JPS588384B2 - Separation method of glycine and iminodiacetic acid - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for separating glycine and iminodiacetic acid from an aqueous solution containing glycine or a salt thereof and iminodiacetic acid or a salt thereof. The pH of the aqueous solution was adjusted to 1.5 by adding sulfuric acid.
The present invention relates to a method for selectively crystallizing and separating iminodiacetic acid from the aqueous solution as described below.

BACKGROUND ART Effectively separating glycine and iminodiacetic acid from an aqueous solution containing glycine or a salt thereof and iminodiacetic acid or a salt thereof is an extremely important technique for industrially producing glycine.

In other words, glycine refers to the corresponding glycinonitrile as an alkali metal (or an alkali metal, hereinafter simply referred to as an alkali metal to simplify the explanation, but the alkali metal 10 is included as its equivalent). Hydrolysis with an aqueous hydroxide solution yields an aqueous alkali metal salt solution of glycine, which is neutralized to its isoelectric point with an inorganic acid such as sulfuric acid or hydrochloric acid to contain glycine and an alkali metal neutral salt of the inorganic acid. It can be produced by preparing an aqueous solution and fractionally crystallizing glycine from this aqueous solution.

However, a small amount of iminodiacetic acid is produced as a by-product during the hydrolysis, and coexists with the inorganic acid salt in the glycine-containing aqueous solution as a monoalkali metal salt near pH 6, which is the isoelectric point of glycine.

Since the amount of by-product of iminodiacetic acid is relatively small and the solubility of its alkali metal salt in water is considerably higher than that of glycine and inorganic acid salts, when performing the fractional crystallization of glycine and inorganic acid salts, The alkali metal salt of iminodiacetic acid is not crystallized out and remains in the mother liquor.

According to a typical conventional method for separating and obtaining glycine, for example, as described in JP-A-51-34113, a glycine-containing aqueous solution neutralized with an inorganic acid is first heated and concentrated to neutralize the inorganic acid. The salt is crystallized and filtered while hot, then the filtrate is cooled and glycine is crystallized and obtained separately, and the mother liquor containing a large amount of glycine together with the alkali metal salt of iminodiacetic acid is circulated to form a new raw aqueous solution. are combined and subjected to a repeated fractional crystallization process.

However, if this mother liquor is circulated as it is, the highly soluble alkali metal salt of iminodiacetic acid will gradually accumulate in the circulating mother liquor, resulting in a decrease in the yield of glycine obtained in a single fractional crystallization operation, and (Glycine is used as an animal feed and food additive, so contamination with such impurities must be avoided as much as possible.) Furthermore, there was a problem in that the crystal size of the glycine produced became very fine, making filtration and separation difficult.

On the other hand, since iminodiacetic acid is also useful as a chelate compound, it is also desirable to separate and recover iminodiacetic acid from the glycine-containing solution.

In order to prevent the above-mentioned alkali metal salt of iminodiacetic acid from accumulating in the circulating mother liquor, part or all of the mother liquor may be continuously or intermittently drained (liquid renewal); This is not preferable since the remaining glycine therein is also lost.

For this reason, in JP-A-51734112 (or JP-A-52-118421), an inorganic acid is added to at least a part of the circulating mother liquor to pH 2.4±0.5 (% JP-A-52-118421). In the publication, a method is proposed in which iminodiacetic acid is selectively released and separated by adjusting the pH to 2 to 2.8.

This method is based on the same concept as the above-mentioned method of neutralizing glycine metal salt to its isoelectric point to liberate glycine and crystallizing it. This is based on the principle that the solubility is lowest at ±0.5).

However, according to this method, the recovery rate in one pass when recovering iminodiacetic acid from a three-component aqueous solution of glycine, sodium sulfate, and monosodium iminodiacetate, for example, was not necessarily satisfactory.

Therefore, an object of the present invention is to provide a method for efficiently and selectively recovering iminodiacetic acid from an aqueous solution containing glycine (or a salt thereof) and iminodiacetic acid (or a salt thereof) and separating glycine and iminodiacetic acid. There is a particular thing.

Another object of the present invention is to prevent the accumulation of iminodiacetic acid in the circulating mother liquor in the process of fractionally obtaining glycine from an aqueous solution containing glycine (or its salt) and iminodiacetic acid (or its salt), It is an object of the present invention to provide a method for separating glycine and iminodiacetic acid that substantially avoids renewing the mother liquor.

The method for separating glycine and iminodiacetic acid according to the present invention includes:
The pH of a glycine aqueous solution containing glycine and iminodiacetic acid in the form of free acid and/or salt, respectively, was set to 1.5.
Hereinafter, iminodiacetic acid is crystallized and separated under strong acidity of preferably 0.4 to 1.2.

The present invention will be explained in more detail below.

In the following, in order to make the description concrete and simple, sodium salt will be explained as an example of an alkali metal salt, but the scope of the present invention is not limited to the following explanation. Needless to say.

Glycinonitrile (which can be obtained as an aqueous solution, for example, by reacting formalin with hydrocyanic acid to form glycolonitrile, followed by amination with ammonia) is added with a stoichiometric amount or a slight excess of caustic soda. Alkaline hydrolysis in aqueous solution produces an aqueous solution containing the sodium salt of glycine and a small amount of iminodiacetic acid disodium salt as a by-product.

When sulfuric acid is added to this aqueous solution to neutralize it to a pH of approximately 6 to 7,
An aqueous solution containing free glycine, sodium sulfate and iminodiacetic acid monosodium salt is obtained.

As a method for separating glycine from such an aqueous solution, first, the aqueous solution is heated and concentrated to crystallize sodium sulfate, and then filtered while hot to separate the crystallized sodium sulfate.
Next, the P solution is cooled to crystallize glycine and obtained by fractionation, or the aqueous solution is first cooled and glycine is crystallized and obtained by fractionation, and the filtrate is heated and concentrated to crystallize sodium sulfate. A method of separation by filtering while hot is commonly used.

In any case, the remaining mother liquor, which still contains large amounts of glycine together with iminodiacetic acid monosodium salt and sodium sulfate, is preferably recycled again to a fresh raw aqueous solution for glycine recovery, after the iminodiacetic acid component has been removed.

As mentioned above, if the mother liquor is circulated as it is, the iminodiacetic acid component will gradually accumulate, which is undesirable. Therefore, if the aqueous solution of iminodiacetic acid monosodium salt is made acidic by adding an inorganic acid (for example, sulfuric acid), the monosodium salt will be released. Based on the knowledge that the solubility of iminodiacetic acid in water is lower than that of monosodium salt and reaches its minimum at around pH 2.4, sulfuric acid is further added to the mother liquor to adjust the pH of the solution to 2.4±0. 5, a method of crystallizing and separating iminodiacetic acid has been proposed (Japanese Unexamined Patent Application Publication No. 1983-1992).
-34112).

It is true that the solubility of iminodiacetic acid that does not contain other impurities reaches its minimum near its isoelectric point of pH 2.4, and when sulfuric acid or caustic soda is added to make it acidic or alkaline, the solubility increases in both cases. .

However, as a result of further research by the present inventors, it was found that in the three-component system of sodium iminodiacetic acid monosulfate and glycine, the solubility of iminodiacetic acid does not reach its minimum when the pH of the solution is around the isoelectric point of pH 2.4. , the pH of the liquid is 1.5 or less, especially pH 0
．． The surprising fact has been found that the solubility of iminodiacetic acid is minimized in the range of 4 to 1.2.

Iminodiacetic acid (IDA) Sodium monosulfate (1 mole per mole of IDAI) Monoglycine (1 mole per mole of IDA)
The attached graph shows the results of actually measuring the solubility (room temperature) of iminodiacetic acid in the three-component system.

In the figure, curve A plots the solubility of iminodiacetic acid in the above three-component aqueous solution, and curve B plots the solubility of iminodiacetic acid containing no other impurities.

From the attached graph, iminodiacetic acid has extremely low solubility in the three-component system at pH 1.5 or lower, preferably in the pH range of 0.4 to 1.2, and the iminodiacetic acid component can be selectively and efficiently separated from the mother liquor. It will be obvious that it is suitable to do so.

The detailed mechanism of the above behavior of iminodiacetic acid at pH 1.5 or below is not necessarily clear, but the analysis results of the crystals that crystallize indicate that iminodiacetic acid sulfate and sodium sulfate are co-products, or that iminodiacetic acid and acidic sodium sulfate are present. It appears that a double salt of .

Moreover, in order for iminodiacetic acid to exhibit the behavior described above at pH 1.5 or lower, it is necessary for a sodium salt to be present in the aqueous solution system. It was found that acetic acid could not be crystallized.

Therefore, when a compound other than sodium is used in the alkaline hydrolysis step of dalicinonitrile, it is necessary to add a sodium salt, such as sodium sulfate, before crystallizing and separating iminodiacetic acid from the mother liquor.

Practically preferred amount of the sodium salt is 0.5 mol or more per 1 mol of iminodiacetic acid in the liquid, more preferably 1 mol or more up to saturation concentration.

After acidifying part or all of the mother liquor to pH 1.5 or less and crystallizing and separating iminodiacetic acid, the mother liquor is decolorized with activated carbon according to a conventional method if necessary, and then mixed with a fresh glycine-containing raw aqueous solution. Therefore, the neutralization step and the glycine fractional crystallization step can be repeatedly and smoothly carried out without increasing the concentration of iminodiacetic acid in the liquid.

Note that the mother liquor does not necessarily need to be acidified in its entirety, and a portion of the mother liquor can be taken and acidified within a range where the concentration of the iminodiacetic acid component in the circulating mother liquor does not become excessive.

Although the continuous method in which the mother liquor is circulated and added to the raw aqueous solution has been described above, it goes without saying that the mother liquor may be further repeatedly treated to crystallize and fractionate glycine.

On the other hand, the iminodiacetic acid compound or double salt, which has been crystallized and fractionated by acidifying the mother liquor to pH 1.5 or lower, is purified by once separating and redissolving it in water to adjust the pH to 2.4±0.5. It can be recovered as iminodiacetic acid.

As explained above, according to the method of the present invention, α-monoamino acids and iminodicarboxylic acids can be converted into free acids and/or
Alternatively, the iminodicarboxylic acid component can be efficiently and selectively recovered from an aqueous solution containing it in the form of a salt, and α-amino acids can be very efficiently fractionated and obtained without substantially renewing the mother liquor. Became.

The present invention will be explained in more detail below using actual cases.

Example A conventional method (J. Am. Chem. Soc, 56
, 2197 (1934)).

After returning the resulting slightly brown aqueous solution to normal pressure and removing unreacted ammonia, a 48% by weight aqueous solution of caustic soda was added at a ratio of 1405 mol per 1 mol of glycinonitrile.
The reaction was carried out at 100° C. for 1 hour to obtain an aqueous glycine sodium salt solution having the following composition.

Composition Weight % Glycine sodium salt 34,4 iminodiacetic acid disodium salt 1.1 Caustic soda
1.3 water
63.2 Using this aqueous solution as a stock solution, the following fractional crystallization operation was performed.

(1) First step (neutralization step) 98% sulfuric acid was added to the above aqueous solution to neutralize it to pH 6-7.

(2) Second step (fractional crystallization step) The neutralized liquid produced in the first step is heated and concentrated to the boiling point to crystallize sodium sulfate, and the concentration is stopped just before glycine begins to crystallize, followed by hot centrifugation. The crystallized sodium sulfate was removed, and the filtrate was cooled to about 34° C. to crystallize glycine, which was obtained by centrifugation and the mother liquor was collected as a filtrate.

The by-product iminodiacetic acid remains in the mother liquor as iminodiacetic acid monosodium salt.

(3) Third step (fractional crystallization step) The mother liquor from the second step is heated and concentrated again to the boiling point to crystallize sodium sulfate, and the concentration is stopped just before glycine begins to crystallize, followed by hot centrifugation. After removing the crystallized sodium sulfate, the solution was cooled to about 34°C to crystallize glycine, which was then centrifuged to obtain PM. The mother liquor was collected.

This operation was repeated two more times.

(4) Fourth step (iminodiacetic acid recovery step) After repeating the fractional crystallization operation of sodium sulfate and glycine three times in total,
A fairly concentrated mother liquor of iminodiacetic acid monosodium salt was obtained.

Its composition is as follows.

Composition Weight % Glycine 13.9 Iminodiacetic acid monosodium salt 18.2 Sodium sulfate 14,4 Water
53-5 This mother liquor 2007 was stirred for 3 hours at room temperature (approximately 20° C.) under various pH conditions, and the crystallized precipitate was filtered under suction to obtain a cake and a slurry.

The results are shown in Table 1 below.

(Note) (1) pH adjustment was performed using approximately 80% sulfuric acid.

(2) Cake weight is the total weight of the cake after drying at 105°C for 16 hours.

(3) The weight percent of iminodiacetic acid in the cake is the weight percent of iminodiacetic acid (free acid form) in the cake.

From the results in Table 1, the recovery rate of iminodiacetic acid was large at pH around 0 to 1.5, and the higher the pH, the lower the recovery rate.

The purity of the recovered iminodiacetic acid was almost the same regardless of the pH conditions.

Further, almost no glycine was crystallized and more than 90% remained in the filtrate.

Next, redissolve the experimental cup 30 cake in water, add a small amount of powdered activated carbon to decolorize it, and add aqueous sodium hydroxide solution to pH 2.
．． 4 and concentrated by heating until just before sodium sulfate started to crystallize.

This concentrated solution was then stirred and allowed to cool.

Iminodiacetic acid crystallized at 34° C. was separated by fj, washed with water and dried to obtain 22.7 g of white crystals.

The purity of this iminodiacetic acid was 98.9%.

Recovery rate from mother liquor was 73% and recovery rate from cake was 79%.
%Met.

[Brief explanation of the drawing]

The attached diagram is a graph showing the relationship between the solubility of iminodiacetic acid and pH in an aqueous solution containing iminodiacetic acid. Curve A is iminodiacetic acid-sodium sulfate-glycine:
This is a graph for a three-component system, and curve B is a graph for iminodiacetic acid alone.

Claims (1)

[Claims] 1. Sulfuric acid is added to a glycine aqueous solution containing glycine and iminodiacetic acid in the presence of a sodium salt to adjust the pH of the aqueous solution.
1. A method for separating glycine and iminodiacetic acid, characterized by crystallizing and separating iminodiacetic acid as a strongly acidic acid of 5 or less. 2. The method according to claim 1, wherein the aqueous solution has a pH of 0.4 to 1.2. 3. The method according to claim 1 or 2, wherein the total amount of sodium salts present in the glycine aqueous solution is 0.5 mol or more per 1 mol of iminodiacetic acid in the solution. 4. The method according to any one of claims 1 to 3, wherein the mother liquor after crystallizing and separating the iminodiacetic acid is decolorized with activated carbon and then recycled to the glycine separation step. 5 After separating the crystallized iminodiacetic acid, dissolve it in water and
The method according to any one of claims 1 to 4, wherein iminodiacetic acid is recovered by adjusting the H2.4±0.5.