JPS61261488A - Electrolyzing method for alkaline metallic salt of amino acid - Google Patents

Abstract

PURPOSE:To obtain a free amino acid at a good yield with less electric power consumption by using a cation exchange membrane as a diaphragm, adding the alkaline metallic salt of a neutral amino acid into an anolyte having positive pH and electrolyzing the same with an aq. alkaline metallic hydroxide as a catholyte. CONSTITUTION:An electrolytic cell is constituted by providing a sheet of the cation exchange membrane 3 as the diaphragm between the anode 1 and the cathode 2. The stock soln. F consisting of the alkaline metallic salt of the neutral amino acid having each one amino group and carboxyl group is added to the anolyte A circulated and passed in an anode chamber 4 of the above-mentioned cell and the pH of the above-mentioned anolyte A is maintained at <=9.5, more preferably <=9.0. On the other hand, the catholyte C consisting of the aq. soln. of the alkaline metallic hydroxide is passed through the chamber 5. Electric current is then passed between both electrodes 1 and 2 to form the free amino acid in the anolyte A, the alkaline metallic hydroxide is obtd. in the catholyte C. The amino acid and the alkaline metallic hydroxide are respectively recovered as an ion exchange liquid E and recovered alkali R by gas-liquid separators 6, 7.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an electrolytic method for obtaining free amino acids and alkali hydroxides from alkali metal salts of so-called neutral amino acids having one amino group and one carboxyl group. More specifically, the present invention relates to an electrolytic method that consumes less electricity and does not involve decomposition loss of amino acids.

Among amino acids, many of them, such as glycine, α-alanine, β-alanine, and α-phenylalanine, are liberated by ion exchange of alkali metal salts of amino acids (hereinafter abbreviated as amino acid salts) obtained through processes such as reactions. It is obtained through a process of converting it into an amino acid.

The main methods for this ion exchange are: (1) Contact with a weakly acidic cation exchange resin in the H+ type (2) After neutralization with mineral acid, the resulting mineral salt is subjected to fractional crystallization or electrolysis. Either method of separation by dialysis is performed.

However, in method (1), in order to regenerate the resin used, and in method (2), for neutralization, acid is added in an amount approximately equivalent to the alkali metal ion contained in the raw amino acid salt solution. Consume. In any of these methods, a waste liquid containing a large amount of salt is produced. This waste liquid usually contains
Since organic substances, especially those containing nitrogen, coexist in relatively high concentrations, it is difficult to treat them easily.

On the other hand, as a method for obtaining alkali hydroxide by electrolyzing inorganic salts such as common salt, a method using an ion exchange membrane as a diaphragm has been developed. By analogy with this method, if an aqueous solution of amino acid salts is used as the anolyte in an electrolysis cell with a single cation exchange membrane separating the anode and cathode chambers, the amino acid salts will be decomposed into amino acids and alkali hydroxide. However, it is expected that amino acids will be obtained in the anolyte and alkali hydroxide will be obtained in the catholyte. If this method is realized as expected,
Since no acid is required and the alkali is recovered, there is no generation of waste liquid containing large amounts of salt.

However, when electrolysis is carried out using an aqueous amino acid salt solution as the anolyte, decomposition of the amino acids occurs, which not only results in a negligible loss of amino acids but also often results in coloring of the solution and generation of off-flavors. Carboxylic acids are also said to undergo an anodic reaction and decompose depending on the conditions, but amino acids are even more easily decomposed.

Therefore, in order to obtain free acids and alkalis by electrolyzing organic acid salts, Podamer's proposal (Special Publication Publication No. 30-S61S) was proposed.
Accordingly, it has been thought that it is necessary to use a so-called royal method electrolytic cell in which two cation exchange membranes are provided as a diaphragm between a cathode and an anode. In this method, an aqueous solution of mineral acid is passed through the anode chamber, an aqueous solution of alkali hydroxide is passed through the cathode chamber, and an alkali metal salt of an organic acid is placed in an intermediate chamber separated from both electrodes by two cation exchange membranes. Electrolysis is performed by circulating an aqueous solution. According to this method, the organic acid and its salt do not come into contact with the anode, and therefore the organic acid is not lost due to the anodic reaction. It has already been confirmed by the present inventors that this method can also be used for the purpose of obtaining amino acid salts, diamino acids, and alkali hydroxides (1% Publication No. 58-000755). However, in this royal method electrolysis, two sheets of Since the current must be passed across the ion exchange membrane and the three liquid chambers,
The voltage required for electrolysis is high, which results in large power consumption. Furthermore, since the structure of the electrolytic cell is complicated, the equipment cost is also high. The present inventors have determined that there are conditions under which decomposition of amino acids does not occur even when electrolysis is performed using a so-called two-base electrolytic cell that uses only one ion exchange membrane, and that such conditions can be maintained. We thought that there might be a way to maintain and operate the vehicle, and as a result of extensive research, we were able to arrive at the present invention. This will be explained in detail below with reference to FIG.

The unit cell constituting the electrolyzer used in the method of the present invention has a cation exchange membrane 3 between an anode 1 and a cathode 2.
By providing the anode chamber 4 and the cathode chamber 5, the anode chamber 4 and the cathode chamber 5 are isolated. An aqueous solution containing amino acids and their alkali metal salts as anolyte A is passed through the anode chamber of each cell. The anolyte may also contain an acid stronger than the amino acid, such as an organic acid such as acetic acid, a mineral acid such as sulfuric acid, or an alkali metal salt of these acids. The anolyte is dry unless it has a composition such that 72H is 9.5 or less. Also, the alkali metal ion concentration CM in the anode
It is desirable that the composition be such that the ratio [M]/[H] of hydrogen ion concentration CH] is greater than 50. An aqueous solution of an alkali metal hydroxide is passed through the cathode chamber as a catholyte C. The alkali hydroxide used here is preferably an alkali metal hydroxide constituting the amino acid salt as a raw material.

When a direct current is applied between the two electrodes while circulating such a bipolar liquid, oxygen and hydrogen ions are generated by water decomposition at the anode. Hydrogen ions replace alkali metal ions in amino acid salts to yield amino acids. The liberated alkali metal ions pass through the cation exchange membrane and move to the cathode chamber. After leaving the anode chamber together with the anolyte, oxygen is separated from the anolyte in the gas-liquid separator 6 and pumped out of the system.

The anolyte separated from oxygen is circulated to the anode chamber. At the cathode, water decomposition produces hydroxide ions and hydrogen.

The hydroxide ions form alkali hydroxide together with the alkali metal ions that have migrated from the anode chamber. After hydrogen leaves the catholyte together with the catholyte, it is separated from the catholyte in the gas-liquid separator 7 and pumped out of the system.

The catholyte separated from hydrogen is circulated to the cathode chamber.

When electrolysis is continued in this manner, the amino acid salt in the anolyte is gradually converted to an amino acid, and the alkali metal ion concentration [M+] of the anolyte decreases, and at the same time, the pH decreases. That is, the hydrogen ion concentration + CM ) increases. There the pH and preferably C
A new aqueous solution F (hereinafter referred to as stock solution) containing an amino acid salt as a raw material is added to the anolyte so that M )/(ff'') is maintained within the range specified above.

As a result, the amount of anolyte increases, leaving the amount necessary for circulation and discharging the excess as ion exchange fluid E.

It is desirable to perform the operations of adding the stock solution and draining the ion exchange solution continuously, but if the capacity of the anolyte circulation route is large or if a storage tank is installed in the route, it is desirable to perform the operations intermittently. You can also do that.

On the other hand, in the cathode chamber, water is lost by the cathode reaction and at the same time alkali hydroxide is produced, so water is added to the catholyte so as to maintain an appropriate alkali hydroxide concentration. As a result, the amount of catholyte increases, and the excess amount is taken out of the system as recovered alkali R, leaving only the amount necessary for circulation. The obtained recovered alkali can be used again in a reaction step, etc., as it is or after being concentrated. The alkali hydroxide concentration in the catholyte is determined by considering the performance of the ion exchange membrane and the use of the recovered alkali, but it should be at least 0.5 in order to have sufficient conductivity.
It is desirable that the number is N or more.

Generally, an aqueous solution of a neutral amino acid alkali salt has a p of 11 or more.
Indicates H. When this is ion-exchanged, the pH decreases as the proportion of free amino acids increases. However, 'I'
If the anode is brought into contact with a high H content, amino acids are likely to be decomposed as described above. Even if the loss of amino acids due to decomposition is small, undesirable results such as coloring of the liquid or generation of off-flavors occur.

In contrast, in the method of the present invention, the pH of the anolyte is constantly maintained at 9.5 by adding a high-pH stock solution to the anolyte that is being circulated at a relatively large flow rate as electrolysis progresses.
The first feature is that electrolysis is performed while maintaining the following conditions. The inventors of Moto discovered through repeated research that by doing this, the decomposition of amino acids can be stopped to a negligible level. For example, when a current equivalent to the amount of glycine present is passed through an aqueous solution containing sodium glycine and glycine in various proportions, the relationship between the pH of the solution and the decomposition loss rate of glycine is as shown in Figure 2. l), 73
The loss rate rises rapidly above H9.5. Of course, the degree of decomposition varies depending on the type of amino acid, the type of anode used, current density, coexisting substances, etc., but since the influence of pH is overwhelmingly large, the limit value of pH = 9.5 can be used as a rough guide. It holds true universally. However, the pH
The lower the pH, the more stable the amino acid is, so it is desirable to maintain the pH as low as possible under other conditions. By this method almost all alkali metal salts of neutral amino acids can be electrolyzed. However, amino acids with thioether bonds, such as methionine,
Even if the pH is lowered, the present invention cannot be applied because it easily decomposes and causes non-negligible loss.

Since the ion exchange solution obtained by the method of the present invention is a part of the anolyte, it has the same pH as the anolyte.
is 9.5 or less. Therefore, most of the amino acids contained in the ion exchange solution are free amino acids, and only a small proportion are in the form of salts. This ratio is determined by the pH, but for example, the pH of an aqueous solution containing sodium α-alanine and α-alanine in a ratio of 1:4.1:9.1:99 at room temperature is 9.5.
9.07, a04. Of course, these values may differ somewhat if other electrolytes coexist. The isoelectric point pH of neutral amino acids is about 6, but as this example shows, most amino acids become free amino acids in a wide range of pH around 1. From the ion exchange solution in which most of the amino acid salts supplied in this manner have been converted into free amino acids, amino acids can be easily separated by methods such as concentration and crystallization. At this time, the unconverted amino acid salt remains in the mother liquor, and can be recovered by adding it to the stock solution and electrolyzing it again. However, it may be easier to operate the crystallization process table if the conversion rate to free amino acids is extremely high by operating at a pH as close to the isoelectric point as possible.

When electrolysis is carried out on an industrial scale, a large electrolyzer is required unless the electrolyzer is operated at a current density above a certain level, resulting in an excessive investment in equipment. In the case of amino acids handled in the present invention, at least 10 A/d,
It is desirable to operate at a current density of 15 A/d Bi or more if possible. However, when an aqueous solution containing only amino acids and their alkali metal salts is operated at a high current density while maintaining the pH l1c required by the method of the present invention, the electrolytic voltage often becomes too high. This is especially the case when operating at a low pH of 11C in order to obtain a high conversion rate. This is because aqueous solutions of amino acid salts exhibit relatively high conductivity, whereas aqueous amino acid solutions have extremely low conductivity. In order to perform electrolysis efficiently and economically, it is necessary to maintain high conductivity of the anolyte during operation, and for this purpose it is effective to coexist with another electrolyte as a supporting electrolyte. As the supporting electrolyte, for example, an acid stronger than the amino acid, such as acetic acid, iminodicarboxylic acid, phosphoric acid, or sulfuric acid, or an alkali metal salt thereof can be used. It is desirable that the alkali metal ions contained in the supporting electrolyte be the same as those constituting the raw material amino acid salt. Otherwise, the recovered alkali hydroxide appears as a mixture of two types of alkali hydroxides. Of course, salts of different alkali metals may be used as supporting electrolytes if such mixtures are available.

By the way, for example, in an amino acid alkali metal salt solution obtained by alkaline hydrolysis of aminonitrile produced by the reaction of aldehyde cyanohydrin and ammonia, a small amount of the corresponding alkali metal salt of iminodicarboxylic acid is usually contained as a by-product. However, it satisfies the above-mentioned conditions as a supporting electrolyte.

If such impurities are allowed to coexist as they are and electrolyzed, they will function as a supporting electrolyte. However, this alone is rarely sufficient, and it is often better to add other supporting electrolytes.

The additional supporting electrolyte is preferably one that is stable when in contact with the anode, such as sulfuric acid, phosphoric acid, and alkali metal salts thereof.

In the anolyte containing the supporting electrolyte, if the pH is higher than the isoelectric point of the amino acid, the amino acid salt is preferentially ion-exchanged and converted to the amino acid by electrolysis, and the supporting electrolyte remains as a salt. The pH of the anolyte containing the supporting electrolyte can be below the isoelectric point of the amino acid. In this case, all the amino acids have been converted to free amino acids, so part of the supporting electrolyte is electrolyzed to produce acid in the anolyte and alkali hydroxide in the catholyte. This acid then removes dialkali metal ions from the newly added amino acid salt in the stock solution, converts it into salt again, and liberates the amino acid, resulting in the smooth production of free amino acids and alkali hydroxide. Proceed to.

Moreover, since amino acids are not negatively charged at all at pg lower than the isoelectric point, there is even less possibility that the amino acids will reach the anode and be decomposed.

However, the pH becomes too low and the ratio of alkali metal ion concentration [M] to hydrogen ion concentration [H] is CM ]/C
As H) becomes smaller, hydrogen ions with higher conductivity permeate the cation exchange membrane and move to the cathode chamber, resulting in a larger proportion of current flowing. Since this current is a reactive current that does not contribute to the purpose of the present invention, as its proportion increases, the current efficiency of electrolysis decreases. This is likely to occur when a strong acid or a salt of a strong acid is used as the supporting electrolyte. As a result of studying many systems, the present inventors found that
It has been found that by adjusting the composition of the anolyte so as to maintain a large value of CM ]/CH), it is possible to prevent a decrease in current efficiency due to this cause. According to the findings of the present inventors, it is desirable to keep the value of CM )/[I ] at least 50, preferably 200 or more. For example, at pH 5, [H)=0.001&, so in order to maintain high current efficiency in this case, it is desirable that [M] be 0.2M or more. Furthermore, when 7)H in the anolyte becomes lower than the isoelectric point of the amino acids, some of the amino acids become positively charged and try to move to the cathode chamber. The amino acids transferred to the catholyte chamber are used as the catholyte (if the obtained alkali is reused in the reaction process, it will be recovered, so it will not be lost, but it will make process management more complicated.The amount of amino acids permeated is determined by its molecular weight. The selection of the membrane is important because it depends on the amount of electricity and the type of membrane.However, it is also effective to maintain a large value of CM]/CH] in order to reduce the movement of amino acids in proportion to the amount of current applied.

The higher the concentration of the amino acid, amino acid salt, and supporting electrolyte in the anolyte, the higher the conductivity of the solution, which is preferable, but is subject to solubility limitations. Additionally, in general, the solubility of amino acids increases greatly by increasing the temperature, and even for solutions with the same concentration, the higher the temperature, the higher the electrical conductivity. This is desirable.

Although the higher the concentration of the supporting electrolyte is to a certain extent, the higher the effect of lowering the electrolytic voltage, the higher the concentration of the supporting electrolyte, the greater the effect of lowering the electrolytic voltage, but this may make it difficult to operate the step of separating diamino acids from the obtained ion exchange solution.

Even so, since the effect of reducing the electrolytic power obtained by adding a supporting electrolyte is significant, it is sometimes desirable to perform electrolysis in the presence of a supporting electrolyte in an amount equivalent to or greater than that of the amino acid. This is especially the case when dealing with amino acids with low solubility. Even from an ion exchange solution containing a large amount of supporting electrolyte, highly pure amino acids can be obtained by repeating fractional crystallization or desalting by electrodialysis before crystallization. I can do it. Most of the supporting electrolyte can be recovered and reused as a solid or solution through fractional crystallization or electrodialysis steps. Of course, if an inexpensive salt or the like is used as the supporting electrolyte, it may be necessary to collect it. Taking all these into consideration, the optimum supporting electrolyte concentration is determined, which is usually in the range of Ll-AO#.

Generally, the pH of an aqueous solution of an alkali metal salt of a neutral amino acid is 1.
1 or more, whereas in the method of the present invention, the pH of the anolyte is limited to 9.5 or less. It is not possible to perform so-called batch circulation operation in which electrolysis is performed while circulating until a predetermined conversion rate is reached.

When electrolyzing a large amount of alkali amino acid salts using the method of the present invention, normally the stock solution F is added to the anolyte circulation system as shown in Figure 1.
It must be operated using the so-called partial circulation method, in which the excess circulating fluid is taken out as ion exchange fluid while supplying ion exchange fluid. When a supporting electrolyte is used, it may be added to the stock solution in advance, or it may be added alone to the anolyte circulation system. The supply amount of the stock solution and supporting electrolyte is such that the pH of the anolyte is always 9.5 or less and preferably (
f'')/(H] is 50 or more, more preferably 20
As already mentioned, it must be adjusted so that it is 0 or more. In order to confirm the value of CM)/[H], it can be estimated from the measured values of pH and conductivity by obtaining data in advance for the system to be handled, without having to perform analysis each time. Further, the conductivity can also be estimated from the relationship between current density and electrolytic voltage. especially,
If the ratio of supplied amino acid salt and supporting electrolyte is fixed, the value of [M]/+CH) can be determined from the pH value alone. In this way, process control for maintaining the conditions required by the present invention is easy.

In addition, if the pH of the anolyte is varied within an allowable range by providing a storage tank on the circulation path or by intermittently supplying the stock solution,
Alternatively, it is also possible to mix part of the ion exchange solution and the stock solution in a separate storage tank and supply it to the circulation system in a large diameter, but both of these can be considered as variations of the partial circulation method described above. .

It is desirable that both the anolyte and catholyte be circulated at as large a flow rate as possible in order to prevent an increase in electrical resistance due to the shielding effect of bubbles generated from the electrode surface. Circulation flow rate is current amount iA
It is desirable that the H value is 0.517 or more. Of course, by devising the structure of the cell so that convective circulation and gas-liquid separation take place inside the anode chamber, the apparent amount of circulation through the external path can be slightly reduced, but even in this case, the amount of gas that exists inside the anode chamber The apparent circulation rate must be determined in such a way that the anolyte is kept within the above-mentioned conditions for pH and + CM :l/[:H].

As the anode of the electrolyzer used in the method of the present invention, it is desirable to use an electrode with low overvoltage during oxygen generation. Titanium whose surface is coated with a catalyst layer containing iridium oxide as the main component is suitable. Suitable cation exchange membranes include Noguichi 70 carbon type cation exchange membranes, such as those commercially available under the trade name Nafion. Many metals can be used as the cathode, but nickel-plated iron is the cheapest and has the best performance.

A technique for assembling a large number of cells having such a configuration to produce an apparatus capable of performing electrolysis on an industrial scale has already been established in the field of salt electrolysis.

Furthermore, the so-called SPE electrolysis method, in which electrolysis is carried out by integrating a porous anode, cathode, or both with a cation exchange membrane and flowing an electrolyte behind it, can also be carried out under exactly the same operating conditions as described above. However, materials that can be used for industrial-scale electrolysis are not yet commercially available, and further development is expected.

To summarize the above explanation, the present invention (1) electrolyzes amino acids by adding an aqueous solution containing an amino acid alkali metal salt to the circulation system of the anolyte maintained at a pH lower than 9.5. (2) By coexisting a supporting electrolyte in the anolyte, it is possible to convert amino acid salts into amino acids with negligible decomposition. (3) However, the ratio of the alkali metal ion concentration CM ] to the hydrogen ion concentration [H+] in the anolyte CM )/
It has been clarified that it is desirable to prevent a decrease in current efficiency and the movement of amino acids to the cathode chamber by setting [H] to 50 or more, more preferably 200 or more. The effects of these conditions and their combination were newly discovered by the present inventors, and as a result, the electrolysis of amino acid alkali metal salts, which was previously thought to be possible only by using a Royal Law electrolyzer, has become possible. It is of great significance that the production of free amino acids by ion exchange can now be carried out at lower voltages using simpler and cheaper two-base electrolyzers.

Next, embodiments of the present invention and its effects will be explained in more detail by giving examples. In addition, in the following examples and comparative examples, a titanium plate coated with iridium oxide was used as an anode, iron plated with nickel was used as a cathode,
Experiments were conducted using an electrolysis cell with an effective cross-sectional area of 1 dbi using Nafion 315 (trade name, manufactured by DuPont) or Nafion 901 (trade name, manufactured by DuPont) as a cation exchange membrane.

Example 1 and Comparative Example 1 By adding a 2M α-alanine aqueous solution to a 2M α-alanine sodium aqueous solution, the α-alanine sodium/α-alanine ratio was reduced to Ilo > 1/1.1, respectively.
15.1/9.1/19 A 5S aqueous solution prepared to give 1/19 was used as the anolyte, and a 2N aqueous solution of sodium hydroxide was used as the catholyte. DC current was applied at a voltage of 4 V while circulating while maintaining the temperature at 60°C. Then, electrolytic ion exchange was performed until the pH of the anolyte became approximately 7.0. The cation exchange membrane used was Nafion 31.
It is 5. Recovery rate of alanine in the anolyte solution determined by analysis of the anolyte solution and catholyte solution after electrolysis, permeation rate of alanine into the catholyte solution, total recovery rate of both, and FH% of the anolyte solution before electrolysis. Table 1 shows the properties of the anolyte after electrolysis.

It can be seen that when a solution with a pH exceeding 9.5 is electrolyzed, loss of alanine due to decomposition, coloring of the solution, and generation of off-odor become noticeable.

Example 2 An aqueous solution containing α-alanine sodium collected from the α-alanine manufacturing process (α-alanine root concentration 2.1 M
) to which sodium sulfate was added as a supporting electrolyte so that the equivalent ratio to the alanine root was α2 was used as a stock solution. The concentration of sodium sulfate in the stock solution is approximately 0.42N. A portion of the stock solution was subjected to electrolytic ion exchange using a royal method electrolysis cell until the pH reached 6. 1 liter was charged to the anolyte circulation tank of the dual method electrolysis cell, and a 2N aqueous sodium hydroxide solution was added to the catholyte circulation tank. I prepared it. 6 bipolar fluids
While maintaining the temperature at 0°C and circulating the anolyte with a pump and passing a DC current of 15.4 (current density 15.4/dm), the pH of the anolyte was 6-6.
The stock solution was supplied to maintain a range of 7. The cation exchange membrane used was Sufion 315. After supplying 9 liters of the stock solution, the entire amount of the anolyte and catholyte was collected and analyzed. The cell voltage was 4.7 V, the current efficiency (calculated from the amount of recovered sodium hydroxide) was 82%, and the recovery rate of alanine was 99% in the anolyte and 1% in the catholyte, for a total of 100%.

Example 3 Electrolysis was carried out using the same azinine aqueous solution as used in Example 2, without adding a supporting electrolyte, and in the same manner as in Example 2 except for the addition of a supporting electrolyte. The cell voltage was 98V, the current efficiency was 80%, and the alanine recovery rate was 99% in the anolyte and 1% in the catholyte, for a total of 100%.

Although no decomposition loss of alanine was observed in both Examples 2 and 3,
By comparing the cell voltages of the two, the effect of sulfuric acid (IJ) added as a supporting electrolyte can be clearly seen.

Example 4 A stock solution was prepared by adding sodium sulfate as a supporting electrolyte to a 3M sodium glycine aqueous solution at an equivalent ratio of 0.5 to the glycine root. The sodium sulfate concentration in the stock solution is approximately 0.2N. Separately, prepare a pH 6 aqueous solution with the same concentrations of glycine and sodium sulfate as the original solution, and charge it into an anolyte circulation tank equipped with oats-fluorocarbons, and a 2N aqueous sodium hydroxide solution into the anode solution circulation tank. is. The bipolar liquid is kept at 70℃ and circulated with a pump.
DC current 20A (current density 20A/dm”)
The stock solution was supplied so that the pH of the anolyte was maintained within the range of 6-7, and the overflowing anolyte was recovered as an ion exchange solution. The cation exchange membrane used was Sufion 901. The cell voltage was 4.4 V, the current efficiency was 95%, and the glycine recovery rate was 90% in the anolyte and 9% in the catholyte, for a total of 99%.

Comparative Example 2 An ion exchange solution was obtained in the same manner as in Example 4, except that the pH of the anolyte was maintained at 115. The cell voltage was 4.2 V, the current efficiency was 95%, and the glycine recovery rate was 97% in the anolyte and 0% in the catholyte, for a total of 97%. The ion exchange rate of the ion exchange solution was 40%, and the ratio of lost glycine to liberated glycine was 15%.

Example 5 A solution in which sodium sulfate was added as a supporting electrolyte to a 0.12M sodium phenylalanine aqueous solution at an equivalent ratio of 2 to phenylalanine roots (the concentration of sodium sulfate in solution i was (L24A') was used as the stock solution, and An aqueous solution with the same concentration of phenylalanine and sodium sulfate as the original solution and a pH of 6 was prepared as the initial anolyte, and the operation was the same as in Example 4 except that a direct current of 15 A was passed.The cell voltage was 5.2 V, and the current efficiency was was 84%, and the recovery rate of phenylalanine in the anolyte was 100%.

[Brief explanation of drawings]

FIG. 1 is a conceptual diagram of an example of an electrolysis device used in the present invention. FIG. 2 shows the relationship between the pH of an aqueous glycine solution and the loss rate due to electrolysis. In Figure 1, 1 is an anode, 2 is a cathode, 6 is a cation exchange membrane, 4 is an anode chamber, 5 is a cathode chamber, 6 and 7 are gas-liquid separators, A is an anolyte, C is a catholyte, F is stock solution, E is ion exchange solution, R is recovered alkaline earth metal pH (i group)

Claims (1)

[Claims] 1. An amino acid having one amino group and one carboxyl group in the anolyte that circulates through the anode chamber of an electrolytic cell equipped with a single cation exchange membrane as a diaphragm between the anode and cathode. an alkali metal salt or its aqueous solution is added, and while an aqueous solution of alkali metal hydroxide is passed through the cathode chamber as the catholyte, free amino acids are generated in the anolyte by passing a direct current between the two electrodes. Additionally, a method for obtaining free amino acids from amino acid alkali metal salts, which comprises maintaining the pH of the anolyte at 9.5 or less when obtaining the alkali metal hydroxide in the catholyte. 2. The method according to claim 1, which is carried out by maintaining the pH of the anolyte at 9.0 or less. 3. The method according to any one of claims 1 and 2, which is carried out in the presence of an acid stronger than the amino acid or an alkali metal salt thereof as a supporting electrolyte in the anolyte. 4. The method according to claim 3, wherein the concentration of the supporting electrolyte in the anolyte is 0.1-3.0N. 5. The method according to any one of claims 3 and 4, wherein the supporting electrolyte is sulfuric acid or a sulfate. 6. Claims 3 to 6 are carried out by maintaining the ratio [M^+]/[H^+] of alkali metal ion concentration [M^+] and hydrogen ion concentration [H^+] in the anolyte at 50 or more. 5. The method according to any one of 5. 7. The method according to any one of claims 1 to 6, wherein the amino acid does not contain a thioether group. 8. The method according to any one of claims 1 to 6, wherein the amino acid is glycine, α-alanine, β-alanine, or α-phenylalanine.