Method for ammoniaceation of bromoalkanoates

Abstract

This invention provides a method for producing ω-aminoalkanoic acid that minimizes the production of secondary amines while keeping the size of the plant down. [Solution] The reaction of the corresponding ω-bromoalkanoic acid with ammonia produces the compound NH2-(CH2). n A method for producing ω-aminoalkanoic acid of the form -COOH (wherein n is an integer between 9 and 11), comprising the following steps: i) Reaction of ω-bromoalkanoic acid with excess aqueous ammonia solution, and ii) Separation of ω-aminoalkanoic acid formed from the reaction mixture The method is characterized in that the aqueous ammonia solution has a concentration of 35% to 70% by weight, and step i) is carried out under an absolute pressure of 0.11 to 2.0 MPa, which is higher than atmospheric pressure.

Description

Technical Field

[0001] The present patent application relates to a process for the ammonolysis of ω-bromoalkanoic acids to produce the corresponding ω-aminoalkanoic acids, which are useful as monomers for polyamides. Background Art

[0002] Processes using ammonia for the ammonolysis of ω-bromoalkanoic acids of formula Br-(CH2) n -COOH (n=9~11) to obtain ω-aminoalkanoic acids NH2-(CH2) n -CO2H are known in the art.

[0003] Accordingly, document FR988699 describes reacting 10-bromodecanoic acid with a 25% aqueous ammonia solution at 15°C for 6 days to form 10-aminodecanoic acid in a yield of 77%. This process suffers from the disadvantage of a very long reaction time.

[0004] Increasing the temperature makes it possible to accelerate the reaction, but it also promotes side reactions.

[0005] Accordingly, document FR928265 reports the reaction of 11-bromoundecanoic acid with a 25% aqueous ammonia solution carried out at 60°C for 10 hours in a closed vessel, thus under autogenous pressure. The yield of this reaction is 53%, which is very low.

[0006] This is because when ammonolysis is carried out, secondary amines of formula HO2C-(CH2) n -NH-(CH2) n -CO2H are by-produced in a relatively large amount. These impurities cause problems when ω-aminoalkanoic acids are used to produce polyamides, since they lead to chain branching. These secondary amines reduce the yield and are difficult to separate from the desired primary amine, so it is desirable to minimize their formation.

[0007] Patent application CN103804209B describes, in Example 3, the ammonia monolysis of 11-bromoundecanoic acid with anhydrous ammonia at a pressure of 0.1–0.15 MPa in the presence of a solvent and a phase transfer catalyst. This method allows for a reduction of reaction time to less than 24 hours, but it operates in a very dilute medium and therefore requires a large industrial plant, and still shows a not-so-high yield of 84.3%.

[0008] Patent application EP2358662B1 proposes reducing the reaction time and even the secondary reaction for the ammoniaxation of 11-bromoundecanoic acid by using an increasing temperature profile and providing the reaction medium with a regular steady-state temperature rise between an initial temperature of 15-25°C and a final temperature of 26-40°C.

[0009] The search for a technical solution that would allow for minimizing the production of secondary amines while keeping the plant size down is still ongoing. [Overview of the project]

[0010] The object of the present invention is to provide a solution to one or more of the aforementioned problems.

[0011] This invention is based on the unexpected observation that by combining a titer of aqueous ammonia solution higher than 35% by weight with a pressure higher than atmospheric pressure, it is possible to control the amount of secondary amine produced and thus accelerate the reaction while increasing the yield.

[0012] Therefore, according to the first aspect, the subject of the present invention is the reaction of the corresponding bromoalkanoic acid with ammonia of formula NH2-(CH2) n A method for producing ω-aminoalkanoic acid of the form -COOH (wherein n is an integer between 9 and 11), comprising the following steps: i) Reaction of ω-bromoalkanoic acid with excess aqueous ammonia solution, ii) Separation of ω-aminoalkanoic acid formed from the reaction mixture In a method including, The method is characterized in that the aqueous ammonia solution has a concentration of 35% to 70% by weight, and step i) is carried out under an absolute pressure of 0.11 to 2.0 MPa, which is higher than atmospheric pressure.

[0013] Preferably, step i) is carried out at a temperature of 0 to 60°C. This may be at a constant temperature or at an increasing temperature. If carried out at an increasing temperature, step i) may be advantageously carried out using an initial temperature in the range of 0 to 25°C and a final temperature in the range of 26 to 60°C.

[0014] Preferably, the aqueous ammonia solution has a concentration of 36% to 60% by weight, preferably 38% to 45% by weight.

[0015] Advantageously, the weight ratio of ω-bromoalkanoic acid to aqueous ammonia at the start of step i) is 1:3 to 1:20.

[0016] Step i) of the method according to the present invention may be carried out under a pressure of 0.125 to 0.5 MPa absolute pressure, or even 0.13 to 0.3 MPa absolute pressure.

[0017] The method of the present invention may be carried out continuously or in batches.

[0018] Advantageously, the method according to the present invention further includes step iii) of washing and draining the ω-aminoalkanoic acid obtained as a result of step ii).

[0019] The method may additionally include step iv) in which the crude ω-aminoalkanoic acid obtained as a result of step ii) or iii) is purified, preferably by recrystallization from boiling water.

[0020] Furthermore, the method may additionally comprise a step v) of recovering residual ω-aminoalkanoic acid from the various filtrates and aqueous washing solutions obtained in step ii), iii) and / or iv), in particular by degassing of ammonia, liquid-liquid extraction, crystallization, filtration and washing.

[0021] Finally, the method according to the present invention may additionally comprise a step vi) of drying the obtained ω-aminoalkanoic acid. MODE FOR CARRYING OUT THE INVENTION

[0022] Definition of Terms Throughout the present disclosure, unless otherwise stated, percentages are to be understood as weight percentages relative to the composition under consideration.

[0023] Furthermore, pressure values given in the present disclosure are to be understood as absolute pressure values, that is, pressure values relative to absolute vacuum, unless otherwise stated.

[0024] The term "aqueous ammonia solution" is understood to mean a solution of NH3 in water. The ammonia content thereof is expressed as the weight of NH3 relative to the weight of the solution (NH3 and water).

[0025] According to the present invention, the method for producing an ω-aminoalkanoic acid of formula NH2-(CH2) n -COOH, wherein n is an integer from 9 to 11, by reaction of a corresponding ω-bromoalkanoic acid with ammonia therefore comprises the following steps: i) reacting a ω-bromoalkanoic acid with an excess of aqueous ammonia solution, ii) separating the ω-aminoalkanoic acid formed from the reaction mixture and is characterized in that the aqueous ammonia solution has a concentration of 35 wt% to 70 wt%, and step i) is carried out under a pressure higher than atmospheric pressure, specifically an absolute pressure of 0.11 MPa to 2.0 MPa. The ω-bromoalkanoic acid may be 10-bromodecanoic acid, 11-bromoundecanoic acid, or 12-bromododecanoic acid.

[0026] These ω-bromoalkanoic acids can be obtained, in particular, by homobromination reactions of the corresponding unsaturated acids, namely 9-decanoic acid, 10-undecanoic acid, or 11-dodecanoic acid. These compounds are commercially available. Furthermore, 9-decanoic acid can be obtained from oleic acid-based vegetable oils according to the method described in WO2018 / 080869. 10-undecanoic acid can be obtained from castor oil according to FR928265.

[0027] The name ω-bromoalkanoic acid is used to refer to the compound in a somewhat purified form, and therefore may contain impurities. Commercially available ω-bromoalkanoic acid generally has a purity of over 98%. However, according to one embodiment, the purity of the ω-bromoalkanoic acid used can be 90% to 98%, preferably 93% to 96%. ω-bromoalkanoic acid may contain impurities, particularly those of the formula CH3-CH2Br-(CH2) n-2 - May contain bromoalkanoic acid of CO2H.

[0028] The method of the present invention first comprises step i) mixing ω-bromoalkanoic acid with an excess aqueous ammonia solution and then reacting it.

[0029] ω-bromoalkanoic acid can be added in solid or liquid form, particularly in molten form. The solid form can be powder, granules, or flakes. Advantageously, ω-bromoalkanoic acid is used in molten form at a temperature preferably higher than its melting point, such as 5-60°C, preferably 10-40°C, and particularly 15-30°C.

[0030] According to the present invention, the aqueous ammonia solution used contains 35% to 70% by weight of ammonia. Preferably, the aqueous ammonia solution contains 36% to 60% by weight of ammonia, more preferably 38% to 45% by weight of ammonia. According to one embodiment, the ammonia content of the aqueous ammonia solution can be 35% to 40% by weight, or 40% to 45% by weight, or 45% to 50% by weight, or 50% to 55% by weight, or 55% to 60% by weight, or 60% to 65% by weight, or even 65% to 70% by weight.

[0031] Advantageously, a portion of this aqueous ammonia solution is derived from the recovery of excess ammonia and ammonium present in the reaction medium at the outlet of this method.

[0032] Advantageously, the aqueous ammonia solution introduced into the reactor will have a temperature of 25°C or lower. Preferably, the aqueous ammonia solution is cooled to a temperature of -20°C to 20°C, preferably -10°C to 10°C.

[0033] The weight ratio of ω-bromoalkanoic acid to aqueous ammonia introduced in step i) is such that ammonia is present in a stoichiometric excess. This excess not only promotes the reaction but also allows for the dispersion or dilution of the ω-bromoalkanoic acid and the resulting product. Generally, the weight ratio is 1:20 to 1:3, preferably 1:10 to 1:4, and preferably 1:8 to 1:4. In this specification, the term “weight ratio” refers to both the weight ratio of reactants used in batch methods and the flow rate ratio by weight of reactants in continuous methods.

[0034] The method of the present invention further comprises step ii) separating the formed ω-bromoalkanoic acid from the reaction mixture.

[0035] Reaction mixtures are generally heterogeneous. This may particularly include a gas phase, one or more liquid phases, and / or one or more solid phases.

[0036] The method of the present invention can be carried out continuously or in batches.

[0037] When the method is carried out continuously, the reactants can be mixed in a tank equipped with a stirrer. In an alternative configuration, mixing can also be performed in an external mixing device, such as a static mixer, a Venturi apparatus, or a recirculation loop into which ω-bromoalkanoic acid is injected.

[0038] Step i) of the method can be carried out in the same apparatus. According to one embodiment, step i) can be carried out in one or more stirred tanks. According to a preferred embodiment, step i) can be carried out in a series of 2 to 25 reactors connected in series, where the reaction mixture is transferred from one reactor to another using a pump or by gravity flow. Each reactor may consist of a tank equipped with stirring. This stirring can be produced by a stirring module within the reactor or by external recirculation.

[0039] Preferably, step i) is carried out at a temperature of 0 to 60°C. According to one embodiment, the temperature can be 0 to 5°C, or 5 to 10°C, or 10 to 15°C, or 15 to 20°C, or 20 to 25°C, or 25 to 30°C, or 30 to 35°C, or 35 to 40°C, or 40 to 45°C, or 45 to 50°C, or 50 to 55°C, or even 55 to 60°C.

[0040] The reactor temperature can be advantageously controlled by the circulation of heat transfer fluid in the reactor jacket, by heat exchangers inside or outside the reactor, or by the injection of a thermal fluid, particularly water or steam, into one or more reactors.

[0041] The temperature can also be controlled by evaporating some of the ammonia and cooling the reaction medium, as will be explained in more detail later.

[0042] When the method is carried out in a series of reactors, as described above, the temperature of the first reactor is preferably 0-25°C, and the temperature of the last reactor is 26-60°C, with the temperature increasing from reactor to reactor. In such cases, it is advantageous to have individual temperature control for each reactor. Advantageously, the first reactor can be cooled and the last reactor can be heated.

[0043] The total residence time in step i) (calculated as the ratio of the total volume of the liquid phase in the reactor to the total flow rate of the reactants) is generally 20 to 100 hours, preferably 40 to 80 hours.

[0044] According to a second alternative embodiment, step i) of the method is carried out in a batch manner in a reactor, and the reactor may be a tank equipped with a stirring means. According to one embodiment, the reactants are mixed outside the reactor and then introduced into the reactor as a mixture. According to another embodiment, the ammonia solution is first introduced into the reactor and then ω-bromoalkanoic acid is added.

[0045] The mixing of ω-bromoalkanoic acid in an aqueous ammonia solution can be carried out in a tank equipped with a stirrer. In an alternative configuration, mixing can be carried out by an external mixing device, such as a static mixer, or by a Venturi device that allows mixing of two flows of reactants in the line before injection into the reactor, or even by an external recirculation loop into which the ω-bromoalkanoic acid is injected.

[0046] After mixing the reactants, step i) involves stirring the reaction medium for a sufficient amount of time, generally 20 to 100 hours, preferably 40 to 80 hours.

[0047] According to one embodiment, the reaction in step i) is carried out isothermally, that is, at a temperature that is maintained at the same value throughout the reaction time.

[0048] In this case, step i) is carried out at a temperature of 0 to 60°C. According to one embodiment, the temperature can be 0 to 5°C, or 5 to 10°C, or 10 to 15°C, or 15 to 20°C, or 20 to 25°C, or 25 to 30°C, or 30 to 35°C, or 35 to 40°C, or 40 to 45°C, or 45 to 50°C, or 50 to 55°C, or even 55 to 60°C.

[0049] In another embodiment, the reaction is carried out in an increasing temperature mode. Among the various possible thermal profiles, it has been found to be advantageous to establish a steady-state period at a temperature that rises particularly in the range from an initial temperature of 0–25°C to a final temperature of 26–60°C.

[0050] According to an alternative embodiment, step i) is carried out in a series of parallel reactors R1, R2, ..., Rn (2 ≤ n ≤ 25), each reactor being maintained at an independently variable temperature. Each reactor has an available program to raise its temperature over a predetermined period of time, the time of which depends on the selected temperature. In each reactor, the initial temperature of the program is preferably 0–25°C, and the final temperature is 26–60°C. To maintain constant, regular, and continuous feed and draw at the inlets and outlets of the series of reactors, each reactor operates according to a charge / reaction / ejection cycle with a time offset corresponding to the reaction time divided by the number of reactors (n).

[0051] In all alternative configurations, the reactor pressure, generally measured at the top of the gas-upper space, is kept higher than atmospheric pressure during step i). This is because it allows for the maintenance of a high concentration of ammonia in the liquid reaction phase, thereby promoting high selectivity for primary amines. Thus, it is possible to limit the formation of impurities, particularly secondary amines, and in fact even tertiary amines. However, to limit the reactor cost, it is preferable to limit the pressure.

[0052] Therefore, the reactor pressure is 0.11 to 2.0 MPa in absolute pressure, preferably 0.125 to 0.5 MPa in absolute pressure, preferably 0.13 to 0.3 MPa in absolute pressure. According to one embodiment, the pressure is 0.11 to 0.15 MPa in absolute pressure, or 0.15 to 0.2 MPa in absolute pressure, or 0.2 to 0.25 MPa in absolute pressure, or 0.25 to 0.3 MPa in absolute pressure, or 0.3 to 0.35 MPa in absolute pressure, or 0.35 to 0.4 MPa in absolute pressure, or 0.4 to 0.45 MPa in absolute pressure, or 0.45 to 0.5 MPa in absolute pressure, or 0.5 to 0.55 MPa in absolute pressure, and This refers to absolute pressures of 0.55-0.6 MPa, or 0.6-0.65 MPa, or 0.65-0.7 MPa, or 0.7-0.75 MPa, or 0.75-0.8 MPa, or 0.8-0.85 MPa, or 0.85-0.9 MPa, or 0.9-0.95 MPa, or 0.95-1.0 MPa, or 1.0-1.05 MPa. , or absolute pressure 1.05~1.1 MPa, or absolute pressure 1.10~1.15 MPa, or absolute pressure 1.15~1.2 MPa, or absolute pressure 1.2~1.25 MPa, or absolute pressure 1.25~1.3 MPa, or absolute pressure 1.3~1.35 MPa, or absolute pressure 1.35~1.4 MPa, or absolute pressure 1.4~1.45 MPa, or absolute pressure 1.45~1.5 MPa, or absolute pressure 1.5~1. The absolute pressure can be 55 MPa, or 1.55-1.6 MPa, or 1.6-1.65 MPa, or 1.65-1.7 MPa, or 1.7-1.75 MPa, or 1.75-1.8 MPa, or 1.8-1.85 MPa, or 1.85-1.9 MPa, or 1.9-1.95 MPa, or 1.95-2.0 MPa.

[0053] If step i) is carried out in several reactors, the reactor openings can be connected so that the reactors operate at substantially the same pressure. According to another embodiment, it may be advantageous to place the reactors under different pressures. Thus, if the temperature is increased from reactor to reactor as described above, the pressure in the reactors can also be increased from reactor to reactor. According to one embodiment, the pressure that prevails within the reactor is an inert pressure exerted mainly by the vapor pressure of ammonia, which is related to the composition of the reaction mixture and its temperature.

[0054] According to one embodiment, partial evaporation of the ammonia is possible to maintain the temperature of the reaction medium. Therefore, when operating continuously, this means can be used to cool the first reactor. When operating in batch mode, this means can be used to cool the reactor at the start of the reaction. It is possible to either adjust the flow rate of ammonia evaporation (in this case, the pressure) or to handle the evaporation of ammonia under a pressure slightly below liquid-vapor equilibrium. Advantageously, 0.1% to 50%, preferably 10% to 30%, of the injected ammonia evaporates during step i). How to adjust the amount of ammonia evaporating from the reaction medium to maintain the thermal profile during the reaction is known to those skilled in the art. This form of operation makes it possible to limit or avoid expensive heat exchangers while providing a temperature profile that enables an optimal yield.

[0055] Therefore, the method of the present invention makes it possible to significantly limit the amount of secondary amine formed, and as a result, to increase the reaction yield.

[0056] According to the present invention, the method further comprises step ii) separating ω-aminoalkanoic acid from the reaction mixture as a result of step i).

[0057] The ω-aminoalkanoic acid formed as a result of step i) can itself be separated from the reaction mixture by conventional methods, for example, by the following steps.

[0058] The reaction mixture obtained from step i) can be diluted with water and heated until boiling. The released ammonia can be washed with water to form an aqueous ammonia solution, which can be recycled back into step i) of this method. The ammonia-depleted reaction mixture can then be separated from any oily layer that may form by separation under high-temperature conditions, and subsequently cooled to separate the ω-aminoalkanoic acid by recrystallization and solid-liquid separation.

[0059] Furthermore, the ammonium bromide-rich filtrate recovered from solid-liquid separation can be treated with, for example, sodium hydroxide, for the purpose of reforming ammonia (which is evaporated and then washed in water) to obtain an aqueous ammonia solution.

[0060] ω-aminoalkanoic acid can also be separated from the reaction mixture obtained as a result of step i) by a stripping step to remove ammonia, washed with water, and then subjected to solid-liquid separation, such as filtration in a filter or drainage. The recovered mother liquor can be subjected to liquid-liquid extraction, recrystallization, and / or filtration to form an aqueous solution rich in ammonium bromide and depleted of ω-aminoalkanoic acid. This ammonium bromide-rich aqueous solution can be treated with sodium hydroxide to reform ammonia, which can then be evaporated and washed with water to form an aqueous ammonia solution.

[0061] The method of the present invention may also include an additional step iii) of subjecting the ω-aminoalkanoic acid obtained in step ii) to washing and drainage. Washing can be carried out using water in particular.

[0062] The method of the present invention may additionally include step iv) purifying the crude ω-aminoalkanoic acid obtained as a result of step ii) or iii).

[0063] This purification process may particularly include one or more of the following operations: recrystallization in a suitable solvent, e.g., water or a basic or acidic aqueous solution, e.g., a mixture of water and a carboxylic acid; filtration; washing; and drainage. Preferably, the resulting crude ω-aminoalkanoic acid is purified by recrystallization from very hot water.

[0064] Therefore, the method of the present invention may additionally include step v) of recovering residual ω-aminoalkanoic acid in the various filtrates and aqueous washing solutions obtained in steps ii), iii), and / or iv), particularly by degassing of ammonia, liquid-liquid extraction, crystallization, filtration, and washing.

[0065] Finally, the method of the present invention may additionally include step vi) drying the obtained ω-aminoalkanoic acid.

[0066] Advantageously, the method according to the present invention makes it possible to obtain ω-aminoalkanoic acid in which, as a result of step i), and therefore before purification, the content of ω-aminodialkanoic acid relative to the content of ω-aminoalkanoic acid is less than 1.8% by weight, preferably less than 1.5% by weight.

[0067] Furthermore, the method according to the present invention advantageously enables the complete conversion of ω-bromoalkanoic acid over the duration of the ammoniax process i) in a reaction time of less than 75 hours.

[0068] The present invention will be described in more detail in the following embodiments. [Examples]

[0069] Example 1 660 g of 40 wt% aqueous ammonia solution cooled to 0°C is placed in a 1-liter autoclave equipped with a mechanical stirrer having two propellers with five blades each, a Rushton turbine rotating at 400 rpm, a coil to allow circulation of heat transfer fluid, and a discharge valve set to an absolute pressure of 0.15 MPa, and the reactor is then closed. 110 g of molten 11-bromoundecanoic acid (98% purity) at 90°C is rapidly added dropwise, and the temperature of the reaction medium is adjusted to 22°C by the heat transfer fluid circulating in the coil. The pressure is adjusted very rapidly to an absolute pressure of 0.15 MPa and maintained at this value throughout the reaction time. After 12 hours and 30 minutes, the temperature of the reaction medium is raised, and steady-state periods of 12 hours and 30 minutes are successively performed at 24, 26, 28, 30, and 32°C, respectively. Subsequently, the reactor opening is opened and the reactor is brought to atmospheric pressure.

[0070] Next, the reaction medium is analyzed. By quantitatively measuring bromide ions with silver nitrate using a silver electrode, it is found that all of the 11-bromoundecanoic acid has reacted. Quantitative HPLC measurement using external calibration reveals that 1.3% by weight of 11-aminodiundecanoic acid is present relative to 11-aminoundecanoic acid.

[0071] Example 2 (Comparative Example) The procedure in Example 1 is repeated, but the operation is carried out at atmospheric pressure throughout the experiment, and the rate of addition of molten 11-bromoundecanoic acid is controlled to prevent the medium from foaming uncontrollably.

[0072] Analysis of the reaction medium indicates that all of the 11-bromoundecanoic acid has reacted. 1.9% by weight of 11-aminodiundecanoic acid is measured relative to 11-aminoundecanoic acid.

[0073] Example 3 (Comparative Example) Repeat Example 1, but operate at atmospheric pressure throughout the experiment and use 660g of a 32% by weight ammonia aqueous solution.

[0074] Analysis of the reaction medium indicates that all of the 11-bromoundecanoic acid has reacted. 2.0% by weight of 11-aminodiundecanoic acid is measured relative to 11-aminoundecanoic acid.

[0075] [List of References] FR988699 WO2018 / 080869A1 FR928265 CN103804209B EP2358662B1

Claims

1. The reaction of the corresponding ω-bromoalkanoic acid with ammonia is shown by formula NH ２ - (CH ２ ) ｎ A method for producing ω-aminoalkanoic acid of -COOH (wherein n is an integer from 9 to 11), comprising the following steps: i) Reaction of ω-bromoalkanoic acid with excess aqueous ammonia solution, and ii) Separation of ω-aminoalkanoic acid formed from the reaction mixture In a method including, A method characterized in that the aqueous ammonia solution has a concentration of 35% to 70% by weight, and step i) is carried out under an absolute pressure of 0.11 to 2.0 MPa, which is higher than atmospheric pressure.

2. The manufacturing method according to claim 1, wherein step i) is performed at a temperature between 0 and 60°C.

3. The manufacturing method according to claim 2, wherein step i) is performed at a constant temperature.

4. The manufacturing method according to claim 2, wherein step i) is performed at an elevated temperature.

5. The manufacturing method according to claim 4, wherein step i) is performed at an increasing temperature, the initial temperature is in the range of 0 to 25°C, and the final temperature is in the range of 26 to 60°C.

6. The manufacturing method according to any one of claims 1 to 5, wherein the aqueous ammonia solution has a concentration of 36% to 60% by weight, preferably 38% to 45% by weight.

7. The manufacturing method according to any one of claims 1 to 6, wherein the weight ratio of ω-bromoalkanoic acid to aqueous ammonia at the start of step i) is 1:3 to 1:

20.

8. The manufacturing method according to any one of claims 1 to 7, wherein the process is carried out under an absolute pressure of 0.125 to 0.5 MPa.

9. The manufacturing method according to claim 8, wherein the process is carried out under an absolute pressure of 0.13 to 0.3 MPa.

10. A manufacturing method according to any one of claims 1 to 9, which is carried out continuously.

11. A manufacturing method according to any one of claims 1 to 9, carried out in a batch manner.

12. The method according to any one of claims 1 to 11, further comprising step iii) washing and draining the ω-aminoalkanoic acid obtained as a result of step ii).

13. The method according to claim 12, further comprising step iv) purifying the crude ω-aminoalkanoic acid obtained as a result of step ii) or iii) preferably by recrystallization from boiling water.

14. The method according to claim 12 or 13, further comprising step v) of recovering residual ω-aminoalkanoic acid in various filtrates and aqueous washing solutions obtained in steps ii), iii), and / or iv) particularly by degassing of ammonia, liquid-liquid extraction, crystallization, filtration, and washing.

15. The method according to any one of claims 1 to 14, further comprising step vi) drying the obtained ω-aminoalkanoic acid.