Method for producing methionine

Abstract

The present invention relates to a process for the alkaline hydrolysis of 5-(2-methylthioethyl)hydantoin of formula (1) [Chemical Formula 1] or its selenoized equivalent 5-(2-methylselenoethyl)hydantoin, respectively, to methionine or selenomethionine salts, said process being carried out in a packed reactive stripping column in an alkaline aqueous medium, and to a process for the production of methionine and selenomethionine using the same.

Description

Technical Field

[0001] This invention relates to an improvement on a method for producing methionine in salt form or free form, or a selenized analogue (seleniated methionine) of methionine in salt form or free form, from the methionine precursor 5-(2-methylthioethyl)hydantoin and the selenomethionine precursor 5-(2-methylselenoethyl)hydantoin. Background Technology

[0002] The size of the methionine market needs no introduction, especially in animal nutrition, where production methods aimed at achieving greater cost-effectiveness while reducing pollution and energy consumption remain a key area of ​​development. Selenized derivatives of methionine are also a major focus in animal nutrition.

[0003] The preparation of methionine can be carried out by various methods involving a variety of synthetic intermediates, particularly 5-(2-methylthioethyl)hydantoin. This compound corresponds to the following formula (1):

[0004] [Chemical Formula 1]

[0005]

[0006] Furthermore, its synthesis is widely documented (see, for example, US5990349A).

[0007] 5-(2-methylthioethyl)hydantoin can be hydrolyzed in an alkaline medium to obtain methionine salt, which can then be neutralized to methionine if desired.

[0008] Therefore, according to WO2013 / 030068A2, a method for the continuous production of methionine salts is known, which involves the alkaline hydrolysis of 5-(2-methylthioethyl)hydantoin to methionine salts in a reactive distillation plate column, preferably a porous plate column. The porous plate column must meet the following characteristics: number of plates, overflow height, plate spacing, column diameter to overflow length ratio, and column cross-section to gas flow surface ratio. These characteristics have been determined very precisely, and have the advantage of minimizing the formation of byproducts such as methionine dipeptides.

[0009] An aqueous solution of hydantoin is introduced at the horizontal level of the upper tray of the column, while an alkaline solution based on an alkali metal carbonate is fed at the horizontal level of the tray below the lower tray. The heat required for the reaction is provided by a steam stream supplied to the bottom of the column.

[0010] The alkaline hydrolysis of methionine hydantoin results in the formation of ammonia and carbon dioxide. This is a very rapid process, and one of the problems encountered in reactive distillation is the untimely generation of these gases, which must be controlled by any means. On the one hand, it is necessary to control the rate of the hydrolysis reaction; on the other hand, it is necessary to vent the generated gases, especially carbon dioxide, as they are released. In fact, carbon dioxide in the reaction medium will produce carbonic acid, leading to a decrease in the pH of the medium and a reduction in the selectivity of methionine. Summary of the Invention

[0011] This invention provides a method for alkaline hydrolysis of methionine hydantoin, which uses reactive stripping technology to overcome these obstacles. For this purpose, the reaction is carried out completely or partially in a reactive stripping packed tower.

[0012] This invention relates to 5-(2-methylthioethyl)hydantoin of formula (1).

[0013] [Chemical Formula 1]

[0014]

[0015] Alternatively, its selenized equivalent (5-(2-methylselenoethyl)hydantoin) can be obtained by alkaline hydrolysis to methionine salt or selenomethionine salt, respectively.

[0016] The method is carried out in a packed tower of reactive gas in an alkaline aqueous medium.

[0017] According to a variant of the invention, the aforementioned alkaline hydrolysis method is carried out in an alkaline aqueous medium, first in a reaction stripping packed tower, and then in at least one reactor that is the same as or different from the reaction stripping packed tower.

[0018] Before elaborating on the invention in more detail, the following provides definitions of some terms used herein.

[0019] The 5-(2-methylthioethyl)hydantoin or methionine hydantoin corresponding to formula (1) above can be in the form of a salt. It can be pure or in a mixed state. The mixture may include: one or more precursors for the production of methionine, which is typically the case when the present invention falls within the scope of a method for the industrial-scale production of methionine; methionine or methionine salt, particularly when the hydrolysis of methionine hydantoin has begun; secondary products; and impurities. Of course, this definition also applies to 5-(2-methylselenoethyl)hydantoin and the entire description herein.

[0020] Reactive stripping, reactive distillation, or reactive rectification, within the scope of this invention, should be understood as a reaction process within the same column (i.e., reactive stripping column, reactive distillation column, or reactive rectification column), namely, hydrolyzing hydantoin to methionine salt (or selenomethionine salt) in a liquid phase and separating at least a portion of the generated gas from that phase, which is a well-documented technique known to those skilled in the art.

[0021] The expressions “first in a reactive stripping packed column” and “then in at least one reactor” mentioned in variations of the method of the present invention refer to the sequential concept in the method, wherein, according to the invention, hydantoin is first treated in a reactive stripping packed column, and then the resulting stream is processed in one or more consecutive reactors. However, they do not impose any restrictions on the arrangement of the packed column and one or more reactors. Thus, the packed column and reactor can be connected in series, optionally separated by, for example, a shell. According to this variation of the invention, a reactive stripping column, or a reactive distillation column, or a reactive rectification column, should be understood to include columns comprising different fillings (e.g., packing, trays, and any other fillings), each capable of constituting a reactor. Thus, when one or more reactors are stripping columns arranged in a continuation of a packed column, the stripping column will become a reactive stripping column, which is equipped with packing at its upper part and at least one other filling at its lower part.

[0022] As previously stated, the alkaline hydrolysis of hydantoin is a reaction well known to those skilled in the art, and "basic or alkaline medium" should be understood as a medium with a pH that enables the hydrolysis of hydantoin to methionine salt; the pH is preferably at least 8, preferably at least 9; the pH can reach 13; even though it may change as the reaction progresses, the pH is ideally maintained at a value of at least 8. Attached Figure Description

[0023] The invention is described in more detail below, along with preferred variations for carrying out the invention and in the following sections. Figure 1 , 2 The specific implementations shown in 3 and 5, Figure 4 Methods known in the prior art are shown and provided for comparison:

[0024] [ Figure 1 [This indicates that the method of the present invention is carried out in a reaction stripping packed tower and then in a reactor consisting of a reaction stripping plate tower.]

[0025] [ Figure 2 The term "[]" indicates that the method of the invention is carried out in a single and identical tower, which first comprises a first part, a reaction stripping packed tower, and then comprises a second part, a reaction stripping plate tower.

[0026] [ Figure 3 This indicates that the method of the present invention is first carried out in a reaction stripping packed tower and then in a CSTR reactor.

[0027] [ Figure 4 [] indicates a hydrolysis method performed in a reactive stripping plate column according to an embodiment that does not form part of this invention, for comparison purposes.

[0028] [ Figure 5 [This indicates that the method of the present invention is carried out in a reaction stripping plate tower and then in a reaction stripping packed tower.] Detailed Implementation

[0029] According to the method of the present invention, the alkaline hydrolysis of hydantoin is carried out in a reaction stripping packed tower.

[0030] Any type of reactive stripping packed tower can be used. Therefore, the packing can be ordered (also known as structured) packing or random packing.

[0031] The packing material consists of one or more elements made of materials capable of withstanding reaction conditions. Advantageously, they are selected from metals and stainless steel, as well as corrosion-resistant metal alloys, such as zirconium, tantalum, titanium, and stainless steel. Alloys; plastics, such as fluoropolymers like polytetrafluoroethylene (PTFE) and perfluoroalkoxy (PFA); ceramics.

[0032] The tower packing can consist of at least two different types of packing materials in continuous arrangement. Their arrangement can be different (orderly and / or random) and / or their elemental properties can be different.

[0033] Reactive stripping packed columns typically have an inlet for a steam-type hot gas at the bottom of the column, which moves upwards. Alternatively, a heating device can be provided at the bottom, along with an inlet for at least one inert gas, such as nitrogen, which reaches the desired temperature through the heating device and rises within the column. Those skilled in the art can adjust the circulation conditions of the hot gas flow to optimize alkaline hydrolysis.

[0034] Regardless of whether the packing is ordered or dispersed, the column can be equipped with any means to optimize the distribution of the feed flow across all packing elements, thereby optimizing the residence time of the alkaline aqueous medium in the column containing hydantoin, while allowing for rapid venting of any gases formed. These means can consist of distributors and collectors, which are commonly used in distillation techniques. It can also be provided with any other known means to facilitate the reaction.

[0035] When the alkaline hydrolysis of hydantoin is not completely or almost completely finished in the so-called reactive stripping packed tower, that is, when it only partially occurs in the tower, the alkaline hydrolysis can continue in one or more reactors.

[0036] The one or more reactors may be selected from reaction stripping towers, such as any type of reaction stripping packed tower, reaction stripping plate tower or reaction stripping bubble tower.

[0037] The one or more reactors may also be selected from continuous stirred tank reactors (CSTRs) and plug flow reactors (PFRs). They are preferably selected from reactors suitable for continuous processes, such as plug flow reactors.

[0038] When multiple reactors are used, they can be the same or different. Different reactors should be understood to mean, for example, reactors selected from reaction stripping towers, whose packing materials differ in properties (packed tower, plate tower, bubble tower, etc.), materials, etc. Furthermore, it should be understood that at least one reactor is selected from a reaction stripping tower, another from a CSTR or PFR reactor, or multiple reactors are selected from CSTR or PFR reactors.

[0039] According to the present invention, the method can be accomplished by any finishing step of the reaction in one or more additional towers.

[0040] The alkaline aqueous medium contains an alkaline hydrolysis reagent, preferably an alkali metal salt. It is advantageously selected from alkali metal carbonates, alkali metal hydroxides, and any mixtures of said carbonates and hydroxides, and even more preferably from potassium carbonate, potassium bicarbonate, sodium hydroxide, potassium hydroxide, and mixtures thereof.

[0041] The method of the present invention is applied to 5-(2-methylthioethyl)hydantoin, which is provided in the form of a stream containing only hydantoin, but may also contain one or more compounds selected from the following precursors: 5-(2-methylthioethyl)hydantoin, methionine, salts and peptides of methionine, especially methionine dipeptides and derivatives such as hydantoin salts of methionine, 2-amino-4-methylthio-butyramide, 4-methylthio-2-ureo-butyramide, formate, 2-hydroxy-4-methylthio-butyrate, and impurities.

[0042] According to one variant, the method is carried out at a temperature of 160 to 200 °C, preferably 170 to 190 °C. When the method is carried out first in a reactive stripping packed column and then in one or more reactors, the temperatures in the column and the reactors may be the same or different. Below 160 °C, the reaction does not occur or is incomplete. Above 200 °C, the selectivity for methionine salts decreases, particularly resulting in the formation of unacceptable amounts of methionine dipeptides.

[0043] According to one variant, the method is carried out at a pressure of 7 to 15 bar, preferably 8 to 12 bar. When the method is first carried out in a reactive stripping packed tower and then in one or more reactors, the pressures in the tower and the one or more reactors may be the same or different.

[0044] A key advantage of this invention is that it overcomes the drawbacks associated with the hydrolysis reaction rate and optimizes the yield and selectivity of methionine salt (or selenomethionine salt). To this end, the residence time of the liquid reactant stream in the reactive stripping packed column is preferably at least 1 minute, and more preferably about 1 to 3 minutes. When the method is carried out in two stages, namely in the reactive stripping packed column and in one or more reactors, the residence time of the liquid reactant stream throughout the entire assembly of the reactive stripping packed column and one or more reactors can be 6 to 10 minutes.

[0045] The method of the present invention may or may not be applicable to continuous mode. Advantageously, it is implemented continuously.

[0046] Figures 1 to 3 Examples of variations of the invention are illustrated in 5.

[0047] according to Figure 1 An aqueous solution of hydantoin and an aqueous solution of potassium carbonate are fed together to the top of a reactive stripping packed column. A steam stream is supplied through an inlet at the bottom of the column and circulates countercurrently relative to the hydantoin solution. Carbon dioxide and ammonia are discharged from the top of the column. The reactant stream generated by the packed column is extracted at the bottom of the column to feed from the top into a reactive stripping plate column, where the steam stream circulates countercurrently. Aqueous methionine salts are recovered at the bottom of this column.

[0048] according to Figure 2 The method is carried out in a reaction stripping column, which is packed at the top and has trays at the bottom. An aqueous solution of hydantoin and an aqueous solution of potassium carbonate are fed to the top of the reaction stripping column, and a steam stream is supplied from the bottom inlet of the column and circulates countercurrently relative to the hydantoin solution along the entire length of the column. Carbon dioxide and ammonia are discharged from the top of the column, and the aqueous methionine stream is recovered from the bottom of the column.

[0049] according to Figure 3 An aqueous solution of hydantoin and an aqueous solution of potassium carbonate are fed to the top of a reaction stripping packed tower. A steam stream is supplied from an inlet at the bottom of the tower and circulates countercurrently relative to the hydantoin solution. Carbon dioxide and ammonia are discharged from the top of the tower. The reaction stream obtained through the packed tower is extracted at the bottom of the tower to feed a CSTR-type reactor, which also includes a steam inlet. Aqueous methionine stream is recovered from this reactor.

[0050] The present invention also relates to methods for producing methionine or selenomethionine from 5-(2-methylthioethyl)hydantoin or its selenized equivalent 5-(2-methylselenoethyl)hydantoin, including the hydrolysis method as described above.

[0051] To obtain methionine or selenomethionine in its free form, the production method involves neutralizing methionine salt to methionine and neutralizing selenomethionine salt to selenomethionine. This neutralization is well-known and is advantageously carried out in the presence of CO2.

[0052] Alkaline hydrolysis methods, whether standalone or integrated into methionine or selenomethionine production methods, can be supplemented by any recycling and / or gas or heat recovery system for reuse within the method or for another improvement.

[0053] The experimental section described below compares the alkaline hydrolysis of hydantoin of formula (1) in an alkaline medium under the same conditions in a prior art reaction stripping tray column according to Example 1 and a reaction stripping column according to the invention according to Example 2. The reaction stripping column according to the invention according to Example 2 is equipped with structured packing in the upper part of the column and multiple trays in the lower part.

[0054] Example 1: Reaction Stripping Plate Column

[0055] This embodiment was carried out on a reaction stripping test tower with a total height of 6m and a diameter of DN50.

[0056] according to Figure 4 The tower shown in the diagram is equipped with a tray.

[0057] An aqueous solution of 12 kg / h is continuously fed at 180°C at the top of the column, which corresponds to a residence time of 10 minutes in the liquid phase.

[0058] The feed aqueous solution consists of the following:

[0059] 19.3% (w / w) of 5-(2-methylthioethyl)hydantoin + precursor

[0060] 15.2% (w / w) potassium carbonate

[0061] Stripping was performed by injecting 2 kg / h of steam at 190°C.

[0062] The tower operates at a pressure of 10.5 bar, with a temperature distribution ranging from 180°C at the top to 190°C at the bottom.

[0063] Under steady-state conditions, the composition of the liquid reaction mixture obtained at the bottom of the column is as follows:

[0064] 0.2% (w / w) of 5-(2-methylthioethyl)hydantoin + precursor

[0065] 20.4% (w / w) methionine salt (methionine potassium)

[0066] 0.64% (w / w) methionine dipeptide

[0067] These results correspond to a conversion of 99% for 5-(2-methylthioethyl)-hydantoin [+ precursor], a selectivity of 96% for methionine salt, and a selectivity of 4% for methionine dipeptide.

[0068] Example 2 - Reaction stripping plate tower, then packed tower

[0069] This embodiment was carried out on a reaction stripping test tower with a total height of 6m and a diameter of DN50.

[0070] according to Figure 5 The diagram shows a tower equipped with structured packing at the top and trays at the bottom:

[0071] An aqueous solution of 12 kg / h is continuously fed at the top of the column at 180°C. This flow rate corresponds to a total residence time of 10 minutes for the liquid phase, including 2 minutes in the packing section and 8 minutes in the tray section.

[0072] The feed aqueous solution consists of the following:

[0073] 19.3% (w / w) of 5-(2-methylthioethyl)hydantoin + precursor

[0074] 15.2% (w / w) potassium carbonate

[0075] Stripping is performed by injecting 2 kg / h of steam at 190°C.

[0076] The tower operates at a pressure of 10.5 bar, with a temperature distribution ranging from 180°C at the top to 190°C at the bottom.

[0077] Under steady-state conditions, the composition of the liquid reaction mixture obtained at the bottom of the column is as follows:

[0078] 0.1% (w / w) of 5-(2-methylthioethyl)hydantoin + precursor

[0079] 20.6% (w / w) methionine salt (methionine potassium)

[0080] 0.56% (w / w) methionine dipeptide

[0081] These results correspond to a conversion of 99.5% for 5-(2-methylthioethyl)-hydantoin [+ precursor], a selectivity of 96.5% for methionine salt, and a selectivity of 3.5% for methionine dipeptide.

[0082] Compared to Example 1, in Example 2 according to the present invention, an increased conversion rate of hydantoin, an increased selectivity for methionine salt, and a decreased selectivity for methionine dipeptide were observed. These changes are quite interesting on an industrial scale.

Claims

1. A 5-(2-methylthioethyl)hydantoin of formula (1) [Chemical Formula 1] Alternatively, a method for alkaline hydrolysis of its selenized equivalent, 5-(2-methylselenoethyl)hydantoin, to methionine salt or selenomethionine salt, respectively. Its features The method is carried out in an alkaline aqueous medium, first in a reaction stripping packed tower, and then in at least one reactor selected from reaction stripping plate towers.

2. The method according to claim 1, characterized in that... The reaction stripping packed tower includes one or more packing materials selected from structured packing and random packing.

3. The method according to claim 1, characterized in that... The packing material of the reaction stripping packed tower is made of one or more materials selected from the following: metals and stainless steel and corrosion-resistant metal alloys; plastics; ceramics.

4. The method according to claim 1, characterized in that... The method is further carried out in one or more reactors.

5. The method according to claim 4, characterized in that... The one or more reactors are selected from reaction stripping towers.

6. The method according to claim 5, characterized in that... The one or more reactors are selected from reaction stripping packed towers, reaction stripping plate towers, and reaction stripping bubble towers.

7. The method according to claim 4, characterized in that... The one or more reactors are selected from continuous stirred tank reactors (CSTRs) and plug flow reactors (PFRs).

8. The method according to claim 1, characterized in that... The alkaline aqueous medium includes alkaline hydrolysis reagents selected from the following: alkali metal carbonates and alkali metal hydroxides.

9. The method according to claim 8, characterized in that... The alkaline hydrolysis reagent is selected from potassium carbonate, potassium bicarbonate, sodium hydroxide, and potassium hydroxide.

10. The method according to claim 1, characterized in that... 5-(2-methylthioethyl)hydantoin is provided in the form of a stream, the stream further comprising one or more compounds selected from the precursors of: 5-(2-methylthioethyl)hydantoin, methionine, salts and peptides or dipeptides of methionine and their derivatives, or hydantoin salts of methionine, 2-amino-4-(methylthio)-butyramide, 4-(methylthio)-2-ureo-butyramide, formate, 2-hydroxy-4-(methylthio)-butyrate, and impurities.

11. The method according to claim 1, characterized in that... The method is carried out at a temperature of 160 to 200°C.

12. The method according to claim 1, characterized in that... The method is carried out under a pressure of 7 to 15 bar.

13. The method according to claim 1, characterized in that... The residence time of the liquid reactant stream in the reaction stripping packed tower is at least 1 minute.

14. The method according to claim 1, characterized in that... The residence time of the liquid reactant stream in the entire assembly of the reaction stripping packed tower and one or more reactors is 6 to 10 minutes.

15. A method for producing methionine from 5-(2-methylthioethyl)hydantoin of formula (1) [Chemical Formula 1] Or a method for producing selenomethionine from 5-(2-methylselenoethyl)hydantoin, characterized in that The method includes the method of hydrolyzing 5-(2-methylthioethyl)hydantoin or 5-(2-methylselenoethyl)hydantoin as defined in claim 1.

16. The method according to claim 15, characterized in that... The method includes neutralizing methionine salt to methionine or neutralizing selenomethionine salt to selenomethionine.

17. The method according to claim 16, characterized in that... The neutralization of the methionine salt or selenomethionine salt is carried out in the presence of CO2.

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