JPH06170174A - Selective separation of amino acid and separation and concentration of aqueous amino acid solution by use of porous glass film - Google Patents

Abstract

PURPOSE:To selectively separate amino acid and to separate and concentrate an aqueous amino acid soln. with excellent separation accuracy, separation stability and separation efficiency. CONSTITUTION:After the pH of a aqueous soln. containing two or more kinds of amino acids having different isoelectric points is adjusted to the falue between the isoelectric points of amino acids, the aqueous soln. is transmitted through a porous glass film having negative charge to selectively separate amino acids. An aqueous amino acid soln. is separated and concentrated using the porous glass film.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for selectively separating amino acids using a porous glass membrane and a method for separating and concentrating an amino acid aqueous solution.

[0002]

2. Description of the Related Art Amino acids are extremely important substances industrially. For example, in the food industry, L-sodium glutamate is used as a raw material for chemical seasonings and processed foods, or in the medical field L- is an essential amino acid component. Tryptophan, L-isoleucine and the like are widely used as nutritional supplements. These amino acids are mainly produced in large quantities by fermentation, but the treatment of waste liquid containing low-concentration amino acids by-produced during this production process is effective in separating and recovering useful amino acids and reducing pollutants in the waste liquid. , With extremely important significance.

As a general separation / purification method which has been conventionally performed, there are methods such as dissolution, crystallization and distillation, but these methods have many problems in terms of separation performance and efficiency. Therefore, in order to solve these problems, a separation technique using a functional separation membrane has been proposed. Further, such a separation membrane enables highly accurate separation operation, and the separation technique has made remarkable progress in the fields of ultrafiltration and microfiltration in recent years.

However, even if it is called a functional separation membrane, the principle of the separation merely utilizes the "sieving effect", and therefore the particles to be separated have the same particle size. If so, it was not possible to separate them, and the separation ability of the functional separation membrane was naturally limited. Therefore, as a means for solving this problem, a separation method using a charged polymer membrane has also been proposed. This method imparts a positive or negative charge to the surface of the organic polymer film, and causes an electrical interaction (charge effect) between the film and the electrostatic force peculiar to the substance existing on the surface of the particle.
Is used to separate charged substances.

However, this organic polymer film has various problems due to the material of the film. That is: (1) It is extremely difficult to uniformly control the pore size of the membrane.

(2) Since the membrane itself is thermally unstable, stable separation performance cannot be exhibited in a high temperature range.

(3) The chemical modification method for imparting charge to the film surface is complicated and laborious.

(4) Durability and corrosion resistance are relatively low.

In particular, the above problem (1) hinders improvement of separation accuracy, and the above problems (2), (3) and (4) cause reduction of separation efficiency at high temperature. Is.

Therefore, at present, there is a strong demand for the development of a new separation technique capable of solving these problems.

[0011]

The present invention solves the above-mentioned drawbacks of the separation method using an organic polymer membrane, and provides a method for selective separation of amino acids, which is excellent in separation accuracy, separation stability, separation efficiency, etc. An object is to provide a method for separating and concentrating.

[0012] In view of the above problems, the present inventor diligently studied the effective separation method for amino acids, and as a result, utilizes the isoelectric point of amino acids and simultaneously separates amino acids using a porous glass membrane as a separation membrane. in case of,
The present inventors have completed the present invention by discovering that amino acids can be selectively separated relatively easily and reliably.

That is, the present invention is: Selection of amino acids by adjusting the pH of an aqueous solution containing two or more amino acids having different isoelectric points between the isoelectric points of the amino acids and then allowing the aqueous solution to pass through a porous glass membrane having a negative charge. A method for selectively separating amino acids using a porous glass membrane, which comprises performing separation, and 2.1. Adjusting the pH of an aqueous solution containing one kind of amino acid to be equal to or higher than the isoelectric point of the amino acid, and then making the aqueous solution negative. The present invention relates to a method for separating and concentrating an amino acid aqueous solution, which comprises increasing the amino acid concentration of the aqueous solution by permeating it through a porous glass membrane having the above-mentioned charge.

The present invention will be described in detail below.

As the porous glass membrane used in the present invention, known ones can be used. For example, the porous glass having CaO—B ₂ O ₃ —SiO ₂ —Al ₂ O ₃ system disclosed in Japanese Patent No. 1504002 as a mother glass is used. Quality glass, Patent No. 1518989
CaO-B ₂ O is disclosed in US ₃ -SiO ₂ -Al ₂ O
Porous glass or C containing _3- Na ₂ O as a mother glass
The _{aO-B 2 O 3 -SiO 2} -Al 2 O 3 -MgO based include those with film-like body a porous glass or the like for the mother glass. Membranes made of these porous glasses utilize microphase separation of glass, and the pore diameter can be widely controlled by changing the conditions of such phase separation. Further, since the membrane made of the porous glass as described above has a skeleton made of durable glass itself, it is excellent in high temperature stability, mechanical strength and the like, and the surface of the membrane body is compared by the presence of silanol groups. Have a strong negative charge. In particular, it has superior characteristics to ceramics membranes in terms of uniformity of pore size, charging power on the membrane surface, etc.
Therefore, it can be said that the porous glass membrane is extremely advantageous for charge-type membrane separation.

Further, the porous glass preferably has the following characteristics as the separation membrane of the present invention.
That is; (a) Pore diameter is 20 to 500 nm, preferably 30 to 6
Must be 0 nm.

(B) The film itself has a negative charge, and pH = 2.
The zeta potential is -20 to -80 mV at ~ 9.

(C) Stable separation performance is exhibited even in the temperature range of 50 to 100 ° C., and performance is not deteriorated even at a high temperature near 100 ° C.

(D) It has excellent corrosion resistance and chemical resistance that is not attacked by acid or weak alkali.

(E) It should be highly durable and have sufficient mechanical strength (radial crushing strength of about 300 to 700 kg / cm ² ) so that the membrane will not be broken even if the pressure required for separation is taken for a long time.

The above-mentioned porous glass film can be used as it is as a film having a negative charge, or the surface thereof can be chemically modified with a functional group having a negative or positive charge to reinforce the negative charge. Alternatively, it can be used in a state where the charge of the film is modified to a positive charge. As a method of reinforcing with a negative charge, for example, there is a method of reacting a silanol group with a silane coupling agent having a benzene ring and then introducing a sulfone group into the benzene ring. On the other hand,
Examples of the method of reforming to a positive charge include a method of reacting a silanol group with a silane coupling agent to introduce an amino group.

Next, as a method for separating amino acids by the above-mentioned porous glass membrane, first, the amino acids are dissolved in a suitable solvent such as water, and the pH is adjusted in consideration of the isoelectric point of the amino acids. Since amino acids are amphoteric electrolytes, each has a unique isoelectric point depending on the type of amino acid. Therefore, in the aqueous solution, the amino acid becomes an anion when the pH is higher than the isoelectric point and becomes a cation when the pH is lower than the isoelectric point. Therefore, in a multi-component amino acid aqueous solution, the sign of the charge and the charge amount of each amino acid can be adjusted appropriately by changing the pH. pH
For the adjustment of, a commonly used hydrochloric acid, aqueous sodium hydroxide solution or the like may be used.

Next, the amino acid solution is passed through the porous glass membrane. In this case, the permeation method may be a conventional method, for example, a known method such as a dead end method using a porous glass membrane or a cross flow method can be adopted.
Further, the permeation conditions vary depending on the membrane charge amount of the porous glass membrane, the pore diameter of the membrane, other kinds of amino acids, the desired rejection rate (separation accuracy), etc. 1000 ppm, pressure 20-100
It is carried out in a range of about kPa, a linear velocity of about 0.5 to 2.0 m · s ⁻¹ and a temperature of about 20 to 95 ° C.

By this operation, the amino acid ionized by the anion is electrically repulsed by the negative charge of the porous glass membrane and the membrane permeation is blocked. On the other hand, an amino acid ionized by a cation or an amino acid at the isoelectric point is not affected by electric repulsion, and therefore can pass through the membrane as it is. For example,
When selective separation of a binary amino acid mixture is performed, the pH can be adjusted by adjusting the pH between the isoelectric points of both amino acids.
Amino acids having an isoelectric point lower than H are blocked from permeating the membrane by ionizing anions, and amino acids having an isoelectric point higher than the pH permeate the membrane, so that both can be selectively separated. In addition, 100 times the above-mentioned ions in one operation
If the% blocking cannot be achieved, the blocking rate can be further increased by repeating the same operation as described above. Also,
By raising the temperature of the solution to around 100 ° C., it is possible to reduce its viscosity and increase the membrane permeation flux. In this case, since the thickness of the electric double layer on the film surface and the surface of the charged particles also increases with temperature, the transmittance can be increased without decreasing the blocking rate.

Further, by adjusting the pH of an aqueous solution containing one kind of amino acid to be equal to or higher than the isoelectric point of the amino acid and carrying out membrane permeation by the same operation as the above-mentioned selective separation,
Concentration of the amino acid aqueous solution can be suitably performed. This method is extremely useful in treating waste liquid containing low concentrations of amino acids. Even in the case of this method, the concentration of amino acid can be further increased by repeating membrane permeation.

[0026]

According to the present invention, the following remarkable effects are brought about.

1) The porous glass membrane used in the present invention is
Even if the membrane is not charged as in the organic polymer membrane, it has a sufficient negative charge as it is, so that amino acids can be efficiently and selectively separated or concentrated.

2) Further, since the porous glass membrane is excellent in heat resistance, it can be selectively separated even at high temperature. For this reason, the membrane can be permeated in a state where the viscosity of the solution is low, whereby a permeation flux about three times that at room temperature can be obtained, and excellent separation accuracy and separation efficiency can be achieved at the same time.

3) If the separation is performed at a high temperature, it is possible to prevent bacteria from invading and contaminating the process. Also,
Since the membrane module can be steam sterilized, it has excellent sanitary properties.

4) The amino acid aqueous solution to be separated does not require any complicated operation except adjustment of pH, and the amino acids can be separated relatively easily and reliably.

5) The method of the present invention can be applied not only to separation of ampholytes such as various proteins and peptides, but also to selective separation or concentration of other charged molecules or fine particles.

[0032]

EXAMPLES Examples and comparative examples will be shown below to further clarify the characteristics of the present invention.

Example 1 Using a porous glass membrane, the pH of an amino acid mixture of L-glutamic acid and L-isoleucine was adjusted to 9.1 to 3.
While changing to 2, L-glutamic acid was selectively separated.

As the porous glass film, Japanese Patent No. 1518
S produced according to the production method disclosed in No. 989.
A cylindrical porous glass membrane (outer diameter 5 mm, wall thickness 0.5 mm, length 210 mm) based on iO ₂ —Al ₂ O ₃ —B ₂ O ₃ —Na ₂ O—CaO system and having an average pore diameter of 50 nm was used. .
The concentration of the amino acid stock solution is L-glutamic acid and L-
All isoleucine was 100 ppm. Undiluted p
For the adjustment of H, 1N hydrochloric acid aqueous solution and 1N caustic soda aqueous solution were used.

As the membrane separation device, a device as shown in FIG. 1 was used, with a pressure of 54 kPa, a linear velocity of 0.7 m.s ^-1 and a temperature of 2.
FIG. 2 shows changes with time in the permeation flux of the solution and the rejection rate of the amino acid when the membrane was permeated while changing the pH from 9.1 to 3.2 under the condition of 0 ° C.

From these results, at pH 9.1, both L-glutamic acid and L-isoleucine ionize into anions, so that a repulsive effect due to charge was observed and the blocking rate was increased. Next, when the pH was adjusted to 5.9, L-glutamic acid ionized into anions was blocked from permeating the membrane due to the repulsive effect of charge with the negatively charged porous glass membrane.
Since L-isoleucine had an isoelectric point, its permeation was not blocked. Furthermore, at pH 3.2, L-glutamic acid had an isoelectric point, and L-isoleucine was ionized into cations, so no charge repulsion effect was observed.

As described above, it was possible to selectively separate the desired amino acid by adjusting the pH appropriately.

Example 2 Example 1 except that the pH was changed from 3.2 to 9.1.
L-glutamic acid and L using a porous glass membrane similarly to
-L-glutamic acid was selectively separated from the mixture with isoleucine.

As in Example 1, at pH 3.2, L-glutamic acid has an isoelectric point and L-isoleucine is ionized into cations, so that the repulsive effect of charge is not observed.
Next, at pH 5.9, L-glutamic acid ionized by anions was blocked from permeating the membrane due to the repulsive effect of charge with the negatively charged porous glass membrane, whereas L-isoleucine has an isoelectric point. So it wasn't stopped. Further pH
At 9.1, both amino acids were ionized to anions, so that a repulsion effect due to charge was observed and the blocking rate was increased.

In this case, the inhibition rate values at pH 5.9 and pH 9.1 are different from those in Example 1, but the amounts of hydrochloric acid and caustic soda required for pH adjustment are different from those in Example 1. This is because it was affected by the coexisting salt concentration.

Example 3 When separating and concentrating L-glutamic acid from an L-glutamic acid solution, changes in permeation flux and rejection of the solution with temperature were examined.

The concentration of the L-glutamic acid solution is 100 pp.
m, and the same porous glass membrane and device as in Example 1 were used. Moreover, the pressure is 54 kPa and the linear velocity is 0.7 m · s.
Under the condition of ^-1, the membrane was permeated while changing the permeation flux by changing the temperature from 20 ° C to 95 ° C. The results are shown in Table 4.

As a result, when the temperature was raised, the viscosity of the solution was lowered and the permeation flux was significantly increased, but the rejection rate was 9%.
The value did not decrease even at a high temperature of 5 ° C. and maintained a substantially constant value.

From the above, it can be seen that the separation efficiency can be improved by raising the temperature of the permeating solution.

Example 4 L-glutamic acid was separated by changing the pore size of the porous glass membrane.

As the porous glass film, Japanese Patent No. 1518
S produced according to the production method disclosed in No. 989.
A cylindrical porous glass membrane (outer diameter 5 mm, wall thickness 0.5 mm, length 210 mm) based on iO ₂ —Al ₂ O ₃ —B ₂ O ₃ —Na ₂ O—CaO system and having an average pore diameter of 100 nm was used. . The same membrane separation device as in Example 1 was used, and the pressure was 54
kPa, linear velocity 0.7 m · s ⁻¹ , pH 6.3 and temperature 2
When the membrane separation was performed at 0 ° C, the rejection rate was 25
Was 30%.

From this, it can be seen that as the pore diameter of the porous glass membrane becomes larger, its rejection rate decreases.

[Brief description of drawings]

FIG. 1 is an example of a separation apparatus for carrying out the present invention.

FIG. 2 is a graph showing liquid permeation flux and amino acid rejection in Example 1.

FIG. 3 is a graph showing liquid permeation flux and amino acid rejection in Example 2.

FIG. 4 is a graph showing the influence of temperature on the permeation flux of liquid and the rejection rate of glutamic acid in Example 3.

[Explanation of symbols]

 1 module 2 porous glass membrane 3 undiluted solution tank 4 pump 5 pressure gauge 6 line 7 pressure gauge 8 flow meter 9 line 10 thermostat 11 valve 12 valve

 ─────────────────────────────────────────────────── ─── Continued Front Page (72) Inventor Shinichi Nakao 4-13-14-203 Akatsuka, Itabashi-ku, Tokyo (72) Inventor Tadao Nakajima Miyajima Prefecture Miyazaki City 501 Oji Shioji (72) Inventor Masato Hisakizaki Miyazaki Prefecture 4-5-2 Ikimedahigashi, Miyazaki City (72) Inventor Masataka Shimizu 11074 Shimanouchi, Miyazaki, Miyazaki City, Miyazaki Prefecture

Claims (2)

[Claims] 1. A method for adjusting the pH of an aqueous solution containing two or more amino acids having different isoelectric points to the isoelectric point of each amino acid and then allowing the aqueous solution to permeate through a negatively charged porous glass membrane. A method for selectively separating amino acids using a porous glass membrane, characterized in that the amino acids are selectively separated. 2. The pH of an aqueous solution containing one kind of amino acid.
Is adjusted to the isoelectric point of the amino acid or higher, and then the aqueous solution is permeated through a negatively charged porous glass membrane to increase the amino acid concentration of the aqueous solution. .