JPH03240759A - Method for preventing discoloration of glycine - Google Patents

Abstract

PURPOSE:To obtain the subject compound without causing discoloration at a low cost by reacting glycolonitrile with carbon dioxide gas and ammonia in the presence of water until glycolonitrile in the reaction system is consumed and continuing the reaction in the presence of oxygen. CONSTITUTION:Glycolonitrile is made to react with carbon dioxide gas and ammonia in the presence of water at 150-200 deg.C (preferably 150-170 deg.C) in a reaction system free from oxygen for 0.5-1hr after the start of the reaction until glycolonitrile becomes undetectable in the system. The reaction of the reaction liquid is continued preferably for 1-5hr in the presence of oxygen to obtain the objective compound. The 1st stage reaction in the absence of oxygen is preferably carried out by purging the reactor with an inert gas such as nitrogen and using deaerated water. Air is used as the oxygen for the 2nd stage reaction and the partial pressure of oxygen is preferably 0.2kg/cm<2>.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for preventing discoloration of glycine. In particular, it relates to preventing discoloration in a method of producing glycine by reacting glycolonitrile with ammonia and carbon dioxide.

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

[Prior art]

Conventionally, known methods for producing glycine include the amination method of monochloroacetic acid, the Strecker method, and the hydantoin method. In all of these methods, the reaction solution is colored, which greatly affects the quality of glycine.

These decolorization methods usually include a method of adsorbing and removing the colored substance itself using activated carbon, ion exchange resin, etc., a method of converting the colored substance into another stable compound that does not show coloring using an oxidizing agent or a reducing agent, and a method of using oxidation. Reaction methods have been carried out in which the by-product of colored substances is suppressed in advance by using agents or reducing agents.

It is presumed that these colored substances are in an unstable oxidation state and become stable when reduced or oxidized. These are used as coloring inhibitors to suppress coloring during the reaction, and as decoloring agents to treat the colored liquid after the reaction.

As a reaction method for suppressing the by-product of colored substances in advance, for example, in a method for producing hydantoin by reacting glycolonitrile with carbon dioxide and ammonia, the reaction product liquid obtained in the -th stage reaction is treated with an acid. A method of performing activated carbon treatment together with cyclization treatment (Japanese Patent Application Laid-Open No. 61-72761
). In addition, when producing hydantoin by reacting glycinonitrile with ammonium bicarbonate, etc. in water or an aqueous solution, a method is proposed in which sulfite or acidic sulfite is allowed to coexist to prevent coloring of the reaction solution (Japanese Patent Application Laid-Open No. 6-11991). -167670
) etc. are disclosed.

On the other hand, as a method for decolorizing the reaction solution after the reaction, for example, for glycine obtained by the Strecker method, monochloroacetic acid method, etc., a crude glycine aqueous solution with a pH of 7 or less is heated at 50°C or less with a weakly basic anion exchange resin or a medium base. Purification method of glycine by treatment with anion exchange resin (Special Publication No. 54-1)
686), but also a method for decolorizing a colored glycine soda salt aqueous solution using air or hydrogen peroxide (Japanese Patent Application Laid-Open No. 1999-1-1989)
254649) etc. have been disclosed.

However, in the case of glycine, the use of activated carbon or ion exchange resin is undesirable because the amount used becomes large.

Furthermore, the use of reducing agents such as sulfites not only does not necessarily have a sufficient decolorizing effect, but also their contamination adversely affects the purity of glycine.

On the other hand, JP-A-1-25464 uses air as an oxidizing agent.
Method 9 is preferable as there is no contamination of foreign substances, but only the glycine soda aqueous solution obtained by the Strecker method is used, and decolorization with air not only requires a processing time of 60 hours or more, but also is also not enough.

Normally, depending on the coloring substance, the processing agent effective for decolorizing or preventing coloration also differs. The coloring substances differ slightly depending on the reaction conditions, but the differences are particularly noticeable when the raw materials are different, and the reality is that these studies are conducted individually depending on the differences in the manufacturing method.

[Problem to be solved by the invention]

However, none of the conventional decolorization methods or coloration prevention methods described above have been applied to glycine obtained by the hydantoin method; When air is passed through the colored crude glycine solution, its coloration increases significantly, which is further accelerated by temperature, and the hydantoin method is not necessarily an effective decolorization method, so the hydantoin method is more economical. There is a strong need for a coloring prevention method that suppresses the by-product of colored substances and is effective.

[Means to solve the problem]

The present inventors conducted intensive studies on methods for suppressing the by-product of colored substances in the production of glycine using the Yudantoin method. As a result, the presence of oxygen promotes coloring in reactions involving glycolonitrile, but glycolonitrile The present invention was completed by discovering that coloring can be significantly prevented by reacting to glycine in the presence of oxygen in a state where it is no longer detected. That is, the present invention provides a method for producing glycine by reacting glycolonitrile, carbon dioxide gas, and ammonia in the presence of water, in which oxygen is allowed to coexist after glycolonitrile is substantially no longer present in the reaction system. This is a method for preventing glycine from discoloring, which is characterized by further reaction.

The most common and economical method for producing glycolonitrile used in the method of the present invention is to use hydrocyanic acid and formalin as raw materials. However, paraformaldehyde can also be dissolved in water and used as a source of formalin. Moreover, the glycolonitrile used in the method of the present invention can be used even if it contains sulfuric acid, phosphoric acid, etc. used as a stabilizer.

The ammonia and carbon dioxide gases 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 under the reaction conditions, such as ammonium carbonate or ammonium bicarbonate, may be used. Also, preferable results can be obtained by using a mixture of these.

The amount of ammonia used is 2 to 12 times the amount of glycolonitrile used. More preferably, it is in the range of 4 to 9 times the mole. If the amount is less than this, the reaction will be slow. If more than this amount is used, the reaction rate will increase, but by-products will increase and the reaction pressure will also increase, which is not preferable. Further, the amount of carbon dioxide gas used is preferably in the range of 1/3 to 1 in molar ratio to ammonia.

The amount of water used in the method of the present invention is 5 to 15 times the amount of ammonia used by mole. If the amount is less than this, the selectivity of glycine will be poor and the crystallization rate of glycine will be extremely reduced. On the other hand, if it is used in excess of this amount, although the selectivity of glycine is improved, the concentration of glycine in the reaction solution is reduced, which not only increases the cost of concentration for crystallization but also increases the volume of the reactor, which is not economical. Moreover, when the reaction temperature is set high, the larger the molar ratio is, the better.

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

The lower the reaction temperature used in the method of the present invention, the higher the yield of glycine, but the slower the reaction rate. Therefore, the reaction temperature is 150-200°C, preferably 150-170°C.
'C.

In the method of the present invention, the term "after glycolonitrile substantially ceases to exist" means 0.0% after the start of the reaction, with the time during which the raw material liquid is heated or the time when it reaches a predetermined temperature being taken as the reaction start time.
Glycolonitrile reacts to below the detection limit in 5 to 1 hour. This shows the state at this time.The main products at this time are hydantoic acid, hydantoic acid amide, and hydantoin, and little glycine is produced.The presence of oxygen in this reaction involving glycolonitrile promotes coloration. Undesirable.

What is important in the present invention is that the reaction is first carried out for 0.5 to 1 hour after the start of the aforementioned reaction in a reaction system in the absence of oxygen;
Next, the reaction solution in which glycolonitrile was no longer detected,
That is, oxygen is allowed to coexist in a reaction solution in which hydantoic acid, hydantoic acid amide, and hydantoin are present as main products, and of course carbon dioxide gas and ammonia are also present, thereby suppressing the by-production of colored substances. The objective is to continue the reaction for ~5 hours to obtain a glycine-producing reaction solution with little coloring.

As a method to eliminate the presence of oxygen, simply purging the reactor with an inert gas such as nitrogen is effective enough, but
It is more preferable to also use degassed water together with the purge.

The oxygen used in the method of the present invention may be pure oxygen or oxygen diluted with an inert gas, and even if air is used as the oxygen source, the effect is sufficient, it is safe and economical, and it is particularly preferable. The amount of oxygen used is 0,2 in terms of oxygen partial pressure.
kg/cd is sufficient, and the presence of more than that does not improve the coloring prevention effect, but only dilutes the raw material gases such as ammonia and carbon dioxide gas and slows down the reaction.

The method of the present invention can be carried out in batch mode, semi-flow mode, or flow mode.

Examples of methods for carrying out the reaction in the presence of oxygen in the method of the present invention include, in the case of a batch reaction, a method of injecting air during the reaction; in the case of a flow reaction, a method of injecting air in the middle of the reaction zone; In addition, a method of mixing a reaction solution of the same composition in contact with air into the middle of the reaction zone, and a method of crystallizing glycine.
One method is to contact the separated residual liquid with air and mix it into the middle of the reaction zone. However, the method of the present invention is not limited to carrying out the reaction in the presence of oxygen using other methods.

〔Example〕

The method of the present invention will be explained in detail by way of examples.

Example 1 3.2 g (55.7 s+mol) of glycolonitrile, 21.4 g (223 mmol) of ammonium carbonate, and 45 g of water were placed in a titanium-lined 100 m autoclave, pressurized with nitrogen to 10 kg/cj, and decompressed to normal pressure. After repeating the pressurizing operation three times to purge air, it was heated to 150° C. in 1 hour. The reaction pressure at this time was 38 kg/cd. This time was the reaction start time, and the reaction continued for 1 hour.Next, air was introduced into the reactor at a partial pressure of 0.5K.
g/d and reacted for an additional 4 hours, making the total reaction time 5 hours. It was confirmed that glycolonitrile was no longer detected in the reaction solution at the time of air injection, and that glycine production was 20 mmol or less. Cool the autoclave to room temperature;
As a result of analyzing the reaction solution by liquid chromatography, glycine 42.33 m5 ol, hydantoic acid 3.10 ■ a + o
The chromaticity of the reaction solution containing 0.82 mmol of glycylglycine was 91 on Hazen's scale.

Examples 2 to 3 The reaction was carried out in the same manner as in Example 1, except that the time during which air was injected and the air partial pressure were changed as shown in Table 1, and the reaction was conducted so that the total reaction time was 5 hours. . The results are shown in Table 1.

Comparative Example 1 A reaction was carried out in the same manner as in Example 1 except that air was not injected during the reaction, and the resulting reaction liquid had a chromaticity of 187 on Hazen's scale, showing significant coloration. The results are shown in Table 1.

Comparative Example 2 The reaction was carried out in the same manner as in Example 1, except that the reaction system was not purged with nitrogen before charging the raw materials and air was not pressurized during the reaction. The results are shown in Table 1.

Comparative Example 3 The reaction was carried out in the same manner as in Example 1, except that the raw materials were charged without purging the reaction system with nitrogen, and air was injected at a partial pressure of 0.2 kg/cd before raising the temperature. The results are shown in Table 1.

Example 4 The amounts of water and ammonium carbonate used were changed so that the molar ratio of water/ammonia/carbon dioxide/glycolonitrile was 42/8/4/1, and the reaction temperature was set at 170°C. The reaction was carried out in the same manner as in Example 1 except that air was pressurized after the reaction for .5 hours to make the total reaction time 2.5 hours. The results are shown in Table 1.

Examples 5 to 6 The reaction was carried out in the same manner as in Example 4, except that the time during which air was injected and the air partial pressure were changed as shown in Table 1, and the reaction was conducted so that the total reaction time was 2.5 hours. went. The results are shown in Table 1.

Comparative Example 4 The reaction was carried out in the same manner as in Example 4, except that air was not pressurized during the reaction. The results are shown in Table 1.

Comparative Example 5 The reaction was carried out in the same manner as in Example 4, except that the reaction system was not purged with nitrogen before charging the raw materials and air was not pressurized during the reaction. The results are shown in Table 1.

〔Effect of the invention〕

By using the method of the present invention, it is possible to suppress the by-product of wasteful colored substances and reduce the coloring of the obtained reaction solution to about 50% of the conventional level, making it possible to industrially improve the production of glycine via hydantoin. This has been improved to an advantageous method.

Claims (1)

[Claims] In a method for producing glycine by reacting glycolonitrile, carbon dioxide, and ammonia in the presence of water, after glycolonitrile is substantially no longer present in the reaction system, oxygen is allowed to coexist and further reaction is performed. A method for preventing discoloration of glycine, which is characterized by: