A concentrated crystallization process for gulonic acid

Abstract

The present invention relates to an important intermediate in the production process of vitamin C - L-2-keto-gulonic acid, and in particular to a concentration and crystallization process of gulonic acid. The method of the present invention comprises the following steps: concentrating the gulonic acid nanofiltrate by reduced pressure evaporation in an evaporator, the concentration condition being that the relative vacuum degree is greater than or equal to 0.090 MPa, concentrating to an end point solid content of 50-62%, cooling and crystallizing, and washing the crystals with low-temperature water during centrifugation. The mother liquor washed with water is directly concentrated and crystallized to obtain a dry mother liquor. The present invention solves the current situation of large-scale use and recovery of methanol in the production of gulonic acid, and high explosion-proof grade of production equipment and regions, improves the quality of the intermediate gulonic acid, reduces production costs, and improves production safety.

Description

Technical Field

[0001] The present invention relates to L-2-keto-gulonic acid, an important intermediate in the production process of vitamin C, and in particular to a concentrated crystallization process of gulonic acid, belonging to the technical field of vitamin C production. Background Art

[0002] Vitamin C is one of the 26 essential medicines jointly identified by the World Health Organization and the United Nations Industrial Development Organization. It is a nutrient that the human body needs but cannot synthesize on its own. Its disease prevention and health care functions and auxiliary therapeutic effects play an increasingly important role in people's health. Therefore, the production scale of vitamin C continues to expand and the process technology continues to improve. At present, vitamin C production generally consists of fermentation, extraction, conversion, and crystallization. The citric acid prepared in the extraction process is an important intermediate for the preparation of crude vitamin C. At present, in the production process of the intermediate citric acid, the conventional process mainly adopts the preparation method of concentrating the citric acid liquid and then adding methanol for crystallization, centrifugation, and washing the crystals with methanol. The above-mentioned existing process has the problems of large methanol consumption, high explosion-proof level of production equipment, high requirements for transportation and storage of intermediates, and difficulty in recovering mother liquor. Summary of the Invention

[0003] In order to solve the above problems, the object of the present invention is to provide a method with simple process, high safety and no methanol crystallization.

[0004] The objectives of the present invention are achieved by the following process: evaporating and concentrating the gulonic acid liquid under vacuum conditions (hereinafter referred to as primary concentration), cooling and stirring to crystallize, controlling the crystallization temperature during the process, centrifuging, and washing the crystals with cold water to obtain the gulonic acid finished product and a primary mother liquor; and evaporating and concentrating the primary mother liquor under vacuum conditions (hereinafter referred to as secondary concentration), stirring and crystallizing at room temperature, centrifuging, and washing with a small amount of cold water to obtain the gulonic acid mother liquor dry product and a secondary mother liquor. The present invention is characterized in that the entire production process does not involve the use of methanol or any other organic solvents.

[0005] The process steps of the present invention are as follows: the gulonic acid exchange liquid is concentrated by nanofiltration and triple-effect vacuum concentration, the concentrated liquid is evaporated and concentrated under vacuum conditions to a gulonic acid content of 50-62% (w / w) (hereinafter referred to as primary concentration), cooled and stirred for crystallization for 3 hours, the crystallization temperature is controlled at 2-5°C during the process, centrifuged, and the crystals are washed with 4°C cold water to obtain a gulonic acid finished product and a primary mother liquor. The primary mother liquor is evaporated and concentrated under vacuum conditions to a gulonic acid content of 45-50% (w / w) (hereinafter referred to as secondary concentration), stirred at room temperature for 8 hours to crystallize, centrifuged, and washed with a small amount of cold water to obtain a dry gulonic acid mother liquor and a secondary mother liquor.

[0006] The present invention solves the problems of large-scale methanol use and recovery in the production of gulonic acid and high explosion-proof grade of production equipment and areas, improves the quality of the intermediate gulonic acid, reduces production costs and improves production safety. DETAILED DESCRIPTION

[0007] The following is a clear and complete description of the technical solutions in the examples of implementation of the present invention. The described embodiments are only part of the embodiments of the present invention, not all of them. All other embodiments obtained based on the embodiments of the present invention without making creative work in the art are within the scope of protection of the present invention.

[0008] Example 1: The gulonic acid feed solution has a gulonic acid content of 37.08% (w / w). 4000 g of the above feed solution was evaporated and concentrated under vacuum to 2695 g, with a gulonic acid content of 55% (w / w), and transferred to a 3L open glass beaker. Cool and stir to crystallize for 3 hours, and control the crystallization temperature in a water bath at 2-5°C during the process. The crystallization liquid was centrifuged and washed with 4°C cold water to obtain 1350.4 g of gulonic acid. The primary mother liquor was evaporated and concentrated under vacuum to 534.5 g, and the gulonic acid content was measured to be 49% (w / w). Crystallization was stirred for 8 hours at room temperature, centrifuged, and washed with a small amount of cold water to obtain 249 g of dry gulonic acid mother liquor and 255 g of secondary mother liquor with a viscosity of 28.4 mPa·s. The total crystallization yield was 96.35%.

[0009] Comparative methanol process: 4000g of the same batch of gulonic acid solution was concentrated under vacuum evaporation to 2180.6g, with a gulonic acid content of 68% (w / w). 563ml of methanol was added and the product was transferred to a 3L three-necked glass flask. Cooling and stirring allowed to crystallize for 3h, maintaining the crystallization temperature at -4-2°C in an ice-salt bath. The crystals were centrifuged and washed with -2°C ice-cold methanol to yield 1449.4g of gulonic acid. The primary mother liquor was concentrated under vacuum to 489.5g, with a gulonic acid content of 36% (w / w). The methanol content of the concentrated water was determined to be 40% (w / w). Crystallization was allowed to proceed with stirring at room temperature for 8h, followed by centrifugation and washing with a small amount of cold water to yield 138g of the dry gulonic acid mother liquor and 268.7g of the secondary mother liquor with a viscosity of 48.6mPa·s. The total crystallization yield was 95.18%.

[0010] Example 2: The gulonic acid feed solution had a gulonic acid content of 36.7% (w / w). 4000 g of the above feed solution was evaporated and concentrated under vacuum to 2488 g, with a gulonic acid content of 59% (w / w). The solution was then transferred to a 3L open glass beaker and cooled and stirred for crystallization for 3 hours. During the crystallization process, the temperature was controlled at 2-5°C in a water bath. The crystallization solution was centrifuged and washed with 4°C cold water to obtain 1367.2 g of gulonic acid. The primary mother liquor was evaporated and concentrated under vacuum to 545 g, with a gulonic acid content of 43% (w / w). Crystallization was stirred for 8 hours at room temperature, centrifuged, and washed with a small amount of cold water to obtain 218 g of the dry gulonic acid mother liquor with a viscosity of 23.5 mPa·s and a total crystallization yield of 96.53%.

[0011] Comparative methanol process: 4000g of the same batch of gulonic acid solution was concentrated under vacuum evaporation to 2158.8g, with a gulonic acid content of 68% (w / w). 558ml of methanol was added and transferred to a 3L three-necked glass flask. Crystallization was carried out by cooling and stirring for 3 hours, maintaining the crystallization temperature at -4-2°C in an ice-salt bath. The crystals were centrifuged and washed with -2°C ice-cold methanol to yield 1430.2g of gulonic acid. The primary mother liquor was concentrated under vacuum to 443g, with a gulonic acid content of 38% (w / w). The methanol content of the concentrated water was 42% (w / w). Crystallization was carried out by stirring at room temperature for 8 hours, centrifuging, and washing with a small amount of cold water to yield 158g of the dry gulonic acid mother liquor and 260.6g of the secondary mother liquor with a viscosity of 45.9 mPa·s. The total crystallization yield was 95.88%.

[0012] Example 3: Production line scale-up test: 4.78 mL of gulonic acid feed solution, with a gulonic acid content of 36.47% (w / w), was evaporated and concentrated in a concentrator under vacuum to a gulonic acid content of 55.93% (w / w). The solution was then discharged to a crystallizer and crystallized by cooling and stirring for 3 hours. The crystallizer was cooled with chilled water. The crystallized solution was centrifuged and washed with 4°C cold water to yield 1,962 kg of gulonic acid. The primary mother liquor was evaporated and concentrated in a mother liquor concentrator to a gulonic acid content of 45% (w / w). Crystallization was carried out by stirring at room temperature for 8 hours, centrifuged, and washed with cold water to yield 318 kg of recovered gulonic acid mother liquor and 0.31 mL of secondary mother liquor with a viscosity of 28.4 mPa·s. The total crystallization yield was 94.1%.

[0013] Comparative methanol process: 4.86 mL of the same batch of gulonic acid feed solution was concentrated under vacuum in a concentrator to a gulonic acid content of 68.2% (w / w). This was then discharged to a crystallizer, where 0.8 mL of methanol was added and stirred for 3 hours of crystallization. The crystallizer was cooled with icy brine. The crystallization solution was centrifuged and washed with -2°C icy methanol to yield 2068 kg of gulonic acid. The primary mother liquor was concentrated under vacuum to a gulonic acid content of 36.6% (w / w). Crystallization was stirred at room temperature for 8 hours, centrifuged, and washed with a small amount of cold water to yield 227 kg of recovered gulonic acid mother liquor and 0.3 mL of secondary mother liquor with a viscosity of 35.9 mPa·s. The total crystallization yield was 93.6%.

[0014] Examples 1-3 are all comparisons of alcohol-free crystallization and the existing methanol crystallization process, among which Example 3 is a production line amplification process. Through implementation, it was found that the alcohol-free process has a low degree of vacuum concentration, no problem of difficult discharge, and no methanol is used, which reduces the safety risk level and solves the problem of stickiness in the secondary concentration process in the methanol crystallization process. The total crystallization yield of gulonic acid has not only not decreased but has been improved, the quality of the secondary crystals of gulonic acid has also been improved, and the viscosity of the secondary mother liquor has been reduced.

[0015] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. All modifications, equivalent substitutions, etc. made within the claims of the present invention should be included in the protection scope of the present invention.

Claims

1. A concentrated crystallization process for gulonic acid, comprising: After the citric acid liquid is evaporated and concentrated under vacuum conditions, the concentration end point of the citric acid liquid after evaporation and concentration under vacuum conditions is controlled at 50-62% (w / w), and the liquid is cooled and stirred for crystallization. The crystallization temperature of the citric acid liquid after evaporation and concentration under vacuum conditions is controlled at 2-5°C. During the process, the crystallization temperature is controlled, the liquid is centrifuged, and the crystals are washed with cold water to obtain the citric acid finished product and the primary mother liquor. After the primary mother liquor is evaporated and concentrated under vacuum conditions, the concentration end point of the citric acid liquid after evaporation and concentration is controlled at 42-50% (w / w). The crystals after evaporation and concentration are stirred for 8 hours at room temperature for crystallization, centrifuged, and washed with a small amount of cold water to obtain the dry citric acid mother liquor and the secondary mother liquor. Methanol and any other organic solvents are not used in the preparation process.