JPH0687803A - Production of glycine - Google Patents

Abstract

PURPOSE:To obtain glycine in high purity and yield by reaction between glyconitrile, carbon dioxide and ammonia in the presence of water, and, during the reaction, by drawing part of the crystallization mother liquor to be circulated to the system out of the system to conduct hydrolysis to recover glycine. CONSTITUTION:A reaction is made among glyconitrile, carbon dioxide and ammonia in the presence of water and glycine is crystallized from the reaction liquor. When this crystallization mother liquor is to be circulated to the reaction system, part of the mother liquor is drawn out of the system and subjected to hydrolysis to easily convert the by-products therein to glycine which is then recovered. By this operation, impurities contributing to declining in the final product quality can effectively be prevented from being accumulated in the reaction system. Besides, the equipment involved can be saved because of a smaller quantity of the mother liquor to be treated than the case for recovering glycine by immediate hydrolysis of the crystallization mother liquor produced after crystallization of glycine from the reaction liquor; therefore, this production method is more advantageous.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a method for producing glycine, and more particularly to an improved method for producing glycine by reacting glyconitrile, ammonia and carbon dioxide in the presence of water. Glycine is a useful compound as a raw material for manufacturing additives such as processed foods, pharmaceuticals, agricultural chemicals and industrial chemicals.

[0002]

2. Description of the Related Art Conventionally, as a method for producing glycine, an amination method of monochloroacetic acid, a Strecker method, and a hydantoin method have been known. Among them, the amination method of monochloroacetic acid has an advantage that hydrogen cyanide is not used, but has a drawback that secondary and tertiary amine homologues are by-produced and the glycine yield is low. Further, the Strecker method has a drawback that it requires separation and subsequent treatment of iminodiacetic acid produced as a by-product during the reaction and neutralized salt after hydrolysis.

As a method for producing glycine that does not form a neutralized salt as a by-product, a method of reacting glyconitrile, ammonia and carbon dioxide gas in the presence of water (hereinafter sometimes abbreviated as "glyconitrile method") is known. Has been. However, in this method, in addition to the desired glycine, hydantoic acid, 2,5-diketopiperazine, glycylglycine,
A large amount of side reaction products such as hydantoinamide is produced, and the yield of glycine relative to glyconitrile is about 50-.
In addition to being as low as 70%, there were drawbacks such as difficulty in purifying glycine because the reaction product contained a large amount of side reaction products.

In the glyconitrile method, in order to suppress the formation of side reaction products and increase the conversion rate of glycine, a small amount of uncrystallized glycine after crystallization treatment of the reaction solution to separate glycine crystals is carried out. A method has been proposed in which a crystallization mother liquor containing a side reaction product such as and hydantoic acid is circulated in the reaction system (JP-A-3-223238). Using this method, the yield of glycine can be improved to 90%. However, according to the study by the present inventors, the glycine obtained by this method contains a large amount of impurities and is not colored. It has been found that there is a defect that the quality is inferior in some respects.

Further, by treating (hydrolyzing) the reaction liquid in the glyconitrile method with an alkaline substance, the production of glycine for increasing the yield of glycine and removing side reaction products which make purification of glycine difficult A method has been proposed (JP-A-53-31616). However, in this method, since the entire amount of the reaction solution is treated with an alkali, not only the processing equipment becomes large, but also a large amount of an alkaline substance is required, and a part of the glycine once produced is said alkali. There were drawbacks such as decomposition caused by the treatment.

[0006]

DISCLOSURE OF THE INVENTION According to the present invention, a high yield of glycine at the time of reaction, a high final yield of glycine with respect to the raw material glyconitrile, and an excellent quality of glycine with a low content of impurities can be easily obtained. It is intended to provide an improved method of the resulting glyconitrile method.

[0007]

The inventors of the present invention have conducted various studies to solve the above-mentioned problems, and as a result, in the glyconitrile method in which the crystallization mother liquor is circulated in the reaction system, the crystallization in the circulation is carried out. By extracting a part of the mother liquor to the outside of the system and purging it, it is possible to effectively prevent accumulation of impurities in the reaction system, which cause deterioration of the quality of the product glycine, and
When an alkaline substance is added to the purged crystallization mother liquor and subjected to hydrolysis treatment, side reaction products such as hydantoic acid and glycylglycine contained in the purged crystallization mother liquor are easily converted into glycine, The amount of the crystallization mother liquor that can be recovered as glycine, and in which the hydrolysis treatment is performed in this case, is significantly smaller than the amount of the crystallization mother liquor separated from the reaction liquid in the usual glyconitrile method, It was found that the scale of the apparatus used for the hydrolysis treatment can be much smaller, and that the amount of the alkaline substance will be relatively small.
The present invention has been achieved based on these findings.

That is, the method for producing glycine of the present invention is to crystallize a reaction solution obtained by reacting glyconitrile, carbon dioxide gas and ammonia in the presence of water to obtain crystals of glycine, In the method for producing glycine in which the crystallization mother liquor is circulated in the reaction system, a part of the crystallization mother liquor circulated in the reaction system is extracted out of the system and subjected to hydrolysis treatment to obtain glycine from the resulting hydrolysis-treated liquid. It is a method characterized by that.

In the present invention, the reaction of glyconitrile (abbreviated as GCN), ammonia and carbon dioxide gas in the presence of water is carried out by NH ₃ / GCN molar ratio = 1 to 50, CO ₂ / GC.
N molar ratio = 50, and GCN / H ₂ O molar ratio = 0.
The mixture of 01 to 0.5 is usually heated to room temperature to 220 under pressure.
React at a temperature of ° C. The reaction pressure is not particularly limited, and ammonia, carbon dioxide gas and water vapor generated during the reaction may be appropriately extracted and reacted. The lower the reaction temperature, the higher the yield of glycine and the less coloration of the product glycine, but the reaction rate decreases.
A reaction temperature of 00 ° C. or higher is preferred. The reaction time is usually
It is 0.5 to 10 hours, preferably 1 to 6 hours. The reaction system may be a batch system, a flow system, or a semi-flow system.

In the reaction solution obtained by this reaction,
About 60% by weight of glycine, 5% by weight or less of hydantoic acid, 2% by weight or less of 2,5-diketopiperazine, other glycylglycine, hydantoinamide, etc. Contains the product. This reaction liquid is usually C generated by heating.
After separating O ₂ and NH ₃ (the separated C
O ₂ and NH ₃ are appropriately reused in the above reaction system), further heated and concentrated, and then crystallized to separate glycine crystals. The separated crystal of glycine is obtained as a product glycine after being subjected to purification treatment such as recrystallization, ion exchange resin treatment, activated carbon treatment and the like, if necessary.

The crystallization of the glycine crystals is usually 20 to 70% by weight, preferably 30 to 50% by weight, based on the amount of glycine present in the reaction solution. If too much glycine is crystallized with respect to the amount of glycine present in the reaction solution, the content of impurities in the glycine crystal will increase, which is not preferable, and if the proportion of glycine to be crystallized is too small, the efficiency of the method will be poor. Become.

Even in the conventional method, 10 to 30 is usually contained in the crystallization mother liquor after such crystallization.
%, Glycine is contained in a dissolved state, so that the crystallization mother liquor had to be industrially subjected to glycine recovery treatment by some method.

The crystallization mother liquor from which the glycine crystals after crystallization are separated contains not only unreacted glyconitrile and uncrystallized glycine but also a large amount of various side reaction products described above. In the present invention, while the crystallization mother liquor is circulated in the reaction system, a part of the crystallization mother liquor is taken out of the system, an alkaline substance is added, and a hydrolysis treatment is carried out. As it is converted to glycine,
The glycine contained in the taken-out crystallization mother liquor and the glycine produced by the conversion are collected and obtained as glycine.

The amount of the crystallization mother liquor taken out of the system can be variously changed according to the content of impurities in the reaction liquid, etc., but usually 2 to the total amount of the mother liquor obtained by crystallization. 5
It is 0% by weight, preferably 5 to 30% by weight. If the amount of the mother liquor taken out of the system is too small, impurities causing deterioration of the quality of glycine will be accumulated in the reaction system, resulting in deterioration of quality of the product glycine. Further, when the amount of mother liquor taken out of the system is too large, the amount of mother liquor circulated in the reaction system becomes small, the effect of improving the glycine selectivity in the reaction system cannot be sufficiently obtained, and the amount of mother liquor to be hydrolyzed is small. More,
As the size of the hydrolysis treatment equipment increases, the amount of alkaline substance used increases.

The crystallization mother liquor circulated in the reaction system contains the above-mentioned NH ₃ / GCN molar ratio of the reaction mixture and CO ₂
/ GCN molar ratio, and as GCN / H ₂ O molar ratio is maintained, glycolate nitrile, after the addition of carbon dioxide, ammonia and water suitably is subjected again to the reaction. In this case, the circulating crystallization mother liquor contains various side reaction products by-produced in the previous reaction, and those contained side reaction products produce similar side reaction products. Since it acts to suppress side reactions, the selectivity of glycine is improved. That is, although the selectivity of glycine to glyconitrile is about 60% in the usual glyconitrile method in which the crystallization mother liquor is not circulated,
In the present invention in which the crystallization mother liquor is circulated in the reaction system, the yield of glycine with respect to glyconitrile can be improved to 70 to 90%.

Next, the crystallization mother liquor taken out of the system is subjected to hydrolysis treatment by adding an alkaline substance as a hydrolyzing agent, as described above. As the hydrolyzing agent,
For example, hydroxides, carbonates, bicarbonates of alkali metals or alkaline earth metals such as sodium hydroxide, potassium hydroxide, sodium carbonate, potassium carbonate, sodium bicarbonate, potassium bicarbonate, calcium hydroxide, barium hydroxide. Alkaline substances such as ammonium carbonate are used. Particularly preferred hydrolyzing agents are ammonium carbonate and calcium hydroxide. Since ammonium carbonate does not contain a metal component, glycine can be easily purified, and calcium hydroxide can easily remove the calcium component as calcium carbonate. In this case as well, glycine can be easily purified.

In the hydrolysis treatment, a predetermined amount of an alkaline substance as a hydrolyzing agent is added to the crystallization mother liquor taken out of the system, and the temperature is usually 100 to 200 ° C., preferably 150 to 170 ° C. under pressure. It is carried out by treating for 20 hours. There is no particular limitation on the pressurizing pressure, and it may be a naturally occurring pressure in the hydrolysis treatment under heating in a closed treatment apparatus, or the carbon dioxide gas or steam generated during the treatment may be appropriately extracted while the hydrolysis is performed. You may perform a decomposition process.

The addition amount of the alkaline substance as the hydrolyzing agent varies depending on the amount of the side reaction product contained in the crystallization mother liquor taken out of the system. The standard of the amount of addition of the alkaline substance is 0.1 to 10 times the molar amount of glycine produced by the hydrolysis treatment from the side reaction product contained in the crystallization mother liquor subjected to the hydrolysis treatment, preferably Is 0.5 to 3 times the molar amount.

Since the treatment liquid thus hydrolyzed contains glycine produced by the hydrolysis treatment, glycine crystals are separated from the reaction liquid obtained in the above reaction system by crystallization separation. Glycine crystals are collected by a method similar to the method.

[0020]

The following effects are obtained in the present invention.

Since the crystallization mother liquor in which glycine crystals are crystallized from the reaction solution is circulated in the reaction system, it is possible to suppress the production of side reaction products in the reaction and improve the selectivity of glycine in the reaction.

Since a part of the crystallization mother liquor is extracted from the reaction system, accumulation of impurities that are difficult to purify in the reaction system is prevented and the obtained glycine crystals are obtained regardless of the method of circulating the crystallization mother liquor into the reaction system. It is possible to prevent the deterioration of quality.

Since the extracted crystallization mother liquor is hydrolyzed to recover glycine from the side reaction product, the final yield of the product glycine with respect to the raw material glyconitrile is improved in combination with the high glycine selectivity. Can be made.

Compared with the method of recovering glycine by immediately hydrolyzing the crystallization mother liquor (including the dried solid matter) obtained by crystallizing glycine crystals from the reaction solution, the amount of crystallization mother liquor to be treated is small. The processing equipment can be small, and the amount of alkaline substance required for the hydrolysis treatment can be small.

[0025]

[Examples] Examples and comparative examples will be described in more detail below.

EXAMPLE 1 Glyconitrile / NH ₃ / CO ₂ / water molar ratio = 1/2/2/50 in a titanium lined autoclave.
The raw materials were charged in the ratio of and reacted at 165 ° C. for 3 hours.
The obtained reaction solution was heated at 80 ° C. under reduced pressure to remove NH ₃ , CO 2.
₂ and water were removed to obtain a concentrated solution containing a glycine concentration of about 30% by weight.

To this concentrated solution, an equal volume of a mixed solution of methanol / water volume ratio = 90/10 was added to precipitate and separate glycine crystals. At this time, the yield of glycine (the yield for glyconitrile, the same applies hereinafter) was 50.5%.

On the other hand, 20% of the crystallization mother liquor from which the glycine crystals were separated was concentrated at 80 ° C. under reduced pressure to obtain a dry solid. To this dried product, 2 parts by weight of ammonium carbonate and 50 parts by weight of water were added, and the mixture was hydrolyzed at 165 ° C. for 3 hours. After allowing the obtained treatment liquid to cool to room temperature, an equal volume of methanol / water volume ratio =
When a 90/10 mixed solution was added and glycine crystals were precipitated and separated, glycine crystals were recovered at a yield of 2.5%. Therefore, the total yield of glycine recovered in the first reaction was 50.5% + 2.5% = 53%.

Next, with respect to the remaining 80% of the crystallization mother liquor from which the glycine crystals were separated, this was circulated in the above autoclave, and the same amount of glyconitrile, NH ₃ , CO ₂ and water as above was added. The same second reaction was carried out by charging the above, and glycine was recovered by the same method from 20% of the crystallization mother liquor from which the glycine crystals were similarly precipitated and separated from the reaction solution. 8 remaining
A similar reaction was carried out by circulating 0% into an autoclave. When the same reaction was repeated 10 times thereafter, the total yield of glycine recovered gradually increased, and the total yield of glycine after the 5th time was stable at 82.0 ± 0.5%. In addition, the recovered glycine crystals were neither crystallized / separated from the reaction solution nor recovered from the crystallization mother liquor by hydrolysis, and almost no coloring was observed, and the quality was good. there were.

Comparative Example 1 A reaction similar to the reaction of Example 1 was repeated 10 times while circulating the entire amount of the crystallization mother liquor, and the yield of glycine gradually increased and the yield of glycine at the 4th time was increased. It was 78.0%. However, the yield of glycine after the 5th time showed a downward trend, and the yield of glycine at the 10th time was 75.5%.
The crystals of glycine obtained at this time were colored in a light brown color.

Comparative Example 2 The total amount of the crystallization mother liquor from which the glycine crystals were separated from the first reaction mixture of Example 1 was concentrated under reduced pressure at 80 ° C. to obtain a dry solid. To this dried solid matter, 2 parts by weight of ammonium carbonate and 50 parts by weight of water were added, and the mixture was heated at 165 ° C. for 3 hours for hydrolysis treatment.

After allowing the hydrolyzed treatment liquid to cool to room temperature, an equal volume of methanol / water volume ratio = 90/1 with respect to the treatment liquid.
When a glycine crystal was precipitated and separated by adding a mixed solution of 0, glycine crystals were recovered with a glycine yield of 16.2%. Therefore, the total glycine yield in this case is 50.
It was 5% + 16.2% = 66.8%.

Claims (1)

[Claims] 1. Glycine is obtained by crystallization from a reaction solution obtained by reacting glyconitrile, carbon dioxide gas and ammonia in the presence of water to obtain crystals of glycine, and circulating the obtained crystallization mother liquor in the reaction system. In the manufacturing method of
A method for producing glycine, characterized in that a part of the crystallization mother liquor circulated in the reaction system is extracted to the outside of the system and subjected to hydrolysis treatment, and glycine is obtained from the resulting hydrolysis-treated liquid.