L-ascorbic acid crystal form control process

Abstract

The invention belongs to the technical field of synthesis of vitamin C, and particularly relates to an L-ascorbic acid crystal form control process which comprises the following steps: S1, dissolving a crude L-sodium ascorbate mother liquor recovery dry product in a dissolving tank by using a washing solution to obtain a recovery dry product solution, feeding the recovery dry product solution into a recovery acidification tank, feeding a gulonic acid esterification conversion solution into a certified product acidification tank, respectively adding a sulfuric acid solution into the recovery acidification tank and the certified product acidification tank to obtain a sodium sulfate solid and a decolorizing solution; s2, feeding the decolored solution into a concentrating pan, and circularly concentrating the decolored solution between the concentrating pan and a heater through a circulating pump to obtain an L-ascorbic acid concentrated solution; and S3, crystallizing the L-ascorbic acid concentrated solution in a crystallization cylinder, then centrifuging to obtain crude L-ascorbic acid crystals, dissolving the crude L-ascorbic acid crystals to obtain a crude L-ascorbic acid solution, and sending out the crude L-ascorbic acid solution for refining. The crystallization rate is effectively increased, the production cost is reduced, and the product quality is improved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of synthesis of vitamin C, and particularly relates to a crystal form control process of L-ascorbic acid. BACKGROUND

[0002] L-ascorbic acid (vitamin C) is a water-soluble vitamin with strong reducing property, and is widely used in the fields of medicine, food, cosmetics and feed additives. The molecular structure of L-ascorbic acid contains an enediol structure, and L-ascorbic acid is easily soluble in polar solvents such as water and methanol, but the solubility in organic solvents changes significantly with temperature, and this property is often used in crystallization and purification processes. Industrially, L-ascorbic acid is mainly produced by a two-step fermentation method: taking glucose as a raw material, 2-keto-L-gulonic acid is generated by fermentation through the sorbitol pathway, and then L-ascorbic acid is obtained by chemical conversion. In the purification process of L-ascorbic acid, the solvent crystallization method is the mainstream technology, and methanol-water system is usually used for dissolution, concentration and crystallization.

[0003] In the production process, the methanol solution of ascorbic acid enters a forced circulation evaporator for vacuum concentration, and after the solvent water methanol is evaporated, the supersaturated solution is formed to precipitate ascorbic acid crystals. The crystallization is further increased and the crystalline particles are increased by cooling, and then the L-ascorbic acid crystalline particles are separated out by a centrifugal machine, and are transferred to the next process by an air flow conveying system. Since the crystal form of L-ascorbic acid is irregular and the fine particles are more, the material quality and the crystallization rate are affected, and therefore the crystal form control of L-ascorbic acid is carried out. SUMMARY

[0004] To solve the above technical problems, the application provides a crystal form control process of L-ascorbic acid, which effectively improves the crystallization rate, reduces the production cost and improves the product quality.

[0005] The crystal form control process of L-ascorbic acid provided by the application comprises the following steps:

[0006] S1, the crude L-ascorbic acid sodium mother liquor dry product is dissolved in a dissolving tank to obtain a recovered dry product solution, the recovered dry product solution enters a recovered acidification tank, the gulonic acid esterification conversion liquid enters a normal product acidification tank, sulfuric acid solution is added into the recovered acidification tank and the normal product acidification tank respectively to obtain sodium sulfate solid and a decolorizing liquid, and the sodium sulfate solid is washed with water methanol to obtain a washing liquid;

[0007] S2, the decolorizing liquid in the recovered acidification tank and the normal product acidification tank is sent into a concentration pot, the concentration pot is connected with a circulating pump through a circulating pipeline one, the circulating pump is connected with a heater through a circulating pipeline two, the heater is connected with the concentration pot through a circulating pipeline three, the decolorizing liquid is circulated between the concentration pot and the heater by the circulating pump to concentrate, the concentration rate is adjusted by adjusting the frequency of the circulating pump to obtain an L-ascorbic acid concentrated solution;

[0008] S3, the L-ascorbic acid concentrated solution is crystallized in a crystallization cylinder, then centrifuged to obtain crude L-ascorbic acid crystals, the crude L-ascorbic acid crystals are dissolved in a water dissolving tank to obtain a crude L-ascorbic acid solution, and the crude L-ascorbic acid solution is sent out for refining through a liquid conveying pipeline.

[0009] Preferably, the concentration of the sulfuric acid solution is 50%-60%.

[0010] Preferably, the proportion of methanol in the water-containing methanol is 80%-90%.

[0011] Preferably, the concentration is divided into an initial stage, a transition stage and a final concentration stage, the solvent volume concentrated in the initial stage accounts for 35%-40% of the total volume of the solution to be concentrated, and the time is 90-100 min; the solvent volume concentrated in the transition stage accounts for 20%-25% of the total volume of the solution to be concentrated, and the time is 110-120 min; and the solvent volume concentrated in the final concentration stage accounts for 10%-15% of the total volume of the solution to be concentrated, and the time is 30-60 min.

[0012] Preferably, the first circulating pipeline is provided with a vacuum sampling device.

[0013] Preferably, the vacuum sampling device comprises a sampling branch pipe connected with the first circulating pipeline, a sampling valve is arranged on the sampling branch pipe, and the sampling branch pipe is connected with a sampler through a quick connector.

[0014] Preferably, a back-pumping pipe is arranged on the sampling branch pipe, and a back-pumping valve is arranged on the back-pumping pipe.

[0015] Compared with the prior art, the present application has the following advantages:

[0016] 1. The concentration of the sulfuric acid solution used for acidification in the present application is higher, the present application directly uses a sulfuric acid solution for acidification, while the prior art uses a sulfuric acid solution and water as the acidification liquid (removing the process of adding 70 L of water in 1 cubic meter of conversion liquid in the previous process); the dry product recovered from the crude L-ascorbic acid sodium mother liquor in the present application is dissolved by a washing liquid, while the prior art uses water-containing methanol for dissolution, and the washing liquid contains a certain amount of L-ascorbic acid; through the above two measures, the content of L-ascorbic acid in the decolorizing liquid is increased by about 3% (from 15% to 18%), and the concentration temperature is reduced; with the increase of the content of L-ascorbic acid in the decolorizing liquid, the concentration kettle is closed with small steam before the crystal nucleus is precipitated, the crystallization time is prolonged, and the crystal growth is promoted;

[0017] 2. The concentration rate is adjusted by adjusting the frequency of the circulating pump: in the early stage, the frequency is increased to increase the evaporation speed when there is no crystal; in the middle stage, the frequency is reduced to avoid the breakage of the crystal when the crystal starts to form; and in the later stage, the frequency is adjusted to the appropriate value to increase the crystal particles with the increase of the crystal.

[0018] 3. The present invention adds a vacuum sampling device. In order to check the test results at any time, a vacuum sampling device is added to the circulation pipeline to ensure that samples can be taken at any time under vacuum evaporation.

[0019] 4. This invention changes the conveying method of crude L-ascorbic acid crystals. The original process used airflow to convey crude L-ascorbic acid crystals. During the conveying pipeline, the crude L-ascorbic acid crystal particles tumble and rub against each other for a long time, which destroys the crystal form, makes the particles smaller, and causes losses in quality and crystallization rate. After the improvement, the crude L-ascorbic acid solution is directly conveyed, and liquid conveying replaces airflow conveying. After the crude L-ascorbic acid crystals are centrifuged, they directly enter the water-soluble tank, thereby avoiding damage to the crystallized particles and improving the material quality and crystallization rate. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the process equipment structure of the present invention;

[0021] Figure 2 yes Figure 1 Enlarged structural diagram at point A in the middle;

[0022] In the diagram, 1. Dissolving tank; 2. Recycling acidification tank; 3. Authentic acidification tank; 4. Crystallization tank; 5. Concentrator; 6. Circulation pipeline 1; 7. Circulation pump; 8. Heater; 9. Water dissolving tank; 10. Liquid delivery pipeline; 11. Sampling branch pipe; 12. Sampling valve; 13. Quick connector; 14. Sampler; 15. Back-pull valve; 16. Acid mixing tank; 17. Centrifuge. Detailed Implementation

[0023] The technical solution of the present invention will now be clearly and completely described in conjunction with the accompanying drawings and embodiments.

[0024] Unless otherwise specified, all raw materials used in the examples were commercially available.

[0025] Example 1

[0026] like Figure 1 As shown, the L-ascorbic acid crystal form control process includes the following steps:

[0027] S1. The crude L-ascorbate sodium mother liquor is dissolved in the washing solution in the dissolving tank 1 to obtain the recovered dry product solution. The recovered dry product solution enters the recovery acidification tank 2. The gulon acidification conversion solution enters the normal product acidification tank 3. Sulfuric acid solution is added to the recovery acidification tank 2 and the normal product acidification tank 3 respectively to obtain sodium sulfate solid and decolorizing solution. The sodium sulfate solid is washed with water-containing methanol (methanol content 85%) to obtain the washing solution.

[0028] The sulfuric acid solution is prepared by mixing concentrated sulfuric acid and water in acid mixing tank 16, with a concentration of 60%.

[0029] S2, the decoloring solution in the recovery acidification tank 2 and the normal acidification tank 3 is sent to the concentration pot 5, the concentration pot 5 is connected with the circulating pump 7 through the circulating pipeline one 6, the circulating pump 7 is connected with the heater 8 through the circulating pipeline two, the heater 8 is connected with the concentration pot 5 through the circulating pipeline three, the decoloring solution is circulated between the concentration pot 5 and the heater 8 through the circulating pump 7 to concentrate, the concentration rate is adjusted by adjusting the frequency of the circulating pump 7, and the L-ascorbic acid concentrated solution is obtained;

[0030] Specifically, the concentration is divided into an initial stage, a transition stage and a final concentration stage, the solvent volume in the initial stage accounts for 40% of the total volume of the solution to be concentrated, and the time is 90 min; the solvent volume in the transition stage accounts for 25% of the total volume of the solution to be concentrated, and the time is 120 min; the solvent volume in the final concentration stage accounts for 10% of the total volume of the solution to be concentrated, and the time is 30 min. When the solvent is concentrated to 40% of the total volume of the solution to be concentrated, the crystal begins to precipitate, at this time, the concentration pot steam valve opening is reduced (from 80% to 40%), the solvent evaporation speed is reduced, the number of crystal nuclei precipitated is reduced, and the crystal growth time is prolonged, so that the ascorbic acid crystal with good crystal form is obtained.

[0031] As shown in Figure 2 The circulating pipeline one 6 is provided with a vacuum sampling device. The vacuum sampling device comprises a sampling branch pipe 11 connected with the circulating pipeline one 6, the sampling branch pipe 11 is provided with a sampling valve 12, and the sampling branch pipe 11 is connected with a sampler 14 through a quick connector 13. The sampling branch pipe 11 is provided with a back suction pipe, and the back suction pipe is provided with a back suction valve 15.

[0032] S3, the L-ascorbic acid concentrated solution is crystallized in the crystallization cylinder 4, then the crude L-ascorbic acid crystal is obtained by centrifugation with a centrifugal machine 17, the crude L-ascorbic acid crystal is dissolved in the water dissolving tank 9 to obtain a crude L-ascorbic acid solution, and the crude L-ascorbic acid solution is sent out for refining through the liquid conveying pipeline 10.

[0033] The crystallization cylinder is provided with a speed reducer (the maximum rotating speed is: under the condition that the motor frequency is 50 Hz, the stirring speed is 45 r / min), the stirring speed is adjusted by frequency conversion, specifically, in the initial stage of 1 h before crystallization, the frequency conversion is 35 Hz, the rotating speed is adjusted to 31.5 r / min, the number of crystal nuclei is reduced by reducing the rotating speed, and the crystal growth is promoted; in the second hour and the third hour of crystallization, since the consistency of the crystallization liquid increases with the increase of the crystal, the frequency conversion is adjusted to 40 Hz, and the rotating speed is 36 r / min; in the fourth hour of crystallization, the crystallization is in the final stage, the frequency conversion is adjusted to 45 Hz, and the rotating speed is 40.5 r / min, the rotating speed is appropriately increased under the premise of ensuring the crystal particles, and the cooling effect is improved.

[0034] The application improves the concentration crystallization rate by 2 percentage points (the crystallization rate is improved from 83% to 85%), improves the workshop yield by 1 percentage point (from 87% to 88%), and the annual economic benefit is 2 million yuan. The content of the decolorizing liquid L-ascorbic acid is improved by 3% (from 15% to 18%), 1200 tons of steam are saved per month, and the annual economic benefit is 1.6 million yuan.

Claims

1. A process for controlling the crystalline form of L-ascorbic acid, characterized in that, It comprises the following steps: S1, the recovered dry product of crude L-sodium ascorbate is dissolved in a dissolving tank (1) with a washing solution to obtain a recovered dry product solution, which enters a recovered acidification tank (2), and the gulonic acid esterification conversion solution enters a normal product acidification tank (3), sulfuric acid solution is added to the recovered acidification tank (2) and the normal product acidification tank (3) respectively to obtain sodium sulfate solid and a decolorizing solution, and the sodium sulfate solid is washed with water-containing methanol to obtain a washing solution; S2, the decolorizing solution in the recovered acidification tank (2) and the normal product acidification tank (3) is sent to a concentration pot (5), the concentration pot (5) is connected to a circulating pump (7) through a circulating pipeline one (6), the circulating pump (7) is connected to a heater (8) through a circulating pipeline two, and the heater (8) is connected to the concentration pot (5) through a circulating pipeline three, the decolorizing solution is circulated between the concentration pot (5) and the heater (8) through the circulating pump (7) to concentrate, the concentration rate is adjusted by adjusting the frequency of the circulating pump (7) to obtain an L-ascorbic acid concentrated solution; S3, the L-ascorbic acid concentrated solution is crystallized in a crystallization cylinder (4), and then centrifuged to obtain crude L-ascorbic acid crystals, the crude L-ascorbic acid crystals are dissolved in an aqueous solution tank (9) to obtain a crude L-ascorbic acid solution, and the crude L-ascorbic acid solution is sent out for refinement through a liquid conveying pipeline (10).

2. The L-ascorbic acid crystalline form control process of claim 1, wherein, The concentration of the sulfuric acid solution is 50%-60%.

3. The L-ascorbic acid crystalline form control process of claim 1, wherein, The proportion of methanol in the water-containing methanol is 80%-90%.

4. The L-ascorbic acid crystalline form control process of claim 1, wherein, The concentration is divided into an initial stage, a transition stage and a final concentration stage, the volume of the solvent concentrated in the initial stage accounts for 35%-40% of the total volume of the solution to be concentrated, and the time is 90-100 min; the volume of the solvent concentrated in the transition stage accounts for 20%-25% of the total volume of the solution to be concentrated, and the time is 110-120 min; The volume of the solvent concentrated in the final concentration stage accounts for 10%-15% of the total volume of the solution to be concentrated, and the time is 30-60 min.

5. The L-ascorbic acid crystalline form control process of claim 1, wherein, A vacuum sampling device is arranged on the circulating pipeline one (6).

6. The L-ascorbic acid crystalline form control process of claim 5, wherein, The vacuum sampling device comprises a sampling branch pipe (11) connected to the circulating pipeline one (6), a sampling valve (12) is arranged on the sampling branch pipe (11), and the sampling branch pipe (11) is connected to a sampler (14) through a quick connector (13).

7. The L-ascorbic acid crystalline form control process of claim 6, wherein, A back-pumping pipe is arranged on the sampling branch pipe (11), and a back-pumping valve (15) is arranged on the back-pumping pipe.

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