JP2764346B2 - Glycine production method - Google Patents

Description

The present invention relates to a method for producing glycine. More particularly, the present invention relates to a method for producing glycine by reacting glycolonitrile with ammonia and carbon dioxide gas.

Glycine is a useful compound widely used as a food additive for processed foods, a raw material for agricultural chemicals and pharmaceuticals.

(Prior art)

Conventionally, as a method for producing glycine, an amination method of monochloroacetic acid, a Strecker method, a hydantoin method and the like have been known. The monochloroacetic acid method has the advantage of not using the toxic hydrogen cyanide, but has secondary tertiary and homologous tertiary amines as by-products, resulting in low glycine yield. In the Strecker method, it is necessary to separate iminodiacetic acid salt by-produced during the reaction and neutralized salt after hydrolysis.

The hydantoin method is a method of producing glycine by hydrolysis through hydantoin obtained using hydrogen cyanide and formaldehyde as raw materials. For example, a method of heating hydrogen cyanide, aldehyde, ammonia and carbon dioxide in an aqueous solvent at 100 ° C. or more (US Pat. No. 3,536,72)
6) Other than the above, a method of heating hydrogen cyanide, formaldehyde and ammonium carbonate in an aqueous medium (JP-A-49-127)
915), a method in which glycolonitrile, ammonia and carbon dioxide are heated to remove ammonia and carbon dioxide, and then treated with an alkylamine or an alkylammonium hydroxide (JP-A-53-28115). A method in which a gas is heated to remove ammonia and carbon dioxide, followed by treatment with a mineral acid for hydrolysis (JP-A-53-28116), by heating glycolonitrile, ammonia and carbon dioxide to form an alkali metal or alkaline earth. A method of treating with an alkaline substance such as metal hydroxide, carbonate and bicarbonate (JP-A-53-316161) is known.

[Problems to be solved by the invention]

However, all of these methods have many by-products, and the glycine selectivity is not sufficient. In the method of hydrolysis with an alkali salt or metal, the selectivity of glycine is improved, but not only does it require an equimolar amount or more of alkali than the charged glycolonitrile, but it also requires hydrolysis of the glycine salt. There is. In addition, the step of separating the produced salt and glycine is complicated, which not only greatly impairs the economic efficiency of glycine production, but also poses a problem in treating this salt. In addition, glycine must be isolated from the liquid as crystals for industrial implementation, but the glycine yield in this case is naturally worse than the one-pass glycine yield.
In the aforementioned USP 3,536,726, via hydantoin,
A method (hereinafter abbreviated as a mother liquor circulation method) of circulating a residual liquid (hereinafter abbreviated as a mother liquor) obtained by separating most of glycine from a reaction solution to the reaction zone without generating such a side salt has been disclosed. However, further improvement in glycine yield and reduction of by-products are desired.

[Means for solving the problem]

The present inventors, in the production of hydantoin glycine,
After intensive studies on a method for improving the glycine yield,
First, at a temperature lower than the reaction temperature, glycolonitrile is pre-reacted in advance to convert it to another compound that is more stable than glycolonitrile, and then this reaction is performed at a predetermined reaction temperature to obtain glycine and glycine. It has been found that the yield of a product which can be converted into benzene is greatly improved, and the present invention has been completed. That is, the present invention is a method for producing glycine by reacting glycolonitrile, carbon dioxide and ammonia in the presence of water.First, water, glycolonitrile, carbon dioxide and ammonia are reacted at 80 to 120 ° C., This is a method for producing glycine, which comprises pre-reacting in 0.5 to 1 hour and then main-reacting at 150 to 200 ° C.

In the most preferred embodiment of the present invention, glycine is separated from the reaction solution containing glycine by separation means such as crystallization, and the remaining mother liquor obtained by separating glycine from the reaction solution is then treated with water, The pre-reaction and the main reaction are carried out by circulating in a system consisting of glycolonitrile, carbon dioxide and ammonia (mother liquor circulation method).

What is important in the present invention is that prior to the glycine production reaction, glycolonitrile is pre-reacted with carbon dioxide gas and ammonia in the presence of water at a temperature lower than the production reaction temperature, that is, 80 to 120 ° C. By doing so, glycolonitrile is converted to a more stable compound.
In addition, since a by-product which can be converted into glycine as described below is obtained, further improvement in glycine yield can be expected by using this pre-reaction in the mother liquor circulation method.

Glycolonitrile used in the method of the present invention is most commonly and economically produced using hydrocyanic acid and formalin as raw materials. Therefore, even if paraformaldehyde is dissolved in water, it can be used as a formalin source. However, regarding the production of glycine, the concentration of glycolonitrile is not particularly limited, and it is most economical to use an aqueous solution of about 37 wt% formalin as formalin. It is an easy way. Since this reaction proceeds quantitatively, the glycolonitrile concentration thus obtained is about 50% by weight, and it is extremely reasonable to use this 50% by weight aqueous solution of glycolonitrile as it is as a raw material for producing glycine.
It is also an economical method. Further, the aqueous solution of glycolonitrile used in the method of the present invention can be used even if it contains sulfuric acid, phosphoric acid or the like used as a stabilizer of glycolonitrile.

The aqueous solution of glycolonitrile is preferably stored at a low temperature from the viewpoint of preventing polymerization, decomposition, or coloring accompanying the polymerization until it comes into contact with carbon dioxide gas and ammonia. Above, there is no serving.

The ammore and carbon dioxide gas used in the method of the present invention may be used as they are, but compounds known to those skilled in the art that produce these compounds (ammonia and carbon dioxide) under the reaction conditions, for example, ammonium carbonate Alternatively, ammonium bicarbonate may be used. Further, even when these are mixed and used, preferable results are obtained.

The amount of ammonia used is 2 to 12 times the molar amount of the total amount of glycolonitrile. Preferably it is in the range of 4 to 9 moles. If the amount of ammonia used is less than 2 mole times, the reaction slows down, and if it exceeds 12 mole times, the reaction rate increases, but the by-products increase and the reaction pressure increases, which is not preferable.

The amount of carbon dioxide gas to be used is 1/3 to 1 mole ratio to ammonia, and approximately 1/2 mole ratio is preferable because the reaction speed is high and the reaction pressure is low.

The amount of water used is 5 to 15 times the amount of ammonia used.
It is molar times. If the amount of water used is less than 5 mol times, the selectivity of glycine will be poor, and the crystallization rate of glycine will be extremely reduced. On the other hand, when the molar ratio exceeds 15 moles, the selectivity of glycine is improved, but the glycine concentration in the reaction solution is decreased, which increases not only the cost of concentration for crystallization but also the volume of the reactor, which is not economical. When the reaction temperature is set higher, it is preferable that the molar ratio is larger.

The reaction pressure is not particularly limited, and the reaction may be performed at a pressure equal to or higher than the pressure generated during the reaction, ammonia generated during the reaction,
The reaction can be carried out by appropriately extracting carbon dioxide gas or solvent vapor.

In the method of the present invention, the lower the reaction temperature, the higher the glycine yield, but the lower the reaction rate. Therefore, the reaction temperature is 150-200 ° C, preferably 150-180 ° C, more preferably 150-170 ° C.

The reaction solution obtained by the method of the present invention contains by-products such as glycine, hydantoic acid, glycylglycine, hydantoic acid amide, triglycine, hydantoin, and 2,5-diketopiperazine. First, glycine is separated from these reaction solutions by a crystallization method described later or the like. In addition, these by-products, which are contained together with the mother liquor after separation, are circulated to a reactor for performing a reaction (more precisely, a pre-reaction and / or a main reaction) of a system composed of water, glycolonitrile, carbon dioxide, and ammonia. It has been found that the glycine yield is greatly improved by performing the method. These by-products and glycine exist in equilibrium during the reaction, and the equilibrium is reduced by the amount of glycine separated and removed by crystallization and the like circulating in a reactor (hereinafter referred to as a reactor) in which the above mother liquor is applied. This is probably due to the novel finding we have found to migrate from the product to the glycine side. Therefore, we have found that by circulating this mother liquor to the reactor (particularly in the region where the main reaction takes place), the yield of glycine isolated as crystals to glycolonitrile is significantly improved by more than 75%. . When the mother liquor is not circulated, even if the glycine yield in one pass is high, the yield of isolated glycine actually isolated as crystals from it is at most about 60%.

That is, it is considered that at least the by-products described above can be converted to glycine under the reaction conditions specified in the present invention. In the method of circulating the mother liquor to the reactor, the glycine yield is greater as the sum of these yields is greater than the one-pass glycine yield.

The composition of glycine and by-products that can be converted to glycine during the reaction is determined by the reaction temperature, ammonia, carbon dioxide, water, glycolonitrile concentration and the reaction time. The total average residence time including the average residence time at the reaction temperature is so long that it is not economical. If the pre-reaction time is too short, the effect is small. The preferred pre-reaction time is
0.5 to 1 hour. On the other hand, when the pre-reaction temperature is lower than 80 ° C., the amount of side reaction of glycolonitrile with the coloring substance increases, and the yield of glycine and by-products that can be converted to glycine decreases. On the other hand, if the pre-reaction temperature is much higher than 120 ° C., the effect of the pre-reaction does not appear. A more preferred pre-reaction temperature is 100 to 120 ° C.

This pre-reaction method may be carried out by installing another preliminary reactor in front of the glycine production main reactor, or, depending on the residence time, a certain section from the inlet of the vertically elongated tubular reactor to 80 to 80.
The reaction can also be carried out by controlling the temperature to 120 ° C. and performing the pre-reaction in this section (region).

The amount of glycolonitrile used in the above method is preferably supplied such that the sum of the amount of the product in the mother liquor circulated to the reactor and the amount converted to glycolonitrile is constant. In the method of the present invention, the total amount of glycolonitrile means this total amount.

The reaction solution obtained by the method of the present invention is concentrated at 50 to 150 ° C. to separate and remove most of water, ammonia and carbon dioxide from the reaction mixture.

Next, the reaction mixture is cooled to 5 to 80 ° C. to obtain a mother liquor containing glycine crystals.

The method of crystallizing glycine from the reaction mixture is performed by a method known to those skilled in the art, and does not limit the method of the present invention. For example, crystallization methods such as a cooling crystallization method, an evaporation crystallization method, and a vacuum crystallization method are preferably used industrially.

The mother liquor containing glycine crystals obtained by this crystallization is then subjected to solid-liquid separation using a general-purpose separator, and usually 50% or more of glycine is separated. On the other hand, all or a part of the obtained mother liquor is supplied to the reaction step. A desired result can be obtained by circulating the mother liquor which has been subjected to the decoloring step, if necessary, in which all or part of the mother liquor has been purged.

Glycine in the mother liquor circulated by the method of the present invention,
The amount of by-products such as glycylglycine, triglycine, hydantoin, hydantoic acid, hydantoic amide, and 2,5-diketopiperazine is determined by the amounts of glycine and by-products in the reaction solution and the purity of the target glycine. It depends on the crystallization rate to be performed. That is, if the crystallization rate of glycine is reduced to produce high-purity glycine, the amount of mother liquor recycled increases, and the energy for concentration and crystallization increases, which is not preferable. On the other hand, if the crystallization rate is increased in order to reduce the amount of recycling, the purity of glycine obtained generally decreases. Therefore, the amount of reduced glycolonitrile in the mother liquor is usually 30 mol% or more and 200 mol% or less based on newly supplied glycolonitrile.

〔Example〕

 The method of the present invention will be described in detail with reference to examples.

Example 1 50 wt% aqueous solution of glycolonitrile at 25 ° C. per hour
230 g (2.01 mol) and 206 g (1
Aqueous solution 19 containing 2.1 mol) and 267 g (6.1 mol) of carbon dioxide
90 g were mixed and fed to a 10 l tubular reactor. The reaction is performed by controlling 1/5 of the reactor from the inlet of the reactor at 100 ° C and controlling the remaining 4/5 at 150 ° C.
The test was performed at 50 kg / cm ² . The raw material composition is H ₂ O / NH ₃ / CO ₂ / glyconitrile = 45/6/3/1 molar ratio, the average residence time at 100 ° C. is 1 hour, and the average residence time at 150 ° C. is 4 hours. , Which is equivalent to a total of 5 hours.

When the reaction became steady, the reaction solution was concentrated with a concentrator, and water, ammonia and carbon dioxide gas were removed for crystallization (crystallization rate 55%).
%), And 0.890 mol (purity 98.2%) of glycine was separated per hour. As a result of analyzing the remaining mother liquor, 0.97 mol of hydantoic acid in terms of glycolonitrile, glycylglycine, hydantoic acid amide 2,5-diketopiperazine,
Hydantoin, triglycine and glycine were detected. Thus, a mother liquor for initial supply was prepared.

Next, this mother liquor and 50 wt.
% Glycolonitrile aqueous solution and ammonium carbonate aqueous solution were supplied to the reactor. That is, the mother liquor, 118 g (1.04 mol) of a 50 wt% aqueous solution of glycolonitrile and an aqueous solution containing 6.1 mol as ammonium carbonate are supplied to a reactor,
The reaction was performed for 24 hours after it became stationary. As a result, 1.64 kg of isolated glycine was recovered. This corresponds to a yield of 88.2% based on the glycolonitrile fed. The results are shown in Table 1.

On the other hand, after reaching a steady state, a part of the reaction solution was separately sampled, the concentration ratio was increased, and a larger amount of glycine was crystallized. As a result, glycine having a crystallization ratio of 66% and a purity of 98.0% was able to be separated. That is, it means that the crystallization rate can be increased from 55% to 66% in the method of Example 1. If this condition is adopted, the circulation amount of the mother liquor can be further reduced.

Comparative Example 1 An aqueous solution of glycolonitrile and an aqueous solution of ammonium carbonate
Mixing was performed at 25 ° C., and the same procedure as in Example 1 was performed except that the pretreatment was not performed and the total residence time was the same. The results are shown in Table 1.

Comparative Example 2 The same procedure as in Example 1 was carried out except that the aqueous solution of glycolonitrile was mixed with an aqueous solution of ammonium carbonate which had been preheated to a reaction temperature of 150 ° C. in advance without performing the pretreatment. The results are shown in Table 1.

In this comparative example, a part of the reaction solution that became steady was separately sampled, the concentration was increased, and an attempt was made to crystallize a large amount of glycine. However, during the concentration, the viscosity of the reaction solution sharply increased, and the reaction solution became tar-like, so that the crystallization operation was completely impossible. This indicates that, in the case of the comparative example, impurities (by-products) that hinder the fractional crystallization operation with a low glycine yield
Is presumed to be a large amount of by-product (accumulation). The present inventors have confirmed that glycine of high purity does not become tar-like even if the concentration ratio is increased no matter how much, and the crystallization operation can always be performed.

Example 2 An aqueous solution of glycolonitrile was mixed with an aqueous solution of ammonium carbonate preheated to 120 ° C., and a pre-reaction was performed at 120 ° C. for 0.5 hour.
The procedure was carried out in the same manner as in Example 1 except that the main reaction was carried out so that the total residence time was the same. The results are shown in Table 1.

Example 3 The raw material composition was H ₂ O / NH ₃ / CO ₂ / glyconitrile = 45/5/2.
5/1 molar ratio, pre-reaction time 0.5 hours, main reaction temperature 17
The procedure was performed in the same manner as in Example 1, except that the temperature was set to 0 ° C. for 2 hours. The results are shown in Table 1.

Further, a part of the reaction solution was separately concentrated in the same manner as in Example 1 to obtain a high concentration ratio.
Separation was achieved at 97.8%.

Example 4 The preheating temperature and the pre-reaction temperature of the aqueous solution of ammonium carbonate were
The procedure was performed in the same manner as in Example 3 except that the temperature was changed to 120 ° C. The results are shown in Table 1.

Comparative Example 3 A reaction was carried out in the same manner as in Example 3, except that a pre-reaction was not performed, and an aqueous solution of glycolonitrile was mixed with an aqueous solution of ammonium carbonate which had been preheated to a reaction temperature of 170 ° C. in advance. The results are shown in Table 1.

Furthermore, as in Example 3, an attempt was made to sample and concentrate a part of the reaction solution. However, during the concentration, the mixture became tar-like as in Comparative Example 2, and the crystallization operation was completely impossible. That is, in the case of the comparative example, it can be seen that there is a large problem that crystal precipitation does not immediately occur when the concentration ratio is increased.

As described above, the accumulation of impurities during the production of glycine has a great effect on the crystallization operation, and thus the crystallization rate of glycine is greatly changed.

According to the method of the present invention, not only the yield is improved, but also the accumulation of such impurities is small, so that there is a great feature that the crystallization operation is not hindered even if the concentration ratio is considerably increased.

[Effects of the Invention] In the present invention, a stable compound can be obtained by pre-reacting a raw material in the production of glycine, and a substance that can be converted to glycine can be obtained in a high yield. Therefore, glycine,
In particular, the yield of glycine actually obtained as crystals is greatly improved. Furthermore, by applying the mother liquor circulation method, which is a process that does not produce waste liquid, the glycine yield can be further greatly improved, and the production of glycine via hydantoin has been improved to a method that can be carried out industrially. is there.

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Claims (3)

(57) [Claims] 1. A method for producing glycine by reacting glucoronitrile, carbon dioxide and ammonia in the presence of water, wherein glycolonitrile, carbon dioxide and ammonia are first reacted at 80-120 ° C. and 0.5-1 Pre-reacting in a time, followed by a main reaction at 150-200 ° C. 2. A pre-reaction and / or a main reaction is performed by circulating the remaining mother liquor obtained by separating glycine from a reaction solution containing glycine by crystal removal through a system comprising water, glycolonitrile, carbon dioxide and ammonia. The method of claim 1. 3. The process according to claim 1, wherein glycolonitrile is introduced into water, carbon dioxide gas and ammonia preheated to 80 to 120 ° C., and reacted at the temperature for 0.5 to 1 hour.