A method for the preparation of folic acid
By conducting folic acid synthesis reactions under deoxygenated water and vacuum oxygen-free environments, and using deoxygenated weak alkaline solutions and deoxygenated water to dissolve raw materials, the problems of high water consumption and oxidation control in folic acid production have been solved, achieving efficient folic acid synthesis and improving the quality and yield of crude product.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- WENGYUAN GUANGYE QINGYI FOOD TECH
- Filing Date
- 2023-11-20
- Publication Date
- 2026-05-19
AI Technical Summary
Existing folic acid production processes consume large amounts of water, have incomplete reactions, low purity and yield of crude products, require large amounts of antioxidants, have high production costs, and are difficult to control oxidation.
Folic acid synthesis is carried out in a deoxygenated water and vacuum oxygen-free environment. The raw materials are dissolved in a deoxygenated weak alkaline solution and deoxygenated water. The reaction is carried out by vacuum liquid-liquid drop addition to avoid oxidation, thereby improving the reaction rate and the quality of crude product.
It significantly reduces process water consumption and antioxidant usage, improves the quality and yield of crude folic acid synthesis, and reduces production costs.
Abstract
Description
Technical Field
[0001] This invention belongs to the field of organic chemical engineering and relates to a method for preparing folic acid. Background Technology
[0002] Folic acid is a water-soluble B vitamin that plays a vital role in the metabolism of higher animals and humans. It appears as a yellow to orange crystalline powder and is used in medicine, food, and animal feed. In medicine, folic acid is used as a preventative and therapeutic agent for anemia due to its significant effect on the condition. It also promotes development, maintains normal gastrointestinal function, enhances the absorption of vitamin A, and participates in the formation of red blood cells and other body cells. In the food and animal feed industries, folic acid is commonly used as an additive in anti-anemia medications and as a nutritional supplement.
[0003] The current mainstream folic acid production process is characterized by a long synthesis reaction time, generally 6-8 hours, and a large water consumption. The water consumption of the crude folic acid synthesis step in existing processes reaches more than 120 times the required amount. Because the raw material 6-hydroxy-2,4,5-triaminopyrimidine sulfate is insoluble in the reaction solution, the reaction is a solid-liquid mixture. The folic acid produced during the reaction is difficult to separate from the raw material, leading to incomplete reaction and low purity of the synthesized crude product, generally 65-72%, with a low yield of 70-75%. After alkali purification and acid purification, the final folic acid product is obtained, with an overall yield of approximately 60-65%.
[0004] In practical applications, to prevent material oxidation, the folic acid cyclization process requires the addition of large amounts of antioxidants, leading to increased production costs and greater difficulty in treating wastewater from the synthesis process. While some improved solutions employ nitrogen protection to isolate oxidation, the large amount of water used as a solvent in folic acid synthesis means that dissolved oxygen in the water cannot be isolated by nitrogen. This makes it difficult to reduce the amount of antioxidants used and effectively control the oxidation process. Summary of the Invention
[0005] This invention provides a method for preparing folic acid to address the problems existing in the prior art. The method uses a deoxygenated weak alkaline solution and deoxygenated water to dissolve the raw materials for folic acid synthesis, and carries out the synthesis reaction in a deoxygenated water and vacuum oxygen-free environment. This method can accelerate the folic acid synthesis reaction rate, reduce the amount of water consumed in the process and the amount of antioxidants used, and improve the quality and yield of crude folic acid.
[0006] To solve the above problems, the present invention adopts the following technical solution:
[0007] Step (1) Add N-(4-aminobenzoyl)-L-glutamic acid, trichloroacetone and antioxidant to deoxygenated water according to the proportion, heat to 40℃~50℃, stir and dissolve in a vacuum range of -0.095Mpa~-0.04Mpa, keep warm and pressurized for 30min~60min to obtain deoxydiammonia solution;
[0008] In this step, the mass ratio of N-(4-aminobenzoyl)-L-glutamic acid, trichloroacetone, antioxidant, and deoxygenated water is 1:(1.05~16):(0.02~0.06):(15~25); the trichloroacetone is any one of trichloroacetone stock solution, trichloroacetone aqueous extract, and purified trichloroacetone crystals, and the content of 1,1,3-trichloroacetone in the trichloroacetone stock solution, the trichloroacetone aqueous extract, and the purified trichloroacetone crystals is 10%~98% by mass percentage.
[0009] Step (2) Add 6-hydroxy-2,4,5-triaminopyrimidine sulfate and antioxidant to deoxygenated water in proportion, and then slowly add deoxygenated weak base aqueous solution under vacuum of -0.04Mpa to -0.095Mpa. Remove the generated gas (carbon dioxide) under vacuum until the pH value of the system is 8 to 10. Heat the material to 50℃ to 60℃, dissolve the material until it is clear, and then keep it at the temperature and pressure for 30min to 60min to obtain deoxytriamine solution.
[0010] In this step, the mass ratio of 6-hydroxy-2,4,5-triaminopyrimidine sulfate, antioxidant, and deoxygenated water is 1:(0.02~0.06):(18~25); the deoxygenated weak alkaline aqueous solution is an aqueous solution of sodium deoxycarbonate and / or sodium deoxybicarbonate, and the concentration of the deoxygenated weak alkaline aqueous solution is 10%~25%.
[0011] In step (3), under vacuum of -0.04 MPa to -0.095 MPa and temperature of 40°C to 50°C, the deoxytriammonium solution is slowly added to the deoxydiammonium solution for reaction. The gas (carbon dioxide) in the system is removed under vacuum. In this step, the mass ratio of the triammonium solution to the diammonium solution is 10:(12~16). After the triammonium solution is added, the reaction is maintained at the same temperature and pressure for 30 to 60 minutes. The reaction mixture is then cooled to 35°C to 40°C, and after crystallization, pressure filtration, and washing, crude folic acid is obtained. The obtained crude folic acid is then purified by acid, alkali, and drying to obtain the final folic acid product.
[0012] Preferably, the deoxygenated sodium carbonate aqueous solution is obtained by preparing sodium carbonate and deoxygenated water, or by dissolving sodium carbonate and non-deoxygenated water together and then deoxygenating it in a deoxygenation tower.
[0013] The deoxygenated sodium bicarbonate aqueous solution is obtained by preparing sodium bicarbonate and deoxygenated water, or by dissolving sodium bicarbonate and non-deoxygenated water together and then deoxygenating it in a deoxygenation tower.
[0014] The non-deoxygenated water is tap water or pure water.
[0015] Preferably, the mass ratio of deoxytriammonium solution and deoxydiammonium solution in step (3) is 10:(12~14).
[0016] The above technical solution has the following technical effects: The efficient folic acid preparation method of this technical solution uses a deoxygenated weak alkaline solution and deoxygenated water to dissolve the folic acid synthesis raw materials. The liquid-liquid dropwise reaction is carried out in a deoxygenated water and vacuum oxygen-free environment, which can avoid the dissolution-reaction time required by triammonium salt in the reaction process, avoid the problem of undissolved raw materials being wrapped by folic acid in the reaction process, and significantly reduce the oxidation of raw materials and products by oxygen in the reaction process. Therefore, this technical solution can accelerate the folic acid synthesis reaction rate, reduce the process water consumption and antioxidant dosage, and improve the quality and yield of crude folic acid synthesis. Detailed Implementation
[0017] The technical solution of the present invention will be further illustrated below through embodiments and comparative examples.
[0018] Example 1
[0019] 1900 L of deoxygenated water (0.2 mg / L dissolved oxygen) was pumped into the cyclization reactor. 115.0 kg of N-(4-aminobenzoyl)-L-glutamic acid (0.453 kmol, main content 99.0%, solid content 90.0%) and 6.0 kg of sodium metabisulfite were added. 700 kg of trichloroacetone aqueous extract (0.651 kmol, 1,1,3-trichloroacetone content 15%) was added. The mixture was stirred and dissolved at 50 °C until clear. The vacuum inside the reactor was gradually increased from -0.04 MPa to -0.095 MPa and maintained at this temperature and pressure for 60 min to obtain a deoxydiammonia solution.
[0020] 2600L of deoxygenated water (0.2mg / L dissolved oxygen) was pumped into a triammonium dissolving vessel. 130Kg of 2,4,5-triamino-6-hydroxypyrimidine hydrochloride (0.480Kmol, main content 93.0%, solid content 95.1%) and 5.0Kg of sodium metabisulfite were added. Stirring was started, and the material was heated to 55℃. Deoxysodium bicarbonate solution (0.4mg / L dissolved oxygen) was slowly added dropwise to the dissolving vessel under vacuum. The vacuum degree in the vessel was gradually increased from -0.04Mpa to -0.095Mpa. The pH value of the material in the vessel was adjusted to 10.0. The dropwise addition was stopped, and the material in the vessel was stirred and dissolved until clear. The mixture was kept at temperature and pressure for 60min to obtain a deoxytriammonium solution.
[0021] The deoxytriammonium solution was slowly added dropwise to the cyclization reactor via a dropper at a temperature of 40℃~50℃. As the addition proceeded, the vacuum level inside the reactor gradually increased from -0.04 MPa to -0.095 MPa, with the addition time controlled between 90 and 120 minutes. After the addition was complete, the reaction continued for another 60 minutes. The reactants were then cooled to 30℃~35℃, nitrogen was introduced to ventilate the reactor, and the mixture was pressure filtered. The filter cake was washed to obtain crude folic acid. 407.8 kg of crude folic acid was obtained. After drying, the crude folic acid content was determined to be 55.0%, and the folic acid content was 74.6% as determined by HPLC, resulting in a folic acid yield of 83.7%.
[0022] Crude folic acid was dissolved in 1.5 times its weight of 40% dilute sulfuric acid, filtered through a bag filter, and then subjected to water separation with 6 times its weight of water. The solution was filtered, washed, and the resulting product was purified. The purified product was dispersed in 3.5 times its weight of pure water, and the pH was adjusted to 9.5-9.0 by adding 10% sodium carbonate solution. The solution was heated to 85°C, and 2% activated carbon was added for decolorization. The solution was filtered, and the filtrate was back-adjusted to pH 3.5 with sulfuric acid. The solution was then slowly cooled to 40°C, filtered under pressure, washed with pure water, dried, and pulverized to obtain the purified folic acid product. 153.4 kg of folic acid product was obtained, with a purity of 98.3% and a yield of 75.4%.
[0023] Example 2
[0024] 1500L of deoxygenated water (dissolved oxygen 0.2mg / L) was pumped into the cyclization reactor. 115.0Kg of N-(4-aminobenzoyl)-L-glutamic acid (0.453Kmol, purity 99.0%, solid content 90.0%), 3.0Kg of sodium hydrosulfite, and 1100Kg of trichloroacetone aqueous extract (0.682kmol, 1,1,3-trichloroacetone content 10%) were added. The mixture was stirred and dissolved at 50℃ until clear. The vacuum inside the reactor was gradually increased from -0.04Mpa to -0.095Mpa and maintained at this temperature and pressure for 45min to obtain a deoxydiammonia solution.
[0025] 2600L of deoxygenated water (0.2mg / L dissolved oxygen) was pumped into the triammonium dissolving vessel. 130Kg of 2,4,5-triamino-6-hydroxypyrimidine hydrochloride (0.480Kmol, purity 93.0%, solid content 95.1%) and 2.5Kg of sodium hydrosulfite were added. Stirring was started, and the material was heated to 50℃. Deoxysodium carbonate solution (0.3mg / L dissolved oxygen) was slowly added dropwise to the dissolving vessel under vacuum. The vacuum in the dissolving vessel was gradually increased from -0.04Mpa to -0.095Mpa. The pH of the solution in the vessel was adjusted to 9.5, and the dropwise addition was stopped. The material in the vessel was stirred and dissolved until clear. The mixture was kept at the same temperature and pressure for 60min to obtain the deoxytriammonium solution.
[0026] The deoxytriammonium solution was slowly added dropwise to the cyclization reactor via a dropper at a temperature of 40℃~50℃. As the addition proceeded, the vacuum level inside the reactor gradually increased from -0.04 MPa to -0.095 MPa, with the addition time controlled between 90 and 120 minutes. After the addition was complete, the reaction was continued for 60 minutes. The reactants were then cooled to 30℃~35℃, nitrogen was introduced to ventilate the reactor, and the mixture was pressure filtered. The filter cake was washed to obtain 432.4 kg of crude folic acid. The crude folic acid was dried and the solid content was measured to be 54.0%. HPLC analysis showed that the folic acid content was 73.9%, with a yield of 86.3%.
[0027] Crude folic acid was dissolved in 1.5 times its weight of 40% dilute sulfuric acid, filtered, and then subjected to water separation with 6 times its weight of water. The solution was filtered, washed, and the resulting product was purified. The purified product was dispersed in 3.5 times its weight of pure water, and the pH was adjusted to 9.5-9.0 by adding sodium carbonate solution. The solution was heated to 85°C, and 2% activated carbon was added for decolorization. The solution was filtered, and the filtrate was back-adjusted to pH 3.5 with sulfuric acid. The solution was then slowly cooled to 40°C, filtered under pressure, washed with pure water, dried, and pulverized to obtain the purified folic acid product. 154.2 kg of folic acid product was obtained, with a purity of 98.8% and a yield of 76.2%.
[0028] Example 3
[0029] 2600L of deoxygenated water (dissolved oxygen 0.1mg / L) was pumped into the cyclization reactor. 115.0Kg of N-(4-aminobenzoyl)-L-glutamic acid (0.453Kmol, purity 99.0%, solid content 90.0%), 6.0Kg of sodium metabisulfite, and 105Kg of purified trichloroacetone crystals (0.618Kmol, 1,1,3-trichloroacetone content 95%) were added. The mixture was stirred at 40℃ until clear. The vacuum inside the reactor was gradually increased from -0.04Mpa to -0.095Mpa and maintained at this temperature and pressure for 30min to obtain a deoxydiammonia solution.
[0030] 2600L of deoxygenated water (0.1mg / L dissolved oxygen) was pumped into the triammonium dissolving vessel. 130Kg of 2,4,5-triamino-6-hydroxypyrimidine hydrochloride (0.480Kmol, purity 93.0%, solid content 95.1%) and 2.5Kg of sodium hydrosulfite were added. Stirring was started, and the material was heated to 60℃. A 15% deoxygenated sodium bicarbonate solution (0.3mg / L dissolved oxygen) was slowly dripped into the dissolving vessel under vacuum. The vacuum degree inside the vessel was gradually increased from -0.04Mpa to -0.095Mpa. The pH value of the material inside the vessel was adjusted to 8.0. The material inside the vessel was stirred and dissolved until clear. The mixture was kept at the same temperature and pressure for 45min to obtain the deoxygenated triammonium solution.
[0031] The deoxytriammonium solution was slowly added dropwise to the cyclization reactor via a dropper at a temperature of 40°C to 50°C. As the reaction proceeded, the vacuum level inside the reactor gradually increased from -0.04 MPa to -0.095 MPa. The dropwise addition time was controlled between 90 and 120 minutes. After the addition was complete, the reaction continued for another 60 minutes. The reactants were then cooled to 30°C to 35°C, nitrogen was introduced to ventilate the reactor, and the mixture was pressure filtered. The filter cake was washed to obtain crude folic acid. 395.9 kg of crude folic acid was obtained. After drying, the folic acid content was measured to be 55.6%, the folic acid content was 76.3%, and the crude folic acid yield was 84.0%.
[0032] Crude folic acid was dissolved in 1.5 times its weight of 40% dilute sulfuric acid, filtered, and then 6 times its weight of water was added for water separation. The solution was filtered, washed, and the resulting product was purified. The purified product was dispersed in 3.5 times its weight of pure water, and the pH was adjusted to 9.5-9.0 by adding sodium carbonate solution. The solution was heated to 85°C, and 2% activated carbon was added for decolorization. The solution was filtered, and the filtrate was back-adjusted to pH 3.5 with sulfuric acid. The solution was then slowly cooled to 40°C, filtered under pressure, washed with pure water, dried, and pulverized to obtain the purified folic acid product. 155.6 kg of folic acid product was obtained, with a purity of 98.3% and a yield of 76.5%.
[0033] Example 4
[0034] 2400L of folic acid purified washing solution and deoxygenated water (dissolved oxygen 0.2mg / L) was pumped into the cyclization reactor. 115.0Kg of N-(4-aminobenzoyl)-L-glutamic acid (para-ammonia salt) (0.453Kmol, purity 99.0%, solid content 90.0%), 5.0Kg of sodium hydrosulfite, and 190Kg of trichloroacetone stock solution (0.648Kmol, 1,1,3-trichloroacetone content 55%) were added. The mixture was stirred at 50℃ until clear. The vacuum inside the reactor was gradually increased from -0.04Mpa to -0.095Mpa and maintained at this temperature and pressure for 45min to obtain a deoxydiammonia solution.
[0035] 2600L of deoxygenated water (dissolved oxygen 0.2mg / L) of folic acid-refined washing solution was pumped into a triammonium dissolving vessel. 130Kg of 2,4,5-triamino-6-hydroxypyrimidine hydrochloride (0.480Kmol, purity 93.0%, solid content 95.1%) and 2.5Kg of sodium hydrosulfite were added. Stirring was started, and the material was heated to 60℃. A 15% deoxysodium bicarbonate solution (dissolved oxygen 0.7mg / L) was slowly dripped into the dissolving vessel under vacuum. The vacuum degree inside the vessel was gradually increased from -0.04Mpa to -0.095Mpa. The pH value of the material inside the vessel was adjusted to 9.0. The material inside the vessel was stirred and dissolved until clear. The mixture was kept at temperature and pressure for 60min to obtain a deoxytriammonium solution.
[0036] The deoxytriammonium solution was slowly added dropwise to the cyclization reactor via a dropper at a temperature of 40℃~50℃. As the reaction proceeded, the vacuum level inside the reactor was gradually increased from -0.04 MPa to -0.095 MPa, with the addition time controlled between 90 and 120 minutes. After the addition was complete, the reaction continued for another 60 minutes. The reactants were then cooled to 30℃~35℃, nitrogen was introduced to purge the atmosphere, and the mixture was pressure filtered. The filter cake was washed to obtain 381.4 kg of crude folic acid. The crude folic acid sample was dried and the solid content was measured to be 57.6%. HPLC analysis determined the crude folic acid content to be 77.1%, with a yield of 84.7%.
[0037] Crude folic acid was dissolved in 1.5 times its weight of 40% dilute sulfuric acid, filtered, and then 6 times its weight of water was added for water separation, followed by filtration, washing, and collection of the purified folic acid product. The washing liquid was collected separately in a folic acid purification washing liquid storage tank. The purified folic acid product was dispersed in 3.5 times its weight of pure water, and the pH was adjusted to 9.5-9.0 by adding sodium carbonate solution. The temperature was raised to 85°C, and 2% activated carbon was added for decolorization. The product was then filtered, and the filtrate was back-adjusted to pH 3.5 with sulfuric acid. After slowly cooling to 40°C, the product was pressure filtered, washed with pure water, dried, and pulverized to obtain the purified folic acid product. The pure water washing liquid was collected separately in a folic acid purification washing liquid storage tank. 152.2 kg of folic acid product was obtained, with a purity of 98.3% and a yield of 74.8%. The folic acid refined washing solution is pumped from the storage tank into the deoxygenation tower. Pure carbon dioxide is introduced into the bottom of the deoxygenation tower to remove dissolved oxygen from the folic acid refined washing solution. The oxygen content of the deoxygenated folic acid refined washing solution is 0.1 mg / L. The resulting deoxygenated folic acid refined washing solution is pumped into the process water storage tank for the next batch of feed.
[0038] Comparative Example
[0039] Comparative Example 1: The procedure for adding a large dose of antioxidants under normal pressure, with crude folic acid as follows:
[0040] 11,000 L of water was pumped into the cyclization reactor, and 115.0 kg of N-(4-aminobenzoyl)-L-glutamic acid (0.453 kmol, purity 99.0%, solid content 90.0%), 60.0 kg of sodium metabisulfite, and 700 kg of trichloroacetone aqueous extract (0.651 kmol, 1,1,3-trichloroacetone content 15%) were added. The mixture was stirred and heated at 40-50 °C until completely dissolved to obtain a diammonium solution.
[0041] 130 kg of 2,4,5-triamino-6-hydroxypyrimidine hydrochloride (0.480 kmol, purity 93.0%, solid content 95.1%) was added to a cyclization reactor and stirred for 60 min. Then, sodium carbonate solution was slowly added dropwise to a dissolving reactor at 40℃~45℃. The pH of the solution in the reactor was adjusted to 4.5. After the addition was complete, the reaction continued for 360 min. After the reaction was complete, the material was cooled to 35℃~40℃, filtered under pressure, and the filter cake was washed to obtain 379.5 kg of crude folic acid. The crude folic acid was dried and the solid content was determined to be 56%. HPLC analysis showed that the crude folic acid content was 72%, with a yield of 76.0%.
[0042] Crude folic acid was dissolved in 1.5 times its weight of 40% dilute sulfuric acid, filtered, and then 6 times its weight of water was added for water separation. The mixture was then filtered, washed, and the resulting product was purified. The purified product was dispersed in 3.5 times its weight of pure water, and the pH was adjusted to 9.5-9.0 by adding sodium carbonate solution. The mixture was heated to 85°C, and 2% activated carbon was added for decolorization. After filtration, the filtrate was back-adjusted to pH 3.5 with sulfuric acid, slowly cooled to 40°C, and then filtered under pressure. The filtrate was washed with pure water, dried, and pulverized to obtain the purified folic acid product. 133.2 kg of folic acid product was obtained, with a purity of 97.2% and a yield of 64.8%.
[0043] Comparative Example 2: Nitrogen-protected operation procedure, the operation steps of which are as follows:
[0044] 11,000 L of water was pumped into the cyclization reactor, and 115.0 kg of N-(4-aminobenzoyl)-L-glutamic acid (0.453 kmol, purity 99.0%, solid content 90.0%), 60.0 kg of sodium metabisulfite, and 700 kg of trichloroacetone aqueous extract (0.651 kmol, 1,1,3-trichloroacetone content 15%) were added. The mixture was stirred and heated at 40-50 °C until completely dissolved to obtain a diammonium solution.
[0045] 130 kg of 2,4,5-triamino-6-hydroxypyrimidine hydrochloride (0.480 kmol, purity 93.0%, solid content 95.1%) was added to a cyclization reactor and stirred for 30 min. Nitrogen gas was introduced at a pressure of 0.3 MPa by opening the nitrogen valve. The nitrogen valve was then closed, and the vent valve was opened to release the fumes. Nitrogen was purged three times until the oxygen content in the reactor was below 5000 ppm. Sodium carbonate solution was then slowly added dropwise to a dissolving reactor at 40℃~45℃ under nitrogen protection. The pH of the solution in the reactor was adjusted to 4.5. After the addition was complete, the reaction continued for 360 min. After the reaction was complete, the material was cooled to 35℃~40℃, filtered under pressure, and the filter cake was washed to obtain 136.9 kg of crude folic acid. The crude folic acid was dried and the solid content was measured to be 57%. HPLC analysis showed that the crude folic acid content was 72.8%, with a yield of 77.4%.
[0046] Crude folic acid was dissolved in 1.5 times its weight of 40% dilute sulfuric acid, filtered, and then 6 times its weight of water was added for water separation. The mixture was filtered, washed, and the resulting product was purified. The purified product was dispersed in 3.5 times its weight of pure water, and the pH was adjusted to 9.5-9.0 by adding sodium carbonate solution. The mixture was heated to 85°C, and 2% activated carbon was added for decolorization. After filtration, the filtrate was back-adjusted to pH 3.5 with sulfuric acid, slowly cooled to 40°C, and then filtered under pressure. The filtrate was washed with pure water, dried, and pulverized to obtain the purified folic acid product. 140.0 kg of folic acid product was obtained, with a purity of 97.5% and a yield of 66.8%.
[0047] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.
[0048] Based on the above-described preferred embodiments of the present invention, and through the foregoing description, those skilled in the art can make various changes and modifications without departing from the inventive concept. The technical scope of this invention is not limited to the contents of the specification, but must be determined according to the scope of the claims.
Claims
1. A method for preparing folic acid, characterized in that, Includes the following steps: (1) Add N-(4-aminobenzoyl)-L-glutamic acid, trichloroacetone and antioxidant to deoxygenated water in a specified ratio, heat to 40℃~50℃, gradually increase the vacuum degree of the system from -0.04Mpa to -0.095Mpa, stir the material to dissolve until clear, keep warm and pressurized for 30min~60min to obtain deoxydiammonia solution; (2) Add 6-hydroxy-2,4,5-triaminopyrimidine sulfate and antioxidant to deoxygenated water in a specified ratio. Heat the material to 50℃~60℃, slowly add the deoxygenated weak alkaline aqueous solution, remove the generated gas under vacuum, adjust the pH value of the material to 8~10, stop the dripping, dissolve the material until it is clear, keep it warm and pressurized for 30min~60min to obtain deoxytriamine solution; (3) Under a vacuum of -0.04 MPa to -0.095 MPa and a temperature of 40°C to 50°C, the deoxytriammonium solution is slowly added to the deoxydiammonium solution. After the deoxytriammonium solution is completely added, the material continues to react for 30 to 60 minutes. The reactants are then cooled to 35°C to 40°C, purged with nitrogen, filtered, and washed to obtain crude folic acid. The crude folic acid is then purified by acid, alkali, and dried to obtain the final folic acid product. The deoxygenated water mentioned in steps (1) and (2) is: deoxygenated water from folic acid refined detergent, deoxygenated pure water, and deoxygenated tap water, wherein the dissolved oxygen content in the deoxygenated water is 0-0.2 mg / L; The deoxygenated weak alkaline aqueous solution mentioned in step (2) is a sodium deoxycarbonate aqueous solution and / or a sodium deoxybicarbonate aqueous solution with a concentration of 10%~25%.
2. The method for preparing folic acid as described in claim 1, characterized in that, The deoxygenated sodium carbonate aqueous solution is obtained by preparing sodium carbonate and deoxygenated water, or by dissolving sodium carbonate and non-deoxygenated water together and then deoxygenating it in a deoxygenation tower. The deoxygenated sodium bicarbonate aqueous solution is obtained by preparing sodium bicarbonate and deoxygenated water, or by dissolving sodium bicarbonate and non-deoxygenated water together and then deoxygenating it in a deoxygenation tower. The non-deoxygenated water is tap water or pure water.
3. The method for preparing folic acid as described in claim 1, characterized in that, In step (2), the mass ratio of 6-hydroxy-2,4,5-triaminopyrimidine sulfate: antioxidant:deoxygenated water is 1:(0.02~0.06):18~25.
4. The method for preparing folic acid as described in claim 1, characterized in that, In step (1), trichloroacetone is any one of trichloroacetone stock solution, trichloroacetone aqueous extract, and purified trichloroacetone crystals; The contents of 1,1,3-trichloroacetone in the stock solution, the aqueous extract, and the purified crystals are 10% to 98% by mass.
5. The method for preparing folic acid as described in claim 1, characterized in that, In step (1), the mass ratio of N-(4-aminobenzoyl)-L-glutamic acid, trichloroacetone, antioxidant, and deoxygenated water is 1:(1.05~16):(0.02~0.06):(15~25).