A method for purifying feed-grade isoleucine

Abstract

The present invention is applicable to the field of isoleucine purification, and proposes a method for purifying feed-grade isoleucine, comprising the following steps: filtering the isoleucine fermentation broth with a ceramic membrane to obtain a ceramic membrane filtrate; then adding activated carbon for decolorization to obtain a decolorized liquid; then further filtering through a nanofiltration membrane to obtain a nanofiltration membrane filtrate; the nanofiltration membrane filtrate enters a concentration evaporator for concentration, and the solid content of the feed liquid is concentrated to 23% to 25% to obtain a concentrated solution; the concentrated solution enters a cooling crystallization tank, controls the cooling speed to 8 to 13 min / °C, cools to 30 to 35°C for centrifugation, and finally obtains isoleucine. In summary, the present invention has a simple extraction process, high product yield and quality, is environmentally friendly, and greatly reduces production costs.

Description

Technical Field

[0001] The invention relates to the technical field of isoleucine purification, and in particular to a method for purifying feed-grade isoleucine. Background Art

[0002] Isoleucine, also known as isoleucine, is one of the essential amino acids for humans and animals. It is optically active and belongs to a type of neutral aliphatic amino acid. It is widely used in the fields of pharmaceuticals, medical treatment, food and feed additives. In biological organisms, isoleucine can control blood sugar, repair muscles, improve immunity, and regulate protein synthesis. Studies have shown that the lack of isoleucine during animal growth will have a negative effect on ketone body traits and muscle fat. Currently, it can only be supplemented by feeding feed during animal breeding, and it is called a limiting amino acid.

[0003] At present, there are several methods for extracting isoleucine, including precipitation method, full membrane method, ion exchange adsorption method, etc. The precipitation method has the advantages of simple process flow and high purity of extracted products. The disadvantage is that the precipitant is difficult to completely remove in the product, the subsequent purification process consumes high costs, and it also causes problems such as difficulty in sewage treatment. Although the full membrane method produces less wastewater in the process of producing isoleucine, the purity of isoleucine in the finished product is low and contains many miscellaneous acids with molecular weight close to that of isoleucine. The ion exchange adsorption method has the advantages of simple operation, good extraction effect, and simple equipment, but it has a long production cycle, high production cost, and will cause problems such as difficulty in treating organic wastewater.

[0004] The patent with the authorization announcement number CN109836346B discloses a purification process of isoleucine fermentation broth. The purification process in the patent sequentially uses a ceramic membrane, a nanofiltration membrane, a chromatographic separation, a reverse osmosis membrane and activated carbon for purification, and the cost investment is relatively high. The final isoleucine yield is more than 88%, and the purity is 99.5~99.8%. Summary of the invention

[0005] In view of this, the present invention proposes a method for purifying feed-grade isoleucine, which has simple extraction process, high product yield and quality, is environmentally friendly and significantly reduces production costs.

[0006] The technical solution of the present invention is achieved in this way:

[0007] The present invention provides a method for purifying feed-grade isoleucine, comprising the following steps:

[0008] Step 1: The isoleucine fermentation broth is adjusted to pH 5.0-7.0 using concentrated sulfuric acid, and filtered using a 50 nm pore size ceramic membrane at a pressure of 0.20-0.26 MPa and a temperature of 45-65° C. The retentate is macromolecular proteins and bacterial cells, and the ceramic membrane filtrate is subjected to the next step of treatment;

[0009] The concentrated sulfuric acid used in the present invention is commercially available analytically pure concentrated sulfuric acid. The ceramic membrane filtrate contains unfiltered soluble proteins, inorganic salts, impure amino acids, etc.;

[0010] Step 2: Add activated carbon to the ceramic membrane filtrate for decolorization. The amount of activated carbon added is 5% of the solid mass in the ceramic membrane filtrate. The decolorization temperature is 50-65°C and the decolorization time is 25-35 minutes. Most of the pigments are removed. The activated carbon is removed by plate-frame separation to obtain a decolorized liquid.

[0011] Step 3: The decolorized liquid is filtered through a nanofiltration membrane with a pore size of 800D to further remove pigments and soluble proteins at a pressure of 2.4-2.6Mpa to obtain a nanofiltration membrane filtrate with a light transmittance of more than 90%;

[0012] Step 4: The nanofiltration membrane filtrate enters the concentrating evaporator, the evaporator is controlled at a temperature of 75-85°C, a vacuum degree of -0.095-0.1Mpa, and the solid content of the feed liquid is concentrated to 23%-25% to obtain a concentrated solution;

[0013] Step 5: The concentrated liquid enters the cooling crystallization tank, and the cooling rate is controlled at 8-13 min / ℃. The temperature is cooled to 30-35℃ for centrifugation at a centrifugal speed of 3000-5000 r / min to obtain a crystalline wet finished product. The crystalline wet finished product enters the rotary flash dryer for drying, and the outlet air temperature is controlled at 105-107℃. The finished product enters the finished product collection tank with the dry air to obtain isoleucine. The mother liquor is collected and concentrated, and the separated mother liquor wet crystals are then added with water to be mixed back into the nanofiltration membrane filtrate to enter the next batch of products.

[0014] The method for purifying feed-grade isoleucine of the present invention has the following beneficial effects compared with the prior art:

[0015] 1. The production process of the present invention is simple. After the fermentation liquid is treated with the ceramic membrane, powdered activated carbon is directly used to decolorize and remove impurities from the ceramic membrane filtrate, which can remove most pigments and soluble impurities, reduce the working pressure for subsequent nanofiltration membrane filtration, effectively improve the membrane efficiency and effect, reduce membrane clogging problems, and reduce the frequency of nanofiltration membrane cleaning.

[0016] 2. The present invention uses a method combining membrane filtration and activated carbon to purify the isoleucine fermentation broth, and does not use traditional ion exchange equipment to treat the material, which effectively reduces the discharge of wastewater and waste and saves production costs; the present invention does not add chemical reagents such as flocculants, thereby avoiding the contamination of the amino acid finished product by drug residues.

[0017] 3. The present invention first controls the purity and transmittance of the concentrated solution by a method combining membrane filtration and activated carbon; after the concentrated solution is well controlled, the crystallization process needs to be controlled to prevent impurities from crystallizing and precipitating, therefore, the solid content at the concentration end point is controlled to be 23%-25%, the cooling rate is 10 min / °C, and the centrifugation temperature is 30-35°C; by controlling the above two processes, the impurities in the material can be effectively reduced from participating in the isoleucine crystallization process, the purity and yield of the isoleucine product can be effectively improved, and the quality of isoleucine can be improved.

[0018] 4. The present invention does not add chemical reagents such as flocculants used in the precipitation method; does not use the reverse osmosis membrane used in the full membrane method, which has a very slow membrane permeation rate, a short lifespan, and a high cost; does not use chromatographic separation, which requires relatively high labor, equipment, and raw material inputs; and does not use the ion exchange resin used in the ion exchange adsorption method; therefore, the method of the present invention can significantly reduce labor costs, equipment costs, and raw material costs.

[0019] 5. The present invention can make the isoleucine content higher than 99.4%, and the isoleucine yield is 91.8-92.6%. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0021] Figure 1 The effect of the amount of activated carbon added on the isoleucine content of the finished product of the present invention;

[0022] Figure 2 This is the effect of the amount of activated carbon added on the light transmittance of the mother liquid. DETAILED DESCRIPTION

[0023] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0024] Example 1

[0025] A method for purifying feed-grade isoleucine comprises the following steps:

[0026] (1) Select a small-scale isoleucine fermentation liquid and add concentrated sulfuric acid to adjust the pH to 5.0, and then filter it through a ceramic membrane with a pore size of 50 nm to remove the macromolecular protein of the bacteria; the membrane filtration temperature is 45°C, the membrane filtration pressure is 0.20 MPa, and the ceramic membrane filtrate and retentate are obtained. The retentate enters the downstream feed production workshop; the ceramic membrane flow time is 25 minutes;

[0027] The isoleucine fermentation broth used in this example is the fermentation broth produced by our company, with a pH of 7.40, a conductivity of 11.88 mS / cm, and a solid content of 9.7%;

[0028] (2) adding Yuanli 303 activated carbon with a solid content of 5% to the ceramic membrane filtrate obtained in step (1) for decolorization, controlling the temperature to 50°C for decolorization for 25 minutes, and removing the activated carbon to obtain a decolorized liquid;

[0029] (3) The decolorized liquid from step (2) was further treated by passing through a nanofiltration membrane with a pore size of 800D and a pressure of 2.4 MPa to obtain a nanofiltration membrane filtrate with a light transmittance of 93.5%;

[0030] (4) The nanofiltration membrane filtrate obtained in step (3) is pumped into a concentration evaporator, the evaporator temperature is controlled at 75°C, the vacuum degree is -0.095 MPa, and the concentration is stopped when the solid content of the concentrated liquid reaches 23%;

[0031] (5) The concentrated solution obtained in step (4) is poured into a cooling crystallization tank, and the cooling rate is controlled at 8 min / °C. The solution is cooled to 30°C and centrifuged at a centrifugal speed of 3000 r / min. The mother liquor is collected and concentrated. After the wet crystals of the mother liquor are separated, water is added back into the nanofiltration membrane filtrate to enter the next batch of products. The wet crystal product enters a rotary flash dryer for drying. The outlet air temperature is controlled at 105°C. The finished product enters a collection tank along with the dry air.

[0032] The isoleucine obtained by the present invention has a light yellow crystal appearance, and the content is 99.40% according to the method in the industry standard QBT5633.1-2021, which meets the content requirement of feed-grade isoleucine. The yield of isoleucine is 91.8%.

[0033] Example 2

[0034] A method for purifying feed-grade isoleucine comprises the following steps:

[0035] (1) The small-scale fermentation liquid was added with concentrated sulfuric acid to adjust the pH to 6.0, and then filtered through a ceramic membrane with a pore size of 50 nm to remove the macromolecular proteins of the bacteria; the membrane filtration temperature was 60°C, and the membrane filtration pressure was 0.22 MPa. The ceramic membrane filtrate and the retentate were obtained, and the retentate entered the downstream feed production workshop; the ceramic membrane flow time was 22 minutes;

[0036] The isoleucine fermentation broth used in this example is the fermentation broth produced by our company, with a pH of 7.66, a conductivity of 8.18 mS / cm, and a solid content of 7.4%;

[0037] (2) adding Yuanli 303 activated carbon containing 5% of total solids to the ceramic membrane filtrate obtained in step (1) for decolorization, controlling the temperature to 60°C for decolorization for 30 minutes, and removing the activated carbon to obtain a decolorized solution;

[0038] (3) The decolorized liquid from step (2) is further processed through a nanofiltration membrane with a pore size of 800D and a pressure of 2.5 MPa to obtain a nanofiltration membrane filtrate having a light transmittance of more than 94.8%;

[0039] (4) The nanofiltration membrane filtrate obtained in step (3) is pumped into a concentration evaporator, the evaporator temperature is controlled at 80°C, the vacuum degree is -0.098 MPa, and the concentration is stopped when the solid content of the concentrated liquid reaches 24%;

[0040] (5) The concentrated solution obtained in step (4) is poured into a cooling crystallization tank, and the cooling rate is controlled at 10 min / °C. The temperature is cooled to 33°C and centrifuged at a centrifugal speed of 4000 r / min. The mother liquor is collected and concentrated. After the mother liquor wet crystals are separated, water is added back to the nanofiltration membrane filtrate to enter the next batch of products. The crystallized wet finished product enters a rotary flash dryer for drying. The outlet air temperature is controlled at 106°C. The finished product enters a collection tank along with the dry air.

[0041] The isoleucine obtained by the present invention has a light yellow crystal appearance, and the content is 99.90% according to the method in the industry standard QBT5633.1-2021, which meets the requirements of feed-grade isoleucine content. The yield of isoleucine is 92.6%.

[0042] Example 3

[0043] A method for purifying feed-grade isoleucine comprises the following steps:

[0044] (1) The small-scale fermentation liquid was added with concentrated sulfuric acid to adjust the pH to 7.0, and then filtered through a ceramic membrane with a pore size of 50 nm to remove the macromolecular proteins of the bacteria; the membrane filtration temperature was 65°C, and the membrane filtration pressure was 0.26 MPa. The ceramic membrane filtrate and the retentate were obtained, and the retentate entered the downstream feed production workshop; the ceramic membrane flow time was 24 minutes;

[0045] The isoleucine fermentation broth used in this example is the fermentation broth produced by our company, with a pH of 7.97, a conductivity of 8.10 mS / cm, and a solid content of 7.4%;

[0046] (2) adding Yuanli 303 activated carbon with a total solid content of 5% to the ceramic membrane filtrate obtained in step (1) for decolorization, controlling the temperature to 65°C for decolorization for 35 minutes, and removing the activated carbon to obtain a decolorized solution;

[0047] (3) The decolorized liquid from step (2) is further treated by passing through a nanofiltration membrane with a pore size of 800D and a pressure of 2.6 MPa to obtain a nanofiltration membrane filtrate having a light transmittance of more than 93.6%;

[0048] (4) The nanofiltration membrane filtrate obtained in step (3) is pumped into a concentration evaporator, the evaporator temperature is controlled at 85°C, the vacuum degree is -0.1 MPa, and the concentration is stopped when the solid content of the concentrated liquid reaches 25%;

[0049] (5) The concentrated solution obtained in step (4) is poured into a cooling crystallization tank, and the cooling rate is controlled at 13 min / °C. The temperature is cooled to 35°C for centrifugation at a centrifugal speed of 5000 r / min. The mother liquor is collected and concentrated. After the mother liquor wet crystals are separated, water is added back to the nanofiltration membrane filtrate to enter the next batch of products. The crystallized wet finished product enters a rotary flash dryer for drying. The outlet air temperature is controlled at 107°C. The finished product enters a collection tank along with the dry air.

[0050] The isoleucine obtained by the present invention has a light yellow crystal appearance, and the content is 99.60% according to the method in the industry standard QBT5633.1-2021, which meets the requirements of feed-grade isoleucine content. The yield of isoleucine is 92.2%.

[0051] Comparative Example 1

[0052] On the basis of Example 2, in the method for purifying feed-grade isoleucine, only ceramic membrane is used, activated carbon and nanofiltration membrane are not used, and other conditions are the same.

[0053] Comparative Example 2

[0054] On the basis of Example 2, in the method for purifying feed-grade isoleucine, only ceramic membrane and activated carbon are used, and nanofiltration membrane is not used, and other conditions are the same.

[0055] Comparative Example 3

[0056] On the basis of Example 2, in the method for purifying feed-grade isoleucine, only ceramic membrane and nanofiltration membrane are used, activated carbon is not used, and other conditions are the same.

[0057] It can be seen from Comparative Examples 1-3 that ceramic membrane, activated carbon and nanofiltration membrane need to be used simultaneously to ensure that the light transmittance of isoleucine meets the standard and the content is high.

[0058] Comparative Example 4

[0059] On the basis of Example 2, in the method for purifying feed-grade isoleucine, the ceramic membrane was filtered under the conditions of a pressure of 0.1 MPa and a temperature of 40° C., and other conditions were the same.

[0060] Comparative Example 5

[0061] On the basis of Example 2, in the method for purifying feed-grade isoleucine, the ceramic membrane is filtered under a pressure of 0.1 MPa, and other conditions are the same.

[0062] Comparative Example 6

[0063] On the basis of Example 2, in the method for purifying feed-grade isoleucine, the ceramic membrane is filtered at a temperature of 40° C., and other conditions are the same.

[0064] It can be seen from Comparative Examples 4-6 that if the pressure is lower than 0.20 MPa and the temperature is lower than 45°C, the membrane speed is slow and the production efficiency is reduced.

[0065] Comparative Example 7

[0066] On the basis of Example 2, in the method for purifying feed-grade isoleucine, the ceramic membrane is filtered under a pressure of 0.4 MPa, and other conditions are the same.

[0067] If the pressure is higher than 0.26Mpa, the ceramic membrane will be damaged and the isoleucine content will decrease.

[0068] Comparative Example 8

[0069] On the basis of Example 2, in the method for purifying feed-grade isoleucine, the ceramic membrane is filtered at a temperature of 75° C., and other conditions are the same.

[0070] Temperatures above 65°C will cause the amino acids to undergo a Maillard reaction, leading to denaturation and reduced transmittance of the nanofiltration membrane filtrate.

[0071] Comparative Example 9

[0072] On the basis of Example 1, the amount of activated carbon added was set to 1, 2, 3, 4, and 5% of the solid mass in the ceramic membrane filtrate, respectively, and other conditions were the same.

[0073] like Figure 1 As shown, with the increase of activated carbon addition, the isoleucine content in the finished product did not decrease significantly.

[0074] The change of mother liquid transmittance is as follows Figure 2 As shown in the figure, the transmittance of the mother liquor increases with the increase of the amount of activated carbon added, indicating that the pigment content in the mother liquor gradually decreases. When the activated carbon addition amount is 5%, the transmittance of the mother liquor is >75%, and it has no effect on the quality of the next batch of feed liquid after recovery. Considering the production cost and the mother liquor recovery effect, the most appropriate activated carbon addition amount is 5%.

[0075] Comparative Example 10

[0076] On the basis of Example 1, in step 4, the solid content in the concentrated liquid is 20%, and other conditions are the same.

[0077] Comparative Example 11

[0078] On the basis of Example 1, in step 4, the solid content in the concentrated liquid is 30%, and other conditions are the same.

[0079] It can be seen from Comparative Examples 10-11 that the solid content in the concentrated liquid is low, which affects the yield of isoleucine; the solid content in the concentrated liquid is high, causing excessive impurities to precipitate into the isoleucine crystals, affecting the isoleucine content.

[0080] Comparative Example 12

[0081] On the basis of Example 3, in step 5, the cooling rate is controlled to 6 min / °C, and other conditions are the same.

[0082] In this comparative example, although the lower the cooling rate, the better, it will increase the crystallization time and reduce the preparation efficiency.

[0083] Comparative Example 13

[0084] On the basis of Example 3, in step 5, the cooling rate is controlled to 15 min / °C, and other conditions are the same.

[0085] In this comparative example, the cooling rate is too fast, so that too many impurities are precipitated into the isoleucine crystals, affecting the isoleucine content.

[0086] Comparative Example 14

[0087] On the basis of Example 3, in step 5, the temperature is lowered to 20° C. for centrifugation, and other conditions are the same.

[0088] In this comparative example, the centrifugation temperature is too low, and other impurities in the mother liquor will also precipitate into the isoleucine crystals, affecting the isoleucine content.

[0089] Comparative Example 15

[0090] On the basis of Example 3, in step 5, the temperature is lowered to 45° C. for centrifugation, and other conditions are the same.

[0091] In this comparative example, the centrifugation temperature was too high, which affected the yield of isoleucine.

[0092] The indicators in each embodiment and comparative example were tested, and the test results are shown in Table 1.

[0093] Table 1 Index results in various embodiments and comparative examples

[0094] Ceramic membrane passing time min Transmittance% Isoleucine content% Isoleucine yield% Example 1 25 93.5 99.4 91.8 Example 2 22 94.8 99.9 92.6 Example 3 24 93.6 99.6 92.2 Comparative Example 1 23 68.7 92.4 85.2 Comparative Example 2 24 93 95.7 85.9 Comparative Example 3 22 78.2 96.7 84.7 Comparative Example 4 50 94.1 99.4 86.1 Comparative Example 5 45 92.9 99.2 85.5 Comparative Example 6 42 93.8 99.1 84.8 Comparative Example 7 21 94.0 91.5 85.0 Comparative Example 8 23 84.1 98.7 86.3 Comparative Example 9 / / / / Comparative Example 10 26 92.1 99 76.1 Comparative Example 11 26 93.3 90.6 86.2 Comparative Example 12 23 93.7 99.1 85.3 Comparative Example 13 25 93.2 91.5 84.6 Comparative Example 14 24 94.6 92.7 85.6 Comparative Example 15 25 93.8 99.0 77.4

[0095] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for purifying feed-grade isoleucine, characterized in that: The steps include: Step 1: filtering the isoleucine fermentation broth using a ceramic membrane at a pressure of 0.22 MPa and a temperature of 60° C. to obtain a ceramic membrane filtrate; Step 2: adding activated carbon to the ceramic membrane filtrate for decolorization, wherein the amount of activated carbon added is 5% of the solid matter in the ceramic membrane filtrate to obtain a decolorized liquid; The decolorized liquid in step 3 is further filtered through a nanofiltration membrane to obtain a nanofiltration membrane filtrate; The nanofiltration membrane filtrate in step 4 enters the concentrating evaporator for concentration, and the solid content of the feed liquid is concentrated to 24% to obtain a concentrated liquid; In step 5, the concentrated solution enters a cooling crystallization tank, and the cooling rate is controlled at 10 min / °C, and the temperature is cooled to 33°C for centrifugation to obtain a crystalline wet product, which is then dried to obtain isoleucine.

2. The method for purifying feed-grade isoleucine according to claim 1, wherein: In the step 1, the isoleucine fermentation broth is first adjusted to a pH of 5.0-7.0 using concentrated sulfuric acid, and then filtered using a ceramic membrane with a pore size of 50 nm.

3. The method for purifying feed-grade isoleucine according to claim 1, wherein: In the step 2, the ceramic membrane filtrate is added with activated carbon for decolorization, the decolorization temperature is 50-65° C., and the decolorization time is 25-35 min.

4. The method for purifying feed-grade isoleucine according to claim 1, wherein: In the step 3, the decolorized liquid is filtered through a nanofiltration membrane with a pore size of 800D, and the pressure is controlled at 2.4-2.6Mpa; the transmittance of the obtained nanofiltration membrane filtrate is above 90%.

5. The method for purifying feed-grade isoleucine according to claim 1, wherein: In the step 4, the concentration conditions in the concentration evaporator are: controlling the temperature at 75-85° C. and the vacuum degree at -0.095-0.1 MPa.

6. The method for purifying feed-grade isoleucine according to any one of claims 1 to 5, characterized in that: The content of the feed-grade isoleucine is higher than 99.4%, and the isoleucine yield is 91.8-92.6%.

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