Method for recovering components of a vitamin c crystallization mother liquor

Abstract

The present application relates to a kind of crude vitamin C crystallization mother liquor component recovery method, first determine the content of vitamin C and gulonic acid in crude vitamin C mother liquor, determine the density of the mixture after evaporation of scraper film evaporator discharge;Active carbon is added to the crude vitamin C mother liquor, and decolorization is filtered;The decolorized mother liquor is sent to scraper film evaporator, and evaporated under reduced pressure;The mother liquor after evaporation is sent to crystallization tank and crystallized by cooling, the solubility of vitamin C and gulonic acid is different, the water in the mother liquor is removed by uniform evaporation, the concentration of VC and gulonic acid two components grows in proportion, wherein VC is saturated first and part of crystallization comes out, then gulonic acid just reaches saturation by cooling and no crystal is precipitated. High-purity VC crude product is obtained by cooling and centrifugation, and VC crude product is dissolved and added to the main line of production, and gulonic acid is transferred to the mother liquor for subsequent treatment.

Description

Technical Field

[0001] The present invention relates to a method for recovering a vitamin C mother liquor, in particular to a method for recovering a crude vitamin C crystallization mother liquor component. Background Art

[0002] Vitamin C is currently produced through a two-step fermentation process. L-sorbitol is fermented by microorganisms to produce citric acid. Citric acid is then crystallized and centrifuged to produce a wet citric acid product. The wet citric acid reacts with methanol at 65°C under the catalysis of concentrated sulfuric acid. Sodium carbonate is added to the esterified solution to convert it into sodium vitamin C salt. The sodium vitamin C salt undergoes ion exchange, concentration, crystallization, and centrifugation to produce crude VC and a crude VC mother liquor. During the citric acid esterification process, since citric acid itself contains water of crystallization and its esterification reaction with methanol is reversible, the reaction cannot proceed 100%. As a result, some citric acid will enter the next step and enter the crude VC mother liquor during the centrifugation process.

[0003] The main components of crude VC mother liquor are VC and gulonic acid. Currently, the industry mainly adopts the traditional forced circulation evaporation method to reduce the pressure on VC and gulonic acid to evaporate the density of the mixed liquor to above 1.40 kg / L. After cooling, centrifugation is performed to obtain a solid. This solid contains VC and gulonic acid, of which the VC content is about 70% and the gulonic acid content is about 30%. The material needs to be re-dissolved, crystallized and centrifuged to obtain a high-purity VC wet product, which is then dissolved again and returned to the VC main line production, or directly enters the synthesis section esterification and conversion process for re-reaction to obtain vitamin C sodium salt, and then returned to the VC production line for processing. These two process lines are long, require high energy consumption, and have extremely low yields. The recrystallization process has a yield of about 36%, and a large amount of VC enters the second mother liquor, which puts huge pressure on the mother liquor treatment. The esterification conversion process line is longer and has higher energy consumption. Therefore, further research is needed to study the separation of VC and gulonic acid in crude VC mother liquor in vitamin C production. Summary of the Invention

[0004] In view of the deficiencies in the prior art, the present invention aims to provide a method for recovering crude vitamin C crystallization mother liquor components.

[0005] In order to achieve the above object, the technical solution adopted by the present invention is:

[0006] A method for recovering crude vitamin C mother liquor components comprises the following steps:

[0007] (1) Determine the contents of vitamin C and gulonic acid in the crude vitamin C mother liquor and determine the density of the discharge mixture after evaporation using a scraped film evaporator;

[0008] (2) adding activated carbon to the crude vitamin C mother liquor and decolorizing it through a leaf filter;

[0009] (3) feeding the decolorized mother liquor into a scraped thin film evaporator for evaporation under reduced pressure; wherein the relative vacuum degree is -0.090 MPa to -0.096 MPa, the evaporation temperature is 38-45°C, and the evaporation time is 10-20 seconds;

[0010] (4) The evaporated mother liquor is sent to a crystallization tank for cooling and crystallization. The terminal temperature of the cooling is controlled at 5°C and the crystallization time is 6-8 hours. Due to the different solubilities of vitamin C and gulonic acid, vitamin C is crystallized out of the crystallization tank first.

[0011] (5) After crystallization, centrifugation is performed to separate the wet vitamin C product. The remaining liquid is gulonic acid and part of the unprecipitated vitamin C.

[0012] In the recovery method, when the mass content of vitamin C in the crude vitamin C mother liquor is 16%-18%, the mass content of citric acid is 8%-12%, and the density of the discharge mixture after evaporation in the scraper film evaporator is controlled to be 1.30-1.26 kg / L.

[0013] Preferably, when the mass content of citric acid is 8%, the density of the discharged mixture is 1.30 kg / L; when the mass content of citric acid is 9%, the density of the discharged mixture is 1.29 kg / L; when the mass content of citric acid is 10%, the density of the discharged mixture is 1.28 kg / L; when the mass content of citric acid is 11%, the density of the discharged mixture is 1.27 kg / L; when the mass content of citric acid is 12%, the density of the discharged mixture is 1.26 kg / L.

[0014] In the recovery method, the amount of activated carbon added is 2-5% of the mass content of VC in the crude vitamin C mother liquor; the decolorization time is 10-30 minutes; the extinction coefficient of the crude vitamin C mother liquor after decolorization is less than 0.14; and the cooling rate during cooling crystallization is 3-7°C / h.

[0015] Beneficial effects of the present invention:

[0016] Vitamin C is a heat-sensitive material, and factors such as evaporation temperature and time significantly impact its quality and yield. In particular, crude vitamin C mother liquor contains miscellaneous acids such as sulfuric acid, which have a strong oxidizing effect on the vitamin C mother liquor, easily leading to problems such as high extinction and low yield. The present invention uses a scraped film evaporator instead of a traditional evaporator. During the entire evaporation process, material enters the scraped film evaporator by gravity from the top and exits from the bottom. The evaporation time is 10-20 seconds, resulting in short material heating time and low evaporation temperature. This effectively mitigates the effects of high temperatures and prolonged evaporation time on vitamin C.

[0017] The present invention adopts a scraper film evaporator and utilizes the different solubilities of VC and gulonic acid to remove moisture from the mother liquor through uniform evaporation, so that the concentrations of the two components, VC and gulonic acid, increase in the same proportion. The VC component first reaches saturation and partially crystallizes out, and then the gulonic acid is cooled until it reaches a saturated state without crystal precipitation. A high-purity crude VC product is then obtained through cooling, crystallization, and centrifugation. After the crude VC product is dissolved, it is returned to the main production line and incorporated into the main production line. The gulonic acid is transferred to the mother liquor for subsequent treatment. This method has been shown to be very effective through more than two years of practical application and is therefore worth promoting and utilizing.

[0018] Since the content of gulonic acid is unstable in actual production, when gulonic acid is not crystallized, the higher the density of the evaporated mixture after evaporation (commonly known as evaporation specific gravity), the higher the VC yield. Therefore, it is necessary to control the evaporation specific gravity of the scraper film evaporator according to the gulonic acid content. The gulonic acid content in the mother liquor of the present invention is 8%-12%, and the corresponding evaporation density is 1.26-1.30kg / L. After cooling and crystallization centrifugation, the VC wet product content is 96%-99%, and after dissolution, it enters the main line production.

[0019] Compared with the traditional process, the process of the present invention shortens the route, reduces energy consumption, and improves yield. According to calculations, the vitamin C yield can be increased by more than 2% compared with the original process, and energy consumption can be saved by more than 50%. Based on an annual production capacity of 10,000 tons of vitamin C, the annual comprehensive economic benefit is more than 7 million yuan, which is a good economic benefit and worthy of promotion and application. DETAILED DESCRIPTION

[0020] The specific embodiments of the present invention are further described in detail below with reference to the examples.

[0021] Table 1 Solubility of VC and gulonic acid at different temperatures (g / L)

[0022]

[0023] Example 1 A method for recovering crude vitamin C mother liquor components comprises the following steps:

[0024] (1) Determine the contents of VC and gulonic acid in the crude vitamin C mother liquor and determine the evaporation specific gravity of the scraped film evaporator; wherein, the crude vitamin C mother liquor is 6 cubic meters, the density is 1.09 kg / L, the crude vitamin C mother liquor contains VC: 18% (wt), and gulonic acid: 9% (wt). Based on the solubility of gulonic acid at 5°C of 272.92 g / L, it is determined that the concentration is three times, that is, the VC content is 54% (wt), and the gulonic acid content is 27% (wt). The density of the mixed solution after evaporation by the scraped film evaporator is controlled to be 1.29 kg / L (i.e., the evaporation specific gravity is 1.29);

[0025] (2) Activated carbon was added to the crude vitamin C mother liquor and decolorized by a leaf filter. The amount of activated carbon added was 4% of the VC mass (pure VC) content in the crude vitamin C mother liquor. The decolorization time was 20 min. The extinction coefficient of the decolorized mother liquor was 0.13 (the extinction coefficient refers to the light absorption value of the solution being tested, measured at a wavelength of 420 nm and a 3 cm cuvette).

[0026] (3) The decolorized mother liquor is fed into a scraped film evaporator and evaporated under reduced pressure; wherein, the relative vacuum is -0.092 MPa, the evaporation temperature is ≤45°C, and the evaporation time is 20 seconds; the vitamin C mother liquor is concentrated to 3 times the original solution, that is, the crude vitamin C mother liquor after reduced pressure evaporation is 2 cubic meters;

[0027] Under the action of the scraper blade of the scraper film evaporator, the mother liquor is evenly heated in contact with the inner wall of the evaporator, and the water is evaporated. During this process, due to the different solubilities of VC solution and gulonic acid, the VC solution reaches supersaturation and some crystals have precipitated, while the gulonic acid has not reached saturation.

[0028] (4) The evaporated mother liquor was sent to the crystallization tank for further cooling and crystallization at a cooling rate of 5°C / h, with the cooling end temperature controlled at 5°C and a crystallization time of 7h;

[0029] Due to the difference in solubility, when citric acid just reaches saturation, no crystals are precipitated or a small amount of crystals are precipitated. At this time, VC is precipitated to the maximum extent, ensuring the yield and quality of VC.

[0030] (5) After crystallization, centrifugation is performed to separate the wet VC product. The remaining liquid is gulonic acid and part of the VC that has not been precipitated. The wet VC product is dissolved and then added into ion exchange liquid to produce crude VC. The remaining liquid is transferred to the mother liquor for subsequent treatment (such as continuing evaporation and crystallization to obtain a mixture of VC and gulonic acid, and then performing esterification and conversion treatment).

[0031] The VC wet product obtained by centrifugal separation has a VC content of 99% (wt), a VC yield of 74%, and a gulonic acid content of 0.35% (wt).

[0032] Example 2 A method for recovering crude vitamin C mother liquor components comprises the following steps:

[0033] (1) Determining the contents of VC and gulonic acid in crude vitamin C mother liquor and determining the evaporation specific gravity of a scraped film evaporator; wherein, 6 cubic meters of crude vitamin C mother liquor had a VC content of 16.8% (wt) and a gulonic acid content of 9.07% (wt); the vitamin C mother liquor was concentrated 3 times to a VC content of 50.4% (wt) and a gulonic acid content of 27.21% (wt); and the evaporation specific gravity of the scraped film evaporator was 1.28;

[0034] (2) Adding activated carbon to the crude vitamin C mother liquor and decolorizing it through a leaf filter. The amount of activated carbon added is 4% of the mass of VC (pure VC) in the crude vitamin C mother liquor. The decolorization time is 20 minutes. The extinction coefficient of the mother liquor after decolorization is 0.14.

[0035] (3) The decolorized mother liquor is fed into a scraped film evaporator and evaporated under reduced pressure; wherein, the relative vacuum is -0.092 MPa, the evaporation temperature is ≤45°C, and the evaporation time is 20 seconds; after the reduced pressure evaporation, the crude vitamin C mother liquor is 2 cubic meters;

[0036] (4) The evaporated mother liquor was sent to a crystallization tank for cooling and crystallization. The cooling rate was 5°C / h, the end temperature of the cooling was 5°C, and the crystallization time was 7h. Due to the difference in solubility, a large amount of VC crystals were precipitated at this time, while gulonic acid just reached saturation and no crystals were precipitated.

[0037] (5) After crystallization, centrifugation is performed to separate the wet VC product. The remaining liquid is gulonic acid and the unprecipitated VC.

[0038] The VC wet product is dissolved and incorporated into the main production line, and the remaining liquid is transferred to the mother liquor for subsequent treatment; the VC wet product obtained by centrifugation has a VC content of 99% (wt), a VC yield of 72%, and a gulonic acid content of 0.27% (wt).

Claims

1. A method for recovering crude vitamin C mother liquor components, characterized in that: The following steps are involved: (1) Determine the content of vitamin C and gulonic acid in the crude vitamin C mother liquor and determine the density of the discharge mixture after evaporation in a scraped film evaporator; (2) Adding activated carbon to the crude vitamin C mother liquor and decolorizing it through a leaf filter; (3) The decolorized mother liquor is fed into a scraped thin film evaporator for evaporation under reduced pressure; wherein the relative vacuum degree is -0.090 MPa to -0.096 MPa, the evaporation temperature is 38~45°C, and the evaporation time is 10-20 seconds; (4) The evaporated mother liquor is sent to a crystallization tank for cooling and crystallization. The end temperature of the cooling is controlled at 5°C and the crystallization time is 6-8 hours. Taking advantage of the different solubility of vitamin C and gulonic acid, vitamin C is crystallized out of the crystallization tank first. (5) After crystallization, centrifugation is performed to separate the wet vitamin C product. The remaining liquid is gulonic acid and some unprecipitated vitamin C. The mass content of vitamin C in the crude vitamin C mother liquor is 16%-18%, the mass content of citric acid is 8%-12%, and the density of the discharge mixture after evaporation in the scraped film evaporator is 1.30-1.26 kg / L.

2. The recycling method according to claim 1, wherein When the mass content of citric acid is 8%, the density of the discharge mixture is 1.30 kg / L; when the mass content of citric acid is 9%, the density of the discharge mixture is 1.29 kg / L; when the mass content of citric acid is 10%, the density of the discharge mixture is 1.28 kg / L; when the mass content of citric acid is 11%, the density of the discharge mixture is 1.27 kg / L; when the mass content of citric acid is 12%, the density of the discharge mixture is 1.26 kg / L.

3. The recycling method according to claim 1, wherein: The amount of activated carbon added is 2-5% of the VC mass content in the crude vitamin C mother liquor; the decolorization time is 10-30 minutes.

4. The recycling method according to claim 1, wherein The extinction coefficient of the crude vitamin C mother liquor after decolorization is less than 0.

14.

5. The recycling method according to claim 1, wherein: The cooling rate during cooling crystallization is 3-7°C / h.

6. The recycling method according to claim 1, wherein: In step (4), due to the different solubilities of vitamin C and citric acid, the terminal temperature during cooling and crystallization is controlled so that vitamin C crystals are precipitated after cooling, while citric acid just reaches a saturated state and no crystals are precipitated.

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