Preparation method of D-erythorbic acid and sodium salt thereof

Abstract

The invention relates to the technical field of preparation of D-erythorbic acid, in particular to a preparation method of D-erythorbic acid and sodium salt thereof. In an alkaline environment of methanol / sodium methoxide, 2-keto-D-methyl gluconate is converted into D-sodium erythorbate and generates water, the microporous molecular sieve is adopted to absorb the water generated in the reaction, on one hand, generation of a large number of by-products in the conversion process can be effectively avoided, and on the other hand, the reaction time is shortened; the method can effectively ensure the purity and yield of the converted product, on the other hand can effectively improve the conversion reaction rate, generated water is absorbed, so that the chemical equilibrium right shift in the conversion process is facilitated, in addition, in the conversion process, more violent reaction conditions such as higher pH control and higher temperature can be adopted, and the conversion efficiency is improved. Therefore, the improvement of the conversion reaction rate is further promoted. The method provided by the invention has the advantages of simple process, recyclable raw materials, low production cost, high product purity and better application prospect.

Description

Technical Field

[0001] The invention relates to the technical field of D-isoascorbic acid preparation, and in particular to a method for preparing D-isoascorbic acid and its sodium salt. Background Art

[0002] D-isoascorbic acid is an optical isomer of vitamin C, and therefore has similar chemical properties to vitamin C. It is a water-soluble antioxidant. D-isoascorbic acid is a food additive produced by fermenting 2-keto-D-glucose acid with glucose as raw materials, and then through esterification, conversion, acidification, and refining.

[0003] D-isoascorbic acid has poor stability, so D-isoascorbic acid or its sodium salt should be selected according to the type of food. Sodium D-isoascorbate is a safe and non-toxic food antioxidant preservative that can effectively reduce the oxidation of food and prevent its color, aroma and taste from fading. It has a color-enhancing effect on meat products and seafood. It can also inhibit the formation of nitrite, a carcinogen in food, and has the effects of lowering blood pressure, diuresis and detoxification in medicine. Currently, this product has been widely used in foods such as meat, fruit, and beverages. It can also be used in wool spinning, electroplating, feed processing, industrial water treatment, and petrochemical industries.

[0004] Existing methods for preparing sodium D-isoascorbate have been reported from time to time, but due to process and cost limitations, they have not been widely used in industry; the traditional mature direct fermentation method and indirect fermentation method are still the mainstream preparation processes. Domestic manufacturers generally use the indirect fermentation method, that is, glucose is first fermented by bacteria to produce 2-keto-D-gluconic acid calcium salt, and then esterified, converted, and refined to obtain the finished sodium D-isoascorbate.

[0005] In the preparation process of D-isoascorbic acid and sodium D-isoascorbate, both need to be purified. This is because a large amount of by-products are generated during the conversion reaction, which affects the yield and purity of the product, resulting in a complex entire production process and high production cost. Therefore, a simpler production process while ensuring product yield and purity is a technical problem that needs to be solved. Summary of the invention

[0006] The purpose of the present invention is to provide a method for preparing D-isoascorbic acid and its sodium salt, so as to solve the problem that the existing preparation method has low product purity and yield, thereby resulting in a complicated process flow.

[0007] To achieve the above object, the present invention adopts the following technical scheme: a method for preparing D-isoascorbic acid and its sodium salt, comprising the following steps:

[0008] S1, mixing 2-keto-D-gluconate methyl ester and methanol, and adding microporous molecular sieves to the mixed system;

[0009] S2, adding methanol alkali to the mixed system of S1 to carry out conversion reaction;

[0010] S3, filtering and cooling the reaction system after the conversion reaction in S2 to precipitate sodium D-isoascorbate, and then separating and drying to obtain sodium D-isoascorbate product;

[0011] S4, adding sulfuric acid to the reaction system after the conversion reaction in S2 for acidification, and then filtering and cooling to precipitate D-isoascorbic acid, and then separating and drying to obtain a D-isoascorbic acid product.

[0012] Furthermore, in the S1, the mass ratio of 2-keto-D-gluconate methyl ester to methanol is 1:1-3; the pore size of the microporous molecular sieve is 1-2 nm; and the mass ratio of 2-keto-D-gluconate methyl ester to the microporous molecular sieve is 1:1-2.

[0013] Furthermore, in the S2, the methanol alkali is a heterogeneous system obtained by mixing methanol and alkali and then mixing them evenly through a colloid mill.

[0014] Furthermore, the alkali is one of sodium hydroxide, sodium bicarbonate and sodium carbonate.

[0015] Furthermore, in the methanol alkali, the mass ratio of alkali to methanol is 1:1-3.

[0016] Furthermore, the methanol alkali is added slowly and evenly. During the addition of the methanol alkali, the pH of the mixed system is controlled to be 8-9. When the pH of the mixed system continues to rise, the addition is stopped and the conversion reaction ends.

[0017] Furthermore, in the above-mentioned S1-S2, the stirring intensity is 300-500 r / min.

[0018] Furthermore, in the S2, the reaction temperature is 70-90°C.

[0019] Furthermore, in the S3, the filtration is performed while hot; the filtrate obtained after filtration is cooled to 0°C; a small amount of seed crystals is added during precipitation, and the precipitation time is 1 to 3 hours; centrifugation, filtration, and vacuum drying are performed to obtain a D-sodium isoascorbate product, and the drying temperature is 50 to 60°C.

[0020] Furthermore, in the S4, the sulfuric acid is 98wt% concentrated sulfuric acid; the reaction system is cooled to 50-60°C before acidification with concentrated sulfuric acid; the temperature of the reaction system is controlled not to exceed 80°C during the addition of concentrated sulfuric acid, and the stirring intensity is 300-500r / min; after acidification with concentrated sulfuric acid, it is filtered while hot; after filtration, it is cooled to 0°C; a small amount of seed crystals is added during precipitation, and the precipitation time is 1-3h; centrifugation, filtration, and vacuum drying are performed to obtain a D-isoascorbic acid product, and the drying temperature is 50-60°C.

[0021] Beneficial effects of the present invention:

[0022] 1. The method of the present invention can timely absorb the water generated by the reaction during the conversion reaction by adding a microporous molecular sieve to the mixed system, thereby effectively solving the problem of hydrolysis side reaction during the conversion reaction and directly obtaining a high-purity, high-yield product;

[0023] 2. The process flow of the method of the present invention is simple. Since the side reactions in the conversion process are controlled, a high-purity product can be obtained without refining operation when the product is obtained by the method of the present invention, which can effectively improve production efficiency and reduce production costs, and has good application prospects;

[0024] 3. The method of the present invention can effectively improve the rate of the conversion reaction. In the method of the present invention, since the water generated by the reaction is absorbed, there is no need to consider the process of intensifying the hydrolysis reaction under high temperature conditions. Therefore, more intense reaction conditions can be used in the conversion reaction process, such as higher pH and higher temperature, thereby improving the rate of the conversion reaction, which plays a positive and beneficial role in improving production efficiency. DETAILED DESCRIPTION

[0025] The technical solution of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention.

[0026] Example 1

[0027] Preparation of Sodium D-Isoascorbate:

[0028] Take 100g of sodium carbonate and 200g of methanol to prepare methanol alkali, use a colloid mill to grind the sodium carbonate and methanol into a colloid mill and then set aside for later use. During the setting process, stir continuously to maintain a uniformly dispersed heterogeneous system.

[0029] Take 100 g of methyl 2-keto-D-gluconate, 200 g of methanol and 150 g of microporous molecular sieve and add them into a three-necked flask, stir and mix at 400 r / min and control the reaction temperature to 80° C. in a water bath.

[0030] A peristaltic pump is used to pump methanol alkali dropwise into the three-necked flask. During the process, the flow rate of the peristaltic pump is adjusted so that the pH in the three-necked flask is controlled at 8-9. At this time, the pH in the three-necked flask shows a trend of continuous fluctuation. When a drop of methanol alkali is dripped into the three-necked flask, the pH will rise, and then as the alkali is consumed, the pH will decrease. This cycle is repeated until the conversion reaction is completed. When the pH in the three-necked flask continues to rise, it means that the dripped methanol alkali is no longer consumed, indicating that the conversion reaction has ended at this time. The process takes about 1.5 hours in total.

[0031] After the conversion reaction is completed, the mixture is filtered while hot, and the filtrate is cooled to 0°C. 1 g of sodium D-isoascorbate is added as a seed crystal, and the mixture is allowed to stand for 2 hours for crystallization. The mixture is then centrifuged and dried in vacuo at 50°C to obtain 93.63 g of sodium D-isoascorbate with a purity of 99.82%. The yield is 96.67% after removing the mass of the added seed crystals.

[0032] Preparation of D-isoascorbic acid:

[0033] The steps of the conversion reaction are the same as those for the preparation of sodium D-isoascorbate.

[0034] After the conversion reaction is completed, the three-necked flask is cooled to 50°C, and 30 g of 98wt% concentrated sulfuric acid is slowly added to the three-necked flask at a stirring intensity of 400 r / min. During the process, the dropping rate of the concentrated sulfuric acid is controlled so that the temperature in the three-necked flask is not higher than 80°C. After the acidification is completed, it is filtered while hot. After filtration, the filtrate is cooled to 0°C, 1 g of D-isoascorbic acid is added as a seed crystal, and crystallization is allowed to stand for 2 hours, followed by centrifugation and vacuum drying at 50°C to obtain 82.41 g of D-isoascorbic acid with a purity of 99.57%. The yield is 95.34% after removing the mass of the added seed crystals.

[0035] It can be seen that the method of the present invention can obtain D-isoascorbic acid and sodium D-isoascorbate products with higher purity, and the reaction yield is high, which is convenient for industrial application. At the same time, by recovering the product in the crystallization mother liquor, it is hoped that the yield of the product can be further improved, and the method has good application prospects.

[0036] Comparative Example 1

[0037] In this comparative example, sodium D-isoascorbate was prepared without adding microporous molecular sieves during the conversion reaction. Other steps were the same as those in Example 1.

[0038] In this comparative example, the conversion reaction took a short time, about 1.25 h.

[0039] In this comparative example, the obtained sodium D-isoascorbate product was not purified, and finally 86.64 g of crude sodium D-isoascorbate was obtained with a purity of 82.33%. After deducting the mass of the added seed crystals, the yield was 73.71%.

[0040] Comparative Example 2

[0041] In this comparative example, sodium D-isoascorbate was prepared. No microporous molecular sieve was added during the conversion reaction. The parameters of the conversion reaction were controlled by common parameters, with the temperature controlled at 65° C. and the pH controlled at 7-8. Other conditions were the same as in Example 1.

[0042] In this comparative example, the conversion reaction took a long time, about 2.5 h.

[0043] In this comparative example, the obtained sodium D-isoascorbate product was not purified, and finally 91.74 g of crude sodium D-isoascorbate was obtained with a purity of 91.26%. After deducting the mass of the added seed crystals, the yield was 86.57%.

[0044] Comparative Example 2 is a controlled preparation method commonly used in existing industrial production. It can be seen from Comparative Examples 1-2 that when the temperature and pH control of the existing commonly used method are consistent with the method of the present invention, it is obviously not conducive to improving the purity and yield of the product. In the existing method, directly increasing the control temperature and pH of the conversion reaction is not advisable.

[0045] In addition, it can be clearly seen that when the method of the present invention is adopted, it plays a significant role in promoting the improvement of product yield and purity.

[0046] Comparative Example 3

[0047] In this comparative example, sodium D-isoascorbate was prepared. In this comparative example, a microporous molecular sieve was added during the conversion reaction, and the temperature control parameters and pH control parameters commonly used in the conversion reaction process were adopted by the existing method; the rest were the same as in Example 1.

[0048] In this comparative example, the temperature of the conversion reaction was controlled at 65° C., the pH value during the conversion process was controlled at 7-8, and the final conversion process took about 3 hours.

[0049] Finally, 93.71 g of sodium D-isoascorbate was obtained with a purity of 99.69%. Excluding the mass of the added seed crystals, the yield was 96.62%.

[0050] By comparison, it can be found that the method of the present invention can still be implemented under the conditions of the existing commonly used temperature control parameters and pH control parameters, and has good results; however, the time consumed by the conversion reaction is significantly longer. It can be seen that the method of the present invention can effectively increase the rate of the conversion reaction and help improve production efficiency.

[0051] Comparative Example 4

[0052] In this comparative example, sodium D-isoascorbate was prepared. The difference from Example 1 is that in this comparative example, methanol alkali was added separately, that is, a sufficient amount of methanol was first added, and then sodium carbonate was added in small amounts and multiple times. The addition amount and control conditions during the process were the same as in Example 1.

[0053] During the implementation process, the conversion process took significantly longer, about 3 hours, and ultimately, 91.54 g of finished sodium D-isoascorbate was obtained with a purity of 97.33%. Excluding the mass of the added seed crystals, the yield was 92.13%.

[0054] The difference between this comparative example and Example 1 is only in the addition method of methanol alkali, but the difference is obvious. On the one hand, the conversion reaction time is significantly longer, and on the other hand, the purity and yield of the obtained product are reduced; the reason for the longer conversion reaction time is that the directly added sodium carbonate has a larger particle size and is not easy to mix evenly in the reaction system, thereby significantly reducing the reaction efficiency; there are two reasons for the decrease in product and yield. On the one hand, part of the sodium carbonate is contaminated on the bottle wall and does not participate in the reaction, and the loss of alkali will have a certain impact on the conversion reaction. On the other hand, although a small amount of multiple addition method is adopted, at the moment of batch sodium carbonate addition, the pH of the reaction system is too high, and too high pH will lead to instability of the conversion system, increase the formation of by-products, thereby reducing the purity and yield of the product.

[0055] It can be seen that the addition method of methanol base also has an important influence on the quality of sodium D-isoascorbate product.

[0056] The present invention is not limited to the above-mentioned optimal implementation mode. Anyone can derive other various forms of products under the inspiration of the present invention. However, no matter what changes are made in the shape or structure, all technical solutions that are the same or similar to those of the present application fall within the protection scope of the present invention.

Claims

1. A method for preparing D-isoascorbic acid and its sodium salt, characterized in that: The following steps are involved: S1, mixing 2-keto-D-gluconate methyl ester and methanol, and adding microporous molecular sieves to the mixed system; S2, adding methanol alkali to the mixed system of S1 to carry out conversion reaction; S3, filtering and cooling the reaction system after the conversion reaction in S2 to precipitate sodium D-isoascorbate, and then separating and drying to obtain sodium D-isoascorbate product; S4. Add sulfuric acid to the reaction system after the conversion reaction in S2 for acidification, and then filter and cool to precipitate D-isoascorbic acid, and then separate and dry to obtain a D-isoascorbic acid product.

2. The method for preparing D-isoascorbic acid and its sodium salt according to claim 1, characterized in that: In the S1, the mass ratio of 2-keto-D-gluconate methyl ester to methanol is 1:1-3; the pore size of the microporous molecular sieve is 1-2 nm; and the mass ratio of 2-keto-D-gluconate methyl ester to the microporous molecular sieve is 1:1-2.

3. The method for preparing D-isoascorbic acid and its sodium salt according to claim 1, characterized in that: In the above-mentioned S2, the methanol alkali is a heterogeneous system obtained by mixing methanol and alkali and then mixing them by colloid milling.

4. The method for preparing D-isoascorbic acid and its sodium salt according to claim 3, characterized in that: The alkali is one of sodium hydroxide, sodium bicarbonate and sodium carbonate.

5. The method for preparing D-isoascorbic acid and its sodium salt according to claim 3, characterized in that: In the methanol alkali, the mass ratio of alkali to methanol is 1:1-3.

6. The method for preparing D-isoascorbic acid and its sodium salt according to claim 3, characterized in that: The methanol alkali is added slowly and evenly. During the addition of the methanol alkali, the pH of the mixed system is controlled to be 8-9. When the pH of the mixed system continues to rise, the addition is stopped and the conversion reaction ends.

7. The method for preparing D-isoascorbic acid and its sodium salt according to any one of claims 1 to 6, characterized in that: In the above-mentioned S1-S2, the stirring intensity is 300-500r / min.

8. The method for preparing D-isoascorbic acid and its sodium salt according to claim 1, characterized in that: In the S2, the reaction temperature is 70-90°C.

9. The method for preparing D-isoascorbic acid and its sodium salt according to claim 1, characterized in that: In the S3, the filtration is performed while hot; the filtrate obtained after filtration is cooled to 0°C; a small amount of seed crystals is added during precipitation, and the precipitation time is 1 to 3 hours; centrifugation, filtration, and vacuum drying are performed to obtain a D-sodium isoascorbate product, and the drying temperature is 50 to 60°C.

10. The method for preparing D-isoascorbic acid and its sodium salt according to claim 8, characterized in that: In the S4, the sulfuric acid is 98wt% concentrated sulfuric acid; the reaction system is cooled to 50-60°C before acidification with concentrated sulfuric acid; the temperature of the reaction system is controlled not to exceed 80°C during the addition of concentrated sulfuric acid, and the stirring intensity is 300-500r / min; after acidification with concentrated sulfuric acid, the concentrated sulfuric acid is filtered while hot; after filtration, the concentrated sulfuric acid is cooled to 0°C; a small amount of seed crystals is added during precipitation, and the precipitation time is 1-3h; centrifugation, filtration, and vacuum drying are performed to obtain a D-isoascorbic acid product, and the drying temperature is 50-60°C.