JP2000143617A - Production of methionine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce methionine having a large bulk density capable of being readily treated by adding an acid to a hydrolyzed solution of methylmercaptoethylhydantoin to neutralize the solution and crystallize the methionine, separating the crystallized methionine, washing the separated methionine with water to provide a hydrous cake of the methionine, and drying the obtained cake. SOLUTION: An acid is added to a hydrolyzed solution obtained by hydrolyzing 5-(β-methylmercaptoethyl)hydantoin to neutralize the solution and to crystallize methionine, and the crystallized methionine is separated. The separated methionine is washed with water, and the hydrous cake of the washed methionine is dried under mechanical stirring. The drying is carried out preferably at 60-150 deg.C, more preferably 100-140 deg.C preferably while regulating the oxygen concentration in the drying atmosphere so as to be <=5 vol.%, for about 0.5-2 hr, at least under stirring preferably during the time from the point at which the water content of the water-including cake is about 9 wt.% to the point at which the water content is the one required for the product, more preferably during the time from the point at which the water content of the water-including cake is about 12 wt.% to the point at which the water content is the one required for the product.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for producing methionine, and more particularly to a method for producing methionine which is easy to handle and has a high bulk specific gravity. Methionine is mainly useful as an animal feed additive.

[0002]

2. Description of the Related Art As a method for producing methionine, 5- (β
-Methylmercaptoethyl) hydantoin is hydrolyzed in the presence of potassium carbonate or caustic soda, and then neutralized by adding an acid such as carbon dioxide or sulfuric acid to the hydrolyzed solution, and methionine is crystallized, separated by filtration, and the filtrate is concentrated. A method is known in which methionine is then circulated to a hydantoin hydrolysis step, and the separated methionine is washed with water and dried to obtain a product methionine.

[0003]

[Problems to be Solved by the Invention] Japanese Patent Publication No. 54-9174
In the publication, 5- (β-methylmercaptoethyl) hydantoin is hydrolyzed in the presence of potassium carbonate, and then neutralized by adding carbon dioxide gas to the hydrolyzed solution to crystallize methionine, which is separated by filtration. A method is disclosed in which methionine is concentrated and circulated to a hydantoin hydrolysis step, and the separated methionine is washed with water and dried to obtain a product methionine.

However, the crystals of methionine obtained by the method disclosed in Japanese Patent Publication No. 54-9174 are scaly, have a small bulk specific gravity of 0.3 to 0.4, have a large amount of dust, and have a large amount of methionine. It is not preferable in handling. As a countermeasure for this, there is a method of recrystallizing flaky methionine into plate-like methionine having a large bulk specific gravity, but it is not economical because the equipment becomes complicated.
Prior literatures such as Japanese Patent Publication No. 54-9174 do not disclose any method for drying a methionine-containing cake. The present inventor has conducted intensive studies on a method of producing methionine having a large bulk specific gravity that is easy to handle, and as a result, the bulk specific gravity is changed by a drying method, that is, crystallization, separation, and a water-containing cake of methionine obtained by washing with water. Was dried under mechanical stirring to find that the bulk specific gravity of the obtained methionine was increased, thus completing the present invention.

[0005]

That is, the present invention provides a 5-
(Β-Methylmercaptoethyl) In a method for producing methionine by hydrolyzing hydantoin, an acid is added thereto to neutralize the solution by adding an acid to crystallize and separate methionine, followed by washing with water and drying to produce methionine. A method for producing methionine, comprising drying a methionine-containing cake obtained as described above under mechanical stirring.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION In the present invention, 5- (β-methylmercaptoethyl) hydantoin is hydrolyzed, and then an acid is added to the hydrolysis solution to neutralize it, thereby crystallizing and separating methionine. The filtrate is concentrated and circulated to the hydantoin hydrolysis step, and the separated methionine is washed with water to obtain a product methionine. Specifically, 5- (β-methylmercaptoethyl) hydantoin is hydrolyzed in the presence of potassium carbonate, and then the hydrolysis solution is neutralized with carbon dioxide to separate methionine by crystallization or 5- (β -Methylmercaptoethyl) hydantoin is hydrolyzed in the presence of caustic soda and then neutralized by adding an acid such as sulfuric acid to the hydrolyzed solution to crystallize out methionine. Among them, the method of hydrolyzing in the presence of potassium carbonate and then neutralizing the hydrolysis solution with carbon dioxide is preferably used because the recycling and recycling of alkali is easy.

In this method, first, 5- (β-methylmercaptoethyl) hydantoin is hydrolyzed to potassium methionine in the presence of potassium carbonate. The hydrolysis is usually about 5-10 kg / cm ² G, about 150-20
The reaction is performed at 0 ° C., and the generated ammonia and carbon dioxide gas are collected in the hydantoin process.

[0008] Carbon dioxide gas is introduced into the hydrolyzed solution thus obtained to neutralize the solution pH to 7 to 8, and methionine is crystallized. This neutralization crystallization can be carried out by a batch method or a continuous method. However, a part of the hydrolysis solution described below is crystallized batchwise (batch crystallization), and then the remaining hydrolysis solution is semi-crystallized. By adopting a method of continuous crystallization (semi-continuous crystallization), methionine having a granular shape and a higher bulk density can be obtained.

Hereinafter, the batch crystallization-semi-continuous crystallization will be described. Using a stirred tank equipped with a jacket, first, a hydrolyzing solution and a flocculant of 15 to 40% of the total charged amount are charged, carbon dioxide is added thereto, and the mixture is batchwise crystallized under stirring (batchwise crystallization). The remaining 60-85% of the hydrolysis solution, coagulant and carbon dioxide gas are continuously supplied, and the resulting slurry is continuously crystallized without extraction (semi-continuous crystallization).

It is presumed that in the batch crystallization, seed crystals are formed and then semi-continuous crystallization is performed to grow the seed crystals, thereby obtaining aggregated crystals having a large bulk specific gravity.
Batch crystallization is about 20-50 minutes, semi-continuous crystallization is about 40-
It is preferably performed over 90 minutes. In particular, the time of semi-continuous crystallization affects the bulk specific gravity. If it is less than about 40 minutes, the bulk specific gravity will not be sufficiently large, and if it exceeds about 90 minutes, the equipment efficiency will be deteriorated, and the aggregated crystals will change to scaly crystals. Is not preferred.

The crystallization is performed with carbon dioxide gas at about ^{2 to} 6 kg / cm ² G.
And at about 15-30 ° C. Neutralization is carried out until the pH is between 7.5 and 8. The completion of the neutralization can be known from the fact that the absorption rate of the carbon dioxide gas decreases and the pH does not decrease. It takes a long time to complete the neutralization reaction to 100%, and if the reaction rate is low, the yield of methionine is small, and from the viewpoint of economy, usually pH 7.8 is preferably used.
This is done until 8.0. When the crystallization temperature is low, the solubility of methionine decreases and the amount of methionine deposited increases, but potassium bicarbonate may be precipitated. It is necessary to adjust the concentration of potassium bicarbonate so as not to precipitate.

As the coagulant, an organic coagulant is used,
Among them, sorbitan laurate, polyvinyl alcohol and hydroxypropyl methylcellulose are preferably used. The coagulant is about 1000 to 3000 ppm with respect to methionine in batch crystallization, and about 500 ppm in semi-continuous crystallization.
２０００2000 ppm is used. If the amount is too small, methionine having insufficient bulk due to insufficient aggregation cannot be obtained, and even if the amount is too large, the effect corresponding thereto cannot be obtained.

The stirring is not particularly limited as long as the crystal is not crushed. The stirring power per unit liquid weight is about 0.7 in batch crystallization in terms of a state without carbon dioxide gas aeration. １．２1.2 kW / m ³ , and about 0.5-1.2 kW / m ³ ton in semi-continuous crystallization. If the stirring is too strong, the aggregated crystals are crushed, and if the stirring is too weak, gas absorption and neutralization become insufficient, which is not preferable.

The methionine precipitated by neutralization is filtered, separated, washed with water, neutralized and dried to obtain methionine of the product.
The filtrate and washings are recovered in the hydantoin hydrolysis step.

In the present invention, the methionine water-containing cake obtained by washing and neutralizing usually contains about 10 to 25% by weight of water, depending on the production method. The methionine water-containing cake has a water content of about 9% by weight to the water content of the desired product (usually about 0.5% by weight or less, usually about 0.3% by weight or less), preferably about 12% by weight. Dry at least with mechanical stirring between% and the moisture content of the desired product. By drying under mechanical stirring, dried methionine having a higher bulk density can be obtained as compared with the case of standing drying or flash drying. In the above-mentioned drying, usually, industrially, the product is dried while mechanically stirring to a desired moisture content. However, for the purpose of the present invention, if the mechanical stirring is performed until the moisture content becomes about 2% by weight, For example, even if further drying is performed by another drying method, for example, still drying, dried methionine having a large bulk density can be obtained.

Specifically, the bulk density of methionine can be increased by drying using a dryer of the type that mechanically stirs and dries the cake, for example, a paddle type drier, a rotating disk type drier, or the like. it can.

The drying treatment under mechanical stirring as a method for increasing the bulk density of methionine after drying need not be carried out in all the steps of drying a water-containing cake obtained by washing with water to a desired water content. , The water content of the wet cake is about 9
The drying may be carried out with at least mechanical stirring between about 12% by weight and the moisture content of the desired product, preferably between about 12% by weight and the moisture content of the desired product. In the case of a cake having a moisture content exceeding about 12% by weight, a method is employed in which the cake is dried by standing drying or the like to about 12% by weight, and then dried with stirring to a desired moisture content. It is also possible. Of course, it is possible to perform all the drying steps using mechanical stirring, which is a method with high adoption probability.

[0018] The drying temperature is 60 to 150 ° C, preferably 100 to 140 ° C. If the temperature is too high, methionine is thermally degraded. If the temperature is too low, drying takes a long time, a heat transfer area needs to be increased, and a pressure reducing device needs to be provided, which is not economical.

The oxygen concentration in the dry atmosphere is 5% by volume.
It is preferable to carry out in the following manner in order to prevent deterioration of methionine.

The drying time depends on the dryer used, the temperature, the amount of dry air flow, the water content and the like, but is usually about 0.5 to 2 hours.

[0021]

According to the method of the present invention, methionine which is easy to handle and has a large bulk specific gravity can be easily produced.

[0022]

EXAMPLES The present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples. In the examples, the bulk density was determined by placing a sample to be measured gently from the top into a 100 ml graduated cylinder that had been allowed to stand, and then inserting the sample until it overflowed from the top. The sample was scraped, the weight of the 100 ml sample in the measuring cylinder was weighed together with the measuring cylinder, and the weight of the measuring cylinder was determined by subtracting the weight of the measuring cylinder from the weight.
00 ml) (sample weight g / 100 ml).

Reference Example (Preparation of hydrous methionine) Hydrolysis solution obtained by hydrolyzing 5- (β-methylmercaptoethyl) hydantoin in the presence of potassium carbonate (potassium methionine: 14.2 wt%, K 10 liters of other potassium salt in terms of ₂ CO ₃ : containing 6.2 wt%) and 200 ml of a 2 wt% aqueous solution of polyvinyl alcohol as a flocculant (3000 ppm of polyvinyl alcohol to methionine)
m) in a crystallization tank at 20 ° C. under a pressure of carbon dioxide 4
kg / cm ² G, the stirring power per unit liquid weight was converted to a value of 0.7 kw / m ³ in terms of a state without ventilation of carbon dioxide gas.
Batch crystallization was performed for 0 minutes.

Next, the hydrolysis solution was added to the crystallization tank at 330 ml / mi.
n, 3.3 ml / min of polyvinyl alcohol aqueous solution
(Polyvinyl alcohol is 1500 to methionine
ppm), while continuously supplying at 20 ° C., a pressure of 4 kg / cm ² G by carbon dioxide gas, the stirring power per unit liquid weight is just before the end of the reaction, and converted to a state without carbon dioxide gas aeration.
Semi-continuous crystallization was performed for 60 minutes with stirring to 0.5 kw / m ³ (the total amount of the continuously supplied hydrolysis solution was 2
0 liter).

Immediately after the neutralization crystallization, the liquid was withdrawn and filtered.
Then, it was washed with water and neutralized with an acid to obtain a water-containing cake of methionine (water content: 20.0% by weight).

Example 1 Inner diameter 1 provided with anchor-type stirring blades having a diameter of 110 mm
20mm, 1000ml separable flask,
Methionine water-containing cake 200 prepared in the above reference example
g. Nitrogen gas is introduced into this flask at 1500
The mixture was flowed at a rate of ml / hour, the stirring blade was rotated at 80 rpm, the flask was placed in a 120 ° C. oil bath, heated, and dried for 40 minutes. Table 1 shows the results. In addition, the description of the blade stirring type in the table indicates a stirrer using an anchor type stirring blade.

Comparative Example 1 50 g of the water-containing methionine cake prepared in the Reference Example was dried under vacuum (75 ° C. × 1 Torr) for 15 hours. Table 1 shows the results.

Examples 2 and 3 The methionine water-containing cake prepared in the same manner as in the Reference Example was dried using a rotating disk type drier and a paddle type drier tester. Table 1 shows the results.

[0029]

[Table 1]

Example 4, Comparative Example 2 5- (β-methylmercaptoethyl) hydantoin was hydrolyzed in the presence of sodium hydroxide, and then neutralized by adding sulfuric acid to the hydrolyzed solution to separate methionine by crystallization. Using a water-containing methionine cake obtained by washing with water, drying was performed in the same manner as in Example 1 and Comparative Example 1. Table 2 shows the results.

[0031]

[Table 2]

Example 5 Using the water-containing cake obtained by the method of Reference Example, under the conditions shown in Table 3, using the same blade type stirrer as used in Example 1, drying was performed to a predetermined water content (pre-stage drying). It dried (the latter stage drying) using the same vacuum stationary type drier as used in Comparative Example 1. Table 3 shows the results.

[0033]

[Table 3]

Examples 6 and 7 Using the water-containing cake obtained by the method of Reference Example, under the conditions shown in Table 4, using the same vacuum stationary type drier as used in Comparative Example 1, it was dried to a predetermined water content ( Drying in the first stage), and then in Example 1.
Using the same blade-type stirrer as used in (1), drying was performed (second-stage drying). Table 4 shows the results.

[0035]

[Table 4]

Claims (5)

[Claims] 1. A hydrolysis solution obtained by hydrolyzing 5- (β-methylmercaptoethyl) hydantoin is neutralized by adding an acid thereto to crystallize and separate methionine, followed by washing with water and drying to obtain methionine. A method for producing methionine, which comprises drying a water-containing methionine cake obtained by washing with water under mechanical stirring. 2. The method for producing methionine according to claim 1, wherein the water content of methionine dried under mechanical stirring is from 9% by weight to the water content of a desired product. 3. The method for producing methionine according to claim 1, wherein the water content of methionine dried under mechanical stirring is from 12% by weight to the water content of a desired product. 4. The method for producing methionine according to claim 1, wherein the drying temperature is 60 to 150 ° C. 5. The method for producing methionine according to claim 1, wherein the oxygen concentration in the dry atmosphere is 5% by volume or less.