Extraction method for fermenting polyglutamic acid based on glutamic acid isoelectric crystallization mother liquor

Abstract

The invention belongs to the technical field of polyglutamic acid extraction processes, and particularly relates to an extraction method for fermenting polyglutamic acid based on glutamic acid isoelectric crystallization mother liquor. According to the method, polyglutamic acid fermentation liquor based on glutamic acid isoelectric crystallization mother liquor is used as a raw material, on the basis of a graded salting-out extraction method, flocculants such as sodium polyacrylate are added, the flocculation capacity of polyglutamic acid is improved, cationic surfactants such as hexadecyl trimethyl ammonium chloride are added, the viscosity of a polyglutamic acid salting-out product is reduced, and the polyglutamic acid isoelectric crystallization mother liquor is obtained. And the polyglutamic acid is collected by using a pressurized dissolved air flotation technology, so that the loss in the polyglutamic acid extraction process is greatly reduced, and the bubble amount in the polyglutamic acid product is increased, thereby achieving the purposes of simplifying the polyglutamic acid extraction process, improving the extraction yield and reducing the drying energy consumption. The method is novel in process route and large in industrialization potential, and full-water-phase extraction of polyglutamic acid can be achieved.

Description

Technical Field

[0001] The invention belongs to the technical field of bio-based macromolecular compound extraction, and specifically relates to an extraction method for producing polyglutamic acid by fermentation using glutamic acid or other electrocrystallization mother liquor as a raw material. Background Art

[0002] Polyglutamic acid (γ-PGA) is a water-soluble polyamino acid produced by microbial fermentation. It has excellent water retention properties and plays a role in balancing soil pH, precipitating toxic heavy metals, enhancing plant disease resistance / stress resistance, and promoting crop yields in agricultural production.

[0003] Polyglutamic acid is mostly biosynthesized by microorganisms such as Bacillus licheniformis and Bacillus subtilis. Currently, most agricultural-grade polyglutamic acid products on sale are liquid products, namely polyglutamic acid fermentation broth, which is easy to deteriorate and degrade, and has significant problems such as poor stability and high storage and transportation costs. The industrial preparation method of polyglutamic acid powder products is mostly organic solvent precipitation method, which has significant problems such as large amount of organic solvent, low recovery rate, large equipment investment, complex process operation, high production cost, etc., making it difficult to promote the product. To this end, researchers began to try to use new polyglutamic acid extraction processes such as chemical precipitation, salting-out separation, and membrane filtration, but they were all limited by working conditions and cost factors, making it difficult to achieve industrial production.

[0004] There are documents that disclose the use of ammonium sulfate precipitation to produce polyglutamic acid, which avoids the defects caused by the use of organic solvents, but this method still has the following problems: (1) 30%-60% ammonium sulfate is directly added to the polyglutamic acid fermentation broth for salting out. The amount of ammonium sulfate used is too large. Even if the pH is not adjusted to acidity, about 2%-10% of polyglutamic acid is still salted out, affecting the product yield. Moreover, under this condition, the fermentation broth still maintains a certain viscosity. The filtration flow rate of the plate and frame filter press is low, and it is difficult to quickly remove impurities such as bacterial protein in the slurry. (2) After the pH of the polyglutamic acid fermentation liquid is adjusted to acidic by adding ammonium sulfate, a large amount of polyglutamic acid will precipitate. The precipitate has a large viscosity and can adhere to production equipment such as stirring paddles, tanks or pipelines, making it difficult to effectively achieve solid-liquid separation; (3) The obtained polyglutamic acid purified liquid needs to be processed by a vacuum freeze dryer, and the drying cost is too high.

[0005] Therefore, it is necessary to invent a new method that can effectively solve the above-mentioned problems in order to reduce costs and improve the yield of products. Summary of the invention

[0006] In order to solve the problems of high production cost, large equipment investment and low product yield of polyglutamic acid powdery product extraction, the present invention provides a method for extracting polyglutamic acid based on glutamic acid isoelectrocrystallization mother liquor fermentation. The method adopts technical means such as graded salting out, flocculation, viscosity reduction and air flotation to realize a new all-aqueous phase polyglutamic acid extraction technology, obtain agricultural-grade polyglutamic acid fully soluble powder, which not only improves the product yield but also greatly reduces the production cost.

[0007] The principle of the method for producing polyglutamic acid of the present invention is as follows: Using glutamic acid and other electrocrystallization mother liquor as raw materials, Bacillus licheniformis Bacillus licheniformis A-A2-10 is a strain that synthesizes polyglutamic acid from residual glutamic acid, residual sugar and other substances in the mother solution of glutamic acid and other electrocrystallization (ammonium sulfate content is 10-15% (w / v)); the content of polyglutamic acid in the fermentation broth reaches 8-15g / L; and due to the characteristics of the mother solution of glutamic acid and other electrocrystallization, the fermentation broth contains 10%-15% ammonium sulfate. At this ammonium sulfate concentration, by adding a small amount of sulfuric acid to adjust the pH value to 2.5-4.0, the polyglutamic acid in the fermentation broth will form a flocculent precipitate. After standing, Fermented liquid realizes layering, forms the turbid liquid phase containing polyglutamic acid precipitate in the upper clear liquid phase and the lower floor, after the supernatant is separated, adds dispersant to the turbid liquid, further improves ammonium sulfate concentration, reduces pH value, can effectively reduce the moisture in the above-mentioned flocculent precipitation, accelerates polyglutamic acid aggregation and agglomeration, in this process, by pressurized dissolved air flotation equipment, forms the polyglutamic acid precipitate containing a large amount of bubbles, the product surface viscosity significantly reduces, and drying efficiency is high, can adopt vacuum drying to quickly dehydrate and pulverize, obtain target product. Certainly also can adopt other modes to dry, such as freeze drying or forced air drying, all can realize dry mode, all within protection scope of the present invention.

[0008] The specific steps are as follows: (1) Bacillus licheniformis Bacillus licheniformis A-A2-10 is a strain, which ferments the mother solution of glutamic acid and other electrocrystallization to obtain a fermentation liquid; the details of this step have been disclosed in CN111876347B; (2) The pH of the fermentation broth obtained in (1) is adjusted to acidic, a flocculant is added, the mixture is stirred thoroughly, and the mixture is allowed to stand. When adjusting the pH, sulfuric acid is first diluted to 2M~6M, and then added to the fermentation broth to adjust the pH value to 2.5~4.0. The added flocculant is selected from at least one of sodium polyacrylate and cationic ammonium polyacrylate, and the flocculant is first diluted to 3~8g / L before being added. The mass volume ratio of the flocculant to the fermentation broth is 0.1~0.3 g / L. After adding the flocculant, the mixture is stirred for 1~6h, and then allowed to stand for 24~72h. (3) After standing, the supernatant liquid phase and the turbid liquid phase containing the precipitate are separated; the inventors take the supernatant liquid, and the polyglutamic acid concentration in the taken supernatant liquid is less than 0.5 g / L, which indicates that the loss rate of polyglutamic acid is extremely low and the loss can be ignored; (4) adding anionic dispersant to the turbid liquid of (3), stirring and mixing, and recording as material I; adding dispersant under stirring conditions, the dispersant is selected from at least one of hexadecyltrimethylammonium chloride and anionic polyacrylate ammonium, and the mass volume ratio of dispersant to turbid liquid is: 0.2~1g / L; (5) Add ammonium sulfate to the material I mixed in (4) and stir evenly, which is recorded as material II; the weight ratio of the added ammonium sulfate to the volume of the turbid liquid is 5-20 g / L, until the final volume ratio of the mass of ammonium sulfate (material I itself still contains a part of ammonium sulfate, which is calculated based on the total weight of the added ammonium sulfate) to material I is 15-30 g / L; (6) First, air is introduced into material II in (5), and acid is added to adjust the pH value, and then the polyglutamic acid precipitate is recovered by flotation. In a small-scale experiment, a microporous aeration head can be used for aeration, and 0.5M-2M dilute sulfuric acid can be introduced by a peristaltic pump to adjust the pH to 2.0-2.5, and the upper layer of flotation product is recovered to obtain the polyglutamic acid precipitate; During pilot or large-scale production, air is introduced into material II of (5), which is pressurized to 0.25-0.4 MPa by a pressure pump, and then 0.5M-2M dilute sulfuric acid is added to adjust the pH to 2.0-2.5. The material is then transported to a pressure gas dissolving tank, sprayed to a flotation tank, and scraped by a scraper. The material is then transported to a sieve to drain excess water to obtain a polyglutamic acid precipitate.

[0009] (7) Dry the polyglutamic acid salt precipitate obtained in (6) until the water content is less than 8 wt %, and grind it to obtain polyglutamic acid powder. The drying may be performed by vacuum drying or forced air drying, or other drying methods may be used.

[0010] The beneficial effects of the present invention are: (1) The present invention adopts graded salting-out to reduce the amount of ammonium sulfate used: Due to the advantage that the fermentation broth obtained by fermenting the glutamic acid crystallization mother liquor contains 10-15% (w / v, g / L, if w / v appears in this application and is not otherwise specified, it refers to g / L) of ammonium sulfate, without the need to add additional ammonium sulfate, the polyglutamic acid is flocculated and precipitated by adding only a small amount of flocculant and lowering the pH value, and more than 80% of the clear liquid is separated from the polyglutamic acid; further a small amount of ammonium sulfate is added to reduce the water content of the polyglutamic acid precipitate, and then the solid-liquid separation of the polyglutamic acid is achieved by means of the above-mentioned graded salting-out process, thereby significantly reducing the amount of ammonium sulfate used; (2) Optimizing dispersants and reducing the viscosity of polyglutamic acid salting-out products: Adding anionic dispersants reduces the viscosity of polyglutamic acid precipitates and reduces the adhesion of polyglutamic acid to production equipment, thereby helping to reduce equipment operating requirements and achieve industrial production; (3) The step of pressurized dissolved air flotation is adopted to realize low-cost solid-liquid separation and drying of polyglutamic acid salting out: The present invention adopts pressurized dissolved air flotation treatment to float out the polyglutamic acid precipitate, thereby avoiding the problem of polyglutamic acid precipitate clogging equipment during the operation of equipment such as plate and frame filter and centrifuge, and realizing low-cost solid-liquid separation of polyglutamic acid; at the same time, the pressurized dissolved air flotation process will cause the polyglutamic acid precipitate to contain a large number of bubbles, thereby increasing the specific surface area of ​​the product and effectively reducing the influence of ammonium sulfate forming a salt film on the surface of the polyglutamic acid product, which leads to a decrease in the evaporation rate of water, thereby significantly improving the drying efficiency and reducing production energy consumption. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1 This is a picture of the sedimentation process of polyglutamic acid fermentation broth; Figure 2 This is a photo of the sedimentation supernatant of polyglutamic acid fermentation broth; Figure 3 This is a photo of the flotation process of the polyglutamic acid precipitated product; Figure 4 This is a photo of polyglutamic acid powder; Figure 5 This is a photograph of the polyglutamic acid precipitate adhering to the stirring paddle in Comparative Example 1. DETAILED DESCRIPTION

[0012] In order to enable those skilled in the art to better understand the present invention, the present invention is further described in conjunction with specific implementation methods.

[0013] Example 1 Preparation of polyglutamic acid fermentation broth using glutamic acid isoelectric crystallization mother liquor as raw material Bacteria selection: Bacillus licheniformis Bacillus licheniformis A-A2-10, this strain was deposited in the China Center for Type Culture Collection on March 6, 2020, with the deposit number CCTCC NO: M 2020051.

[0014] Seed culture medium: Add 2% peptone and 2% yeast powder to glutamic acid isoelectric crystallization mother solution (ammonium sulfate content 10 ~ 15% (w / v)), adjust the pH to 7.0, and sterilize at 115℃ for 20min; Fermentation medium: Add 1% peptone and 1% yeast powder to the mother solution of glutamic acid isoelectric crystallization (ammonium sulfate content 10 ~ 15% (w / v)), adjust the pH to 7.0, and sterilize at 115℃ for 20min; Fermentation culture: fermentation is carried out using a 500L stirred fermenter, the seed liquid inoculum amount is 2.5 vol%, the fermenter needs ventilation and stirring, the ventilation volume is about 0.3vvm, the tank pressure is 0.06Mpa, and the dissolved oxygen is maintained at 15% by controlling the stirring speed. The pH value of the fermentation process is maintained between 6.3 and 6.6, and the fermentation cycle is about 26h. The fermented liquid formed after the fermentation is completed is suitable for the extraction process of the present invention. The fermentation process is referred to the steps described in patent document CN111876347B. The above process is only to obtain fermented liquid, and is not an improvement of the important description of the present invention. In the obtained fermented liquid, the ammonium sulfate content is 120g / L, and the polyglutamic acid concentration is 11g / L.

[0015] Example 2 Based on the extraction method of polyglutamic acid fermented by glutamic acid isoelectric crystallization mother liquor, the laboratory pilot extraction process is as follows: (1) Take 5 L of the polyglutamic acid fermentation liquid obtained in Example 1, adjust the pH value to 3.0 with 2.5 M sulfuric acid, add cationic ammonium polyacrylate to a final concentration of 0.12‰ (w / v), and add the cationic ammonium polyacrylate to a liquid with a concentration of 3 g / L. Use a laboratory stirring device and set it to 50 rpm to slowly stir for 2 h. After standing for 48 h, the layers are obvious, the upper layer is a clear liquid, and the lower layer is a turbid liquid containing polyglutamic acid flocculent precipitates. Pour out the supernatant. The flow rate needs to be controlled during the pouring process to prevent the loss of polyglutamic acid flocculated precipitates. After measurement, the turbid liquid phase is about 0.8 L; (2) Add hexadecyltrimethylammonium chloride to the turbid solution in (1) to a final concentration of 0.4‰ (w / v), use a laboratory stirring device at 50 rpm to slowly stir and mix for 5 min, and add ammonium sulfate to a concentration of 18% (w / v); then use a microporous aeration head to treat the turbid solution, and use a peristaltic pump to slowly add 1.5M dilute sulfuric acid from the bottom to adjust the pH to 2.2, and continue to ventilate with the microporous aeration head for 120 min. The polyglutamic acid precipitate continues to aggregate to form large floating objects, and then the floating upper layer of polyglutamic acid precipitate is placed on gauze and allowed to stand for 5 h to drain excess water; (3) The upper layer of polyglutamic acid precipitated product in (2) was placed in a forced air drying oven for drying, and the dried product was further powdered to obtain polyglutamic acid powder. The total yield was 132.6 g, the polyglutamic acid content was 40.02 wt%, the water content was 6.5 wt%, and the extraction yield was about 96.4%.

[0016] The calculation method of extraction yield is: Extraction yield (wt%) = (weight of polyglutamic acid powder × polyglutamic acid content) / (volume of polyglutamic acid fermentation broth × polyglutamic acid concentration) × 100%.

[0017] For the detection method of polyglutamic acid content, please refer to the Light Industry Standard of the People's Republic of China (QBT5189-2017).

[0018] The extraction yield and the detection method of polyglutamic acid content in the following examples are the same as those in Example 2.

[0019] Example 3 Based on the extraction method of polyglutamic acid from glutamic acid isoelectric crystallization mother liquor fermentation, the extraction process of the laboratory test is as follows: (1) 50 L of the polyglutamic acid fermentation liquid obtained in Example 1 was taken and placed in an 80 L stainless steel barrel. The pH value was adjusted to 2.8 with 2 M sulfuric acid. Sodium polyacrylate was added to a final concentration of 0.18‰ (w / v) based on the polyglutamic acid fermentation liquid. The sodium polyacrylate was first prepared into a liquid with a concentration of 3 g / L before being added. The mixture was slowly stirred at 20 rpm for 1 h. After standing for 32 h, obvious stratification occurred. The upper layer was a clear liquid phase, and the lower layer was a turbid liquid phase containing polyglutamic acid flocculent precipitates. The supernatant was extracted with a peristaltic pump. The flow rate was controlled during the extraction process to prevent the loss of polyglutamic acid precipitates. After measurement, the volume of the extracted supernatant was 44 L, in which the polyglutamic acid content was only 0.1 g / L.

[0020] (2) Add anionic ammonium polyacrylate to the turbid liquid phase in (1) to a final concentration of 0.28‰ (w / v), slowly stir at 20 rpm for 5 min, and add ammonium sulfate to a concentration of 20% (w / v); during the addition process, use a microporous aeration head to treat the precipitate, and use a peristaltic pump to slowly add 0.5 M dilute sulfuric acid from the bottom to adjust the pH to 2.0, then continue to ventilate with the microporous aeration head for 70 min, and then place the floating upper layer of polyglutamic acid precipitate on a filter cloth and let it stand for 3 h to drain; (3) The upper layer of polyglutamic acid precipitate in (2) was placed in a vacuum drying oven for drying, and the dried product was further powdered to obtain polyglutamic acid powder. The total yield was 1.25 kg, the polyglutamic acid content was 43.3 wt%, the water content was 5 wt%, and the extraction yield was about 98.4%.

[0021] Example 4 Based on the extraction method of polyglutamic acid fermented by glutamic acid isoelectric crystallization mother liquor, the extraction process of laboratory pilot is as follows: (1) 150 L of the polyglutamic acid fermentation liquid obtained in Example 1 was taken and added to an open reactor. The pH value was adjusted to 3.0 with 2 M sulfuric acid. Sodium polyacrylate was added to a final concentration of 0.22‰ (w / v) based on the volume percentage of the polyglutamic acid fermentation liquid. The sodium polyacrylate was first prepared into a liquid with a concentration of 3 g / L before being added. The mixture was slowly stirred at 50 rpm for 2 h. After standing for 60 h, obvious stratification occurred. The upper layer was a clear liquid phase, and the lower layer was a turbid liquid phase containing polyglutamic acid flocculent precipitates. The open reactor was tilted and the supernatant was poured out. The flow rate needed to be controlled during the pouring process to prevent the loss of polyglutamic acid precipitates. After measurement, the volume of the poured out supernatant was 128 L, of which the polyglutamic acid content was only 0.03 g / L. (2) Add hexadecyltrimethylammonium chloride to the turbid liquid phase in (1) to a final concentration of 0.36‰ (w / v), slowly stir at 20 rpm for 5 min, and add ammonium sulfate to a concentration of 17% (w / v); during the addition process, use 5 aeration heads to treat the precipitate, and use a peristaltic pump to slowly add 0.5M dilute sulfuric acid from the bottom to adjust the pH to 2.4, then continue to ventilate with a microporous aeration head for 200 min, and then place the floating upper layer of polyglutamic acid precipitate on a 100-mesh filter cloth and let it stand for 8 h to drain; (3) The upper layer of polyglutamic acid precipitate in (2) was placed in a vacuum drying oven for drying, and the dried product was further powdered to obtain polyglutamic acid powder with a total output of 3.93 kg, a polyglutamic acid content of 40.9 wt%, a water content of 7.1 wt%, and an extraction yield of about 97.41%.

[0022] Example 5 The method for extracting polyglutamic acid based on the fermentation of glutamic acid isoelectric crystallization mother liquor is different from that of Examples 1, 2, 3, and 4 in that Example 5 is a case of scaled-up trial production, and the specific steps are as follows: (1) 10 ml of polyglutamic acid fermentation liquid (containing 12 g / L polyglutamic acid and 13.1% (w / v) ammonium sulfate) was obtained by fermentation of glutamic acid isoelectric crystallization mother liquor. 10 ml of fermentation liquid was placed in a reaction tank with a columnar window and a stirrer. 2 M sulfuric acid was used to adjust the pH value to 2.6. Sodium polyacrylate was added to a concentration of 0.13‰ (w / v) based on the volume percentage of the polyglutamic acid fermentation liquid. Sodium polyacrylate was first prepared into a liquid with a concentration of 3 g / L before being added. The liquid was slowly stirred at 15 rpm for 1.2 h. After standing for 72 h, the layers were clearly separated. The upper layer was a clear liquid phase and the lower layer was a turbid liquid phase containing a large amount of polyglutamic acid flocculent precipitates. The supernatant was observed to be clear from the columnar window. The supernatant was sucked out by a submersible pump. The volume of the supernatant was about 8.6 ml. It was calculated that the concentration of polyglutamic acid in the clear liquid was only 0.05 g / L. (2) Stirring the turbid liquid phase in (1) and pumping it into the pretreatment tank in the pressurized dissolved air flotation equipment, adding hexadecyl trimethyl ammonium chloride to a concentration of 0.6‰ (w / v) based on the volume of the turbid liquid, slowly stirring and mixing at 30 rpm for 10 minutes, and adding ammonium sulfate to an ammonium sulfate concentration of 22% (w / v), and pumping it into the pressure dissolved air tank with a pressure pump, connecting air to the pipeline before entering the pressure pump, and connecting the pressurized pipeline to the dilute sulfuric acid pipeline, adding dilute sulfuric acid by adjusting the flow rate, and controlling the pH value to about 2.2. After the material stays in the pressure vessel tank for a short time, it enters the flotation tank through the pressure valve, and floats the polyglutamic acid precipitate in the flotation tank, and then is processed by a scraper and enters the screen, overflowing excess water. According to measurement, no polyglutamic acid is detected in the water; (3) Place the precipitate in (2) on a tray and place it in a vacuum drying oven for drying. After three batches of experiments, the average yield of polyglutamic acid was about 96.4%.

[0023] Comparative Example 1 Referring to the polyglutamic acid salting-out extraction scheme described in the patent with application number 202010647427.6, 50L of the polyglutamic acid fermentation broth described in Example 1 was used, and 20kg of ammonium sulfate was added while stirring (after adding ammonium sulfate, the final concentration of ammonium sulfate in the fermentation broth will reach 32% (w / v)), and the pH of the fermentation broth was adjusted to 8.0. After the ammonium sulfate was completely dissolved, it was allowed to stand at room temperature for 30 minutes. The obtained mixed solution was stirred while adjusting the pH to 2.5 with a 6M sulfuric acid solution. During the pH adjustment process, a large amount of polyglutamic acid was precipitated, most of which were entangled on the stirring paddle, making it difficult to separate. After the polyglutamic acid salting-out product was taken out, it was vacuum dried. During the drying process, ammonium sulfate gathered on the surface of the product to form a salt film, and the drying efficiency was low, proving that this scheme is difficult to apply and promote in industrial production.

[0024] Table 1 Comparison results of Example 5 and Comparative Example 1

[0025] It can be seen from Table 1 that, compared with the traditional method, the method of the present invention can greatly improve the extraction yield of polyglutamic acid, and the highest extraction yield can reach more than 96%.

Claims

1. A method for extracting polyglutamic acid based on glutamic acid isoelectric crystallization mother liquor fermentation, comprising the following steps: (1) Bacillus licheniformis Bacillus licheniformis A-A2-10 is a strain that ferments glutamic acid isoelectric crystallization mother liquor to obtain a fermentation liquid; (2) adjusting the pH of the fermentation liquid obtained in (1) to acidic, adding a flocculant, stirring thoroughly, and allowing to stand; (3) After standing, separate the supernatant liquid from the turbid liquid containing the precipitate; (4) Add anionic dispersant to the turbid liquid in (3), stir and mix, and record it as material I; (5) Add ammonium sulfate to material Ⅰ in (4) and stir evenly, which is recorded as material Ⅱ; (6) introducing air into material II in (5), adding acid to adjust the pH value, and recovering the polyglutamic acid precipitate by flotation; (7) Drying the polyglutamic acid salt precipitate obtained in (6), and crushing it to obtain polyglutamic acid powder.

2. The method for preparing polyglutamic acid using glutamic acid isoelectric crystallization mother solution as raw material according to claim 1, characterized in that: In (1), the fermentation broth is prepared by the method described in patent CN111876347B.

3. The method for preparing polyglutamic acid using glutamic acid isoelectric crystallization mother solution as raw material according to claim 1, characterized in that: (2), when adjusting the pH, first dilute sulfuric acid to 2M~6M, add it to the fermentation broth, and adjust the pH value to 2.5~4.0; the added flocculant is selected from at least one of sodium polyacrylate and cationic ammonium polyacrylate, and the flocculant is first diluted to 3~8g / L before adding, and the mass volume ratio of flocculant to fermentation broth is 0.1~0.3 g / L. After adding the flocculant, stir for 1~6h, and then let it stand for 24~72h.

4. The method for preparing polyglutamic acid using glutamic acid or the like electrocrystallization mother solution as a raw material according to claim 1, characterized in that: (4), a dispersant is added under stirring, wherein the dispersant is selected from at least one of hexadecyltrimethylammonium chloride and anionic polyacrylate ammonium, and the mass volume ratio of the dispersant to the turbid liquid is 0.2-1 g / L.

5. The method for preparing polyglutamic acid using glutamic acid or the like electrocrystallization mother solution as a raw material as claimed in claim 1, characterized in that: (5), the ratio of the added weight of ammonium sulfate to the volume of the turbid solution is 5-20 g / L, until the final ratio of the mass of ammonium sulfate in material I to the volume of material I is 15-30 g / L.

6. The method for preparing polyglutamic acid using glutamic acid or the like electrocrystallization mother solution as a raw material according to claim 1, characterized in that: (6) In the pilot test, a microporous aeration head was used for aeration, and 0.5M-2M dilute sulfuric acid was introduced by a peristaltic pump to adjust the pH to 2.0-2.5, and the upper layer of flotation product was recovered to obtain polyglutamic acid precipitate; During pilot or large-scale production, air is introduced into material II of (5), which is pressurized to 0.25-0.4 MPa by a pressure pump, and then 0.5M-2M dilute sulfuric acid is added to adjust the pH to 2.0-2.

5. The material is then transported to a pressure gas dissolving tank, sprayed to a flotation tank, and scraped by a scraper. The material is then transported to a sieve to drain excess water to obtain a polyglutamic acid precipitate.

7. The method for preparing polyglutamic acid using glutamic acid or the like electrocrystallization mother solution as a raw material according to claim 1, characterized in that: (7), the polyglutamic acid salting product is dried to a water content of less than 8 wt %.

8. The method for preparing polyglutamic acid using glutamic acid or the like electrocrystallization mother solution as a raw material as claimed in claim 7, characterized in that: Use vacuum drying or air drying.

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