , from 1 :o 15% of NH3 and from 0.1 to 10% of reactant carrying a :arbonyl group. ±u cue present cext, except when otherwise indicated, the percentages shown for the components under percentages expressed by weight. Application EP 0,518,728 gives no teaching > relating to the treatment to be given to the Stream C2. According to this application, it cannot be recycled to the reactor for the synthesis of the azine, since it comprises CO;. The removal of such a Stream C2 might be envisaged by means of known techniques, such as incineration. However, this removal would necessarily be accompanied by releases to the atmosphere of a mixture of compounds of the NO or NO; type, resulting from the combustion of NH3. In point of fact, it is desirable to limit as far as possible the discharge to the atmosphere of such compounds. Furthermore, this removal would also involve the loss of small amounts of reactants which can be used in the process, namely ammonia and reactant carrying a carbonyl group, which loss is harmful to the economics of the process. Application EP 0,518,728 suggests removing the C02 by washing with sodium hydroxide solution, in order to retain the CO; in the form of an aqueous sodium carbonate solution and to leave the ammonia, the reactant carrying a carbonyl group and water vapour in gaseous form. A novel process for the preparation of the azine has now surprisingly been found which, in contrast to the teaching of Patent EP 0,518,728, involves an acid in the treatment of the Stream C2. One aim of the invention is therefore to provide a process for the preparation of azine in which the discharges of effluents to the environment are reduced. Another aim of the invention is to provide a process for the preparation of azine in which the losses of reactants of use in the reaction are reduced. These aims can be achieved, in all or in part, by the process for the preparation of azine which is the subject-matter of the invention, which process is described hereinbelow. The subject-matter of the invention is therefore, firstly, a process for the preparation of azine comprising the stages: (i) in which, successively: (a) ammonia, hydrogen peroxide and a reactant carrying a carbonyl group are brought into contact, in a reactor, with a working solution, (b) the azine thus formed is separated from the working solution, (c) the working solution is regenerated by bringing it to a temperature of at least 130°C, so that the C02 and most of the water (formed during the reaction of Stage a) or contributed by the water of dilution of the hydrogen peroxide) are removed in the form of an aqueous stream CI, which therefore comprises, in the dissolved state, in addition to the C02 (present essentially in the carbonate form), a certain amount of ammonia and of the reactant carrying a carbonyl group employed in Stage a), (d) the working solution, regenerated iccording to Stage c) , is recycled in the reactor of Stage a); and (ii) in which, successively: (a) the said stream CI is treated in a ;tripping column; (b) the top stream is condensed while ■eparating the NK3 in the gaseous state; (c) the liquid phase resulting from the ondensation is separated into an organic phase, rich n reactant carrying a carbonyl group, and an aqueous hase comprising all the C02 present in Cl; (d) the said aqueous phase is fed into a istillation column, from where an aqueous stream evoid of C02 is collected at the top and an aqueous tream C2 comprising virtually all the CO2 present in Cl s collected at the bottom, characterized in that: - at least a portion of the stream C2 is reated with an amount of acid such that the pH of the said stream is brought to a value of less than 6.4, preferably less than 6; then - the said portion (denoted stream C3) thus treated is recycled in the reactor of Stage ti> (a)■ This process is particularly advantageous in that it makes it possible to recover most of the amounts of NH3 and of reactant carrying a carbonyl group present in the stream CI, in order for them to be reused in the reactor for the synthesis of the azine. This results in an appreciable saving. Furthermore, in contrast to the treatment with sodium hydroxide solution suggested by EP 0,518,72j3, it makes it possible to avoid any problem of liquid or solid discharge to the environment, the C02 being removed by simple degassing. The treatment with the acid is usually carried out at a temperature of between 2 0 and 70°C, preferably between 40 and 60°C, and at a pressure of between 0.5 and 4 bar absolute, preferably between 0.5 and 2 bar absolute. The aqueous stream C2 employed usually has a C02 content of between 0.1 and 2 0%, preferably between 0.5 and 5%, an NH3 content of between 1 and 15%, preferably between 1 and 6%, and a content of reactant carrying a carbonyl group of between 0.1 and 10%, preferably between 0.1 and 5%. The pH of the aqueous stream C2 is usually between 8 and 12. It is preferable to subject the whole of the Stream C2 to the treatment with the acid. It is also preferable to employ the process according to the invention while choosing methyl ethyl ketone as reactant carrying a carbonyl group. In this case, the corresponding azine is insoluble in aqueous solution, which facilitates Stage fi) (b) of separation of the azine from the working solution. The acid employed in the treatment of the aqueous stream C2 is advantageously an acid with a pKa of less than 6.3, preferably of less than 5. According to a preferred alternative form of the process according to the invention, the working solution employed comprises an aqueous solution of acetamide and of acetic acid. In this case, it is preferable to use acetic acid in the treatment of the Stream C2, as acid with a pKa of less than 6.3. According to another preferred alternative form of the process according to the invention, the working solution employed comprises an aqueous solution of cacodylic acid and of ammonium cacodylate. In this case, it will be preferable to use cacodylic acid for the treatment of the Stream C2, as acid with a pKa of less than 6.3. In all cases, the treatment by neutralization of the Stream C2 can be carried out in a very simple, more particularly preferred, way by use of the stream of acid introduced into the circuit for the regeneration of the working solution in order to compensate for the losses occasioned by the circulation and treatment of the solution. The treatment of the Stream C2, which is carried out using a reactant already employed in the process, is consequently very advantageous in economic terms. Another subject-matter of the invention is a process for the preparation of hydrazine, comprising the process for the preparation of the azine as described above, in which the azine separated from the working solution in accordance with Stage (i)(b) of the said process is hydrolysed to hydrazine, the reactant carrying a carbonyl group being recovered and recycled in the reactor for the synthesis of the azine. i t Detailed description of the'figures: Figure 1/3: Figure 1/3 represents a device for carrying out the synthesis of hydrazine from ammonia and hydrogen peroxide according to a process mentioned in EP 518,728. The azine is synthesized in the reactor 20. 1 represents the feed of reactant carrying a carbonyl group, composed of the recycling coming from the hydrolysis reactor 50 and of an optional makeup 3. 4 represents the feed of NH3, 12 represents the feed of hydrogen peroxide and 5 represents the recycling of the working solution. The synthesis product is conveyed via a pipe 6 into the separator 30, which produces the crude asine at 7 and the working solution at 8, which working solution also comprises ammonia, a small amount of ketone, the water which is formed by reaction and the water which was contributed by the hydrogen peroxide, since, for reasons of safety, use is made of hydrogen peroxide at a concentration of at most 70% by weight in water. The separator 30 can be a simple settling tank, if the azine is insoluble in the working solution and in the water of reaction; if not, a distillation column is used. The function of the working solution is to catalyse the synthesis of azines and to carry the water of reaction and the water contributed with the hydrogen peroxide via the pipe 8 to the device 40. The working solution is brought in the device 40 to a temperature of at least 130DC and preferably of between 150 and 250°C. A stream CI comprising: - CO2 in the form of ammonium carbonate, - the water formed by the reaction and the i/ater contributed by the hydrogen peroxide, - ammonia, - reactant carrying a carbonyl group, is recovered at 10. The regenerated working solution, which comprises acetamide and acetic acid, is recovered at 5 and is returned to the reactor 20. The stream 10 (stream CI) is conveyed to the treatment unit 60. The following are obtained at the outlet of this unit 60: a stream 13, corresponding to the combination of a gaseous NH3 stream (stream 103 of Figure 2/3), of a stream rich in MEK (stream 104 of Figure 2/3) and of an aqueous stream comprising small amounts of NH3 and MEK (stream 108 of Figure 2/3); this stream 13 is recycled in the reactor 20; - a stream of water 14, - a stream 15 comprising the CO2 present in the stream 10 and small amounts of NH3 and of MEK. The stream for the introduction of acetic acid 16 is provided in order to compensate for the losses occasioned by the circulation and the treatment of the working solution. The azine is hydrolysed at 50 to hydrazine, which is drawn off at 11, and the ketone is recycled to the reactor 20 at 2. Figure 2/3: Figure 2/3 represents the breakdown of the treatment carried out in the unit 60 of Figure 1/3. This treatment is in accordance with a device taught by EP 518,728. for the treatment of the stream CI corresponding to the stream 10 of Figures 1/3 and 2/3. The stream CI, as defined above, arrives at the top of a stripping column 601 equipped with a reboiler. The C02 in 10 is in the form of ammonium carbonate. The water stream 14 is recovered at the bottom and a top stream 102 is recovered and is cooled to between 30 and 50°C in a condenser 602. A portion of MH3 does not condense and is recycled via a stream 103 to the reactor for the synthesis of the azine. The liquid phase passes into the tank 603. Depending on the solubility of the reactant :arrying a carbonyl group, it is possible to have an organic phase which is rich in this reactant. This is Ln particular the case for methyl ethyl ketone. This organic phase is recycled via a stream 104 to the reactor for the synthesis of the azine. The aqueous )hase present in 603 comprises all the C02 (in the form if ammonium carbonate) which existed in the stream Cl stream 10 in the figures). A portion 105 of this .queous phase is conveyed to the column 601 as reflux .nd the stream 106 is flashed under low pressure in a olumn 604. The bottom temperature of the column 604 is .aintained between 20 and 45°C by a reboiler and the ressure is maintained between 8 x 103 Pa (60 mm Hg) and 12 x 103 Pa (90 mm Hg) absolute by a vacuum pump or any equivalent device. The top stream 108 comprises ammonia and the reactant carrying a carbonyl group, and water. This stream is devoid of CO2 and is therefore recycled to the reactor for the synthesis of the azine. The stream C2 is the stream 15, obtained at the bottom of the column 604, which comprises all the C02 (in the form of ammonium carbonate) present in the stream CI, as well as water and small amounts of WH3 and of reactant carrying a carbonyl group. Figure 3/3: This figure illustrates an embodiment of the process according to the invention. In this figure, the treatment unit 60 is identical to that represented in Figure 2/3. Only the differences from Figure 1/3 are commented on hereinbelow. The stream 15 (stream C2) resulting from the bottom of the column 60/ is fed into a stirred reactor 70 maintained at 45°C, into which is introduced the stream 16 of acetic acid introduced in order to compensate for the losses occasioned by the circulation and treatment of the working solution. The stream 17 represents the stream of CO2 removed by degassing and the stream 18 represents the aqueous stream C3 comprising substantially no more CO; and comprising small amounts of NH3 (in the form of ammonium acetate) and of MEK. The following example is given purely by way of illustration of the present invention and should under no circumstances be interpreted as limiting the scope thereof. Example: An azine is synthesized, by reaction of methyl ethyl ketone (MEK), ammonia and hydrogen peroxide in the presence of a working solution comprising acetamide and ammonium acetate, in accordance with Figures 2 and 3. A stream 15 (stream C2) is obtained, with a throughput of 350 kg/h, which comprises the following compounds: CO;: 1.42% (expressed as molar equivalent weight of carbonate) NH3: 4% MEK: 1.5% The pH of this stream is 10.4. The stream 16, corresponding to the introduction of 75% acetic acid into the unit, is 150 kg/h. The whole of the stream 15 is introduced into the acidification reactor maintained at a temperature of 45°C. At the outlet of the acidification reactor, a stream 18 (stream C3) is obtained with a throughput of S00 kg/h, with a pH of 5.5 and with a CO2 content reduced to 0.6%, which comprises: ammonium acetate: 12% acetic acid: 13% MEK: 1% This stream 18 is returned to the reactor for he synthesis of the azine 20 by introduction into the tream 8 of the circuit for the regeneration of the ■orking solution. 1. Process for the preparation of azine comprising the stages: (i) in which, successively: (a) ammonia, hydrogen peroxide and a reactant carrying a carbonyl group are brought into contact, in a reactor, with a working solution, (b) the azine thus formed is separated from the working solution, (c) the working solution is regenerated by bringing it to a temperature of at least 130°C, so that the CO; and most of the water are removed in the form of an aqueous stream CI; (d) the working solution, regenerated according to Stage c) , is recycled in the reactor of Stage a); and (ii) in which, successively: (a) the stream CI is treated in a stripping column; (b) the top stream is condensed while separating the NH3 in the gaseous state; (c) the liquid phase resulting from the condensation is separated into an organic phase, rich in reactant carrying a carbonyl group, and an aqueous phase comprising all the CO2 present in CI; d) the said aqueous phase is fed into a distillation column, from where an aqueous stream devoid of CO2 is collected at the top and an aqueous stream C2 comprising virtually all the C02 present in CI is collected at the bottom, characterized in that: -at least a portion of the stream C2 is treated with an amount of acid such that the pH of the said stream is brought to a value of less than 6.4; then -the said portion (denoted stream C3) thus treated is recycled in the reactor of Stage (i) (a). 2. The process according to Claim 1, wherein the at least portion of the stream C2 is treated with an amount of acid such that the pH of the stream is brought to a value of less than 6.0. 3. The process according to Claim 1 or 2, wherein the treatment with the acid is carried out at a temperature of between 20 and 70°C, and at a pressure of between 0.5 and 4 bar absolute. 4. The process according to Claim 3, wherein the treatment with the acid is carried out at a temperature of between 40 and 60°C. 5. The process according to Claim 3 or 4, wherein the treatment with the acid is carried out at a pressure of between 0.5 and 2 bar absolute. 6. The process according to anyone of Claims 1 to 5, wherein the aqueous stream C2 has a C02 content of between 0.1 and 20%, an NH3 content of between 1 and 15%, and a content of reactant carrying a carbonyl group of between 0.1 and 10%. 7. The process according to Claim 6, wherein the aqueous stream C2 has a C02 content of between 0.5 and 5%. 8. The process according to Claim 6 or 7, wherein the aqueous stream C2 has an NHi content of between 1 and 6%. 9. The process according to anyone of Claims 6 to 8, wherein the aqueous stream C2 has a content of reactant carrying a carbonyl group of between 0.1 and 5%. 10. The process according to anyone of Claims 1 to 9, wherein the whole of the stream C2 is subjected to the treatment with the acid. 11. The process according to anyone of Claims 1 to 10, wherein the reactant carrying a carbonyl group is methyl ethyl ketone. 12. The process according to anyone of Claims 1 to 11, wherein the acid employed in the treatment of the stream C2 is an acid with a pKa of less than 6.3. 13. The process according to Claim 12, wherein the apid employed in the treatment of the stream C2 is an acid with a pKa of less than 5. 14. The process according to anyone of Claims 1 to 13, wherein the working solution employed comprises an aqueous solution of acetamide and of acetic acid and acetic acid is used in the treatment of the stream C2. 15. The process according to any one of Claims 1 to 13, wherein the working solution employed comprises an aqueous solution of cacodylic acid and of ammonium cacodylate and cacodylic acid is used in the treatment of the stream C2. 16. The process according to Claim 14 or 15, wherein the treatment of the stream C2 is carried out by use of the stream of acetic acid or* of cacodylic acid introduced into the circuit for the regeneration of the working solution. 17. A process for the preparation of hydrazine, comprising the process for the preparation of azine as defined in anyone of Claims 1 to 16, in which the azine separated from the working solution in accordance with Stage (i) (b) is hydrolysed to hydrazine, the reactant carrying a carbonyl group being recovered and recycled in the reactor for the synthesis of azine. 18. A process for the preparation of azine substantially as herein above described and illustrated with reference to the accompanying drawing.

Documents:

in-pct-2001-0523-che abstract-duplicate.pdf

in-pct-2001-0523-che abstract.pdf

in-pct-2001-0523-che claims-duplicate.pdf

in-pct-2001-0523-che claims.pdf

in-pct-2001-0523-che correspondence-others.pdf

in-pct-2001-0523-che correspondence-po.pdf

in-pct-2001-0523-che description (complete)-duplicate.pdf

in-pct-2001-0523-che description (complete).pdf

in-pct-2001-0523-che drawings-duplicate.pdf

in-pct-2001-0523-che drawings.pdf

in-pct-2001-0523-che form-1.pdf

in-pct-2001-0523-che form-19.pdf

in-pct-2001-0523-che form-26.pdf

in-pct-2001-0523-che form-3.pdf

in-pct-2001-0523-che form-5.pdf

in-pct-2001-0523-che pct.pdf

in-pct-2001-0523-che petition.pdf