JPH04169570A - Production of methionine - Google Patents

Abstract

PURPOSE:To obtain the subject methionine excellent in powder characteristics by making carbon dioxide gas absorbed in an aqueous solution of methionine potassium salt in the presence of polyvinyl alcohol., neutralizing and simultaneously depositing it. CONSTITUTION:Carbon dioxide gas is absorbed in an aqueous solution of methionine potassium salt obtained by, in the presence of potassium carbonate, hydrolysis of 5-(beta-methylmercaptoethyl)-hydantoin in the presence of polyvinyl alcohol in an amount of 5-20000ppm, preferably 50-3000ppm based on methionine. Neutralization and deposition of methionine are simultaneously carried out thereby. The resultant deposited crystal is a thick plate or a granule having high mechanical fracture resistance and solid-liquid separation is ready. A powdery product is obtained by drying it and the resultant powdery product has a high bulk density. The powdery product is also free from generation of dust during handling and excellent in fluidity.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to an improvement in a method for producing methionine. More specifically, the present invention relates to a method for producing methionine with excellent powder properties.

<Prior art> Methionine is produced by hydrolyzing 5-(β-methylmercaptoethyl)-hydantoin in the presence of potassium carbonate, then neutralizing the solution with carbon dioxide gas, crystallizing methionine, and separating it. can get. (Special Public Interest Publication 54-917
4, Japanese Patent Publication No. 43-19530) Crystals of methionine obtained by neutralizing an aqueous solution containing a potassium salt of methionine with carbon dioxide gas usually exhibit a scale-like or flake-like crystal habit.

Because these scale-like or flaky crystals are very fragile, great care must be taken when transporting or stirring the slurry containing the crystals. A large solid-liquid separator is required due to the poor separability of the crystals, and the resulting cake contains a large amount of mother liquor, so if the mother liquor contains impurities, sufficient washing or recrystallization is required. However, there are problems in producing methionine, such as a decrease in the yield of crystals and the need to evaporate a large amount of water when drying the cake.

Furthermore, methionine products in the form of flakes or flakes have a low bulk specific gravity and generate a lot of dust when handled, which worsens the working environment, and the flowability of the powder is poor, making it difficult to use on powder transportation equipment. This was a major obstacle.

In order to solve these problems, a small amount of a soluble cellulose derivative is mixed into an aqueous solution containing methionine or methionine salts, and then concentrated.
A method has been proposed in which methionine crystals are precipitated by cooling or reaction (Japanese Patent Publication No. 43-22285).

There are also methods for coexisting one or more compounds selected from nonionic surfactants and anionic surfactants (Japanese Patent Publication No. 46-19610),
Publication No. 152451 discloses a secondary method for changing the resulting methionine crystals from scale-like or flaky-like to needle-like or plate-like by coexisting one or more selected from aluminum salts or silicate compounds. It has been suggested that it has a similar effect.

<Problems to be Solved by the Invention> However, conventional additives have little effect when a potassium salt aqueous solution of methionine absorbs carbon dioxide gas to neutralize it and at the same time crystallizes methionine.

In view of these circumstances, the present inventors have developed a crystalline form (with excellent powder properties) when producing methionine by absorbing carbon dioxide gas into an aqueous solution of potassium salt of methionine and simultaneously crystallizing and separating methionine. As a result of intensive studies on a method for obtaining methionine having a crystal habit (crystal habit), it was found that if it is crystallized in the coexistence of polyvinyl alcohol, thick plate-like or granular crystals can be obtained, and these crystals are difficult to break mechanically. Not only is it extremely advantageous in the production of methionine because solid-liquid separation is easy, but the product powder has a large bulk specific gravity, generates little dust when handling the powder, and has good fluidity, making it an excellent product. It was discovered that the powder exhibits powder characteristics, and the present invention was completed.

<Means for Solving the Problems> In other words, the present invention involves the production of methionine by absorbing carbon dioxide gas into an aqueous solution of a potassium salt of methionine to neutralize it, and at the same time crystallizing and separating methionine in the coexistence of polyvinyl alcohol. This is a method for producing methionine, which is characterized by crystallization.

The methionine potassium salt aqueous solution of the present invention includes 5-
Can you name a solution in which (β-methylmercaptoethyl)-hydantoin is hydrolyzed in the presence of potassium carbonate?
It is not limited to this, and any material containing potassium salt of methionine can be applied.

The polyvinyl alcohol (hereinafter abbreviated as PVA) used in the present invention may be one that is normally commercially available, and there are no particular limitations on the degree of polymerization or saponification, and grades of 2 to 4 can also be used.

The amount of PVA used may be very small, usually about 5 to 20,000 ppm, preferably about 50 to 3,000 ppm based on methionine in the aqueous solution. If the amount used is less than the above amount, the effect will be low, and even if it is more than the above amount, the effect commensurate with the amount used will not be obtained.

PVA may be added as is, or may be added in a state dissolved or suspended in water or an appropriate solvent. It is usually added as an aqueous solution,
Needless to say, it is preferable that the methionine be uniformly mixed in the potassium salt aqueous solution. PVA may be added batchwise or continuously.

Of course, PVA can be used alone or in combination with other additives such as soluble cellulose derivatives, -valent alcohols, nonionic surfactants, and anionic surfactants.

PVA may be added and mixed in advance to an aqueous solution containing methionine and then subjected to the crystallization operation, or it may be directly supplied to the crystallizer separately from the aqueous solution containing methionine.

Carbon dioxide gas is absorbed into an aqueous potassium salt solution of methionine in the coexistence of PVA to neutralize it and crystallize methionine. Cooling may be performed if necessary during crystallization. It is also possible to absorb a part of the required amount of carbon dioxide gas, cool it, crystallize and separate methionine, and then absorb the remaining carbon dioxide gas to crystallize methionine.

The operation can also be carried out continuously or batchwise.

The crystallization temperature is about 0 to 100°C, preferably about 10 to 50°C.
°C is good.

Neutralization with carbon dioxide gas and crystallization pressure range from normal pressure to approximately 30k
g/a (G, preferably about 0.5-10 kg/aIrG
is good.

The pH value during neutralization is about 7.0-9.5, preferably about 7.0.
0 to 8.5.

The crystallized crystals are separated by a conventional method such as centrifugation, washed if necessary, and then dried.

The shape of methionine crystals obtained by crystallization in the coexistence of PVA varies somewhat depending on the type and amount of PVA added, crystallization operating conditions, etc., but it is in the form of a thick plate or granules.

<Effects of the Invention> The methionine crystals produced by the method of the present invention are much more mechanically fragile than conventional flake-like or flaky crystals, and solid-liquid separation is easy, making it easier to produce methionine. Extremely advantageous. Furthermore, the product powder obtained by drying has a large bulk specific gravity, generates little dust during handling, and has good powder fluidity, showing excellent product powder characteristics.

<Examples> Hereinafter, the present invention will be explained in more detail by examples.
The invention is not limited to these examples.

The bulk specific gravity of the product powder was calculated by gently filling a 100 cc graduated cylinder with methionine and measuring its weight.

As a guideline for dust generation, 3.
0 g of methionine was allowed to fall naturally, and the proportion of methionine that fell outside the lower saucer was defined as the degree of dust generation.

Example 1 200 g of an aqueous solution containing a potassium salt of methionine (13% by weight as methionine) and 0.2% by weight of PVA (polymerization degree 500, Wako Pure Chemical Industries special grade product) were added per hour to a container equipped with a stirrer with an internal volume of about 11. An aqueous solution of 13 g/hour was continuously fed.

The amount of PVA added was 11,000 pp relative to methionine.

The pressure inside the reactor is constantly maintained at 2.5-3゜0kg/a+f by continuously supplying carbon dioxide gas.
Neutralization crystallization was performed at 20°C while maintaining the temperature within the range of G.

There is always about 0.31 in the container! A slurry containing methionine crystals was continuously extracted. The extracted slurry was filtered, and the cake was further dried to obtain methionine crystals.

The moisture content in the cake after filtration and before drying was approximately 10%, and the cake drained very well.

The obtained methionine crystals were in the form of granules, and the bulk specific gravity of the dried product powder was 0.58 to 0.62 g/cc, which was very compact, and hardly any dust was generated during handling.

The degree of dust generation specified above was 0.9 wt%.

Example 2 Neutralization and crystallization were carried out under the same conditions as in Example 1, except that only the amount of PVA supplied was reduced to 115, and almost the same effects of PVA were obtained.

Some crystals changed from granular to thick plate-like,
The moisture content after filtration and before drying was about 10%, which was almost the same, and the amount of water drained was very low.

The bulk specific gravity of the product was 0.58-0.60 g/cc.

Comparative Example 1 Continuing from Example 1, the supply of the aqueous PVA solution was stopped, and the resulting DL-methionine crystals became flaky flakes with no thickness, and the water content in the cake after filtration was 15 to 2.
0%, resulting in poor filterability.

The product powder had a bulk specific gravity of 0.35 to 0.40 g/cc, was fluffy, generated a lot of dust during handling, and was easily broken mechanically.

Note that the degree of dust generation was 6.3 wt%.

Comparative Example 2 The same procedure as in Example 1 was carried out except that 500 ppm of the additive listed in Table 1 was used instead of 1000 ppm of PVA.

Table 1 shows the bulk specific gravity of the obtained product powder.

Table 1

Claims (1)

[Claims] 1. A method for producing methionine, which is characterized in that methionine is produced by absorbing carbon dioxide gas into an aqueous solution of potassium salt of methionine to neutralize it, and at the same time crystallizing and separating methionine in the presence of polyvinyl alcohol. .