A segmented glutamic acid isoelectric extraction method based on gradient pH regulation

Abstract

This invention discloses a segmented isoelectric extraction method for glutamic acid based on gradient pH control, belonging to the field of glutamic acid extraction technology. It aims to solve problems such as impurity encapsulation in crystals, low purity, difficulty in solid-liquid separation, and poor process stability caused by one-time pH adjustment in traditional isoelectric glutamic acid extraction processes. This method divides the crystallization process into three stages: rapid nucleation, slow crystal growth, and stable crystal growth. Through the synergistic effect of gradient pH control and segmented temperature control: In the first stage, the pH of the fermentation broth is adjusted from the initial pH to 4.2-4.6 at a uniform rate, while the temperature of the fermentation broth is lowered to 20°C within 2 hours; in the second stage, the pH is uniformly lowered to 3.6-3.8, and the temperature is uniformly lowered to 15°C; in the third stage, the pH is uniformly lowered to 3.3, and the temperature is uniformly lowered to 10-12°C. This invention avoids the problems of fine crystal loss and impurity co-crystallization, and the process is stable and easily controlled, increasing the purity of glutamic acid from 95.00% in traditional processes to approximately 98.25%, significantly improving the quality and production efficiency of glutamic acid.

Description

Technical Field

[0001] This invention relates to the field of glutamic acid extraction technology, specifically to a segmented isoelectric extraction method for glutamic acid based on gradient pH control. Background Technology

[0002] Currently, the main methods for extracting glutamic acid include isoelectric point crystallization, ion exchange, solvent extraction, and membrane separation. Among these, isoelectric point crystallization is the most widely used glutamic acid extraction process in industry due to its advantages such as simple operation, low production cost, environmental friendliness, and lack of large amounts of chemical reagent residue. The core principle of this method is to utilize the amphoteric electrolyte properties of glutamic acid, whose isoelectric point (pH) is approximately 3.22. When the pH of the glutamic acid fermentation broth is adjusted to the isoelectric point, the solubility of glutamic acid reaches its minimum, thereby crystallizing and precipitating out, achieving separation from other impurities in the fermentation broth.

[0003] However, the traditional isoelectric point crystallization method suffers from numerous insurmountable technical drawbacks in practical industrial applications, severely hindering the improvement of glutamic acid quality and production efficiency. Firstly, the traditional process involves adjusting the pH to the isoelectric point in a single step, causing glutamic acid molecules in the fermentation broth to rapidly aggregate and crystallize, forming dense crystal clusters. This rapid crystallization process prevents impurities such as other amino acids (e.g., aspartic acid, alanine, leucine), proteins, pigments, and sugars from detaching from the crystal surface in time, trapping them within the crystal clusters. Consequently, the final glutamic acid purity is only around 95%, failing to meet the market demand for high-purity products. To improve purity, a subsequent recrystallization process is often required, which not only increases water and energy consumption but also reduces glutamic acid yield and significantly increases production costs.

[0004] Secondly, the rapid crystallization caused by a single pH adjustment results in glutamic acid crystals with a small, irregular morphology, typically between 20-30 μm in size, and with uneven particle size distribution. These small, irregular crystals easily clog the filter media during solid-liquid separation, significantly increasing filtration resistance and leading to a slow filtration rate (usually only 0.5 m). 3 The solid-liquid separation efficiency is low (approximately 1000 kWh / day), severely impacting production progress. Furthermore, the high surface activity of the fine crystals makes them prone to being lost with the mother liquor during discharge, further reducing the glutamic acid extraction yield.

[0005] In addition, in traditional processes, glutamic acid crystals are prone to co-crystallization with other amino acids, which further exacerbates the problem of impurity residues and makes it difficult to improve the purity of glutamic acid. Moreover, the one-time pH adjustment process is highly sensitive to external factors such as the initial composition of the fermentation broth (such as the concentration of glutamic acid and the content of other amino acids) and fluctuations in ambient temperature. The process has poor stability, and the quality indicators such as purity and crystal morphology of different batches fluctuate greatly (the fluctuation range can reach ±2%), making it difficult to ensure the consistency of glutamic acid quality.

[0006] To address these issues, the industry has undertaken a series of improvement attempts. For example, some companies have adopted a step-by-step pH adjustment method, but they have not developed a systematic gradient control scheme and lack a coordinated design for pH control and temperature control. As a result, they still cannot effectively avoid core problems such as impurities encapsulated in crystal clusters and the loss of fine crystals. Other companies have tried adding seed crystals during the crystallization process in hopes of guiding the directional growth of crystals. However, the selection, amount, and timing of seed crystal addition are difficult to control precisely, which can easily introduce new impurities and increase process complexity and production costs, making it difficult to achieve large-scale industrial application.

[0007] In summary, existing isoelectric extraction processes for glutamic acid still suffer from problems such as low purity, poor crystal morphology, difficulty in solid-liquid separation, low yield, and poor process stability, failing to meet the demands of industrial production for high purity, high efficiency, and low cost. Therefore, developing a new process that can fundamentally overcome these technical pain points and achieve efficient and high-purity extraction of glutamic acid has significant practical implications and broad application prospects. Summary of the Invention

[0008] The purpose of this invention is to overcome the shortcomings of existing isoelectric extraction processes for glutamic acid, such as low purity, poor crystal morphology, low solid-liquid separation efficiency, low extraction yield, and poor process stability, and to provide a segmented isoelectric extraction method for glutamic acid based on gradient pH control.

[0009] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0010] A segmented isoelectric extraction method for glutamate based on gradient pH control includes the following steps:

[0011] S1, Obtain glutamic acid fermentation broth;

[0012] S2, Gradient pH Controlled Segmented Crystallization: The glutamic acid fermentation broth is introduced into the crystallization tank, and the stirring device is started. Gradient pH control and segmented temperature control are carried out in three stages: rapid nucleation, slow crystal growth, and stable crystal growth, as detailed below:

[0013] S21, rapid nucleation stage: The pH of the glutamic acid fermentation broth is adjusted with concentrated sulfuric acid, and the pH is uniformly reduced from the initial pH to 4.2-4.6; at the same time, the temperature of the fermentation broth is reduced to 20℃ within 2 hours.

[0014] S22, slow crystallization stage: Continue to add concentrated sulfuric acid dropwise to lower the pH to 3.6-3.8 at a uniform rate; lower the temperature to 15℃ at a uniform rate.

[0015] S23, stable crystal growth stage: continue to add concentrated sulfuric acid to lower the pH to 3.3 at a uniform rate; lower the temperature to 10-12℃ at a uniform rate;

[0016] S3, Cooling Maintenance: Keep stirring and maintain the temperature of the fermentation broth at 10-12℃ for 10-14 hours;

[0017] S4, Solid-liquid separation and post-processing: Solid-liquid separation is performed on the crystallization solution after cooling and maintenance to obtain glutamic acid crystals, which are then washed to obtain high-purity glutamic acid.

[0018] Furthermore, in step S1, the concentration of the glutamic acid fermentation broth is 100-150 g / L and the temperature is 30-35℃; in step S2, the concentration of the concentrated sulfuric acid is 98%.

[0019] Furthermore, in step S2, the stirring device is an anchor mixer or a paddle mixer, and the stirring speed is 25-35 rpm.

[0020] Furthermore, in step S21, the initial pH is 5.5-6.5, and the pH decrease rate is 0.3-0.5 per hour.

[0021] Furthermore, in step S22, the pH decrease rate is 0.1-0.3 per hour, and the temperature decrease rate is 1-1.5°C per hour.

[0022] Furthermore, in step S23, the pH decreases at a rate of 0.08-0.12 per hour, and the temperature decreases at a rate of 0.8-1.2°C per hour.

[0023] Furthermore, in step S21, concentrated sulfuric acid is used to adjust the pH of the glutamic acid fermentation broth from 5.9 to 4.5 at a rate of 0.4 per hour; at the same time, the temperature of the fermentation broth is lowered to 20°C within 2 hours; in step S22, the pH is lowered from 4.5 to 3.6 at a rate of 0.3 per hour, and the temperature is lowered to 15°C at a constant rate; in step S23, the pH is lowered from 3.6 to 3.3 at a rate of 0.1 per hour, and the temperature is lowered to 11°C at a rate of 1°C / h.

[0024] Furthermore, in step S3, the temperature maintained during the cooling process is 11°C for 12 hours.

[0025] Furthermore, in step S4, solid-liquid separation is performed by centrifugal filtration or plate and frame filtration. The centrifugal filtration speed is 2800-3200 rpm and the centrifugation time is 10-20 minutes; the plate and frame filtration pressure is 0.3-0.5 MPa.

[0026] Furthermore, in step S4, deionized water is used for washing, and the washing is performed 2-3 times, with the amount of water used for each washing being 1.2-1.8 times the mass of the glutamic acid crystals.

[0027] Compared with the prior art, the present invention has the following beneficial effects:

[0028] (1) This invention employs a segmented process of "rapid nucleation + slow crystal growth + stable crystal growth," controlling the crystallization rate of glutamic acid through gradient pH regulation, thus avoiding rapid crystallization and the formation of dense crystal clusters caused by one-time pH adjustment. The rapid nucleation stage quickly forms uniform crystal nuclei, the slow crystal growth stage slowly grows and optimizes the morphology, and the stable crystal growth stage removes surface impurities, effectively reducing the encapsulation and co-crystallization of impurities such as miscellaneous amino acids and proteins. Experimental data show that the purity of glutamic acid produced by this invention can reach over 98.25%, which is more than 3.27% higher than the 95% of the traditional process. It can meet the high-purity market demand without subsequent recrystallization, significantly reducing production costs.

[0029] (2) Through the synergistic design of pH regulation and temperature control, the growth process of glutamic acid crystals is controllable, resulting in regular crystal morphology (mainly needle-like and columnar), with the average particle size increasing from 20-30 μm in traditional processes to 50-80 μm, and the particle size distribution becoming more uniform. The larger crystal particle size reduces filtration resistance, and the solid-liquid separation speed increases from 0.5 m / s in traditional processes. 3 The speed was increased to approximately 1.0 m / h. 3 With a flow rate of over [number] hours, the problem of filter media clogging was avoided, resulting in a significant improvement in production efficiency.

[0030] (3) The present invention significantly improves the yield of glutamic acid extraction by maintaining sufficient crystallization during the cooling stage and suppressing the loss of fine crystals.

[0031] (4) This invention decomposes the crystallization process into three stages, and the pH adjustment rate and temperature change in each stage are quantitatively controlled, reducing the impact of external factors such as fluctuations in the initial composition of the fermentation broth and changes in ambient temperature on the crystallization effect. Experimental verification shows that the purity fluctuation range of different batches of glutamic acid is controlled within ±0.5%, which is far superior to the traditional process, and the quality stability of glutamic acid is significantly improved.

[0032] (5) This invention does not require the addition of seed crystals, flocculants and other chemical reagents, thus avoiding secondary pollution; after the purity of glutamic acid is improved, there is no need for subsequent recrystallization process, which reduces washing water and drying energy consumption, and is in line with the concept of green production. Detailed Implementation

[0033] The present invention will be further described below with reference to the embodiments. The embodiments of the present invention include, but are not limited to, the following embodiments.

[0034] Experimental materials and equipment

[0035] Experimental materials: glutamic acid fermentation broth (glutamic acid concentration 105 g / L, initial pH 5.9, total content of miscellaneous amino acids 0.8 g / L); concentrated sulfuric acid (concentration 98%); deionized water.

[0036] Experimental equipment: 500L crystallizer (with jacketed cooling system and anchor stirrer); peristaltic pump; online pH meter (accuracy ±0.01℃); thermometer (accuracy ±0.1℃); horizontal spiral centrifuge; vacuum drying oven; high performance liquid chromatograph (HPLC); laser particle size analyzer; electronic balance.

[0037] Test methods

[0038] Glutamic acid purity detection: High performance liquid chromatography (HPLC) was used for detection in accordance with the national standard GB / T8967-2007 "Monosodium glutamate (MSG)".

[0039] Crystal particle size detection: The average particle size (D50) of the crystals is detected using a laser particle size analyzer.

[0040] Solid-liquid separation rate: calculated based on filtration area and filtration rate per unit time, with a filtration area of ​​0.5 m². 2 .

[0041] Extraction yield: Calculated according to the formula "Yield = (Glutamic acid mass × Glutamic acid purity) / (Fermentation broth volume × Glutamic acid concentration in fermentation broth) × 100%".

[0042] Example 1

[0043] Take 350L of glutamic acid fermentation broth, with a glutamic acid concentration of 120 g / L and a temperature of 32℃.

[0044] Gradient pH controlled segmented crystallization: Glutamic acid fermentation broth was introduced into a 500 L crystallization tank, and the anchor stirrer was started at a speed of 30 rpm. Concentrated sulfuric acid solution was used as the acid solution and added dropwise via a peristaltic pump, with the process controlled in three stages.

[0045] (1) Rapid nucleation stage: The pH is gradually reduced from the initial 5.9 to 4.5 at a rate of 0.4 per hour. At the same time, the temperature is reduced from 32°C to 20°C within 2 hours by the jacket cooling system.

[0046] (2) Slow crystallization stage: Continue to add concentrated sulfuric acid, the pH drops from 4.5 to 3.6 at a rate of 0.2 per hour, and the temperature drops from 20°C to 15°C at a rate of 1°C per hour;

[0047] (3) Stabilizing crystal growth stage: Continue to add concentrated sulfuric acid, the pH drops from 3.6 to 3.3 at a rate of 0.1 per hour, and the temperature drops from 15°C to 11°C at a rate of 1°C per hour.

[0048] Cooling maintenance: Maintain stirring speed at 30 rpm and temperature at 11°C for 12 hours.

[0049] Solid-liquid separation and post-processing: The crystallization solution was passed into a horizontal screw centrifuge and centrifuged at 3000 rpm for 15 minutes to obtain glutamic acid crystals. The crystals were washed three times with deionized water, each time using 1.5 times the mass of the crystals. High-purity glutamic acid was then obtained. This glutamic acid could be sent to a monosodium glutamate (MSG) processing plant for further processing to obtain monosodium glutamate (MSG).

[0050] Test results: Glutamic acid purity was 98.32%, average crystal particle size was 65 μm, and solid-liquid separation rate was 1.2 m. 3 / h, with an extraction yield of 96.8%.

[0051] Example 2

[0052] The difference between this embodiment and Embodiment 1 is that the pH decrease rate during the rapid nucleation stage is 0.3 per hour, while other parameters are completely consistent with Embodiment 1.

[0053] Test results: Glutamic acid purity was 97.85%, average crystal particle size was 58 μm, and solid-liquid separation rate was 1.0 m. 3 / h, with an extraction yield of 96.2%.

[0054] Example 3

[0055] The difference between this embodiment and Embodiment 1 is that the temperature cooling rate during the slow crystal growth stage is 1.5°C per hour, while other parameters are completely consistent with Embodiment 1.

[0056] Test results: Glutamic acid purity was 97.51%, average crystal particle size was 52 μm, and solid-liquid separation rate was 0.9 m / s. 3 / h, with an extraction yield of 95.9%.

[0057] Example 4

[0058] The difference between this embodiment and Embodiment 1 is that the stirring speed is 25 rpm, while the other parameters are exactly the same as those in Embodiment 1.

[0059] Test results: Glutamic acid purity was 97.23%, average crystal particle size was 50 μm, and solid-liquid separation rate was 1.05 m / s. 3 / h, with an extraction yield of 95.5%.

[0060] Comparative Example 1

[0061] Take 350L of glutamic acid fermentation broth, with a glutamic acid concentration of 120 g / L and a temperature of 32℃.

[0062] One-time pH-adjusted crystallization: The glutamic acid fermentation broth was introduced into a 500 L crystallization tank, stirred at 30 rpm, and concentrated sulfuric acid was added dropwise to adjust the pH to 3.2 (the isoelectric point of glutamic acid). The temperature was then reduced from 32℃ to 11℃ within 4 hours using a jacketed cooling system.

[0063] Cooling maintenance: Maintain stirring speed at 30 rpm and temperature at 11°C for 12 hours.

[0064] Solid-liquid separation and post-processing: Same as in Example 1.

[0065] Test results: Glutamic acid purity was 94.98%, average crystal particle size was 28 μm, and solid-liquid separation rate was 0.5 m / s. 3 / h, with an extraction yield of 92.3%.

[0066] Results Analysis

[0067] A comparison of Examples 1-4 with Comparative Example 1 shows that the stepwise extraction method with gradient pH control in this invention is significantly superior to the traditional single-stage pH adjustment process in terms of purity, crystal morphology, solid-liquid separation speed, and extraction yield. Example 1, as the optimal example, achieved a glutamic acid purity of 98.32%, which is 3.34% higher than Comparative Example 1. The average crystal particle size was 2.32 times that of Comparative Example 1, the solid-liquid separation speed was 2.4 times that of Comparative Example 1, and the extraction yield was increased by 4.5 percentage points.

[0068] In Example 2, the pH decrease rate during the crystal nucleation stage was reduced to 0.3 per hour, the crystal nucleation rate slowed down, and the uniformity of crystal growth decreased slightly, resulting in a slightly lower purity and particle size than in Example 1, but still far superior to the traditional process. In Example 3, the temperature drop rate during the crystal growth stage was accelerated, the crystal growth rate was too fast, some impurities were encapsulated, and the purity and particle size decreased. In Example 4, the stirring speed was reduced, the crystal dispersion deteriorated, and aggregation was prone to occur, affecting the purity and solid-liquid separation efficiency.

[0069] The above experimental results fully demonstrate that the present invention, through the synergistic design of gradient pH regulation and segmented temperature control, can effectively overcome the defects of traditional processes, significantly improve the quality and production efficiency of glutamic acid, and has important industrial application value.

[0070] The above embodiments are merely one of the preferred embodiments of the present invention and should not be used to limit the scope of protection of the present invention. Any modifications or refinements made to the main design concept and spirit of the present invention that are not of substantial significance, but solve the same technical problem as the present invention, should be included within the scope of protection of the present invention.

Claims

1. A segmented isoelectric extraction method for glutamic acid based on gradient pH control, characterized in that, Includes the following steps: S1, Obtain glutamic acid fermentation broth; S2, Gradient pH Controlled Segmented Crystallization: The glutamic acid fermentation broth is introduced into the crystallization tank, and the stirring device is started. Gradient pH control and segmented temperature control are carried out in three stages: rapid nucleation, slow crystal growth, and stable crystal growth, as detailed below: S21, rapid nucleation stage: The pH of the glutamic acid fermentation broth is adjusted with concentrated sulfuric acid, and the pH is uniformly reduced from the initial pH to 4.2-4.6; at the same time, the temperature of the fermentation broth is reduced to 20℃ within 2 hours. S22, slow crystallization stage: Continue to add concentrated sulfuric acid dropwise to lower the pH to 3.6-3.8 at a uniform rate; lower the temperature to 15℃ at a uniform rate. S23, stable crystal growth stage: continue to add concentrated sulfuric acid to lower the pH to 3.3 at a uniform rate; lower the temperature to 10-12℃ at a uniform rate; S3, Cooling Maintenance: Keep stirring and maintain the temperature of the fermentation broth at 10-12℃ for 10-14 hours; S4, Solid-liquid separation and post-processing: Solid-liquid separation is performed on the crystallization solution after cooling and maintenance to obtain glutamic acid crystals, which are then washed to obtain high-purity glutamic acid.

2. The segmented isoelectric extraction method for glutamate based on gradient pH control according to claim 1, characterized in that, In step S1, the concentration of the glutamic acid fermentation broth is 100-150 g / L and the temperature is 30-35℃; in step S2, the concentration of the concentrated sulfuric acid is 98%.

3. The segmented isoelectric extraction method for glutamate based on gradient pH control according to claim 1, characterized in that, In step S2, the stirring device is an anchor mixer or a paddle mixer, and the stirring speed is 25-35 rpm.

4. The segmented isoelectric extraction method for glutamate based on gradient pH control according to claim 3, characterized in that, In step S21, the initial pH is 5.5-6.5, and the pH decrease rate is 0.3-0.5 per hour.

5. The segmented isoelectric extraction method for glutamate based on gradient pH control according to claim 4, characterized in that, In step S22, the pH decrease rate is 0.1-0.3 per hour, and the temperature decrease rate is 1-1.5°C per hour.

6. The segmented isoelectric extraction method for glutamate based on gradient pH control according to claim 5, characterized in that, In step S23, the pH decreases at a rate of 0.08-0.12 per hour, and the temperature decreases at a rate of 0.8-1.2°C per hour.

7. The segmented isoelectric extraction method for glutamate based on gradient pH control according to claim 1, characterized in that, In step S21, concentrated sulfuric acid is used to adjust the pH of the glutamic acid fermentation broth from 5.9 to 4.5 at a rate of 0.4 per hour; at the same time, the temperature of the fermentation broth is lowered to 20°C within 2 hours. In step S22, the pH is lowered from 4.5 to 3.6 at a rate of 0.3 per hour, and the temperature is lowered to 15°C at a constant rate. In step S23, the pH is lowered from 3.6 to 3.3 at a rate of 0.1 per hour, and the temperature is lowered to 11°C at a rate of 1°C / h.

8. The segmented isoelectric extraction method for glutamate based on gradient pH control according to claim 1, characterized in that, In step S3, the temperature maintained during the cooling process is 11°C for 12 hours.

9. The segmented isoelectric extraction method for glutamate based on gradient pH control according to claim 1, characterized in that, In step S4, solid-liquid separation is performed by centrifugal filtration or plate and frame filtration. The centrifugal filtration speed is 2800-3200 rpm and the centrifugation time is 10-20 minutes. The plate and frame filtration pressure is 0.3-0.5 MPa.

10. The segmented isoelectric extraction method for glutamate based on gradient pH control according to claim 1, characterized in that, In step S4, deionized water is used for washing, and the washing is performed 2-3 times. The amount of water used for each washing is 1.2-1.8 times the mass of the glutamic acid crystals.