JPH0317822B2 - - Google Patents

Description

[Detailed description of the invention] <Industrial application field> The present invention relates to a method for producing amino acids.

Specifically, the present invention relates to a method for crystallizing amino acids from an aqueous solution of amino acid salts.

<Prior art> Generally, synthetic amino acids are obtained by hydrolyzing a hydantoin derivative in the presence of caustic alkali to open the hydantoin nucleus, and neutralizing the corresponding amino acid salt with an acid. It will be done. This hydrolysis reaction of hydantoin derivatives with caustic alkali is usually carried out under conditions with an excess of caustic alkali, so the carbon dioxide gas generated by the ring opening of the hydantoin nucleus reacts with the excess caustic alkali and reacts in the form of carbonate ions. It will be present in the liquid. Therefore, a solution of an amino acid salt obtained by hydrolyzing a hydantoin derivative with a caustic alkali inevitably contains carbonate ions.

In order to extract amino acids from such an aqueous solution of amino acid salts containing carbonate ions, it is necessary to neutralize the solution with an acid.

This neutralization operation has conventionally been carried out at reduced pressure or normal pressure.

However, during this neutralization reaction, some or all of the carbonate ions are generated as carbon dioxide gas, which attaches to the formed amino acid crystals and causes them to float, making uniform mixing very difficult and neutralization difficult. Not only does it become incomplete and the amino acid yield tends to decrease, but it also becomes foamy and accumulates in bulk on the liquid, and eventually boils over from the crystallization tank, making the neutralization operation itself almost impossible. To carry out the process industrially, it requires a container with a very large spatial volume compared to the volume of the internal solution, and requires inefficient methods such as allowing the neutralization reaction to take place over a long period of time. I had no choice.

In addition, the concentration of amino acids precipitated varies depending on the type of amino acid, the amount of coexisting inorganic salt, and the temperature.
A so-called two-step method has been adopted in which a neutralization operation with an acid is performed under conditions of concentration and temperature such that the amino acid does not precipitate as crystals, and then crystallization is performed by concentration and/or cooling. However, this method is not economical due to high costs required for concentration and/or cooling.

In addition, in order to suppress foaming, when performing neutralization crystallization while cooling using a cooling surface,
The drawback was that crystals adhered to the cooling surface, significantly deteriorating the cooling efficiency.

In order to recover the generated carbon dioxide gas and reuse it as a raw material for the synthesis of hydantoin derivatives, pressure is usually required for the carbon dioxide gas, and if the neutralization of the amino acid salt is carried out under reduced pressure or atmospheric pressure, the recovered carbon dioxide gas I needed to compress it.

On the other hand, as a method for simultaneous neutralization and crystallization of amino acid salts, a method has been proposed in which the foaming phenomenon is suppressed by adding a third component such as an alcohol or a surfactant (Japanese Patent Laid-Open No. 49-20119). reference). However, this method requires a large amount of alcohol,
Therefore, if these alcohols are not recovered, there are disadvantages such as large economic losses, many of the additives are expensive, and they are mixed into the product.

<Problems to be Solved by the Invention> When an aqueous solution of an amino acid salt containing carbonate ions is neutralized with an acid and the amino acids are crystallized, foaming due to carbon dioxide gas must not be caused.

Further, as a means for achieving this, it is necessary not to increase the capacity of the equipment more than necessary, to simplify the process without requiring two steps, and in particular, to not require any additives.
Furthermore, it may also make it easier to reuse the carbon dioxide gas generated.

<Means for Solving the Problems> The present invention is a method for producing an amino acid, which comprises neutralizing an aqueous solution of an amino acid salt containing carbonate ions with an acid under pressure and simultaneously crystallizing the amino acid.

The aqueous solution of the amino acid salt containing carbonate ions of the present invention can be obtained by hydrolyzing a hydantoin derivative corresponding to the amino acid in the presence of caustic alkali to open the hydantoin ring.

Types of amino acids include alanine, isoleucine, glycine, tyrosine, tryptophan, valine, phenylalanine, methionine, and leucine.

As the acid used for neutralization, in addition to mineral acids such as sulfuric acid, hydrochloric acid, and phosphoric acid, organic acids such as acetic acid can also be used, but sulfuric acid is preferred in view of the solubility of the by-produced inorganic salt and its treatment.

The amount of acid used for neutralization may be adjusted so that the pH corresponds to the isoelectric point of the amino acid.

The pressure can be changed depending on the concentration of carbonate ions in the solution to be neutralized, but it is approximately 0.5 Kg/cm ² G or more, 10 Kg/cm ²
It is up to about G. Preferably 2 to 5 Kg/cm ² G
It is.

Below 0.5Kg/cm ² G, bubbles will appear, and
Extra energy is required to recover and utilize carbon dioxide gas, which is not desirable.

If it exceeds 10 kg/cm ² G, it will only unnecessarily make the device heavier, which is not preferable.

The pressure is adjusted by the amount of carbon dioxide gas extracted.

The device for neutralization and crystallization may be a container with a normal stirring effect so that the neutralizing acid is mixed and the crystallized material is dispersed, such as a mixing tank equipped with a simple stirring blade or a mixing tank equipped with a simple stirring blade. An example is a tank equipped with an external circulation pump. And either continuously or in batches.

The crystallized amino acid crystals are separated by a conventional solid-liquid separation method such as centrifugation, and if necessary, washed or purified and dried to obtain a product.

<Example> Example 1 A 5-(3'-
Add 80 g of (indolylmethyl) hydantoin, 34.9 g of caustic soda, and 250 g of water and heat to 70°C while stirring.
After raising the temperature to , the mixture was allowed to react for 3 hours. Next, the reaction solution was degassed to atmospheric pressure and weighed 330.9 g. Analysis revealed that it contained 77.4 g of DL-tryptophan soda and 27.7 g of soda carbonate. This reaction solution was charged into a glass autoclave with an internal volume of 1, and the pressure was increased to 2Kg/cm ² G with nitrogen gas, and then a 70% by weight sulfuric acid aqueous solution was added at a rate of 15g per minute while stirring to adjust the pH of the reaction solution. I supplied it to make it 6.5. The supply time of the sulfuric acid aqueous solution was about 4 minutes. The generated carbon dioxide gas was continuously extracted out of the system, and the pressure inside the neutralization crystallization tank was always maintained at 2 kg/cm ² G.

As a result of observing the deposition state of the bubbles and the dispersion state of the precipitated DL-tryptophan crystals in the liquid, it was found that although there were slight bubbles, the crystals hardly floated.

Comparative Example 1 The same procedure as in Example 1 was carried out, except that a 70% by weight aqueous sulfuric acid solution was supplied at a rate of 5 g per minute, and carbon dioxide gas was extracted from the system at normal pressure.

In this case, the foaming gradually becomes more intense,
Eventually, bubbles containing crystals spilled out of the glass autoclave in No. 1, and the supply of 70% by weight sulfuric acid had to be interrupted midway through the process.

Example 2 61 g of β-methylmercaptoethylhydantoin, 34.9 g of caustic soda, and 250 g of water were charged into a Ti autoclave with an internal volume of 500 c.c. and heated to 183 g with stirring.
After raising the temperature to ℃, the mixture was allowed to react for 1 hour. Next, degassing was performed to atmospheric pressure, and the reaction solution was taken out, and the result was 328.8
It was hot at g. Analysis revealed that it contained 55.7g of DL-methionine soda and 27.7g of soda carbonate. This reaction solution was charged into a glass autoclave with an internal volume of 1, and the pressure was increased to 3Kg/cm ² G with nitrogen gas, and then a 70% by weight sulfuric acid aqueous solution was added at a rate of 15g/min while stirring until the pH of the reaction solution was 4.5. I supplied it so that it would be. The supply time of the sulfuric acid aqueous solution was about 4 minutes. The generated carbon dioxide gas was continuously extracted out of the system, and the pressure inside the neutralization crystallization tank was always maintained at 3 kg/cm ² G.

As a result, a little foaming occurred, but no DL-methionine crystals were floated.

Comparative Example 2 Carbon dioxide was extracted from the system at normal pressure,
Example 2 was carried out in exactly the same manner as in Example 2, except that a 70% by weight aqueous sulfuric acid solution was supplied at a rate of 5 g per minute. When about 7 minutes had passed after the start of supply of the sulfuric acid aqueous solution, the same phenomenon as in Comparative Example 1 occurred. However, the supply of sulfuric acid aqueous solution had to be interrupted.

Example 3 The same procedure as in Example 2 was carried out except that carbon dioxide gas was extracted from the system at 0.5 kg/cm ² G. As a result, the reaction solution temporarily expanded to 400 c.c. However, neutralization crystallization operation was possible.

<Effects of the Invention> According to the method of the present invention, it is possible to simultaneously perform neutralization and crystallization while preventing the above-mentioned foaming phenomenon.

Not only can the neutralization and crystallization operation of amino acid salts containing carbonate ions be performed continuously, but also the generated slurry can be stirred, transferred, separated, etc., and the generated carbon dioxide gas can be recovered and recycled as a raw material for hydantoin derivatives. It can be used very easily, continuously and economically, and an industrially superior neutralization crystallization method can be implemented. In addition, since the neutralization and crystallization of amino acid salts can be carried out simultaneously, it is possible to maintain a high concentration of hydantoin derivatives in the amino acid salt synthesis process by hydrolysis reaction of hydantoin derivatives using caustic alkali. The increased speed allows the device to be made smaller. Furthermore, since neutralization and crystallization can be carried out at the same time under high concentration of amino acid salts, it is possible to omit all or part of the amino acid crystallization step by concentration to obtain amino acids more completely. Very economical.

Claims (1)

[Scope of Claims] 1. A method for producing an amino acid, which comprises neutralizing an aqueous solution of an amino acid salt containing carbonate ions with an acid under pressure and simultaneously crystallizing the amino acid. 2. The method according to claim 1, wherein the pressure is 0.5 to 10 Kg/cm ² G.