阅读说明：本技术 制备甲硫氨酸的方法 (Process for the preparation of methionine ) 是由 D·菲舍尔 P·施滕纳 S·伯恩哈特 H·雅各布 于 2018-05-09 设计创作，主要内容包括：本发明涉及一种制备甲硫氨酸的方法,包括在碱性处理液中水解5-(2-甲基巯基乙基)乙内酰脲(甲硫氨酸乙内酰脲),其中通过处理液的电渗析除去包含甲酸根和含有1至5个碳原子有机酸的其它阴离子的副产物。(The invention relates to a method for producing methionine by hydrolyzing 5- (2-methylmercaptoethyl) hydantoin (methionine hydantoin) in an alkaline treatment solution, wherein by-products comprising formate and other anions of organic acids having 1 to 5 carbon atoms are removed by electrodialysis of the treatment solution.)

1. A process for the preparation of methionine, comprising alkaline hydrolysis of 5- (2-methylmercaptoethyl) hydantoin (methionine hydantoin) in an aqueous treatment liquor containing alkali metal hydroxide and/or alkali metal carbonate and/or alkali metal bicarbonate to give an alkali metal salt of methionine, and precipitation of methionine by neutralization with carbon dioxide, separation of methionine from the treatment liquor, concentration of the treatment liquor, and use of the treatment liquor for alkaline hydrolysis of the methionine hydantoin which is supplied again to the treatment liquor, characterized in that by-products comprising formate and other anions of organic acids containing 1 to 5 carbon atoms are removed from the treatment liquor by electrodialysis, wherein methionine and/or its alkali metal salts substantially remain in the treatment liquor, and wherein the electrodialysis cell comprises in each case at least two chambers, and one of these chambers is an anode compartment adjoining the ion selective anion exchange membrane and the anode, and the pH in the anode compartment is between 5.8 and 8.0.

2. The method of claim 1, wherein the anion of an organic acid containing 1 to 5 carbon atoms comprises acetate and 2-hydroxy-4-Methylmercaptobutyrate (MHA).

3. The process as claimed in either of claims 1 and 2, wherein the current density in each case in the electrodialysis cell is in the range comprising 1.0A/m²In to contain 200A/m²Within the range of.

4. A method according to any one of claims 1-3, wherein the electrodialysis cell comprises in each case three compartments, wherein one compartment is a cathode compartment adjoining the cation exchange membrane and the cathode.

5. A method according to any one of claims 1-3, wherein an electrodialysis cell comprises two chambers in each case, and one of the two chambers is the anode compartment and the other chamber is the cathode compartment adjoining the ion-selective anion exchange membrane and a cathode.

6. A process as claimed in any of claims 1 to 5, wherein the electrodialysis is carried out in at least two electrodialysis cells, which are in each case separated from one another by bipolar electrodes.

7. The method according to any one of claims 1-6, wherein the pH in the anode compartment is adjusted by partially supplying an aqueous alkali hydroxide solution formed in the cathode compartment.

8. The method according to any one of claims 1-6, wherein the aqueous alkali hydroxide solution formed in the cathode compartment is re-supplied to the treatment liquid.

9. The method of any one of claims 1-8, wherein the alkali metal is potassium.

10. The method of any one of claims 1-8, wherein the alkali metals are potassium and sodium.

Technical Field

The invention relates to a method for producing methionine by hydrolyzing 5- (2-methylmercaptoethyl) hydantoin (methionine hydantoin) in an alkaline treatment solution, wherein by-products containing formate and other anions of organic acids having 1 to 5 carbon atoms are removed from the treatment solution by electrodialysis.

Background

The amino acid methionine is currently produced industrially in large quantities worldwide and is of considerable commercial importance. Methionine is used in many fields, such as pharmaceuticals, health and wellness products, but in particular as a feed additive in many feeds for various livestock. On an industrial scale, methionine is produced chemically via the Bucherer-Bergs reaction, a variant of the Strecker synthesis. Here, the starting materials 3-methylmercaptopropionaldehyde (prepared from 2-acrolein and methyl mercaptan), hydrocyanic acid (hydrogen cyanide), ammonia and carbon dioxide are reacted to give 5- (2-methylmercaptoethyl) hydantoin (methionine hydantoin), and subsequently hydrolyzed by base to alkali metal methionate (e.g. potassium methionate) using alkali metal hydroxide and/or alkali metal carbonate and alkali metal bicarbonate (e.g. potassium hydroxide and/or potassium carbonate and potassium bicarbonate). Methionine is finally liberated from its alkali metal salts, preferably its potassium salt, by carbon dioxide treatment, which can be filtered off as a precipitate from a mother liquor containing alkali metal carbonates and alkali metal bicarbonates, such as potassium carbonate and potassium bicarbonate (US5,770,769). Ammonia, alkali metal carbonate and alkali metal bicarbonate reagents (e.g., potassium carbonate and bicarbonate), and carbon dioxide are typically recycled in industrial methionine production. The alkali metal salt (e.g., potassium salt) present sooner or later in the treatment fluid is deactivated in the form of a neutral alkali metal formate (e.g., potassium formate). Alkali metal formates (e.g. potassium formate) are formed from residues of hydrocyanic acid and alkali metal salts from the hydrolysis of hydantoin present in methionine hydantoin solutions (WO2013030068a 2). Further by-products are, in particular, dipeptide methionylmethylmethionine ("met-met", EP1564208A1), acetate and 2-hydroxy-4-methylmercaptobutyric acid, hydroxy analogues of Methionine (MHA). Therefore, it is necessary to continuously exchange a part of the aqueous treatment liquor of the hydantoin hydrolysis circuit with fresh aqueous alkali metal hydroxide solution (e.g. potassium hydroxide solution). In general, an excessive enrichment of by-products in the hydantoin hydrolysis circuit has to be avoided, since otherwise an interruption of the methionine crystal formation occurs.

A typical process liquid in a hydantoin hydrolysis loop contains the following components: about 10-16% by weight of an alkali metal salt form, 5-8% by weight of methionine, 3-5% by weight of methionyl methionine, 0.7-1.1% by weight of formate and 0.2-0.3% by weight of acetate. Typical cleaning solutions include the following components: about 2-6% by weight methionine, 4-8% by weight methionylmethionine, 6-14% by weight alkali metal salt form of alkali metal, 1-1.7% by weight formate salt and 0.3 to 0.5% by weight acetate salt.

Since the exchanged treatment liquid (purge), apart from about 3% by weight of deactivated alkali metal salt (e.g. potassium salt), still contains about 7-8% by weight of active alkali metal salt and methionine as a further important material, this procedure is undesirable from an economic or ecological point of view.

Electrodialysis is a known method for treating waste water or for desalting water. Electrodialysis is understood to mean processes in which the ionic constituents of an aqueous solution are removed by means of ion-exchange membranes and a potential difference. Another field of use of electrodialysis is, for example, the separation of amino acids having different isoelectric points in electrodialysis cells, the compartments of which are separated from one another by anion and cation exchange membranes at different pH values under the influence of an electric field (h.strathmann and h.chemil, chem.ingg.tech, 56(1984) No.3, 214-.

Perry and Kedem (U.S. Pat. No.3, 4,238,307 and DE 2907450A 1) propose electrodialysis methods by which L-amino acids can be separated from their derived D-enantiomers in aqueous solution by their different isoelectric points, for example L-methionine from N-acetyl-D-methionine. Koberstein and Lehmann (DE 3603986A 1) disclose an electrodialysis method for treating a solution of a racemate resolution of N-acetyl-D, L-aminocarboxylic acids in the presence of an L-amino acid cyclase which remains after removal of the enzyme.

Bachot and Grosbois (US 4,454,012) disclose a process for obtaining free crystalline methionine from alkali metal salts in their treatment liquors comprising aqueous alkali metal salts using an electrodialysis unit and with recovery of alkali metal hydroxide. No method is disclosed for removing formate, acetate and other undesirable anions from the treatment solution.

CN105671587A discloses a process for the preparation of methionine by saponification of methionine hydantoin, wherein the resulting alkali metal salts of methionine and alkali metal carbonates are converted to methionine, alkali metal hydroxides and carbon dioxide by electrodialysis and separated. In the process, methionine hydantoin is hydrolyzed to an alkali metal salt of methionine in a treatment liquid containing an alkali metal carbonate, and methionine and carbon dioxide are released in a weakly acidic medium by repeated treatment in an electrodialysis system containing bipolar membranes and separated from the treatment liquid. Methionine is obtained by concentration and crystallization. Alkali metal carbonate and carbon dioxide are recovered. Also, there is no disclosure of a method for removing formate, acetate and other undesirable anions from the treatment solution.

CN106349131A also discloses a process for the preparation of methionine, wherein methionine hydantoin is hydrolyzed with sodium hydroxide to the sodium salt of methionine, and sulfuric acid is used to liberate methionine. In this case, the concentration of sodium sulfate in the repeatedly used treatment liquid is significantly reduced by using the electrodialysis unit.

CN106432020A discloses a method for preparing methionine, wherein

a) Saponifying methionine hydantoin with an alkaline potassium compound to produce a treatment fluid comprising methionine potassium salt and potassium bicarbonate,

b) neutralizing the treated liquid obtained in step a) with carbon dioxide and separating the crystallized methionine from the treated liquid to obtain a treated liquid comprising potassium bicarbonate and a small amount of methionine,

c) filtering the treatment liquid comprising potassium bicarbonate and a small amount of methionine obtained in step b) and performing electrodialysis with homogeneous membranes until the concentration of potassium bicarbonate in the desalted liquid (diluate) of the electrodialysis performed with homogeneous membranes is lower than 3-7% by weight, and

d) subjecting the electrodialysis treatment solution obtained in step c) to further electrodialysis with heterogeneous membranes until the concentration of potassium bicarbonate in the desalted solution subjected to electrodialysis with heterogeneous membranes is below 0.1 wt.%.

The methionine-containing treatment liquid obtained in step d) is then evaporated to obtain methionine. Potassium bicarbonate obtained from the desalted liquor (see steps c) and d)) (concentrated by evaporation of the desalted liquor at 120 ℃) and recycled to saponification step a). CN106432020A discloses the removal of potassium bicarbonate by electrodialysis from a methionine-containing treatment liquor of a hydantoin hydrolysis circuit and its reuse in the hydrolysis of methionine hydantoin. However, CN106432020A does not disclose a method for removing formate, acetate and other undesired anions from the treatment liquid of the hydantoin hydrolysis circuit, whereby methionine, its potassium salt and potassium bicarbonate remain in the treatment liquid.

Disclosure of Invention

The object of the present invention is to provide a process for the preparation of methionine comprising the steps of hydrolysing 5- (2-methylmercaptoethyl) hydantoin (methionine hydantoin) in an alkaline treatment liquid, releasing methionine from the formed alkali metal methionine salt, and recycling the alkaline treatment liquid to the hydrolysis step after removal of methionine, wherein, by suitable measures, the concentration of by-products, including formate and other anions of organic acids, is reduced, so that the amount of treatment liquid to be exchanged (purified) is reduced.

This object is achieved by a process for preparing methionine, which comprises alkaline hydrolysis of 5- (2-methylmercaptoethyl) hydantoin (methionine hydantoin) in an aqueous treatment liquor containing alkali metal hydroxide and/or alkali metal carbonate and/or alkali metal bicarbonate to give an alkali metal salt of methionine, and precipitation of methionine by neutralization with carbon dioxide, separation of methionine from the treatment liquor, concentration of the treatment liquor, and use of the treatment liquor for alkaline hydrolysis of methionine hydantoin which is supplied again to the treatment liquor, characterized in that by-products comprising formate and other anions of organic acids having from 1 to 5 carbon atoms are removed from the treatment liquor by electrodialysis, wherein methionine and/or its alkali metal salts substantially remain in the treatment liquor, and wherein the electrodialysis cell comprises in each case at least two chambers, and one of these chambers is an anode compartment, which adjoins the ion-selective anion exchange membrane and the anode, and the pH in the anode compartment is between 5.8 and 8.0.

In this process, the anion of the organic acid containing 1 to 5 carbon atoms comprises acetate and 2-hydroxy-4-Methylmercaptobutyrate (MHA).

The current density in each case in the electrodialysis cell is preferably in the range of 1.0A/m²In to contain 200A/m²Within the range of.

In the method according to the invention, the electrodialysis cell comprises in each case three compartments, one of which is a cathode compartment adjoining the cation exchange membrane and the cathode. Optionally, in each case the electrodialysis cell may comprise two chambers, and one of the two chambers is an anode compartment and the other chamber is a cathode compartment adjoining the ion-selective anion exchange membrane and the anode.

In the process according to the invention, the electrodialysis is preferably carried out in at least two electrodialysis cells, which are in each case separated from one another by bipolar electrodes.

In a particular configuration of the method according to the invention, the pH in the anode compartment is adjusted by partially supplying the aqueous alkali metal hydroxide solution formed in the cathode compartment. Incidentally, the aqueous alkali metal hydroxide solution formed in the cathode compartment is supplied again to the treatment liquid.

The alkali metal in the alkali metal salt of the treatment liquor is preferably potassium or optionally potassium and sodium.

Detailed Description